Radio frequency (RF) suspension plasma sprayed ultra-fine hydroxyapatite (HA)/zirconia composite powders

Ultra-fine hydroxyapatite (HA)/ZrO₂ composite powders was synthesised by radio frequency (RF) induction suspension plasma spray. A wet suspension of HA/ZrO₂ was employed as feedstock. The suspension was injected axially into the RF plasma to produce the nano-composite powders, which were subsequently accumulated in cyclone collectors. The particle size and morphology was resolved by using the Zeta potential nano-particle size analyser, scanning electron microscopy, transmission electron microscopy, field emission microscopy techniques. The phase composition, phase concentration, and, molecular structure of the powders were characterised using differential scanning calorimetry, Fourier transform infra-red and X-ray diffractometry with quantitative phase analysis empowered by the Rietveld method. Results indicated that nano-size, spherical HA/ZrO₂ composite powders were produced with varying morphological features that depend on the thermal treatment. Calcium zirconate (CaZrO₃) was produced as a byproduct whose biocompatibility is not well documented. Results also showed that the HA decomposed into α and β-TCP due to decreasing Ca/P ratio with the formation of CaZrO₃.