Influence of iron on the synthesis and stability of yttrium silicate apatite

The stability of yttrium silicate apatite has been investigated by studying the influence of iron as a "stabilising cation" and also by using differen t synthesis routes. The formation of apatite in samples has been followed b y X-ray diffraction and by Si-29 MAS NMR spectroscopy. The apatite phase ap pears to be stable at high temperatures (approximate to 1700 degreesC) espe cially when heated in a nitrogen atmosphere; it can also occur in a metasta ble state when heated in air at lower temperatures; approximate to 1600 deg reesC if prepared from a Y2O3-SiO2 mixture or in the range 950 degreesC < T less than or equal to 1150 degreesC if synthesised by the sol-gel process. Longer heat-treatments result in its decomposition into Y2Si2O7 and Y2SiO5 , Iron appears to have two roles depending on the temperature; it stabilise s the apatite phase at high temperatures when produced by the sol-gel route and catalyses the decomposition of sol-gel derived apatite at low temperat ures. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.