ANODIC-OXIDATION OF ANTIMONY AT HIGH OVERPOTENTIALS - FORMATION OF A BARRIER LAYER AND KLEBELSBERGITE

The anodic oxidation of antimony at potentials higher than 0.0 V (vs. Hg/Hg2SO4/K2SO4) in strong acid solutions was investigated using linear sweep voltammetry, potentiostatic polarization, photo-voltammetry and ac impedance measurements. The anodic layer structure was observed by scanning electron microscopy and its phase composition determined by X-ray diffraction. At potentials higher than 0.0 V, after a certain quantity of charge has passed through the electrode, an anodic multilayer is formed. It.comprises a barrier layer at the metal side, a basic sulphate gel-like layer at the solution side and a hydroxide layer in between. The growth of the barrier layer is determined by a high-field assisted ion migration. This layer has semiconductor properties and a band gap of 2.2+/-0.1 eV. Its formation is essential in order to reach appropriate conditions for the nucleation of klebelsbergite (Sb4O4(OH)2SO4) Which is stable in H2SO4 solutions.