Investigation of clay content and sintering temperature on attrition resistance of highly porous diatomite based material

Abstract

Diatomite based granulates with a diameter of 500 μm were produced by extrusion with the addition of 16, 28 and 48 vol.% kaolin and organic binder in order to optimise the flow behaviour. The influences of clay content and sintering temperature on the microstructure and attrition resistance were investigated. Bimodal pore size distribution was obtained by mercury intrusion porosimetry at 800 °C. Pore sizes smaller than 250 nm were assumed to originate from the diatomite porous structure and the larger ones mainly from the interparticle porosity. Meso and macropores of diatoms tend to close at 1100 °C and due to coalescence at higher temperature a unimodal macro pore size distribution occurs. An increase of the pore size in temperature range between 1100 and 1300 °C was associated with a different sintering behaviour between diatomite and clay. Additionally α-cristobalite crystallization was observed at sintering temperatures between 1100 and 1300 °C. Attrition resistance was determined by a grinding test and a new analysis method to evaluate different attrition behaviour materials. The new analysis method uses the absolute value of the exponent obtained from attrition resistance behaviour versus the number of revolutions. High clay content in diatomite based materials and high sintering temperature lead to an increase of attrition resistance of the material due to phase transformations of the materials into mullite and cristobalite.