Tantalum standard potentials

Table 46 Standard Potentials of Niobium and Tantalum (M6X12),+ in Neutral Aqueous Solutions...

Table 6.8 provides the Gibbs free energy of formation of different oxides and the corresponding standard potentials for aqueous solutions. Generally, the oxides of less noble metals exhibit a lower standard potential of formation. These metals passivate spontaneously in the presence of protons. Furthermore, many oxides exhibit good chemical stability in acidic environments. This explains the higher eorrosion resistance of metals such as titanium, tantalum and chromium. 

---