Effect of atmosphere and heating rate on mechanism of MoSi2 formation during self-propagating high-temperature synthesis

Abstract

To study the effect of atmospheric type and heating rate on formation mechanism of MoSi2, the Mo + 2Si powder mixture was exposed to simultaneous thermal analysis (STA) in air atmosphere at different heating rates (10, 15, and 20 °C/min). To further study the changes, thermal analyses of molybdenum powders and consumed silicon were also performed separately. An amount of aluminum powder (5 wt.%) was also added to Mo + 2Si powder mixture and exposed to thermal analysis at different heating rates (10, 15, and 20 °C/min) to study the effect of the presence of active elements (like aluminum) on the trend of the performance of changes. To perform phase studies on the products of the thermal analysis at a later stage, each product was separately tested by an X-ray diffraction (XRD) method. Contrary to expectations, the XRD patterns showed that the trends of changes during thermal analysis were not in the direction of MoSi2, and the DTA–TG peaks obtained from these analyses were in fact related to other changes. Ultimately, the results showed that the peaks on the DTA curves resulted from the oxidation of molybdenum particles; and the (MoO3) melt of the product, and in continuation of the reduction of a part of this oxide, it resulted during the silicothermic and aluminothermy reactions. The results of this research also showed that with regard to the presence of intensive oxidation tendency of molybdenum particles, there is no chance for the formation of MoSi2 by heating the powder mixture of Mo + 2Si in air atmosphere and at low heating rates.