The main reactions taking place in the gel sintering process were studied by XRD,IR,SEM and 29 Si, 31 PNMR.It is revealed that the main chemical reactions at different stages are as follows:(1)in the range of 673~773K,OHAp is synthesized by the reaction between Ca 2P 2O 7 and Ca(NO 3) 2·4H 2O;(2)in the range of 773~873K,the reaction between Ca 2P 2O 7 and CaO takes place to form β C 3P;(3)in the range of 873~973K, β C 2S is synthesized by the reaction between CaO and SiO 2;thus the main crystalline phases of the powder materials are:OHAp, β C 3P and β C 2S,in which Si and P form solid solution with each other.
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