The effect of mineralogy, microstructure and firing temperature on the effective thermal conductivity of traditional hot processing ceramics

The present work analyses the effect of mineralogy, microstructure and firing temperature on the effective thermal conductivity of traditional hot processing ceramics. Samples prepared with two quartz-rich kaolinitic clays (BAR1 and BAR2), a fine kaolinitic clay (ARG) and a glaucophane-rich clay (SIF), were fired in the range between 950 and 1350 °C. The effective thermal conductivity is principally affected by the porosity of the body. Mullite further improves the thermal conductivity of BAR1 and BAR2 ceramics, while in ARG samples cristobalite is correlated with the increase in thermal conductivity. In SIF ceramics, the higher densification and the formation of spinel, pyroxene and hematite results in a higher conductivity compared to the other samples. The amorphous phase improves the ceramics' thermal conductivity since it seals voids between particles. In samples in which quartz exceeds 50 wt%, the ceramics' thermal conductivity decreases because of fissures and detachment zones formed after the α-β quartz phase transition. Finally, functional conclusions are drawn on traditional cooking pot and Medieval glass crucibles.