Effects of Alloying Elements in Anodizing of Aluminium

Effect of current density and behaviour of second phases in anodizing of a Mg-Zn-RE alloy in a fluoride/glycerol/water electrolyte

“…The latter possibility is consistent with the reduced efficiency estimated at the lowest current density. The enrichment of zinc in a thin alloy layer immediately beneath the anodic film is also found in Al-Zn alloys and has been related to the less negative Gibbs free energy per equivalent for formation of zinc oxide in comparison with that for formation of aluminium oxide [31]. However, since the present films contain greater amounts of fluorine than oxygen, the enrichment may be related to the Gibbs free energy of formation of the fluoride.…”

Composition and growth of thin anodic oxides formed on InP (100)

“…Furthermore, In 2 O 3 is more stable at the higher temperature. Regarding anodic oxide growth, a film composed of units of In 2 O 3 and P 2 O 5 , as pointed out previously [22,26] can be explained in terms of formation of anodic films on alloy substrates, developed for aluminum alloys [27]. Thus, indium and phosphorus are oxidized at the substrate Á/ film interface to form In 3' and P 5' ions within an oxide composed of units of In 2 O 3 and P 2 O 5 .…”

Mobility of lithium ions in anodic alumina formed on an Al–Li alloy

“…Further, the Li/Al atomic ratio in the alumina ®lm material should be less than that in the alloy by a factor dependent on the relative mobilities of Li + and Al 3+ ions. Due to the faster migration of Li + ions, there is a possibility of formation of an outer ®lm layer composed initially of Li 2 O or LiOH, depending upon the composition and pH of the environment [3]. If the eciency of ®lm growth is reduced, with lithium and possibly also aluminium species entering the solution, precipitated material may deposit at the ®lm surface.…”

“…The pre-treatments commonly develop amorphous alumina ®lms, sometimes hydrated, on the alloy surface; examples are acid pickling, alkaline etching, conversion coating and anodizing. From ®ndings of previous work on aluminium alloys, it is anticipated that lithium atoms in solid solution in matrix regions of the alloy are incorporated immediately into the growing amorphous alumina ®lms, presumably as Li + ions, which migrate outward faster than Al 3+ ions [3]. The immediate incorporation of lithium species is associated with the lower Gibbs free energy per equivalent for formation of Li 2 O compared with that for formation of Al 2 O 3 , while the faster migration of Li + ions relates to the lower energy of the Li + ±O bond compared with that of the Al 3+ ±O bond [4].…”

“…However, the general anodic oxidation behaviour of aluminium alloys indicates that enrichment does not occur [3]. Thus, lithium and aluminium atoms are oxidized from the commencement of anodizing and are incorporated into the anodic ®lm in their alloy proportions.…”