Corrosion inhibition of mild steel by polyhydric alcohol phosphate ester (PAPE) in natural sea water

Abstract

The corrosion inhibition of mild steel by polyhydric alcohol phosphate ester (PAPE) in natural sea water has been investigated by polarisation curves, electrochemical impedance spectroscopy (EIS) and surface analytical techniques. The results have shown that PAPE acts as a mixed type (anodic and cathodic) negative catalytic effect interface inhibitor and that the adsorption is of the Langmuir type. The inhibitor can adsorb immediately and compactly on the steel surface, the thickness of the film increasing with time. The adsorption behaviour involves the formation of complexes between the R1 functional group of the PAPE molecular structure and metal ions on the steel surface, such as Fe²⁺, Mg²⁺, Ca²⁺, etc.     

Inhibitive and bactericidal effects of natural naphthenates on steel corrosion in sea water

The inhibitive effects and interfacial tensions of solutions of natural naphthenates in the passivation of the steel surface in sea water were studied by electrochemical and stalagmometric methods. According to the data obtained, Ca²⁺, Ni²⁺, and Co²⁺ naphthenates suppress the anodic and cathodic polarization of steel. The biocidal effects of the naphthenates in sea and stratal waters were determined. It was found that treatment of sea water with calcium naphthenate protects steel equipment from both electrochemical and microbial corrosion. Original Russian Text ? A.M. Samedov, L.I. Alieva, V.M. Abbasov, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 4, pp. 427–431.     

Effect of cations on corrosion of zinc and carbon steel covered with chloride deposits under atmospheric conditions

The effect of sodium, calcium, and magnesium chlorides deposited on zinc and carbon steel surfaces was studied under atmospheric conditions. The cations strongly affected the corrosion rate of zinc, whereas they had a significantly lower impact on the corrosion of carbon steel. The corrosivity of cations of chloride salts for zinc increased in order of Mg²⁺ < Ca²⁺ < Na⁺. The higher corrosion resistance of zinc treated with calcium and magnesium chlorides was connected to prevention of formation of hydrozincite during zinc exposure in wet air. It was observed that zinc weight loss and the carbonate to simonkolleite ratio in corrosion products were correlating. The principal protective effect of bivalent cations can be seen in the decrease of pH of the surface electrolyte, which was caused by hydrolysis of such cations and subsequent formation of simonkolleite that blocked the cathodic sites.     

Synergistic or additive corrosion inhibition of mild steel by a mixture of HEDP and metasilicate at pH 7 and 11

Electrochemical measurements (steady‐state current‐voltage curves and AC impedance) were coupled with mass‐loss measurements, SEM examinations, and EDSX analyses to investigate the inhibition of corrosion of a carbon steel by a mixture of phosphonic acid HEDP (acid 1, hydroxyethylene, 1‐1 diphosphonic) and sodium metasilicate pentahydrate Na₂SiO₃. 5H₂O in an industrial hard water containing 3.10^?3 M Ca²⁺ ions. At pH 7, HEDP and Ca²⁺ act in a synergistic manner, by formation of a HEDP and calcium containing layer. Addition of silicate at this pH value, allows to reach an efficiency of 94% due to an additive inhibition effect. At pH 11, metasilicate, HEDP, and Ca²⁺ ions reinforce the passive layer in a synergistic way. The mixture (1.7 · 10^?5 M HEDP + 2.6 · 10^‐3 M SiO^2?₃) in the Ca²⁺ containing electrolyte is shown to be able to inhibit efficaciously the corrosion of iron at room temperature, considering uniform corrosion at pH 7 or pitting corrosion at pH 11.     

Über den Einfluß der Strömungsgeschwindigkeit und der NaCl-Konzentration auf die Sauerstoffkorrosion unlegierten Stahls in Wässern

Influence of flow velocity and sodium chloride concentration on the oxygen corrosion of unalloyed steels in water Corrosion of mild steel in aerated water normally leads to pitting, and to an enrichment of anions within the pits. Even HCO₃^? ions can support localized corrosion. The intensity of this is remarkably increased by chloride ions. In equilibrium water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂ protective rust layers are formed after about 500 hs exposure not depending on flow rate and salt concentration. These layers decrease the mean corrosion rate to about 0.1 mm/a, but do not prevent localized corrosion. Protective passive layers with extremely low corrosion rates are formed in flowing water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂. The minimum flow rate can be estimated for a 3/4 inch pipe to lie between 0.35 and 1.5 m/s. Investigations with water containing 40 ppm free CO₂ without Ca²⁺ at pH 4.7 and with NaHCO₃ (pH 7.2) show at low pH high corrosion rates – as expected –, and at pH 7.2 formation of protective layers with poor reproducibility in comparison with the situation in equilibrium water. Thus, Ca²⁺ ions support the protective properties of rust layers. HCO₃^? ions are necessary for the formation of protective layers because these are not formed in pure NaCl solutions.     

Evaluation of corrosion inhibitors for cooling water systems operating at high concentration cycles

The present work aimed at evaluating AISI 1020 carbon steel corrosion resistance of a 6:4:1:1 (MoO/HEDP/PO/Zn²⁺) inhibitor mixture present in a solution which simulates an industrial cooling water system operating at high concentration cycles (1050 ppm Cl⁻ and 450 ppm Ca²⁺). High concentration cycles are desirable, because system purge and treated water consumption are decreased. On the other hand, a high number of concentration cycles can increase the concentration of salts and dissolved impurities, causing corrosion, incrustations, and deposits inside the pipes, heat exchangers, and cooling towers. Thus, the chloride (Cl⁻) and calcium (Ca²⁺) ions aggressiveness was studied on the proposed inhibiting mixture, at the temperatures of 40 and 60 °C, through electrochemical techniques like open circuit potential measurements, anodic and cathodic polarization, and weight loss. The results showed that the inhibitor mixture conferred adequate protection to carbon steel in low concentrations, even in high aggressive media.     

Inhibiting the corrosion of stainless steel in phosphoric acid

The effect of Cu²⁺ and NO ₃ ⁻ ions on the stability of the passive state of a X18H10T type steel in phosphoric acid is investigated by constructing true curves of the anodic and cathodic processes. In a 3 M H₃PO₄ at 100°C, the steel is found to be in an unstable passive state. Copper(II)- and nitrate-ions transfer it into a steady passive state. Adding copper (II) ions to phosphoric acid accelerates the cathodic process and impedes the anodic dissolution in the active potential range. The steel passivation potential decreases under their action.     

Corrosion and Corrosion Inhibition of Reinforcing Steel: I. Immersed in Alkaline Solutions

Abstract

The electrochemical behaviour of reinforcing steel in stagnant alkaline solutions, especially calcium hydroxide, has been investigated. It was found that the oxidation processes that take place on steel are determined by the degree of surface oxidation of the sample and by dissolved oxygen, but not by the type of cation present.

In aerated solution, ferrosoferric oxide (Fe₃O₄) is the intermediate oxidation product on the steel surface while ferrous hydroxide is the intermediate product in de-aerated solution.

In pure alkaline solutions, the critical pH above which stable passivity occurs is 11·5. This value increases when the alkaline solution is contaminated with aggressive ions or when reinforcing steel having mill-scale on its surface is used. A linear relationship holds between the pH of the alkaline solution and the highest concentration of sodium chloride that can be tolerated (CC1-): pH = n logCcc^? + K where nand K are constants.

Calcium hydroxide solutions prepared fronl water of different local sources act differently towards steel. Thus, in saturated calcium hydroxide solution prepared from either distilled or tap water, the steel becomes passive. In the corresponding solution in mineral or sea water, the metal corrodes. On the other hand, mineral water becomes inhibitive when the pH is increased to 13. Sea water could not be tolerated by mere increase in pH.     

Anodic Behaviour of 17–7 Precipitation Hardening Stainless Steel in Acid Media

Abstract

The anodic behaviour of 17–7 precipitation hardening stainless steel in 0.5 M H₂SO₄ and 0.5 M H₂SO₄ + Cl^? solutions was investigated in detail. The coulometric areas of the two anodic peaks in the potentiodynamic curve in the chloride-free solution are dependent upon the duration of the free corrosion between the preliminary cathodic activation and the starting of the potentiodynamic scan. When the free corrosion time exceeds 6 minutes the peak at the more active potential disappears completely.

The influence of the free corrosion time was much less evident in the presence of chloride ions; in these conditions anodic currents were greater.

It was also established that the two anodic peaks correspond to the active-passive transitions relative to the two phases composing the steel: austenite and δ-ferrite. This was seen by potentiostatically etching the steel in the active dissolution ranges of both anodic peaks.

Finally it was shown, both micrographically and by comparing the anodic curves of pickled and polished specimens, that ordinary nitric–hydrofluoric pickling solutions selectively attack the austenite.     

Effects of NH4 +, Na+, and Mg2+ ions on the corrosion behavior of galvanized steel in wet–dry cyclic conditions

The effect of cations on the corrosion of galvanized steel (GS) is scarcely reported. In this study, a wet–dry cyclic test was conducted to study NH₄ ⁺, Na⁺, and Mg²⁺ cation effect on the corrosion behavior of GS available in Nepal. Fourteen wet–dry cycles (18 h wet and 6 h dry) were performed by exposing samples at 298 K with a relative humidity of 90% in a wet cycle and 50% in a dry cycle for 14 days. The cations strongly affect the corrosion rate of the GS sample estimated by weight loss and potentiodynamic polarization. The potentiodynamic polarization curves showed the inhibition of cathodic and anodic reactions by Mg²⁺ ion, while the NH₄ ⁺ ion only changed the cathodic reaction. Mg²⁺ ion was found to shift the corrosion potential to noble values compared with NH₄ ⁺ and Na⁺ ions. A compact and thin corrosion products layer was developed in Mg²⁺ salt solution in contrast to a thick and porous corrosion products layer in NH₄ ⁺ and Na⁺ salt solutions. Red rust due to corrosion of underlying steel appeared in the presence of NH₄ ⁺ and Na⁺ salt solutions. Finally, the weight loss data revealed that the corrosivity of cations for GS decreased in the order Na⁺ > NH₄ ⁺ > Mg²⁺.     

Rotating split ring disc electrode study of corrosion of iron in near neutral and alkaline solutions

Abstract

A rotating split ring disc electrode (RSRDE) with a sensitive triple potentiostat was constructed and used for determination of soluble ferrous and ferric species during potentiodynamic polarisation of iron in borate buffer solution (pH 8·4) and in 1 M NaOH at 25°C. The high sensitivity of the RSRDE apparatus enabled determination of these species in both solutions. In the borate solution shielding and blocking effects were observed. The shielding effect on the half ring detecting Fe³⁺ occurred at high cathodic potentials of the disc and was ascribed mainly to atkalisation of the ring due to hydroxyl ions produced on the disc. The blocking effect on the half ring detecting Fe²⁺ was caused by the deposition of solid ferric products; methods are proposed to diminish the inaccuracy associated with this effect.     

Deposition of calcium ions on rutile (110): a first-principles investigation

The deposition of calcium ions is the first and most crucial step of apatite nucleation on ceramic supports from ionic solution. This process is believed to initiate the growth of bone-like material on the surface of biocompatible implants. We have investigated the adsorption of Ca²⁺ from water solution on the rutile TiO₂ (110) surface by means of first principles techniques. The preferential binding site of the calcium ion on the hydrated oxide surface was determined through a series of static calculations. Molecular dynamics simulations were then performed to elucidate the deposition pathway. The driving force for adsorption is identified in the electrostatic interaction between the Ca²⁺ complexes and negatively charged deprotonated sites present on the hydrated TiO₂ (110) surface.     

Hydrogen absorption resulting from the simulated pitting corrosion of carbon-manganese steels

Hydrogen permeation measurements were performed on membranes of BS4360 Grade 50D C-Mn steel in the quenched and tempered condition. The rates of hydrogen absorption resulting from exposure to FeCl₂ solutions in a simulated corrosion pit were measured and found to be lower than those occurring in artificial sea water at applied potentials in the range commonly used for cathodic protection. A progressive decrease in the hydrogen permeation flux was recorded during simulated pitting and was attributed to the formation of a partially protective film of magnetite on the steel surface. At cathodic applied potentials iron plating was observed on the membranes. It is suggested that a similar process occurs in the cathodic protection of steel containing real corrosion pits and leads to a lowering of the Fe²⁺ ion concentration within the pits and a decrease in the aggressiveness of the local environment.     

Use of SECM to compare corrosion resistance of DIN W. Nr. 1·4460 high N and AISI 316L austenitic stainless steels in physiological solutions

Abstract

The pitting corrosion resistance of DIN W. Nr. 1·4460 stainless steel (SS) with high amounts of nitrogen (0·87%) was evaluated to be used for medical implants. The SS pitting corrosion resistance was tested in a minimum essential medium at 37°C by electrochemical impedance spectroscopy and potentiodynamic polarisation curves and in a 0·1 mol L^?1 NaCl solution at 25°C, by scanning electrochemical microscopy. This last technique measures the concentration of chemical species released by corrosion processes. The potential of an ultramicroelectrode was set to amperometrically detect the Fe²⁺ ions released at the anodic areas and also the depletion of oxygen due to the cathodic reactions in the vicinity of the cathodic areas. The AISI 316L stainless steel was also tested for comparison reasons. The results showed that the DIN W. Nr. 1·4460 with 0·87% nitrogen presents higher pitting corrosion resistance than the AISI 316L SS, being a potential candidate for biomaterial applications.     

Characterization of corrosion of X70 pipeline steel in thin electrolyte layer under disbonded coating by scanning Kelvin probe

Scanning Kelvin probe technique was used to characterize the electrochemical corrosion behavior of X70 steel in a thin layer of near-neutral pH and high pH solutions, respectively. Results demonstrate that passivity can be developed on steel in the near-neutral pH solution layer as thin as 60 μm, which is attributed to the fact that Fe²⁺ concentration in aqueous phase could reach saturation in the thin solution layer. The solubility of FeCO₃ is reached to drop out of solution as a precipitate. With the increase of solution layer thickness, it becomes more difficult for Fe²⁺ concentration to reach saturation. Consequently, the passivity cannot be maintained, and the steel shows an active dissolution state. Anodic dissolution rate of steel increases with the immersion time. The electrochemical polarization behavior of X70 steel in high pH solution is approximately independent of the solution layer thickness and immersion time. In thin solution layer, diffusion and reduction of oxygen dominate the cathodic process, as demonstrated by the presence of cathodic limiting diffusive current. In the bulk solution, the absence of limiting diffusive current density in cathodic polarization curve indicates that the main cathodic reaction is reduction of H₂CO₃ and , and the formed film is thus mainly FeCO₃.     

盐水中离子对G105钢腐蚀速率的影响及腐蚀产物分析

    利用正交实验研究了盐水中离子和温度对钻具钢（G105）腐蚀速率的影响,扫描电子显微镜（SEM）对腐蚀产物膜和去除腐蚀产物后的基体形貌进行观察分析,用X-射线衍射（XRD）分析腐蚀产物物相结构.结果表明,对腐蚀速率影响顺序为Cl^->温度>Ca²⁺>Mg²⁺>Br^-.G105钢在复合盐水中为均匀腐蚀,腐蚀产物为β-FeOOH.     

Inhibition of steel and galvanised steel corrosion by zinc and calcium ions in the presence of phosphate

Abstract

Mixtures of zinc, calcium and phosphate ions have been found to be effective (>90%) in inhibiting the corrosion of steel and zinc during immersion in acid rain solution and when used as pigment additions to organic coatings. The presence of calcium ions, in addition to zinc ions, appears to be fundamental in the inhibition mechanism since, in the absence of calcium, the inhibition efficiency is 50% or less. Although some anodic inhibition occurs, the predominant mechanism appears to be classical cathodic inhibition caused by the precipitation of a sparingly soluble, thin, but persistent, solid film. Surface analysis, by XPS, confirms that phosphorus is present in the form of phosphate species containing zinc and calcium. Also, the atomic ratios of zinc:calcium:phosphorus present in the inhibitive film strongly suggest that it consists of a mixture of CaZn₂(PO₄)₂ (Scholzite) and Zn₃(PO₄)₂ (Hopeite) in a 1 : 1 ratio.     

Effect of Caand Mg on corrosion and scaling of galvanized steel pipe in simulated geothermal water

In this paper, the effects of scaling ions (Ca²⁺ and Mg²⁺) on corrosion and scaling processes of galvanized steel pipe in geothermal water are presented. Spherical corrosion products and needle-shaped scale coexisted on the pipe surface. The concentration of Zn²⁺ and OH⁻ affected the nuclei formation of scale. The corrosion products and scale were identified as Zn(OH)₂, ZnO, CaCO₃ and MgCO₃, respectively. When scale formed on the galvanized steel pipe, the corrosion rate slowed down and the pitting region became smaller.     

Inhibition of the Acid Corrosion of Steel by n-Alkyltrimethyland n-Alkyltriethyl-ammonium Compounds

Abstract

Previous experiments with a dropping-mercury electrode indicated that n-alkyltriethylammonium ions are more strongly adsorbed than the corresponding n-alkyltrimethylammonium ions. In parallel with this, it has now been found that the former are better inhibitors of the acid corrosion of steel.

At concentrations giving up to 50% corrosion inhibition, the compounds of either series have no effect on the steel electrode potential, indicating that the anodic and cathodic reactions are equally inhibited. This is taken as evidence that the inhibitor ions are adsorbed generally over the metal surface rather than at specific anodic or cathodic sites.

With increasing concentration of inhibitor above the level for 50% inhibition, the potential begins to be displaced in a positive direction, suggesting that the anodic reaction is being inhibited more than the cathodic reaction. The results show that the proportion of cathodic inhibition is larger with the triethylammonium than with the trimethylammonium compounds.

The cathodic part of the inhibition appears to be due mainly to hindrance of the surface diffusion and recombination of adsorbed hydrogen atoms.     

Electrodeposition of Zn-Co and Zn-Co-Fe alloys from acidic chloride electrolytes

The electrodeposition operating conditions for Zn-Co and Zn-Co-Fe alloys from chloride baths were studied. The electrodeposition was performed on a high strength steel substrate, under galvanostatic conditions, for a range of current densities at varying Co²⁺ and Fe²⁺ bath concentrations and at different temperatures. A transition current density was noticed above which a transition from normal to anomalous deposition took place. Below the transition current density electrodeposition of alloys with a higher amount of Co was obtained. Above the transition current density (i.e. in the anomalous range), both Zn-Co and Zn-Co-Fe alloys were deposited with a Co content lower than the composition reference line. This transition current density that resulted in normal to anomalous deposition was attributed to the shift in cathodic potential or polarization. However, it was found that under certain conditions the transition occurred from very high wt.% Co to almost equal to the amount of Co in the electrolyte. The increase of Fe²⁺ ions in the electrolyte assisted in increasing the Co content and decreasing the Zn content in the deposits. In addition, the increase of Fe²⁺ resulted in shifting the transition current density to a lower value. However, the cathodic current efficiency decreased with the addition of Fe²⁺ ions in the electrolyte.