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.