In situ formation of zirconia–alumina–spinel–mullite ceramic composites

A study was made to prepare and characterize multicomposite containing zirconia–mullite–spinel [ZrO2–Al6Si2O13–xMgAl2O4 (0.25 ≤ x ≤ 4)]. This multicomposite was prepared by reaction sintering of relatively pure commercial grades of zircon, alumina and magnesium carbonate. Spinel and mullite could be in situ formed, while ZrO2 evolved mainly in monoclinic polymorph. The sintering properties in terms of bulk density (BD) and apparent porosity (AP) were measured. The formed phases were identified by X-ray diffraction pattern (XRD). Cold crushing strength (CCS) of the fired and thermally shocked bodies was evaluated. The fractured surfaces of the fired compacts were scanned by SEM. The results showed great dependence on the firing temperature as well as zircon content, type and amount of glassy phase. XRD exhibited that all samples contain m-ZrO2 and Al2O3 and with decreasing the amount of MgO and increasing zircon, the spinel phase decreases while mullite begins to form at high zircon contents. Batches containing mullite, ZrO2 and Al2O3 gave higher mechanical properties. Also, all samples retained more than 90% of their original strength after being subjected to 20 cycles of thermal shock (Δt = 1000 °C).