The Effects of Calcium Fluoride Addition on Crystallization Characteristics of Hydroxyapatite-Zirconia Composite

Hydroxyapatite (HA) doped with 3% Yttria-stabilized 20vol%m-ZrO2 composite were synthesized by solid state reaction between tricalcium phosphate (TCP) and Ca(OH)2 at various temperature(1000 to 1200°C) for 3h with adding 5~20wt% calcium fluoride (CaF2), respectively. The effects of various amount of CaF2 on crystallization characteristics of HA-20vol%ZrO2 composite were investigated in details. The results show that when small amount of CaF2 was added, the reactions of HA with CaF2 occurs, which leads to the formation of fluorapatite (FA). With the increasing of the amount of CaF2, the decomposition of HA to β-TCP decreases gradually and the CaZrO3 peaks disappear, while t-ZrO2 increases because of the formation of thermally stable FHA solid solutions. When the sintered temperature is above 1100°C and the addition of CaF2 is about 10wt%, the main phases are FHA and t-ZrO2 with a negligible amount of Ca5P8, which suppress the reaction between HA and ZrO2. From SEM, it can be seen that with 10wt% of CaF2 addition, the morphology of the composite powder is a mixture of spherical ZrO2 particles embedded within agglomerated HA shaped like a small rod.