Reaction chemistry and thermochemistry of magnesia-graphite systems containing antioxidants

Reaction chemistry and thermochemistry of magnesia-graphite refractory systems containing antioxidants are presented in the form of five different studies. Thermodynamic data for systems Mg-O, Al-O, Si-O, Mg-Al-O, Mg-Si-O, Mg-O-C, Al-O-C, Si-O-C, Mg-Al-O-C and Mg-Si-O-C are presented in the form of volatility diagrams which provide an efficient way to view systems in which non-condensed phases are of paramount importance, as is the case in magnesia-graphite systems. A review of the current literature on the addition of antioxidants to magnesia-graphite brick is presented. The antioxidants considered include Al-metal, Si-metal, Mg-metal, alloys, Mo-metal, ZrB{dollar}sb2{dollar}, Zr-metal, Ti-metal and SiC. Two mechanisms are presented for the formation of a dense magnesia layer, at the hot face of a refractory lining and both arise from a fairly straightforward thermochemical argument. Thermodynamic calculations based on Al{dollar}sb{lcub}rm (l){rcub}{dollar} and Al{dollar}sb4{dollar}C{dollar}sb{lcub}rm 3(s){rcub}{dollar} stability provide a reasonable estimate of the prevailing internal oxygen partial pressure gradient. The values presented are much lower than those typically cited in literature. A new technique has been developed which adequately simulates the temperature and partial pressure gradient that linings are subjected to during service. Results for magnesia-graphite-aluminum and magnesium-graphite-silicon brick are presented and related to the wear resistance of these linings.