Co-reporter:Yu Hui, Sumei Zhao, Jiaying Xu, Binglin Zou, Ying Wang, Xiaolong Cai, Ling Zhu, Xueqiang Cao
Ceramics International 2016 Volume 42(Issue 1) pp:341-350
Publication Date(Web):January 2016
DOI:10.1016/j.ceramint.2015.08.116
Degradation due to molten salt attack is one of the failure mechanisms of thermal barrier coatings. Thermochemical attack of the salt mixture Na2SO4–30 mol% NaVO3 on ZrO2–8 mol% YO1.5 (8YSZ) at 1100 °C for different times was investigated. In the present study, 8YSZ powder was synthesized using co-precipitation route. The graded morphologies and phase compositions were examined using SEM, XRD and Raman before and after hot corrosion test. The results obtained from XRD have shown that m-ZrO2 and YVO4 were the main corrosion products after hot corrosion test at 1100 °C. The results obtained from SEM and EDS observations have shown that large polyhedron crystals of m-ZrO2 and rod-like crystals of YVO4 formed as hot corrosion products after hot corrosion test for 6 h and 24 h. The phase transformation and chemical interaction are the primary corrosion mechanisms for degradation of 8YSZ ceramic.
Co-reporter:Yu Hui, Binglin Zou, Sanxi Liu, Sumei Zhao, Jiaying Xu, Yu Zhao, Xizhi Fan, Ling Zhu, Ying Wang, Xueqiang Cao
Ceramics International 2015 Volume 41(Issue 2) pp:2760-2769
Publication Date(Web):March 2015
DOI:10.1016/j.ceramint.2014.10.091
ZrO2:Eu3+ nanocrystals were synthesized by hydrothermal technique. Effects of Eu3+-doping and annealing on the morphology, crystal structure and fluorescence properties of the resultant ZrO2:Eu3+ nanocrystals were investigated. The morphology and crystal structure of the ZrO2:Eu3+ nanocrystals were characterized by TEM, XRD, FT-IR and Raman, respectively. The fluorescence properties were explored by PL and decay curve. The results showed that both the Eu3+ doping concentration and annealing temperature had influence on the crystal structure and fluorescence properties of ZrO2:Eu3+ nanocrystals. For the low Eu3+-doping concentration, the amount of the tetragonal phase decreased with increasing the annealing temperature. The Eu3+ ion is trivalent rare earth (RE3+) activator, which can stabilize the tetragonal as well as the cubic structure of ZrO2. The ZrO2:Eu3+ nanocrystals with tetragonal or cubic structure may find potential applications as the raw material for producing the transparent ceramics with efficient fluorescence properties.
Co-reporter:Yu Hui, Tao Chen, Sumei Zhao, Jiaying Xu, Binglin Zou, Ying Wang, Xiaolong Cai, Ling Zhu, Xueqiang Cao
Journal of Alloys and Compounds 2015 Volume 626() pp:1-8
Publication Date(Web):25 March 2015
DOI:10.1016/j.jallcom.2014.11.152
•8YSZ:Eu3+ powder with fine particle size was synthesized by co-precipitation route.•Composition and fluorescence variation were investigated after hydrothermal degradation.•Due to the reaction of OH− and oxygen vacancy, the transformation of zirconia occurred.•The fluorescence properties of 8YSZ:Eu3+ powder also undergone slight changes.In the present study, 8YSZ:Eu3+ powder was synthesized using co-precipitation route. The evolution of phase composition and fluorescence properties of 8YSZ:Eu3+ powder have been assessed after being subjected to hydrothermal degradation for different times. Morphology and microstructure of the sintered powder were observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). XRD, Raman spectra, photoluminescence (PL) spectra and the decay curve were used to evaluate the phase composition variation and fluorescence properties variation of the powder. The results showed that 8YSZ:Eu3+ powder had a pure tetragonal phase structure. Under hydrothermal degradation conditions, due to the reaction of OH− and oxygen vacancy, the transformation of tetragonal to monoclinic occurred, furthermore the fluorescence properties of the powder were altered.
Co-reporter:Sumei Zhao, Yu Zhao, Binglin Zou, Xizhi Fan, Jiaying Xu, Ling Zhu, Xueqiang Cao
Journal of Alloys and Compounds 2014 Volume 601() pp:57-62
Publication Date(Web):15 July 2014
DOI:10.1016/j.jallcom.2014.02.151
•The effect of aging on the luminescence properties from 8YSZ:Eu are studied.•The addition of Eu3+ in 8YSZ can improve the phase stability at high temperature.•The changes in the peak properties of 5D0 → 7F2 transition are analyzed.Since the luminescence property of Eu3+-doped zirconia partially stabilized by 8 wt% yttria (8YSZ:Eu) has been widely used in the thermal barrier coatings (TBCs), the effect of high temperature aging on the luminescence properties from 8YSZ:Eu powder and coating are studied in our research. The 8YSZ:Eu powder and free-standing 8YSZ:Eu coating were aged at 1400 °C for 6 h, 12 h, 24 h, 48 h and 96 h, respectively. The addition of Eu3+ ions can improve the phase stability of 8YSZ at high temperature due to the introduction of oxygen vacancies. Except the irregular change in the first several hours, the variations in the peak properties of 5D0 → 7F2 transition with the aging time prolongation at 1400 °C for the 8YSZ:Eu powder and coating are as follows: the peak position is red shift, the peak width (FWHM) is increased and the peak intensity of the 5D0 → 7F2 transition is decreased.
Co-reporter:Yu Hui, Sanxi Liu, Sumei Zhao, Jiaying Xu, Binglin Zou, Ying Wang, Ling Zhu, Xueqiang Cao
Journal of the European Ceramic Society 2014 Volume 34(Issue 10) pp:2465-2474
Publication Date(Web):September 2014
DOI:10.1016/j.jeurceramsoc.2014.03.008
In this contribution, well-size-distributed nanopowder of 8YSZ:Eu3+ composite oxide was synthesized by hydrothermal method. TG-DSC, SEM, TEM and XRD were applied to characterize the thermal decomposition, morphology and crystal structure of nanopowder. The thermal stability of the powder was investigated by thermal treated at temperatures ranging from 500 °C to 1300 °C for 2 h. Fluorescence properties variation and phase composition variation of the powder were investigated after thermal exposure at 1300 °C for 192 h. The relationship between the phase composition variation and fluorescence properties variation was further examined. The results show that when monoclinic phase is absent, the intensity ratio I593/I608 of fluorescence spectroscopy can be used to preliminary assess the extent of the phase transformation.
Co-reporter:Sumei Zhao, Yu Zhao, Binglin Zou, Xizhi Fan, Jiaying Xu, Yu Hui, Xin Zhou, Sanxi Liu, Xueqiang Cao
Journal of Alloys and Compounds 2014 Volume 592() pp:109-114
Publication Date(Web):15 April 2014
DOI:10.1016/j.jallcom.2014.01.001
•A five-layer LZ7C3/8YSZ FG-TBCs has been prepared by atmospheric plasma spraying.•TECs of the five ceramic layers of the graded coating are gradually increased.•The failure mechanism of the graded coating has been analyzed.A five-layer ceramic-ceramic functionally graded thermal barrier coating (FG-TBC) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and 8YSZ has been prepared by atmospheric plasma spraying. The thermal expansion coefficients (TECs) of the five ceramic layers of the graded coating from top layer to the inner layer are gradually increased. Thermal cycling behavior and failure mechanism of the coating have been studied. The abnormal oxidation of the bond coat and sintering of the LZ7C3 are the primary factors for the spot spallation of the graded coating. The effects of thermal expansion mismatch also accelerate the spot spallation. The spallation at the edge of the coating is due to the effect of thermal expansion mismatch and thermal stress produced during thermal cycling.
Co-reporter:Xizhi Fan;Ying Wang;Binglin Zou;Lijian Gu
Journal of Thermal Spray Technology 2014 Volume 23( Issue 3) pp:304-316
Publication Date(Web):2014 February
DOI:10.1007/s11666-013-9985-9
Sprayed Al or diffused Mg-Al layer was designed as interlayer between the thermal barrier coatings (TBCs) and Mg alloy substrate. The effects of the interlayer on the bond properties of the coats were investigated. Al layers were prepared by arc spraying and atmospheric plasma spraying (APS), respectively. Mg-Al diffused layer was obtained after the heat treatment of the sprayed sample (Mg alloy with APS Al coat) at 400 °C. The results show that sprayed Al interlayer does not improve the bond stability of TBCs. The failure of the TBCs on Mg alloy with Al interlayer occurs mainly due to the low strength of Al layer. Mg-Al diffused layer improves corrosion resistance of substrate and the bond interface. The TBCs on Mg alloy with Mg-Al diffused interlayer shows better bond stability than the sample of which the TBCs is directly sprayed on Mg alloy substrate by APS.
Co-reporter:Xizhi Fan, Jiaying Xu, Ying Wang, Hongmei Ma, Sumei Zhao, Xin Zhou, Xueqiang Cao
Surface and Coatings Technology 2014 240() pp: 118-127
Publication Date(Web):
DOI:10.1016/j.surfcoat.2013.12.024
Co-reporter:Wenzhi Huang, Zhen Wang, Jiaying Xu, Xizhi Fan, Ying Wang, Binglin Zou, Xueqiang Cao
Corrosion Science 2013 Volume 74() pp:22-34
Publication Date(Web):September 2013
DOI:10.1016/j.corsci.2013.04.003
•Novel Zr0.75Ce0.25O2/phosphate duplex coating was fabricated on polymer substrate.•The microhardness of the surface was improved effectively by top duplex coating.•The duplex coating exhibited good thermal shock and thermal ablation resistance.•The duplex coating protected the substrate against thermal oxidation.•Failure was attributed to the appearance of the vertical cracks and delamination.Thermal protection coating based on Zr0.75Ce0.25O2/phosphate system was fabricated on polymer–matrix composites via a combined sol–gel/sealing treatment process. Phosphates sealed the cracks and enhanced the adhesion property via chemical bonding and binding. The Zr0.75Ce0.25O2/phosphate duplex coating exhibited good thermal shock resistance and improved thermal oxidation resistance of the substrate. Due to the protection of the duplex coating, the weight loss of the specimen reduced from (4.83 ± 0.12)% to (0.98 ± 0.08)% and the mass ablation rate decreased from 0.088 ± 0.002 mg cm−2 s−1 to 0.018 ± 0.002 mg cm−2 s−1 when testing at 810 °C. Coating failure was attributed to the formation of cracks and delamination.
Co-reporter:Xizhi Fan, Binglin Zou, Lijian Gu, Chunjie Wang, Ying Wang, Wenzhi Huang, Ling Zhu, Xueqiang Cao
Applied Surface Science 2013 Volume 265() pp:264-273
Publication Date(Web):15 January 2013
DOI:10.1016/j.apsusc.2012.10.192
Abstract
Bond coats play a significant role in manipulating the stability of 8YSZ thermal barrier coatings (TBCs) deposited on Mg alloy. In this study, different bond coats from the Al@Ni, Ni@Al and MCrAlY (M = Co, Ni) powders were prepared on the Mg alloy by atmospheric plasma spraying. The spraying behavior of the powders, the microstructure, oxidation and corrosion resistance of the produced bond coats were investigated to find the positive bond coat for TBCs on Mg alloy. Results indicate that the composition and structure of original powders affect the structure and properties of the sprayed bond coats. For the candidate bond coats, the MCrAlY bond coat is demonstrated as the most appropriate one for 8YSZ TBCs deposited on Mg alloy substrate, which is mainly attributed to its moderate thermal expansion match and excellent corrosion and oxidation resistance under the simulated corrosion and relatively high temperature conditions.
Co-reporter:Xizhi Fan, Ying Wang, Binglin Zou, Lijian Gu, Wenzhi Huang, Xueqiang Cao
Applied Surface Science 2013 Volume 277() pp:272-280
Publication Date(Web):15 July 2013
DOI:10.1016/j.apsusc.2013.04.044
Highlights
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MAO/Ni–P coat is designed to improve the corrosion resistance of Mg alloy.
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HF activation is necessary for the deposition of Ni–P coat on MAO layer.
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MAO/Ni–P coat has dense top coat and stable bonding interface.
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MAO/Ni–P coat shows more prominent corrosion resistance than the monolithic coat.
Co-reporter:Sumei Zhao, Yu Zhao, Ling Zhu, Lijian Gu, Wenzhi Huang, Xizhi Fan, Binglin Zou, Ying Wang, Xueqiang Cao
Journal of the European Ceramic Society 2013 Volume 33(Issue 11) pp:2207-2213
Publication Date(Web):October 2013
DOI:10.1016/j.jeurceramsoc.2013.03.002
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and Eu3+-doped zirconia, which was partially stabilised by 8 wt% yttria (8YSZ:Eu), were prepared by atmospheric plasma spraying. A thermal cycling test was carried out. The 8YSZ:Eu sublayer exposed during thermal cycling could produce visible luminescence under ultraviolet (UV) illumination, providing an indication of the spallation and damage degree of the coating. The result shows that the application of a Eu3+-doped luminescence sublayer can be a very simple and useful non-destructive technique to indicate the spallation and damage degree of DCL coatings.
Co-reporter:Lijian Gu, Sumei Zhao, Jiaying Xu, Yu Hui, Xizhi Fan, Binglin Zou, Ying Wang, Xueqiang Cao
Journal of the European Ceramic Society 2013 Volume 33(15–16) pp:3325-3333
Publication Date(Web):December 2013
DOI:10.1016/j.jeurceramsoc.2013.04.031
Beads and coatings of YAG–YSZ composite ceramic were prepared by plasma spray. YAG was applied as an additive in the hope of improving the phase stability and oxygen impermeability of YSZ. To achieve this aim, some basic research about crystallization behavior and chemical compatibility of the composite were carried out. Plasma sprayed YAG tended to form amorphous state. With the different content of YAG in the composite, crystallization of YAG and YSZ was delayed by each other to different extent due to the barrier effect of heavy atoms. The relative low melting point of YAG led to dense coatings without obvious splat structure and further distinctive vertical cracks during crystallization within the coatings. The cracks became less severe when YAG content was lower. With the addition of YAG, the development of monoclinic ZrO2 was suppressed while Y-rich phases were promoted at higher temperature.
Co-reporter:Binglin Zou, Zuhair S. Khan, Xizhi Fan, Wenzhi Huang, Lijian Gu, Ying Wang, Jiaying Xu, Shunyan Tao, Kuiyue Yang, Hongmei Ma, Xueqiang Cao
Surface and Coatings Technology 2013 Volume 219() pp:101-108
Publication Date(Web):25 March 2013
DOI:10.1016/j.surfcoat.2013.01.011
Co-reporter:Wenzhi Huang;Yu Zhao;Xizhi Fan;Xiangsheng Meng
Journal of Thermal Spray Technology 2013 Volume 22( Issue 6) pp:918-925
Publication Date(Web):2013 August
DOI:10.1007/s11666-013-9942-7
Thermal barrier coating systems with different bond coats were fabricated on polymer matrix composites via the air plasma spray process. During a thermal shock test at 400 °C, Zn and Al interlayers were helpful in improving the thermal shock resistance of coatings due to the low melting point. The coating system consisted of a soft zinc layer as a bond coat, and YSZ as a top coat exhibited the best thermal shock resistance, attributed to the lower residual stress and lower thermal stress in the Zn interlayer. The failure mechanism of the coating system was mainly ascribable to the residual stress derived from the deposition process, thermal stress, and further damage of the substrate.
Co-reporter:Binglin Zou, Zuhair S. Khan, Lijian Gu, Xizhi Fan, Wenzhi Huang, Ying Wang, Yu Zhao, Chunjie Wang, Kuiyue Yang, Hongmei Ma, Xueqiang Cao
Corrosion Science 2012 Volume 62() pp:192-200
Publication Date(Web):September 2012
DOI:10.1016/j.corsci.2012.05.020
C/SiC composites were plasma sprayed with an Yb2SiO5/LaMgAl11O19 coating to improve the oxidation resistance. Microstructure, oxidation protection and failure mechanism of the coating during dynamic thermal cycling (DTC) were investigated. The results showed that good interfacial bonding between the substrate and coating was present before and after DTC. Weight loss for the sample coated on one-side was 4.1% after 11 cycles of heating for 85 min, for the uncoated sample it was as high as 20.6%. Failure mechanism of the coating resulted from the reaction sintering of the coating and the formation of bubbles between the substrate and the coating.Highlights► We designed a novel oxidation protective Yb2SiO5/LMA coating for C/SiC composites. ► Microstructure, oxidation protection and failure of the coating were investigated. ► The coating by APS bonds well with the substrate before and after thermal cycling. ► The coating significantly improves the oxidation resistance of substrate at 2273 K. ► The sintering of the coating and formation of bubbles make the coating fail.
Co-reporter:Lijian Gu, Binglin Zou, Xizhi Fan, Shuibing Zeng, Xiaolong Chen, Ying Wang, Xueqiang Cao
Corrosion Science 2012 Volume 55() pp:164-171
Publication Date(Web):February 2012
DOI:10.1016/j.corsci.2011.10.017
Freestanding and inhomogeneous coating was prepared by atmospheric plasma spray using Al@NiCr powder. Oxidation kinetics and mechanism are discussed after cyclic oxidation in air. Slight interdiffusion occurred at 800 °C but oxidation process took a dominant position at higher temperature. The oxidation of Cr turned significant above 1100 °C and volatilized as CrO3. The oxidation of Ni also became severe at 1100 °C. The oxidation was suppressed when internal channels were filled up with oxides. Then two stages for oxidation appeared, both of which obeyed parabolic rate law. The slow oxidation of external surface played a key role at the second stage.Highlights► Freestanding and inhomogeneous coating was prepared using Al@NiCr powder. ► Unalloyed aluminum in as-deposited coating caused a low electric potential. ► Oxidation of Cr and Ni turned significant at 1100 °C since CrO3 volatilized. ► Suppression of internal oxidation resulted in two parabolic stages of kinetic curves.
Co-reporter:Jili Yang, Wenzhi Huang, Yongliang Cheng, Chunjie Wang, Yu Zhao, Ling Zhu and Xueqiang Cao
CrystEngComm 2012 vol. 14(Issue 3) pp:899-907
Publication Date(Web):24 Nov 2011
DOI:10.1039/C1CE06053H
Gadolinium fluoride NaxGdyFx+3y crystals with different morphologies and compositions have been successfully synthesized via a facile ultrasonic and salt assisted method at room temperature without any template or organic additive. Crystal structure and morphology of the fluorides were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reaction conditions, such as ultrasonic irradiation, F/Gd molar ratio (R(F/Gd)), concentration of sodium nitrate and ultrasonic time have a close relationship with the morphology and phase composition of the final products. The growth mechanism of the uniform and monodisperse GdF3 nanospindles was proposed based on the time-dependent experiments. The photoluminescent (PL) properties of the as-obtained products revealed that Eu3+ doped NaGdF4 nanocrystals with different morphologies present characteristic luminescence of Eu3+, and their emission intensities strongly depend on morphology.
Co-reporter:Chunjie Wang, Yue Wang, Wenzhi Huang, Binglin Zou, Zuhair Subhani Khan, Yu Zhao, Jili Yang, Xueqiang Cao
Ceramics International 2012 Volume 38(Issue 3) pp:2087-2094
Publication Date(Web):April 2012
DOI:10.1016/j.ceramint.2011.10.046
Abstract
Nanopowders with cubic fluorite-type structure as well as uniform distribution in particle size were synthesized by hydrothermal method in the ternary oxide zirconia–yttria–ceria system with ceria content of 0–25 mol%. X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimeter (TG/DSC), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), specific surface area (SBET) and high resolution transmission electron microscopy (HRTEM) were applied to characterize the structure, thermal decomposition, morphological characteristic and crystal growth of the produced powders. Qualitative analyses indicate that the as-synthesized nanoparticles are single-phase crystallites with an average particle size of 4–9 nm. The specific surface area, lattice parameter and microstrain are closely related to Ce4+ concentration. Moreover, activation energy of crystal growth is significantly dependent on the dopant (CeO2) concentration. It firstly increased and then decreased with increasing dopant concentration, and the maximum value was observed at the dopant concentration of 5 mol%.
Co-reporter:Chunjie Wang, Yue Wang, Yongliang Cheng, Wenzhi Huang, Binglin Zou, Xueqiang Cao
Powder Technology 2012 Volume 225() pp:130-135
Publication Date(Web):July 2012
DOI:10.1016/j.powtec.2012.03.050
Sm2Zr2O7 nanocrystallines were synthesized via hydrothermal method using polyethyleneglycol (PEG), cetyltrimethyl ammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS) as surfactants, respectively. The effects of surfactants on the structural evolution and the crystal growth of Sm2Zr2O7 were investigated by X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimeter (TG/DSC), Raman spectroscopy, field emission scanning electron microscope (FESEM) and high resolution transmission electron microscopy (HRTEM), separately. The as-prepared products have a spherical morphology, and the average particle sizes are in the range of 4–9 nm. The structure transition from fluorite to pyrochlore structure occurred at 1300 °C with PEG and SDBS, which can be restrained by adding CTAB. The activation energy of crystal growth is significantly dependent on the surfactants, which is in the order of SDBS > PEG > CTAB. Moreover, the effects of surfactant on the sintering-resistance property of the products are also discussed.The surfactants have a significant effect on the activation energy of crystal growth which is with the order of SDBS > PEG > CTAB.Highlights► CTAB can restrain the phase transition from fluorite to pyrochlore structure. ► CTAB has a significant effect on the particle size and the dispersion of products. ► The activation energies of crystal growth are in the order of SDBS > PEG > CTAB. ► CTAB has a significant role on the sintering–resistance property of the products.
Co-reporter:Wenzhi Huang, Jili Yang, Chunjie Wang, Binglin Zou, Xiangsheng Meng, Ying Wang, Xueqiang Cao, Zhen Wang
Materials Research Bulletin 2012 47(9) pp: 2349-2356
Publication Date(Web):
DOI:10.1016/j.materresbull.2012.05.025
Co-reporter:Chunjie Wang, Yue Wang, Xizhi Fan, Wenzhi Huang, Binglin Zou, Xueqiang Cao
Surface and Coatings Technology 2012 Volume 212() pp:88-93
Publication Date(Web):November 2012
DOI:10.1016/j.surfcoat.2012.09.026
Lanthanum zirconate (La2Zr2O7, LZ) has a very important application for thermal barrier coatings (TBCs) due to its higher sintering-resistance than 8 wt.% yttria stabilized zirconia (8YSZ), and this property could be further improved by the proper addition of ceria. In this paper, the La2(Zr0.7Ce0.3)2O7 (LZ7C3) nanoceramics for potential TBC application were synthesized via sol–gel process. The structure evolution, sintering-resistance and thermophysical properties of the synthesized powders and sintered ceramic bodies were investigated in detail. The XRD and Raman spectroscopy results indicate that LZ7C3 keeps a pyrochlore-type structure throughout the sintering temperature from 1000 to 1500 °C. The nano-sized LZ7C3 shows an excellent thermostability after long-term annealing at 1400 °C. The thermal expansion coefficient and thermal conductivity are also investigated. Compared with LZ and 8YSZ, LZ7C3 exhibits the lowest relative density and the highest sintering-resistance, implying that it is a better potential candidate for TBCs.Highlights► LZ7C3 nanopowders keep a pyrochlore structure in the calcination temperature from 1000 to 1500 °C. ► The nano-sized LZ7C3 shows an excellent thermostability after long-term annealing at 1400 °C. ► The lattice parameter has a close relationship with the sintering temperature. ► Compared with LZ and 8YSZ, LZ7C3 exhibits lower relative density and higher sintering resistance.
Co-reporter:Chunjie Wang;Yue Wang;Yongliang Cheng;Wenzhi Huang
Journal of Materials Science 2012 Volume 47( Issue 10) pp:4392-4399
Publication Date(Web):2012 May
DOI:10.1007/s10853-012-6293-6
Rare earth zirconates (Ln2Zr2O7, Ln = La, Nd, Sm, and Gd) with pyrochlore structure were prepared by hydrothermal method with polyethylene glycol as surfactant. X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy were utilized to characterize the phase structure, thermal decomposition, and morphology of the products. Qualitative analysis indicates that the as-prepared zirconates are pyrochlore-type structures. The specific surface area, lattice parameter, and average crystallite size of the as-prepared products are closely related to the ionic radius. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln2Zr2O7 are descending as the order of La2Zr2O7, Nd2Zr2O7, Sm2Zr2O7, and Gd2Zr2O7.
Co-reporter:Lijian Gu, Xizhi Fan, Yu Zhao, Binglin Zou, Ying Wang, Sumei Zhao, Xueqiang Cao
Surface and Coatings Technology 2012 206(21) pp: 4403-4410
Publication Date(Web):
DOI:10.1016/j.surfcoat.2012.04.070
Co-reporter:Chunjie Wang, Wenzhi Huang, Yue Wang, Yongliang Cheng, Binglin Zou, Xizhi Fan, Jili Yang, Xueqiang Cao
International Journal of Refractory Metals and Hard Materials 2012 Volume 31() pp:242-246
Publication Date(Web):March 2012
DOI:10.1016/j.ijrmhm.2011.12.002
Monodispersed and uniformly distributed La2Ce2O7 nanocrystals were synthesized via the hydrothermal method using polyethyleneglycol (PEG) as surfactant. X-ray diffraction (XRD), Thermogravimetric analysis/Differential scanning calorimeter (TG/DSC), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and High resolution transmission electron microscopy (HRTEM) were utilized to characterize the thermal decomposition, phase structure and morphology of the products. Qualitative analysis indicates that the products are comprised of well-dispersed square particles with cubic fluorite structure. The specific surface area and the average crystallite size of the as-prepared products are 195.59 m2 g− 1 and 10–15 nm, respectively. The low effective activation energy (15.27 ± 0.03 kJ mol− 1) for crystal growth was obtained in the calcination temperature range of 700–1300 °C. The sintering behavior of the compacted body was also investigated, revealing that La2Ce2O7 has a low relative density and open channel morphology.Highlights►As-prepared products are comprised of well-dispersed square particles in cubic structure. ►The lower activation energy is observed which has closed relationship with oxygen vacancies. ►The specific surface area and average crystallite size of products are 195.59 m2 g− 1 and 10–15 nm. ►The sintered compacted body has a lower relative density and open channel morphology.
Co-reporter:Xiaolong Chen, Lijian Gu, Binglin Zou, Ying Wang, Xueqiang Cao
Surface and Coatings Technology 2012 206(8–9) pp: 2265-2274
Publication Date(Web):
DOI:10.1016/j.surfcoat.2011.09.076
Co-reporter:Zuhair S. Khan, Binglin Zou, Wenzhi Huang, Xizhi Fan, Lijian Gu, Xiaolong Chen, Shuibing Zeng, Chunjie Wang, Xueqiang Cao
Materials Science and Engineering: B 2012 Volume 177(Issue 2) pp:184-189
Publication Date(Web):15 February 2012
DOI:10.1016/j.mseb.2011.12.004
Rare-earth silicates such as Yb2SiO5 and Er2SiO5 are promising environmental barrier coating materials for ceramic matrix composites. In this work, Yb2SiO5 and Er2SiO5 ceramic powders have been synthesized by solid-state reaction using Yb2O3, Er2O3 and SiO2 as starting materials. The fabricated powders were subjected to spray drying treatment for subsequent synthesis of coatings by plasma spraying. The spray drying resulted in well-dispersed and spherical powder particles with good flowability. Analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry and differential scanning calorimetry (TGA/DSC) and dilatometry were applied to study the microstructural and thermal characteristics of the powders. Ultra-high purity monosilicate powders formed as a result of heating treatments at 1400 °C in a box furnace for 20 h. TG/DSC revealed the genesis temperatures of the silicate formation (low temperature polymorphs) and also showed that the solid-state reactions to form Yb and Er based monosilicates proceeded without any weight-loss in the tested temperature range. The values of coefficients of thermal expansion (CTE) of the fabricated compounds are found to be 7.1 ppm/°C for Yb2SiO5 and 7.5 ppm/°C for Er2SiO5 by dilatometric measurements. Besides these studies, coating formation by plasma spraying of spray-dried Yb2SiO5 powders on the ceramic matrix composite specimen such as C/C–SiC has also been evaluated. Well-adhered and uniformed coatings result on composite specimens whose durability is tested by thermal cycling from ∼400 °C to 1500 °C in a gas burner rig.Highlights► Ultra-pure rare-earth monosilicate powders based on Er and Yb have been fabricated by solid-state reaction. ► Spray-drying treatment results in powders with free flowing characteristics and rounded surface morphologies. ► CTEs are found to be 7.1 ppm/°C for Yb2SiO5 and 7.5 ppm/°C for Er2SiO5. ► Plasma spraying has been used to deposit Yb2SiO5 coatings on C/C–SiC substrate. ► Coatings remain strongly intact with the substrate on thermal cycling between ∼400 °C and 1500 °C in gas burner rig experiment.
Co-reporter:Zuhair S. Khan, Binglin Zou, Xiaolong Chen, Chunjie Wang, Xizhi Fan, Lijian Gu, Wenzhi Huang, Xueqiang Cao
Surface and Coatings Technology 2012 207() pp: 546-554
Publication Date(Web):
DOI:10.1016/j.surfcoat.2012.07.070
Co-reporter:Xizhi Fan, Lijian Gu, Shuibing Zeng, Ling Zhu, Chunjie Wang, Ying Wang, Binglin Zou, Wenzhi Huang, Xiaolong Chen, Zuhair Subhani Khan, Xueqiang Cao
Surface and Coatings Technology 2012 206(21) pp: 4471-4480
Publication Date(Web):
DOI:10.1016/j.surfcoat.2012.05.004
Co-reporter:Shuibing Zeng;Yangjia Liu;Xizhi Fan;Wenzhi Huang
Journal of Thermal Spray Technology 2012 Volume 21( Issue 2) pp:335-343
Publication Date(Web):2012 March
DOI:10.1007/s11666-011-9721-2
Thermal barrier coatings (TBCs) with a typical 8YSZ ceramic top coat and CoNiCrAlY bond coat were deposited on titanium alloy substrate (Ti-6Al-4V in wt.%) by air plasma spraying. Thermal insulation and thermal shock resistance of the TBCs at different temperatures as well as their failure behavior were investigated. The results showed that the test temperature had a significant effect on thermal shock life of the TBCs. Failure of the TBCs systems was caused by the formation of crack, bond coat oxidation and elemental diffusion. The vertical cracks induced by thermal shock cycles were probably responsible for the enhancement in thermal shock resistance of the TBCs. Furthermore, elemental diffusion had a great effect on the acceleration of the TBCs failure. The TBCs could provide a good thermal protection for the titanium alloy substrate.
Co-reporter:Xiaolong Chen, Yu Zhao, Lijian Gu, Binglin Zou, Ying Wang, Xueqiang Cao
Corrosion Science 2011 Volume 53(Issue 6) pp:2335-2343
Publication Date(Web):June 2011
DOI:10.1016/j.corsci.2011.03.019
Hot corrosion studies of thermal barrier coatings (TBCs) with different YSZ/LaMgAl11O19 (LaMA) composite coating top coats were conducted in 50 wt.% Na2SO4 + 50 wt.% V2O5 molten salt at 950 °C for 60 h. Results indicate that TBCs with composite coating top coats exhibit superior oxidation and hot corrosion resistances to the TBC with the traditional YSZ top coat, especially for which has a LaMA overlay. The presence of LaMA can effectively restrain the destabilization of YSZ at the expense of its own partial degradation. The hot corrosion mechanism of LaMA coating and the composite coatings have been explored.Highlights► New YSZ/LaMgAl11O19 (LaMA) composite coatings have been developed. ► The presence of LaMA slows down the degradation of YSZ in molten salt environment. ► LaMA coating can be degraded by molten sulfate–vanadate salt attack. ► The hot corrosion mechanism of LaMA coating has been proposed for the first time. ► Bilayered or graded YSZ/LaMA modes may be the good selections for advanced coatings.
Co-reporter:Yongliang Cheng, Binglin Zou, Chunjie Wang, Yangjia Liu, Xizhi Fan, Ling Zhu, Ying Wang, Hongmei Ma and Xueqiang Cao
CrystEngComm 2011 vol. 13(Issue 8) pp:2863-2870
Publication Date(Web):21 Feb 2011
DOI:10.1039/C0CE00379D
Fe2O3 hollow fibers have been fabricated by direct annealing electrospun polyvinylpyrrolidone (PVP)/Fe(NO3)3 composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/Fe(NO3)3 solution, and then calcined at high temperature with an appropriate heating rate to form hollow Fe2O3 fibers. The solvent composition, the addition amount of Fe(NO3)3·9H2O and PVP, and the heating rate have important influences on the morphologies of Fe2O3 fibers. Morphologies of Fe2O3 could be tuned from solid belt to hollow belts and hollow fibers by controlling appropriate preparation conditions. The crystal structure, morphology, surface composition, magnetic and electrochemical properties of the Fe2O3 hollow fibers were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, SQUID magnetometry and cyclic voltammetry, respectively.
Co-reporter:Yongliang Cheng, Binglin Zou, Jili Yang, Chunjie Wang, Yangjia Liu, Xizhi Fan, Ling Zhu, Ying Wang, Hongmei Ma and Xueqiang Cao
CrystEngComm 2011 vol. 13(Issue 7) pp:2268-2272
Publication Date(Web):24 Jan 2011
DOI:10.1039/C0CE00802H
CoFe2O4 hollow fibers have been fabricated by direct annealing of electrospun polyvinylpyrrolidone (PVP)/nitrate salts composite nanofibers. In this approach, composite fibers were firstly synthesized by electrospinning PVP/nitrate salts solution, and then calcined at high temperature with appropriate heating rate to form hollow CoFe2O4 fibers. The crystal structure, morphology and magnetic properties of the CoFe2O4 hollow fibers were investigated by using the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and SQUID magnetometry, respectively. The results indicate that the phase structure of hollow fibers belongs to cubic spinel structure, hollow fibers after annealing at high temperature still remain the one-dimensional texture and the wall of hollow fibers consists of many nanoparticles. The magnetic measurement showed that the hollow one dimensional structure has some novel magnetic properties, which may make them useful in electromagnetic and spintronic devices
Co-reporter:Ling Zhu, Yangjia Liu, Xizhi Fan, Daowu Yang, Xueqiang Cao
Journal of Luminescence 2011 Volume 131(Issue 7) pp:1380-1385
Publication Date(Web):July 2011
DOI:10.1016/j.jlumin.2011.03.024
Highly uniform and monodisperse KY3F10:Ln3+ (Ln=Eu, Ce, Tb) nanospheres, with an average diameter of 300 nm, have been successfully prepared through a simple template-free and surfactant-free stirring method under ambient conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The SEM images illustrate that these spheres were actually composed of randomly aggregated nanoparticles. The doped rare earth ions show their characteristic emission in the KY3F10 samples, i.e., Eu3+5D0–7FJ (J=1, 2, 3, 4), Tb3+5D4–7FJ (J=6, 5, 4, 3, 2) and Ce3+ 5d–4f transition emissions, respectively. An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in KY3F10 nanospheres, and the energy transfer efficiency depends on the doping concentration of Tb3+ if the concentration of Ce3+ is fixed.Highlights► KY3F10:Ln3+ nanospheres have been prepared via a simple stirring method. ► KY3F10:Ln3+ (Ln=Eu, Ce, Tb) showed strong characteristic fluorescence emissions. ► An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in KY3F10 nanospheres.
Co-reporter:Xiaolong Chen, Yu Zhao, Wenzhi Huang, Hongmei Ma, Binglin Zou, Ying Wang, Xueqiang Cao
Journal of the European Ceramic Society 2011 Volume 31(Issue 13) pp:2285-2294
Publication Date(Web):November 2011
DOI:10.1016/j.jeurceramsoc.2011.05.036
The crystallization behavior of the amorphous phase of the plasma sprayed LaMgAl11O19 (LaMA) coating during thermal aging processes has been investigated. Results indicate that LaMA coating exhibits much similar microstructure and thermal properties such as close coefficient of thermal expansion and specific heat capacity etc. to the sintered LaMA bulk after aging at 1673 K for 20 h. On the other hand, a solid state reaction seems to occur to reform the ideal magnetoplumbite-type LaMA phase coupled with the formations of the La-rich aluminate intermediate phases. When the aging temperature is held between 1273 K and 1473 K, nanosized platelet-like grains as well as sub-grains with high aspect ratios are present. The phase stability has been investigated through the chemical compositions and X-ray diffraction analysis. The recrystallization mechanism of the amorphous LaMA coating has been explored by tracing the microstructure evolutions during thermal aging process.Highlights► The recrystallization mechanism of LaMgAl11O19 (LaMA) coating has been explored. ► High temperature aging imparts LaMA coating with the same microstructure to its bulk. ► LaMA coating exhibits the same thermomechanical properties to its bulk after aging. ► Solid state reaction occurs to LaMA coating to reform the ideal LaMA phase at 1673 K. ► Nano-grains are present when LaMA coating is thermally aged at 1273–1473 K.
Co-reporter:Xiaolong Chen, Yu Zhao, Xizhi Fan, Yangjia Liu, Binglin Zou, Ying Wang, Hongmei Ma, Xueqiang Cao
Surface and Coatings Technology 2011 205(10) pp: 3293-3300
Publication Date(Web):
DOI:10.1016/j.surfcoat.2010.11.059
Co-reporter:Lijian Gu, Xiaolong Chen, Xizhi Fan, Yangjia Liu, Binglin Zou, Ying Wang, Xueqiang Cao
Surface and Coatings Technology 2011 206(1) pp: 29-36
Publication Date(Web):
DOI:10.1016/j.surfcoat.2011.06.030
Co-reporter:Ling Zhu, Yangjia Liu, Xizhi Fan, Daowu Yang, Xueqiang Cao
Materials Research Bulletin 2011 46(2) pp: 252-257
Publication Date(Web):
DOI:10.1016/j.materresbull.2010.11.003
Co-reporter:Xiaolong Chen;Binglin Zou;Ying Wang;Hongmei Ma
Journal of Thermal Spray Technology 2011 Volume 20( Issue 6) pp:1328-1338
Publication Date(Web):2011 December
DOI:10.1007/s11666-011-9683-4
Yttria-stabilized zirconia (YSZ) based composite coatings with the addition of LaMgAl11O19 (LaMA) as the secondary phase, were prepared by air plasma spraying in order to improve the performances of the traditional YSZ coating. Results indicate that the newly developed composite coating shows increased vertical crack density with the enhancement of the LaMA content during thermal cycling process, which results in increased strain tolerance and service lifetime. However, such composite coatings about 200 μm thick, exhibit inferior thermal cycling lifetimes with respect to the typical YSZ coating for surface temperatures above 1400 °C. The presence of amorphous LaMA phase in the composite coating results in increased thermal conductivity and a relative thin top coat leading to a reduced thermal insulation efficiency. These are believed to be responsible for the premature degradation of bond coat and final top coat spallation failure. Such an investigation gives useful guidelines to develop advanced composite coatings based on YSZ/LaMA systems.
Co-reporter:Yongliang Cheng, Yu Zhao, Yanfei Zhang, Xueqiang Cao
Journal of Colloid and Interface Science 2010 Volume 344(Issue 2) pp:321-326
Publication Date(Web):15 April 2010
DOI:10.1016/j.jcis.2009.12.044
One-dimensional SrAl2O4:Eu2+, Dy3+ fibers were fabricated by a simple electrospinning combined with sol–gel process. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence were used to characterize the fibers. The results show that the phase structure of SrAl2O4:Eu2+, Dy3+ belongs to a monoclinic one, the composite fibers and fibers calcined at high temperature remain the original one-dimensional texture, and the SrAl2O4:Eu2+, Dy3+ was a green emission.SrAl2O4:Eu2+, Dy3+ fibers have been fabricated by electrospinning process. The fibers show green emission.
Co-reporter:Yongliang Cheng, Wenzhi Huang, Yanfei Zhang, Ling Zhu, Yangjia Liu, Xizhi Fan and Xueqiang Cao
CrystEngComm 2010 vol. 12(Issue 7) pp:2256-2260
Publication Date(Web):22 Mar 2010
DOI:10.1039/B922564A
TiO2 hollow nanofibers have been fabricated by directly annealing electrospun polyvinylpyrrolidone (PVP)/Tetra-butyl titanate (TBT) composite nanofibers. In this approach, PVP/TBT composite fibers were first synthesized by electrospinning PVP/TBT solution, and then calcined at high temperature with an appropriate heating rate to form hollow TiO2 nanofibers. During the heat treatment, the solvent composition, the amount of TBT and the heating rate have important influences on the morphologies of the TiO2 nanofibers. Morphologies of TiO2 could be tuned from solid nanofibers to belts, hollow nanofibers and rods by controlling the appropriate preparation conditions. The crystal structure, morphology, surface composition and specific surface area of the TiO2 hollow nanofibers were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analysis, respectively.
Co-reporter:Zhenhua Xu, Limin He, Xiaolong Chen, Yu Zhao, Xueqiang Cao
Journal of Alloys and Compounds 2010 Volume 508(Issue 1) pp:94-98
Publication Date(Web):15 October 2010
DOI:10.1016/j.jallcom.2010.04.160
Thermal barrier coatings (TBCs) have very important applications in gas turbines for higher thermal efficiency and protection of components at high temperature. TBCs of rare earth materials such as lanthanum zirconate (La2Zr2O7, LZ), lanthanum cerate (La2Ce2O7, LC), lanthanum cerium zirconate (La2(Zr0.7Ce0.3)2O7, LZ7C3) were prepared by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, cross-sectional morphology and cyclic oxidation behavior of these coatings were studied. These coatings have partially deviated from their original compositions due to the different evaporation rates of oxides, and the deviation could be reduced by properly controlling the deposition condition. A double ceramic layer-thermal barrier coatings (DCL-TBCs) of LZ7C3 and LC could also be deposited with a single LZ7C3 ingot by properly controlling the deposition energy. LaAlO3 is formed due to the chemical reaction between LC and Al2O3 in the thermally grown oxide (TGO) layer. The failure of DCL-TBCs is a result of the sintering-induced of LZ7C3 coating and the chemical incompatibility of LC and TGO. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL-TBCs are an important development direction of TBCs.
Co-reporter:Zhenhua Xu, Limin He, Xiaolong Chen, Yu Zhao, Rende Mu, Shimei He, Xueqiang Cao
Journal of Alloys and Compounds 2010 Volume 508(Issue 1) pp:85-93
Publication Date(Web):15 October 2010
DOI:10.1016/j.jallcom.2010.04.124
Thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) with the addition of 3 wt.% Y2O3 (LZ3Y) were deposited by electron beam-physical vapor deposition (EB-PVD). The phase structures, surface and cross-sectional morphologies, cyclic oxidation behaviors of these coatings were studied in detail. The thermal cycling test at 1373 K in an air furnace indicates that the LZ3Y coating has a lifetime of 617 cycles which is about 10% longer than that of LZ coating. The improvement of chemical homogeneity of the coating, the superior growth behavior of columns and the favorable mechanical properties are all very helpful to the prolongation of thermal cycling life of LZ3Y coating. The failure of LZ and LZ3Y coatings is mainly a result of the excess La2O3, the chemical incompatibility of ceramic coatings with TGO layer, the thermal expansion mismatch between ceramic coatings and bond coat, and the outward diffusion of alloying elements into the ceramic coatings.
Co-reporter:Z.H. Xu, L.M. He, R.D. Mu, S.M. He, G.H. Huang, X.Q. Cao
Applied Surface Science 2010 Volume 256(Issue 11) pp:3661-3668
Publication Date(Web):15 March 2010
DOI:10.1016/j.apsusc.2010.01.004
Abstract
Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2(Zr0.7Ce0.3)2O7 (LZ7C3) and La2Ce2O7 (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO3 is formed due to the chemical reaction between LC and Al2O3 which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.
Co-reporter:Q. Li, Y.F. Zhang, X.F. Ma, J. Meng, X.Q. Cao
Ceramics International 2009 Volume 35(Issue 1) pp:453-456
Publication Date(Web):January 2009
DOI:10.1016/j.ceramint.2007.12.002
Abstract
Fast densification of 8YSZ ceramics under a high pressure of 4.5 GPa was carried out at different temperatures (800, 1000, 1450 °C), by which a high relative density above 92% could be obtained. FT-Raman spectra indicate that the 8YSZ underwent a phase transition from partially tetragonal to partially cubic phase as temperatures increase from 1000 to 1450 °C when sintering under high pressure. The electrical properties of the samples under different high-pressure sintering conditions were measured by complex impedance method. The total conductivity of 0.92 × 10−2 S cm−1 at 800 °C has been obtained for 8YSZ under high pressure at 1450 °C, which is about 200 °C lower than that of the samples prepared by conventional pressureless sintering.
Co-reporter:Jiangfeng Zhang, Xinghua Zhong, Yongliang Cheng, Ying Wang, Zhenhua Xu, Xiaolong Chen, Hongmei Ma, Yu Zhao, Xueqiang Cao
Journal of Alloys and Compounds 2009 Volume 482(1–2) pp:376-381
Publication Date(Web):12 August 2009
DOI:10.1016/j.jallcom.2009.04.025
Lanthanide hexaaluminates including LaMgAl11O19, NdMgAl11O19, SmMgAl11O19 and GdMgAl11O19 were synthesized via Sol–Gel method. Due to the anisotropic crystal growth, these oxides crystallize in the form of platelets and the platelet thickness increases with the decrease of rare-earth ionic radius. It was observed that the thermal-shock resistances of LaMgAl11O19, NdMgAl11O19 and SmMgAl11O19 oxides were superior to 8YSZ as proved by water quenching tests. In addition, the thinner the platelet, the more interstices are retained in the sintered specimen, and the better thermal-shock resistance the oxide has. Based on SEM images, it can be seen that the SmMgAl11O19 sample exhibits a mixture of the intergranular and transgranular fracture after thermal cycling failure.
Co-reporter:Xinghua Zhong, Zhenhua Xu, Yanfei Zhang, Jiangfeng Zhang, Xueqiang Cao
Journal of Alloys and Compounds 2009 Volume 469(1–2) pp:82-88
Publication Date(Web):5 February 2009
DOI:10.1016/j.jallcom.2008.01.156
Nd2CexO3+2x (x = 2.25, 2.5, 2.75, 3.0) were synthesized by solid-state reaction, and their phase stabilities and thermophysical properties were investigated. The X-ray diffraction (XRD) results indicated that Nd2CexO3+2x with fluorite structure were stable after long-term annealing at 1673 K. They have higher thermal expansion coefficients (TECs) than yttria-stabilized zirconia (YSZ) which is the typical thermal barrier coating (TBC) material, especially the thermal expansion as a function of temperature is parallel to that of the nickel-based superalloy. This behavior is beneficial to the reduction of the residual stresses induced by the thermal expansion mismatch at the interface between the ceramic layer and bond coat. The reduction of sintering abilities of Nd2CexO3+2x coatings was achieved by the addition of excess CeO2 into the starting powders to make a nearly stoichiometric Nd2Ce2O7 coating. Nd2CexO3+2x can be explored as a new candidate material for TBCs.
Co-reporter:Yongliang Cheng;Jiangfeng Zhang;Yanfei Zhang;Xiaolong Chen;Ying Wang;Hongmei Ma
European Journal of Inorganic Chemistry 2009 Volume 2009( Issue 28) pp:4248-4254
Publication Date(Web):
DOI:10.1002/ejic.200900418
Abstract
Hollow carbon nanofibers with circular and rectangular opening were prepared by using electrospun silica fibers as templates. Silica fibers were synthesized by electrospinning, and they were coated with a carbon layer formed by thermal decomposition and carbonization of polystyrene under a nitrogen atmosphere. Hollow carbon nanofibers with circular and rectangular openings were then obtained after the silica core was etched by hydrofluoric acid. The carbon nanofibers with different morphologies also could be used as templates to fabricate silicon carbide fibers. The silicon carbide fibers with circular and rectangular openings could be obtained by using hollow carbon nanofibers and carbon belts as templates, respectively. The hollow carbon nanofibers and silicon carbide fibers were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy, and the formation mechanism was also discussed(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Co-reporter:Zhenhua Xu, Rende Mu, Limin He, Xueqiang Cao
Journal of Alloys and Compounds 2008 Volume 466(1–2) pp:471-478
Publication Date(Web):20 October 2008
DOI:10.1016/j.jallcom.2007.11.083
A selective oxidation technique has been applied to form a diffusion barrier on the Ni-based superalloy substrate by heating the substrate with electron beam of the electron beam-physical vapor deposition (EB-PVD) facility. The interdiffusion behavior, cross-sectional morphology, isothermal and cyclic oxidations were studied for thermal barrier coatings (TBCs) with and without diffusion barrier. Under an oxygen partial pressure of about 2.5 × 10−5 kPa and after heating for 30 min, the alloying elements of substrate were selectively oxidized and a thin layer of diffusion barrier with a thickness of 500 nm was formed on the substrate, and the diffusion barrier was composed of mainly α-Al2O3, NiO and Cr2O3. Different alloying elements had different diffusion behaviors, it was observed that Al and Cr diffused inwards from the bond coat to the substrate, and Ti, Mo and W diffused outwards from the substrate to the bond coat. It was also observed that the lifetime of TBC with diffusion barrier could be partially improved, though the experimental results received from isothermal oxidation and cyclic tests are not extremely obvious.
Co-reporter:J.Y. Li, H. Dai, X.H. Zhong, Y.F. Zhang, X.F. Ma, J. Meng, X.Q. Cao
Journal of Alloys and Compounds 2008 Volume 452(Issue 2) pp:406-409
Publication Date(Web):20 March 2008
DOI:10.1016/j.jallcom.2006.11.025
La2Zr2O7 (LZ) is a promising thermal barrier coating material for the high-temperature applications, which could be significantly toughened by the BaTiO3 piezoelectric phase incorporated into the matrix. The composites of xBaTiO3/(1 − x)LZ (x = 5, 10, 15, 20 vol%, LZ-x-BaTiO3) were densified by means of high-pressure sintering (HPS) under a pressure of 4.5 GPa at 1450 °C for 10 min, by which a high relative density above 93% could be obtained. The morphologies of the fractured surfaces were investigated by the scanning electron microscope, and the fracture toughness and Vicker's hardness of the composites were evaluated by the microindentation. The grain size of the LZ matrix drops significantly with the addition of BaTiO3 piezoelectric phase and the fracture type changes from the intergranular to a mixture type of the transgranular and intergranular in the composites. The LZ-10-BaTiO3 composite has a fracture toughness of 1.98 MPa m1/2, which is obviously higher than that of the pure LZ (1.60 MPa m1/2), and the toughening mechanism might be attributed to the ferroelastic domain switching of ferroelectric phase BaTiO3.
Co-reporter:Yanfei Zhang, Yaomin Wang, Maria Ophelia Jarligo, Xinghua Zhong, Qin Li, Xueqiang Cao
Optics and Lasers in Engineering 2008 Volume 46(Issue 8) pp:601-603
Publication Date(Web):August 2008
DOI:10.1016/j.optlaseng.2008.04.001
Lanthanum magnesium hexaalumminate (LMA) is an important candidate for thermal barrier coatings due to its thermal stability and low thermal conductivity. On the other hand, laser glazing method can potentially make thermal barrier coatings impermeable, resistant to corrosion on the surface and porous at bulk. LMA powder was synthesized at 1600 °C by solid-state reaction, pressed into tablet and laser glazed with a 5-kW continuous wave CO2 laser. Dendritic structures were observed on the surface of the laser-glazed specimen. The thicker the tablet, the easier the sample cracks. Cracking during laser glazing is attributed to the low thermal expansion coefficient and large thickness of the sample.
Co-reporter:Xueqiang Cao, Jiayan Li, Xinghua Zhong, Jiangfeng Zhang, Yanfei Zhang, Robert Vassen, Detlev Stoever
Materials Letters 2008 Volume 62(17–18) pp:2667-2669
Publication Date(Web):30 June 2008
DOI:10.1016/j.matlet.2008.01.009
Oxide ceramics with high sintering-resistance above 1473 K have very important applications in thermal barrier coatings (TBCs), catalytic combustion and high-temperature structural materials. Lanthanum zirconate (La2Zr2O7, LZ) is an attractive TBC material which has higher sintering-resistance than yttria stabilized zirconia (YSZ), and this property could be further improved by the proper addition of ceria. The composite La2(Zr0.7Ce0.3)2O7 (LZ7C3) has the highest sintering-resistance, and it is observed that fine particles of the second phase in the composite concentrate at the grain boundary to prevent the grain growth of the main phase. The formation of hollow fibers is helpful to the further improvement of sintering-resistance of LZ7C3, and this technique may be widely applied to protect the catalyst support against thermal sintering.
Co-reporter:Yanfei Zhang, Qin Li, Xianfeng Ma, Xueqiang Cao
Materials Letters 2008 Volume 62(6–7) pp:923-925
Publication Date(Web):15 March 2008
DOI:10.1016/j.matlet.2007.07.039
Lanthanum magnesium hexaaluminate is a very important ceramic material for high temperature applications. In this paper lanthanum magnesium hexaaluminate has been synthesized directly by solid-state reaction. The forming mechanism was investigated by XRD. The SEM photographs show that the prepared powders are made of hexagonal plates. These powders can be well sintered at the high temperature (1600 °C) under the high pressure (4.5 GPa), and the relative density reaches 94.8%. The hardness of the high-pressure sintered lanthanum magnesium hexaaluminate is tested to be 16.68 GPa, which is much larger than that of pressureless sintering. Toughness of high-pressure sintered lanthanum magnesium hexaaluminate is about 5.25 MPa m1/2.
Co-reporter:Ling Zhu;Jian Meng
Journal of Nanoparticle Research 2008 Volume 10( Issue 2) pp:383-386
Publication Date(Web):2008 February
DOI:10.1007/s11051-007-9262-2
La0.45Ce0.45F3:Tb (10 mol% Tb) nanoparticles was synthesized via sonochemical method and then coated with silica (SiO2) shells through a microemulsion process, resulting in the formation of core/shell structured LaCeF3:Tb/SiO2 nanoparticles. The obtained core/shell LaCeF3:Tb/SiO2 nanoparticles are spherical and uniform in size (average size about 60 nm), strongly fluorescent, and long fluorescence lifetime (1.87 ms). This kind of nanoparticles was water-soluble, which could be applied in biological labeling and other fields.
Co-reporter:Yanfei Zhang, Jiayan Li, Qin Li, Ling Zhu, Xiangdong Liu, Xinghua Zhong, Jian Meng, Xueqiang Cao
Journal of Colloid and Interface Science 2007 Volume 307(Issue 2) pp:567-571
Publication Date(Web):15 March 2007
DOI:10.1016/j.jcis.2006.12.048
Electrospinning was employed to fabricate polymer–ceramic composite fibers from solutions containing poly(vinyl pyrrolidone) (PVP), Ce(NO3)3⋅6H2O and ZrOCl2⋅8H2O. Upon firing the composite fibers at 1000 °C, Ce0.67Zr0.33O2 fibers with diameters ranging from 0.4 to 2 μm were synthesized. These fibers exhibit strong resistance to sintering. They still have specific surface area around 11.8 m2/g after being heated at 1000 °C for 6 h.Figure shows that these Ce0.67Zr0.33O2 ceramic fibers calcined at 1000 °C are a mixture of dense and hollow fibers with a diameter of 0.4–2 μm.
Co-reporter:Ling Zhu, Xiaoming Liu, Jian Meng and Xueqiang Cao
Crystal Growth & Design 2007 Volume 7(Issue 12) pp:2505
Publication Date(Web):November 15, 2007
DOI:10.1021/cg070224u
A single-crystalline EuF3 nanoflower with a novel three-dimensional (3D) nanostructure has been successfully synthesized via a facile, fast, efficient, and mild ultrasonic irradiation solution route employing the reaction of Eu(NO3)3 and KBF4 under ambient conditions without any template or surfactant. The ultrasonic irradiation plays an important role and is necessary for the synthesis of EuF3 with the complex structure. The formation mechanism of this complex nanostructure is proposed in this paper. No template or surfactant is used in this method, which avoids the subsequent complicated workup for the removal of the template or surfactant. Furthermore, a substantial reduction in the reaction time as well as the reaction temperature is observed compared with the hydrothermal process.
Co-reporter:Yanfei Zhang, Jiayan Li, Qin Li, Ling Zhu, Xiangdong Liu, Xinghua Zhong, Jian Meng, Xueqiang Cao
Scripta Materialia 2007 Volume 56(Issue 5) pp:409-412
Publication Date(Web):March 2007
DOI:10.1016/j.scriptamat.2006.10.032
Electrospinning was employed to fabricate polymer–ceramic composite fibers from solutions containing polyvinyl pyrrolidone (PVP) and In(NO3)3·412H2O. Upon firing the composite fibers at 800 °C, In2O3 fibers with diameters ranging from 200 to 400 nm were synthesized. This indium oxide calcined at 800 °C is a body-centered cubic cell. The photoluminescence (PL) properties of the as-formed In2O3 nanofibers were investigated. The In2O3 nanofibers show a strong PL emission in the ultraviolet (UV) region under shorter UV light irradiation.
Co-reporter:Ling Zhu;Jian Meng
European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 24) pp:
Publication Date(Web):29 JUN 2007
DOI:10.1002/ejic.200700390
LaF3:Eu3+ (5.0 mol-% Eu3+) nanodisks with perfect crystallinity were successfully synthesized by a simple method. The synthesis was carried out in an aqueous solution at room temperature without the use of templates or organic additives. The mechanism of formation of the nanodisks was explored, and the fluoride source (KBF4) is believed to play a key role in controlling the morphology of the final product. Furthermore, the size of the disk can be simply moderated by varying the concentration of the initial reactants. The room-temperature photoluminescence of LaF3:Eu3+ with different morphologies and sizes were also investigated, and the results indicate that the emission intensity of the product is strongly affected by their size, shape, and other factors.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Co-reporter:Ling Zhu, Jian Meng, Xueqiang Cao
Journal of Solid State Chemistry 2007 Volume 180(Issue 11) pp:3101-3105
Publication Date(Web):November 2007
DOI:10.1016/j.jssc.2007.09.010
BaF2 nanocrystals doped with 5.0 mol% Eu3+ has been successfully synthesized via a facile, quick and efficient ultrasonic solution route employing the reactions between Ba(NO3)2, Eu(NO3)3 and KBF4 under ambient conditions. The product was characterized via X-ray powder diffraction (XRD), scanning electron micrographs (SEM), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra. The ultrasonic irradiation has a strong effect on the morphology of the BaF2:Eu3+ particles. The caddice-sphere-like particles with an average diameter of 250 nm could be obtained with ultrasonic irradiation, whereas only olive-like particles were produced without ultrasonic irradiation. The results of XRD indicate that the obtained BaF2:Eu3+ nanospheres crystallized well with a cubic structure. The PL spectrum shows that the BaF2:Eu3+ nanospheres has the characteristic emission of Eu3+ 5D0–7FJ (J=1–4) transitions, with the magnetic dipole 5D0–7F1 allowed transition (590 nm) being the most prominent emission line.Single-crystalline BaF2:Eu3+ (5.0 mol% Eu3+) caddice spheres has been successfully synthesized via a facile, quick and efficient ultrasonic solution route employing the reactions between Ba(NO3)2, Eu(NO3)3 and KBF4 under ambient conditions. This simple and unique synthetic method without any template or surfactant, which avoids the subsequent complicated workup procedures for the removal of the template or surfactant, has a potential advantage for synthesis of material with novel morphology.
Co-reporter:J. Y. Li;H. Dai;X. H. Zhong;Y. F. Zhang;X. Q. Cao
Advanced Engineering Materials 2007 Volume 9(Issue 3) pp:205-207
Publication Date(Web):26 FEB 2007
DOI:10.1002/adem.200600214
The lanthanum cerium in the fiber is formed by calcination of the electrospinning fibers of polymer/inorganic composite at 600 °C and a polycrystalline hollow fiber with diameter of 1∼5 μm can be obtained at 1000 °C for 12 h. After calcination at 1400 °C, the lanthanum cerium grains are closely connected to each other with clear grain boundaries and the hollow structure can be observed in the cross-section of the fiber.
Co-reporter:Q. Li, T. Xia, X.D. Liu, X.F. Ma, J. Meng, X.Q. Cao
Materials Science and Engineering: B 2007 Volume 138(Issue 1) pp:78-83
Publication Date(Web):15 March 2007
DOI:10.1016/j.mseb.2006.12.012
Nanocrystalline 8YSZ (8 mol% yttria stabilized zirconia) bulk samples with grain sizes of 20–30 nm were synthesized by Sol–Gel method and then densified under a high pressure of 4.5 GPa at 1273 K for 10 min. The method led to the densification of 8YSZ to a relative density higher than 92% without grain growth. Fourier transmission Raman spectroscopy suggested that 8YSZ underwent a phase transition from the cubic phase to a phase mixture (tetragonal plus a trace of monoclinic) after the densification, which decreased the electrical conductivity to a certain degree as concluded from the impedance spectroscopy.
Co-reporter:Ling Zhu;Qin Li;Jiayan Li;Xiangdong Liu;Jian Meng
Journal of Nanoparticle Research 2007 Volume 9( Issue 2) pp:261-268
Publication Date(Web):2007 April
DOI:10.1007/s11051-006-9114-5
A simple and efficient method has been established for the selective synthesis of mesoporous and nanorod CeVO4 with different precursors by sonochemical method. CeVO4 nanorod can be simply synthesized by ultrasound irradiation of Ce(NO3)3 and NH4VO3 in aqueous solution without any surfactant or template. While mesoporous CeVO4 with high specific surface area can be prepared with Ce(NO3)3, V2O5 and NaOH in the same way. Mesoporous CeVO4 has a specific surface area of 122 m2 g−1 and an average pore size of 5.2 nm; CeVO4 nanorods have a diameter of about 5 nm, and a length of 100–150 nm. The ultrasound irradiation and ammonia in the reactive solution are two key factors in the formation of such rod-like products. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and differential thermal analyses (DTA), UV/vis absorption spectroscopy and Brunauer–Emmett–Teller (BET) were applied for characterization of the as-prepared products.
Co-reporter:T. Xia, X.D. Liu, Q. Li, J. Meng, X.Q. Cao
Journal of Alloys and Compounds 2006 Volume 422(1–2) pp:264-272
Publication Date(Web):28 September 2006
DOI:10.1016/j.jallcom.2005.11.084
Sr2Fe1−xZnxNbO6−x/2 (0 ≤ x ≤ 0.5) and Sr2Fe1−xCuxNbO6−x/2 (0.01 ≤ x ≤ 0.05) with the double perovskite structure have been synthesized. The crystal structures at room temperature were determined from Rietveld refinements of X-ray powder diffraction data. The plots of the imaginary parts of the impedance spectrum, Z″, and the electric modulus, M″, versus log (frequency), possess maxima for both curves separated by less than a half decade in frequency with associated capacities of 2 nF. The enhancement of the overall conductivity of Sr2Fe1−xMxNbO6−x/2 (M = Cu and Zn) is observed, as increases from 2.48 (3) × 10−4 S/cm for Sr2FeNbO6 to 3.82 (5) × 10−3 S/cm for Sr2Fe0.8Zn0.2NbO5.9 at 673 K. Sr2Fe0.8Zn0.2NbO5.9 is chemically stable under the oxygen partial pressure from 1 atm to 10−22 atm at 873 K. The p and n-type electronic conductions are dominant under oxidizing and reducing conditions, respectively, suggesting a small-polaron hopping mechanism of electronic conduction. However, for Sr2Fe0.99Cu0.01NbO5.995, the conductivity is almost constant in an oxygen partial pressure range of 1–10−15 atm at 873 K, which indicates that the oxide ion conduction plays a key role in electrical transport.
Co-reporter:J.Y. Li, H. Dai, Q. Li, X.H. Zhong, X.F. Ma, J. Meng, X.Q. Cao
Materials Science and Engineering: B 2006 Volume 133(1–3) pp:209-212
Publication Date(Web):25 August 2006
DOI:10.1016/j.mseb.2006.04.026
The PVP/lanthanum nitrate/zirconium oxychloride (PVP-precursor) nanofiber was prepared by electrospinning technique. Lanthanum zirconate (La2Zr2O7, LZ) in the nanofiber is formed after calcination at 800 °C and the nanofiber with pyrochlore structure and a diameter of 100–500 nm can be obtained by calcination of the above precursor fiber at 1000 °C for 12 h. The surface of the fiber is rough but the continuous microstructure is still maintained after calcination. LZ fibers stack randomly, resulting in a structure with a low contact area between the fibers. This special structure makes the fiber to have a high resistance to sintering at elevated temperatures. The BET (Brunauer–Emmett–Teller) specific surface areas of the LZ fiber and powder calcined at different temperatures are shown in this paper, and the fiber was characterized by TG–DTA (thermal gravimetry–differential thermal analysis), XRD (X-ray diffraction), N2 absorption–desorption porosimetry and SEM (scanning electron microscopy).
Co-reporter:Tian Xia, Jiayan Li, Qin Li, Xiangdong Liu, Jian Meng, Xueqiang Cao
Solid State Ionics 2006 Volume 177(37–38) pp:3267-3273
Publication Date(Web):December 2006
DOI:10.1016/j.ssi.2006.09.011
New series of oxides, La3MMo2O12 (M = In, Ga and Al), have been prepared by the solid-state reaction. The composition and elemental distribution were analyzed by the energy-dispersive X-ray (EDX) analysis. As determined by the X-ray diffraction (XRD), these compounds have similar crystal structures that can be indexed on a monoclinic cell at room temperature. AC impedance spectra and the DC electrical conductivity measurements in various atmospheres indicate that they are oxide ion conductors with ionic conductivities between 10− 2 and 10− 3 S/cm at 800 °C. The conductivity decreases in the order of La3GaMo2O12 > La3AlMo2O12 > La3InMo2O12, implying that the effect of cell volume and polarization associated with In3+, Ga3+ and Al3+ play an important role in the anion transport of these materials. The reversible phase transition was observed in all these compounds as confirmed by the differential thermal analysis (DTA) and dilatometric measurements.
Co-reporter:Xia Tian;Li Jia-Yan;Luo Xin;Li Qin;Meng Jian;Cao Xue-Qiang
Chinese Journal of Chemistry 2005 Volume 23(Issue 6) pp:
Publication Date(Web):12 JUL 2005
DOI:10.1002/cjoc.200590703
The electrical conductivity and thermal expansion of La2Mo2O9 under low oxygen partial pressure were studied with the help of thermoelectric power and dilatometric measurements, respectively. The ionic conduction of La2Mo2O9 was predominant with the electronic transference number less than 0.05 above an oxygen partial pressure of about p=10-7 Pa at 700°C, and below this pressure the electronic conduction became obvious. The defect reaction and small polaron hopping among molybdenum sites were proposed to explain the electronic conduction. Accompanying the phase transition, there was a sharp increase of thermal expansion, which became more serious under low oxygen partial pressure. The substitution of lanthanum by neodymium led to the increase of electrical conductivity but the decrease of phase stability.
Co-reporter:X. Cao;R. Vassen;W. Fischer;F. Tietz;W. Jungen;D. Stöver
Advanced Materials 2003 Volume 15(Issue 17) pp:
Publication Date(Web):1 SEP 2003
DOI:10.1002/adma.200304132
Co-reporter:Ling Zhu, Yangjia Liu, Xizhi Fan, Daowu Yang, Xueqiang Cao
Journal of Luminescence (July 2011) Volume 131(Issue 7) pp:1380-1385
Publication Date(Web):1 July 2011
DOI:10.1016/j.jlumin.2011.03.024
Highly uniform and monodisperse KY3F10:Ln3+ (Ln=Eu, Ce, Tb) nanospheres, with an average diameter of 300 nm, have been successfully prepared through a simple template-free and surfactant-free stirring method under ambient conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The SEM images illustrate that these spheres were actually composed of randomly aggregated nanoparticles. The doped rare earth ions show their characteristic emission in the KY3F10 samples, i.e., Eu3+ 5D0–7FJ (J=1, 2, 3, 4), Tb3+ 5D4–7FJ (J=6, 5, 4, 3, 2) and Ce3+ 5d–4f transition emissions, respectively. An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in KY3F10 nanospheres, and the energy transfer efficiency depends on the doping concentration of Tb3+ if the concentration of Ce3+ is fixed.Highlights► KY3F10:Ln3+ nanospheres have been prepared via a simple stirring method. ► KY3F10:Ln3+ (Ln=Eu, Ce, Tb) showed strong characteristic fluorescence emissions. ► An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in KY3F10 nanospheres.
