Influence of firing temperature and mineralogical composition on bending strength and porosity of ceramic tile bodies

This study is focussed on the behaviour of ceramic clays from the area around Castellon (Spain) having a large ceramic industry. Test samples have been prepared by extrusion and firing in the range of 800–1150 °C. Analysis of the fired samples was carried out by X-ray diffraction. The results from the study of mineralogical transformations show the persistence of illite up to at least 900 °C. From the destruction of illite, an intermediate phase between spinel and hercynite originates. Mixtures of illitic clays containing CaCO3 form gehlenite, wollastonite and anorthitic plagioclases from 950 °C onwards. Quartz and hematites are present in samples poor in CaCO3. The optimum firing temperature for each sample has been established. The maximum bending strength of each ceramic body has been determined. Porosity-strength relations have been established.