Sintering Process of Slip Cast Specimens Made from Various Metal Powders

Abstract

The sintering process of slip cast specimens made from various copper and silver powders was clarified by means of electrical resistivity and dilatometry measurements. It was revealed by the electrical resistivity changes of slip cast specimens as a function of temperature that the decrease in electrical resistivity at the early stages of sintering corresponds to the desorption of water vapor and adsorbed gases, decomposition of deflocculant and bonding of powders. The effect of the addition of deflocculant on the electrical resistivity changes was dependent upon the kind and shape of powders ; the smaller the particle size, the smaller the electrical resistivity values of both as-slip-cast and sintered. The specimens made from powders of complex shapes showed lower electrical resistivity than those from spherical particles. By means of dimensional changes as a function of temperature, the elimination of pores was mainly clarified, along with the other early stages of sintering. The dilatometric behavior of spherical copper powder specimens showed anormal expansion before shrinkage. The smaller the particle size, the faster the shrinkage. In sintering in hydrogen atmosphere the decrease of electrical resistivity and the shrinkage of copper powder specimens occured at lower temperature than in vacuo. The activation energy of densification of superfine silver powder specimens was determined to be 20, 000 cal/mol, which agreed with the activation energy of grain boundary diffusion.