THE FEASIBILITY OF MoSi2 SYNTHESIS DIRECTLY FROM MoO3 VIA MECHANICAL ALLOYING

MoSi2 is known as a ceramic material with attractive properties for high temperature structural applications. In this study, mechanical alloying was used to prepare MoSi2 powder directly from molybdenum oxide. Mixtures of MoO3 and Si powders were exposed to sever mechanical activation in a planetary ball mill. The ball to powder mass ratio was constant at 35:1 and the rotation speed (cup speed) was 600 rpm during the milling operation. Structural evolutions during milling were evaluated by X-ray diffraction analysis. Scherrer and Williamson-Hall methods using XRD patterns were employed to calculate the mean crystallite sizes. The morphology of the milled powders was investigated with SEM. From XRD results, it was observed that within 150 minutes of milling, MoO3 was reduced and fully converted to MoO2. After 17 hours of milling MoO2 also began to reduce and peaks of MoSi2 (both α and β phases) and Mo were detected. Further milling resulted in a gradual decrease in MoO2 peak intensities because of its continuous reduction. Peaks of MoO2 were also broadened due to refinement of crystallite sizes. Calculations indicated that in the sample milled for 50 hours, the mean crystallite size of MoSi2 was less than 100 nm. Also, reaction mechanism of MoSi2 formation was gradually type. In addition, it was observed that MoSi2 particles distribute over the Mo particles during formation by mechanical alloying and annealing causes grain growth and micro strain release. An interesting phenomenon is that powder particles retain their nanocrystalline structure even after annealing.

کلیدواژه ها:

Nano-crystalline ، Mechanical alloying ، Mechanochemical reduction ، MoSi2 ، MoO3