D.P. Schweinsberg

Polyvinylpyrrolidone and polyethylenimine as inhibitors for the corrosion of a low carbon steel in phosphoric acid

Abstract Polarization and weight loss studies showed that both polyvinylpyrrolidonc and polyethylenimine are effective for the inhibition of low carbon steel over a wide concentration range of aqueous phosphoric acid (H3PO4) solutions. Both polymers retard the anodic and cathodic corrosion reactions with emphasis on the former. The results for uninhibited acid confirm the kinetic expression proposed by Mathur and Vasudevan.

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.

SERS study of the interaction of thiourea with a copper electrode in sulphuric acid solution

The electrochemical interaction of thiourea with a copper electrode in sulphuric acid solution was investigated using Fourier transform Raman and in situ surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of thiourea at a copper electrode were obtained in solutions containing greater than 5 ppm thiourea; the spectra obtained were consistent with adsorption of the molecule on the copper electrode via the sulphur atom. The SERS spectra provide evidence of complex formation involving thiourea and sulphate species at the electrode surface.

Inhibitive action of the octyl esters of 4- and 5-carboxybenzotriazole for copper corrosion in sulphate solutions

Abstract The inhibitive action of a mixture of the octyl esters of 4- and 5-carboxybenzotriazole (4-CBTAH-OE and 5-CBTAH-OE) for copper in aerated 0.5 M sulphate solution over a range of pH values (0–8) was investigated. Coupon tests showed that at pH∼0 the inhibition efficiency of the mixture was approximately 98% at the 1×10−4 M level. This is considerably higher than that for benzotriazole (BTAH) (∼50%) under similar conditions. At pH∼8 the inhibition efficiency is still appreciable (∼75%) indicating that the mixed esters (in contrast to BTAH) have practical application for the inhibition of copper corrosion over a relatively wide pH range. Over the pH range no hydrolysis of the esters was observed. Surface enhanced Raman scattering (SERS) indicated that the esters, like BTAH, inhibit copper corrosion at low pH by chemisorption of the protonated species (CBTAH+2-OE) on the metal through an azole nitrogen. The increased inhibition at low pH is attributed to van der Waals’ forces of attraction between adjacent octyl chains oriented away from the copper surface. SERS also suggest that at higher pH chemisorption is replaced by the deposition of a sterically hindered polymeric complex that, in contrast to BTAH, is not as protective as chemisorbed CBTAH+2-OE. Potentiodynamic polarisation also supports the changeover to a different protective mechanism as the pH is raised.

Computer simulation of the corrosion inhibition of copper in acidic solution by alkyl esters of 5-carboxybenzotriazole

A series of alkyl esters (methyl, butyl, hexyl, and octyl) synthesised from a mixture of 4- and 5-carboxybenzotriazole (4-CBTAH and 5-CBTAH) inhibited copper corrosion in aerated solution (pH � 0). Inhibition efficiency (IE%) of the protonated esters (CBTAH þ -R) increased with hydrocarbon chain length and this is attributed to chemisorption (through azole ring N) and increased physical adsorption as more methyl groups are introduced. A modelling package employing molecular mechanics and molecular dynamics has been used to simulate the docking of a single protonated species (5-CBTAH þ -R) onto a clean copper (1 1 0) surface. A decrease in potential energy was associated with the flattening of the ester ring system onto the surface and further decreases in energy were associated with the extension of the aliphatic chain onto the surface. The crude binding energy (Ebind) of each ester with the surface was estimated and this energy also increased regularly with carbon chain length. The study suggests that molecular modelling and calculation of Ebind of a single molecule on a specified metallic surface can be used to predict the inhibition performance of compounds whose structures change in a regular way. 2002 Elsevier Science Ltd. All rights reserved.

An electrochemical and sers study of the effect of 1-[N,N-bis-(hydroxyethyl)aminomethyl]-benzotriazole on the acid corrosion and dezincification of 60/40 brass

Abstract The effect of 1-[N,N-bis-(hydroxyethyl)aminomethyl]-benzotriazole (BTLY) on the corrosion and dezincification of a 60/40 brass in aqueous H 2 SO 4 at 30 °C has been investigated by means of solution analysis, potentiodynamic and surface enhanced Raman scattering (SERS) techniques. Overall inhibition (for copper and zinc dissolution) increased with increasing concentration to a maximum (63.1 %) at the 5 × 10 −4 M level. This was comparable to that observed for benzotriazole (BTAH) under the same conditions. Solution analysis indicates that BTLY is ineffective in preventing dezincification. Polarization studies show that BTLY acts initially to suppress the cathodic and anodic corrosion reactions. The SERS spectra suggest that the adsorption with copper in the brass occurs through nitrogen in the azole ring of the protonated molecule BTLYH.

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.

The effect of potential scan rate on the parameters used to synthesize anodic polarization curves

Abstract The anodic polarization behaviour of pure iron in near neutral 0.1 M sodium benzoate with and without 0.007 M Cl − at different potential scan rates has been studied. The suitability of a computerized curve matching routine for systems exhibiting the typical active-passive transition and subsequent film breakdown has been demonstrated. The effect of potential scan rate on the input parameters required to generate the anodic polarization curve was established and empirical linear relationships were derived. This leads to the prediction of curves at other scan rates and good matches between the predicted and experimental curves are obtained provided the scan rate is not too far outside the initial range chosen.

Studies on alkyl esters of carboxybenzotriazole as inhibitors for copper corrosion

A series of alkyl esters (methyl, butyl, hexyl, octyl) derived from carboxybenzotriazole (CBTAH) have been studied as inhibitors for copper. Coupon tests established that the inhibition efficiency (IE) is concentration, time and pH dependent. At pH � 0 the IEs of the octyl and hexyl esters are considerably higher than that for benzotriazole under similar conditions. As pH increases up to approximately 8 the IE of each ester is decreased, but is still sufficient for practical use. For the butyl and methyl esters an opposite trend was observed; IE increased with increased pH. In acidic sulphate solution (pH � 0) the IE was in the order: octyl > hexyl > butyl > methyl, whilst in the near-neutral solution (pH � 8) this order is reversed. It is proposed that the protonated species (CBTAH þ -R) is chemisorbed on the copper through an azole nitrogen and at low pH IE is determined by van der Waals’ forces of attraction between adjacent alkyl chains oriented away from the copper surface, which are increased with the length of the alkyl chain. On the contrary it is proposed that at high pH a polymeric complex is formed and steric hindrance acts to make the film less protective. Polarisation, EIS and SERS studies confirm these hypotheses. 2002 Elsevier Science Ltd. All rights reserved.