Co-reporter:Lu Liu, Yiqing Wu, Junkai Hu, Dongxia Liu, and Michael R. Zachariah
Energy & Fuels October 19, 2017 Volume 31(Issue 10) pp:11225-11225
Publication Date(Web):September 14, 2017
DOI:10.1021/acs.energyfuels.7b01689
Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion with inherent CO2 separation from flue gases, circumventing high cost for CO2 capture and NOx elimination as in conventional combustion processes. Metal oxides are commonly used as oxygen carriers (OCs) in CLC. However, sintering and coking of OCs and the consequent degradation in their activity and durability during multiple cycles inhibit the practical applications of CLC technology. In the present study, we employed a silicalite-1 zeolite support to achieve OCs with high resistance against sintering and coking in CLC. Iron oxides (Fe2O3) with methane fuel were employed to demonstrate the approach and to quantify the influence of silicalite-1 support on conversion efficiency, durability, and selectivity of these OCs in CLC cycles. Two iron oxide–zeolite geometrical structures, a core–shell Fe2O3@silicalite-1 and a Fe2O3-impregnated silicalite-1 (Fe2O3/silicalite-1), were created to improve Fe2O3 stability. The CLC tests showed that both structures led to less aggregation of Fe2O3 OCs at 1223 K. A comparison between Fe2O3/silicalite-1 and Fe2O3@silicalite-1 in CLC tests illustrates that Fe2O3 impregnated in zeolite had higher durability than in the core–shell structure. The selectivity of CH4 to CO2 followed the order of Fe2O3/silicalite-1 > Fe2O3@silicalite-1 ≫ bare Fe2O3. The high selectivity of Fe2O3/silicalite-1 to CO2 in CLC tests can be attributed to the encapsulation of Fe2O3 inside channels of silicalite-1 that provides physical barriers for aggregation of OCs in CLC cycles as well as coke deposition on OCs. In conclusion, our study of the structure–function relation for silicalite-1-supported Fe2O3 OCs can form the basis for the development of silicalite-1 as an efficient support in chemical looping applications.
Co-reporter:L. Zhou;M. R. Zachariah;S. Chowdhury;N. Piekiel
The Journal of Physical Chemistry C August 26, 2010 Volume 114(Issue 33) pp:14269-14275
Publication Date(Web):Publication Date (Web): July 29, 2010
DOI:10.1021/jp101146a
In this work, heterogeneous nanocomposite reactions of Al/CuO, Al/Fe2O3 and Al/ZnO systems were characterized using a recently developed T-Jump/time-of-flight mass spectrometer. Flash-heating experiments with time-resolved mass spectrometry were performed at heating rates in the range of ∼105 K/s. We find that molecular oxygen liberated during reaction is an active ingredient in the reaction. Experiments also conducted for neat Al, CuO, Fe2O3, and ZnO powders show that the oxygen are produced by decomposition of oxidizer particles. Mass spectrometric analysis indicates that metal oxide particles behave as an oxygen storage device in the thermite mixture and release oxygen very fast to initiate the reaction. A clear correlation is observed between the capability of oxygen release from oxidizing particles and the overall reactivity of the nanocomposite. The high reactivity of the Al/CuO mixture can be attributed to the strong oxygen release from CuO, while Fe2O3 liberates much less oxygen and leads to moderate reactivity, and ZnO’s poor oxygen release capability caused the Al/ZnO mixture to be completely not reacting, even though the reaction is overall exothermic. It is likely that the role of the oxygen species is not only as a strong oxidizer but also an energy propagation medium that carries heat to neighboring particles.
Co-reporter:Xiaofei Ma
The Journal of Physical Chemistry C August 20, 2009 Volume 113(Issue 33) pp:14644-14650
Publication Date(Web):Publication Date (Web): July 28, 2009
DOI:10.1021/jp903502v
Nanosized Zn and ZnO particles have attracted considerable interest for their various potential applications. Zn can act as both the fuel and a working catalyst in the Zn/ZnO thermochemical solar water splitting cycle for hydrogen generation, and ZnO is an important semiconductor. In this work, we combine two different ion-mobility schemes in series to study the size-resolved oxidation kinetics of zinc nanocrystals (NCs). The first mobility characterization size selects the NCs, whereas the second mobility characterization measures changes in mass resulting from a controlled oxidation of the NCs. A shrinking core model is used to extract the size-dependent oxidation activation energies, which are observed to be dependent on NC size. We also observed a strong anisotropy effect in the oxidation, as imaged by electron microscopy. An oxidation mechanism is proposed that qualitatively explains the oxidation anisotropy and its relationship to the surface energy of the Zn NCs.
Co-reporter:Jeffery B. DeLisio, Feng Yi, David A. LaVan, and Michael R. Zachariah
The Journal of Physical Chemistry C 2017 Volume 121(Issue 5) pp:
Publication Date(Web):January 7, 2017
DOI:10.1021/acs.jpcc.6b11114
Highly tunable reactive nanolaminates have been of recent interest for various “on chip” energetic applications. The reaction dynamics of Al/CuO nanolaminates were investigated by nanocalorimetry-coupled time-of-flight mass spectrometry, capable of simultaneous measurement of temporal thermal dynamics and detection of evolved gas phase species at heating rates up to ∼106 K/s. The nanolaminates were synthesized by alternately sputtering Al and CuO onto the heater of nanocalorimeter sensors. For thin films of 80 nm with one bilayer, the stoichiometric ratio of fuel to oxidizer significantly affected the reaction mechanism: initial reactions occurred between 300 and 400 °C, and main reactions varied based on stoichiometry. For thicker films of 199 and 266 nm, a series of samples with varying bilayer numbers were analyzed to determine the effect of diffusion distance and interfacial area. Only one reaction step was observed for a sample with a bilayer thickness of 33 nm. A two-step reaction mechanism is observed as the bilayer thickness was increased to 66 nm and beyond: solid-state reaction occurring at the interfaces of Al and CuO before the melting of Al and a much faster liquid–solid reaction right after the melting of Al. At the same time, interfacial premixed distance during the deposition was also estimated from parallel experiments. Furthermore, the power data from nanocalorimetry provides a more direct method, compared to optical emission and mass spectrometry based methods, in determining the ignition temperature in addition to being able to measure actual energy output for films with nanoscale thicknesses.
Co-reporter:Xizheng Wang, Tao Wu, and Michael R. Zachariah
The Journal of Physical Chemistry C 2017 Volume 121(Issue 1) pp:
Publication Date(Web):November 28, 2016
DOI:10.1021/acs.jpcc.6b10571
Despite our knowledge of the existence of the violent thermite reaction for over 100 years, it is still not yet understood how the properties of a metal oxide oxidizer relate to and influence the ignition temperature. To address this shortcoming, we prepared a series of perovskite-based oxidizers which enable a systematic investigation of how materials properties of the oxidizer relate to the ignition temperature. In this paper, nine lanthanum-based perovskites with different Sr2+ doping of the A-site and different B-site transition metals were synthesized. The perovskite O2 release and ignition temperatures with aluminum were measured by fast heating (>105 K/s) temperature-jump/time-of-flight mass spectrometry coupled with high-speed imaging. These results were then correlated with the average bond energy and overall metal–oxygen electronegativity difference. Remarkably, we found a linear relationship between average bond energy and electronegativity with ignition temperature. To our knowledge this is the first demonstration of the connection between metal–oxygen bond energy, electronegativity, and ignition temperature.
Co-reporter:Philip M. Guerieri, Jeffery B. DeLisio, Michael R. Zachariah
Combustion and Flame 2017 Volume 176(Volume 176) pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.combustflame.2016.10.011
Addition of metal and metal oxide nanoparticles to hydrocarbon fuels has shown the ability to increase the volumetric energy density, decrease ignition delay, increase heat of combustion, and catalyze fuel decomposition in recent research. However, energetic metal nanoparticles are prone to aggregation, which occurs at an increased rate near the regressing surface of a burning liquid droplet where local concentrations increase and can form a transport-inhibiting shell, ultimately decreasing the droplet burning rate. Alternatively, gas ejections from the droplet can disrupt shell formation and transport nanoparticles from the droplet to the flame zone. This study quantifies up to a 12.1% decrease in the burning rate constant of Kerosene droplets when 6.1 wt% nanoaluminum (nAl) particles are added (the maximum stable loading) with a hydrocarbon-based surfactant in a free-falling single droplet combustion experiment. Addition of nitrocellulose (NC) particles to the nanofuel diminishes or fully counteracts the burning rate decreases and provides a means of tuning the burning rate constant higher than that of pure Kerosene (maximum 13.8% increase over control with 2.3 wt% nAl and 0.6 wt% NC added). To reach stable nanofuels at higher particle loadings up to 15.0 wt% solid additives, nAl and NC were electrosprayed into composite mesoparticles (MP) before suspending with surfactant in Kerosene. These MP-based nanofuels boast increased dispersibility and additive loadings and thus higher achievable burning rates (maximum 26.5% increase over control) than physically mixed analogs. A mechanism is proposed in which droplet disruptions influenced by NC addition include cyclical inflations, during which the liquid gasification rate increases, e.g. by expanding the outer surface area of the droplet.
Co-reporter:Haiyang Wang, Rohit J. Jacob, Jeffery B. DeLisio, Michael R. Zachariah
Combustion and Flame 2017 Volume 180(Volume 180) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.combustflame.2017.02.036
Aluminum nanoparticles (Al NPs) are commonly employed as fuel supplement to increase the energy density of propellants. However, due to the highly agglomerated state of the NPs and significant pre-combustion sintering, ignition and combustion are not as facile as they could be. In this work, we employed a spray approach to generate near monodisperse microparticles of Al NP's encapsulated within ammonium perchlorate (AP) and a binder (nitrocellulose (NC)) The results show that Al/AP/NC composites have an ignition temperature (∼700 K), which is significantly lower than Al melting point (∼933 K). The reactivity of Al/AP/NC composites was also tested in a confined cell where we find that although the peak pressure for Al/AP/NC is comparable to that of physically mixed Al/CuO nanothermite, the impulse generated is more than two times higher. The measured flame temperature of Al/AP/NC composites were as high as 2800 K, which is ∼500 K higher than Al/AP composites without NC. Furthermore, the potential mechanism for the early ignition of these composites were investigated. It is proposed that gaseous acid released from AP could play an important role in weakening the protective oxide shell on Al nanoparticles which could subsequently lead to the reaction of Al in the high-pressure oxygenated environment at lower temperature.
Co-reporter:Wenbo Zhou, Jeffery B. DeLisio, Xizheng Wang, Michael R. Zachariah
Combustion and Flame 2017 Volume 177(Volume 177) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.combustflame.2016.05.024
Ignition temperature is a simple and important parameter that pertains to both the practical aspects of thermite usage as well as a key to exploring reaction mechanisms. In this study, nine aluminum-fueled oxysalt-containing thermites including K2S2O8, K2SO4, KIO4, KIO3, KClO4, KClO3, KBrO3, KNO3 and K3PO4, were investigated. Results from combustion cell tests show that these thermites can be divided into two groups, with the reactive thermites (e.g., Al–K2S2O8) generating ∼10× higher of pressure and ∼10× shorter of burn time than the less reactive thermites in the aforementioned list (e.g., Al–K2SO4). Thermal decomposition analysis of these oxysalts at both slow and fast heating rates (0.17 K/s v.s. 105 K/s) demonstrates that these oxysalts have a wide range of oxygen release and melting temperatures. On the other hand, the ignition temperatures of the reactive thermites (in Ar and air) are consistent with the temperature of polymorphic phase change of alumina (close to the melting point of Al), indicating that the limiting initiation step of these thermites is the acceleration of outward diffusion flux of Al. In addition, the ignition temperatures of these reactive thermites in vacuum are much higher than those in Ar, suggesting that ignition is based on the interaction between outwardly diffused Al, and generated gas phase O2. In contrast, the ignition temperatures of the two less reactive thermites are insensitive to pressure. They ignite at temperatures much higher than the melting point of Al, although lower than the decomposition temperature of the corresponding oxysalts, indicating a condensed phase reaction mechanism. Finally, by employing carbon as a non-melting, non-oxide coated fuel, we found an essentially direct correlation between the oxygen release temperature and the ignition temperature.
Co-reporter:Xizheng Wang;Wenbo Zhou;Jeffery B. DeLisio;Garth C. Egan
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 20) pp:12749-12758
Publication Date(Web):2017/05/24
DOI:10.1039/C6CP08532F
Nanothermites offer high energy density and high burn rates, but are mechanistically only now being understood. One question of interest is how initiation occurs and how the ignition temperature is related to microscopic controlling parameters. In this study, we explored the potential role of oxygen ion transport in Bi2O3 as a controlling mechanism for condensed phase ignition reaction. Seven different doped δ-Bi2O3 were synthesized by aerosol spray pyrolysis. The ignition temperatures of Al/doped Bi2O3, C/doped Bi2O3 and Ta/doped Bi2O3 were measured by temperature-jump/time-of-flight mass spectrometer coupled with a high-speed camera respectively. These results were then correlated to the corresponding oxygen ion conductivity (directly proportional to ion diffusivity) for these doped Bi2O3 measured by impedance spectroscopy. We find that ignition of thermite with doped Bi2O3 as oxidizer occurs at a critical oxygen ion conductivity (∼0.06 S cm−1) of doped Bi2O3 in the condensed-phase so long as the aluminum is in a molten state. These results suggest that oxygen ion transport limits the condensed state Bi2O3 oxidized thermite ignition. We also find that the larger oxygen vacancy concentration and the smaller metal–oxide bond energy in doped Bi2O3, the lower the ignition temperature. The latter suggests that we can consider the possibility of manipulating microscopic properties within a crystal, to tune the resultant energetic properties.
Co-reporter:Feng Yi, Jeffery B. DeLisio, Nam Nguyen, Michael R. Zachariah, David A. LaVan
Chemical Physics Letters 2017 Volume 689(Volume 689) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.cplett.2017.09.066
•CuO decomposes by two steps at both slower and higher heating rates.•Reactions at the nanoscale require analytical approaches with greater time resolution.•Coupling nanocalorimetry with TOF MS improves resolution of nano scale reactions.•The nanocalorimeter TOF MS instrument approaches current computational time scales.The thermodynamics and evolved gases were measured during the rapid decomposition of copper oxide (CuO) thin film at rates exceeding 100,000 K/s. CuO decomposes to release oxygen when heated and serves as an oxidizer in reactive composites and chemical looping combustion. Other instruments have shown either one or two decomposition steps during heating. We have confirmed that CuO decomposes by two steps at both slower and higher heating rates. The decomposition path influences the reaction course in reactive Al/CuO/Al composites, and full understanding is important in designing reactive mixtures and other new reactive materials.Download high-res image (111KB)Download full-size image
Co-reporter:Lu Liu, Daniel D. Taylor, Efrain E. Rodriguez and Michael R. Zachariah
Chemical Communications 2016 vol. 52(Issue 68) pp:10369-10372
Publication Date(Web):21 Jul 2016
DOI:10.1039/C6CC01997H
The selection of highly efficient oxygen carriers (OCs) is a key step necessary for the practical development of chemical looping combustion (CLC). In this study, a series of ABO3 perovskites, where A = La, Ba, Sr, Ca and B = Cr, Mn, Fe, Co, Ni, Cu, are synthesized and tested in a fixed bed reactor for reactivity and stability as OCs with CH4 as the fuel. We find that the electronegativity of the transition metal on the B-site (λB), is a convenient descriptor for oxygen storage capacity (OSC) of our perovskite samples. By plotting OSC for total methane oxidation against λB, we observe an inverted volcano plot relationship. These results could provide useful guidelines for perovskite OC design and their other energy related applications.
Co-reporter:Jiaojie Tan, Jingyu Liu, Mingdong Li, Hind El Hadri, Vincent A. Hackley, and Michael R. Zachariah
Analytical Chemistry 2016 Volume 88(Issue 17) pp:8548
Publication Date(Web):August 1, 2016
DOI:10.1021/acs.analchem.6b01544
The novel hyphenation of electrospray-differential mobility analysis with single particle inductively coupled plasma mass spectrometry (ES-DMA-spICPMS) was demonstrated with the capacity for real-time size, mass, and concentration measurement of nanoparticles (NPs) on a particle-to-particle basis. In this proof-of-concept study, the feasibility of this technique was validated through both concentration and mass calibration using NIST gold NP reference materials. A detection limit of 105 NPs mL–1 was determined under current experimental conditions, which is about 4 orders of magnitude lower in comparison to that of a traditional ES-DMA setup using a condensation particle counter as detector. Furthermore, independent and simultaneous quantification of both size and mass of NPs provides information regarding NP aggregation states. Two demonstrative applications include gold NP mixtures with a broad size range (30–100 nm), and aggregated gold NPs with a primary size of 40 nm. Finally, this technique was shown to be potentially useful for real-world samples with high ionic background due to its ability to remove dissolved ions yielding a cleaner background. Overall, we demonstrate the capacity of this new hyphenated technique for (1) clearly resolving NP populations from a mixture containing a broad size range; (2) accurately measuring a linear relationship, which should inherently exist between mobility size and one-third power of ICPMS mass for spherical NPs; (3) quantifying the early stage propagation of NP aggregation with well-characterized oligomers; and (4) differentiating aggregated NPs and nonaggregated states based on the “apparent density” derived from both DMA size and spICPMS mass.
Co-reporter:Jeffery B. DeLisio, Dennis H. Mayo, Philip M. Guerieri, Samantha DeCarlo, Ross Ives, Kit Bowen, Bryan W. Eichhorn, Michael R. Zachariah
Chemical Physics Letters 2016 Volume 661() pp:168-172
Publication Date(Web):16 September 2016
DOI:10.1016/j.cplett.2016.08.065
Highlights
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High heating rate decomposition of [AlBr(NEt3)]4 detected Al and AlHx species.
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Decomposition occurs at ∼220 °C with a determined activation energy of ∼43 kJ/mol.
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Addition of KIO4 resulted in increased Al, AlO, and HBr signal intensities.
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Gas phase oxygen from KIO4 oxidized the cluster during decomposition.
Co-reporter:Garth C. Egan, Kyle T. Sullivan, Tammy Y. Olson, T. Yong-Jin Han, Marcus A. Worsley, and Michael R. Zachariah
The Journal of Physical Chemistry C 2016 Volume 120(Issue 51) pp:29023-29029
Publication Date(Web):November 21, 2016
DOI:10.1021/acs.jpcc.6b11081
The importance of the oxidation state of an oxidizer and its impact on gaseous oxygen and total gas production in nanocomposite thermite combustion was investigated by probing the reaction and ignition properties of aluminum nanoparticles (Al-NPs) with both cupric oxide (CuO) and cuprous oxide (Cu2O) nanoparticles. The gas release and ignition behavior of these materials were tested with >105 K/s temperature jump (T-jump) heating pulses in a high temporal resolution time-of-flight mass spectrometer (ToF-MS) as well as in an argon environment. Reactivity was tested using a constant volume combustion cell with simultaneous pressure and optical measurements. A variety of Cu2O particle sizes ranging from 200 to 1500 nm were synthesized and found to release oxygen at ∼1200 K, which is higher than the values found for a variety of CuO particle sizes (∼1000 K). Both oxides were found to ignite around 1000 K, which implies a consistent ignition mechanism for both through a condensed phase pathway. The higher oxidation state (CuO) thermites were found to react faster and produce higher pressures by several orders of magnitude, which implies that gaseous species play a critical role in the combustion process. Differences in reactivity between argon and vacuum environments and the use of Cu diluent to simulate Cu2O suggest that it is the intermediate product gas, O2, that plays the most significant role in combustion as an enabler of heat transfer and a secondary oxidizer. The lack of any oxidizer size dependence on ignition is suggestive of rapid sintering that wipes out the effect of enhanced interfacial contact area for smaller oxidizers.
Co-reporter:Jeffery B. DeLisio, Xiuli Hu, Tao Wu, Garth C. Egan, Gregory Young, and Michael R. Zachariah
The Journal of Physical Chemistry B 2016 Volume 120(Issue 24) pp:5534-5542
Publication Date(Web):May 26, 2016
DOI:10.1021/acs.jpcb.6b01100
Energetic thin films with high mass loadings of nanosized components have been recently fabricated using electrospray deposition. These films are composed of aluminum nanoparticles (nAl) homogeneously dispersed in an energetic fluoropolymer binder, poly(vinylidene fluoride) (PVDF). The nascent oxide shell of the nAl has been previously shown to undergo a preignition reaction (PIR) with fluoropolymers such as polytetrafluoroethylene (PTFE). This work examines the PIR between alumina and PVDF to further explain the reaction mechanism of the Al/PVDF system. Temperature jump (T-jump) ignition experiments in air, argon, and vacuum environments showed that the nAl is fluorinated by gas phase species due to a decrease in reactivity in a vacuum. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC) was used to confirm the occurrence of a PIR, and gas phase products during the PIR and fluorination of nAl were investigated with temperature jump time-of-flight mass spectrometry (T-jump TOFMS). Results show a direct correlation between the amount of alumina in the PVDF film and the relative signal intensity of hydrogen fluoride release (HF). Although the PIR between alumina and PVDF plays an important role in the Al/PVDF reaction mechanism, burn speeds of Al/PVDF films containing additional pure alumina particles showed no burn speed enhancement.
Co-reporter:Wenbo Zhou, Jeffery B. DeLisio, Xiangyu Li, Lu Liu and Michael R. Zachariah
Journal of Materials Chemistry A 2015 vol. 3(Issue 22) pp:11838-11846
Publication Date(Web):29 Apr 2015
DOI:10.1039/C5TA00756A
Nanoscale potassium persulfate (K2S2O8) was evaluated as an alternative to other peroxy salts, such as periodates (KIO4), in aluminum-fueled energetic nano-composite formulations. High speed imaging coupled with temperature jump (T-jump) ignition found the nano-Al/K2S2O8 reaction to have an ignition temperature of 600 °C which is comparable to nano-Al/KIO4 and lower than nano-Al/K2SO4. The results from constant-volume pressure cell experiments further show that nano-Al/K2S2O8 releases more gas and has a longer burn time than nano-Al/KIO4. Thermal analyses at low heating rates (10 °C min−1) by coupled differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and mass spectrometry (MS) show that there are three main steps of thermal decomposition for nano-K2S2O8, with initial exothermic decomposition to release O2 at 270 °C, and following endothermic decomposition to release both O2 and SO2 at higher temperatures. The heat of formation of K2S2O8 was measured to be −1844.5 kJ mol−1 based on the DSC results. Experiments performed at ultrafast heating rates (∼105 °C s−1) using temperature-jump time-of-flight (T-jump/TOF) MS show that the low O2 generation temperature of nano-K2S2O8 contributes to its high reactivity in nano-thermite compositions. An ignition mechanism involving gaseous oxygen was proposed for nano-thermite compositions containing reactive oxysalts such as nano-K2S2O8. In contrast, a condense phase ignition mechanism was proposed for nano-thermites involving less reactive oxysalts such as nano-K2SO4. Given that the nano-Al/K2S2O8 system is highly exothermic in addition to generating a considerable amount of SO2, it may be a candidate for use in energetic biocidal applications.
Co-reporter:Xiangyu Li, Philip Guerieri, Wenbo Zhou, Chuan Huang, and Michael R. Zachariah
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 17) pp:9103
Publication Date(Web):March 27, 2015
DOI:10.1021/acsami.5b00891
One of the challenges in the use of energetic nanoparticles within a polymer matrix for propellant applications is obtaining high particle loading (high energy density) while maintaining mechanical integrity and reactivity. In this study, we explore a new strategy that utilizes laminate structures. Here, a laminate of alternating layers of aluminum nanoparticle (Al-NPs)/copper oxide nanoparticle (CuO-NPs) thermites in a polyvinylidene fluoride (PVDF) reactive binder, with a spacer layer of PVDF was fabricated by a electrospray layer-by-layer deposition method. The deposited layers containing up to 60 wt % Al-NPs/CuO-NPs thermite are found to be uniform and mechanically flexible. Both the reactive and mechanical properties of laminate significantly outperformed the single-layer structure with the same material composition. These results suggest that deploying a multilayer laminate structure enables the incorporation of high loadings of energetic materials and, in some cases, enhances the reactive properties over the corresponding homogeneous structure. These results imply that an additive manufacturing approach may yield significant advantages in developing a tailored architecture for advanced propulsion systems.Keywords: laminate; mechanical property; nanocomposite; polymer; print; propellant; thermite;
Co-reporter:H. Wang, G. Jian, W. Zhou, J. B. DeLisio, V. T. Lee, and M. R. Zachariah
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 31) pp:17363
Publication Date(Web):July 10, 2015
DOI:10.1021/acsami.5b04589
The biological agents that can be weaponized, such as Bacillus anthracis, pose a considerable potential public threat. Bacterial spores, in particular, are highly stress resistant and cannot be completely neutralized by common bactericides. This paper reports on synthesis of metal iodate-based aluminized electrospray-assembled nanocomposites which neutralize spores through a combined thermal and chemical mechanism. Here metal iodates (Bi(IO3)3, Cu(IO3)2, and Fe(IO3)3) act as a strong oxidizer to nanoaluminum to yield a very exothermic and violent reaction, and simultaneously generate iodine as a long-lived bactericide. These microparticle-assembled nanocomposites when characterized in terms of reaction times and temporal pressure release show significantly improved reactivity. Furthermore, sporicidal performance superior to conventional metal-oxide-based thermites clearly shows the advantages of combining both a thermal and biocidal mechanism in spore neutralization.Keywords: biocidal; electrospray; energetic materials; metal iodate; nanothermite
Co-reporter:Feng Yi, Jeffery B. DeLisio, Michael R. Zachariah, and David A. LaVan
Analytical Chemistry 2015 Volume 87(Issue 19) pp:9740
Publication Date(Web):September 15, 2015
DOI:10.1021/acs.analchem.5b01872
We report on measurements integrating a nanocalorimeter sensor into a time-of-flight mass spectrometer (TOFMS) for simultaneous thermal and speciation measurements at high heating rates. The nanocalorimeter sensor was incorporated into the extraction region of the TOFMS system to provide sample heating and thermal information essentially simultaneously with the evolved species identification. This approach can be used to measure chemical reactions and evolved species for a variety of materials. Furthermore, since the calorimetry is conducted within the same proximal volume as ionization and ion extraction, evolved species detected are in a collision-free environment, and thus, the possibility exists to interrogate intermediate and radical species. We present measurements showing the decomposition of ammonium perchlorate, copper oxide nanoparticles, and sodium azotetrazolate. The rapid, controlled, and quantifiable heating rate capabilities of the nanocalorimeter coupled with the 0.1 ms temporal resolution of the TOFMS provides a new measurement capability and insight into high-rate reactions, such as those seen with reactive and energetic materials, and adsorption\desorption measurements, critical for understanding surface chemistry and accelerating catalyst selection.
Co-reporter:Chuan Huang;Guoqiang Jian;Jeffery B. DeLisio;Haiyang Wang
Advanced Engineering Materials 2015 Volume 17( Issue 1) pp:95-101
Publication Date(Web):
DOI:10.1002/adem.201400151
One of the challenges in the use of energetic nanoparticles within a polymer matrix is the difficulty in processing by traditional mixing methods. In this paper, electrospray deposition is employed to create high loadings of aluminum nanoparticles (Al-NPs) in polyvinylidene fluoride (PVDF) reactive composite films. The deposited films containing up to 50 wt% Al are found to be crack free and mechanically flexible. Thermochemical behavior characterized by thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis shows that the addition of Al-NPs sharply reduces the onset decomposition temperature due to a pre-ignition reaction occurring in the film. The combustion propagation velocity in air at three different mass loading of Al-NPs shows burning rates of 5, 16, and 23 cm s−1 for loadings of 16.7, 30, and 50 wt% Al-NPs. The results suggest electrospray deposition as a direct approach to make bulk polymer composites containing high metal particle mass loading and may be a prelude to 3D printing of rocket motors.
Co-reporter:Garth C. Egan
The Journal of Physical Chemistry C 2015 Volume 119(Issue 5) pp:2792-2797
Publication Date(Web):December 17, 2014
DOI:10.1021/jp5084746
The reaction between metallic fuel and oxygen carriers produced by the laser heating of aluminum and copper oxide (CuO) nanoparticles (NPs) was investigated (NPs) using movie mode dynamic transmission electron microscopy (MM-DTEM), which enables multiframe imaging with nanometer spatial and nanosecond temporal resolution. Nanothermite materials heated in situ at ∼1011 K/s showed significant morphological changes on time scales of 1–5 μs. The resulting structures were typically phase-separated into adjoining spheroids. Further analysis with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED) was used to determine the extent of reaction. Bulk scale reaction experiments using temperature jump wire heating (∼105K/s) revealed that both the reaction products and general processes were comparable to the reactions driven by the DTEM laser heating. These results indicate that condensed phase and interfacial reactions are fast and dominant mechanisms in nanothermite combustion.
Co-reporter:Yichen Zong, Rohit J. Jacob, Shuiqing Li, and Michael R. Zachariah
The Journal of Physical Chemistry A 2015 Volume 119(Issue 24) pp:6171-6178
Publication Date(Web):April 27, 2015
DOI:10.1021/acs.jpca.5b02590
While ultrafine metal particles offer the possibility of very high energy density fuels, there is considerable uncertainty in the mechanism by which metal nanoparticles burn, and few studies that have examined the size dependence to their kinetics at the nanoscale. In this work we quantify the size dependence to the burning rate of titanium and zirconium nanoparticles. Nanoparticles in the range of 20–150 nm were produced via pulsed laser ablation, and then in-flight size-selected using differential electrical mobility. The size-selected oxide free metal particles were directly injected into the post flame region of a laminar flame to create a high temperature (1700–2500 K) oxidizing environment. The reaction was monitored using high-speed videography by tracking the emission from individual nanoparticles. We find that sintering occurs prior to significant reaction, and that once sintering is accounted for, the rate of combustion follows a near nearly (diameter)1 power-law dependence. Additionally, Arrhenius parameters for the combustion of these nanoparticles were evaluated by measuring the burn times at different ambient temperatures. The optical emission from combustion was also used to model the oxidation process, which we find can be reasonably described with a kinetically controlled shrinking core model.
Co-reporter:Garth C. Egan
The Journal of Physical Chemistry C 2015 Volume 119(Issue 35) pp:20401-20408
Publication Date(Web):August 13, 2015
DOI:10.1021/acs.jpcc.5b04117
Al/CuO reactive nanolaminate ignition was studied using temperature jump (T-Jump) heating for rates greater than 105 K/s. Multilayer samples were sputter deposited onto thin platinum filaments in alternating layers of Al and CuO. The filaments were resistively heated in a time-of-flight mass spectrometer (ToF-MS), while ignition and reaction were observed with high-speed video. A total deposited thickness of 1800 nm was maintained for all samples, while the number of bilayers was varied from 1 to 12. Increasing this value decreased the diffusion distances and increased the amount of interfacial area across which reaction could occur, while keeping the overall energy of the system constant. From 2 to 6 bilayers, the ignition temperature decreased from 1250 to 670 K and the overall reactivity increased. Past 6 bilayers, the ignition temperature only decreased slightly and there was little impact on the overall reactivity. This behavior is consistent with a mass-transport model where the predominant diffusing species exhibits a low activation energy (50 kJ/mol). Ignition temperature, which depends upon bilayer thickness, is found to be a good predictor of flame speed.
Co-reporter:Philip M. Guerieri, Samantha DeCarlo, Bryan Eichhorn, Terrence Connell, Richard A. Yetter, Xin Tang, Zachary Hicks, Kit H. Bowen, and Michael R. Zachariah
The Journal of Physical Chemistry A 2015 Volume 119(Issue 45) pp:11084-11093
Publication Date(Web):October 21, 2015
DOI:10.1021/acs.jpca.5b08580
Additives to hydrocarbon fuels are commonly explored to change the combustion dynamics, chemical distribution, and/or product integrity. Here we employ a novel aluminum-based molecular additive, Al(I) tetrameric cluster [AlBrNEt3]4 (Et = C2H5), to a hydrocarbon fuel and evaluate the resultant single-droplet combustion properties. This Al4 cluster offers a soluble alternative to nanoscale particulate additives that have recently been explored and may mitigate the observed problems of particle aggregation. Results show the [AlBrNEt3]4 additive to increase the burn rate constant of a toluene–diethyl ether fuel mixture by ∼20% in a room temperature oxygen environment with only 39 mM of active aluminum additive (0.16 wt % limited by additive solubility). In comparison, a roughly similar addition of nano-aluminum particulate shows no discernible difference in burn properties of the hydrocarbon fuel. High speed video shows the [AlBrNEt3]4 to induce microexplosive gas release events during the last ∼30% of the droplet combustion time. We attribute this to HBr gas release based on results of temperature-programmed reaction (TPR) experiments of the [AlBrNEt3]4 dosed with O2 and D2O. A possible mechanism of burn rate enhancement is presented that is consistent with microexplosion observations and TPR results.
Co-reporter:Guoqiang Jian, Yunhua Xu, Li-Chung Lai, Chunsheng Wang and Michael R. Zachariah
Journal of Materials Chemistry A 2014 vol. 2(Issue 13) pp:4627-4632
Publication Date(Web):14 Feb 2014
DOI:10.1039/C4TA00207E
This work focuses on development of Mn3O4 hollow spheres with high cycling capacity and high rate capability in lithium ion batteries. Hollow Mn3O4 spheres are synthesized by an aerosol based “droplet to particle” strategy. The synthesis process involves producing and heating aerosol precursor droplets in air flow at 600 °C to induce exothermic reactions and gas blowing to form the single phase hollow Mn3O4 spheres. The hollow Mn3O4 spheres, as an anode material, deliver a highly stable cycle performance with capacity retention of ∼980 mA h g−1 for over 140 cycles at 200 mA g−1 and an excellent rate capability by retaining 300 mA h g−1 at high current density of 10000 mA g−1.
Co-reporter:R. You, M. Li, S. Guha, G. W. Mulholland, and M. R. Zachariah
Analytical Chemistry 2014 Volume 86(Issue 14) pp:6836
Publication Date(Web):July 7, 2014
DOI:10.1021/ac403503q
We propose bionanoparticles as a candidate reference material for determining the mobility of nanoparticles over the range of 6 × 10–8–5 × 10–6 m2V–1s–1. Using an electrospray differential mobility analyzer (ES-DMA), we measured the empirical distribution of several bionanoparticles. All of them show monomodal distributions that are more than two times narrower than the currently used calibration particles for mobility larger than 6 × 10–8 m2V–1s–1 (diameters less than 60 nm). We also present a numerical method to calculate corrected distributions of bionanoparticles by separating the contribution of the diffusive transfer function. The corrected distribution is about 20% narrower than the empirical distributions. Even with the correction, the reduced width of the mobility distribution is about a factor of 2 larger than the diffusive transfer function. The additional broadening could result from the nonuniform conformation of bionanoparticles and from the presence of volatile impurities or solvent adducts. The mobilities of these investigated bionanoparticle are stable over a range of buffer concentration and molarity, with no evidence of temporal degradation over several weeks.
Co-reporter:Mingdong Li, Jiaojie Tan, Michael J. Tarlov, and Michael R. Zachariah
Analytical Chemistry 2014 Volume 86(Issue 24) pp:12130
Publication Date(Web):November 8, 2014
DOI:10.1021/ac5030123
A fast and accurate assay to determine the absolute concentration of proteins is described based on direct measurement of droplet entrapped oligomer formation in electrospray. Here we demonstrate the approach using electrospray differential mobility analysis (ES-DMA), which can distinguish monomers and dimers from higher order oligomers. A key feature of the method is that it allows determination of the absolute number concentration of proteins eliminating the need for protein-specific calibration. The method was demonstrated by measuring the concentration of a NIST Standard Reference Material 927e (bovine serum albumin), a high-purity immunoglobulin G 1κ, and a formulated Rituximab. The method may be applied to any electrospray source, regardless of diagnostic tool (e.g., MS or ion-mobility, etc.), provided the electrospray is operated in a droplet-fission mode.
Co-reporter:Yunhua Xu, Guoqiang Jian, Yihang Liu, Yujie Zhu, Michael R. Zachariah, Chunsheng Wang
Nano Energy 2014 Volume 3() pp:26-35
Publication Date(Web):January 2014
DOI:10.1016/j.nanoen.2013.10.003
•Crystalline and amorphous mesoporous Fe2O3 were synthesized using aerosol spray pyrolysis – a scalable and low cost synthesis method.•Both crystalline and amorphous Fe2O3 changed into nano-crystallite porous structure after charge/discharge cycles.•The crystalline Fe2O3 suffers less structure deformation and shows much better cell performance.Mesoporous Fe2O3 spherical particles with amorphous or crystalline structure were prepared at different temperatures using aerosol spray pyrolysis. The crystalline Fe2O3 (C-Fe2O3) anodes pyrolysized at 800 °C show better electrochemical performance than the amorphous Fe2O3 (A-Fe2O3) pyrolysized at 600 °C. Both, however, changed into nano-crystallite porous structure after charge/discharge cycles. The C-Fe2O3 spherical particles provided high reversible capacity of 800 mAh/g at 0.5 C over 300 charge/discharge cycles and retained 300 mAh/g at 10 C. The excellent cycling stability of the C-Fe2O3 spherical particles is mainly attributed to the interior voids in the mesoporous Fe2O3 particles that provide extra space to accommodate volume change and alleviate structural strain/stress during electrochemical reaction. The high rate performance of mesoporous Fe2O3 is attributed to (1) fast charge transfer reaction at the large interfacial area between electrode and liquid electrolyte, and (2) the reduced Li-ion diffusion distances. This study not only provides a simple synthesis method for lithium ion batteries, but also helps in designing novel and high performance electrode materials.
Co-reporter:Guoqiang Jian;Dr. Lei Zhou;Dr. Nicholas W. Piekiel ;Dr. Michael R. Zachariah
ChemPhysChem 2014 Volume 15( Issue 8) pp:1666-1672
Publication Date(Web):
DOI:10.1002/cphc.201301148
Abstract
Oxygen release from metal oxides at high temperatures is relevant to many thermally activated chemical processes, including chemical-looping combustion, solar thermochemical cycles and energetic thermite reactions. In this study, we evaluated the thermal decomposition of nanosized metal oxides under rapid heating (∼105 K s−1) with time-resolved mass spectrometry. We found that the effective activation-energy values that were obtained using the Flynn–Wall–Ozawa isoconversional method are much lower than the values found at low heating rates, indicating that oxygen transport might be rate-determining at a high heating rate.
Co-reporter:Yunhua Xu, Qing Liu, Yujie Zhu, Yihang Liu, Alex Langrock, Michael R. Zachariah, and Chunsheng Wang
Nano Letters 2013 Volume 13(Issue 2) pp:470-474
Publication Date(Web):January 2, 2013
DOI:10.1021/nl303823k
Nano-Sn/C composites are ideal anode materials for high energy and power density Li-ion batteries. However, because of the low melting point of Sn and the tendency of grain growth, especially during high temperature carbonization, it has been a significant challenge to create well-dispersed ultrasmall Sn nanoparticles within a carbon matrix. In this paper, we demonstrate an aerosol spray pyrolysis technique, as a facile and scalable method, to synthesize a nano-Sn/C composite with uniformly dispersed 10 nm nano-Sn within a spherical carbon matrix. The discharge capacity of nano-Sn/C composite sphere anodes maintains the initial capacity of 710 mAh/g after 130 cycles at 0.25 C. The nano-Sn/C composite sphere anodes can provide ∼600 mAh/g even at a high rate of 20 C. To the best of our knowledge, such high rate performance for Sn anodes has not been reported previously. The exceptional performance of the nano-Sn/C composite is attributed to the unique nano-Sn/C structure: (1) carbon matrix offers mechanical support to accommodate the stress associated with the large volume change of nano-Sn, thus alleviating pulverization; (2) the carbon matrix prevents Sn nanoparticle agglomeration upon prolonged cycling; and (3) carbon network provides continuous path for Li ions and electrons inside the nano-Sn/C composite spheres.
Co-reporter:Guoqiang Jian;Lu Liu
Advanced Functional Materials 2013 Volume 23( Issue 10) pp:1341-1346
Publication Date(Web):
DOI:10.1002/adfm.201202100
Abstract
Thermochemical metal/metal oxide redox reactions have twice the energy density of 2,4,6-trinitrotoluene (TNT). They suffer, however, from low pressure-volume work due to low gas expansion from the reaction. This study focuses on the development of a nanocomposite that delivers a high energy density and the potential of rapid gas release. Hollow CuO spheres with nanosized building blocks are fabricated using a “droplet-to-particle” aerosol spray pyrolysis method with the introduction of gas-blowing agents in the synthesis procedure. Nanoaluminum with hollow CuO as an oxidizer ignites in a very violent manner and exhibits excellent gas-generation behavior, demonstrating a high pressurization rate of 0.745 MPa μs−1 and a transient peak pressure of 0.896 MPa with a charge density of 1 mg cm−3, as well as a rapid oxygen release. Compared with wet-chemistry methods, gas-phase processes are relatively low cost, nominally offer a higher purity product, and are usually configured as continuous production processes, with a limited number of steps. The synthesis strategy demonstrated is simple and should be extendable to the preparation of other hollow metal oxide structures.
Co-reporter:Jingyu Feng, Guoqiang Jian, Qing Liu, and Michael R. Zachariah
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 18) pp:8875
Publication Date(Web):August 29, 2013
DOI:10.1021/am4028263
Iodine pentoxide (I2O5), also known as diiodine pentoxide, is a strong oxidizer which has been recently proposed as an iodine-rich oxidizer in nanoenergetic formulations, whose combustion products lead to molecular iodine as a biocidal agent. However, its highly hygroscopic nature hinders its performance as a strong oxidizer and an iodine releasing agent and prevents its implementation. In this work, we developed a gas phase assisted aerosol spray pyrolysis which enables creation of iron oxide passivated I2O5. Transmission electron microscopy elemental imaging as well as temperature-jump mass spectrometry confirmed the core shell nature of the material and the fact that I2O5 could be encapsulated in pure unhydrated form. Combustion performance finds an optimal coating thickness that enables combustion performance similar to a high performing CuO based thermite.Keywords: aerosol spray pyrolysis; biocide; energetic materials; nanocomposite; nanothermite; passivated;
Co-reporter:Haiyang Wang, Guoqiang Jian, Shi Yan, Jeffery B. DeLisio, Chuan Huang, and Michael R. Zachariah
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 15) pp:6797
Publication Date(Web):July 22, 2013
DOI:10.1021/am401238t
Nanometallic fuels with high combustion enthalpy, such as aluminum, have been proposed as a potential fuel replacement for conventional metallic fuel to improve propellant performance in a variety of propulsive systems. Nevertheless, nanometallic fuels suffer from the processing challenges in polymer formulations such as increased viscosity and large agglomeration, which hinder their implementation. In this letter, we employ electrospray as a means to create a gel within a droplet, via a rapid, solvent evaporation-induced aggregation of aluminum nanoparticles, containing a small mass fraction of an energetic binder. The gelled aluminum microspheres were characterized and tested for their burning behavior by rapid wire heating ignition experiments. The gelled aluminum microspheres show enhanced combustion behavior compared to nanoaluminum, which possibly benefits from the nitrocellulose coating and the gelled microstructure, and is far superior to the corresponding dense micrometer-sized aluminum.Keywords: combustion; electrospray; microspheres; nanoaluminum; nitrocellulose; sol−gel;
Co-reporter:Suvajyoti Guha, Joshua Wayment, Vinayak Rastogi, Mingdong Li, Michael J. Tarlov, Michael R. Zachariah
Journal of Colloid and Interface Science 2013 Volume 402() pp:291-299
Publication Date(Web):15 July 2013
DOI:10.1016/j.jcis.2013.02.050
Highlights•Used electrospray-differential mobility analysis for quantifying competitive adsorption–desorption.•IgM dimers always show greater propensity to adsorb to surfaces or stay adsorbed compared to monomers.•“Vroman effect” is observed only for particular surface type.•High shear has no effect on IgM monomer and dimer desorption.Understanding competitive adsorption–desorption of proteins onto surfaces is an important area of research in food processing and biomedical engineering. Here, we demonstrate, how electrospray-differential mobility analysis that has been traditionally used for characterizing bionanoparticles, can be used for quantifying complex competitive adsorption–desorption of oligomeric proteins or multiprotein systems using monomers and dimers of IgM as a model example onto silica and modified silica surfaces. Using ES-DMA, we show that IgM dimers show a preference to stay adsorbed to different surfaces although monomers adsorb more easily and desorption rates of monomers and dimers of IgM are surface-type-dependent and are not significantly affected by shear. We anticipate that this demonstration will make ES-DMA a popular “label-free” method for studying multicomponent multi-oligomeric protein adsorption to different surfaces in the future.Graphical abstract
Co-reporter:Lu Liu and Michael R. Zachariah
Energy & Fuels 2013 Volume 27(Issue 8) pp:4977-4983
Publication Date(Web):July 8, 2013
DOI:10.1021/ef400748x
In this study alkali metal doped Fe2O3 and Fe2O3/Al2O3 composite oxygen carriers were synthesized from spray pyrolysis, and the reactivity and stability as oxygen carrier materials were evaluated in a fixed bed reactor for 50 isothermal redox cycles using CH4 as the fuel. We find that both Fe2O3 and Fe2O3/Al2O3 composite showed reactivity degradation over multiple cycles, with a clear phase separation between Fe and Al, in the composites. In contrast, alkali metal doping (∼5 mol %) with Na, K, and Cs was found to stabilize the reactivity of the Fe2O3 over the 50 redox cycles and prevent phase Fe–Al separation in the composite. Methane to CO2 selectivity was found to be relevant to the dopant type, which decreased in the order of dopant type K, Cs, and Na. The best performing alkali metal, K, enhanced long-term stability significantly, with no observed degradation in kinetics and total conversion performance in the methane step as well as reduced coke formation. Adding an alumina matrix to K doped Fe2O3 helped promote CO2 generation as well as minimize coking and was found to be the best performing material.
Co-reporter:Guoqiang Jian;Jingyu Feng;Rohit J. Jacob;Garth C. Egan ; Michael R. Zachariah
Angewandte Chemie 2013 Volume 125( Issue 37) pp:9925-9928
Publication Date(Web):
DOI:10.1002/ange.201303545
Co-reporter:Guoqiang Jian;Jingyu Feng;Rohit J. Jacob;Garth C. Egan ; Michael R. Zachariah
Angewandte Chemie International Edition 2013 Volume 52( Issue 37) pp:9743-9746
Publication Date(Web):
DOI:10.1002/anie.201303545
Co-reporter:Wenbo Zhou, Sarah K. Watt, De-Hao Tsai, Vincent T. Lee, and Michael R. Zachariah
The Journal of Physical Chemistry B 2013 Volume 117(Issue 6) pp:1738-1745
Publication Date(Web):October 24, 2012
DOI:10.1021/jp307282q
We demonstrate the uniform attachment of bacterial spores electrophoretically onto fine wires in liquids and subsequently quantitatively detached back into suspension. It was found that the use of a pulsed voltage method resulted in a uniform coverage of spores and prevented visible bubble formation resulting from water electrolysis which tended to dislodge the spores from the wires. By monitoring the electrophoretically derived current, this method could also be used to quantitatively measure the surface charges on spores and the deposition rate. The method is generic and should be applicable to the deposition of any charged biological material (e.g., spores, bacteria, viruses) onto metal surfaces.
Co-reporter:X. Ma, C. D. Zangmeister, and M. R. Zachariah
The Journal of Physical Chemistry C 2013 Volume 117(Issue 20) pp:10723-10729
Publication Date(Web):April 12, 2013
DOI:10.1021/jp400477v
The oxidation kinetics of laboratory-generated soot particles has undergone extensive studies because of its importance in combustion-generated emissions and their control. In this study, we employed and compared two tandem ion-mobility methods, a tandem differential mobility analyzer (TDMA) and a differential mobility analyzer–aerosol particle mass analyzer (DMA–APM), to resolve the oxidation kinetics of soot. Whereas the TDMA method measures changes in particle mobility (i.e., size) from which a mass-based reaction rate can be inferred, the DMA–APM is a direct determination of particle mass change. We monitored the structure evolution of soot during oxidation by determining the mass-mobility scaling exponent of the particle population and found that soot structural changes due to oxidative sintering can perturb and corrupt the apparent reaction kinetics extracted from the TDMA method and suggest that the DMA–APM method probably is a more reliable approach to pursue such measurements. By combining the mass change data from DMA–APM with size change data from TDMA, we obtained the material density and primary particle size of soot aggregates during oxidation. Two reaction regimes were identified with oxidation fully penetrating the particle at low temperatures and partial penetration at high temperatures. The activation energies were determined for the two reaction regimes to be 79 and 201 kJ mol–1, respectively. The results should be useful in designing soot oxidation abatement units.
Co-reporter:Juchen Guo;Qing Liu;Chunsheng Wang
Advanced Functional Materials 2012 Volume 22( Issue 4) pp:803-811
Publication Date(Web):
DOI:10.1002/adfm.201102137
Abstract
The realization of manganese oxide anode materials for lithium-ion batteries is hindered by inferior cycle stability, rate capability, and high overpotential induced by the agglomeration of manganese metal grains, low conductivity of manganese oxide, and the high stress/strain in the crystalline manganese oxide structure during the repeated lithiation/delithiation process. To overcome these challenges, unique amorphous MnOx–C nanocomposite particles with interdispersed carbon are synthesized using aerosol spray pyrolysis. The carbon filled in the pores of amorphous MnOx blocks the penetration of liquid electrolyte to the inside of MnOx, thus reducing the formation of a solid electrolyte interphase and lowering the irreversible capacity. The high electronic and lithium-ion conductivity of carbon also enhances the rate capability. Moreover, the interdispersed carbon functions as a barrier structure to prevent manganese grain agglomeration. The amorphous structure of MnOx brings additional benefits by reducing the stress/strain of the conversion reaction, thus lowering lithiation/delithiation overpotential. As the result, the amorphous MnOx-C particles demonstrated the best performance as an anode material for lithium-ion batteries to date.
Co-reporter:Chunwei Wu;Kyle Sullivan;Snehaunshu Chowdhury;Guoqiang Jian;Lei Zhou
Advanced Functional Materials 2012 Volume 22( Issue 1) pp:78-85
Publication Date(Web):
DOI:10.1002/adfm.201100479
Abstract
In this work, high-oxygen-content strong oxidizer perchlorate salts were successfully incorporated into current nanothermite composite formulations. The perchlorates were encapsulated within mild oxidizer particles through a series of thermal decomposition, melting, phase segregation, and recrystallization processes, which occurred within confined aerosol droplets. This approach enables the use of hygroscopic materials by stabilizing them within a matrix. Several samples, including Fe2O3/KClO4, CuO/KClO4 and Fe2O3/NH4ClO4 composite oxidizer particles, have been created. The results show that these composite systems significantly outperform the single metal oxide system in both pressurization rate and peak pressure. The ignition temperatures for these mixtures are significantly lower than those of the metal oxides alone, and time-resolved mass spectrometry shows that O2 release from the oxidizer also occurs at a lower temperature and with high flux. The results are consistent with O2 release being the controlling factor in determining the ignition temperature. High-speed imaging clearly shows a much more violent reaction. The results suggest that a strategy of encapsulating a very strong oxidizer, which may not be environmentally compatible, within a more stable weak oxidizer offers the opportunity to both tune reactivity and employ materials that previously could not be considered.
Co-reporter:Shi Yan, Guoqiang Jian, and Michael R. Zachariah
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 12) pp:6432
Publication Date(Web):November 18, 2012
DOI:10.1021/am3021125
In this work, we present a first time fabrication of thermite-based nanofiber mats with a nitrocellulose composite energetic binder to create a new class of energetic 1D nanocomposite. The as prepared thermite based nanofibrous mats were characterized and tested for their burning behavior, and compared with the pure nitrocellulose and nanoaluminum incorporated nanofibers for their combustion performances. Thermite-based nanofibers show enhanced burning rates in combustion tests, which correlate to the mass loading of nanothermite relative to binder in nanofibers. The electrospinning method demonstrates the possibility of avoiding some of the problems associated with melt casting nanometalized propellants.Keywords: combustion; electrospinning; energetic materials; nanoaluminum; nanofiber; nanothermite; nitrocellulose; propellant;
Co-reporter:Suvajyoti Guha, Xiaofei Ma, Michael J. Tarlov, and Michael R. Zachariah
Analytical Chemistry 2012 Volume 84(Issue 15) pp:6308
Publication Date(Web):July 5, 2012
DOI:10.1021/ac301149k
Although electrospray-differential mobility analyzers (ES-DMA) have been previously employed to characterize ligand binding to nanoparticles, absolute quantification of surface coverage can be inaccurate at times because of ligand conformational effects. In this Letter, we report a quantitative technique by in-flight coupling of a particle mass analyzer (APM) with ES-DMA, thus enabling a direct quantitative analysis of mass independent of particle size, material, morphology and conformation. We demonstrate the utility of ES-DMA–APM by studying two model complex systems (gold nanoparticle–bovine serum albumin and polystyrene bead–antibody) as a function of concentration and pH. Our results obtained with ES-DMA–APM are in excellent agreement with prior work. We anticipate that this will enhance the capabilities of online quantitative characterization of ligand binding to nanoparticles.
Co-reporter:Suvajyoti Guha, Joshua R. Wayment, Mingdong Li, Michael J. Tarlov, Michael R. Zachariah
Journal of Colloid and Interface Science 2012 Volume 377(Issue 1) pp:476-484
Publication Date(Web):1 July 2012
DOI:10.1016/j.jcis.2012.03.059
Adsorbed proteins on walls of glass capillaries used for electrospray (ES) can desorb and potentially affect size distributions and, thus, quantification of aggregates of proteins. In this study we use differential mobility analysis (DMA) to investigate the size distribution of various proteins eluting from bare and passivated glass capillaries. We found no significant differences in aggregate distributions from unpassivated capillaries at ‘steady state’ when compared to aggregate distributions from passivated capillaries implying that desorbing proteins do not influence protein aggregate distribution. Surface passivation with gelatin was found to be considerably more effective in limiting adsorption of two antibodies (Rituxan and polyclonal human IgG) compared to passivation with BSA. Gelatin passivation was also found to be stable for a few days and from a pH range of 4.8–9.0.Graphical abstractHighlights► Developed a new methodology for passivating electrospray capillary surfaces. ► Proteins desorbing from electrospray capillary walls do not appear to influence aggregate distributions. ► Passivation of electrospray capillary surface with gelatin reduces adsorption of immunoglobulins. ► Used electrospray – differential mobility analysis for quantifying protein adsorption to electrospray capillary surface.
Co-reporter:Q. Liu, X. Ma, M.R. Zachariah
Microporous and Mesoporous Materials 2012 Volume 153() pp:210-216
Publication Date(Web):1 May 2012
DOI:10.1016/j.micromeso.2011.11.017
A new application of on-line tandem differential mobility-particle mass analysis (DMA-APM) is used to obtain the density distribution, detect the reaction evolution, and investigate the mechanism of porous particle formation. The expected uncertainty of the density measurement is within 5%. The method has several advantages over absorption methods such as BET in which pore model is required. The methodology also enables a size resolved measurement to understand how particle porosity varies over a given particle population. The DMA-APM method is materials independent, and can measure the density even in a particle with inaccessible pores. In this paper we demonstrate the method during the synthesis of mesoporous iron oxide and copper oxide. For example in the formation of iron oxide we found that small particles (∼50 nm) in the size distribution had a higher density (∼2.6 g/cm3) relative to larger 130 nm particles with a measured density of 2.2 g/cm3. Syntheses at higher temperatures lead to high density particles which were also less size sensitive.Graphical abstractHighlights► We demonstrate an on-line method to measure size resolved density of porous particles. ► Combined differential mobility analyzer with a particle mass analyzer. ► Simultaneous size resolved measurement of size and mass. ► We determined the expected uncertainty of the density measurement to be within 5%. ► Materials independent; measures density even in a particle with inaccessible pores.
Co-reporter:Suvajyoti Guha;Joshua R. Wayment;Michael J. Tarlov
Journal of Pharmaceutical Sciences 2012 Volume 101( Issue 6) pp:1985-1994
Publication Date(Web):
DOI:10.1002/jps.23097
Abstract
The biopharmaceutical industry characterizes and quantifies aggregation of protein therapeutics using multiple analytical techniques to cross-validate results. Here, we demonstrate the use of electrospray–differential mobility analysis (ES–DMA), a gas-phase and atmospheric pressure ion-mobility method for characterizing protein aggregates. Two immunoglobulin Gs are systematically heat treated to induce aggregation and characterized using size-exclusion chromatography (SEC) and ES–DMA. Although ES–DMA is a gas-phase characterization method, we find that aggregation kinetic rate constants determined by ES–DMA is in good agreement with those determined by SEC. ES–DMA appears to have a higher resolution and lower limit of detection as compared with SEC. Thus, ES–DMA can potentially become an important orthogonal tool for characterization of nascent protein aggregates in the biopharmaceutical industry. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:1985–1994, 2012
Co-reporter:Lei Zhou, Michael R. Zachariah
Chemical Physics Letters 2012 Volumes 525–526() pp:77-81
Publication Date(Web):16 February 2012
DOI:10.1016/j.cplett.2011.11.045
Abstract
In this Letter, we employed an ion mobility technique to measure the size-resolved native work function of structure controlled nanoparticles in free flight. We found that the Fowler–Nordheim law is applicable to not only spheres but also aggregates. The measured work functions of spheres are size dependent, and consistent with classical image and Coulomb potentials explanations. On the other hand, the measured work functions of aggregates are independent of mobility size, but depend on the size of primary particles. In addition, the particle photoelectric yield of aggregates and spheres were also evaluated as function of incident photon energy.
Co-reporter:Nicholas Piekiel and Michael R. Zachariah
The Journal of Physical Chemistry A 2012 Volume 116(Issue 6) pp:1519-1526
Publication Date(Web):January 3, 2012
DOI:10.1021/jp203957t
A T-jump/time-of-flight mass spectrometer (T-Jump/TOFMS) is used to probe the decomposition of several aminotetrazole containing energetic materials under very high heating rates of 105–106 K/s. The materials investigated are 5-amino-1-methyl-1H-tetrazolium dinitramide (MeHAT_DN), 1,5-diamino-4-methyl-1H-tetrazolium dinitramide (MeDAT_DN), 1,5-diamino-1H-tetrazolium nitrate (DAT_N), 1,5-diamino-4-methyl-1H-tetrazolium azide (MeDAT_N3), and 5-aminotetrazolium dinitramide (HAT_DN). Subtle differences between materials in functional group placement and anion composition allow for further understanding of the decomposition pathway of the tetrazole structure and various anions. Two decomposition pathways for the tetrazole ring are observed, which result in the primary formation of HN3 or N2. The N2 formation pathway occurs when functional groups are placed symmetrically around the tetrazole ring, whereas asymmetric placement results in HN3 production. The differing anion compositions also show effects on thermal stability of the salts, as is demonstrated by a lower decomposition temperature for the azide containing salt compared to the similar dinitramide containing material. For the decomposition of the dinitramide molecule, high temperature (N2O forming) and low temperature (NO2 forming) decomposition pathways are observed, as has been previously suggested.
Co-reporter:Nicholas W. Piekiel, Garth C. Egan, Kyle T. Sullivan, and Michael R. Zachariah
The Journal of Physical Chemistry C 2012 Volume 116(Issue 46) pp:24496-24502
Publication Date(Web):October 4, 2012
DOI:10.1021/jp304148c
This study investigates the use of metal oxides as an oxygen carrier in chemical looping combustion applications. The initiation and decomposition of C/CuO and C/Fe2O3 are investigated using a time-resolved T-jump/time-of-flight mass spectrometer (T-Jump/TOFMS). Heating of the metal oxide nanopowders produces gaseous O2, but when mixed with the fuel (carbon), gaseous O2 forms temporally after the primary combustion product, CO2. This indicates condensed phase reaction between the metal oxide and carbon as the predominant reaction mechanism rather than gas phase release of O2 and subsequent burning of carbon, at least in the initiation phase. In situ heating TEM, and SEM are used to further investigate the reaction. The oxidation rate of carbon in the present experiment is estimated to be 3 to 5 orders of magnitude greater than that predicted using the Nagle Strickland-Constable model. The activation energy of C/CuO, C/Fe2O3, and C/Bi2O3 are determined using the Ozawa iso-conversion method and are found to be 110, 170, and 230 kJ/mol, respectively. The condensed phase nature of this reaction is compared to our previous studies on aluminum nanothermites and is considered to be further evidence toward a reactive sintering initiation mechanism.
Co-reporter:Dudi Adi Firmansyah ; Kyle Sullivan ; Kwang-Sung Lee ; Yong Ho Kim ; Riyan Zahaf ; Michael R. Zachariah ;Donggeun Lee
The Journal of Physical Chemistry C 2012 Volume 116(Issue 1) pp:404-411
Publication Date(Web):December 13, 2011
DOI:10.1021/jp2095483
The oxidation mechanism of nanoaluminum particles, nominally employed as fuel component, is still an unsettled problem, because of the complex nature of thermomechanical properties of the oxide shell surrounding the elemental core. Although mechanical breakage of the alumina shell upon or after melting of aluminum core has been thought to play a key role in the combustion of aluminum nanoparticles, there has been little direct evidence. In this study, the microstructural behaviors of Al core and alumina shell lattices were investigated with increasing temperatures. Three in situ techniques, high-temperature X-ray diffraction analysis, hot-stage transmission electron microscopy, and high-resolution transmission electron microscopy for heat-treated samples, were employed to probe the thermal behaviors of aluminum and alumina lattices before and after melting of the aluminum core. High-temperature X-ray diffraction analysis revealed that nano aluminum lattice was initially expanded under tension at room temperature, and then when heated passed through a zero-strain state at ∼300 °C. Upon further heating above the bulk melting temperature of aluminum, the aluminum lattice expanded under almost no constraint. This interesting observation, which is contrary to almost all of the previous results and models, was ascribed to the inhomogeneous (localized) crystalline phase transformation of amorphous alumina. High-resolution transmission electron microscopy and in situ hot-stage transmission electron microscopy evidenced localized phase transformation accompanied by a significant shell thickening, presumably resulting from diffusion processes of Al cations and O anions, which is to absorb the pressure built in aluminum core, by creating a more ductile shell.
Co-reporter:Guoqiang Jian ; Nicholas W. Piekiel
The Journal of Physical Chemistry C 2012 Volume 116(Issue 51) pp:26881-26887
Publication Date(Web):December 4, 2012
DOI:10.1021/jp306717m
Aluminum nanoparticles (Al-NPs) and nano-Al/CuO thermite were investigated in a rapid heating environment by temperature jump time-of-flight mass spectrometry. Upon rapid heating (105 to 106 K/s), Al-containing vapor species (Al and Al2O) are observed to slowly increase with increasing temperature, followed by a rapid increase in concentration at ∼2030 K. The temporal evolution of Al, Al2O species observed in time-resolved mass spectra of rapid heated Al-NPs supports the hypothesis that Al containing species diffuse outward through the oxide shell under high heating rate conditions. The rapid rise in Al-containing species above 2030 K, which is below the bulk melting point of Al2O3, implies that the penetration of Al into the shell probably decreases its melting point. The measurements lead to an effective overall diffusion coefficient of ∼10–10 cm2/s. Time-resolved mass spectra of nano-Al/CuO thermite show for the first time the existence of Al, Al2O, AlO, and Al2O2 intermediate reaction products, with Al2O the main intermediate oxidation product, in agreement with thermochemical calculations.
Co-reporter:Xiaofei Ma, Purnendu Chakraborty, Brian J. Henz and Michael R. Zachariah
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 20) pp:9374-9384
Publication Date(Web):09 Apr 2011
DOI:10.1039/C0CP01923B
Organic monolayers at the surfaces of aqueous aerosols play an important role in determining the mass, heat transfer rate and surface reactivity of atmospheric aerosols. They can potentially contribute to the formation of cloud condensation nuclei (CCN) and are involved in a series of chemical reactions occurring in atmosphere. Recent studies even suggest that organic-coated interfaces could have played some role in prebiotic biochemistry and the origin of life. However, creating reproducible, well-characterized aqueous aerosol particles coated with organic films is an experimental challenge. This opens the opportunity for computer simulations and modeling of these complex structures. In this work, molecular dynamics simulation was used to probe the structure and the interfacial properties of the dicarboxylic acid coated aqueous aerosol. Low molecular weight dicarboxylic acids of various chain lengths and water solubility were chosen to coat a water droplet consisting of 2440 water molecules. For malonic acid coated aerosol, the surface acid molecules dissolved into the water core and formed an ordered structure due to the hydrophobic interactions. The acid and the water are separated inside the aerosol. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed on the surface of the particle. To study the water processing of the coated aerosols, the water vapor accommodation factors were calculated.
Co-reporter:Teresa L. Barone, Anshuman A. Lall, John M. E. Storey, George W. Mulholland, Vitaly Y. Prikhodko, Jennifer H. Frankland, James E. Parks, and Michael R. Zachariah
Energy & Fuels 2011 Volume 25(Issue 5) pp:1978-1988
Publication Date(Web):March 30, 2011
DOI:10.1021/ef200084k
We report the first in situ size-resolved density measurements of particles produced by premixed charge compression ignition (PCCI) combustion and compare these with conventional diesel exhaust particles. The effective densities (ρeff) of size-classified particles were determined by measurements with a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). Particle inherent densities (ρi) were calculated using an expression for particle mass given by idealized aggregate (IA) theory, transmission electron microscopy (TEM) measurements of primary particle diameter (dpp), and a comparison of the measured number of particles in each size class with that predicted by a proposed DMA-APM response function for aggregates. The ρeff of PCCI and conventional diesel particles were similar over a range of diameters characteristic of their number-size distributions. The ρeff were 0.89, 0.58, and 0.51 g/cm3 for conventional diesel and 0.90, 0.62, and 0.42 g/cm3 for PCCI particles with 50, 100, and 150 nm electrical mobility diameters (dm), respectively. The error associated with ρeff was about one percent of each measurement. The lowest ρeff were observed for exhaust gas recirculation (EGR) levels somewhat lower than that required for PCCI operation. The ρi of 50 and 100 nm conventional diesel particles were 1.22 ± 0.14 and 1.77 ± 0.29 g/cm3, which is in good agreement with previously reported values. PCCI ρi for these size classes did not differ significantly (1.27 ± 0.16 and 2.10 ± 0.20 g/cm3), suggesting like amounts of adsorbed liquid hydrocarbons. In addition, for 150 nm particles, the PCCI and conventional ρi were the same (2.20 ± 0.34 g/cm3). Given the close density values, we expect that particulate emissions control with diesel particulate filters (DPFs) would not be adversely affected by PCCI particle physical properties.
Co-reporter:Xiaofei Ma, Lu Liu, Natan Aronhime, and Michael R. Zachariah
Energy & Fuels 2011 Volume 25(Issue 9) pp:3925
Publication Date(Web):August 22, 2011
DOI:10.1021/ef200989a
The short residence times available in supersonic combustion require some pre-reaction under mixing-controlled-rich conditions and/or methods to lower the reaction temperature for auto-ignition. Adding catalysts could be such an option to achieve this objective. Catalytic ignition of toluene over the surfaces of in situ-generated free metal (Fe and Ni) nanoparticles was investigated experimentally in an aerosol reactor. The metal nanoparticles (Fe and Ni) were generated by decomposition of the corresponding metal carbonyls. Gas-phase (aerosol) size distributions along with transmission electron microscopy used to characterize the morphology of catalyst particles at different temperatures are presented. The effluent gas product and the fuel ignition temperature were determined by mass spectrometry. In comparison to non-catalytic homogeneous ignition, the addition of metal nanoparticles can lower the ignition temperature by as much as 150 °C under rich conditions but had little effect under lean conditions. Iron was found to be a more active catalyst than nickel. Inspection of the catalyst product indicated that sintering was occurring at relatively low temperatures presumably as a result of the exothermic reaction on the particle surface. Turnover frequency as high as 80 s–1 was achieved, implying a greater catalyst efficiency than commonly found for substrate-stabilized catalysts.
Co-reporter:Nicholas W. Piekiel, Richard E. Cavicchi, Michael R. Zachariah
Thermochimica Acta 2011 Volume 521(1–2) pp:125-129
Publication Date(Web):10 July 2011
DOI:10.1016/j.tca.2011.04.015
A micro-differential scanning calorimeter (μ-DSC) was employed to study the thermal decomposition of organic energetic materials at high heating rates. Heating rates from 1900 to 65,000 K/s were explored, which are many orders of magnitude higher than traditional DSC, but much closer to the conditions these materials would experience in their application. Temperature calibration was done by heating Sn, KNO3, and KClO4 at the desired heating rates to determine the temperature profile at each rate. The samples studied were 5-amino-1H-tetrazole, 5-amino-1-methyl-1H-tetrazolium dinitramide, 1,5-diamino-4-methyl-1H-tetrazolium dinitramide, and 1,5-diamino-4-methyl-1H-tetrazolium azide, which comprise a new class of high-nitrogen containing energetic materials. Activation energies determined using the Kissinger method, are much lower than those reported for the same materials under low heating rates indicating that other decomposition mechanisms are in play at high heating rates.Highlights► Used a μ-DSC device capable of rapid heating rates of up to 107 K/s. ► Rapid heating rate studies may probe different mechanistic pathways. ► Studied reaction of novel tetrazole containing energetic materials. ► Used heating rates that are many orders of magnitude greater than traditional DSC. ► Materials showed much lower activation energies under rapid heating conditions.
Co-reporter:S. H. Kim;C. Wang;M. R. Zachariah
Journal of Nanoparticle Research 2011 Volume 13( Issue 1) pp:139-146
Publication Date(Web):2011 January
DOI:10.1007/s11051-010-0011-6
With the advantage of continuous production of pure carbon nanotubes (CNTs), a new simple aerosol process for the formation of CNTs was developed. A combination of conventional spray pyrolysis and thermal chemical vapor deposition enabled the formation unusual sea-urchin-like carbon nanostructures composed of multi-walled CNTs and metal composite nanoparticles. The CNTs formed were relatively untangled and uniform with a diameter of less than
~10 nm. The key to the formation of CNTs in this way was to create a substrate particle containing both a catalytic and non-catalytic component, which prevented coking. The density of the CNTs grown on the spherical metal nanoparticles could be controlled by perturbing the density of the metal catalysts (Fe) in the host non-catalytic metal particle matrix (Al). Mobility size measurement was identified as a useful technique to real-time characterization of either the catalytic formation of thin carbon layer or CNTs on the surface of the metal aerosol. These materials have shown unique properties in enhancing the thermal conductivity of fluids. Other potential advantages are that the as-produced material can be manipulated easily without the concern of high mobility of conventional nanowires, and then subsequently released at the desired time in an unagglomerated state.
Co-reporter:Suvajyoti Guha, Joshua R. Wayment, Mingdong Li, Michael J. Tarlov, and Michael R. Zachariah
Langmuir 2011 Volume 27(Issue 21) pp:13008-13014
Publication Date(Web):September 9, 2011
DOI:10.1021/la202792g
We quantify the adsorption and desorption of a monoclonal immunoglobulin-G antibody, rituxamab (RmAb), on silica capillary surfaces using electrospray-differential mobility analysis (ES-DMA). We first develop a theory to calculate coverages and desorption rate constants from the ES-DMA data for proteins adsorbing on glass capillaries used to electrospray protein solutions. This model is then used to study the adsorption of RmAb on a bare silica capillary surface. A concentration-independent coverage of ≈4.0 mg/m2 is found for RmAb concentrations ranging from 0.01 to 0.1 mg/mL. A study of RmAb adsorption to bare silica as a function of pH shows maximum adsorption at its isoelectric point (pI of pH 8.5) consistent with literature. The desorption rate constants are determined to be ≈10–5 s–1, consistent with previously reported values, thus suggesting that shear forces in the capillary may not have a considerable effect on desorption. We anticipate that this study will allow ES-DMA to be used as a “label-free” tool to study adsorption of oligomeric and multicomponent protein systems onto fused silica as well as other surface modifications.
Co-reporter:Mingdong Li, Suvajyoti Guha, Rebecca Zangmeister, Michael J. Tarlov, and Michael R. Zachariah
Langmuir 2011 Volume 27(Issue 24) pp:14732-14739
Publication Date(Web):October 27, 2011
DOI:10.1021/la202177s
We have developed a simple, fast, and accurate method to measure the absolute number concentration of nanoparticles in solution. The method combines electrospray differential mobility analysis (ES-DMA) with a statistical analysis of droplet-induced oligomer formation. A key feature of the method is that it allows determination of the absolute number concentration of particles by knowing only the droplet size generated from a particular ES source, thereby eliminating the need for sample-specific calibration standards or detailed analysis of transport losses. The approach was validated by comparing the total number concentration of monodispersed Au nanoparticles determined by ES-DMA with UV/vis measurements. We also show that this approach is valid for protein molecules by quantifying the absolute number concentration of Rituxan monoclonal antibody in solution. The methodology is applicable for quantification of any electrospray process coupled to an analytical tool that can distinguish monomers from higher order oligomers. The only requirement is that the droplet size distribution be evaluated. For users only interested in implementation of the theory, we provide a section that summarizes the relevant formulas. This method eliminates the need for sample-specific calibration standards or detailed analysis of transport losses.
Co-reporter:Xiaofei Ma ; Anshuman A. Lall ; George W. Mulholland
The Journal of Physical Chemistry C 2011 Volume 115(Issue 34) pp:16941-16946
Publication Date(Web):July 25, 2011
DOI:10.1021/jp206174u
We report observations of the evaporation anisotropy of substrate-free Zn nanocrystals (NCs) as imaged from electron microscopy and determine the onset temperature of evaporation as a function of NC size by the gas-phase ion-mobility method. The observed shape transformation of free NCs is fundamentally different from those observed in traditional hot-stage TEM heating experiments. The onset temperature for evaporation decreases as the NC size decreases and is analogous to the Kelvin effect. The cohesive energy of bulk Zn is determined to be 1.8 ± 0.1 eV from the size-dependent evaporation data. A mechanism based on crystal face dependent surface melting is proposed to explain the evaporation anisotropy effect.
Co-reporter:Xiaofei Ma, Anshuman A. Lall, Natan Aronhime, Michael R. Zachariah
International Journal of Hydrogen Energy 2010 Volume 35(Issue 14) pp:7476-7484
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.05.002
Catalytic decomposition of liquid fuels (n-octane, iso-octane, 1-octene, toluene and methylcyclohexane) is achieved in a continuous tubular aerosol reactor as a model for the solar initiated production of hydrogen, and easily separable CO free carbonaceous aerosol product. The effects of fuel molecular structure and catalyst concentration on the overall hydrogen yield were studied. Iron aerosol particles used as the catalysts, were produced on-the-fly by thermal decomposition of iron pentacarbonyl. The addition of iron catalyst significantly decreases the onset temperature of hydrogen generation as well as improves the reaction kinetics by lowering the reaction activation energy. The activation energy without and with iron addition was 260 and 100 kJ/mol, respectively representing a decrease of over 60%. We find that with the addition of iron, toluene exhibits the highest hydrogen yield enhancement at 900 °C, with a 6 times yield increase over thermal decomposition. The highest H2 yield obtained was 81% of the theoretical possible, for n-octane at 1050 °C. The general trend in hydrogen yield enhancement is that the higher the non-catalytic thermal decomposition yield, the weaker the catalytic enhancement. The gaseous decomposition products were characterized using a mass spectrometer. An XRD analysis was conducted on the wall deposit to determine the product composition and samples for electron-microscopic analysis were collected exiting the furnace by electrostatically precipitating the aerosol onto a TEM grid.
Co-reporter:Xiaofei Ma, Michael R. Zachariah
International Journal of Hydrogen Energy 2010 Volume 35(Issue 6) pp:2268-2277
Publication Date(Web):March 2010
DOI:10.1016/j.ijhydene.2010.01.011
The substrate-free hydrolysis of Zn nanocrystals was investigated as the second step in a ZnO/Zn solar water-splitting thermochemical cycle. In this work, we combined two different ion-mobility schemes in series to study the hydrolysis kinetics of size-selected zinc nanocrystals (NCs). The first mobility characterization size selects particles with a differential mobility analyzer (DMA). The second mobility characterization employs an aerosol particle mass analyzer (APM) and measures changes in mass resulting from a controlled hydrolysis of the Zn NCs. A low temperature reaction mechanism is proposed to explain the mass change behavior of Zn NCs hydrolysis at 100–250 °C. An Arrhenius law was used to extract the reaction kinetic parameters. The hydrolysis activation energy and the order of the reaction with respect to water mole fraction were found to be 24 ± 2 kJ/mol and 0.9 ± 0.1, respectively. Complete conversion of 70 nm Zn NCs was achieved at 175 °C with a residence time of about 10 s and water vapor mole fraction of 19%.
Co-reporter:Snehaunshu Chowdhury, Kyle Sullivan, Nicholas Piekiel, Lei Zhou and Michael R. Zachariah
The Journal of Physical Chemistry C 2010 Volume 114(Issue 20) pp:9191-9195
Publication Date(Web):April 29, 2010
DOI:10.1021/jp906613p
Solid−solid reactions at the nanoscale between a metal passivated with a nascent oxide and another metal oxide can result in a very violent reaction. This begs the question as to what mechanism is responsible for such a rapid reaction. The ignition of nanoscale Al/CuO thermites with different aluminum oxide shell thicknesses were investigated on a fast heated (∼105 K/s) platinum wire. Ramping the wire temperature to ∼1250 K and then shutting off the voltage pulse result in ignition well after the pulse is turned off; i.e., an ignition delay is observed. The delay is used as a probe to extract the effective diffusion coefficient of the diffusing species, which is confirmed by fast time-resolved mass spectrometry. The results of this study are consistent with a diffusion controlled ignition mechanism.
Co-reporter:Chunwei Wu, Donggeun Lee and Michael R. Zachariah
Langmuir 2010 Volume 26(Issue 6) pp:4327-4330
Publication Date(Web):December 30, 2009
DOI:10.1021/la903421y
The ability to manipulate miniature object assemblies with well-defined structures in a controllable manner is of both fundamental and applied interests. This article presents general strategies, with nanospheres as building blocks, to engineer mesoscopic spherical architectures via a process of evaporation-driven self-assembly in aerosol droplets. Uniform magnetite iron oxide (Fe3O4, ∼2.5 nm), silica (SiO2, ∼15 nm), and cupric oxide (CuO, ∼6 nm) nanoparticles were employed for the structural architecture. The method enables microstructural control of the self-assembled mesospheres by tuning the competition between solvent evaporation and solute diffusion within an aerosol droplet. Furthermore, we have demonstrated it is technically feasible to assemble surface-dissimilar binary components, i.e., charge-stabilized hydrophilic SiO2 and hydrophobic ligand-capped Fe3O4 nanoparticles, into hierarchical composite structures, which could be extended for preparation of more hierarchically textured materials with desired functionalities.
Co-reporter:S.H. Kim, G.W. Mulholland, M.R. Zachariah
Carbon 2009 Volume 47(Issue 5) pp:1297-1302
Publication Date(Web):April 2009
DOI:10.1016/j.carbon.2009.01.011
We employ a combination of gas phase particle mobility and mass methods to make the first absolute density measurement of gas phase grown carbon nanotubes (CNTs). The approach combines a tandem differential mobility analyzer and aerosol particle mass analyzer in series to achieve two steps of electrical mobility classifications of the CNTs and one of mass classification. In the first mobility classification step a stream of monodisperse catalytic particles was produced by pulsed laser ablation. These mobility-classified catalysts seeded the aerosol growth of CNTs, where were directly passed to a second electrical mobility classification step which allows classification of the diameter-controlled CNTs in length. These diameter- and length-classified CNTs were finally introduced into the aerosol particle mass analyzer to measure their mass distribution. We found that the condensed phase density of CNTs was 1.74 ± 0.16 g/cm3 for two different groups of CNTs with diameters of ∼15 and ∼22 nm. This value is lower (about 3 sigma) than for graphite, and about 1 sigma lower than the average value for density measurements for carbon black.
Co-reporter:D.-H. Tsai, L. F. Pease III, R. A. Zangmeister, M. J. Tarlov and M. R. Zachariah
Langmuir 2009 Volume 25(Issue 1) pp:140-146
Publication Date(Web):December 8, 2008
DOI:10.1021/la703164j
We demonstrate the utility of electrospray gas-phase ion-mobility analysis as a new method to investigate nanoparticle flocculation, or aggregation. Au nanoparticle (Au-NP) solutions were sampled via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the particle mobility distribution. Multimodal size distributions obtained with ES-DMA indicated the presence of single Au-NPs (monomer) as well as larger Au-NP clusters such as dimers, trimers, and tetramers under specific solution conditions. The fraction of each aggregate species as a function of time was quantitatively characterized, from which the degree of aggregation, aggregation rate, and stability ratio at different ionic strengths were determined. The latter enabled the extraction of a surface potential (or surface charge density) of 64 ± 2 mV for 10 nm Au-NPs, which is in good agreement with values obtained from other methods, thus validating our approach. Our results show that ES-DMA is a valuable tool for quantitatively probing the early stages of colloidal aggregation or as a preparatory tool for the size election of aggregates.
Co-reporter:D-H. Tsai, R. A. Zangmeister, L. F. Pease III, M. J. Tarlov and M. R. Zachariah
Langmuir 2008 Volume 24(Issue 16) pp:8483-8490
Publication Date(Web):July 29, 2008
DOI:10.1021/la7024846
We present results of a systematic examination of functionalized gold nanoparticles (Au-NPs) by electrospray-differential mobility analysis (ES-DMA). Commercially available, citrate-stabilized Au colloid solutions (10–60 nm) were sized using ES-DMA, from which changes in particle size of less than 0.3 nm were readily discerned. It was found that the formation of salt particles and the coating of Au-NPs by salt during the electrospray process can interfere with the mobility analysis, which required the development of sample preparation and data correction protocols to extract correct values for the Au-NP size. Formation of self-assembled monolayers (SAMs) of alkanethiol molecules on the Au-NP surface was detected from a change in particle mobility, which could be modeled to extract the surface packing density of SAMs. A gas-phase temperature-programmed desorption (TPD) kinetic study of SAMs on Au-NPs found the data to be consistent with a second-order Arrhenius-based rate law, yielding an Arrhenius factor of 1.0 × 1011 s−1 and an activation energy ∼105 kJ/mol. For the size range of SAM-modified Au-NP we considered, the effect of surface curvature on the energetics of binding of carboxylic acid terminated SAMs is evidently negligible, with binding energies determined by TPD agreeing with those reported for the same SAMs on planar surfaces. This study suggests that the ES-DMA can be added to the tool set of characterization methods used to study the structure and properties of coated nanoparticles.
Co-reporter:Lei Zhou, Ashish Rai, Nicholas Piekiel, Xiaofei Ma and Michael R. Zachariah
The Journal of Physical Chemistry C 2008 Volume 112(Issue 42) pp:16209-16218
Publication Date(Web):2017-2-22
DOI:10.1021/jp711235a
Nanoscaled nickel particles have attracted interest for their potential use as a fuel in energetic materials. In this work, we combined two ion-mobility spectrometry approaches, tandem differential mobility analysis (TDMA) and tandem differential mobility−particle mass analysis (DMA-APM), to study the size-resolved reactivity of nickel nanoparticles. Nickel nanoparticles were generated in situ by using gas-phase thermal pyrolysis of nickel carbonyl. Four particle sizes (40, 62, 81, and 96 nm, mobility size) were then selected by using a differential mobility analyzer. These particles were sequentially oxidized in a flow reactor at various temperatures (25−1100 °C). The size and mass change of the size-selected and -reacted particles were then measured by a second DMA, or an APM. We found that both particle size and mass were increased as the temperature increased. However, at higher temperature (600−1100 °C), a different mass and size change behavior was observed that could be attributed to a phase transition between NiO and Ni2O3. A shrinking core model employed to extract the size-resolved kinetic parameters shows that the activation energy for oxidation decreased with decreasing particle size. The burning time power dependence on particle size was found to be less than 2 and nickel particles were found to be kinetically more active than aluminum.
Co-reporter:T. Hawa ;M. R. Zachariah
The Journal of Physical Chemistry C 2008 Volume 112(Issue 38) pp:14796-14800
Publication Date(Web):August 27, 2008
DOI:10.1021/jp800780s
One of the significant challenges in the use of nanocrystals, is the control of crystal shape when grown from the gas−phase. Recently, the Kortshagen group has succeeded in generating cubic Si nanocrystals in a nonequilibrium plasma. In this paper we consider the energetics of various shaped Si nanocrystals, and the role that hydrogen surface termination plays. We consider cube, truncated octahedron, icosahedron, and spherical shapes for both bare and hydrogen coated silicon nanocrystals for sizes between 2 and 10 nm. From our molecular dynamics (MD) simulations, show that for bare Si crystals, icosahedron crystals are the most energetically stable, and cubic the least. On the other hand, when hydrogenated, the cubic structure comes about because 1) the cubic structure is energetically favored when hydrogen terminated and 2) the plasma that operates with hydrogen also provides a steady source of hydrogen atoms for etching.
Co-reporter:Soo H. Kim, Michael R. Zachariah
Materials Letters 2007 Volume 61(Issue 10) pp:2079-2083
Publication Date(Web):April 2007
DOI:10.1016/j.matlet.2006.08.031
We demonstrate gas-phase (aerosol) generation of diameter-controlled carbon nanotubes (CNTs) by employing size-controlled monodisperse nickel nanoparticles produced by the combination of pulsed laser ablation and electrostatic classification. The electrostatic classifier sorted agglomerated mono-area nickel particles, and then a subsequent heating process at ∼ 1200 °C created sintered single primary particles with very narrow size distribution. These isolated single primary particles were then sent to an aerosol reactor where free-flight CNTs were grown with acetylene and hydrogen mix at temperature of ∼ 750 °C. The resulting CNTs formed in this continuous gas-phase process were found to have a uniform diameter, which is commensurate with the diameter of the size-controlled catalytic nickel particles.
Co-reporter:A. Prakash;A. V. McCormick;M. R. Zachariah
Advanced Materials 2005 Volume 17(Issue 7) pp:
Publication Date(Web):30 MAR 2005
DOI:10.1002/adma.200400853
A new metastable intermolecular composite (MIC) which employs KMnO4 nanoparticles as the oxidizer has been developed for energetic-material applications. The nanoparticles are synthesized by a spray-drying process, and a strong correlation between pressurization rates (measurement schematic shown in Figure) for several MIC combinations and the fraction of reactive oxygen present in the combustion product is observed.
Co-reporter:S. H. Kim;M. R. Zachariah
Advanced Materials 2004 Volume 16(Issue 20) pp:
Publication Date(Web):23 SEP 2004
DOI:10.1002/adma.200306436
Electrostatically enhanced nanocomposite particle assembly as a viable method of enhancing the reactivity of energetic nanocomposites is reported. The kinetics of the burning process can be be tailored, and differential scanning calorimetry (DSC) results demonstrate that bipolar- assembly synthesized aluminum/iron oxide nanocomposite aerosol materials have burning rates an order of magnitude higher than those produced via random Brownian coagulation.
Co-reporter:Suvajyoti Guha, Joshua R. Wayment, Michael J. Tarlov, Michael R. Zachariah
Journal of Pharmaceutical Sciences (June 2012) Volume 101(Issue 6) pp:1985-1994
Publication Date(Web):1 June 2012
DOI:10.1002/jps.23097
The biopharmaceutical industry characterizes and quantifies aggregation of protein therapeutics using multiple analytical techniques to cross-validate results. Here, we demonstrate the use of electrospray–differential mobility analysis (ES–DMA), a gas-phase and atmospheric pressure ion-mobility method for characterizing protein aggregates. Two immunoglobulin Gs are systematically heat treated to induce aggregation and characterized using size-exclusion chromatography (SEC) and ES–DMA. Although ES–DMA is a gas-phase characterization method, we find that aggregation kinetic rate constants determined by ES–DMA is in good agreement with those determined by SEC. ES–DMA appears to have a higher resolution and lower limit of detection as compared with SEC. Thus, ES–DMA can potentially become an important orthogonal tool for characterization of nascent protein aggregates in the biopharmaceutical industry. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:1985–1994, 2012
Co-reporter:Xiaofei Ma, Christopher D. Zangmeister, Julien Gigault, George W. Mulholland, Michael R. Zachariah
Journal of Aerosol Science (December 2013) Volume 66() pp:209-219
Publication Date(Web):1 December 2013
DOI:10.1016/j.jaerosci.2013.08.001
•We monitor the restructuring of soot during water processing.•We observed soot restructuring takes place above certain critical saturation ratio.•The mechanism of soot restructuring was explored.•Experiments indicate that soot restructuring occurs during evaporation, not during condensation.•Calculation shows the restructuring is driven by capillary forces.Soot aggregate restructuring is explored in laboratory prepared soot particles upon exposure to high humidity environment followed by rapid water evaporation. Soot was generated in a Santoro style ethylene diffusion burner, and condensation of water on the soot particles was realized in a temperature-controlled water growth tube. The structure transformation of soot particles under different humidity conditions was monitored using a Differential Mobility Analyzer – Aerosol Particle Mass Analyzer (DMA-APM) and Tandem Differential Mobility Analyzer (TDMA) methods. The primary measured properties were mass-mobility scaling exponent, particle mass and mobility size before and after processing. A critical saturation ratio was observed above which aggregate restructuring occurred. The morphological change was visualized by taking electron microscopic images. X-ray photoelectron spectroscopy (XPS) analysis found that the chemical structures of different processed soot were indistinguishable. To assess if soot collapse occurred during water condensation or evaporation, water-coated soot was directly injected into water, where multi-angle light scattering showed that the structure was uncollapsed. This result indicates that soot restructuring driven by capillary forces occurs during evaporation, not condensation.
Co-reporter:S.H. Kim, G.W. Mulholland, M.R. Zachariah
Journal of Aerosol Science (August 2007) Volume 38(Issue 8) pp:823-842
Publication Date(Web):1 August 2007
DOI:10.1016/j.jaerosci.2007.06.003
In a previous experimental study, we demonstrated that gas phase electrophoretic mobility separation enables one to classify diameter-selected carbon nanotubes (CNTs) by length [Kim, S. H. & Zachariah, M. R. (2005). In-flight size classification of carbon nanotubes by gas phase electrophoresis. Nanotechnology, 16, 2149–2152] and have subsequently used this capability to track the growth rate of CNTs in free-flight [Kim, S. H. & Zachariah, M. R. (2006). In-flight kinetic measurements of the aerosol growth of carbon nanotubes by electrical mobility classification. Journal of Physical Chemistry B, 110, 4555–4562]. In this paper, we develop a theoretical model to describe the behavior of nanotubes (or nanowires) undergoing Brownian rotation in an electric field, and provide a more rigorous interpretation of the experimental results. The Boltzmann expression for the orientation probability includes both the free charge energy as well as the polarizability energy. In the theoretical model, we computed the orientation-averaged electrical mobility and the precipitating time of a rotating nanowire in DC electric field in the free-molecular limit. This analysis was used to obtain the precipitation time of a nanowire in a differential mobility analyzer (DMA). Based on the theoretical model and its comparison with experimental measurement, we found that: (i) a stronger electric field was required to select longer nanowires for a given diameter and (ii) shorter nanowires with the aspect ratio of β<∼30(df=15nm) freely rotate for applied electric field up to ∼1kV/cm, while longer nanowires (β>∼30) were aligned by the electric field. The experimentally determined nanowire length was in fair agreement with that computed by our theoretical model, in which the effect of the nanowire's alignment on mobility classification in various electric fields was accounted for. The over prediction of the model for longer nanowires is shown to result from the bent structure of the longer nanowires. The methodology should be generic to other nanostructures with high aspect ratio.
Co-reporter:T. Hawa, M.R. Zachariah
Journal of Aerosol Science (August 2007) Volume 38(Issue 8) pp:793-806
Publication Date(Web):1 August 2007
DOI:10.1016/j.jaerosci.2007.05.008
A simple modification to the Frenkel sintering law is developed for nanoparticle fractal aggregates, based on molecular dynamics (MD) simulations. The fractal aggregates investigated consist of up to 110 primary particles, with primary particles of 2.5 nm in diameter, and the fractal dimension of 1 (wire), 1.9 (complex), and 3 (compact). In addition simple prototype L- and T-shape aggregate were considered. We found that L-shape aggregates behaved similar to straight chains and thus did not impact the overall sintering time. By contract T-shape aggregate sintering kinetics was controlled by the longest contiguous branch in the system (i.e. effective primary branch length). We found that sintering of fractal aggregates is a combination of local sintering processes of line-, L- and T-shape structures. As expected, sintering time increases with increasing mass of the aggregate and with decreasing the fractal dimension. The sintering times normalized by the primary particle diameter showed a universal relationship which depends only on the number of particles in an aggregate and its fractal dimension. The MD results were found to be qualitatively consistent with a continuum viscous flow model, and was used as the basis from which a phenomenological sintering law for fractal aggregates could be derived. The phenomenological model is a power law modification of the Frenkel sintering equation to include a dependence on the number of particles in a fractal aggregate and fractal dimension:t=tFrenkel*(N-1)0.68∧Df.This relationship is amenable for use in phenomenological aerosol models that might include sintering effects.
Co-reporter:Dan A. Kaplowitz, R.J. Jouet, Michael R. Zachariah
Journal of Crystal Growth (1 December 2010) Volume 312(Issue 24) pp:3625-3630
Publication Date(Web):1 December 2010
DOI:10.1016/j.jcrysgro.2010.09.015
We show a low temperature gas-phase synthesis route to produce faceted aluminum crystals in the aerosol phase. Use of triisobutylaluminum whose decomposition temperature is below the melting point of elemental aluminum enabled us to grow nanocrystals from its vapor. TEM shows both polyhedral crystalline and spherical particle morphologies, but with the addition of an annealing furnace one can significantly enhance the production of just the polyhedral particles. The results on surface passivation with oxygen suggest that these nanocrystals are less pyrophoric than the corresponding spherical aluminum nanoparticles, and combustion tests show an increase in energy release compared to commercial nanoaluminum.
Co-reporter:Xizheng Wang, Wenbo Zhou, Jeffery B. DeLisio, Garth C. Egan and Michael R. Zachariah
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 20) pp:NaN12758-12758
Publication Date(Web):2017/05/05
DOI:10.1039/C6CP08532F
Nanothermites offer high energy density and high burn rates, but are mechanistically only now being understood. One question of interest is how initiation occurs and how the ignition temperature is related to microscopic controlling parameters. In this study, we explored the potential role of oxygen ion transport in Bi2O3 as a controlling mechanism for condensed phase ignition reaction. Seven different doped δ-Bi2O3 were synthesized by aerosol spray pyrolysis. The ignition temperatures of Al/doped Bi2O3, C/doped Bi2O3 and Ta/doped Bi2O3 were measured by temperature-jump/time-of-flight mass spectrometer coupled with a high-speed camera respectively. These results were then correlated to the corresponding oxygen ion conductivity (directly proportional to ion diffusivity) for these doped Bi2O3 measured by impedance spectroscopy. We find that ignition of thermite with doped Bi2O3 as oxidizer occurs at a critical oxygen ion conductivity (∼0.06 S cm−1) of doped Bi2O3 in the condensed-phase so long as the aluminum is in a molten state. These results suggest that oxygen ion transport limits the condensed state Bi2O3 oxidized thermite ignition. We also find that the larger oxygen vacancy concentration and the smaller metal–oxide bond energy in doped Bi2O3, the lower the ignition temperature. The latter suggests that we can consider the possibility of manipulating microscopic properties within a crystal, to tune the resultant energetic properties.
Co-reporter:Lu Liu, Daniel D. Taylor, Efrain E. Rodriguez and Michael R. Zachariah
Chemical Communications 2016 - vol. 52(Issue 68) pp:NaN10372-10372
Publication Date(Web):2016/07/21
DOI:10.1039/C6CC01997H
The selection of highly efficient oxygen carriers (OCs) is a key step necessary for the practical development of chemical looping combustion (CLC). In this study, a series of ABO3 perovskites, where A = La, Ba, Sr, Ca and B = Cr, Mn, Fe, Co, Ni, Cu, are synthesized and tested in a fixed bed reactor for reactivity and stability as OCs with CH4 as the fuel. We find that the electronegativity of the transition metal on the B-site (λB), is a convenient descriptor for oxygen storage capacity (OSC) of our perovskite samples. By plotting OSC for total methane oxidation against λB, we observe an inverted volcano plot relationship. These results could provide useful guidelines for perovskite OC design and their other energy related applications.
Co-reporter:Xiaofei Ma, Purnendu Chakraborty, Brian J. Henz and Michael R. Zachariah
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 20) pp:NaN9384-9384
Publication Date(Web):2011/04/09
DOI:10.1039/C0CP01923B
Organic monolayers at the surfaces of aqueous aerosols play an important role in determining the mass, heat transfer rate and surface reactivity of atmospheric aerosols. They can potentially contribute to the formation of cloud condensation nuclei (CCN) and are involved in a series of chemical reactions occurring in atmosphere. Recent studies even suggest that organic-coated interfaces could have played some role in prebiotic biochemistry and the origin of life. However, creating reproducible, well-characterized aqueous aerosol particles coated with organic films is an experimental challenge. This opens the opportunity for computer simulations and modeling of these complex structures. In this work, molecular dynamics simulation was used to probe the structure and the interfacial properties of the dicarboxylic acid coated aqueous aerosol. Low molecular weight dicarboxylic acids of various chain lengths and water solubility were chosen to coat a water droplet consisting of 2440 water molecules. For malonic acid coated aerosol, the surface acid molecules dissolved into the water core and formed an ordered structure due to the hydrophobic interactions. The acid and the water are separated inside the aerosol. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed on the surface of the particle. To study the water processing of the coated aerosols, the water vapor accommodation factors were calculated.
Co-reporter:Guoqiang Jian, Yunhua Xu, Li-Chung Lai, Chunsheng Wang and Michael R. Zachariah
Journal of Materials Chemistry A 2014 - vol. 2(Issue 13) pp:NaN4632-4632
Publication Date(Web):2014/02/14
DOI:10.1039/C4TA00207E
This work focuses on development of Mn3O4 hollow spheres with high cycling capacity and high rate capability in lithium ion batteries. Hollow Mn3O4 spheres are synthesized by an aerosol based “droplet to particle” strategy. The synthesis process involves producing and heating aerosol precursor droplets in air flow at 600 °C to induce exothermic reactions and gas blowing to form the single phase hollow Mn3O4 spheres. The hollow Mn3O4 spheres, as an anode material, deliver a highly stable cycle performance with capacity retention of ∼980 mA h g−1 for over 140 cycles at 200 mA g−1 and an excellent rate capability by retaining 300 mA h g−1 at high current density of 10000 mA g−1.
Co-reporter:Wenbo Zhou, Jeffery B. DeLisio, Xiangyu Li, Lu Liu and Michael R. Zachariah
Journal of Materials Chemistry A 2015 - vol. 3(Issue 22) pp:NaN11846-11846
Publication Date(Web):2015/04/29
DOI:10.1039/C5TA00756A
Nanoscale potassium persulfate (K2S2O8) was evaluated as an alternative to other peroxy salts, such as periodates (KIO4), in aluminum-fueled energetic nano-composite formulations. High speed imaging coupled with temperature jump (T-jump) ignition found the nano-Al/K2S2O8 reaction to have an ignition temperature of 600 °C which is comparable to nano-Al/KIO4 and lower than nano-Al/K2SO4. The results from constant-volume pressure cell experiments further show that nano-Al/K2S2O8 releases more gas and has a longer burn time than nano-Al/KIO4. Thermal analyses at low heating rates (10 °C min−1) by coupled differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and mass spectrometry (MS) show that there are three main steps of thermal decomposition for nano-K2S2O8, with initial exothermic decomposition to release O2 at 270 °C, and following endothermic decomposition to release both O2 and SO2 at higher temperatures. The heat of formation of K2S2O8 was measured to be −1844.5 kJ mol−1 based on the DSC results. Experiments performed at ultrafast heating rates (∼105 °C s−1) using temperature-jump time-of-flight (T-jump/TOF) MS show that the low O2 generation temperature of nano-K2S2O8 contributes to its high reactivity in nano-thermite compositions. An ignition mechanism involving gaseous oxygen was proposed for nano-thermite compositions containing reactive oxysalts such as nano-K2S2O8. In contrast, a condense phase ignition mechanism was proposed for nano-thermites involving less reactive oxysalts such as nano-K2SO4. Given that the nano-Al/K2S2O8 system is highly exothermic in addition to generating a considerable amount of SO2, it may be a candidate for use in energetic biocidal applications.
