Effects of Surface Morphology and Chemical Composition on the Durability of Adhesively Bonded Aluminum Structures.
Abstract
The hydration of aluminum surfaces prepared for adhesive bonding by anodization in phosphoric acid has been studied using surface behavior diagrams. These surface behavior diagrams, which are similar to phase diagrams for equilibrium bulk phases, trace the evolution of the aluminum adherend surface composition, obtained by X-ray photoelectron spectroscopy, during the hydration process. When supplemented with high resolution scanning electron micrographs and Auger depth profiles, the surface behavior diagrams show that hydration proceeds in three steps. The first is reversible and consists of the adsorption of water by the monolayer of A1PO4 initially present on the surface. It involves no change in the oxide morphology. The second, which appears to be rate controlling, involves the slow dissolution of the phosphate followed by rapid hydration of the exposed alumina to the oxyhydroxide, boehmite. During this stage, extensive morphological changs occur as the boehmite fills the pore cells and bridges the whiskers of the original surface. The final step consists of the nucleation and growth of the trihydroxide, bayerite, on top of the boehmite. Using these results as examples, we propose the surface behavior diagram approach as a new tool for the study of surface reactions in general. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1981
- Accession Number
- ADA107664
Entities
People
- Guy D. Davis
- Jar-mo Chen
- John D. Venables
- Tsishung Sun
Organizations
- Martin Marietta