Metal adhesion mechanisms

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

Moisture acts as a debonding agent through one of or a combination of the following mechanisms 1) attack of the metallic surface to form a weak, hydrated oxide interface, 2) moisture assisted chemical bond breakdown, or 3) attack of the adhesive. (2 ) A primary drawback to good durability of metal/adhesive bonds in wet environments is the ever present substrate surface oxide. Under normal circumstances, the oxide layer can be altered, but not entirely removed. Since both metal oxides and water are relatively polar, water will preferentially adsorb onto the oxide surface, and so create a weak boundary layer at the adhesive/metal interface. For the purposes of this work, the detrimental effects of moisture upon the adhesive itself will be neglected. The nitrile rubber modified adhesive used here contains few hydrolyzable ester linkages and therefore will be considered to remain essentially stable. 

Additional work must be completed before these hydration inhibitor treatments will be widely used. However, it appears that combined FPL/inhibitor pretreatments have the potential of producing water stable aluminum oxides with structures that promote mechanical aspects of adhesion in a relatively simple manner. Since mechanical adhesion mechanisms are not greatly affected by water, these pretreatments show promise as a means of increasing the durability of metal/polymer adhesion systems in wet environments. 

Although the mechanisms of polyimide/metal adhesion remain to be fundamentally elucidated, it is generally accepted that the interfacial diffusion of metallic entities into the polyamic acid plays a key role at the interface [156-158]. Two main theories have been reported explaining the adhesion of the Pl/metal bond chemical and mechanical bonding [159]. Initial work emphasized mechanical bonding and most efforts were dedicated to the physical roughening of the substrate by different abrasive methods as well as chemical treatments in order to improve metal to polyimide adhesion by increasing the metal surface area [156,160-164]. 

Barthes-Labrousse MG, Joud JC (2000) Acid-Base Characterization of metallic materials and the use of model molecules in the study of adhesion mechanism. Acid-Base Interactions Relevance to Adhesion Science and Technology, Mittal KL (ed) VSP Utrecht, 453... 

The metal polymer interface can be studied in a variety of ways using surface science methods. Recently, much emphasis has been placed on the understanding of the initial stages of metallization of polymers. In particular, the role of metal-organic interactions as they relate to the fundamentals of adhesion mechanisms are of interest. One experimental approach is to examine the first monolayers of metal as they are deposited on a polymer surface (1), i.e the polymer is the substrate. However, the organic polymer-metal interface may be studied in the opposite perspective, via understanding the roles of organic molecular or macromolecular structure and chemistry of the metal surface qua substrate (2). In the present paper, recent ion and electron spectroscopic studies of the... 

Components with improved mechanical properties can be produced by mixing the above processable polymers with other polymers. For example, we have mixed conducting polymer colloids with water based latex paints to form conductive, electroactive paints with excellent adhesion to a range of metals [132], Interestingly, the paint-metal adhesion was actually increased by addition of the conducting polymer colloid. 

It was shown in Section 11.C.8.C how numerical simulations can be used to predict whether failure is more likely to occur via a cohesive or an adhesive mechanism in a joint consisting of an epoxy thermoset glue between two metal plates. 

To explain the pronounced effect of additives on tool wear in metal cutting, Dorinson [74] developed a theory of the inhibition of junction growth at contacting asperities based on the concept of dynamic competition between asperity adhesion and the quenching of such adhesion by additive reaction. The adhesion mechanism involves the following sequence migration of metal on the chip side of the contact interface to the tool side,... 

Production of loose particles is often attributed to the fatigue mechanism, the process being differentiated from macroscopic spalling in scale but not in kind. As cited previously [15], metallic particles transferred to the countersurface from the rider by the adhesive mechanism can be detached by the fatigue mechanism on subsequent reiterated rubbing Kerridge and Lancaster [15], and Hirst and Lancaster [30], have also ascribed the formation of transferable particles to fatigue as a primary mechanism. 

It can be concluded after all that the results reveal very specific features caused by metal-polymer interactions in the interphase of cured PU on different metal surfaces, though further experimental efforts are needed to gain a more complete understanding of the underlying chemical reactions and adhesion mechanisms. Furthermore, remarkable quantitative differences can be seen in the chemical structure formation of thin PU films with regard to reaction rate and degree of isocyanate consumption. 

A complementary view is presented of the adhesion and de-adhesion mechanisms, especially in humid and corrosive environments, which are predominant and most important for the application of metal/adhesive composites in engineering applications. The transport of hydrated ions at metal/adhesive interfaces is considered as an important premise for corrosive reactions. 

The rapid rate of reaction of iron above 570 °C causes thick scales to develop quickly and, in spite of the relatively high plasticity of the FeO layer, scale-metal adhesion is lost and a porous inner layer of FeO is formed, next to the metal, by the mechanism described earlier. The stresses associated with rapidly growing scale undoubtedly induce physical defects in the outer scale and the penetration of gas molecules, especially those belonging to the CO-CO2 and H2-H2O redox systems, will play a role in scale formation. 

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