Optical Microscopy of MoSi2 Powder and Optical Microscopy of Al2O3 Nanocomposite

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Molybdenum disilicide (MoSi2) is an intermetallic compound forming a silicide of molybdenum and silicon with the formula MO(Si)2. It has the characteristics of both metal and ceramic, such as high-temperature plasticity, electrical conductivity, and oxidation resistance. It is used as a component in the production of ceramics, high-emissivity coatings, and heat shields. MoSi2 has a moderate density and melting point of 2030 degC. It is a gray metallic-looking material and has a tetragonal crystal structure. It is insoluble in water and most acids, but soluble in nitric acid and hydrofluoric acid.

Optical microscopy of the powder as well as polished specimen from hot pressed compact was carried out under unetched and etched conditions to assess grain size of MoSi2 and distribution of SiC particles in its matrix. It was found that the equiaxed shape of the SiC grains in MoSi2 matrix is maintained even after hot pressing. Bulk hardness of the composite was measured using Vicker’s microhardness tester. Machinability of the composite was investigated to determine whether critical shapes including through holes could be made by EDM.

Oxidation behavior of the MoSi2@Al2O3 nanocomposite was studied by observing its chemical reactions in dry hydrogen atmosphere. It was observed that oxygen adsorption on the surface of MoSi2 is significantly lower than that on Al2O3 surface and the dense core-shell structure can protect it from further oxidation by preventing air penetration into the matrix. It was also found that the maximum temperature limit of the element can be increased by increasing the dew point and gas velocity of hydrogen in the endogas atmosphere.