16 - Sintering

Abstract

This chapter provides a description of sintering of ceramics by solid state sintering, reactive sintering, and pressure sintering. In addition, grain growth and cooling have been discussed. In solid state sintering, there are three stages: initial, intermediate, and final. During the initial stage, necks are formed between the particles in the ceramic green body. During the intermediate stage, the cylindrical pores are located at the three-grain junctions between grains. These pores shrink until they become unstable and form spherical pores at the same three-grain junction. The spherical pores move to the grain intersections during the final stage of sintering, where they can be eliminated. If the grains grow relatively fast, then the pores may become separated from the grain boundary and left within a grain, where they are difficult to remove by further sintering. Grain growth plays an important role in manipulating the grain size in the final microstructure. Reactive sintering includes liquid phase sintering, solid state reaction sintering, and gas-solid reactive sintering. Liquid phase sintering and pressure sintering are used to prevent abnormal grain growth from occurring, so that high densities can be obtained maintaining fine-grained microstructure.