Takenori Notoya

A study of the electrochemical formation of Cu(I)-BTA films on copper electrodes and the mechanism of copper corrosion inhibition in aqueous chloride/benzotriazole solutions

Cu electrode behaviour in Cl− and benzotriazole (H-BTA) containing acidic or neutral solutions was studied by voluntary, ammetry, photocurrent response, impedance measurements and chemical analysis of BTA consent in passive layers. It was shown that the rate of formation of Cu-BTA films in acidic solutions is controlled by the transport of CuCl2 ions through pores in the film at an early stage of film formation and later by the volume diffusion rate in the film. The photocurrent measurements have revealed that Cu-BTA formation is accompanied by the simultaneous deposition of a Cu2O underlayer. The main portion of the polarisation resistance of the passive layer was ascribed to the Cu2O underlayer. It is proposed that the role of the Cu-BTA overlayer is to stabilize the Cu2O underlayer and maintain its high resistance by preventing it from being doped by Cl− ions resulting in the formation of solid CuCl on tope of the Cu2O.

A near-infrared FT-Raman (SERS) and electrochemical study of the synergistic effect of 1-[(1′,2′-dicarboxy)ethyl]-benzotriazole and KI on the dissolution of copper in aerated sulfuric acid

The adsorption on copper in aerated 0.5 m sulphuric acid (30°C) of 1-[(1′,2′-dicarboxy)ethyl]-benzotriazole (BTM) has been investigated by means of surface enhanced Raman scattering (SERS) techniques. The inhibition efficiency in aerated acid increased with increasing BTM concentration to a maximum (52%) at the 1 × 10–3 m level. Benzotriazole (BTAH) was found to be about 20% more efficient as an inhibitor for copper corrosion under the same conditions. BTM (1 × 10–3 m) showed increased inhibition with increasing pH reaching a maximum value of 78.3% at pH 8. Polarization studies showed that BTM suppressed both the cathodic and anodic corrosion reactions. The SERS studies suggest that, like BTAH, BTM inhibits copper corrosion by adsorption through the azole nitrogen. This study also showed that the performance of BTM can be significantly improved by adding KI. SERS indicates that the iodide ions displace the protonated BTM on the copper surface and this is followed by an overlayer of protonated BTM molecules.

The corrosion and polarization behaviour of copper in domestic water in the presence of Ca, Mg and Na-salts of phytic acid

Abstract Phytic acid has been proposed as an inhibitor of copper corrosion in potable waters. This paper is concerned with the inhibiting action of the Ca, Mg and Na salt derivatives of phytic acid which have, to date, been little studied. A synthetic domestic water (SDW) (pH = 6.8) containing 36.6 mg 1 −1 HCO 3 − , 42.6 mg l −1 Cl −1 , 76.8 mg l −1 SO 4 2− and 100 mg l −1 NaClO was prepared and the corrosion and polarization behaviour of copper in solutions containing different levels of the three salts alone was evaluated by weight loss, potentiodynamic and potentiostatic techniques at 30 °C and in some cases at 65 °C. Uniform corrosion was found to occur in the SDW and this was inhibited by the Ca and Mg salts. These salts have a limited solubility (approx. 4 × 10 −4 M) and the relative inhibition efficiency of Ca and Mg phytate saturated solutions was calculated at 90.1 and 91.0%, respectively. The Na phytate was completely soluble and promoted the formation of a passive film. Maximum inhibition (65.3%) was obtained at the 1 × 10 −2 M level and this salt, unlike the other two, would not be a suitable candidate for the inhibition of copper corrosion in potable waters. Surface analysis indicated the formation of a Cu phytate film on top of the copper oxide(s) film.

Which Is Easier to Reduce, Cu2O or CuO ?

Chronopotentiometry (CP) using 0.1 M KCl as the electrolyte has been most frequently used for selective determination of cuprous and cupric oxides (Cu 2 O and CuO) formed on copper surfaces. However, there are conflicting views regarding the order of reduction of the oxides. This study was carried out to settle this problem. Differently prepared samples of Cu-duplex oxide films were partially reduced by means of CP with 0.1 M KCl and then submitted to X-ray diffractometry and also linear sweep voltammetry using a strongly alkaline electrolyte (6 M KOH + 1 M LiOH) in which reduction peaks of Cu 2 O and CuO could be obtained with good separation. The results clearly demonstrated that CuO was first reduced in 0.1 M KCl, followed by the reduction of Cu 2 O. However, the reductions of both oxides were found to occur simultaneously, to a greater or lesser extent, in 0.1 M KCl. It was also revealed that CuO was reduced to metal Cu in one step and that a partially reduced Cu-duplex oxide sample had an expected Cu|Cu 2 O|Cu sandwich structure.

Inhibitive effect of 4- and 5-carboxybenzotriazole oncopper corrosion in acidic sulphate and hydrogen sulphidesolutions

Abstract Commercial carboxybenzotriazole (CBT) usually consists of a mixture of the 4- and5-substituted isomers and as such has been used to inhibit copper corrosion. Little work has beendone on the inhibiting action of the individual compounds in different corrodents, and this paperdescribes their effect on the corrosion of copper in aerated acidic sulphate solution (pH=0 and 4),and in an aqueous sulphidising environment. Gravimetric and potentiodynamic polarisationmethods were employed in the acid corrosion studies, whilst coulometry was used to analyse thesurface products formed in the H 2 S containing solutions. Finally, surface enhancedRaman scattering (SERS) spectroscopy was used to examine the initial interaction of thecompounds with the copper surface in acidic solution. The coupon tests in aerated acidic sulphate showed that the inhibition efficiency of eachisomer was pH, concentration, and time dependent. At lower pH the 5-isomer is by far the betterinhibitor, and this behaviour continues at a higher pH where 4-CBT promotes corrosion. Theinhibition efficiency of the 5-isomer increased markedly with exposure time and this wasattributed to the increase in thickness of the underlying oxide layer. SERS revealed the presenceof a broad peak at approx. 250 cm −1 and this has been assigned to the Cu-Nstretching mode, resulting from adsorption of CBT onto the copper surface, and subsequentcoordination through a triazole nitrogen. The anti-tarnishing tests showed that whilst both isomersexhibited these properties, once again 5-CBT was the superior inhibitor.

A Mechanism for the Atmospheric Corrosion of Copper Determined by Voltammetry with a Strongly Alkaline Electrolyte

A recently developed voltammetric technique using a strongly alkaline electrolyte (6 M KOH + I M LiOH) was successfully applied to clarify a corrosion mechanism of copper under atmospheric conditions. In contrast to conventional potentiometric methods with neutral or weak alkaline electrolytes (e.g., 0.1 M KCl), the developed method could give qualitative and quantitative information about the corrosion products of copper, including oxides (i.e., Cu 2 O and CuO) and hydroxide [Cu(OH) 2 ]. In the presence of water under such atmospheric conditions, Cu(OH) 2 was the initial corrosion product formed on a copper surface. However, the surface Cu(OH) 2 layer did not grow much but dehydrated to become a layer of CuO. The thus-formed CuO layer grew until it became several molecules thick (∼2 nm). For further progress of corrosion, an inner Cu 2 O layer was generated by the proportionation reaction between the CuO layer and the base metal Cu. The inner Cu 2 O layer grew for the subsequent oxidation until the thickness reached a certain value (∼35 nm). For further oxidation, the top CuO layer grew again preferentially over the inner Cu 2 O laver.