Comparative studies on the pest reactions of single- and poly- crystalline MoSi2

Molybdenum disilicide (MoSi2) has many attractive properties, e.g., high melting point (2020 degrees C), relatively low density (6.28 g/cm3), good thermal stability and thermal shock resistance, and excellent oxidation resistance, for potential high temperature applications. Specifically, it is oxidation resistant at temperatures up to about 1900 degrees C, resulting from the formation of a self-healing, glassy silica (SiO2) surface layer. Because of its suitability for use as a high temperature coating and as heating elements, the oxidation properties of MoSi2 have been extensively studied in the past 30 years, but mainly in the high temperature regimes. In this paper, the authors investigate the evolution and morphological characteristics of the oxidation products of both MoSi2 single crystals and cast polycrystals. Special attention is given to addressing the nucleation of pest in single crystalline material. The results from both the single- and poly-crystalline samples are correlated with an effort to resolve the origin of MoSi2 pest. Their implications to the early-stage formation (nucleation) of pest are discussed