THE INFLUENCES OF PLASMA SPRAYING PARAMETERS ON THE CHARACTERISTICS OF HYDROXYAPATITE COATINGS - A QUANTITATIVE STUDY

AII laboratory-made plasma-sprayed hydroxylapatite coatings (HACs) wer e found to undergo, to different degrees, changes in phase composition , crystallinity, morphology and roughness dependent on plasma spraying parameters (PSPs). The PSPs, which were systematically varied, includ ed the plasma atmosphere, the spraying current and the stand-off dista nce. Through the determinations of the concentration of impurity phase (CIP) and the index of crystallinity (IOC), the extent of phase purit y and the degree of crystallinity of HACs were quantitatively assessed , respectively. Coatings consisting of at least 50% (IOC > 50%) of the original crystalline structure and almostly 95% (CIP < 5%) apatite wi th barely detectable extra phases were obtained. The microstructure of HACs exhibited great deviations both in morphology from molten to par tial molten state and in roughness from coating of high irregularity ( R(a) = 14.48 mu m) to a smoother (R(a) = 4.46 mu m) one, dominantly in fluenced by the spraying atmosphere, As the terms of CIP and IOC are d efined and established, the biological responses related to phase puri ty and crystallinity of HACs can be further evaluated in vitro and in vivo.