Conventional ceramic sintering

Figure 6-11. Typical X-ray pattern of nanocrystalline Pb(Zrg.sTio,s)03 ceramics obtained by conventional ceramic sintering at Ts = 927° C (Reproduced, with permission from Surowiak et ak (2001) J. Eur. Ceram. Soc., 21 1377-1381 Copyright 2001 Elsevier Science Ltd.).

Conventional Sintering. Ceramic sintering is usually accompHshed by heating a powder compact to ca two-thirds of its melting temperature at ambient pressure and hoi ding for a given time. Densification can occur by soHd-state, Hquid-phase, or viscous sintering mechanisms. 

Conventional ceramics initially take shape on a potter s wheel or by slip casting and are fired (sintered) in kilns advanced ceramics are formed and sintered in more complex processes such as hot isostatic pressing. 

Sol-gel techiuques are of interest because they can be used to prepare powders with a narrow distribution of particle size. These small particles undergo sintering to high density at temperatures lower by several hundred degrees centigrade than those used in conventional ceramic processing. Sol-gel processes may also be used to prepare novel glasses and ceramics such as... 

Almost all ceramic/ceramic bulk FGMs are sintered by conventional pressureless sintering (Wu etal, 1996 Marple and Boulanger, 1994 Cichocki andTrumble, 1998) or hot pressing (Kawai and Wakamatsu, 1995 Vanmeensel... 

A conventional ceramic method, known as solid-state reaction, consists of a diffusional process for obtaining the ceramic phase from the mechanical mixture of oxides, in pre-set stoichiometric amounts. This process is followed by suitable thermal treatment, generally at high temperature (800-1300 °C). After the thermal treatment, calcining and sintering methods lead to a crystalline and homogeneous product. 

In the 1970 s, a full-scale effort to produce the ceramic gas turbine was initiated in the USA. It was realised early in the programme that, since hot-pressing is limited to simple shapes, the objectives would not be achieved unless sintering without pressure could be achieved where shaping of components could be carried out by more conventional ceramic fabrication processes. 

Low sintering temperature usually, the heat-treatment temperature is lower than the sintering temperature of conventional ceramics and much lower than the melting temperature of metal oxides. 

---