On the swelling of silver powder during sintering

Silver powder compacts may suffer an overall expansion during sintering. A simultaneous analysis of dimensional changes, mass loss and pore closing in the course of sintering showed that volume change results from the competition between classical sintering phenomena inducing densification and material creeping under stresses caused by internal gas pressure, which induces swelling. The internal gas includes air trapped during pressing and oxygen released from particle surface inside the pores that closed during pressing or sintering. This swelling phenomenon is particularly strong with powders with large specific surface area and compacts with high green density. It is less effective during fast sintering, as observed during direct induction heating experiments. Electrical conductivity is strongly affected by swelling. Powder compacts may exhibit a lower conductivity after sintering when interparticle bonding does not balance the density decrease occurring during sintering.