The rubber-brass adhesion is influenced by the chemical composition and thickness of the interfacial layer. The effects of inorganic compounds at the interface consisting of CuxS, ZnS and ZnO on the adhesion phase have been investigated.
The CuxS has been formed by the reaction between brass and sulfur, being highly non-stoichiometric. The values of x may vary between 1.0 and 2.0. There is an evolution from Cu1.8S over Cu1.93-1.97S to fully stoichiometric Cu2S.
This Cu2S is basically non-bonding because of its inability to form donor-acceptor bonds.
Although minute amount of CuxS are a prerequisite, an excess of this compound is detrimental to adhesion, as thick films are brittle and non-adherent to the brass substrate.