"Glass-ceramic stoneware" as a promising application for waste glasses

One typical application of glasses from the melting of several inorganic waste is the manufacturing of glass-ceramics. These products generally exhibit interesting physical and mechanical properties, but their processing is quite complex and expensive. In this paper it is reported an alternative approach, consisting in replacing the feldspar flux, in the formulation of porcelain stoneware, with two waste glasses of the CaO-Al2O3-SiO2 system, in the form of fine powders. For an optimized glass/clay ratio, the obtained ‘glass-ceramic stoneware’ samples, sintered at temperatures ≤1000°C, exhibited a complex of mechanical properties (bending strength approaching 90 MPa, fracture toughness exceeding 2 MPa m0.5) similar to that of conventional porcelain stoneware, sintered at much higher temperatures. This was mainly attributable to the formation of several crystal phases upon sintering, due to both surface nucleation (yielding wollastonite or gehlenite) and chemical iinteractions between the glass and clay (yielding Ca-rich feldspars).