Preparation and properties of lightweight corundum-spinel refractory with density gradient

Lightweight refractories are expected to achieve excellent thermal insulation property and high-temperature performance while reducing energy consumption. In this study, a novel method for preparation of lightweight corundum-spinel (Al2O3-MgAl2O4) refractory was proposed. Through the carbothermal reduction of MgO, the oxygen diffusion rate controlled oxidation of Mg vapor and subsequent reaction between MgO and Al2O3, lightweight Al2O3-MgAl2O4 refractory was obtained with a density gradient structure. The reaction mechanism was elucidated by combining the thermodynamic and kinetic analysis with the experimental results. The effects of preparation parameters on the phase composition, microstructure and properties of the resulting lightweight refractory were also investigated by means of X-ray diffraction, scanning electron microscopy and a series of performance testing techniques. The results indicated that the density of the obtained Al2O3-MgAl2O4 was distributed in a gradient along the radial direction with lower value in the center, and higher near the surface. Meanwhile, the composition of matrix and the firing temperature profoundly affected the structure and properties of the refractory. In order to achieve high compressive strength and refractoriness under load of the lightweight Al2O3-MgAl2O4 material, it is feasible to decrease the mass ratio of (MgO + C) to Al2O3 in the matrix, and raise the firing temperature appropriately.