Abstract
Combustion synthesis involving metallothermic reduction of MoO3 by dual reductants, Mg and Al, to enhance the reaction exothermicity was applied for the in situ production of Mo3Si–, Mo5Si3− and MoSi2–MgAl2O4 composites with a broad compositional range. Reduction of MoO3 by Mg and Al is highly exothermic and produces MgO and Al2O3 as precursors of MgAl2O4. Molybdenum silicides are synthesized from the reactions of Si with both reduced and elemental Mo. Experimental evidence indicated that the reaction proceeded as self-propagating high-temperature synthesis (SHS) and the increase in silicide content weakened the exothermicity of the overall reaction, and therefore, lowered combustion front temperature and velocity. The XRD analysis indicated that Mo3Si–, Mo5Si3– and MoSi2–MgAl2O4 composites were well produced with only trivial amounts of secondary silicides. Based on SEM and EDS examinations, the morphology of synthesized composites exhibited dense and connecting MgAl2O4 crystals and micro-sized silicide particles, which were distributed over or embedded in the large MgAl2O4 crystals.
Highlights
The in situ fabrication of Mo3 Si, Mo5 Si3 – and MoSi2 –MgAl2 O4 composites was investigated by the SHS process integrating metallothermic reduction of MoO3 with combustion synthesis
Molybdenum silicides were synthesized from the elemental reactions between Mo and Si
Experimental results showed that the formation of MoSi2 –MgAl2 O4 composites was the most exothermic and characterized by the highest combustion front temperature and fastest combustion velocity, while that of Mo5 Si3
Summary
Molybdenum silicides, Mo3 Si, Mo5 Si3 and MoSi2 , are promising intermetallic materials for ultrahigh-temperature structural applications. Besides a high melting point over 2020 ◦ C, they possess high strength, excellent oxidation resistance, corrosion resistance, creep resistance and good compatibility with ceramic reinforcements [1,2,3,4,5,6,7,8]. To improve the refractory property of transition metal silicides, magnesium aluminate spinel (MgAl2 O4 ). Has been one of the potential additives, because of its unique combination of properties, including a high melting point (2135 ◦ C), relatively low density, chemical inertness, high hardness, high mechanical strength and good thermal shock resistance [9,10,11,12]. Preparation of MgAl2 O4 via either wet chemical methods or solid-state reactions required several complicated steps under the long processing time [9,10,11,12]
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