Novel mullite-based ceramics manufactured from inorganic wastes: II: Mechanical behaviour

Mullite-based refractory bodies were manufactured using powder technology by mixing slate sludges resulting from the cutting and polishing operations with alumina obtained by treating spent baths generated in industrial plants dealing with manufacturing and finishing of aluminium-made architectural profiles.The elastic moduli and mechanical strength of the sintered bars were measured as a function of the sintering temperature by the impulse excitation method and three-point bending, respectively. The mean values of elastic moduli and flexural strength were found to be dependent on both the density and the resulting microstructures. Both the elastic moduli and the strength were found to increase with decreasing of porosity in accordance to the available theoretical models. Mechanical strength values over 110 MPa in three-point bending were achieved under optimised conditions (about twice as high as that obtained for slate tiles produced in an industrial plant). Also noted was that the Poisson's ratio (ν = 0.20 ± 0.01) was independent upon the density of the mullite-based ceramic bodies which is consistent with the theoretical predictions.