On the swelling of silver powder during sintering

Abstract

International audienceSilver 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

Mechanical behaviour of thermoelectric materials – a perspective

“…Another phenomenon linked to high-temperature deformation without externally applied stresses is swelling or bloating [59–61], when gas bubbles, entrapped during powder densification via sintering in a non-evacuated environment, expand by creep deformation of the surrounding matrix. This phenomenon has been observed for various metallic alloys [62,63] and ceramics [64,65], and it causes dimensional instability which, for a TE module, may lead to failure. However, if failure is avoided, the dimensionless figure of merit zT may not be affected significantly, as increasing micron-size porosity changes electrical and thermal conductivity in concert [60].…”

Preparation of feedstock containing water-soluble binder for powder injection moulding of silver

“…Small number of shrinkage of silver specimens observed in this work might occur due to the swelling of silver. The swelling of silver has previously been investigated [2]. It was proposed that the air-trap in closed pores that formed during fabrication process as well as the release of oxygen from particle surface, resulted in swelling of silver components.…”

“…Silver is generally known as a precious metal which can be used in various applications such as jewelry, electronic parts, water purification and dental amalgams. Silver (Ag) is a soft and ductile materials which can be produced conventionally by powder metallurgy or investment casting (lost-wax technique) [1,2]. However, investment casting consists of many processing steps and this method produces several waste materials such as ceramic moulds during the production.…”

A review of processing of Cu/C base plate composites for interfacial control and improved properties

“…Therefore, an external pressure is very often applied on the powder mixture during the sintering step to favor the densification of MMC. Uniaxial hot pressing (HP), hot isostatic pressure, spark plasma sintering (SPS), etc, are different techniques that refer to HP processes that are mainly used to prepare MMC and especially Cu/C composite materials [29].…”