In this investigation, titanium dioxide and hydroxyapatite (HA) suspensions are plasma sprayed onto stainless steel, titanium, and aluminum substrates and the structure and properties of the resulting layers are correlated with spraying conditions. The suspensions were formulated with fine TiO 2 pigment and HA milled from spray-dried powder or synthesized from calcium nitrate and ammonium phosphate. In some experiments, an atomizer was used to inject the suspensions into the plasma jet, and in others, the suspensions were fed into the jet using continuous stream injection. The deposits are characterized on the basis of morphology, chemical and phase composition, scratch hardness, and dielectric strength.

The synthetic hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) is a very useful biomaterial for numerous applications in medicine, especially in view of using as fine powder for suspension plasma spraying. The powder was synthesized using aqueous solution of ammonium phosphate (H 2 (PO 4 )NH 4 ) and calcium nitrate (Ca(NO 3 ).4H 2 O) in carefully controlled experiments. The synthesized fine powder was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The powder was formulated into water and alcohol based suspension and used to carry out the initial tests of plasma spraying onto titanium substrate. The phase analysis of sprayed coating was made with the used of XRD.

Spray process of hydroxyapatite was optimized by an advanced statistical planning of experiments. Full factorial design of 24 experiments was used to find effects of four principal plasma spray parameters, i.e. electric power, plasma forming gas composition, carrier gas flow rate and distance of spraying onto microstructure of hydroxyapatite (HA) coatings and powders. The Nemrod software has been applied to obtain the mathematical model of influence of these parameters onto experimental response. The chosen response was the volume fraction of HA crystal phase with regard to its decomposition phases. Two most important factors influencing this response are electric power supplied to torch and art of powder injection. The crystal phase content of powders and coatings was determined using X–ray diffraction (XRD) quantitative analysis. The morphologies of coatings surfaces, cross sections were characterized using scanning electron microscope (SEM).