Aluminium alloys for battery anodes in alkaline systems
Aluminium alloys for battery anodes in alkaline systems
Standard electrochemical techniques have been used to study the behaviour of pure aluminium and tin, as well as some alloys of aluminium containing tin and magnesium in sodium hydroxide solutions of varying strength. The materials studied are of particular significance as anodes for alkaline battery systems. The effect of additions of tin, in the form of stannate, on the behaviour of aluminium and an aluminium/magnesium alloy in 1M NaOH was also investigated. The growth and dissolution of anodic films on the materials was followed in-situ in 1M NaOH by means of an automated, null-seeking ellipsometer using a wavelength of 6329A*. Complex models of theoretical film systems were constructed in order to try to interpret the results, and these models have been correlated with observations made by scanning electron microscopy. Cyclic voltammetry has demonstrated the phenomena of `superactivation' and `hyperactivation' of aluminium by tin, both as an alloying dopant and an electrolyte additive, in 1M, 4M and 8M NaOH. Hyperactivation of pure aluminium has also been observed in 8M NaOH. Electrochemical studies of pure tin have confirmed that the superactivation of tin-containing alloys of aluminium in alkaline electrolytes is controlled by the electrochemical behaviour of tin. The presence of magnesium as an alloying addition was found to have no effect on either pure aluminium or aluminium/tin alloy. Ellipsometric investigation of the growth and dissolution of anodic oxide films on pure aluminium and aluminium/tin alloy in 1M NaOH demonstrated the porous nature of the films in this medium. The results were found to be very sensitive to solution turbulence. Film growth is essentially self-limiting under pumped-flow conditions but stagnant solutions produce deceptive ellipsometric traces due to tenuous layers at the film/electrolyte interface or localised solution effects. Magnesium-containing alloys of aluminium produced complex ellipsometric traces suggestive of a thick top layer of low refractive index. SEM examination has confirmed the presence of thick films of hydrated material on the surface of such specimens. The passivation of tin in alkaline media proved unsuitable for ellipsometric study due to difficulty in separating film growth processes from roughening of the metal surface. Theoretical models have been devised for the growth of anodic oxide films on pure aluminium which incorporate initial substrate roughening and graded refractive index due to the porous nature of the material. Further work needs to be done in the case of magnesium-containing alloys to produce a model for the top layer which gives a good fit with the experimental results.
University of Southampton
1992
Dodson, Matthew William
(1992)
Aluminium alloys for battery anodes in alkaline systems.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Standard electrochemical techniques have been used to study the behaviour of pure aluminium and tin, as well as some alloys of aluminium containing tin and magnesium in sodium hydroxide solutions of varying strength. The materials studied are of particular significance as anodes for alkaline battery systems. The effect of additions of tin, in the form of stannate, on the behaviour of aluminium and an aluminium/magnesium alloy in 1M NaOH was also investigated. The growth and dissolution of anodic films on the materials was followed in-situ in 1M NaOH by means of an automated, null-seeking ellipsometer using a wavelength of 6329A*. Complex models of theoretical film systems were constructed in order to try to interpret the results, and these models have been correlated with observations made by scanning electron microscopy. Cyclic voltammetry has demonstrated the phenomena of `superactivation' and `hyperactivation' of aluminium by tin, both as an alloying dopant and an electrolyte additive, in 1M, 4M and 8M NaOH. Hyperactivation of pure aluminium has also been observed in 8M NaOH. Electrochemical studies of pure tin have confirmed that the superactivation of tin-containing alloys of aluminium in alkaline electrolytes is controlled by the electrochemical behaviour of tin. The presence of magnesium as an alloying addition was found to have no effect on either pure aluminium or aluminium/tin alloy. Ellipsometric investigation of the growth and dissolution of anodic oxide films on pure aluminium and aluminium/tin alloy in 1M NaOH demonstrated the porous nature of the films in this medium. The results were found to be very sensitive to solution turbulence. Film growth is essentially self-limiting under pumped-flow conditions but stagnant solutions produce deceptive ellipsometric traces due to tenuous layers at the film/electrolyte interface or localised solution effects. Magnesium-containing alloys of aluminium produced complex ellipsometric traces suggestive of a thick top layer of low refractive index. SEM examination has confirmed the presence of thick films of hydrated material on the surface of such specimens. The passivation of tin in alkaline media proved unsuitable for ellipsometric study due to difficulty in separating film growth processes from roughening of the metal surface. Theoretical models have been devised for the growth of anodic oxide films on pure aluminium which incorporate initial substrate roughening and graded refractive index due to the porous nature of the material. Further work needs to be done in the case of magnesium-containing alloys to produce a model for the top layer which gives a good fit with the experimental results.
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Published date: 1992
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Local EPrints ID: 461045
URI: http://eprints.soton.ac.uk/id/eprint/461045
PURE UUID: 273f41fa-3e5e-4e00-92c7-ee4286a0cbae
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Date deposited: 04 Jul 2022 18:34
Last modified: 04 Jul 2022 18:34
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Author:
Matthew William Dodson
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