Influence of ultrasound on pitting corrosion and crevice corrosion of SUS304 stainless steel in chloride sodium aqueous solution

The change of polarization curves and surface morphologies of SUS304 stainless steel was investigated in 3.5 mass% NaCl solution with or without the application of ultrasound (US). As the result, both the pitting corrosion and the crevice corrosion were largely suppressed by the application of US. The reason is attributed to the decrease in the concentration of hydrogen and chloride ions in pits or in the crevice by removing the corrosion product and stirring the liquid there.     

Effect of Mo and Cu on stress corrosion cracking of ferritic stainless steel in chloride media

Stress corrosion cracking behaviour of ferritic stainless steels with copper and molybdenum additions in 42?wt-% boiling magnesium chloride at 143?±?1°C has been determined. The nature of the corrosion products was analysed by X-ray photoelectron spectroscopy (XPS). XPS results show that the presence of Fe(0), Cr(0) and Mo(0) unoxidised states on the crack tips of (copper+molybdenum) addition ferritic stainless steel cannot form the stable passive film and causes the further corrosion in the chloride solution. The addition of both copper and molybdenum to 19% Cr ferritic stainless steel causes stress corrosion cracking. The susceptibility to stress corrosion cracking increases with the growth of ε-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of ε-copper phases, then propagates to molybdenum atoms, and finally propagates to the other ε-copper precipitations perpendicular to the direction of maximum strain.     

Influence of flow on the corrosion inhibition of carbon steel by fatty amines in association with phosphonocarboxylic acid salts

This work was carried out to study the inhibition mechanism of a carbon steel in a 200 mg l⁻¹ NaCl solution by a non-toxic multi-component inhibitor used for water treatment in cooling circuits. The inhibitive formulation was composed of 50 mg l⁻¹ fatty amines associated with 200 mg l⁻¹ phosphonocarboxylic acid salts. Steady-state current-voltage curves, obtained with a rotating disc electrode, revealed that the properties of the protective layer were dependent on the electrode rotation rate and on the immersion time. The cathodic process of oxygen reduction was not modified in the presence of the inhibitive mixture. As expected, the current densities increased when the rotation rate was increased. In the anodic range, original behaviour was observed: the current densities decreased when the electrode rotation rate increased. The morphology and the chemical composition of the inhibitive layers allowed the electrochemical results to be explained. Two distinct surface areas were visualised on the metal surface and the ratio between the two zones was dependent on the flow conditions. This behaviour was attributed to a mechanical effect linked to centrifugal force. XPS analysis revealed that the formation of a chelate between the phosphonocarboxylic acid salt molecules and the iron oxide/hydroxide was enhanced by the increase of the electrode rotation rate.     

An infrared and Raman spectroscopy study of the corrosion products on carbon steel and weathering steel

Infrared and Raman spectroscopy are two analytical tools which have recently been applied to the study of corrosion products formed on metal surfaces. The two techniques are complementary and give structural information similar to that provided by X-ray and electron diffraction. However, they are unlike X-ray and electron diffraction in that they do not require crystalline solids to provide structural identification. Weathering steels are an important class of metals which form noncrystalline corrosion products. This report describes infrared and Raman spectra obtained from a weathering steel and compares the spectra to those obtained for carbon steel which had been exposed to the same environment.     

X-ray photoelectron spectroscopy study of the corrosion behaviour of galvanised steel implanted with rare earths

The present paper studies the effect of ion implantation of 2 × 10¹⁶ ions/cm² of Ce⁺ and 2 × 10¹⁶ ions/cm² of La⁺ at 150 keV on the corrosion behaviour of hot-dip galvanised steel. After implantation, galvanised steel was characterised by means of XPS previous to and following immersion in the medium. The results revealed incorporation of cerium and lanthanum on the surface as Ce₂O₃ and La₂O₃, respectively. Electrochemical impedance spectroscopy was carried out in order to evaluate its corrosion behaviour in 0.6 M NaCl during 1 month of immersion. The corrosion resistance was improved by an increase in the charge transfer resistance of the implanted specimens in the medium. This effect could be associated with changes in the morphology/microstructure of the corrosion products layer rather than in its composition variations.     

The inhibition activity of ascorbic acid towards corrosion of steel in alkaline media containing chloride ions

The activity of ascorbic acid towards steel corrosion in saturated Ca(OH)₂ solution containing chloride ions was investigated in this study. Concentration and time dependence of the protective properties of the passive film were acquired by electrochemical impedance spectroscopy. The best inhibitive performance, i.e. the longest pitting initiation time was obtained in the presence of 10⁻³ M ascorbic acid, while both lower and higher concentrations showed shortening of the pitting-free period. The overall behaviour of ascorbic acid was attributed to its ability to form chelates of various solubility having various metal/ligand ratios and oxidation states of the chelated iron. The assumption of ascorbic acid assisted reductive dissolution of the passive layer at higher inhibitor concentrations was confirmed by cyclic voltammetry and ATR FTIR spectroscopy. It is proposed that the overall inhibitive effect at lower concentrations is due to the formation of insoluble surface chelates and the effective blocking of the Cl⁻ adsorption at the surface of passive film. A pronounced inhibitive effect observed after the pitting had initiated was ascribed to the formation of a resistive film at the pitted area.     

Microstructure and pitting corrosion resistance of annealed duplex stainless steel

The transition from metastable to stable pitting was studied in 0.5 M NaCl water solution for two cast duplex stainless steels under different microstructural conditions achieved by annealing in the range from 900 °C to 1200 °C. The ensuing microstructural changes in heat treated steels were defined and correlated with established pitting potentials (E_p) and sites of corrosion damage initiation. The variations in E_p have been discussed in terms of secondary phases precipitation. The critical condition for pit stability was quantified and used to select an appropriate microstructural state, resulting in the higher potential at which stable pit growth is first observed.     

Influence of input power to vibrator and vibrator-to-specimen distance of ultrasound on pitting corrosion of SUS304 stainless steel in 3.5% chloride sodium aqueous solution

The pitting corrosion of SUSU304 steel can be suppressed by the application of a 19.5 kHz ultrasound (US) in 3.5% NaCl aqueous solution. At a constant vibrator-to-specimen distance of d = 76 mm equal to the wavelength, the suppression effect increased with the input power to vibrator and the largest effect was obtained at the power of I = 8. At constant input powers of I = 2 or 8, the suppression effect decreased with the increase in the vibrator-to-specimen distance, but the largest effect was obtained at d = 68 mm in each case of I = 2 and 8.     

Study of the correlation between pitting corrosion and the component ratio of the dual phase in duplex stainless steel welds

Three duplex stainless steel weldments were produced by changing the chromium element to study the correlation between the pitting corrosion characteristics and the component ratio of the dual phase. The pit morphologies showed that metastable pits were generated at a lower pitting resistance equivalent number (PREN) phase. The secondary austenite phases seemed to serve as a path for the corrosive environment regardless of the ferrite number (FN). There is some discrepancy between the measured values (pitting potential (E_p) through polarization test) and expected values (sequence ranked by PREN of weaker phase) in 1 mol l⁻¹ NaCl solution at 60 °C.     

Environmental factors affecting the corrosion behaviour of reinforcing steel. V. Role of chloride and sulphate ions in the corrosion of reinforcing steel in saturated Ca(OH)2 solutions

The corrosion behaviour of reinforcing steel in saturated naturally aerated Ca(OH)₂ solutions in absence and presence of different concentrations of NaCl, NH₄Cl, Na₂SO₄ and (NH₄)₂SO₄ is followed by measuring of the open circuit potential complemented with SEM and EDS investigation. These salts cause breakdown of passivity and initiation of pitting corrosion. The rates of oxide film thickening by OH⁻ ions and oxide film destruction by the aggressive ions follow a direct logarithm law and depend on the concentration and type of aggressive salts anions and cations. The values of the activation energies for oxide film thickening are calculated and discussed.     

In situ investigation of crevice corrosion on UNS S32101 duplex stainless steel in sodium chloride solution

The crevice corrosion of UNS S32101 in neutral 0.1 M NaCl solutions at room temperature was investigated directly by a facile method. Experimental results showed that both delayed and immediate crevice corrosion can be initiated. Morphology study indicated that the heaviest corrosion attack happened just below the passive/active boundary on the crevice wall. The relocation of the active dissolution regions during crevice corrosion was observed and explained by established theory. The mechanisms of the delayed and immediate types of crevice corrosion on UNS S32101 duplex stainless steel were discussed.     

Effects of solution heat-treatment and nitrogen in shielding gas on the resistance to pitting corrosion of hyper duplex stainless steel welds

The effects of solution heat-treatment and shielding gas on the pitting corrosion of hyper duplex stainless steel (HDSS) welds were investigated in highly concentrated chloride environments. The pitting resistance of a solution heat-treated HDSS after welding with an Ar shielding gas supplemented with N₂ was greatly increased due to the dissolution of Cr₂N in α-phase, which followed the diffusion of N atoms from the α-phase to the γ-phase and an increase of the γ-phase in the weld metal and heat affected zone. It was also attributed to a decrease of the pitting resistance equivalent number difference between the two phases.     

Mathematical and electro-chemical characterisation of the layer of corrosion products on carbon steel in various environments

The properties of the corrosion products for carbon steel were characterized using the data from 39 corrosion stations in varying environments (urban, rural, marine and marine-industrial) in the province of Las Palmas (The Canary Islands, Spain) using electro-chemical impedance spectroscopy and the gravimetric method via mathematical data modelling. The behaviour of the layer was analysed using a model which established a hyperbolic relation between the quotient of loss of weight (WL) and monthly accumulated weight loss (AM) suffered by the metal test-piece relative to time of exposure. It was found that as the WL/AM increases, the protective capacity of the layer also increases. From the data taken from the 39 stations with respect to degree of corrosivity, it was found that the corrosion products were more protective in urban than in other less aggressive environments at the end of one year's exposure. We also studied the protective capacity via electro-chemistry. The results were compared with the hyperbolic law and were found to concord completely.     

Effect of chloride ions on 316L stainless steel in cyclic cooling water

The effect of Cl^- on the 316L stainless steel in simulated cooling water has been studied using polarization curves, electrochemical impedance spectroscopy (EIS), Mott-Schottky plot and scanning electron microscopy (SEM) techniques. Cl^- concentrations vary from 200 to 900 mg/L. Results reveal that the corrosion resistance increases with the decrease of Cl^- concentration in simulated cooling water. The increase of Cl^-concentration leads to the shift of the corrosion potential towards the positive direction. Mott-Schottky curves show that in the passive film, Cr₂O₃ and FeO at the inner layer exhibit P-type but Fe₂O₃ and CrO₃ (CrO₄^2-) N-type semiconductive properties. The SEM/EDX data demonstrate that elements such as Fe, O, C, Si and Cl as well as the presence of calcium and aluminum are presented on the surface of the metal.     

Synergistic effect of sulfate-reducing bacteria and elastic stress on corrosion of X80 steel in soil solution

In this paper, the individual and simultaneous effects of stress and sulfate-reducing bacteria on corrosion of X80 steel were conducted by electrochemical impedance spectroscopy, scanning electron microscope and X-ray photoelectron spectroscopy. Both elastic stress and activity of SRB enhance corrosion of the steel and, furthermore, they have synergistic effects on corrosion behavior of the steel. The activities of SRB give rise to the initiation of pits, and the applied elastic stress keeps and promotes the growth of pits. The activities of SRB and the applied elastic stress induce tiny secondary corrosion pitting at the bottom of the primary pitting.     

Erosion resistance of CO2 corrosion scales formed on API P110 carbon steel

The erosion resistance of CO₂ corrosion scales formed on carbon steel was investigated in water–sand two-phase flow utilizing weight loss test, scanning electron microscopy, and X-ray diffraction. The effects of CO₂ partial pressure, stirring speed, test time, and grain size on the erosion resistance of the scales were analysed. Results show that several characteristics of CO₂ corrosion scales are key factors affecting erosion resistance. Cubic polynomials are used to fit the erosion rate data, and effectively evaluate the ability of CO₂ corrosion scales to resist erosion. An erosion mechanism, based on fluid dynamics and CO₂ corrosion scales characteristics, is discussed.     

A study on the localized corrosion of cobalt in bicarbonate solutions containing halide ions

The localized attack of cobalt in bicarbonate aqueous solutions containing halide ions was investigated using electrochemical techniques, scanning electron microscopy, UV-visible and Raman spectroscopies. Rotating disc and rotating ring-disc electrodes were used to determine the effect of bicarbonate concentration, solution pH, nature and concentration of the halide ions, convection and potential sweep rate on the corrosion processes. These parameters were found to play a key role on the localized attack induced by halide ions by influencing the production of a Co(HCO₃)₂ precipitate on the pit surface. Potentiostatically generated cobalt oxide films (CoO and Co₃O₄) were found to be efficient to reduce pitting corrosion of cobalt.     

Nano-pit corrosion of the tabs in aluminum electrolytic capacitor: Polarization characteristics of the tabs in ethyleneglycol-borate solution with chloride ions

To evaluate the corrosion behavior of the anode tab in aluminum electrolytic capacitor, we performed some electrochemical and morphology analysis using the polarization curves in conjunction with atomic force microscope (AFM), scanning electronic microscope (SEM) and optical microscope (OM). The results suggest that the current oscillation was found to be associated with nano-pit, which is defined as the rectangular pit (β) with a depth less than 55 nm and a width no more than 100 nm. Furthermore, elevation of Cl⁻ concentration widened the crevices caused by electrolytic tension, enlarged the nano-pit area, and accelerated the electrochemical reaction rate of the anode tab in ethyleneglycol-borate solution. These findings may have implications for the failure of aluminum electrolytic capacitor.     

Degradation mechanism of galvanized steel in wet-dry cyclic environment containing chloride ions

The wet-dry cyclic test of a galvanized steel (GI) and pure zinc (ZN), which simulates marine atmospheric environment, has been conducted to clarify the degradation mechanism of galvanized steel. The samples were exposed to alternate conditions of 1 h-immersion in a 0.05 M NaCl solution and 7 h-drying at 25 °C and 60%RH, and the corrosion was monitored for 10 days (30 cycles) using a two-electrode type probe. Simultaneously, the corrosion potential was measured every three cycles only during the immersed conditions. The reciprocal of polarization resistance R_p⁻¹ was taken as an index of the corrosion rate. Several sample plates of GI and ZN were exposed, together with the monitoring probes. They were removed from the test chamber at the end of 1st, 3rd, 9th, 18th, and 30th cycles of exposure and were analyzed for the corrosion products with XRD and laser Raman spectroscopy. Further, their cross sections were analyzed with FESEM-EDS. The FESEM photographs and elemental analysis of cross sections confirmed that the R_p⁻¹ value commences to decrease when the corrosion front reaches Zn-Fe alloy layers (boundary layers of zinc coating and steel substrate) due to localized nature of attack. A schematic model of degradation mechanism and the role of galvanic protection have been discussed.     

Effect of chloride ions on corrosion behaviour of austenitic nickel and nickel free stainless steels in phosphoric acid solutions

The effect of chloride ions' presence (0·005–1·0M NaCl) in phosphoric acid solutions (5, 40 and 75%) on the corrosion behaviour of three austenitic stainless steels (an experimental steel Fe–18Cr–12Mn–0·6N and two trade grades, Fe–18Cr–9Ni and Fe–14Cr–15Mn–0·2N) has been studied by potentiodynamic polarisation measurements. The surface examinations of the samples tested involved X-ray photoelectron spectroscopy as well as optical and scanning electron microscopy. It was established that chlorides added to phosphoric acid solutions deteriorate the general corrosion resistance, and under anodic polarisation, they provoke pitting corrosion. The composition of the stainless steels significantly influences its corrosion behaviour in the phosphoric acid solutions containing chloride ions. The replacement of nickel with manganese and nitrogen on top of lower chromium content has a strong negative effect on the corrosion resistance.