Growth and Electrochemical Stability of Compact Tantalum Oxides Obtained in Different Electrolytes for Biomedical Applications

Tantalum has been cited to have many biomaterial applications, exhibiting biocompatibility and outstanding corrosion resistance. Tantalum may be covered with tantalum oxide using the electrochemical process of anodic oxidation. The oxide surface is known to be bioactive and more corrosion resistant. In this research, compact tantalum oxide films were obtained by potentiostatic and potentiodynamic methods in H₂SO₄ and H₃PO₄ (1 mol.L^-1) electrolytes. By XPS analysis the stoichiometry Ta₂O₅ was detected. The thermodynamic stability of those oxides was compared and the results indicated that Ta₂O₅ obtained in H₂SO₄ has higher thermodynamic stability than Ta₂O₅ obtained in H₃PO₄. The incorporation of (PO₄)^3- ions and the formation of a bilayer oxide are responsible for the reduced stability. Also, the better control of chemical kinetic of oxide formation allows potentiodynamic oxides to be more stable. Ta₂O₅ shows spontaneous dissolution in artificial blood, nevertheless, it remains stable even after 60 days of immersion. By scratching tests was possible to notice that Ta₂O₅ is highly adherent to the tantalum metallic substrate and by mechanical indentation was possible to measure a lower elastic modulus for the Ta₂O₅ than the metallic substrate, what can be considered as distinguished properties for biomedical applications.

Keywords:
biomaterial; tantalum; anodic oxide; electrochemical stability