The anodic behaviour of aluminium alloys in alkaline solutions
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The electrochemical behaviour of aluminium in alkaline solutions, with small amounts (<0.1 wt%) of indium, magnesium and gallium as alloying constituents, and the identification of the parameters that will most effect an operating A1 / air battery system have been investigated. The alloys investigated were suggested by Comalco Research Laboratories, Melbourne and had the following analysis: Pure Aluminium (better than 99.995%) A1- 0.016%In. A1 - 0.046%Ga. A1- 0.045%In. A1- O.067%Ga. A1- 0.10%In. A1- 0.110%Ga. A1- 0.1%Mg. A1- 0.1 %Mg - 0.1 %In. A1- 0.085%In - 0.09%Ga. It has been found that the peak potential, using the fast cut technique, is independent of indium concentration for indium alloys of less than 0.1 %In, and that the reaction kinetics for the aluminium dissolution at the peak potential change as the aluminate concentration in the alkaline solution is increased. The steady state potential shows a logarithmic relationship to the indium content of the binary alloys and this showed that there is little advantage in using an indium content of greater than 0.04%. The flowcell experiments showed that the indium containing alloys become coated with a black film, and that onset of significant polarization coincided with the disappearance of this film. X-ray analysis has confirmed that both indium and gallium concentrate on the reaction surface during polarization. This work has shown the ternary A1-0.1%Mg - 0.1%In alloy to be the best from those tested. The magnesium in the alloy has been shown to refine the electrode grain structure and to significantly reduce the parasitic corrosion rate. The effects of aluminate accumulation in the electrolyte on polarization were measured and increasing the flowrate and temperature have been shown to increase the maximum current density attainable.