Environmental Durability of Aluminum Adhesive Joints Protected with Hydration Inhibitors.
Third year rept. 1 Jul 82-30 Jun 83,
MARTIN MARIETTA LABS BALTIMORE MD
Pagination or Media Count:
The adsorption of selected, organic, hydration inhibitors onto and the subsequent hydration of Forest Products Laboratory FPL-etched surfaces has been studied using X-ray photoelectron spectroscopy XPS and surface behavior diagrams SBDs supplemented by inelastic electron tunneling spectroscopy IETS and Fourier Transform Infrared Spectroscopy FTIR. The results indicate that nitrilotris methylene phosphonic acid NTMP and related compounds adsorb to the alumina surface via the POH bonds of the phosphonic acid groups, resulting in a displacement of water normally adsorbed onto the surface. A model of adsorption was developed that suggests that at very low treatment solution concentrations approx 1 ppm only one leg of the NTMP molecule adsorbs onto the surface although at higher concentrations approx 100 ppm all three legs do. Hydration is a three-step process 1 a reversible physisorption of water, 2 a slow dissolution of the inhibitor followed by a rapid hydration of the freshly exposed A1203 to boehmite A100H, and 3 a further hydration of the A100H to bayerite A10H3. It is during the second step that bond failure occurs with the dissolution of the inhibitor being the rate limiting reaction. Analysis of the adsorption, hydration, and wedge tests results using different inhibitors suggests four criteria of an inhibitor to promote good bond performance occupation of all active sites on the A1203 surface, strong inhibitor surface bonds, insolubility of the resulting inhibitor-aluminum complex in aqueous solutions, and compatibility with the adhesiveprimer.
- Polymer Chemistry