G. Poggi

A study of the de-alloying of 70Cu-30Ni commercial alloy in sulphide polluted and unpolluted sea water

Abstract The behaviour of 70Cu-30Ni commercial alloy in quiescent sulphide polluted and unpolluted sea water at 25°C was examined by free corrosion and electrochemical tests. In aerated sea water the presence of sulphides enhances the average corrosion rate in a range of concentrations (0–10 ppm) while promoting preferential copper dissolution. In de-aerated sea water, alloy corrosion behaviour is strictly linked to sulphide concentration. In low polluted sea water, the mean corrosion rate of the alloy increases and slightly selective copper dissolution takes place. In highly polluted sea water, the corrosion rate decreases while slightly selective nickel dissolution takes place.

Corrosion of Lead in Sea Water

AbstractThe mechanism of the corrosion of lead in sea water has been investigated in stationary and laminar flow conditions (from 0·3 to 3 m/min). Some experiments were carried out in NaCl and Na2SO4 solutions in order to discriminate more efficiently between the action of certain ions (Cl−, SO42−) that might affect the corrosion kinetics, while using the same environmental parameters (temperature, dissolved oxygen, fluid flow rate).These solutions all had the same anionic concentration and the same pH value as sea water. The primary lead passivation film consists of basic salts resulting from the simultaneous precipitation of various anions (OH−, Cl−, sO42−) together with Pb2+ ions. In particular, the non-conductive corrosion products forming the primary film leading to ‘mechanical’ passivation in sea water are Pb(OH)Cl and Pb3(OH)2(CO3)2 and, after 360 h immersion, they were found to be: Pb(OH)Cl, Pb3(OH)2(CO3)2, PbCO3,PbCl2, PbO, Pb2O3, and PbCl2. SOO42− ions do not inteifere with the lead passivation ...

The effect of change of pH on the inhibitory action of 3-(trimethoxysilyl)propanethiol-1 on corrosion behaviour of carbon steel in NaCl solutions

Abstract The inhibitory action of 3-(trimethoxysilyl)propanethiol-1 (TMSPT) on carbon steel corrosion in NaCl 3.5% solutions of different pH (2, 6 and 12) at 25°C and with an initial dissolved oxygen content of 6.5 ppm was examined. Different amounts of TMSPT (0.5 × 10 −3 , 1.1 × 10 −3 and 2.7 × 10 −3 mol l −1 ) were added to NaCl solutions. Electrochemical and weight loss tests show that the inhibitory action of TMSPT increases with increasing TMSPT concentration, and decreases with increasing exposure time, more strongly in solutions at pH 2 and 12 and weakly in solutions at pH 6. At pH 2 and 6 TMSPT acts as both an anodic and cathodic inhibitor, reaching an inhibiting power of 60% at its highest values; at pH 12, TMSPT mainly acts as a cathodic inhibitor, reaching a comparable inhibiting power.

A study of the corrosion products of aluminum brass formed in sodium sulfate solution in the presence of chlorides

Abstract The surface film forming on Al brass specimens immersed in stagnant Na2SO4 solutions containing chlorides at pH values 3.0–7.25 was examined by using chemical, electrochemical and X-ray techniques. In the absence of chlorides the surface film consists of oxides (CuO, Cu2O) and cupric basic sulfates Cu3(SO4)2.4H2O, stable in the whole range of pH; the surface film is quite homogeneous and no dezincification or localized corrosion occurs. In the presence of chlorides, the surface film consists also of cuprous chloride (CuCl) and of cupric [Cu(OH,Cl)2.2H2O] and aluminum oxychlorides [Al45O45(OH)45Cl] and aluminum oxides (Al(OH)3]. The weight of the corrosion products is a maximum in solutions containing 5 × 10−3 M NaCl at each pH value. In the most acidic solutions the surface film is physically and chemically extremely unhomogeneous, thus favouring the occurrence of dezincification or localized corrosion phenomena.

Effect of sulphides on corrosion of Cu–Ni–Fe–Mn alloy in sea water

Abstract The corrosion behaviour of Cu–30Ni–2Fe–2Mn commercial alloy (similar to C71640) in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated. The corrosion resistance was examined using free corrosion and electrochemical tests and the surface film was characterised by chemical analysis and X-ray photoelectron spectroscopy. The different susceptibilities to corrosion were closely linked to the initial sulphide concentration; the accelerated attack occurring with an initial sulphide concentration of 4 ppm correlated with the amount of dissolved oxygen in solution and with the chemical composition of the corrosion layer.

Behaviour of Zinc in Sea Water in the Presence of Sulphides

AbstractThe effect of sulphides on the corrosion of zinc in artificial sea water has been studied over the pH range 6·5 to 8·6. A comparison of the weight loss and potential values of specimens in aerated and deaerated sea water, with or without the addition of sulphide, has shown that at pH values > 7·2 the presence of sulphides increases the corrosion, while at lower pH values it is partially inhibited. This is related to changes in the concentration of S2- ions in the solution. The corrosion products formed in the more corrosive solutions were shown to consist mainly of ZnS, which is believed to cause loss of adhesion of the corrosion products on the zinc surface, and thus to accelerate the corrosion.

Corrosion behaviour of aluminium-lithium alloy 8090-T81 in sea water

Abstract In order to test the applicability of 8090-T81 alloy in a marine environment, its corrosion behaviour was investigated in natural sea water at 25°C. Corrosion resistance was examined using free corrosion and electrochemical tests. The swface film was characterised by ir spectroscopy, X-ray microdijfractometry, and X-ray photoelectron spectroscopy. Microstructural heterogeneity increases susceptibility to localised attack, particularly to crevice corrosion, thus discouraging any marine use of this alloy in a non-protected form.

Gas chromatographic determination of carbonates and sulphides in the corrosion products of metals

A method has been developed for the gas chromatographic (GC) determination of sulphides in the corrosion products formed on the surface of metals immersed in sea water. The samples are treated at room temperature with 30% glycine solution, which dissolves the compounds of bivalent metals, but leaves unchanged other corrosion products and the metallic matrix. The evolved gases (carbon dioxide and hydrogen sulphide) are stripped with a flow of purified inert gas and trapped at liquid nitrogen temperature in the modified loop of a gas sampling valve. They are then thermally desorbed and injected into a gas chromatograph equipped with a Porapak Q column and a thermal conductivity detector.The method permits the simultaneous determination of CO2 and H2S and the measurement of the amounts of carbonates, oxycarbonates and sulphides in the corrosion layers. The detection limit is about 1 µg of H2S (with a precision of ±15%). The GC method is therefore about ten times more sensitive than the spectrophotometric method using methylene blue.The performance of different methods was evaluated by analysis of the corrosion products of copper and iron specimens subjected to corrosion in surface and deep (200 m) sea water.

Analysis of admiralty brass corrosion products in sea water and brackish water

A method was developed for the separation and analysis of corrosion products formed on admiralty brass surfaces immersed in sea water at 40 °C and pH 8.2. This method is based on the selective dissolution of various oxidation compounds with suitable solvents (i.e., that dissolve the metal matrix to only a negligible extent). These analyses can be performed in oxidation films of more than 10 nm thickness. The following solvents were used: (1) methanol to dissolve Na+, Cu2+ and Zn2+ chlorides and sulphates; (2) glycine to dissolve bivalent metal compounds—Cu2+ and Zn2+ oxides, oxysulphates, oxycarbonates; and (3) ammonia solution to dissolve Cu+ compounds.Reasonable agreement between the results of X-ray analyses and chemical analyses was observed only for copper and zinc compounds, which are the main constituents of the corrosion products. The presence of tin compounds in the corrosion products was observed with chemical analyses, which yielded quantitative results, but was not observed with X-ray diffractometric analyses. The chemical methods can therefore either integrate the results obtained with other methods or be complementary to them.

Corrosion inhibitive mechanism of silane coupling agent 3-(trimethoxysilyl)propanethiol-(1) for mild steel in sodium chloride solutions

Abstract The corrosion behaviour of mild steel in 3·5%NaCl solutions at pH 6 with initial dissolved oxygen contents of 6·5 ppm, containing 0·5, 1·1, or 2·7 mmol L−1 additions of the silane coupling agent 3-(trimethoxysilyl)propanethiol-(1), has been studied at 25°C. Electrochemical polarisation tests, weight loss measurements, and surface analyses of the corrosion layers were carried out. It was found that the coupling agent, which is known to be an adhesion promoter, acts by inhibiting anodic and cathodic processes, providing reductions in corrosion rate of up to 60%.