The Influence of Texture and Firing on Thermal and Elastic Properties of Illite-Based Ceramics

Abstract

The texture in illite-based ceramics was introduced by spreading a large number of thin layers of a wet plastic mass one on top of the other. The basal planes of the plate-like illite crystals are predominantly oriented parallely with the direction of spreading. The samples were fired at different temperatures ranging from room temperature up to 1100 °C with a heating rate of 5 °C/min, then freely cooled and measured at room temperature. We determined Young modulus (E), thermal diffusivity (a) and relative dimension changes (Δl/l0) in two directions: parallely to the basal planes (a subscript ||) of the illite crystals and perpendicularly to these planes (a subscript ⊥). It was found that the ratio E|| / E⊥ ≈ 2.9 and a|| / a⊥ ≈ 2.0 up to 900 °C. Above 900 °C, the values of E and a increase due to sintering, and the differences between the values measured in the two directions decrease. In the case of the thermal diffusivity these differences do not disappear even after firing at the temperature of 1200 °C.