Preperation of hydroxyapatie-alumina coated zirconia composites

Abstract

Hydroxyapatite (HAp) bioceramics as bone substitute materials have unique biocompatibility feature among phosphate groups. How ever, the low fracture strength and poor fatigue resistance due to the instability of OH- groups limit the use of HAp for load-bearing applications. In present research, we investigated the effects of TZP powder coated with Al2O3 on the phase stability of HAp .The coated TZP powder was expected to be effective as a reinforcing agent for the HAp. In order to prepare the composite, calcined ZrO2 powder was dispersed in aqueous aluminium chloride solution (0.75mol/liter). The suspension was added drop by drop into ammonia solution which is kept at a pH around 6-7. This pH is carefully selected by considering zeta potential of boehmite and Zirconia for promoting heterofloculation. The resultant precipitate was calcined at 8500 C/4hour. The calcined powder was added to required amount of diammonium hydrogen orthophosphate and calcium nitrate (Ca/P ratio 1.67). This combined suspension was added drop by drop into ammonia solution kept at a pH around 10. The precipitates were dried, calcined at 850 0C, followed by compaction of the calcined powder and sintering at 1250 0C. The results show that the degree of decomposition of HAp is least in case of HAp-TZP composite where as the reaction tendency of HAp with Al2O3 is prominent. This adverse reaction increases with the increase in alumina content in the system. Thus the obtained result contradicts the previously found observations, i.e. the tendency of reaction of HAp with ZrO2 is more feasible than that with Al2O3. For further comparison we studied different HAp- Al2O3 coated ZrO2. It was inferred that the reaction tendency of HAp- Al2O3 coated ZrO2 composites with HAp is less with respect to HAp- Al2O3. The reaction tendency is found to increase in accordance with increase in Al2O3 content in the composites.