STUDIES OF THE ANODIC FILM ON LEAD PLUS BISMUTH ALLOY IN SULFURIC-ACID-SOLUTION

The anodic film formed on Pb + 9 at.%Bi at 0.9 V vs. Hg/Hg2SO4 in 4.5 mol dm-3 H2SO4 at 25-degrees-C was studied using X-ray diffraction (XR D) chronoamperometry and ac impedance spectroscopy. The XRD analysis s hows that the anodic film on the alloy is composed of tet-PbO, PbSO4, Bi2O3, PbO.PbSO4 and probably Bi2(SO4)3. The current-time transient sh ows that the growth of the anodic film is controlled by a diffusion me chanism. The dielectric constant of the film determined from the capac itance-time relationship measured at 2500 Hz is 243. The Mott-Schottky plot shows that the film is an n-type semiconductor. The flat-band po tential of the film is -0.836 V vs. Hg/Hg2SO4 and the donor density is 2.73 x 10(15) cm-3.