CHARACTERIZATION OF VARIOUS APATITES POWDERS PREPARED BY ULTRASONIC SPRAY-PYROLYSIS TECHNIQUE

Various apatites powders with the formula of Mio(PO4)6(OH)2 (M=Mg, Ca, Sr, Ca+Sr and Ba) were prepared by ultrasonic spray-pyrolysis technique. In the cases of M=Ca, Sr, Ca+Sr and Ba, the hydroxyapatite, strontium apatite, strontium-substituted hydroxyapatite and barium apatite were respectively formed. In the case of M=Mg, however, no crystalline compound was present in the resulting powder; Mg3(PO4)2 formed at •`700•Ž. The relative densities of the hydroxyapatite, strontium apatite and strontium-substituted hydroxyapatite compacts fired at 1200•Ž for 5h attained •`93%, 96% and 95%, respectively. INTRODUCTION An ultrasonic spray-pyrolysis technique is one of the powder preparation techniques for ceramics1; this technique has advantages to prepare the stoichiometoric and homogenerous compounds instantaneously by spraying the solutions with the desired amounts of cations into the hot zone of an electric furnace. This technique is especially effective for the preparation of hydroxyapatite-family powders containing the hydroxyl group in a crystal structure, because the powder is directly prepared in a steam atomosphere during spray-pyrolysis 2-4. The purposes of the present investigation were to prepare various apatites powders with the formula of M10(PO4)6(OH)2 (M=Mg, Ca, Sr, Ca+Sr and Ba) by this technique and to examine some properties of the resulting powders. EXPERIMENTAL PROCEDURE PREPARATION AND SPRAY-PYROLYSIS OF THE STARTING SOLUTION Sixteen kinds of the starting solutions with M/P ratio of 1.67 were prepared by mixing M(NO3)2 (M=Mg, Ca, Sr and Ba), (NH4)2HPO4 and HNO3. Table 1 shows the composition of the starting solutions and the temperatures for spray-pyrolysis. The hot zone in this spray-pyrolysis apparatus was composed of two electric furnaces; the lower furnace was used for the drying of the droplets and the upper furnace for the spraypyrolysis. Sample Nos. 1-10 correspond to M=Ca or hydroxyapatite (HAp) ; Sample Nos. 11-13 to M=Sr, strontium apatite (SrAp); Sample Nos. 14-17 to M=Ca+Sr, strontium-