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Thermochemical stability of Y2Si2O7 in high‐temperature water vapor
Journal of the American Ceramic Society ( IF 3.9 ) Pub Date : 2020-03-17 , DOI: 10.1111/jace.17114
Robert A. Golden 1 , Kendall Mueller 1 , Elizabeth J. Opila 1
Affiliation  

The thermochemical stability of Y2Si2O7 was assessed in a high‐temperature high‐velocity water vapor environment to improve the understanding of the mechanisms that lead to SiO2 depletion. Spark plasma sintered Y2Si2O7 specimens were exposed in a steam‐jet furnace at 1000°C and 1200°C for 3‐250 hours, steam velocities of 131‐174 m/s and at 1 atm H2O pressure. These exposures resulted in the selective volatilization of SiO2 to form volatile Si(OH)4 and porous Y2SiO5. Microstructural evolution from fine rectangular pores at short times to larger rounded pores at longer times was observed. Mechanisms contributing to the overall depletion reaction kinetics were evaluated and include the interface reaction to form Y2SiO5 and Si(OH)4 (g), Y2SiO5 coarsening, development of tortuosity in the pore network and diffusion of H2O (g) and Si(OH)4 (g) through pores by molecular diffusion and/or Knudsen diffusion. SiO2 depletion was found to follow parabolic volatilization kinetics (k p = 0.38 µm2/h) at 1200°C indicating the reaction is limited by a diffusion process, most likely the outward diffusion of Si(OH)4 (g) through pores. Results are utilized to assess the viability of Y2Si2O7 and other rare‐earth silicates as environmental barrier coating (EBC) materials for SiC ceramic matrix composites (CMCs).

中文翻译:

Y2Si2O7在高温水蒸气中的热化学稳定性

在高温高速水蒸气环境中评估了Y 2 Si 2 O 7的热化学稳定性,以增进对导致SiO 2耗尽的机理的理解。火花等离子体烧结Y 2的Si 2个ö 7样品在1000暴露在蒸汽喷射炉℃与1200℃下的131-174米/秒,在1个大气压ħ3-250小时,蒸汽速度2 ö压力。这些暴露导致SiO 2选择性挥发,形成挥发性Si(OH)4和多孔Y 2 SiO 5。观察到从短时间的细矩形孔到较长时间的较大圆形孔的微观结构演变。评估了有助于整体耗竭反应动力学的机理,包括形成Y 2 SiO 5和Si(OH)4(g)的界面反应,Y 2 SiO 5粗化,孔网络中曲折的发展以及H 2 O的扩散。(g)和Si(OH)4(g)通过分子扩散和/或Knudsen扩散通过孔。发现SiO 2损耗遵循抛物线挥发动力学(k p  = 0.38 µm 2/ h)在1200°C时表明反应受扩散过程的限制,很可能是Si(OH)4(g)通过孔向外扩散。结果被用来评估Y 2 Si 2 O 7和其他稀土硅酸盐作为SiC陶瓷基复合材料(CMC)的环境屏障涂层(EBC)材料的可行性。
更新日期:2020-03-17
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