Sinterability of macrocrystalline and cryptocrystalline magnesite to refractory magnesia

Abstract

The purpose of this paper is to present the results of an investigation aiming at obtaining high quality sintered magnesia from two well-known Chinese magnesite. Two types of natural magnesite have been considered, one macrocrystalline, from Liaoning, with the grain size of 60-100 µm and one cryptocrystalline, from Tibet, with 2-4 µm grains. Calcining characteristics to transform the two magnesite to caustic magnesia have been studied at first. Subsequently, the calcining-sintering characteristics using a two- and a three-step process for both raw materials at different temperatures have been determined. A DTA–TGA study reveals that the minimum endothermic peak during the calcining step differs by 28°C (624 vs 652°C between the crypto- and macrocrystalline magnesite). It has also been observed that by using a two-step sintering process, it is possible to obtain a magnesia with a bulk density of 3.26 and 3.14 g/cm3, respectively, for cryptocrystalline and macrocrystalline, while with a three-step process, it is possible to reach a bulk density of 3.48 g/cm3, even at a temperature <1750°C.