Effect of silica additions on strength and elastic modulus of Kenyan industrial clay ceramics

Abstract

The effect of silica additions on material properties of Kenyan industrial clay ceramics composed of 0- 50% wt silica and a feldspar-kaolin content ratio in the range 1:1 to 5:8 was investigated. Highest sintered density and material strength are obtained for samples fired at 1f50°C and containing 20% wt. silica with a feldspar-kaolin ratio of 5:8. For samples containing more than 30% wt. of silica, the densification is enhanced above 11500C due to the dissolution of silica in the feldspathic melt. The decrease in porosity is found to be the predominant factor contributing to improvement of mechanical strength. The microstructural changes (pore size and shape) ofsintered samples was examined through microscopy and the observed variations in the material properties are explained as a function of the amount and nature of the pore phases present. The porosity - strength relationship is found to best correlate with the equation of the form M = M, (l-kP 213), where M, is the strength (elastic modulus or modulus of rupture) at zero porosity, M is the strength at porosity P and k is a constant. The value ofk is dependent on the shape of the pores and any concentration of fracture flaws