Sintering at External Pressures

When compared to sintering, hot pressing produces an increase in the driving force for densification. For an equivalent microstructure, the dependence of the densification rate on the driving force can be written as follows  

When 2, there is [p/G) (p/G). Therefore, by using hot pressing, it is possible to produce ceramics with high density coupled with small grain size, due to the ability to increase the value of p/G. This is the simple reason why HP, HIP, and SPS could be used to produce ceramics with high densification and small grain sizes. 

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