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| A Comparison of the Oxidation Behaviors of Poly-Crystalline and Single Crystalline NbSi2 at 1023 K |
| ZHANG Fang; ZHANG Lanting; YU Jinxing; WU Jiansheng |
| Key Laboratory of the Ministry of Education for High Temperature Materials and Testing; School of Materials Science and Engineering; Shanghai Jiaotong University; Shanghai 200030 |
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Cite this article:
ZHANG Fang; ZHANG Lanting; YU Jinxing; WU Jiansheng. A Comparison of the Oxidation Behaviors of Poly-Crystalline and Single Crystalline NbSi2 at 1023 K. Acta Metall Sin, 2005, 41(6): 645-648 .
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Abstract 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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Received: 24 April 2004
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