Ageing of the Rubber-Brass Bond

In due course, the formation of ZnO/Zn(OH)2 from the precipitation of Zn destroys the integrity of the Cu, S layer and debonding occurs [25]. Such processes are generally 

Brass plated steel cord that contains low levels of copper is not so sensitive to decohesion caused by moisture. Initial adhesion may be lower because of fewer copper inclusions, but a more coherent ZnO is formed which reduces the amount of Zn ions diffusing through the Cu S layer and so less ZnO/Zn(OH)2 is formed at the interface. Compounding with high levels of ZnO also helps to inhibit the dezincification process by reducing the diffusion rate of Zn ions to the cord surface. 

Tyre cords are liable to corrosion under wet and saline conditions by various routes, including dezincification and electrochemical reactions [26, 27]. The major reactions, determined by the effect on brass of a 3% NaCl solution, are the preferential diffusion of Zn ions from the bulk of the brass to the ZnO/Zn(OH)2 layer and the partial dissolution of copper ions with some ZnO. As the concentration of ZnO increases, a surface layer of Zn(OH)2 forms which is then slowly dissolved. 

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