Rubber-brass bond

FIGURE 17 Interfacial copper sulfide film in rubber-brass bonding. (From Gough [7].)... 

An important additive to NR compounds used for bonding rubber to brass is a cobalt salt, such as cobalt naphthenate. While this additive improves the stability of the rubber-brass bond, especially in a corrosive environment, it exerts a negative effect on the stability of the rubber network, in that it accelerates reversion phenomena especially in the presence of oxygen and at elevated temperatures. 

Figure 6.1 Mechanism of rubber-brass bonding after van Ooij [4], Shown are a) the original brass surface composition and, b) the interfacial copper sulphide dendrites interlocked with the crosslinked rubber compound (Reprinted with permission, from W. J. van Ooij, Rubber Chemistry and Technology, 1984, 57, 3, 426, Figure 1 and 445, Figure 11. 1984, Rubber Division, American Chemical Society, Inc.)...

The main emphasis of the work on rubber-brass bonding published in the last 10 years has been on elucidating mechanisms further. The adhesion model accepted since 1984 in which the formation of a film of non-stoichiometric copper sulphide has been confirmed in all studies. It has now become clearer how to obtain a thin copper sulphide film with... 

Analysis of failure surfaces can also lead to information about the reactions which occurred in the interface. Results of an XPS analysis(39) of a vulcanized rubber/brass interface are shown in Figure 34. Products formed at the interface were identified as ZnO, ZnS, and Cu S the latter two were confirmed by X-ray diffraction analysis. The components of the vulcanizing rubber attack the brass leading to the formation of an interfacial film of reaction products, which become an integral part of the rubber-brass bond. Ageing in either steam or oxygen leads to further reaction and the formation of a weak boundary layer and low strength. 

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