Sintering and crystal growth of magnesia in the presence of lime and forsterite

SUMMARY. The densification of pure magnesia was examined along with mixtures containing 0'5 and I.O mol To of calcium oxide and forsterite. The sintering behaviour at temperatures between x4oo and 1800 ~ was studied and measurements made of changes in shrinkage, porosity, bulk density, and grain size for sintering times of up to 8 h at sintering temperature. It was found that both the o'5 and I.O mol % additions enhanced the sintering of pure magnesia in the temperature ange I5oo-17oo ~ Increased grain growth was found for mixtures containing forsterite but little change occurred for mixtures containing lime. Examination of the grain growth data showed that the mixtures obeyed a relationship: Time at temperature • Constant ~ (grain size) n, where n = 2 for the grain growth of pure magnesia nd mixtures containing lime, but n = 3 for mixtures of magnesia with additions of a silicate such as forsterite. A value of 78 kcal/mole was obtained for the grain growth of pure magnesia, which agrees with other researches. The extent of the solubility of lime in periclase for each lime-magnesia mixture at each temperature was also examined using electron probe analysis and related to the sintering behaviour observed for these mixtures. INTEREST in magnesia stems from the wide use of this oxide as a refractory in th