A comparative study on the microstructures and mechanical properties of a dense and a lightweight magnesia refractories

Abstract

A new lightweight magnesia refractory for working linings of high-temperature furnaces was prepared by using microporous magnesia aggregates instead of conventional dense magnesia aggregates. The median pore size of the microporous magnesia aggregates was 2.97 μm, while the apparent porosities of the microporous and dense aggregates were 33.3% and 5.5%, respectively. The phase composition, microstructures, fracture behaviors and strengths at room and high temperature of the lightweight magnesia refractory in comparison with those of the dense one were measured by means of XRD, SEM and three-point bending instrument. After the dense aggregates were replaced by the microporous ones, a better aggregate/matrix interface bonding was observed and the fracture mode changed from intergranular to transgranular fracture, which significantly improved the mechanical properties. Thus, the lightweight magnesia refractories had a lower bulk density of 11.8%, a higher apparent porosity of 56.2% as well as a higher flexural strength at room and high temperature of 48.4% and 160.0% comparing with the dense one, respectively.