Interactive Resource icon  Corrosion Prevention: Pore Sealing

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Description: Pore sealing is a hydrothermal treatment in hot water, water vapour or aqueous organic and inorganic salts. Moisture transforms aluminium oxide to hydroxide – initially boehmite AlO(OH) (or pseudo-boehmite i.e. a poorly crystallised oxyhydroxide similar to boehmite but containing excess water) and in the final hydration stage bayerite Al(OH)3 - with accompanying morphological change, which leads to pore closure due to the larger specific volume of the hydroxides. To a certain extent, the plugged pores deny aggressive ions from a corrosive environment access to the underlying aluminium substrate and hence inhibit corrosion. The animation schematically illustrates this process. The oxide film forms an effective barrier between the aluminium and the corrosive environment, superior to the corrosion protection provided by other surface treatments like chemical conversion. Anodization layers can be used without an additional paint layer on top, e.g. colored anodized window frames.
Keywords: pore sealing • anodising • porosity • anodic film • hydrothermal treatment • aluminium hydroxide
Categories: Science approaches > Corrosion & degradation
Science approaches > Corrosion & degradation > Corrosion protection
Materials > Metals & alloys > Aluminium & alloys
Processes > Thermal treatments
Created by: MATTER, The University of Liverpool
Steven Meijers, Corus
Carlos Caicedo-Martinez, Corus
Contributions: Andreas Blistein, Alcan
Herman Terryn, Vrije Universiteit Brussel (VUB)
Iris De Graeve, Vrije Universiteit Brussel (VUB)
Marc Ryckeboer, Sapa
Published by: European Aluminium Association, Brussels
License: This resource is released under the Creative Commons Attribution Non-Commercial No Derivatives license (2.0 UK: England & Wales).
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Date created: 21 August 2006
Date added: 07 July 2010
Resource ID: 2877