Due to the application of refractories, these materials are frequently submitted to high temperatures and loads. The performance under such hard conditions is closely related to the microstructural changes during use. This work is focused on microstructural evolution of high-alumina refractories containing mullite-zirconia aggregate in various concentrations. The materials were submitted to heat treatments at 1400 ºC and 1500 ºC, for periods of 2, 6 and 18 days to bring the characteristics of refractories in use. Some formulations incorporated microssilica, in order to induce mullitization, though reaction with alumina. These compositions were heat treated at 1500 ºC for 6 days. Scanning electronic microscopy and X-ray diffraction were applied to phase characterization. For the quantitative phase analyses Rietveld technique was used. Reaction in the interface between alumina and aggregate as well as between alumina and microsilica took place as a result of heat treatments, causing mullitization. This effect was mainly noted for results of modulus of rupture for compositions containing microsilica.
Refractories; microstructure; heat treatment; aggregate; rietveld
