High Current Anodization of Magnesium and Magnesium Alloys

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dc.contributor.advisor Graham Wright en
dc.contributor.author Carter, Ellen Angharad en
dc.date.accessioned 2008-01-09T01:09:51Z en
dc.date.available 2008-01-09T01:09:51Z en
dc.date.issued 1996 en
dc.identifier.citation Thesis (PhD--Chemistry)--University of Auckland, 1996. en
dc.identifier.uri http://hdl.handle.net/2292/2289 en
dc.description.abstract High current anodization of magnesium and magnesium alloys Ellen Angharad Carter Pure magnesium and three magnesium alloys containing different amounts of aluminium (2-9%) plus zinc and manganese were anodized with constant current density in sodium hydroxide solution with and without fluoride or phosphate ions. Electric field strengths of resultant anodic films were calculated from galvanostatic transients. These transients showed three characteristic features: linear voltage increase, noisy high voltage signals accompanied by sparking, and sawtooth-like events characterized by instantaneous voltage drops followed by slower voltage increases. Each feature was linked to certain physical processes occurring in the metal/film/solution system. Oxidation of magnesium and magnesium alloys formed anodic films with bilayer structures: a passive barrier layer adhering to the metal electrode, topped by a porous secondary layer. Cation injection into the barrier film across the metal/oxide interface was the rate determining step for film growth. Interstitial cations migrated through the film under the influence of the electric field. At the film/solution interface they reacted with electrolyte species and either thickened the film or dissolved in solution. Electric field strength was constant for particular metal/solution combinations and was independent of applied current density. Changing the electrode material altered the resultant electric field strength: pure magnesium produced oxides with lower electric field strengths than films formed on the three magnesium alloys. Changing the electrolyte had no discernable effect on the electric field strength. Charge efficiency of the film growth process was investigated by oxygen gas evolution; efficiency decreased during sparking. Ion beam analysis (Rutherford backscattering, fluorine depth profiling and nuclear reaction analysis) coupled with X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction studies and Raman spectroscopy gave information about the anodic film surface. These techniques showed that oxides formed on magnesium-aluminium alloys were thinner than those formed on pure magnesium caused by aluminium dissolution. Fluorine depth profiling revealed that concentration profiles for fluorine in anodic oxides formed in fluoride-containing solution altered depending on the aluminium content of the electrode material. en
dc.format Scanned from print thesis en
dc.language.iso en en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA670632 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title High Current Anodization of Magnesium and Magnesium Alloys en
dc.type Thesis en
thesis.degree.discipline Chemical Sciences en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.subject.marsden Fields of Research::250000 Chemical Sciences en
dc.rights.holder Copyright: The author en
pubs.local.anzsrc 03 - Chemical Sciences en
pubs.org-id Faculty of Science en

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