Sintering behaviour of submicron silica particles

Abstract

The sintering process is the final step in the preparation of transparent silica glass via a powder ceramic route starting from fumed silica glass powder. As high green densities can be obtained with this method the shrinkage during drying and sintering is small and compacts like rods and tubes can be easily prepared. The study of the sintering behaviour of these compacts made from submicron particles was based on two aspects, namely that of the parameters influencing the sintering rate of the sample (macroscopic behaviour) and that of the interaction between single particles (microscopic behaviour). The sintering rate depends on the furnace temperature and the thermal conductivity of the sample. As the thermal conductivity in the sintered silica glass is about two orders of magnitude higher than in the porous compact, a dominant axial heat flux during zone sintering should be expected. This could be experimentally confirmed by measuring the sintering behaviour of rods and tubes and making the isotherms of the samples in the sintering zone visible. The viscous flow of single particles was measured by the decrease of the surface area of the compact during sintering. As the correspondence with calculations based on known models was not sufficient and no interpretation of the deviations was possible, new calculations were performed based on an improved Frenkel model. Due to the close approximation of this model to the spherical particles, the differences of model calculations and measurements with increasing sintering time could be interpreted by agglomerates in the compacts.