FEATURES OF CALCIUM-PHOSPHATE PLASMA-SPRAYED COATINGS - AN IN-VITRO STUDY

Factors involved with the plasma-spray coating procedure, such as star ting powder compound (fluorapatite, hydroxylapatite, magnesium-whitloc kite, or tetra-calcium phosphate), powder particle distribution 145 or 1-125 mu m), powder port gun (port 2 or 6), and post-heat treatment o f 1 h at 600 degrees C, were examined for their effects on crystallini ty and solubility/stability of the coating. From solubility tests, X-r ay diffractometry, and scanning microscopy studies, the solubility and crystallinity were found to be dependent on Ca/P ratio, particle dist ribution, and post-heat treatment. The post-heat treatment influenced the degree of both crystallinity and solubility. The plasma-spray powd er port factor for the hydroxylapatite coatings was not significant. I ncubation in buffer of the coatings introduced precipitation at the su rfaces of all non-heat-treated coatings except fluorapatite. No precip itation could be observed in any of the heat-treated coatings. (C) 199 4 John Wiley and Sons, Inc.