Solid-phase interaction in the hydroxyapatite/titanium heterostructures upon high-temperature annealing in air and argon

Samples of 100- and 500-nm-thick hydroxyapatite films on titanium were investigated using scanning electron microscopy, electron probe X-ray microanalysis, and X-ray powder diffraction. The films were prepared by high-frequency magnetron sputtering of a target in an argon atmosphere (1 × 10 ^-1 Pa) at a magnetron power density of 40-70 W/cm ². These conditions provided growth of films at a rate as high as 0.7 nm/s. It was demonstrated that the hydroxyapatite film annealed in argon is characterized by deep pores that have diameters ranging from 0.3 to 8.0 μm and are uniformly distributed throughout the film surface. The electron probe X-ray microanalysis confirmed the presence of all elements (Ti, O, Ca, P) under investigation, except for hydrogen, in the samples of the films. For biologically compatible hydroxyapatite, the optimum ratio Ca: P ≈ 1.5-1.7 was achieved in the hydroxyapatite/titanium system with a 500-nm-thick hydroxyapatite layer upon annealing in argon at a temperature of 1050°C for 30 min. It was established that the hydroxyapatite/titanium system contains intermediate phases, including calcium titanate CaTiO ₃, which proved the interaction of hydroxyapatite with titanium.