Preparation and Anti-oxidation Mechanism of Mullite/Yttrium Silicate Coatings on C/SiC Composites

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.

Fabrication and oxidation resistance of mullite/yttrium silicate multilayer coatings on C/SiC composites

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.

Y_2Si_2O_7涂层的制备及其对C/SiC复合材料的氧化保护作用（英文）

以Y_2O_3粉和硅树脂配制成的浆料为原料,通过浸涂提拉法在C/SiC复合材料表面制备Y_2Si_2O_7涂层,研究Y_2Si_2O_7相的合成、涂层结构和氧化保护效果以及抗氧化机制。结果表明,质量比为54.2:45.8的Y_2O_3粉/硅树脂混合物先在800°C空气中裂解再在1400°C Ar惰性气氛下热处理,能够完全转化成Y_2Si_2O_7。Y_2Si_2O_7涂层致密度高且与基体结合紧密,在氧化过程中发生进一步致密化而呈现出优异的抗氧化性能,分别在1400、1500和1600°C氧化30 min后,复合材料的强度保留率达到130%~140%。此外,在1500°C下Y_2Si_2O_7涂层会与氧化铝支撑体之间发生反应,生成具有低共熔点的Y-Si-Al-O玻璃相。

硅酸钇高温抗氧化涂层的研究进展

针对硅酸钇的结构特点和物理化学特性,阐述了硅酸钇材料在高温抗氧化涂层领域的应用现状,总结了近年来国内外硅酸钇涂层制备技术的最新研究进展,展望了硅酸钇高温抗氧化涂层下一步研究重点和发展趋势。指出:硅酸钇涂层在高于1700℃下的抗氧化和失效机理和致密硅酸钇涂层的低温制备工艺的进一步开发和完善是下一步的研究重点。

Preparation of spherical Y_2SiO_5 powders for thermal-spray coating

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.

C_f/SiC复合材料SiC/Yb_2SiO_5抗氧化复合涂层研究

硅酸镱(Yb2SiO5)是Cf/SiC复合材料非常理想的抗氧化涂层材料。用脉冲CVD法在Cf/SiC复合材料上先制备SiC粘附层。用溶胶凝胶法制备粒径为200～300nm的单相Yb2SiO5粉体,然后用PCS-SiC-Yb2SiO5浆料浸涂法制备SiC-Yb2SiO5过渡层,因PCS粘结强度大,且热解后能在原位生成SiC,故能大大增加涂层的结合力。配备低粘度、高固含量的Yb2SiO5浆料,并用浆料浸涂烧结法制备致密、细晶粒的Yb2SiO5涂层。1500℃静态空气中氧化实验表明:SiC/Yb2SiO5复合涂层具备优异的抗氧化性能。

面向高温抗氧化的硅酸钇涂层研究进展

硅酸钇具有高熔点、低热膨胀系数、低氧气渗透率、低模量、低热导率、化学和热稳定性好等特性,是C/C和C/SiC复合材料抗氧化涂层的最佳候选材料之一。综述了硅酸钇涂层的结构形式和抗氧化效果,介绍了常见的制备方法,并分析指出了今后发展需要关注的问题。

C/SiC复合材料用莫来石/硅酸钇双层涂层的抗氧化性能研究

针对C/SiC复合材料的防氧化要求,在材料表面通过等离子喷涂法制备了莫来石/硅酸钇的双层涂层,对涂层的形貌、组成和结构及其与基底的结合强度进行了表征,开展了1500℃、1h静态空气氧化实验,对抗氧化涂层的结构演变进行了分析,并对C/SiC复合材料氧化实验前后的质量和力学性能变化进行了研究。结果表明,莫来石/硅酸钇双层涂层抗氧化作用较好,涂层C/SiC复合材料的强度保留率达95.3%。