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

Received 28 Nov 2014 Accepted 05 Jan 2015 Available online 30 June 2015 The influence of the magnesium content on the mechanosynthesis of ZrB2–SiC–ZrC composite in the Mg/ZrSiO4/B2O3/C mixture was investigated. Thermodynamic evaluations revealed that the amount of Mg played a main role and, as a consequence, the overall reaction enthalpy and adiabatic temperature (Tad) changed by the variation of the magnesium content. According to the differential thermal analysis (DTA) results, after 45 min of milling, the temperature of the combustion reaction decreased to 576 ◦C and all the reactions occurred simultaneously. The experimental findings indicated that 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 the range of 6-7mol, the magnesiothermic reduction occurred in the MSR mode and the carbothermal reaction was activated; hence, the carbon acted not only as a carbide former agent but also as a reductant. The MSR mode magnesiothermic reduction and gradual carbothermal reduction occurred when the Mg value was 11/2-6 mol. At lower Mg contents in the mixture (5mol), the reduction reaction proceeded through a gradual mode and no carbothermal reaction occurred.

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