Compression during sintering
Parameters for the optimal sintering process
In general, the degree of compaction can be increased in any process by using finer powders and increasing the temperature. However, this can become critical if the amount of liquid is reduced. Exactly which process is to be used is determined by the properties expected of the product and by the parameters that limit the processes.
Viscose flow sintering is recommended due to its convenience and the easy availability of raw materials. If the expectations are very specific, e.g. if the product is to carry high loads at high temperatures, the avoidance of a liquid phase becomes particularly critical. In this example, solid phase sintering is recommended. Liquid phase sintering can be regarded as a compromise solution given that the requirements for powder quality and high temperatures are less stringent than those for solid phase sintering. Careful control of the distribution, quantity and potentially the uniformity of the liquid phase during crystallisation when cooling offers further possibilities for structural improvements.
Usually, the driving force for fusion is considered in terms of surface energy reduction. An additional driving force can be exerted by applying pressure to the powder during heat treatment. This technique of hot pressing can be very helpful for materials that are otherwise difficult to sinter.
 M.N. Rahaman, "Ceramic Processing and Sintering" 2nd edition, CRC Press, 2003, New York
 R.J. Brook (edt.) "Concise Encyclopedia of Advanced Ceramic Materials", Pergamon, 1991, Oxford