Calcination and sintering of fluorapatite under argon atmosphere

The calcining and sintering behaviour of fluorapatite synthesised by precipitation has been studied. During the calcination process, in the temperature range 400-900 degreesC, the specific surface area decreases with a rise in temperature. Below 715 degreesC, the decrease is associated with grain growth according to a superficial diffusion mechanism. Above this temperature, several mechanisms may take part in the coarsening. Sintering of fluorapatite is performed between 690 and 1320 degreesC, under an argon atmosphere when the gas atmosphere is not fittingly dried; hydroxyfluorapatite can be formed during sintering. Densification appears to be governed by grain growth. At moderate temperatures coarsening leads to dense bodies. A relative density of about 97% is obtained at 1020 degreesC. Above 1100 degreesC densification is hindered by coarsening which becomes important and much quicker when the liquid phase is formed at 1180 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.