Combustion Synthesis of MoSi2-Al2O3 Composites from Thermite-Based Reagents

• Main Authors: Chun-Liang Yeh, Je-An Peng
• Format: Article
• Language: English
• Published: MDPI AG 2016-09-01
• Series: Metals
• Subjects: self-propagating high-temperature synthesis (SHS); thermite reaction; MoSi2; Al2O3; combustion temperature
• Online Access: http://www.mdpi.com/2075-4701/6/10/235

Formation of MoSi2–Al2O3 composites with a broad range of the MoSi2/Al2O3 ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO3 + 2Al and 0.6MoO3 + 0.6SiO2 + 2Al into the Mo–Si reaction systems facilitated self-sustaining combustion and contributed to in situ formation of MoSi2 and Al2O3. The samples adopting the former thermite reagent were more exothermic and produced composites with MoSi2/Al2O3 from 2.0 to 4.5, beyond which combustion failed to proceed. Because of lower exothermicity of the reactions, the final products with MoSi2/Al2O3 from 1.2 to 2.5 were fabricated from the SHS process involving the latter thermite mixture. Combustion temperatures of both reaction systems decreased from about 1640 to 1150 °C with increasing MoSi2/Al2O3 proportion, which led to a phase transition of MoSi2. It was found that the dominant silicide was β-MoSi2 when the combustion temperature of the synthesis reaction exceeded 1550 °C and shifted to α-MoSi2 as the combustion temperature fell below 1320 °C. The results of this study showed an energy-efficient fabrication route to tailor the phase and content of MoSi2 in the MoSi2–Al2O3 composite.