MINERALOGICAL AND CERAMIC PROPERTIES OF REFRACTORY CLAYS FROM CENTRAL MISSOURI (USA)

Quantitative XRD analysis of a series of 64 refractory clays from central Missouri was carried out to establish correlations between their mineralogy and ceramic behavior. The quantitative analyses were corroborated by means of chemical analyses of the bulk samples. These fireclays are composed of kaolinite and minor and variable amounts of illite, chlorite, and an illite/smectite mixed-layer phase. In addition, quartz and diaspore are present only in the so-called plastic clays and high-alumina clays, respectively. The pyrometric cone equivalent (PCE) values are controlled primarily by the contents of diaspore and kaolinite, the latter controlling the linear fired shrinkage. These two minerals exert also some influence over the specific gravity of fired bodies, but this property is affected mainly by the illite and I/S (illite/smectite) content. The plasticity of the raw materials is controlled by both illite content and the kaolinite crystallinity, being higher in poorly crystalline kaolinite-bearing clays.