Impurity effects in MoSi2 composites fabricated by self-propagating high temperature synthesis

MoSi2 composites were fabricated by a self-propagating high temperature synthesis (SHS) reaction from a mixture of Mo and Si powders with various purities (including Fe impurity). In order to understand the impurity effects in the synthesized MoSi2 compound according to the change of source material purity, we investigated the chemical states, microstructures and phase structures of the composites by XPS, SEM and XRD. The granule size of the synthesized powders decreased according to an increase of the Fe impurity content (from < 100 ppm to < 400 ppm). The impurity Fe existed as Fe-silicide in the synthesized powders. The powders synthesized by the SHS method had a typical body-centered tetragonal MoSi2 structure and other structures such as Fe and/or Fe-silicides were not detected by XRD at all. However, the crystal size and average lattice spacing, d, decreased with an increase in the Fe content. From these results, we can suggest that the Fe impurity atoms substitute for Mo in the MoSi2 structure. Finally, we found that including the impurity in source materials is one of the important parameters in synthesized MoSi2 compound by SHS.