The influence of chloride and sulphate ions on the corrosion behavior of Ti and Ti-6Al-4V alloy in oxalic acid

The electrochemical behavior of pure Ti and Ti-6Al-4V alloy was investigated in oxalic acid solution using various electrochemical techniques, i.e. open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS) and surface examination via scanning electron microscope (SEM) technique. The influence of concentration and temperature on the electrochemical behavior of TI and its alloy were also studied. The results of polarization measurements showed that corrosion current density (icorr) increases with increasing either temperature or oxalic acid concentration for both samples. Moreover, the value of icorr for Ti was found to be lower than that for Ti–6Al–4 V alloy, where the corrosion resistance for titanium was always higher. The effect of additives as SO42− and Cl− ions was studied; results indicated that the oxide film resistance (Rox) value decreases with increasing the concentration of SO42− ion. However, for Cl− ion, the value of Rox decreases with increasing Cl− ion concentration up to 1 mM before it starts to increase at higher concentrations. EIS and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination.