SOME CHARACTERISTICS OF HYDROXYLAPATITE POWDER PARTICLES AFTER PLASMASPRAYING

We have studied the particles of hydroxylapatite (HA) powder, the part icles after plasma spraying, their distribution on substrate surface a nd their condition after transfer through the plasma torch. Mean parti cle size of HA powders was as follows: HA-A: 3.8 mu m, HA-B 88.2 mu m, The area of HA coating after plasma spraying, when the torch had a co nstant position against the substrate surface, shows two characteristi c zones: the central part of coating formed mainly from deformed parti cles and the marginal part of coating with small non-deformed particle s. These small non-deformed particles can be found in all zones of the coating and together with greater non-deformed particles and partiall y deformed particles will unfavourably affect the adhesive and cohesiv e strength of the coating and its porosity. The maximum diameter of th e molten (spherical) particles in the conditions of Ar + H-2 plasma, o utput P = 24 kW was: D-A = 25 mu m (HA-A) and D-n = 65 mu m (HA-B). Th e intervals of dimensions in which most of molten particles occurred w ere HA-A: 0-15 mu m (98%), HA-B: 5-35 mu m (84%). From comparison of H A-A and HA-B powders it can be concluded that the transport of HA-A po wder was not continuous, the amount of molten HA-A particles was consi derably greater (90%) than that of HA-B powder (63%). Phase decomposit ion and also solubility of HA-A powder (at in vitro tests) was greater . If we consider transport of particles, their melting, splitting and spraying efficiency, the suitable size of HA powder particles for the given spraying conditions is somewhere between the size of HA-A and HA -B particles-let us say-in the interval from 20 to 60 mu m. (C) 1998 P ublished by Elsevier Science Ltd. All rights reserved.