Thermomechanical behaviour of alumina-mullite refractories developed by recycling industrial ceramic wastes

Alumina-mullite (AM) refractories are widely used as liners for the thermal insulation of the combustion chambers in gas turbines for power production. A complete thermomechanical characterization of a commercial AM refractory was performed according to the international standards for dense ceramic or ceramic composites. Four-point flexural test were carried out on standard specimens to determine the values of Modulus of Rupture (MOR) and Young’s modulus (E), at room temperature and up to 1500 °C: this temperature was chosen because the inlet temperature of the turbines for energy production was around 1400 °C. The most important property required to refractories for this application is the thermal shock resistance. In order to quantify it, four-point flexural tests at room temperature after quenching were carried out to calculate the residual MOR, according to the standard procedure for dense ceramics. The tests were performed with temperature differences up to 1000 °C, which is comparable to operating conditions during the turbine shutdown. New AM refractories were developed, by recycling a large amount (20 wt%) of industrial ceramic wastes coming from gas turbine investment casting process, and also adding zircon (ZrSiO4). Also for these materials, a thermomechanical characterization was performed, in order to compare the behaviour of the new materials to the commercial refractory’s one. Interesting results were found about the mechanical properties of the new materials. The refractories developed by recycling industrial ceramic wastes generally show better mechanical and thermal shock resistance than the commercial refractory taken into account.