Sintering early stages

In the early stage of sintering, the rate at which the contact increases is described... 

During the early stages of the sintering process, and particularly at lower tem-... 

A catalyst. for the direct reaction is desirable, not only to improve the reactivity and yield, but also to smooth the reaction and make the result more reproducible than otherwise would be the case. One effective catalyst is metallic copper, which may be powdered and mixed with the silicon or (better still) sintered with the silicon by heating the mixture in hydrogen.16 The initial distribution of the catalyst has much to do with the behavior of the reaction during the early stages, as is evident upon consideration of the proposed mechanism for the reaction.17... 

Processes (c) and (d) are of less significance for ceramics where densification is usually required. Surface diffusion, however, is probably involved in the early stage of sintering when partial strengthening of the powder compacts occurs with no shrinkage involved. 

Spreading is the process in which the liquid distributes itself to cover the surfaces of the particles. It is important in the early stage of liquid phase sintering because the liquid normally forms in isolated regions of the compact. A spreading liquid has a contact angle of zero. 

Densification results from particle rearrangement under the influence of capillary forces and the filling of pores by the liquid phase. This process is very rapid, and if during the early stages of sintering, the liquid flows and completely fills the finer pores between the particles, 100 percent densification can result almost instantaneously. 

Power-law creep can also be a major densification mechanism in pressure-assisted sintering. At the early stage of densification achieved by power-law... 

Sheehan, J. E., Lend, F. V. and Ansell, G. S., Investigation of the early stages of sintering by transmission electron micrography, in Sintering and Related Phenomena, G. C. Kuczynski (ed.), Plenum Press, New York, 201 208, 1971. 

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