Effect of quartz amount and size on dimension changes of illite-based ceramics during firing

Quartz is a very common constituent of the materials of traditional ceramics – natural clays. These clays frequently contain illite as the main mineralogical phase. The effect of quartz amount and particle size in the illite-quartz system without impurities has not yet been studied systematically. This study aims to fill this gap using samples made of purified illite and quartz sand in amounts ranging from 5 wt.% to 40 wt.% and in three size fractions: (0 – 50) µm, (50 – 100) µm, and (100 – 200) µm. The influence of quartz amount on firing shrinkage was small until at least 20 wt.% of quartz was used. Above this amount, the total firing shrinkage decreased due to the retardant effect of quartz on the viscous flow sintering. This was found to be less pronounced if the finest fraction (0 – 50) μm of quartz was used. With the addition of at least 30 wt.% of quartz, dimension changes around 570 °C during heating were affected. The influence of quartz β – α transition during cooling on the rate and extent of shrinkage was linear in terms of quartz amount. The extent and rate of shrinkage due to β – α quartz transition on cooling were not influenced by particle size.