G. Trabanelli

Tetrazole derivatives as corrosion inhibitors for copper in chloride solutions

Abstract The inhibiting action of some tetrazole derivatives on the copper corrosion in chloride solutions has been studied. Experiments have been carried on OFHC copper in 0.1 M NaCl solutions with the following tetrazole derivatives at the 10 −3 M concentration: tetrazole (T), 5-mercapto-1-methyl-tetrazole (5Mc-1Me-T), 5-mercapto(Na salt)-1-methyl-tetrazole (5NaMc-1Me-T), 5-mercapto-1-acetic acid(Na salt)-tetrazole (5Mc-1Ac-T), 5-mercapto-1-phenyl-tetrazole (5Mc-1Ph-T), 5-phenyl-tetrazole (5Ph-T) and 5-amino-tetrazole (5NH 2 -T) in the range of pH from 4 to 8 and at temperatures of 40 and 80 °C. Some inhibitors have been studied from 10 −5 to 6 × 10 −3 M. Cathodic and anodic polarisation curves were recorded after 1 h of immersion. Polarisation resistances measurements have been made as a function of the time in the 300 h experiment. The weight loss measurements have confirmed the electrochemical trend. The prefilming action of some tetrazole derivatives has been evaluated. The interaction between the organic molecules and the metal surface has been studied by means of FTIR reflection spectra. All the inhibitors, except the 5Mc-1 Ac-T which stimulates the corrosion, show an inhibiting efficiency from 50 to 99%. In every case the inhibiting efficiency increases with increasing pH value. 5Mc-1Ph-T and 5Ph-T show the better protective characteristics.

A study on corrosion inhibitors for concrete application

Abstract The inhibiting behavior of many organic and inorganic substances against steel corrosion was evaluated in an alkaline chloride solution, constituted by a saturated calcium hydroxide solution containing 0.1 M chloride ions. Besides 0.05 M sodium nitrite (SN), among the tested substances, only 0.005 M 5-hexyl-benzotriazole (C6BTA), 0.05 M sodium β-glycerophosphate (GPH), and saturated dicyclohexylammonium nitrite (DCHAMN) were able to prevent pitting corrosion over 30-day exposures to the aggressive electrolyte. Moreover, very good results were obtained with steel specimens coated by DINITROL AV 30®, which is a commercial corrosion inhibitive filming product. Chloride-polluted mortars embedding steel rods were also prepared to assess the influence of the most promising inhibitors, added either as admixtures or as impregnation agents, under conditions closer to those experienced in concrete. The inhibiting efficiencies (IE) were tested by Electrochemical Impedance Spectroscopy (EIS). Good results were obtained with admixed tungstosilicic acid (TSAH), with GPH or DCHAMN penetrated from the outside or in the presence of DINITROL AV 30® coating.

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.

The inhibition of copper corrosion in 0.1 M NaCl under heat exchange conditions

Abstract The inhibiting effects of 5-methylbenzotriazole, 5-chlorobenzotriazole, 5- n -hexylbenzotriazole, 2,4-dimercaptopyrimidine and 2-amino-5-mercaptothiadiazole at 0.1 and 0.5 mM concentrations on the copper corrosion in 0.1 M NaCl solutions under heat exchange conditions ( ΔT = 60 ° C ) are examined. The inhibiting efficiency of the different additives is evaluated from anodic and cathodic polarization curves and from the polarization resistance values after 2 h. The variation of the corrosion rate of copper with time is followed through the measurement of the polarization resistance values for a period of 100 h. The influence of the inhibitors is evaluated by the changes of the polarization resistance values with time. All the tested inhibitors at 0.5 mM concentration show high inhibiting efficiency. Only at 0.1 mM concentration, an appreciable decrease of the inhibiting efficiency of the thiadiazole derivative is observed. The examined compounds can afford protection to an already corroded copper surface, blocking or at least reducing significantly the corrosion process. In all experimental conditions investigated 5- n -hexylbenzotriazole provides the best inhibition efficiency.

Study of corrosion inhibition of copper in 0.1 M NaCl using the EQCM technique

Abstract The inhibition of Cu corrosion in 0.1 M NaCl solution was studied using the EQCM technique. Some organic compounds, at 10 −3 M concentration, were tested as inhibitors. The inhibiting effect of these additives was evaluated by recording the anodic and cathodic polarization curves on Cu, electroplated on quartz crystals. At the same time the mass changes of the electrode, as a function of the potential, were recorded. The formation of the protective film during immersion in distilled water or 0.1 M NaCl solution containing the inhibitors was followed by variation of the EQCM frequency. The protective characteristics of these films were evaluated by the mass variations of the electrode immersed in 0.1 M NaCl solution and by the voltammograms recorded after 1 min or 5 h immersion in 0.1 M NaCl solution. FTIR reflection spectra were recorded on Cu sheets immersed for 1 or 60 min in NaCl solution in the presence of inhibitors. They showed a very rapid interaction between metal surface and organic molecule. The results obtained allow us to conclude that EQCM technique has a valuable part to play in the interpretation of corrosion and corrosion inhibition mechanisms.

Evaluation of Corrosion Inhibitors by Electrochemical Noise Analysis

The corrosion potential fluctuations of aluminum alloy AA 6351 electrodes in 0.5M chloride solutions were recorded both in the absence and in the presence of the following inhibitors: 2-mercaptopyrimidine, sodium molybdate, and sodium nitrate. The corresponding spectral density plots, calculated over a wide frequency range, are discussed in order to evaluate the possibility of finding the mechanism of action of the additives, by analyzing the electrochemical noise. As a reference, the polarization curves of the alloy in the various solutions are reported

Pitting and stress corrosion cracking resistance of friction stir welded AA 5083

The corrosion behaviour of friction stir welded (FSW) joints of AA 5083 has been compared to that of MIG welded joints. Pitting and stress corrosion cracking (SCC) resistance in 3.5% NaCl + 0.3 g/l H2O2 and in EXCO (4 M KCl + 0.5 M KNO3 + 0.1 M HNO3) solutions has been determined at 25°C. SCC susceptibility was evaluated by slow strain rate tests (SSRT), at a strain rate of 1 × 10−6 s−1.Welds obtained by FSW technique showed a higher corrosion resistance in EXCO solution and a lower pitting tendency than the base alloy. Electrochemical measurements (corrosion potential measurements, polarization curves recording) evidenced that FSW weld was cathodic to base alloy. FSW joints were not susceptible to SCC in both test solutions, whereas MIG joints cracked in both solutions. Lochkorrosions- und Spannungsrisskorrosionswiderstand von ruhrreibgeschweistem Aluminium Al 5083 Das Korrosionsverhalten von ruhrreibgeschweisten Verbindungen aus AA 5083 wurde mit dem von MIG-geschweisten Verbindungen verglichen. Der Lochkorrosions- und Spannungsrisskorrosionswiderstand in einer Losung mit 3,5% NaCl + 0,3 H2O2 und in EXCO-Losung (4 M KCl + 0,5 M KNO3 + 0,1 M HNO3) wurde bei 25°C bestimmt. Die Spannungsrisskorrosionsempfindlichkeit wurde mittels Versuchen mit niedriger Dehngeschwindigkeit (Dehngeschwindigkeit 1 × 10−6 s−1) abgeschatzt. Die mittels Ruhrreibschweisung hergestellten Schweisungen zeigten einen hoheren Korrosionswiderstand in der EXCO-Losung und eine geringere Lochkorrosionsneigung als das Grundmetall. Die elektrochemischen Messungen (Korrosionspotential, Polarisationskurven) wiesen nach, dass die Ruhrreibschweisung sich gegenuber dem Grundmetall kathodisch verhielt. Die ruhrreibgeschweisten Verbindungen waren in beiden Pruflosungen nicht gegenuber Spannungsrisskorrosion empfindlich, wahrend die MIG-Verbindungen in beiden Losungen gebrochen sind.

Corrosion inhibition of steel in chloride-containing alkaline solutions

Some organic inhibitors of steel corrosion in saturated calcium hydroxide solutions containing 0.1 M chlorides were investigated to elucidate their interactions with the steel surface. The compounds studied were dicyclohexylammonium nitrite (DCHAMN), dicyclohexylamine (DCHA), sodium β-glycerophosphate (GPH) and 5-hexyl-benzotriazole (C6BTA). Sodium nitrite (SN) was also studied as a reference. The techniques applied were electrochemical impedance spectroscopy (EIS), polarization curves, cyclic voltammetry (CV) and Fourier transform infrared (FTIR) spectroscopy. FTIR spectra showed that DCHAMN, DCHA, GPH and C6BTA interact with the steel surface by chemisorption and some information about the mechanism also emerged. From DCHAMN solution, DCHA chemisorption is induced by slow salt hydrolysis. CV tests show that, among chemisorbed substances, only GPH avoids chloride penetration on cycling, most likely due to a quick chemisorption, while DCHAMN can only enlarge the passive potential range. Addition of SN also prevents chloride attack on cycling. Twenty days of immersion in inhibited solutions revealed that, besides SN, GPH and DCHAMN also form an impervious surface film on steel, which blocks any localized corrosion attack, whereas in the case of DCHA and C6BTA solutions, pitting corrosion is slowed down, but not avoided. DCHAMN exhibits the highest inhibiting efficiency at long immersion times, as a result of a synergetic inhibitive action which develops between nitrite and chemisorbed DCHA.

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.

The anodic dissolution of iron and the behaviour of some corrosion inhibitors investigated by the potentiodynamic method

The influence of the anion, of oxygen and of some corrosion inhibitors on the shape of the anodic polarization curve of iron has been investigated by the potentiodynamic method, under controlled conditions. For samples annealed in hydrogen atmosphere in N HClO4 the anodic polarization curve shows two distinct slopes, 60 mV at low current densities and of 30 mV at higher current densities. In N H2SO4 the slopes are respectively of 70 mV and 40 mV. A single slope of 60 mV is obtained in HCl solution. A comparison of these results is made with those obtained by other authors by the transient method. The small influence of iodide ions on the polarization curves obtained in the presence of phenylthiourea seems to demonstrate that this compound is adsorbed in molecular rather than ionic form. As expected, the inhibiting power of polybutanimine is increased by the presence of iodide ions.