Anorthite ceramics: grog and clay selection for lowering the sintering temperature

A research investigation was conducted on two variables that are indicative of plastic raw materials based on kaolin vs. interstratified illite-smectite clay and a non-plastic admixture including grog (quartz vs. alumina) during the sintering process of an anorthite porcelain body beginning at 950°C, up to the sintering temperature. A correlation was found between the mineralogical composition and various parameters of the fired bodies. A purely anorthic sintered body can be produced using interstratified illite-smectite clay with quartz as a grog, which has the lowest coefficient of linear thermal expansion in the temperature range of 30°C to 700°C and highest bending strength – modulus of rupture of sintered body. When alumina is present in the raw material mixture, the coefficient of linear thermal expansion is lower due to the absence of the SiO2 phases. Quartz in combination with interstratified illite-smectite clay significantly reduces the sintering temperature through the formation of an amorphous melt up to the sintering temperature.