This paper illustrates the retarding effects of welan gum on the hydration of C4A3$ both in the absence and presence of gypsum. By using the methods of isothermal calorimetry, X-ray diffractometry, mercury instruction porosimetry, thermogravimetry and scanning electron microscopy, it reveals that the hydration of C4A3$ is significantly retarded and reduced in the presence of welan gum, while the total hydration heat of C4A3$ is reduced with the rise of dose of welan gum. The retarding effect of welan gum on the hydration of C4A3$ in the absence of gypsum is much stronger than that in the presence of gypsum. The hydration product of AFm is AFm-12 at curing time longer than 1 d at the w/c ratio of 1. As a whole, welan gum will not affect the composition of hydration products of C4A3$, even though the AFm phase grains grown well and are better shaped with addition of 0.50% welan gum.

•Nanorod-like MgAl2O4 spinel aerogel is firstly synthesized.•This approach is straightforward, inexpensive, and safe.•The formation temperature of spinel aerogel is as low as 500 °C.•The BET area of the spinel aerogel is 81.87 m2/g after calcining at 1200 °C.A novel nanorod-like spinel aerogel is synthesized by the sol-gel method combined with the supercritical technique. The Mg4Al2(OH)14·3H2O and boehmite is formed in the spinel precursor aerogel and Mg4Al2(OH)14·3H2O transforms into MgO and spinel at 350 °C. Structural transition of boehmite to γ-Al2O3 occurs at ca. 400 °C, which is favorable to the further solid reaction between MgO and γ-Al2O3 forming spinel aerogel at 500 °C. This formation temperature is much lower than the conventional methods. The highly pure nanorod spinel with length of 150–200 nm and width of 5–10 nm is well crystallized after 800 °C. The nanocrystal maintains a large specific surface of 81.87 m2/g after calcining at 1200 °C.

•A metal silicide–glass hybrid coating was developed by rapid sintering method.•The coating exhibiting an excellent oxidation behavior at 1773 K in air for 50 h.•The total emissivity is about 0.9 without obvious degradation during oxidation.•Emissive mechanism regarding electron transition is discussed by DFT method.To develop a high emissivity, high-temperature-resistant coating for a reusable thermal protection system, a metal silicide–glass hybrid coating was prepared on fibrous ZrO2 ceramic by rapid sintering method, which comprises a TaSiO glass layer and a dense MoSi2–TaSi2–glass layer and exhibits improved oxidation behavior at 1773 K in air for 50 h. During oxidation, the total emissivity in 0.3–2.5 μm slightly fluctuates around 0.9 without obvious degradation. The emissive mechanism was identified as electron transition in interband of metal silicides and in impurity states of amorphous SiO2 and lattice vibration of crystalline SiO2.

•A high emissivity MoSi2- aluminaborosilicate glass hybrid coating was prepared.•The viscosity of the coating surface was indirectly characterized by XPS.•The surface roughness and morphology were characterized by CLSM.•The M30 coating showed the best thermal shock resistance.•The total emissivity values of all the coatings exceeded 0.85 in 0.8–2.5 μm.To develop a flexible reusable surface insulation for thermal protection system, MoSi2-aluminoborosilicate glass hybrid coatings have been prepared on Al2O3 fiber reinforced Al2O3-SiO2 aerogel composite by slurry dipping and rapid sintering method. The effect of MoSi2 content on radiative property and thermal shock behavior was investigated. The total emissivity values of all the coatings exceeded 0.85 in the wavelength of 0.8–2.5 μm. The M10 and M50 coatings were up to 0.9, which was due to the highest amorphous glass content of the M10 coating and the largest surface roughness of the M50 coating. The M30 coated composite showed the best thermal shock resistance with only 0.023% weight loss after 20 thermal shock cycles between 1473 K and room temperature, which was attributed to the similar thermal expansion coefficients between the coating and the substrate and the appropriate viscosity of aluminoborosilicate glass at 1473 K. The cracks resulted from CTE mismatch stress with different sizes formed and grew on the surface of M10, M40 and M50 coated samples, leading to the failure of the composites.

Amine-modified SiO2 aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO2 adsorption performance was investigated. The amine-modified SiO2 aerogel remains porous, the specific surface area is 654.24 m2/g, the pore volume is 2.72 cm3/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO2 aerogel (AMSA) showed the highest CO2 adsorption capacity of 52.40 cm3/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO2 adsorption–desorption performance. The CO2 adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO2 sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature.

•MoSi2-TaSi2-borosilicate glass coating was prepared by a rapid sintering method.•The coating presents a top Ta-Si-O compound glass layer and a porous inner layer.•The total emissivity is up to 0.88 in 0.3–2.5 μm and 0.87 in 2.5–15 μm.•The thermal shock behavior and mechanism are evaluated.A MoSi2-TaSi2-borosilicate glass porous coating was designed and prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent rapid sintering method. The microstructure, radiative property and thermal shock behavior of the coating have been investigated. The results show the coating presents a top Ta-Si-O compound glass layer and a porous MoSi2-TaSi2-borosilicate glass inner layer. The total emissivity of the coating is up to 0.88 in the range of 0.3–2.5 μm and 0.87 in the range of 2.5–15 μm at room temperature. The increased surface roughness leads to the increased emissivity, which can be explained by “V-shaped grooves” model. The coating turns into a dense structure and presents an interlocking structure in the interfacial layer after thermal cycling between 1673 K and room temperature 10 times, exhibiting excellent thermal shock resistance, which was attributed to the synergistic effect of porous structure and the match of thermal expansion coefficient between the coating and substrate.

•The design principles of high emissivity coating on fibrous ceramic were proposed.•A novel high emissivity WSi2-Si-glass hybrid coating was developed.•The total emissivity of the coating is above 0.92 in 0.3–2.5 µm.•The coating exhibits excellent self anti-oxidation property.•A competitive mechanism between defects formation and healing was discussed.The objective of this research was to develop a high emissivity coating on the low thermal conductive insulation for reusable thermal protection system. The design principles including high emissivity, match of the coefficients of thermal expansion and excellent high temperature stability were proposed for the first time. A novel WSi2-Si-glass hybrid coating with optimized composition was successfully prepared on fibrous ZrO2 ceramic insulation by slurry dipping and subsequent high temperature rapid sintering method. The total emissivity of the as-prepared coating is up to 0.92 in wavelength of 0.3–2.5 µm. After oxidation at 1673 K for 100 h and 1773 K for 20 h, the total emissivity values of the coatings are still as high as 0.89 and 0.87. A competitive mechanism between the “defects formation” caused by aging stress, the CTE mismatch stress and the volatilization of low melting point oxides and the “defects healing” resulted from self–healing phases during the different oxidizing conditions was discussed.Download high-res image (298KB)Download full-size image

Amine hybrid titania/silsesquioxane composite aerogel (AHTSA) was prepared by an one-pot sol–gel process without any catalyst. The sol-gel reaction mechanism of AHTSA was proposed. The use of 3-aminopropyltriethoxysilane (APTES) plays as an “internal catalyst” and promotes the formation of gel during sol–gel process. The morphology, microstructure, pore structure and CO2 capture performances of AHTSA were investigated. AHTSA exhibits microstructure of the typical silica aerogels with colloidal structure. Moreover, AHTSA has a large number of macropores which favor the CO2 adsorption. Thermogravimetric analysis reveals that AHTSA has a high CO2/N2 selectivity in CO2/N2 mixture gas. CO2 adsorption capacity with dry and humid 1 vol% CO2 is as high as 4.19 and 5.04 mmol/g, respectively. Correspondingly, amine efficiency under dry and humid conditions is 0.37 and 0.44, respectively. AHTSA has very short adsorption halftime below 4 min, and its CO2 adsorption capacity do not show obvious attenuation after 30 adsorption-regeneration cycles, indicating AHTSA is a dynamic and regenerable sorbent.Open image in new window

•A Stöber method was used to synthesize core/shell TiO2@SiO2 nanoparticles.•Core/shell TiO2@SiO2 nanoparticles with a uniform coating layer were successfully prepared.•Core/shell TiO2@SiO2 nanoparticles accelerated hydration and lowered porosity of cement paste.•Core/shell TiO2@SiO2 nanoparticles can better modify cement hydration than nano-TiO2 did.TiO2@SiO2 nanoparticles with a core/shell structure widely used in photocatalytic fields were used in this paper to improve the hydration properties of the Portland cement. To this end, the core/shell TiO2@SiO2 nanoparticles were synthesized first and then characterized by a series of techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectra (XPS). Second, the influence of the core/shell TiO2@SiO2 nanoparticles on cement hydration was investigated and compared with nano-TiO2 through isothermal calorimetry, XRD, thermo gravimetric/derivative thermo-gravimetric (TG/DTG) and mercury intrusion porosimetry (MIP) analyses. The results showed that an amorphous SiO2 layer can be deposited uniformly on nano-TiO2 particles by forming new SiOTi chemical bonds at the interface between the SiO2 coating layer and nano-TiO2 particle surface. This uniform layer was conducive to decrease the aggregation of nano-TiO2 effectively. Compared with nano-TiO2, the core/shell TiO2@SiO2 nanoparticles exhibited better hydration properties in terms of accelerated cement hydration, higher degree of hydration and lower porosity, even though both particles modified cement hydration.

•A “co-precipitation” method was used to synthesize C-S-H/PCE nanocomposites.•A Box-Behnken design was employed to design the experiments.•PCE polymers were adsorbed on surface or chemically incorporated into C-S-H structure.•C-S-H/PCE nanocomposites accelerated hydration and lowered porosity of cement paste.•C-S-H/PCE nanocomposites was conduce to early strength improvement of the mortar.This work investigates the influence of synthetic C-S-H/polycarboxylate(PCE) nanocomposites (CPNs) on the hydration and properties of hydrated cement pastes. HPEG-PCE copolymers exhibiting side chain length of 45 ethylene oxide (EO) units was utilized to synthesize CPNs by precipitating C-S-H from Na2SiO3 and Ca(NO3)2 in the PCE solution. A Box-Behnken Design (BBD) for the Response Surface Methodology (RSM) was employed to statistically optimize the sizes of the resultant. The prepared CPNs were characterized by particle size distribution (PSD), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and thermo gravimetric/derivative thermo gravimetric (TG/DTG) analyses. The influence of CPNs on the hydration properties of cement were assessed and discussed in terms of hydration kinetics, mechanical properties, phase composition and pore structure analysis. The experimental results showed that the optimum synthetic parameters, an experimental temperature of 30.1 °C, reactant flow velocity of 0.63 ml/min and initial volume of PCE solution of 28.5 ml, produced CPNs with a minimum size of 329.12 nm. It was demonstrated that PCE polymers were either grafted on the surface or partially intercalated in the interlayer regions of C-S-H, and their introduction also increased the distance between C-S-H interlayers. Cement hydration was significantly promoted as a result of an increased heat release, even at low CPNs content. The early compressive strength of the mortar significantly improved with increasing CPNs content due to the accelerated cement hydration of the CPNs: the 0.6 wt.% CPNs content improved the compressive strength by 18.97%. Moreover, the inclusion of CPNs is advantageous for pore modification: the total porosity decreased by 25.77% after 3 days. Finally, phase composition analysis confirmed that no new crystalline phase was produced upon CPNs addition.

We have developed a new sol–gel route to synthesise Al2O3–SiO2 composite aerogels with different alumina/silica (Al/Si) molar ratios using an inexpensive inorganic salt. The approach is straightforward, inexpensive, and it produces monolithic mesoporous material with high specific surface area heat-treated at elevated temperatures. The effects of different Al/Si molar ratios and calcination temperatures on the microstructures and properties of Al2O3–SiO2 composite aerogels are investigated in this study. Results show that SiO2 is essentially amorphous, while Al2O3 predominately exists as polycrystalline boehmite for the as-dried composite aerogels. With the increase of Al/Si molar ratios, the morphologies change from connected spheroidal particles to nanometer-sized fibrous particles and web-like microstructures with varying diameters. As the heat treatment temperature increases to 600 °C, structural transition from boehmite to γ-Al2O3 occurs within all the composite aerogels, and mullitization firstly occurs with the Al/Si molar ratio of 1 at around 1000 °C. The specific surface area undergoes an increase–decrease–increase process at 600 °C and 1200 °C for the composite aerogels with different Al/Si molar ratios. The specific surface area is as high as 166 m2 g−1 at 1200 °C for the sample with an Al/Si molar ratio of 8, which is higher than ever reported. The thermal conductivities of mullite fiber mat reinforced aerogel composites at room temperatures are 0.023 W m−1 K−1, 0.029 W m−1 K−1 and 0.025 W m−1 K−1 with the Al/Si molar ratios of 2, 3 and 8, respectively, suitable for efficient thermal insulations uses.

In this paper, the preparation of Fe3O4/PTX/HSA nanoparticles with magnetic resonance imaging (MRI) and slow release functionality by a self-assembly method is presented. Firstly, hydrophobic Fe3O4 nanoparticles with an average size of 10 nm are synthesized by thermal decomposition of an iron–oleate complex and then modified and stabilized by hydrophobic paclitaxel (PTX). Lastly, Fe3O4/PTX nanoparticles with a 3 nm PTX shell on the Fe3O4 surface are loaded into human serum albumin (HSA) to form uniform Fe3O4/PTX/HSA nanoparticles by PTX–HSA interaction after breaking the disulfide bond and unfolding hydrophobic region of HSA. The novel PTX modified Fe3O4/PTX nanoparticles have good dispersity in ethanol and strong binding capacity with HSA, which can be homogenously dispersed in HSA matrices to form novel Fe3O4/PTX/HSA nanoparticles with a pie structure by the self-assembly method. The resulting Fe3O4/PTX/HSA nanoparticles with a high saturation magnetization value of 10.2 emu g−1, good T2 imaging functionality and excellent ability to cross the cell membrane have been demonstrated by magnetization curves, in vitro MRI and cellular uptake. Furthermore, the in vitro antitumor ability of the system has also been evaluated.

•High emissivity TaSi2–SiO2-borosilicate glass coating was prepared.•SiB6 addition can form borosilicate glass and seal the micro cracks.•The emissivity of coating in 0.3–2.5 μm reached 0.9 at room temperature.•Increasing surface roughness led to the increasing emissivity.•The coating shows great thermal shock resistance.The objective of this research was to develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation, which can be used in a reusable thermal protective system for short-term applications. The effects of SiB6 and heat-treatment time on the microstructures and radiative properties of the TaSi2–SiO2-borosilicate glass composite coatings prepared on fibrous ZrO2 ceramic with slurry dipping and subsequent sintering method were investigated. The coating prepared in the presence of SiB6 with a heat-treatment time of 15 min maintains a dense structure and infiltrates into the ZrO2 substrate, possessing a gradient structure and good compatibility. The emissivity of the coating is up to 0.9 in the range of 0.3–2.5 μm and 0.8 in the range of 3–30 μm at room temperature. The emissivity mechanism regarding electron transition absorption, lattice vibration absorption and the effect of surface roughness on the emissivity is discussed. The increased roughness leads to the increased emissivity, which can be explained by “circular grooves” and “pyramidal grooves” models. After thermal cycling between 1573 K and room temperature 10 times, the weight gain of the coating prepared with SiB6 is only 0.29%. The high emissivity TaSi2–SiO2-borosilicate glass coatings with high temperature resistance show a promising potential for application in thermal insulation materials.

•AHZSA is simply synthesized by a facile and environment-friendly process.•One-step sol-gel reaction of AHZSA does not need catalyst.•AHZSA shows high CO2 adsorption performance with 1% CO2.•AHZSA is dynamic and regenerable for dilute CO2 capture.Amine hybrid zirconia/silica composite aerogel (AHZSA) was prepared via a simple, low-cost and environment-friendly method, i.e. one-pot sol-gel process along with supercritical drying. The pore strucutre, morphology, surface chemistry and CO2 capture performances of AHZSA were investigated. AHZSA possesses microstructure of the typical aerogels and has a large amount of macropores, which favors the gas diffusion in the pore space. The amine loading and surface amine content of AHZSA is 8.18 and 9.60 mmol/g, respectively. The CO2 adsorption capacity of AHZSA at 30, 50, 70 and 90 °C in the absence of water vapor is 2.70, 2.10, 2.00 and 1.48 mmol/g, respectively. The CO2 adsorption capacity at 30 °C increases to 3.40 mmol/g after the introduction of water vapor. Adsorption and desorption kinetics of AHZSA suggest that AHZSA is dynamic for low-concentration CO2 capture. The adsorbent preparation method is inspiring and the resulting adsorbent is capable, dynamic, and regenerable for low-concentration CO2 capture.

To develop a high emissivity coating on the low thermal conductivity ZrO2 ceramic insulation for reusable thermal protective system, the MoSi2–ZrO2–borosilicate glass multiphase coatings with SiB6 addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB6 content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB6 included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3 wt% SiB6 addition was up to 0.8 in the range of 0.3–2.5 μm and 0.85 in the range of 0.8–2.5 μm at room temperature, and the “V-shaped grooves” surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773 K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB6 and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi2–ZrO2–borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.

•Mixture design introduced to interpret the strength development of a ternary blend, showing that the interactions of CaCO3 and slag with TIPA were pronounced.•Hydration of C4AF phase promoted by TIPA resulting in consumptions of CH and sulfate in the early stage.•Reaction of slag improved by TIPA in two ways: acceleration of the silicate reaction yielding more CH, and the faster dissolution of slag under highly alkaline conditions.•Formation of carboaluminate hydrates favored as the result of boosted C4AF/C3A–CaCO3 reactions by TIPA.The effects of triisopropanolamine (TIPA) on the strength development and hydration kinetics of a ternary cement containing slag and CaCO3 were investigated by mixture design. The strength development of the blend was considerably enhanced by the accelerated chemical reactions on each component. A very strong interaction effect of slag and CaCO3 on the strength enhancement prior to 7 d was observed. The addition of TIPA promoted the hydration of laboratory cement by promoting the dissolution of ferrite, which resulted in more CH being released to participate in the reaction with slag. The dissolution of the slag itself was markedly accelerated by TIPA in a simulated highly alkaline pore solution. The use of TIPA promoted the formation of carboaluminate due to the accelerated C4AF/C3A–CaCO3 reaction, which stabilized the formation of AFt during hydration. In addition, it confirmed that Fe ions were able to enter the AFt structure during hydration with TIPA.

Spinel LiMn2−xSixO4 (x< 1, through substituting Mn4+ with Si4+ in cubic spinel LiMn2O4) was synthesized successfully by a facile sol-gel method. The as-prepared LiMn2−xSixO4 consisted of pores with large size distribution range from a few nanometers to over 200 nm and possessed specific surface area of 8.76 m2 g−1. Results of X-ray powder diffraction and X-ray photoelectron spectroscopy confirmed that Si atoms entered the host lattice. As a cathode material for rechargeable lithium-ion batteries, spinel LiMn2−xSixO4 exhibited excellent structural reversibility and integrity during the charging-discharging process. The result indicated that substitution of Mn4+ by Si4+ in spinel LiMn2O4 material effectively alleviated the phase transition caused by Jahn-Teller effect. The initial discharge capacity of the as-prepared spinel LiMn2−xSixO4 was 147 mA h g−1 over the voltage range of 1.5–4.8 V. However, after 51 cycles, the specific capacity was 88 mA h g−1 with capacity retention of 60 %. More work is needed to understand the effects of substituting Mn4+ by Si4+ and to improve the cyclic stability.本文通过溶胶凝胶法成功制备了尖晶石型LiMn2−xSixO4 (x < 1, 用Si4+替代尖晶石LiMn2O4中的Mn4+). 制备的LiMn2−xSixO4由几纳米至200纳米的孔组成, 比表面积为8.76 m2 g−1. XRD和XPS的结果表明Si原子进入到晶格中. 作为可充电锂离子电池的正极材料, 充放电过程中 LiMn2−xSixO4展现出了优异的结构可逆性及完整性. 结果表明用Si4+替代尖晶石LiMn2O4中的Mn4+能有效缓解由Jahn-Teller效应引起的相转变. 尖晶石LiMn2−xSixO4在1.5–4.8 V的电压窗口下, 首次放电比容量为147 mA h g−1. 51次循环后, 比容量仅为88 mA h g−1, 容量保持率为60%. 因此, 需要进一步了解Si4+替代Mn4+的机理, 从而提高其循环稳定性.

•Li2CoTiO4 cathode materials with tunable nanostructures were synthesized.•Small particle or grain size can increase the Li ion diffusion rate.•Li2CoTiO4 with small particle size has good cycle stability and rate capability.Cation disordered Li2CoTiO4 titanate with 3D lithium ion channels could be a promising new cathode material for lithium ion batteries due to its high theoretical capacity. Herein the Li2CoTiO4 materials with tunable nanostructures were synthesized by a sol–gel method and subsequent heat treatment at different temperatures. The microstructure and electrochemical properties of the nanocrystalline Li2CoTiO4 materials have been systematically investigated. The Li2CoTiO4 material synthesized at lower temperature possessed smaller particle size and grain size, and allowed a higher reversible extraction of lithium ions per formula unit. Furthermore, the small particle size enabled insertion of lithium along short diffusion paths, and thus an increase of the lithium ion diffusion coefficient.

•Synthesis of aerogels with hierarchical nanostructures.•Research of mechanical properties of hierarchical nanoporous aerogels.•Research of the correlation of mechanical properties and nano-pore size.•Building a model of hierarchical nanoporous aerogel according to the mechanical parameters of aerogels.The high-polymeric degree or molecular-weight of self-made polyethoxydisiloxane (PEDS) was successfully used to synthesize aerogels with several advantageous mechanical characteristics, compared with those based on conventional tetraethylorthosilicate (TEOS) aerogel preparation methods. The first advantage is their lower initial values of bulk modulus (K0), compared with those prepared via the two-step method; this is due to release of internal stress during the shrinkage of wet gel. Secondly, a collapse index n of −0.125 is obtained by the collapse law; this implies a new buckling destruction model. This is different from those prepared via the two-step method, and suggests that a hierarchical filament structure, formed by the connection of nano-particles, constitutes the solid skeleton of pores. In this paper, average aerogel pore sizes between 16.0 and 39.3 nm are analyzed by the combination of Mercury Intrusion Porosimetry (MIP) and Nitrogen Adsorption–Desorption (NAD). The microstructure and morphology of the aerogels are demonstrated by Transmission Electron Microscopy (TEM) and Field Emission Scan Electron Microscopy (FE-SEM).Graphical abstract

A new, highly capable and dynamic aerogel adsorbent for CO2 capture was developed using a one-step sol–gel process along with solvent exchange and supercritical drying. The highest CO2 adsorption capacity in a 1% CO2 flow stream (5.55 mmol g−1) is much higher than other aerogel adsorbents obtained using a 10% or even higher CO2 gas mixture.

The decomposition of alite (C3S) in Portland cement clinker was investigated by isothermal annealing, aiming to provide more fundamentals for the cooling process of cement clinker so as to search for potential chance for modification of the ongoing cooling process. Clinker phases were analyzed with quantitative X-ray diffraction technique. Scanning electron microscope and microscopy were used to investigate the microstructure. The fastest decomposition rate appeared at 1125–1150 °C in a temperature–time–transformation diagram. The decomposition of alite primarily occurred at the cracks, edges, and defects of the clinker. The resultant f-CaO segregated, which mainly controlled the decomposition rate of alite. The three-dimensional diffusion model (Jander) was suitable for the decomposition kinetics of alite with a non-Arrhenius behavior for the activation energy which was a piecewise linear function with temperature. Interstitial phases recrystallized during the annealing process, accompanied by an increase of the C3A and C4AF contents. The recrystallization of C3A was temperature-dependent, especially above 1000 °C.

•A novel method was used to synthesize RF/SiO2 aerogel by using hybrid silica source.•APTES plays an important role on the pore structure of aerogels.•C/SiC aerogel presents lower thermal conductivity than carbon aerogel.The subject of this paper is the investigation of the effect of silica sources on microstructure of resorcinol–formaldehyde/silica composite (RF/SiO2) and carbon/silicon carbide composite (C/SiC) aerogels. Hybrid silica sources (HSS) were composed of 3-(aminopropyl)triethoxysilane (APTES) and tetraethoxysilane (TEOS) with different molar ratio. RF/SiO2 aerogel was obtained by a single-step sol–gel process followed by supercritical fluid drying (SCFD). C/SiC aerogel was formed from RF/SiO2 aerogel after carbothermal reduction. Scanning electron microscopy (SEM) and N2 adsorption/desorption were used to investigate the evolution of morphology and pore structures of aerogels. X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrated that the as-prepared C/SiC aerogel was composed of carbon nanoparticle and α-SiC nanocrystal. The microstructure was hugely affected by the component of HSS. When the molar fraction of APTES in HSS was 60%, RF/SiO2 and C/SiC aerogels possessed the highest surface area and pore volume and the lowest thermal conductivity.Graphical abstract

The objective of this research was to develop a new high-performance CO2 sorbent with a simple method. A new CO2 aerogel sorbent was synthesized by using one-pot wet gel or sorbent precursor preparation, and supercritical drying (SCD). The performance of the aerogel sorbent prepared with SCD, A-SCD, is much better than that prepared with ambient pressure drying (APD). The highest CO2 sorption capacity achieved with the new sorbent in 1% CO2 flow stream within 20 min is 4.51 mmol g−1, much higher than its state-of-art counterparts even with a 10% CO2 gas mixture which is favorable to increase in CO2 sorption capacity of any given sorbent. According to XPS data, the theoretical equilibrium CO2 sorption capacity of the A-SCD is 7.99 mmol g−1. The characterization results of N2 adsorption/desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements used for the first time in CO2 research demonstrate that the pore structure and surface N concentration of the sorbent are significantly improved because of the use of SCD. The sorbent preparation method is inspiring and its resulting sorbent is exceptional in capacity and regenerability.

Resorcinol–formaldehyde/alumina composite (RF/Al2O3) gels were initially prepared using sol–gel techniques, and then dried to aerogels with supercritical fluid CO2. RF/Al2O3 aerogels were successfully converted to monolithic carbon/alumina composite (C/Al2O3) aerogels after carbonization under flowing Ar at 800 °C. The samples were characterized by Brunauer–Emmett–Teller, scanning electron microscopy, transmission electron microscope and X-ray diffraction, and the compressive strengths were also measured. The results indicated that the resulting C/Al2O3 aerogels prepared from hydrated AlCl3 possessed microstructures containing highly reticulated networks of fibers, 2–5 nm in diameter and of varying lengths, whereas the samples prepared from hydrated Al(NO3)3 were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5–15 nm range and the alumina were surrounded by amorphous carbon. The difference in microstructure resulted in each type of aerogels displaying distinct physical and mechanical properties. In particular, the as-prepared C/Al2O3 aerogels with the weblike microstructure were far more mechanically robust than those with the colloidal network. Correspondingly, the compressive strengths are 5.6 and 2.8 MPa, respectively.

A new, highly capable and dynamic aerogel adsorbent for CO2 capture was developed using a one-step sol–gel process along with solvent exchange and supercritical drying. The highest CO2 adsorption capacity in a 1% CO2 flow stream (5.55 mmol g−1) is much higher than other aerogel adsorbents obtained using a 10% or even higher CO2 gas mixture.