G. Brunoro

On the protective action of 1,2,3-benzotriazole derivative films against copper corrosion

The inhibiting effects of 1,2,3-benzotriazole (BTA), 5-methyl-BTA (Cl-BTA), 5-butyl-BTA (C4-BTA), 5-hexyl-BTA (C6-BTA) and 5-dodecyl-BTA (C12-BTA) films on the corrosion of copper in 3.5% NaCl (pH = 7 and 2.5) and 0. 1 m NaClO4 (pH = 7) were evaluated from polarization curves and EIS spectra. The characteristics of the inhibitor films were investigated by means of wetting tests and XPS analysis. The tested compounds (almost insoluble C12-BTA excepted) produce films able to inhibit the oxygen reduction process depending on the alkyl chain length, but only C6-BTA film succeeds in hindering the copper oxidation reaction, even in acid NaCl. The protective action expecially exerted by the C6-BTA film should be related to the hydrophobic effect of the alkyl chain, rather than to an electron releasing inductive stabilisation effect.

The influence of the chromium content on the inhibitive efficiency of some organic compounds

The inhibitive action of some series of organic compounds against the corrosion of four steels, with increasing Cr content, has been studied. The examined steels were: a low carbon steel, AISI 430. ELI 82 and ELI 84 superferritic steels. The composition of the two last steels was very similar to that of the ferritic phase of duplex steels. The organic compounds, tested in 4 N HCl solutions at 60°C, were: N-containing compounds—2,2′-biquinoline, n-dodecylpyridinium chloride, n-dodecylquinolinium bromide, n-dodecyltrimethylammonium bromide; HS-containing compounds—2 mercaptopyrimidine, 2 mercaptobenzimidazole, n-dibutylthiourea, phenylthiourea; compounds with multiple bonds—1-octyn-3-ol, 1-iodo-1-butyn-3-methyl-3-ol, propargyl alcohol, propargylamine, trans-cinnamaldehyde. Anodic and cathodic polarization curves have been recorded with a scanning rate of 1 mV s−1. The electrochemical results have been confirmed by some series of weight loss determinations. The results showed that the N-containing compounds exerted the same inhibitive effect on all the steels. The inhibitors containing multiple bonds reduced satisfactorily the corrosion of carbon steel and AISI 430, but they were either not efficient or stimulated the corrosion of superferritic steels. The HS-containing compounds usually showed a good inhibition on the superferritic steels; their inhibitive efficiency decreased on carbon steel and approached zero on AISI 430.

Influence of the alkyl chain on the protective effects of 1,2,3-benzotriazole towards copper corrosion. Part I : inhibition of the anodic and cathodic reactions

Abstract 1,2,3-Benzotriazole (BTAH) and some of its 5-alkyl-derivatives (methyl-, butyl-, hexyl-, octyl-, dodecyl-) were tested by using different electrochemical techniques in order to investigate the influence exerted by the aliphatic chain length on the inhibiting action of the base molecule towards OFHC copper corrosion in acidic sulphate and saline solutions. The polarization curves, recorded after a 3 h immersion in acidic sulphate solution, showed that: • more than 1 μmole l -1 of the additives had to be in the solution to reduce the copper corrosion rate; • the BTAH inhibiting e.ciency increased with the length of the side alkyl chain up to six carbon atoms; • chiefly, the action of the anodic inhibitor of the base molecule is strengthened. The hexyl derivative also exhibited a good e.cacy in acidic chloride solution. 1999 Elsevier Science Ltd. All rights reserved.

Organic films for protection of copper and bronze against acid rain corrosion

In this paper, the anticorrosive effects of surface films formed on copper and bronzes by different organic inhibitors (mainly benzotriazole derivatives) are evaluated. Several alloys, nominally similar in composition to ancient artistic bronzes, were studied in comparison with copper. The protective efficiency of the organic coatings was tested by electrochemical ac and dc measurements performed both in acid and neutral rain. The experimental data show that benzotriazole derivatives with a long aliphatic chain form thin and very protective films on copper. The presence of the alloying elements (e.g. Sn, Zn, Pb) and multiphasic structures decrease the organic film performances. Nevertheless, among the compounds used, the most efficient, 5-octyl-1,2,3-benzotriazole (C8), seems to be a promising coating in the bronze conservation field.

Influence of the alkyl chain on the protective effects of 1,2,3-benzotriazole towards copper corrosion. Part ii: formation and characterization of the protective films

Abstract EIS measurements show that thicker, less defective, more protective and persistent surface films of BTAH alkyl-derivatives can be built up on OFHC copper by increasing the side chain length (up to six CH2 units) or the additive amount in the solution. At the same time, the process of film formation becomes more rapid. In the sulphate solution, the films are less defective and more resistent than in the chloride one, in which only the higher homologues are efficient. In the case of 10−3–10−2 M BTAH containing solutions, the film thicknesses calculated by EIS spectra are not too far from those derived by QCM measurements. Moreover, these results support an almost flat orientation of the BTAH molecule on the copper surface. Although it is difficult to perform such a comparison in the case of C4-BTAH or C6-BTAH, nevertheless a likely agreement between EIS and QCM data of the film thicknesses may be determined, if low dielectric constant (er) values are taken into account.

Corrosion and corrosion inhibition of alumina particulate/aluminium alloys metal matrix composites in neutral chloride solutions

A study of the corrosion behaviour and corrosion inhibition of AA 6061 and AA 2014 metal matrix composites (MMCs) reinforced with alumina particles, during exposures to 0.1m NaCl solution is reported. Many tungsten and molybdenum-containing inorganic salts were tested as corrosion inhibitors, but only ammonium tetrathiotungstate afforded good inhibiting properties, particularly towards the AA 2014-based MMC. The corrosion behaviour of the composites in uninhibited or inhibited solutions was compared by different techniques to that exhibited by the corresponding matrices. The techniques adopted included weight loss measurements, electron probe microanalysis (EPMA), scanning electron microscopy (SEM), linear polarization resistance measurements, polarization curve recordings and current noise analysis. The analysis of the current fluctuations showed that different patterns of the time records were obtained during pit initiation, stable pitting and general corrosion. The power spectrum density plots exhibited f−α trends, with α values around 20dBdecade−1 when corrosion was mainly localized in pits, while values tending to zero were measured when general corrosion became dominant.

Surface-active substances as inhibitors of localized corrosion of the aluminium alloy AA 6351

Abstract Some surface-active substances were tested as corrosion inhibitors of the aluminium alloy AA 6351 in 0.01 M NaCl under both free corrosion conditions and anodic polarization. The substances used were sodium salts of N-dodecanoyl-N-methylglycine (NLS), dodecylsulphate (LS), N-dodecanoyl-N-methyltaurine (NLT) and dodecylbenzensulphonate (DBS). The tests performed to measure the efficiencies of these substances and to study their inhibition mechanism (gravimetric measurements, electron probe micro-analysis, potentiodynamic, potentiostatic and galvanostatic tests and electrochemical impedance spectroscopy) suggest that these substances act by adsorption on the aluminium surface oxide and displacement of adsorbed chloride ions. An attempt was made to explain the marked inhibiting properties shown by NLS.

Iron corrosion inhibition in hot 4 M HCl solution by t-cinnamaldehyde and its structure-related compounds

The inhibiting action of t-cinnamaldehyde (TCA) and some of its structure-related derivatives, against corrosion of ARMCO iron in 4 M HCl, has been studied, in the temperature range between 40 and 90°C. Other than TCA, α-chlorocinnamaldehyde (αCl), α-bromocinnamaldehyde (αBr), cinnamyl alcohol (OH) and cinnamnitrile (CN) have been considered. The average corrosion rates and the inhibiting efficiencies have been calculated by weight loss measurements at the end of 6-h tests; the dissolution kinetics have been determined on aliquots, by spectrophotometric analysis of the dissolved iron during the 6-h testing. The anodic and cathodic polarisation curves have been recorded in all the tested conditions, at the end of the 6-h tests with the purpose of obtaining some information on the action mechanisms of the inhibitors. CN and TCA are the best inhibitors, showing efficiencies >94% in the whole interval of temperature examined. CN seems to act mainly through a chemisorption process, whereas in the case of TCA the adsorption process is followed by some polymerisation-reduction reactions.

Corrosion evaluation of artificially aged 6 wt-% tin bronze

Abstract This study concerns the corrosion behaviour of wrought 94 wt-%Cu–6 wt-%Sn (B6) bronze, whose composition is similar to materials used for outdoor bronze artefacts. In order to investigate the influence of the composition and microstructure on bronze corrosion processes, electrochemical ac and dc measurements in synthetic acid rain and chloride solutions were performed on the B6 binary alloy in comparison with an as cast bronze having a different degree of purity. Moreover, to perform thin layer activation (TLA) measurements of thickness loss, a suitable radio nuclide 65Zn (t½ = 244 days) was produced on B6 specimens by a high energy proton beam. Artificial weathering experiments have been carried out by exposing activated and non-activated B6 specimens: to selected pollutants including NOx and SO2 at different concentrations to simulate urban and industrial atmospheres; in a cyclic salt spray cabinet to investigate the effects of marine environments; to basic (NH4)2SO4 solutions reproducing the aggressiveness of ammonia containing wet deposits. At the end of each test, the B6 corrosion rates obtained by weight loss determinations have been compared with those arising from the TLA method. Finally, the nature and microstructure of the surface oxidation products were investigated.

The corrosion behaviour of titanium diboride in neutral chloride solution

Abstract The corrosion of a dense TiB2 material (hot pressed with 1.5 wt.% Ni as sintering aid) in 3.5% NaCl aqueous solution was studied at T=25°C, T=45°C, T=65°C for exposure times up to 30 days. Results revealed by polarization curves, polarization resistance measurements and potentiostatic tests, coupled with microstructure analyses of the sample surface and chemical analyses of the solutions after the corrosion tests, allowed us to asses that TiB2 behaves like a passive metal at 25°C and 45°C as a rather protective hydrated titanium oxide film forms, the film protectivity is markedly reduced at 65°C, the corrosion attack is preferentially localized on a Ni-rich grain boundary phase, besides electrochemical corrosion, chemical corrosion also occurs, which plays an important role in the whole corrosion process as long as passive conditions are maintained.