Calcination and sintering of fluorapatite under argon atmosphere

The calcining and sintering behaviour of fluorapatite synthesised by precip itation has been studied. During the calcination process, in the temperatur e range 400-900 degreesC, the specific surface area decreases with a rise i n temperature. Below 715 degreesC, the decrease is associated with grain gr owth according to a superficial diffusion mechanism. Above this temperature , several mechanisms may take part in the coarsening. Sintering of fluorapa tite 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 grow th. At moderate temperatures coarsening leads to dense bodies. A relative d ensity of about 97% is obtained at 1020 degreesC. Above 1100 degreesC densi fication is hindered by coarsening which becomes important and much quicker when the liquid phase is formed at 1180 degreesC. (C) 2001 Elsevier Scienc e B.V. All rights reserved.