EFFICIENCY OF FORMATION OF NANOPOROUS ALUMINA FILMS IN FLUORIDE ION-CONTAINING ELECTROLYTE

The formation of porous anodic films on Al was carried out in electrolytes based on 0.5 M (NH4)(2)SO4 with the addition of NH4F. The anodization was performed in two stages. In the first stage the formation voltage is reached at a scan rate of 50 mV s(-1). In the second stage, the anodization was continued tensiostatically for up to 1 hour. Current density / formation voltage (first stage) and current density / time curves (second stage) were found to be in agreement with previous results of other authors. The current efficiency of film formation has been estimated by determining the concentration of Al, dissolved in electrolyte during anodization by inductively coupled plasma optical emission spectrometry (ICP-OES). Assuming that all the Al ions that migrate through the film are ejected in the solution, the transference number for Al3+ is also estimated. The obtained estimates allowed the determination of the total porosity of the alumina templates by re-anodization in 1 M AS/DMF (ammonium salycilate in dimethyl formamide) electrolyte. The obtained porosity values decreased with the increased voltage in the tensiodynamic stage and slightly increased with the time during the tensiostatic stage, in general agreement with the results, reported during porous anodization of Al in acidic electrolytes.