3.4. Rutherford backscattering spectroscopy
Rutherford backscattering spectroscopy (RBS) was undertaken on the as-deposited model Al2Cu and Al7Cu2Fe second phases and after anodizing in chromic acid and sulphuric acid electrolytes, with typical spectra for as-deposited and anodized Al2Cu alloys shown in Fig. 8. Relevant information calculated from fitting of the RBS spectra are presented in Table 3. Thus, from RBS, the composition and thickness of the model second phase particles, expressed as atoms cm−2 of aluminium, copper and/or iron, are obtained before and after anodizing. Subtraction of the previous values gives the number of atoms cm−2 that are oxidized from metal to cations. RBS also provides the number of cations that constitute the anodic film material; subtracting the number of oxidized atoms cm−2 from metal to cations and those that comprise the anodic film gives the losses to the anodizing electrolyte. Such calculations quantify the charge densities consumed by the various electrode reactions, e.g. anodic film formation, losses to the electrolyte and oxygen generation (Table 3).