Mixed solutions of Ca(NO,), and (NH,),HPO, with Ca/P = 1.50 were spray-pyrolyzed at 600°C to produce p-calcium orthophosphate (P-Ca,(PO,),) powder; the spray-pyrolyzed powder was ground and then calcined at 600°C for 1 h. The best crystalline p-Ca,(PO,), powder was obtained from the solution with 1.80 mo1.L-l Ca(NO,),, 1.20 mo1-L-I (NH,),HPO,. The resulting powder was composed of primary particles with sizes of <0.5 pm. Dense P-Ca,(PO,), ceramics with a relative density of 96.1% could be fabricated by firing this compressed powder at 1070°C for 5 h.

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Sinterability of β-Calcium Orthophosphate Powder Prepared by Spray-Pyrolysis.-Crystalline β-Ca3(PO4)2 powders are prepared by spray pyrolysis of mixed solutions of Ca(NO3)2 and (NH4)2HPO4 at 600 • C followed by grinding and calcination at 600 • C for 1 h. The . beta.-Ca3(PO4)2 powder obtained from 1.80 mol/l Ca(NO3)2 and 1.20 mol/ l (NH4)2HPO4 exhibits excellent sinterability and a relative density of 96.1% can be achieved by firing the compressed powder at 1070 . degree.C for 5 h. -(ITATANI, K.; NISHIOKA, T.; SEIKE, S.; HOWELL, F. S.; KISHIOKA, A.; KINOSHITA, M.; J. Am. Ceram. Soc. 77 (1994) 3, 801-805; Dep. Chem., Fac. Sci. Eng., Sophia Univ., Chiyoda, Tokyo 102, Japan; EN)

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