Experimental insight into the chemical corrosion mechanism of copper with an oil-in-water emulsion solution

Abstract

Chemical corrosion mechanism of copper in an oil-in-water (O/W) emulsion is worthy of study since it would contribute to emulsion-lubrication in a metal-working process and for copper storage. The immersion experiments were carried out and the corrosion rates were measured using the weight-loss method. Surface morphology of the copper specimen was observed using a scanning electron microscope (SEM). The compositions of the corrosive residues were analyzed using an energy dispersive spectrometer (EDS) and an X-ray photoelectron spectrometer (XPS). It was found that the corrosion rate of copper in an emulsion linearly increases and the kinetics relationship could be deduced as D₁ = 2.66 × 10⁻³t^11.68 at room temperature (25 °C). After 1488 h of immersion time, the corrosion products on the copper surface were determined to be Cu₂O, CuO, Cu(OH)₂, CuCO₃ and Cu₂(OH)₂CuCO₃, which also changed the appearance of the emulsion. During adsorption, copper is more likely to coordinate with hydroxide, carboxylate or ester anions to generate copper compounds. The surfactants were consumed and the efficiency of emulsification characteristics was lost and finally, the O/W emulsion separated into two layers, which might hint the significance of introducing an inhibitor to protect the copper surfaces.