A. Zingales

Inhibition of copper corrosion by isatin in aerated 0.5 M H2SO4

The corrosion inhibition of commercial copper by means of isatin was studied in aerated 0.5 M H2SO4 in the temperature range 25–55 °C using weight-loss, potentiodynamic and spectrophotometric tests, and determination of double layer capacitance. Inhibition efficiencies up to 94% in the concentration range of 1×10−4–7.5×10−3 M of isatin were obtained. The corrosion rates estimated with weight-loss measurements were higher than those correspondingly determined with the potentiodynamic test, especially at higher concentrations of inhibitor. This is in accord with other researches that have pointed out the limitation of the Tafel line extrapolation method in the determination of corrosion rates. The kinetics of cuprous and cupric ion formation and UV–visible spectra support the formation hypothesis of a complex between copper and isatin. The adsorptive behaviour of isatin on copper 0.5 M H2SO4 was also investigated.

Acidity and reactivity of trifluoromethanesulfonic acid in liquid and solid acid catalysts

Abstract The acidic properties of CF 3 SO 3 H/SiO 2 acid catalysts have been investigated by the protonation of weak bases (B) (B+H + ⇌BH + ) and the proton-transfer process from (H + A − ) to (BH + A − ) has been analysed by a thermodynamic procedure used to account the variation of the activity coefficient terms of the species involved. Acid–base systems with different substituted pyridines as back-titrating agents of BH + (i.e. BH + →B) have also been studied and the changes observed in the acid–base interactions according to basicity of pyridines are discussed. The results in solid phase have been compared with those observed in concentrated aqueous solutions (i.e. CF 3 SO 3 H+H 2 O) where “acidity” and “protonating ability” have been distinguished as parameters of interest in the description of nonideal acid systems. Silica loaded with CF 3 SO 3 H, with H 2 SO 4 and with a mixture of both acids have been tested in acid catalysed reactions and their catalytic effectiveness has been explored towards substrates with high acid requirements for the conversion reagents–products. From the available observations in liquid and in solid phase, CF 3 SO 3 H has been proved to be a less effective acid catalyst than expected from the observed protonating ability of acidic medium. Strong interactions between ionic species and the involvement of ion-pairs in concentrated acid systems have been suggested.

Sigma Phase Intergranular Corrosion Effects in Austenitic Welds Containing Ferrite

Abstract It has been suggested that the sigma phase and its preliminary phases are responsible for intergranular corrosion of molybdenum-containing austenitic stainless steels in such environments ...

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 ).

Corrosion Inhibition of Copper in Aerated 0.5 M Sulfuric Acid by Indole-2-Carboxylic Acid

Abstract The inhibiting action of indole-2-carboxylic acid (C9H7NO2) on the corrosion of commercial copper in aerated 0.5 M sulfuric acid (H2SO4) has been investigated in the temperature range from 25°C to 55°C by weight loss, potentiodynamic and analytical tests, and the determination of double-layer capacitance. The results have revealed a good inhibitor efficiency, up to 98% in the concentration range from 1 × 10−4 M to 4 × 10−3 M. Indole-2-carboxylic acid has been found to act as a mixed inhibitor. The kinetics of Cu+ and Cu2+ formation that followed in 72 h of gravimetric testing shows that indole-2-carboxylic acid probably affects the corrosion reaction mechanism through complexes with cuprous ions. The corrosion rates determined through weight-loss measurements are much higher than those obtained with potentiodynamic tests. This is in accord with other researchers who have found limitations to the extrapolation of polarization curves (and to the theory of mixed potentials) in the determination of c...

Behaviour of the mild steel and aisi 316 l stainless steel in the venice lagoon environment

Abstract The problem related to the cyclic aerobic and anoxic exposition of marine constructions in Mild Steel (MS) and/or AISI 316L stainless steel (SS), immersed in the peculiar Venice Lagoon environment was studied. The influence of the annual macro fouling settlement on the corrosion behaviour of these metals was investigated by means of corrosion rates (CRs), electrochemical, crevice corrosion (CC) and tensile stress tests. Results indicate that the abnormal biofouling growth, the CC for SS and the hydrogen embrittlement can worsen the normal behaviour of these metals in marine constructions.

Inhibitive action of some dibenzofuran derivatives on corrosion of iron in sulphuric acid media

Abstract The inhibitive properties of Dibenzofuran (D.B.F.) and some derivatives (3-NH2-, 2-NH2-, 2,3-NH2-, 3-NHCOCH3-, 2-SH-, 3-SH-, 3-NO2) against the corrosion of iron in H2SO4 1N at 25°C and 50°C have been investigated. Experimental data of electrochemical, colorimetric and weight loss measurements are reported. The results show that these molecules act as quite effective inhibitors at 25°C. They do show instead not a same effectiveness at 50°C.