Shenhao Chen

The influence of hydrogen sulfide on corrosion of iron under different conditions

Abstract Hydrogen sulfide (H 2 S) can either accelerate or inhibit corrosion of iron under different experimental conditions. What H 2 S has done to both the anodic iron dissolution and cathodic hydrogen evolution, in most cases, is to have a strong acceleration effect, causing iron to be seriously corroded in acidic medium, but H 2 S can also have a strong inhibition on the iron corrosion under certain special conditions where H 2 S concentration is below 0.04 mmol dm −3 , pH value of electrolyte solution is within 3–5 and the immersion time of the clectrode is over 2 h. The inhibition effect of H 2 S on the iron corrosion is attributed to formation of ferrous sulfide (FeS) protective film on the electrode surface. Moreover, the structure and composition of the protective film is closely related to H 2 S concentration, pH of solutions and the immersion time of iron. Accordingly, the influence of the three factors on the inhibition effect is investigated in this paper by means of AC impedance technology together with the potentiostatic steady-state polarization. A probable reaction mechanism is proposed to interpret theoretically how H 2 S inhibits the corrosion of iron.

Impedance spectroscopic study of corrosion inhibition of copper by surfactants in the acidic solutions

The inhibitive action of the four surfactants, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate, sodium oleate and polyoxyethylene sorbitan monooleate (TWEEN-80), on the corrosion behavior of copper was investigated in aerated 0.5 mol dm(-3) H2SO4 solutions, by means of electrochemical impedance spectroscopy. These surfactants acted as the mixed-type inhibitors and lowered the corrosion reactions by blocking the copper surface through electrostatic adsorption or chemisorption. The inhibitor effectiveness increased with the exposure time to aggressive solutions, reached a maximum and then decreased, which implies the orientation change of adsorbed surfactant molecules on the surface. CTAB inhibited most effectively the copper corrosion among the four surfactants. The copper surface was determined to be positively charged in sulfuric acid solutions at the corrosion potential, which is unfavourable for electrostatic adsorption of cationic surfactant, CTAB. The reason why CTAB gave the highest inhibition efficiency was attributed to the synergistic effect between bromide anions and positive quaternary ammonium ions. C16H33N(CH3)(4)(+) ions may electrostatically adsorbed on the copper surface covered with primarily adsorbed bromide ions. On the basis of the variation of impedance behaviors of copper in the surfactant-containing solutions with the immersion time, the adsorption model of the surfactants on the copper surface was proposed

Investigation on some Schiff bases as HCl corrosioninhibitors for copper

The inhibiting action of some Schiff bases on the corrosion of copper inhydrocholoric has been studied. The Schiff bases N, N′-p-phenylen-bis (3-methoxy-salicylidenimine) (V-pph-V), N, N′-o-phenylen-bis (3-methoxy-salicylidenimine) (V-oph-V), and N′-histidine-3-methoxy-salicylidenimine (V-his) were synthesized by reacting3-methoxy-salicylaldehyde with aromatic amines and histidine. The inhibiting action of theseSchiff bases has been studied on the corrosion of copper in 5% HCl solution. The potentiostaticpolarization and AC impedance studies reveal that all the studied Schiff bases inhibit thecorrosion of copper in the solution and that the inhibiting efficiency increases with a decrease intemperature or an increase in concentration of the Schiff base. The Schiff base of V-pph-V at aconcentration of 10−3 mol⧸dm3 can give 99.4% inhibition efficiency at 20°C.

Corrosion of stainless steels in acid solutions with organic sulfur-containing compounds

Abstract The influence of the organic sulfur-containing compounds on the corrosion of ferrite and austenitic stainless steels in sulfuric acid was studied. The results showed that the anodic dissolution and self-corrosion of stainless steels were remarkably accelerated in solutions with a low amount of the organic sulfur-containing compounds (0.02 mmol/dm3). With an increase of the organic sulfur-containing compound concentration, more and more the organic sulfur-containing compound molecules adsorbed on the electrode surface and segregated the metal surface from the solution, which caused the decrease of the anodic dissolution and hydrogen evolution current of stainless steels. The anodic polarization behaviors of stainless steels were also changed with the various types of the organic sulfur-containing compounds and stainless steels.

A study of the passive films on chromium by capacitance measurement

Using capacitance measurement and Mott-Schottky analysis, the semiconducting properties of passive films formed on chromium within the passive potential range under different conditions were investigated. The study reveals a p-type behavior of the passive layers. Two semiconductive parameters, i.e., the acceptor density (N-A) and the flatband potential (E-FB), which are mainly related to composition and surface charges of the passive films, have been measured. The effect of film formation potential, passivation time, pH and composition of solutions on the parameters are discussed. N-A increases either with lowering film formation potentials or with prolonging passivation times. This is attributed to the transformation of a less hydrated oxide film into a more hydrated form. The changes of E-FB are discussed as a function of adsorptive anions and pH values of electrolyte solution

Adsorption behaviour of Schiff base and corrosion protection of resulting films to copper substrate

Self-assembled (SA) films of Schiff base were prepared on the copper surface. The corrosion protection abilities of SA films in chloride solution were evaluated using electrochemical impedance spectroscopy and polarization curves. A subsequent adsorption of 1-dodecanethiol on the original SA films of Schiff base improved significantly the protection ability to the copper substrate. The behavior of Schiff base adsorption on copper surface and subsequent adsorption of 1-dodecanethiol was probed by X-ray photoelectron spectroscopy. It was found that copper exists mainly in Cu(I) state in the SA films of Schiff base, and the thiol molecules subsequently adsorbed was bonded directly on copper surface rather than physisorbed on the previous SA films

An ac impedance study of the anodic dissolution of iron in sulfuric acid solutions containing hydrogen sulfide

Abstract The anodic dissolution of iron in sulfuric acid solutions with H 2 S was investigated by means of ac impedance and steady-state polarization curves. The results show that H 2 S can accelerate markedly both the anodic dissolution and cathodic hydrogen evolution in most cases, but it can also exhibit a strong inhibiting effect upon iron dissolution under certain special conditions. Usually, the Nyquist diagrams measured at lower positive potentials consist of two overlapping capacitive loops, one of which is a characteristic capacitive loop caused by the adsorption of H 2 S on the electrode surface. At higher positive potentials, the original characteristic low frequency capacitive loop disappears, and the complex plane impedance diagrams for the iron electrode consist of an inductive loop and a capacitive loop. Based on the impedance behaviour of iron in the presence of H 2 S, two reaction models were proposed to interpret its dissolution mechanism in acidic solutions with H 2 S.

Inhibition Effect of AC-Treated, Mixed Self-Assembled Film of Phenylthiourea and 1-Dodecanethiol on Copper Corrosion

A new method for preparing effective inhibition film on copper has been developed. Phenylthiourea was first adsorbed to a copper surface to form a self-assembled film. 1-Dodecanethiol was then self-assembled on the surface for subsequent modification. Finally, ac voltage was loaded on copper covered with the mixed film to further modify the film. After these procedures, an effective inhibition film was obtained as indicated by the low corrosion current density in polarization curves. High charge-transfer resistance in electrochemical impedance spectra reveals that the film hinders corrosion electrochemical reaction between the copper surface and NaCl solution. Film coverage on the copper surface is more than 99.0%, and inhibition efficiency is more than 97.2% in 0.5 mol dm(-3) NaCl solutions. The mixed films before and after ac treatment are stable in a wide region of potentials. X-ray photoelectron spectroscopy analysis reveals that the effect of ac treatment may associate with the formation of a new complex compound

Electrochemical sensing of glucose by carbon cloth-supported Co3O4/PbO2 core-shell nanorod arrays.

A novel electrochemical sensor for the detection of glucose was constructed based on the use of Co3O4/PbO2 core-shell nanorod arrays as electrocatalysts. In this paper the Co3O4/PbO2 core-shell nanorod arrays grow directly on a flexible carbon cloth substrate by the combination of hydrothermal synthesis and electrochemical deposition methods. The as-prepared hierarchical nanocomposites show the structural characteristics of nanowire core and nanoparticle shell. The carbon cloth-supported Co3O4/PbO2 nanorod array electrode exhibits higher sensitivity (460.3 μA mM(-1)cm(-2) in the range from 5 μM to 1.2mM) and lower detection limit (0.31 μM (S/N=3)) than the carbon cloth-supported Co3O4 nanowire array electrode. Both the three-dimensional network of carbon cloth substrate and the hierarchical nanostructure of binary Co3O4/PbO2 composites make such an electrode have high electrocatalytic activity towards the glucose oxidation. Due to the excellent sensitivity, repeatability and anti-interference ability, the carbon cloth-supported Co3O4/PbO2 nanorod arrays will be the promising materials for fabricating practical non-enzymatic glucose sensors.

Corrosion of Iron in Acid Solutions with Hydrogen Sulfide

Abstract The influence of pH and the concentration of hydrogen sulfide (H2S) on corrosion of iron in acid solutions was studied using a potentiostatic polarization method. The alternating current (AC) impedance technique also was used to characterize the active dissolution process of iron. Results showed the dissolution process was accelerated by H2S. The anodic dissolution current (ia) increased with pH and H2S concentration with reaction orders of about npH = nH2S = 0.25 when the ratio of H2S concentration and hydrogen ion (H3O+) concentration was 101.5. The Nyquist diagram corresponding to the active dissolution process in the Tafel range exhibited two capacitive loops in addition to the well-known, high-frequency capacitive loop. A mechanism was proposed to explain the results in which H2S chemisorbed first on the electrode surface and then catalyzed the anodic dissolution of iron in two discharging steps.