Influence of alumina content in the raw clay on the sintering behavior of Karatsu ware

In this paper, mineral and sintering properties of high alumina-containing clay (Yamase clay) derived from a weathered granite stone were investigated, and compared with those of low alumina-containing clay derived from a weathered sandstone (Hobashira clay) for the ancient Karatsu ware. Content of Al2O3 in Yamase clay was 30.8–33.1 mass %, and showed higher than that of Hobashira clay (13.1–15.8 mass %). Yamase and Hobashira clay had a mineral composition of kaolinite (64.3), α-quartz (10.6), muscovite (11.9), albite (10.3), and microcline (2.9 mass %), and kaolinite (12.9), α-quartz (52.9), muscovite (23.4), albite (6.9), and microcline (3.9 mass %), respectively, by the Rietveld analysis. Bulk densities of Yamase clay heated at 1200, 1300, and 1400°C were 1.99, 2.15, and 2.35 g/cm3, and Yamase clay had a higher refractoriness than Hobashira clay. After heating Yamase clay at 1300–1400°C, the heated body was composed of fine needle-like mullite (49.8) and glass (50.2 mass %) without the bloating of the body.