Influence of concentration and temperature on the corrosion behavior of titanium, titanium-20 and 40% tantalum alloys and tantalum in sulfuric acid solutions

Titanium (Ti) exhibits an excellent corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum (Ta) presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The Ti–Ta alloys are promising materials for replacing Ta, due to their lower cost and density when compared to Ta, and their expected higher corrosion resistance when compared to Ti. The corrosion behavior of Ti, Ti-20 and 40% Ta alloys and Ta in sulfuric acid (H2SO4) solutions at 25, 50 and 75 °C was studied using open-circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different corrosion behaviors (spontaneous passivation, spontaneous activation and cathodically induced activation) were observed depending on the Ta content, acid concentration and temperature. Increasing of Ta content and decreasing of both H2SO4 concentration and temperature led to an increase in corrosion resistance. A transition in corrosion behavior was observed between 20 and 40% Ta content: Ti and Ti–20Ta alloy presented similar corrosion behavior, whereas Ti–40Ta behaved like Ta. This is related to the nature of the respective oxide films formed on the four materials.