Surface deposit effects in the kinetics of copper cementation by iron

Abstract

The nature of the cement copper deposit was shown to control the kinetic response of the cementation reaction under certain circumstances. In essence, the nature of the surface deposit determines the effective cathodic area and is controlled by a number of variables. What appeared to be a temperature region (0 to 35°C) where a surface reaction mechanism was rate controlling, ΔE _a ≊10 kcal per mole, was, in fact, a consequence of the variation of the area of the surface deposit with temperature. Further evidence of this phenomenon was demonstrated by the results of cementation experiments in an ultrasonic field, and by the results obtained from initial “strike” experiments. Also considered in this study was the effect of the initial cupric ion concentration and the back reaction kinetics. The basic conclusion reached from this investigation was that the cementation reaction rate is controlled by boundary layer diffusion processes at all temperatures and concentrations with an activation energy of approximately 5 kcal per mole. When surface deposit effects are neglected, interpretation of cementation rate data, as well as rate data of any heterogeneous reaction involving a solid phase, can often be misleading.