Abstract (Summary)The interactions between an epoxy/dicyandiamide adhesive and chemically treated aluminum surfaces were studied using Fourier Transform Infrared Spectroscopy (FTIR) microscopy and Nuclear Magnetic Resonance Imaging (NMRI). Applying these techniques in a concerted way provided answers to several key questions related to the phenomena of adhesion. FT-IR was used to characterize the surfaces of Al after various chemical treatments. All of the oxide surfaces were composed of anhydrous alumina, aluminum oxyhydroxide and aluminum hydroxide. The major contaminants found in the different oxides are chemisorbed CO2, carbonates and bi-carbonates. The chromic acid anodized surfaces (CAA) contain more hydroxyls and water than the sulfuric acid anodized surfaces (SAA). The SAA contain more alumina (Al2O3). The CAA surfaces have a duplex structure mainly of hydrated and oxyhydroxylated layers over a hydrated alumina layer. The SAA surfaces have a triplex structure composed mainly of hydrate and hydroxylated layers over a oxyhydroxylated layer which is over hydrated alumina. The chemically converted surfaces by the Iridite process are made up of a duplex structure composed of a mixed organic-inorganic layer over hydrated alumina. The organic portion of the layer was identified as a carbamate species. Microscopic reflection-absorption FTIR spectra obtained from epoxy adhesive films on treated and untreated aluminum samples showed compositional differences normal to the interphase. The results indicate the surfaces induce selective adsorption depending on the surface treatment. NMRI was used to analyze the curing behavior of epoxy adhesives in the presence of anodized and chemically treated aluminum surfaces. The proton images of the epoxy for the untreated Al samples images are characterized by a variety of inhomogeneities (fine texture of uncured and cured domains) finely distributed throughout the sample. Large uncured domains of epoxy were found aggregated near the center of the bonded adhesive sample. Diffusion of uncured material was observed during the curing process. The anodized aluminum/epoxy samples, on the other hand, showed very small contrast and coarse texture images characteristic of phase separation phenomena. However, the onset of curing was clearly shown with increases in contrast and texture. Large amounts of uncured material were seen near the surface indicating the anodized surfaces influence the curing behavior of the adhesive near the interface. This effect was more pronounced in the CAA/epoxy samples. (Abstract shortened by UMI.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:epoxy aluminum interphases
Date of Publication:01/01/1992