Fabrication and characterization of multi phase ceramic composites based on zircon–alumina–magnesia mixtures

Five composites were prepared from zircon, alumina and magnesia. The variation of densification parameters, phase composition, thermo-mechanical properties, and microstructure with the firing temperatures were investigated. The rate of zircon dissociation was very low in the free magnesia composite, while it increased abruptly when 2.5 mass% MgO was added, then changed gradually in the followed batches. At low silica content, the formation of magnesium silicate and magnesia alumina spinel was more preferred than the mullite. Firing at 1300 °C did not show remarkable variations in the sintering of the investigated composites, while great discrepancies were observed at higher temperature. Firing at 1500 °C resulted in dense bodies (1–5.5% apparent porosity) for all composites excepting the magnesia free one (26% apparent porosity). The optimum properties were attained by the composite prepared from 62.5% zircon, 35% alumina and 2.5% magnesia, when fired at 1500 °C, 2 h.

► Five composites were prepared from zircon, alumina and magnesia.
► The rate of zircon dissociation increased abruptly with the addition of 2.5% MgO.
► At low silica content forsterite and spinel were formed rather than mullite.
► Alumina content contradicted the effect of porosity on thermo-mechanical properties.
► 62.5% zircon, 35% alumina and 2.5% magnesia showed the optimum properties.