Copper Dissolution in Ammonia Solutions: Identification of the Mechanism at Low Overpotentials

Abstract

Corrosion of copper in ammonia solutions is significantly affected by a large number of parameters such as the concentration of ammonia, pH, temperature, concentration of Cu2+ , the presence/absence of dissolved oxygen, the chemical nature, and the concentration of the anion but also by selected corrosion products, in particular, Cu+ , various adsorbed intermediates, and finally passive films. In the present work we try to elucidate the corrosion of copper in a wide potential window [from −1.4 to 0 vs mercury/mercurous sulfate electrode (MSE)] and in a broad range of concentrations of various species (0.2–3.5 mol/L NH3 , 0–0.1 mol/L Cu2+ , pH 10–12.5). Then, we focus on the first peak occurring within −1.0 to −0.6 V vs MSE with the aim to explain the underlying mechanism. We show that the reaction order of the dissolution reaction with respect to ammonia is 2. We further show that using conventional electrochemical methods in combination with an optical method (scanning electron microscopy), a two-step (electrochemical-chemical) reaction yielding Cu2O is identified as the most likely passivation mechanism, consistent with previous assumptions by other authors. Finally, we confirm this mechanism by performing impedance analysis at various experimental conditions.

Kinetics of carbon steel dissolution in ammonium chloride solution containing sodium thiosulfate

“…The steel surface was polished as described above to confirm that the results are reproducible, and the electrochemistry and corrosion kinetics of the specimen is not affected. The methodology adopted in the present work for pretreatment of carbon steel specimen is also reported in the literature …”

“…The methodology adopted in the present work for pretreatment of carbon steel specimen is also reported in the literature. 26,28 Prior to each electrochemical experiment, open circuit potential (OCP) measurement was conducted for a period of 1 h. The anodic polarization was performed at a scan rate of 1 mV s −1 starting from OCP to +250 mV w.r.t. OCP.…”

Adsorption of Poly(vinylformamide-co-vinylamine) Polymers (PVFA-co-PVAm) on Copper

“…Iron and zinc are ignoble metals that readily undergo redox reactions in water. However, copper is a seminoble metal, but the dissolution processes can be accelerated by complex formation between copper metal ions and suitable chelating agents as known for ammonia solutions. , Furthermore, the complex formation of metal ions with PVAm has already been described. − In this work, the influence of the degree of hydrolysis of PVFA, concentration, pH, and redox and dissolution reactions on adsorption as well as the interactions between the polymers and the surface was studied for seminoble metal copper. Copper was used as a metal powder and a planar smooth surface.…”

Ammonia stripping in open‐recirculating cooling water systems

“…Ammonia is a concern when using MWW in cooling water systems , as concentration in MWW can range from 3 to 73 mg N/L , and the presence of ammonia can cause severe metal alloy corrosion, especially for copper and copper alloys. Ammonia can form soluble complexes with copper, thus enhancing corrosion rate . It has been recommended that if copper alloys are present in cooling systems, the ammonia concentration should not exceed 1.65 mg N/L .…”