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

Abstract

Formation of MoSi 2 -Al 2 O 3 composites with a broad range of the MoSi 2 /Al 2 O 3 ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO 3 + 2Al and 0.6MoO 3 + 0.6SiO 2 + 2Al into the Mo-Si reaction systems facilitated self-sustaining combustion and contributed to in situ formation of MoSi 2 and Al 2 O 3 . The samples adopting the former thermite reagent were more exothermic and produced composites with MoSi 2 /Al 2 O 3 from 2.0 to 4.5, beyond which combustion failed to proceed. Because of lower exothermicity of the reactions, the final products with MoSi 2 /Al 2 O 3 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 MoSi 2 /Al 2 O 3 proportion, which led to a phase transition of MoSi 2 . It was found that the dominant silicide was β-MoSi 2 when the combustion temperature of the synthesis reaction exceeded 1550 • C and shifted to α-MoSi 2 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 MoSi 2 in the MoSi 2 -Al 2 O 3 composite.

Effects of Fe/Si Stoichiometry on Formation of Fe3Si/FeSi-Al2O3 Composites by Aluminothermic Combustion Synthesis

“…According to Guan et al [15], Fe 3 Si-Al 2 O 3 nanocomposites were produced from Fe 3 O 4 , Al, and Si reactant powders through 4-h mechanical alloying followed by an annealing process at 900 • C for 1 h. Besides, Li et al [16] produced iron silicide nanoparticles of various phases by thermal annealing of Fe-FeSi 2 samples with a core-shell structure and identified the phase transformation from Fe-FeSi 2 to FeSi and Fe 3 Si under an annealing time of 2 h and temperatures of 600 and 700 • C. Recently, an in situ fabrication approach combining the chemical interaction between Fe and Si with aluminothermic reduction of Fe 2 O 3 and SiO 2 has been attempted to produce FeSi-Al 2 O 3 and α-FeSi 2 -Al 2 O 3 composites in the mode of self-propagating high-temperature synthesis (SHS) [17,18]. With the advantages of energy efficiency, rapid reaction, simplicity, and high-purity products [19], the SHS scheme has been recognized as one of the most effective methods for preparing transition metal silicides in monolithic and composite forms [20][21][22][23].…”

In Situ Formation of TiB2/Al2O3-Reinforced Fe3Al by Combustion Synthesis with Thermite Reduction

“…Among them, the SHS method takes advantage of highly exothermic reactions, and hence has the merits of a low energy requirement, a short reaction time, inexpensive equipment, simplicity of operation, and a structural and functional diversity of final products [14][15][16]. When combined with a thermite reaction using Al as the reducing agent, combustion synthesis represents an in situ fabrication route to prepare Al 2 O 3 -reinforced intermetallics and ceramics [12,13,17,18]. Moreover, aluminothermic reduction of metal oxides is thermally beneficial for the SHS process.…”