EFFECT OF ATMOSPHERE ON PHASE-TRANSFORMATION IN PLASMA-SPRAYED HYDROXYAPATITE COATINGS DURING HEAT-TREATMENT

The purpose of this study was to evaluate the effect of atmosphere on the phase transformation in hydroxyapatite (HA) coatings during heat t reatment by varying the atmosphere in the furnace pipe. Heat treatment always increased the crystallinity of HA coatings regardless of the k ind of atmosphere. Water molecules in atmosphere further promoted HA r ecrystallization during heat treatment. In a dry atmosphere, tricalciu m phosphate (TCP) and tetracalcium phosphate (TTCP) were more stable t han HA, so heat treatment could not convert them into HA. However, in a humid atmosphere, heat treatment would transform TCP and TTCP into H A by hydrolytic reactions. (C) 1997 John Wiley & Sons, Inc.