Structural evaluation of brushite/gelatine coatings on graphite substrate

Brushite is one of the most frequently formed products of the electrochemical deposition. It has shown excellent biological behaviour of calcium phosphate coatings on carbon composites. Calcium phosphate coatings were obtained by the electrochemical deposition from the solution of calcium and phosphate ions at pH = 2.4 and with 0.2 or 1 wt.% gelatine addition. Graphite substrate was used as cathode and Pt basket as anode. Electrochemical deposition of brushite/gelatine composite layer was carried out at current densities from 5 to 20 mA/cm2. Coatings were examined before and after annealing at 850 °C in Ar. The large channels were observed in coatings at higher concentrations of gelatine and high current densities in microstructure. The adhesive strength of thin brushite/gelatine coating was around 7 MPa. Linear dependence of deposit weight increase with electrolysis time was observed. Similarly, the gelatine content in coating rose linearly with gelatine concentration in electrolyte. After annealing of coatings at 850 °C in argon, the brushite was transformed to hydroxyapatite and CaO, the size of the needle-like brushite particles decreased and small spherical or regular shaped particles of CaO were formed. The weak bonding of thermal treated brushite/gelatine deposits to graphite was found.