A study on mechanochemical behavior of MoO3–Mg–C to synthesize molybdenum carbide

• Molybdenum carbide has been synthesized starting with Mg, MoO3 and C.
• Mg content plays a key role in the mechanochemical behavior of the ternary system MoO3–Mg–C.
• By increasing milling time, an exothermic reaction occurs before magnesium melting.
• Magnesiothermic reaction provided enough heat for activating carbothermic reaction.

The influence of Mg value in the MoO3–Mg–C mixture on the molybdenum carbide formation and the mechanism of reactions during mechanochemical process were investigated. In keeping with this aim, magnesium and carbon contents of the mixture were changed according to the following reaction: 2MoO3 + (6 − x) Mg + (1 + x) C = (6 − x) MgO + Mo2C + x CO. The value of x varied from 0 to 6. Differential thermal analysis (DTA) results for sample with stoichiometric ratio (x = 0) revealed that in the early stage, carbon reduced the MoO3 to MoO2 and subsequently highly exothermic magnesiothermic MoO2 reduction occurred after magnesium melting. Also, it was indicated that the exothermic reaction temperature shifted to before magnesium melting in the 11 h-milled sample (x = 0) and all the exothermic reactions happened, simultaneously. According to the experimental findings, molybdenum carbide (Mo2C) was synthesized in the mixture powder with stoichiometric ratio (x = 0) after 12 h milling process and the type of reactions was mechanically induced self-sustaining reaction (MSR). However, at lower Mg content in the MoO3–Mg–C mixture (0 < x ≤ 2), the magnesiothermic reduction occurred in MSR mode and activated the carbothermal reaction. Further decrease in Mg value (2 < x ≤ 3) resulted in MSR mode magnesiothermic reaction and gradual carbothermal reduction. In samples with lower magnesium contents, partial molybdenum oxide reduction proceeded through a gradual mode magnesiothermic reaction.