Changes in cold sealed aluminium oxide films during ageing

EIS in the 100 kHz-1 mHz frequency range was applied to the study of change s in cold sealed aluminium oxide films exposed to highly wet and extremely dry atmospheres. Information about these changes was obtained from evolutio n of the impedance diagrams and, in particular, from film resistance and ca pacitance values determined from them. Results show that sealing quality, a ssessed from EIS, increases over months and years as ageing proceeds in a n atural atmosphere. The analysis was completed with the aid of XPS and EDX t echniques and standard quality control tests. Measurements show that specim ens aged very rapidly in wet atmospheres, so that they passed all sealing q uality tests within 72 h. The sealing quality improves with ageing even in highly dry atmospheres despite the fact that pores lose part of their initi al filling water. XPS analysis revealed that fluorine and nickel concentrat e in the outer layers of cold sealed anodic films; on the other hand, films obtained by the traditional HTS procedure exhibit a uniform composition th roughout their thickness.