选择NbSi2的单晶、放电等离子烧结(SPS)多晶和电弧熔炼多晶样品在 1023 K下氧化, 研究了微裂纹、孔隙和晶界对NbSi2氧化行为的影响. 结果表明, 含有大量微裂纹的电弧熔炼多晶样品经3 h氧化后完全粉化, 而单晶 和SPS样品经89 h氧化亦未出现粉化. 无论是单晶还是多晶样品, 氧化产物均为 Nb2O5和SiO2, 生成的Nb2O5易剥落, 样品的氧 化动力学曲线均呈直线规律, 证明NbSi2的氧化过程是一种本征无保护 条件下氧元素与基体元素直接反应的过程. 多晶样品的氧化速率明显高于单 晶样品的氧化速率, 分析表明晶界和孔隙相当于增加了氧化反应的有效面积, 提出了相应模型.
Single crystalline, arc-melted and SPS poly-crystalline NbSi2 samples were prepared for oxidation experiment at 1023 K, and the effects of cracks, pores and grain boundary on the oxidation behavior of NbSi2 were investigated. For arc-melted poly-crystalline samples, NbSi2 fully turned into powders after 3 h exposure at 1023 K, which is known as the “pesting” phenomenon. As a comparison, no pesting was found in the dense SPS poly-crystalline samples and single crystals after 89 h. The oxide formed on NbSi2 at 1023 K consists of Nb2O5 and minor SiO2. The Nb2O5 is lose and nonprotective, which spalls from the sample during oxidation. The oxidation kinetics of all the NbSi2 samples at 1023 K follows a linear law. The oxidation rate is intrinsically determined by the reaction rate between the matrix and the oxygen in air, which in turn is determined by the exposure area of the sample. The NbSi2 poly-crystalline sample shows a much larger weight change than that of the single crystalline sample, indicating grain boundaries and pores increase the effective area of oxidation reaction. A relevant model was proposed.
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