Barrier‐type anodic films on aluminium in aqueous borate solutions: 2—Film compositions by Rutherford backscattering spectroscopy and nuclear reaction methods

Compositions and elemental distributions of anodic films formed on aluminium in aqueous borate electrolytes have been investigated by Rutherford backscattering spectroscopy (RBS) and associated nuclear reaction methods, together with controlled crystallization of film sections in the transmission electron microscope (TEM). Films were found to consist principally of Al 2 O 3 ; the outer regions of the films were contaminated with boron and, for all cases studied, the inner regions were boron‐free. In the absence of film dissolution the contaminated region represented approximately 40% of the film thickness, and this proportion did not vary significantly with changes in current density of film formation. The outer region contained about 1.5 wt% boron, probably as B 2 O 3 , and the densities of the inner and outer regions were similar to an accuracy of about 10%.