Reaction chemistry in the Mg-B2O3-MoO3 system reactive mixtures

Fundamental aspects of reaction path in the MoO3 + B2O3 + Mg system to synthesize molybdenum boride have been investigated. The phase transformation and structural evaluation were studied by means of differential thermal analysis (DTA) techniques, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Thermodynamic evaluations indicated that the reaction was highly exothermic and should be a mechanically induced self-sustaining reaction (MSR). According to DTA results, for unmilled sample, the reaction's sequence includes the following reactions: MoO3 reduction → B2O3 reduction → molybdenum boride formation. For 3 h-milled sample, the temperature of exothermic reaction decreased significantly and all the reactions occurred, simultaneously. Based on XRD results, the mechanochemical products including MgO and mix of molybdenum boride phases were achieved after 4 h of high energy ball milling. SEM and TEM observations confirmed that the range of particle size was within 100 nm.