COMPOSITIONAL CHANGE IN SURFACE OF TI-ZR ALLOYS IN ARTIFICIAL BIOLIQUID

The surfaces of Ti-Zr alloys before and after immersion in an electrolyte which contains inorganic ions found in the biological system were characterized using X-ray photoelectron spectroscopy (XPS), in order to know the changes in the surfaces of the system. Plates of Ti-25Zr, Ti-50Zr, Ti-60Zr, and Ti-75Zr alloys (in mass%) and metallic Ti and Zr were polished and immersed in the solution at 310 K for 3.6 ks (1 h), 86.4 ks (1 d), or 2.6 Ms (30 d) in sealed bottles. After immersion, the specimens were washed and analyzed using XPS. The XPS data revealed that the ratios of the relative concentrations of Ti to those of Zr in the surfaces were almost the same as those in the bulks. In the surface oxide layer, Ti and Zr were uniformly distributed along the depth direction. The thickness of the surface oxide of the alloys before immersion increased with increasing the Zr content in the alloys. The chemical state of Zr was stabler than that of Ti in the surface oxide layer. In surface layers of the alloys, mainly oxidation primary proceeded by the immersion and then hydroxidation occurred. Calcium phosphate was only formed on Ti-25Zr immersed for 2.6 Ms and metallic Ti whereas titanium phosphates and/or zirconium phosphates were formed under other conditions.