8 - Preparation of monolithic nanocrystalline ceramics

Abstract

Publisher Summary This chapter presents that nanocrystalline ceramics, due to their wide range of specific properties and potential applications, continue to be an exciting subject for research. Within a range of synthesis methods, the processing and sintering of ultrafine powders occupies a prominent position in spite of the inherent difficulty that densification and grain growth are based on the same class of thermally activated processes. It was demonstrated by many examples that grain sizes below 100 nm can be achieved by powder technological methods if attention is paid to the fact that non-agglomerated starting powders and very homogeneous green microstructures are required for sintering. A great deal of motivation for devising novel sintering methods stems from the requirement of making larger parts with a larger freedom of shape and better economy. This favors free sintering techniques over pressure-assisted methods, such as sinter forging and pulsed electric current sintering, and recent work suggests that there may actually be good prospect for advances in this direction. It was suggested that a deepened understanding of grain boundary segregation phenomena during the densification of nanocrystalline powders may be the key to categorizing the results obtained by advanced sintering techniques and, eventually, devising novel methods for decoupled densification and grain growth kinetics.