Effect of Al addition on the microstructure and low-temperature reactivity to oxygen of pre-formed MoSi2

The effect of aluminum addition on the structural and low-temperature oxidation behavior of commercially available MoSi2 was investigated by means of X-ray diffraction and thermogravimetric analysis. MoSi2 + x Al compounds (with x = 0.0, 0.10, 0.20, 0.30, and 0.40) were mechanically processed for 6 h starting from α-MoSi2 and Al powders. It is shown that Al can substitute Si atoms in pre-formed MoSi2 leading to the formation of β-MoSi2 (the high temperature phase). The unit cell volume of β-MoSi2 increases linearly with the Al content. For x < 0.20, a clear onset temperature for the oxidation of MoSi2 is discernable at ca. 420 °C, while it is barely noticeable for x ≥ 0.20. The normalized mass gain decreases from ~12 % m−2 to less than 2 % m−2 when the Al content varies from 0.0 to 0.2. For x ≥ 0.20, the normalized mass gain stays constant at less than 2 % m−2.