XPS AND SEM CHARACTERIZATION OF HYDRATED CERIUM OXIDE CONVERSION COATINGS

Cerium-rich conversion coatings have been deposited onto aluminium 202 4-T351 alloy by immersion into a solution containing 10 g L(-1) CeCl3 and 1% H2O2 in a process described as 'cerating'. Prior to deposition the alloy had been prepared either by using a standard chemical pretre atment used for aerospace alloys before conversion coating or by polis hing. X-ray photoelectron spectroscopy and scanning electron microscop y have been used to characterize these cerium-containing conversion co atings. It was found that, during deposition, hydrated cerium oxide in itially covered the intermetallics present in the alloy surface and th en covered the surface generally. Deposition continued over the interm etallics throughout the conversion coating process, resulting in thick , heavily-cracked regions considerably greater than the average thickn ess of the film (>0.3 mu m). Elsewhere the coating was generally up to 0.2 mu m thick, and appeared to comprised of deposited particles arou nd 100 nm in size.