The Effect of the Mg Content on Mechanosynthesis of ZrB2–SiC–ZrC Composite in the Mg/ZrSiO4/B2O3/C System

Abstract

The influence of magnesium content on the mechanosynthesis of ZrB2–SiC–ZrC composite in Mg/ZrSiO4/B2O3/C mixture was investigated. Thermodynamic evaluations revealed that the amount of Mg played a main role, thereby; the overall reaction enthalpy and adiabatic temperature (Tad) changed by variation of magnesium content. According to differential thermal analysis (DTA) results, after 45min milling, the temperature of combustion reaction decreased to 576 ◦C and all the reactions occurred, simultaneously. The experimental findings indicated the type of reactions in the mixture powder with stoichiometric ratio (7mol Mg) was mechanically induced self-sustaining reaction (MSR). When the Mg content was within a range of 6-7mol, the magnesiothermic reduction was occurred in MSR mode and the carbothermal reaction was activated, hence; the carbon acted not only as a carbide former agent but also as a reductant. MSR mode magnesiothermic reduction and gradual carbothermal reduction were occurred when the Mg value was 11/2-6 mol. At lower Mg contents in mixture (5mol), the reduction reaction proceeded through a gradual mode and no carbothermal reaction occurred.