Effects of forming process and firing temperature on thermal expansion coefficient of ceramic bodies

Abstract

The objective of this research is to study the effects of forming process on the physical properties of ceramic body after firing. The body is used in this research are porcelain, vitreous china, stoneware, earthenware, and terracotta. The specimens were formed by pressing, extruding, and slip casting and fired at 950- 1250 degree Celsius depending on types of body. The following properties: firing shrinkage, bulk density, water absorption, modulus of rupture (MOR), phase composition, microstructure and thermal expansion coefficient of the fired bodies were investigated. Based on the experimental results, it was found that the physical properties of fired specimens in each ceramic body were depended on forming process and its parameters. The crystal phases of fired specimens from different forming processes determined by XRD were the same but morphologies of crystals and pores were significantly different. Thermal expansion coefficient can be estimated from bulk density of fired specimens. At the same firing temperature, the specimen with high bulk density has higher thermal expansion coefficient than lower bulk density specimen. Forming process has strong effect on densification of the specimen and related to the difference of thermal expansion as well. The specimens formed by extrusion obtained almost equivalent bulk density and physical properties as 150 bar pressed specimens. Empirical models were developed based on measured data which related bulk density and thermal expansion. The experimental data were compared to the predicted data of the models.