Effect of fluoride concentration on niobium anodic dissolution

Anodic behaviour of niobium in HF was investigated using potentiodynamic polarization technique. The effect of concentration was studied by varying the nominal HF concentration and few experiments were carried out by adding H2SO4 and KF to HF solutions, to determine the effect of various species on Nb dissolution. In the potentiodynamic polarization curves, distinct active and passive regions were seen at all the concentrations studied. A kinetic model involving a chemical and an electrochemical dissolution step in parallel was proposed to model the observed results. The model captures all the major characteristics of the polarization curves. HF2- is identified as the contributing species for the chemical dissolution and remaining HF as the contributing species for the electrochemical dissolution.