Vitrification of illitic clay from Malaysia

Abstract Illite has been widely used as a fluxing material for many years, particularly in the ceramic industries of countries located in and around the north Pacific Rim. It is believed that the finer particle size, the location in the matrix and the high K content with lower melting point of illite enable to serve as a superb melting agent to the body. The vitrification of natural illitic clay via phase and microstructural changes was studied. Clay powder was heated from 800–1250 °C. Illite transformed into sericite below 800 °C and to mullite around 1100 °C while spinel formation either from kaolinite or illite transformation was suppressed. However, most mullite crystals in the body occurred in the kaolinite particle matrix while mullite crystals grown in the illite relicts occurred only in a small amount but with faster growth rate and to larger size (1–2 μm). Diffusion of K in the illite structure resulted in unknown rectangular crystals located close to the illite relicts. EDS results also showed that the kaolinitic-mullite crystals had higher Al to Si ratio than other areas. Firing shrinkage showed that densification of this body should start around 900 °C and was highly achieved at 1200 °C.