Breakdown of the niobium oxide film under galvanostatic polarisation and in acid solutions

The breakdown process of niobium oxide process depends on the current density, the concentration and the composition of the electrolyte and the time that the film is maintained under galvanostatic polarisation. The electrical breakdown is associated with small oscillations in the breakdown potential, the presence of sparks, anion incorporated in the film and small holes in the film surface. The mechanical breakdown is associated with sudden variations in the potential; there are no anions in the niobium oxide to start the avalanche process and large fractures in the film. Electrical and mechanical breakdown processes can proceed in the same anodisation.