In order to enhance the oxidation resistance of C/Si C composites, mullite/yttrium silicate coatings were fabricated on C/Si C composites through dip-coating route. Al_2O_3-SiO_2 sol with high solid content was select...In order to enhance the oxidation resistance of C/Si C composites, mullite/yttrium silicate coatings were fabricated on C/Si C composites through dip-coating route. Al_2O_3-SiO_2 sol with high solid content was selected as the raw material for mullite and ＂silicone resin ＋ Y_2O_3 powder＂ slurry was used to synthesize yttrium silicate. The microstructure and phase composition of coatings were characterized, and the investigation on oxidation resistance and anti-oxidation mechanism was emphasized. The as-fabricated coatings consisting of SiO_2-rich mullite phase and Y_2Si_2O_7 phase show high density and favorable bonding to C/Si C composites. After oxidized at 1 400 ℃ and 1 500 ℃ for 30 min in static air, the coating-containing C/Si C composites possess 91.9% and 102.4% of the original flexural strength, respectively. The desirable thermal stability of coatings and the further densification of coatings due to viscous flow of rich SiO_2 and Y-Si-Al-O glass are responsible for the excellent oxidation resistance. In addition, the coating-containing composites retain 99.0% of the original flexural strength and the coatings exhibit no cracking and desquamation after 12 times of thermal shock from 1 400 ℃ to room temperature, which are ascribed to the combination of anti-oxidation mechanism and preferable physical and chemical compatibility among C/Si C composites, mullite and Y_2Si_2O_7. The carbothermal reaction at 1 600 ℃ between free carbon in C/Si C substrate and rich SiO_2 in mullite results in severe frothing and desquamation of coatings and obvious degradation in oxidation resistance.展开更多
A tri-layer coating of mullite/Y_(2)Si_(2)O_(7)/(70wt%Y_(2)Si_(2)O_(7)+30wt%Y_(2)SiO_(5))was prepared on carbon fiber reinforced silicon carbide(C/SiC)composite substrate through dip-coating route for the sake of impr...A tri-layer coating of mullite/Y_(2)Si_(2)O_(7)/(70wt%Y_(2)Si_(2)O_(7)+30wt%Y_(2)SiO_(5))was prepared on carbon fiber reinforced silicon carbide(C/SiC)composite substrate through dip-coating route for the sake of improving oxidation resistance of C/SiC composites.An Al_(2)O_(3)-SiO_(2) sol with high solid content was selected as raw material for mullite,and a slurry of Y_(2)O_(3) powder filled silicone resin was used to synthesize yttrium silicate.The microstructure,phase composition,and oxidation resistance of the coating were investigated.The as-fabricated coating shows high density and favorable bonding to C/SiC substrate.After oxidation at 1400 and 1500℃for 30 min under static air,the flexural strengths of coated C/SiC composite were both increased by~30%.The desirable thermal stability and the further densification are responsible for excellent oxidation resistance.With the additional help of compatible thermal expansion coefficients among substrate and sub-layers in coating,the coated composite retained 111.2%of original flexural strength after 12 times of thermal shock in air from 1400℃ to room temperature.The carbothermal reaction at 1600℃ between free carbon in C/SiC substrate and rich SiO_(2) in mullite resulted in severe frothing and desquamation of coating and obvious degradation in oxidation resistance.展开更多
Y/Bi co-doped silicate glasses were prepared,and the effects of Y 2 O 3 on the absorption and emission properties were investigated by spectrum measurement.It was found that the absorption intensity in visible region ...Y/Bi co-doped silicate glasses were prepared,and the effects of Y 2 O 3 on the absorption and emission properties were investigated by spectrum measurement.It was found that the absorption intensity in visible region decreases with increase of Y 3＋ concentration in（70-x）SiO 2 xY 2 O 3-30CaO-1.5Bi 2 O 3（x=0 mol.%,1 mol.%,3 mol.%,5 mol.%,7 mol.%） glasses.The emissions centered at 410,630,1200 and 1290 nm were observed under 280,470,514 and 808 nm excitation,respectively.The emission intensity had the similar change tendency in the visible and near infrared region.We also discussed the actual role of Y 3＋ ions playing in the visible and near infrared emissions of the silicate glasses.展开更多
Yttrium silicate （Y2Si2O7） coating was fabricated on C/SiC composites through dip-coating with silicone resin ＋ Y2O3 powder slurry as raw materials. The synthesis, microstructure and oxidation resistance and the an...Yttrium silicate （Y2Si2O7） coating was fabricated on C/SiC composites through dip-coating with silicone resin ＋ Y2O3 powder slurry as raw materials. The synthesis, microstructure and oxidation resistance and the anti-oxidation mechanism of Y2Si2O7 coating were investigated. Y2Si2O7 can be synthesized by the pyrolysis of Y2O3 powder filled silicone resin at mass ratio of 54.2：45.8 and 800 °C in air and then heat treated at 1400 °C under Ar. The as-fabricated coating shows high density and favorable bonding to C/SiC composites. After oxidation in air at 1400, 1500 and 1600 °C for 30 min, the coating-containing composites possess 130%-140% of original flexural strength. The desirable thermal stability and the further densification of coating during oxidation are responsible for the excellent oxidation resistance. In addition, the formation of eutectic Y-Si-Al-O glassy phase between Y2Si2O7 and Al2O3 sample bracket at 1500 °C is discovered.展开更多
Yttrium silicate, for its high oxidation resistance, is an important candidate for protective coating for carbon-fiber-reinforced composites at temperatures above 1600 ℃. A novel method, consisting of coprecipitation...Yttrium silicate, for its high oxidation resistance, is an important candidate for protective coating for carbon-fiber-reinforced composites at temperatures above 1600 ℃. A novel method, consisting of coprecipitation, spray-drying, heat-treatment and plasma-densification, is developed to prepare Y2SiO5 powders for thermal-spraying. The composition, morphology and flowability of the synthesized Y2SiO5 powders are investigated by XRD, SEM and Hall Flowmeter, respectively. The results show that the synthesized Y2SiO5 powders are nearly spherical with high purity. The apparent density and flowability of the Y2SiO5 powders are 1.87 g/cm^3 and 37 s/50 g, respectively, which lead to a high deposition efficiency of up to 80700 for atmospheric plasma spraying.展开更多
基金Funded by the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Provincethe Aid Program for Innovative Group of National University of Defense Technologythe Science Innovation Foundation of Shanghai Academy of Spaceflight Technology(No.SAST2015043)
文摘In order to enhance the oxidation resistance of C/Si C composites, mullite/yttrium silicate coatings were fabricated on C/Si C composites through dip-coating route. Al_2O_3-SiO_2 sol with high solid content was selected as the raw material for mullite and ＂silicone resin ＋ Y_2O_3 powder＂ slurry was used to synthesize yttrium silicate. The microstructure and phase composition of coatings were characterized, and the investigation on oxidation resistance and anti-oxidation mechanism was emphasized. The as-fabricated coatings consisting of SiO_2-rich mullite phase and Y_2Si_2O_7 phase show high density and favorable bonding to C/Si C composites. After oxidized at 1 400 ℃ and 1 500 ℃ for 30 min in static air, the coating-containing C/Si C composites possess 91.9% and 102.4% of the original flexural strength, respectively. The desirable thermal stability of coatings and the further densification of coatings due to viscous flow of rich SiO_2 and Y-Si-Al-O glass are responsible for the excellent oxidation resistance. In addition, the coating-containing composites retain 99.0% of the original flexural strength and the coatings exhibit no cracking and desquamation after 12 times of thermal shock from 1 400 ℃ to room temperature, which are ascribed to the combination of anti-oxidation mechanism and preferable physical and chemical compatibility among C/Si C composites, mullite and Y_2Si_2O_7. The carbothermal reaction at 1 600 ℃ between free carbon in C/Si C substrate and rich SiO_2 in mullite results in severe frothing and desquamation of coatings and obvious degradation in oxidation resistance.
基金the financial supports from the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province,and the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology(No.SAST2015043).
文摘A tri-layer coating of mullite/Y_(2)Si_(2)O_(7)/(70wt%Y_(2)Si_(2)O_(7)+30wt%Y_(2)SiO_(5))was prepared on carbon fiber reinforced silicon carbide(C/SiC)composite substrate through dip-coating route for the sake of improving oxidation resistance of C/SiC composites.An Al_(2)O_(3)-SiO_(2) sol with high solid content was selected as raw material for mullite,and a slurry of Y_(2)O_(3) powder filled silicone resin was used to synthesize yttrium silicate.The microstructure,phase composition,and oxidation resistance of the coating were investigated.The as-fabricated coating shows high density and favorable bonding to C/SiC substrate.After oxidation at 1400 and 1500℃for 30 min under static air,the flexural strengths of coated C/SiC composite were both increased by~30%.The desirable thermal stability and the further densification are responsible for excellent oxidation resistance.With the additional help of compatible thermal expansion coefficients among substrate and sub-layers in coating,the coated composite retained 111.2%of original flexural strength after 12 times of thermal shock in air from 1400℃ to room temperature.The carbothermal reaction at 1600℃ between free carbon in C/SiC substrate and rich SiO_(2) in mullite resulted in severe frothing and desquamation of coating and obvious degradation in oxidation resistance.
基金supported by Science and Technology Project of Guangdong (2009A090100044)National High-Technology Research and Development Program of China ("863"Program) (2011AA030201)
文摘Y/Bi co-doped silicate glasses were prepared,and the effects of Y 2 O 3 on the absorption and emission properties were investigated by spectrum measurement.It was found that the absorption intensity in visible region decreases with increase of Y 3＋ concentration in（70-x）SiO 2 xY 2 O 3-30CaO-1.5Bi 2 O 3（x=0 mol.%,1 mol.%,3 mol.%,5 mol.%,7 mol.%） glasses.The emissions centered at 410,630,1200 and 1290 nm were observed under 280,470,514 and 808 nm excitation,respectively.The emission intensity had the similar change tendency in the visible and near infrared region.We also discussed the actual role of Y 3＋ ions playing in the visible and near infrared emissions of the silicate glasses.
基金Project supported by the Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province,ChinaProject(CJ12-01-01)supported by the Innovative Group of National University of Defense Technology,ChinaProject(SAST2015043)supported by the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology,China
文摘Yttrium silicate （Y2Si2O7） coating was fabricated on C/SiC composites through dip-coating with silicone resin ＋ Y2O3 powder slurry as raw materials. The synthesis, microstructure and oxidation resistance and the anti-oxidation mechanism of Y2Si2O7 coating were investigated. Y2Si2O7 can be synthesized by the pyrolysis of Y2O3 powder filled silicone resin at mass ratio of 54.2：45.8 and 800 °C in air and then heat treated at 1400 °C under Ar. The as-fabricated coating shows high density and favorable bonding to C/SiC composites. After oxidation in air at 1400, 1500 and 1600 °C for 30 min, the coating-containing composites possess 130%-140% of original flexural strength. The desirable thermal stability and the further densification of coating during oxidation are responsible for the excellent oxidation resistance. In addition, the formation of eutectic Y-Si-Al-O glassy phase between Y2Si2O7 and Al2O3 sample bracket at 1500 °C is discovered.
基金supported by the National Fundamental Research Program (No. A1320070102)
文摘Yttrium silicate, for its high oxidation resistance, is an important candidate for protective coating for carbon-fiber-reinforced composites at temperatures above 1600 ℃. A novel method, consisting of coprecipitation, spray-drying, heat-treatment and plasma-densification, is developed to prepare Y2SiO5 powders for thermal-spraying. The composition, morphology and flowability of the synthesized Y2SiO5 powders are investigated by XRD, SEM and Hall Flowmeter, respectively. The results show that the synthesized Y2SiO5 powders are nearly spherical with high purity. The apparent density and flowability of the Y2SiO5 powders are 1.87 g/cm^3 and 37 s/50 g, respectively, which lead to a high deposition efficiency of up to 80700 for atmospheric plasma spraying.
