The differences between alkaline- and alkaline-earth-flux effects on high-temperature phase change of clay based ceramic

The differences of the effects of alkaline (illitic clay, K and Ca-Na feldspar) and alkaline-earth flux additions (sepiolitic-dolomite, talc, huntite, hydromagnesite, magnesitic clay and Calcite) on the high-temperature-phases (HTP) of ceramic bodies derived from ball clay of Westerwald-(Germany) or Sile (Turkey) area were investigated. This investigation was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) attached with energy dispersive spectrometry (EDS). The type and amount of HTP do not only depend on the type and amount of flux additions alone but also depend on the optimal distribution of these flux cations which are largely determined by the extent of the mixing. No Cristobalite was present and secondary mullite and quartz were the only crystalline phases present in these bodies composed of 50 wt% illite KW and Westerwald ball clay HB or this mixture mixed with 20% K or Ca-Na feldspar. These additions render ≥2 wt% K2O in bulk chemical composition of these alkaline bodies and are enough to inhibit cristobalite formation. The identified major HTP in ceramic bodies derived from 15 wt% Ca carbonate and 5 wt% sepiolitic dolomite, or magnesitic clay or talc and Sile ball clay were identified only as melilite (gehlenite) and plagioclase (anorthite) group minerals. The pyroxene group minerals (protoenstatite, clinoenstatite, and diopside) occurred only in the body derived from Sile ball clay mixture mixed with >5 wt% Mg-Ca flux at over 1000 °C.