G. Capobianco

Using Indole to Inhibit Copper Corrosion in Aerated 0.5 M Sulfuric Acid

Abstract Inhibition of copper corrosion in aerated 0.5 M sulfuric acid (H2SO4) solutions containing various concentrations of indole was studied in the temperature range from 25°C to 55°C using pot...

Study of inhibition mechanism and efficiency of indole-5-carboxylic acid on corrosion of copper in aerated 0,5M H2SO4

Abstract Inhibition of the corrosion of copper in aerated 0·5M sulphuric acid solutions containing various concentrations of indole-5-carboxylic acid was studied in the temperature range 25–55°C using potentiodynamic curves (Tafel lines), weight loss, analytical methods, and determination of double layer capacitance. The corrosion rates reveal good corrosion inhibition, up to 95% in the concentration range of 1 × 10-4–4 × 10-3M. Tafel anodic slopes in inhibited acid solutions are considerably higher than those in uninhibited acid solutions. This points to a change in the corrosion mechanism of copper in the presence of indole-5-carboxylic acid. Under these conditions, copper could electro-oxidise primarily to Cu+ rather than to Cu2+, forming slightly soluble [Cu–(indole-5-carboxylic)n ]+(ads) complexes. Corrosion rates determined by the weight loss method in both the absence and presence of inhibitor are much higher (on average by a factor of about 6) than those obtained with the potentiodynamic method. This points to a limitation of the Tafel line extrapolation method in corrosion rate determination. The double layer capacitance–potential curves indicate considerable adsorption of the inhibitor over a wide potential range (-600 to +200 mV with regard to Ecorr ).

EDTA-Hydroxylamine Sulfate-Fe2+: An Efficient Corrosion Inhibitor System for an Industrial Crystallization Plant

Abstract Unexpected corrosion problems that arose in a crystallization plant with evaporators made entirely of type 316L (UNS S31603) stainless steel (SS) were solved using a corrosion inhibitor system of ethylenediaminetetraacetic acid (EDTA)-hydroxylamine sulfate (Sl)-iron anions (Fe2+). An experimental statistical plan reduced the number of experiments needed to optimize the concentration of EDTA-Sl-Fe2+. Moreover, the plan allowed more rapid and economical study of the action of each component in the inhibition mechanism. Statistical processing of the data collected from the potential-vs-time, anodic, and cathodic potentiodynamic measurements permitted estimations of the influence of each independent variable (EDTA, Sl, and Fe2+concentrations). Voltammetric, polarographic, anodic potentiodynamic curves, and Flade potential measurements helped further understanding of the inhibiting system.

New passivating pastes for stainless steel without nitric acid

Handled stainless steel (SS) structures often need accurate passivating treatments before use. Until now the most frequently used passivating pastes have been based on nitric (fluoridric) acid and, as a result, are responsible for consequent environmental problems. This work addresses the SS passivation quality of two low environmental impact pastes, based on peroximonosulfate (P2) or sodium perborate (P3). Tests were conducted on various materials using electrochemical tests (cyclic voltammetry, anodic potentiostatic transients, open-circuit potential (E) decay), Microscopic and Inductively Coupled Plasma (ICP) measurements. The results, when compared with those obtained on the same materials by using a conventional nitric acid paste (P1), indicate that the proposed pastes P2 and P3 are time stable, non toxic and as efficient as the P1 paste. Moreover, the protection of the tested SS can be further enhanced by adding small amounts of citric acid to, in particular, the P3 paste.

Corrosion Behaviour of Ni in Aprotic Solvents an Electrochemical, XPS and AFM Study

Electrochemical and X-ray photoelectron spectroscopic (X.P.S.) techniques have been used to study the passivation of nickel in 0.1 M H 2 SO 4 DMF and ACN solutions with different water content. Electrochemical results indicate the anodic formation of a thin, poor protective layer and the possibility of salt precipitation onto the metallic surface. A.R.X.P.S. results indicate that while in the anodic film formed in DMF, Ni(OH) 2 constitute the superficial component under which a discontinuous layer of NiO and NiSO 4 is present. Ni(OH) 2 and NiSO 4 are the more superficial constituents in the passivation layer formed in ACN, while NiO becomes prevalent in the underlying layers. A.F.M. images show that in both the solvents the sample surface is very dishomogeneous with flakes and fractures.