Metal Analysis of Structural Adhesives

A Practical Approach to Quantitative Metal Analysis of Organic Matrices Martin Brennan 2008 John Wiley Sons, Ltd 

For an adhesive to be successful it must compete with non-adhesive joining techniques such as welding, nuts and bolts, rivets and staples. Modern adhesive joining can be used to replace or supplement traditional joining methods only when the quality, performance and economics are acceptable. 

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It has been shown that Impedance Spectroscopy (IS) is a promising, non-destructive tool for the analysis of incipient adhesion failure in metal-insulator structures. This contribution presents a complete analysis of experimental impedance spectra, carried out by using numerical simulation and analytical techniques. 

In previous publications 2 it has been shown that Low-Frequency Impedance Spectroscopy can be considered a promising, non-destructive toot for the evaluation and the analysis of incipient adhesion failure in some metal-insulator structures. The technique is based on the effect of the interface modifications on the diffusivity of chemical species such as water, which is ubiquitously present in polymers used for packaging. Since such... 

Table 1 contains the metal-to-metal engineering property requirements for Boeing Material Specification (BMS) 5-101, a structural film adhesive for metal to metal and honeycomb sandwich use in areas with normal temperature exposure. The requirements are dominated by shear strength tests. Shear strength is the most critical engineering property for structural adhesives, at least for the simplistic joint analysis that is commonly used for metal-to-metal secondary structure on commercial aircraft. Adhesive Joints are purposefully loaded primarily in shear as opposed to tension or peel modes as adhesives are typically stronger in shear than in Mode I (load normal to the plane of the bond) loading. 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in. adhesive bonding research. The combination of SIMS with complementary methods such as ISS or AF.S provides a powerful tool for elemental end limited structural characterization of metals, alloys and adhesives. The results shown here indicate that surface chemistry (and interface chemistry) can be decidedly different from bulk chemistry. Often it is this chemistry which governs the quality and durability of an adhesive bond. These same surface techniques also allow an analysis of the locus of failure of bonded materials which fail in service or test. 

In this paragraph we will examine first the adhesion properties and the structure of aluminum films evaporated i) on oi-axially oriented polymer and ii) on treated (corona and fluorine) polymer samples. Then, an analysis of the influence of some parameters of the metallization such as the thickness of the aluminum film, the evaporation angle and the aluminum deposition by sputtering, will be presented. 

Additional evidence of oxygen being involved as pait of the metal polymer link was obtained by examining the thiclmess of the metal oxide layer on the outer surface of the metal and at the metal/polymer interface prior to and subsequent to the heat-tieatment step. Analysis of the backside of the intetphase region was accomplished via dissolution of the polymer substrate The data in Table VI show that the oxide thicknesses were nominally equal at the air and polymer sides of the structure. The oxide thicknesses were independent of metal deposition technique although the presence of the palladium catalyst employed for electroless deposition complicated the analyses. X-ray photoelectron spectroscopy identified the oxide species as cuprous oxide 10,17. Excellent adhesion was obtained once the oxide thickness exceeded 3 nm at the metal/polyetherimide interfacial zone. 

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