Electrochemical study of corrosion and dissolution of Tc metal in 0.5–6.0 M HNO3

Electrochemical dissolution of Tc metal in 0.5–6.0 M HNO3 was studied. The quantitative characteristics of corrosion and dissolution were determined. At the HNO3 concentration in the electrolyte below 2.0 M and potentials below 650 mV (vs. Ag/AgCl), the metal surface is passivated owing to the formation of difficultly soluble hydrated Tc(IV) dioxide. An increase in the potential leads to the transition of Tc metal to the transpassive state. In solutions containing more than 2.0 M HNO3, hydrated Tc(IV) oxide loses passivating properties. The oxidation of Tc(IV) to Tc(V) is the main reaction controlling the corrosion rate. The results of corrosion rate measurements show that Tc metal can be quantitatively dissolved in HNO3 of concentration higher than 4.0–6.0 M. The dissolution rate at room temperature is 0.3 mg cm−2 h−1.