Liquid Phase Sintering of Ceramics

Abstract

Liquid phase sintering is widely used for consolidation of ceramics as well as metallic powders into final shapes. Main advantages of this production method are low sintering temperatures, fast densification, high final densities and resulting microstructures often providing mechanical or physical material properties superior to solid state sintered materials. Densification during liquid phase sintering is based on rearrangement and shape change of solid constituents. Rearrangement of larger particles (<10 μm) is caused by short range movements due to capillary forces between a few adjacent particles. ¹ In systems containing particles and pores of a smaller scale or larger content of melt, pores may be eliminated by cooperative movements of particles and liquid, comparable to viscous flow of a dispersion.² Shape change of particles is due to matter transport from solid areas near solid/liquid interfaces to similar areas of lower chemical potential by diffusion either in the solid or in the melt. The latter is connected to the dissolution and reprecipitation of solid material in and from the liquid. This paper is intended to discuss some features of liquid phase sintering which may be of relevance to the processing of ceramics. Ceramic powders are usually characterized by small average grain sizes (often <1 μm) and broad ranges of reduced particle sizes. To circumvent the poor flow properties of fine powders preagglomeration is usual causing frequently inhomogeneous pore distributions after compaction. Areas of small approximately equal sized pores alternate with areas of lower density including pores much larger than the average particle and pore size.