Avoiding crevice corrosion by laser surface treatment

The present work shows that laser surface alloying of the creviced area on Al 7175-T7351 with chromium can avoid crevice corrosion. Corrosion takes places outside the crevice in conditions where the ratio of anodic area to cathodic area is favourable to minimize corrosion. As laser surface processing is adequate for treating small areas there is an enormous potential in this technology.     

The role of some organic anions in promoting or inhibiting the corrosion of zinc

The corrosion behaviour of zinc in solutions of the sodium salts of formate, acetate, propionate, citrate, tartrate, oxalate or benzoate anions was studied by determining the steady state potentials. The first five anions behave unifunctionally, promoting the corrosion of zinc. The extent to which corrosion is promoted depends on the type, the concentration and the dissociation constants of the corresponding acids. The oxalate ion behaves bifunctionally, promoting corrosion of zinc at high dilutions and inhibiting it at higher concentrations. The benzoate ion shifts the steady state potential of zinc in the noble direction, indicating the occurrence of corrosion inhibition.Chloride ions destroy the passive film formed on a zinc electrode previously equilibrated in solutions of benzoate anions. The concentration C_inh of the inhibitive anion required to prevent the corroding action of the aggressive anion at a concentration C_agg can be obtained from the relation log C_inh = A + n log C_agg where A is a constant and n is approximately the ratio of the ionic charges of the inhibitive and aggressive anions.     

Fabrication of corrosion inhibiting microcapsules functional coating and their high-efficiency corrosion resistance

<正>Benzotriazole (BTA) was loaded into calcium carbonate microsphere shell by self-assembly method and a new type of high-efficiency corrosion inhibiting microcapsules(CIMs) were fabricated,which were added and dispersed into epoxy resin coating to obtain a new corrosion resistance functional coating.The corrosion inhibition effect of benzotriazole on aluminum alloy matrix was verified by polarization curve test.The effectiveness of the CIMs and their loading capacity on inhibitor were eva...     

Influence of bacteria on film formation inhibiting corrosion

Mild steel coupons were incubated separately in two bacterial cultures namely Pseudomonas flava and Pseudomonas stutzeri. A significant reduction in the corrosion rate was observed in presence of P. flava. With a view to understand the mechanisms of microbially influenced corrosion/corrosion inhibition, various electrochemical and biological experiments such as weight change measurements and electrochemical impedance spectroscopy (EIS) measurements were made. The exposed surfaces were examined using scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX). The scraped surface film was also examined using FT-IR (Fourier transform infra red) spectroscopy. The results suggest that P. flava have enhancing effect on corrosion inhibitive properties of phosphate film.     

The inhibiting effect of underpotential metal deposits on iron corrosion

The polarization behaviour of iron in perchlorate, chloride and sulphate base electrolytes at pH values ranging from 0.3 ≤ pH ≤ 3.5 was found to be changed drastically by the addition of small amounts of the heavy metal ions Me^z+ = Pb²⁺, Tl⁺ to the electrolyte solutions. At potentials positive to the corresponding Me/Me^z+-electrode a strong inhibition of the active iron dissolution process as well as the charge transfer controlled hydrogen evolution was observed. This effect can be explained by an underpotential deposition of Me^z+ leading to a complete coverage of Me-adsorbate on the iron surface. In deaerated solution an inhibition factor of 98% can be obtained, whereas in aerated solutions especially under rotating conditions the corrosion rate was not decreased. In the latter case the corrosion process is dominantly determined by the limiting diffusion controlled oxygen reduction reaction which was found to be not markedly inhibited by the metal adsorbates. In acid chloride solutions a competetive adsorption of Cl^? must be taken into account.     

Environmental corrosion resistance of porous TiAl intermetallic compounds

Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic compound was investigated. The kinetic equation for the cyclic oxidation of porous TiAl alloy at 600 ℃ is determined to be Δm2=1.08×10-5t. After total oxidation of 140 h, porous TiAl intermetallic compound shows more stability of pore structure and the mass gain of TiAl alloy is 0.042 g/m2, which is only 10.6% that of porous 316L stainless steel. The kinetic equation for the cyclic corrosion behavior of porous TiAl alloy in hydrochloric acid with pH=2 at 90 ℃ is determined to be Δm2=5.41×10-5t-2.08×10-4. After 50 h exposure, the mass loss of TiAl alloy is 0.049 g/m2, which is only 14.8% and 5.57% that of porous Ti and stainless steel, respectively. The kinetic equation in hydrochloric acid with pH=3 is determined to be Δm2=2.63×10-6t-3.72×10-6.     

Theoretical evaluation of corrosion inhibition performance of imidazoline compounds with different hydrophilic groups

Corrosion inhibition performance of four 1-R-2-undecyl-imidazoline compounds (RCH₂COOH (A), CH₂CH₂OH (B), CH₂CH₂NH₂ (C) and H (D)) for carbon steel was evaluated by quantum chemistry and molecular mechanics methods. Results indicated that the hydrophilic groups (R) have remarkable influence on molecular reactivity, binding strength between self-assembled monolayer (SAM) and Fe surface, and compactness of the inhibitor SAM. The inhibition efficiency evaluated via theoretical methods was well accorded with reported experimental ones, following the same order as A > B > C > D. This research might provide a theoretical inhibition performance evaluation approach for homologous inhibitors.     

Steric hindrance as a rate controlling step in stress corrosion cracking

The effect of steric hindrance in the stress corrosion cracking (SCC) of Ag-15Pd (a/o) in AgI forming solutions was studied at room temperature. The solutions used were 1 M KI at a potential higher than that of AgI formation, and iodine dissolved in different n-alcohols. It was found that Ag-15Pd (a/o) is susceptible to intergranular stress corrosion cracking in those solutions. The SCC susceptibility measured as percentage of elongation to rupture and crack propagation rate is related to the size of the active species. While in KI aqueous solutions, as well as in iodine saturated benzene or iodine saturated toluene, the rate controlling step (RCS) was the reaction at the tip of the crack, in alcoholic-iodine solutions, the diffusion rate of the iodine containing molecules became the RCS.     

Bioorganic compounds as copper corrosion inhibitors in hydrocarbon media

The corrosion protection of copper by four bioorganic compounds; adenine, purine, cysteine and histidine, in hydrocarbon media has been examined by in situ ellipsometry, atom absorption spectroscopy and a standard corrosion test. Adenine and purine were found to irreversibly bind to the copper surface. The amount of dissolved copper was severely lowered and the copper surface appeared unaffected. It was concluded that adenine and purine exhibited a surface passivating effect, whereas the effect of cysteine and histidine was significantly lower. The influence on oxidation stability of the medium by addition of the compounds was examined and found to be minor.     

Effect of the molecular structure of some quinones on their corrosion inhibiting action

The molecular characteristics obtained by quantum chemical self‐consistent field (SCF) calculations of a series of quinones are correlated with the experimentally determined inhibitor efficiency for mild steel corrosion in neutral aqueous medium. It was established that the decrease of the ionization potential and the increase of the dipole moment of the quinone molecules favor the higher protective effect. The electron density and the geometric molecular structure have also been computed and are discussed in view of the corrosion inhibition.     

镁合金结构全寿命过程腐蚀控制

针对镁合金结构全寿命过程的各个阶段,围绕热处理、表面处理、涂装、产品装配及使用过程一系列关键环节,提出了腐蚀控制的措施和建议,特别是将微弧氧化表面处理新技术应用到了镁合金的腐蚀防护,为镁合金结构使用寿命的提高提供重要保证。     

Inhibition of copper corrosion in chloride solutions by heterocyclic compounds

Following a research programme on copper corrosion inhibition in neutral aqueous solutions, the present paper deals with the results obtained with some heterocyclic organic compounds as copper corrosion inhibitors in 0.1 NaCl solutions. The results are compared with those obtained with 1,2,3-benzotriazole and 2-benzothiazolethiol. The inhibiting action of the compounds mentioned has been determined by measuring corrosion rates and by tracing polarization curves. The characteristics of the surface layers have been investigated by recording the photopotentials by a pulse technique. The oscillographic recording of the sign, amplitude and time-constant of the photopotentials has been obtained on electrodes in free corrosion conditions and during anodic and cathodic polarization. These measurements allow the determination of the semiconducting properties of the surface layers. Attentative is made to correlate the photopotentials data with the inhibiting efficiency of the compounds studied.     

Inhibition of pitting corrosion of AISI 304 by organic compounds

The influence of N-lauroylsarcosine, laurylaminedicarboxylic acid, Na-dodecylbenzene sulphonate and Na-laurylsulphate on the pitting corrosion of AISI 304 stainless steel has been studied in 0.1 N NaCl solutions, buffered in the pH range 2.2 to 7.5, at 50°C. The steel pitting potentials have been determined by potentiostatic measurements and by a scratching electrode technique. The potential value at which active pits could be repassivated has been identified. The pitting incubation times have been determined on the steel electrodes prepassivated for different times at 0.5 V/Ag/AgCl in buffer solutions in the absence or in the presence of inhibitors. The overall results confirmed the inhibiting effect of the mentioned substances against the intiation of pitting, just emphasized by the means of potentiodynamic tests. On the contrary, the examined compounds do not show any effect on the pitting propagation. Some more information on the mechanism of action of the mentioned inhibitors are obtained from the incubation time values: in order to explicate their action they must either find sufficiently stable oxide film or can contribute to the stabilization of the passive film during its formation.     

Unsteady state mass transfer coefficients controlling steel pipe corrosion under isothermal flow conditions

Corrosion tests of commercial steel pipe in aerated natural water under variable flow isothermal conditions were made by weight loss determinations over periods up to 210 days. The porosity, density, and the average thickness of the corrosion product layer were determined. Friction coefficients were evaluated through precise pressure drop measurements as a function of exposure time for the various flow rates (Reynolds number range 4000–25,000).The corrosion mechanism was analysed as a mass transfer operation by considering all the plausible unsteady state process characteristics, involving growth of corrosion product on the metal surface and change of surface roughness. The general mathematical model postulated from that analysis fitted the experimental data with acceptable precision. The model permitted, using corrosion data only, the prediction of values for the porosity and friction coefficient which were in good agreement with the experimental data. The average thickness of the damped turbulence layer for the smooth pipe was also calculated from the corrosion data, using the same model, and showed an excellent agreement with values estimated from usual hydrodynamic relationships.The effect of the surface roughness on the mass transfer coefficients in the damped turbulence layer, K_L, and in the corrosion product layer, K_s, were examined in detail. It was found that K_L controls the overall mass transfer process for the time range and flow rate range examined.     

Carbonyl compounds as corrosion inhibitors for mild steel in HCl solutions

The paper gives an account of the performance of a number of carbonyl compounds as corrosion inhibitors of mild steel in 1–6 N solutions of hydrochloric acid. Furfuraldehyde seems to be the best inhibitor of all the carbonyl compounds investigated. Activation energies in the presence and absence of inhibitors have been evaluated. In cathodic protection studies furfuraldehyde reduces the protective current density considerably. The difference effect is positive in the absence and presence of inhibitors. Galvanostatic polarization data indicate that all these compounds are predominantly cathodic inhibitors. These substances are more effective in preventing the corrosion of aluminium alloys in hydrochloric acid solutions than the corrosion of mild steel.     

Recent developments in corrosion inhibitors based on rare earth metal compounds

Abstract

Rare earth organic compounds can provide an environmentally safe and non-toxic alternative to chromates as corrosion inhibitors for some steel and aluminium applications. For steel lanthanum 4-hydroxy cinnamate offers corrosion protection and reduces the susceptibility to hydrogen embrittlement. Recent work has also indicated that it inhibits the corrosion of steel in environments containing high levels of carbon dioxide. For aluminium alloys, cerium diphenyl phosphate provides excellent corrosion inhibition in chloride environments, and reduces susceptibly to stress corrosion cracking. Furthermore, for both steel and aluminium alloys filiform corrosion can be suppressed when rare earth inhibitor compounds are added as pigments to polymer coatings. The levels of inhibition observed are thought to be due to synergistic effects between the rare earth and organic parts of these novel compounds, and are related to the various species that may be present in the complex chemical conditions that develop in solution close to a metal surface. This paper reviews some of the published research conducted by the group at Deakin University over recent years.     

Inhibition of acidic corrosion of pure aluminum by some organic compounds

Inhibition of the corrosion of aluminum (Al) in hydrochloric acid (HCl) by sulfonic acid (SA), sodium cumene sulfonate (SCS), and sodium alkyl sulfate (SAS) has been studied using weight-loss and potentiostatic polarization methods. The results drawn from the two techniques are comparable and exhibit small discrepancy. The inhibition action depends on the chemical structure and the concentration of the inhibitors, the concentration of the corrosive medium, and the temperature. The efficiency of inhibitors increases in the order: SAS < SCS < SA in the studied concentration range. Results for weight loss indicated inhibitor efficiency (I%) increased with increasing inhibitor concentration, reaching a maximum inhibiting power of 85.6% at its highest values. The inhibitor efficiency (I%) decreased as the concentration of HCl increases. For the tested additives, the increase in temperature resulted in decreasing of the inhibitor efficiency (I%) and decreasing in the degree of surface coverage (θ). These results were indicative of increased aluminum dissolution with increasing temperature. The degree of surface coverage (θ) increased linearly with the logarithm of the inhibitor concentration fitting a Temkin isotherm.     

The inhibition of copper corrosion by azole compounds in humid environments

The ability of azole compounds, benzotriazole (BTA), 2-undecylimidazole (UDI) and poly-N-vinylimidazole (PVI-1) to inhibit copper corrosion in humid environments is studied using Fourier transform infrared reflection-absorption spectroscopy (FT-IR RAS). The corrosion product of bare Cu is shown to be Cu₂O even when moisture is present. The appearance and intensity of its characteristic vibration frequency can be used to monitor corrosion. It is found that dissolution of the Cu substrate, caused by local anodic and cathodic sites set up on the surface, accelerates the degradation process of BTA, UDI and PVI-1. The degradation of UDI on Cu apparently follows the same mechanism in both dry and wet environments while the degradation of PVI-1 on Cu does not. The BTA film is a better corrosion inhibitor than UDI or PVI-1 in this environment although some corrosion is observed. It is concluded that the inhibition ability of an inhibitor compound depends on the stability of the compound in the environment.