Anodic Dissolution Of Steel Research Articles

Specifics and Methods of Inhibiting the Underfilm Corrosion of Carbon Steel.

The process of metal dissolution under a delaminated insulating polymer coating (underfilm dissolution) has been studied. For this purpose, we used an experimental setup that simulates the process of corrosion of underground metal structures in the presence of through defects in the polymer coating and/or extended areas of peeling of the polymer coating from the metal (loss of adhesion)-subfilm cavities partially or completely filled with electrolyte. In particular, the distribution of the protective current under a peeled polymer coating was studied, and a sharp decrease in the value of the protective current was shown at a distance of 1-3 cm from the edge of the defect with a gap between the metal and the coating of 1-6 mm. The localized nature of metal corrosion under the exfoliated polymeric coating has been demonstrated. The ratio of the areas with accelerated corrosion to the total area of the metal can be 1 to 100. It has been established that there are areas of anodic dissolution of the metal during cathodic polarization of the entire sample with a peeled coating. The activating effect of carbon dioxide and hydrogen sulfide on the corrosion and anodic dissolution of steel under the coating was shown. So, it has been established that the dissolution current flowing from the anodic sections on a surface can increase approximately 10 times in the presence of carbon dioxide and hydrogen sulfide. A synergistic effect of these compounds on the process of localized underfilm corrosion of steel was detected. It has been developed a mechanism for the formation of localized corrosion damage to steel under a delaminated polymeric coating, which can be the nuclei of corrosion cracks upon reaching a certain level of mechanical loads, i.e., stress corrosion cracking (SCC) of carbon steel. Possible manners of inhibiting underfilm dissolution of metals are considered, and a method for pre-treatment of the surface with solutions of organosilanes, which ensures the formation of surface self-assembled polymeric siloxane nanolayers responsible for inhibiting underfilm corrosion of steel, is proposed.

Investigating the synergism of some hydrazinecarboxamides and iodide ions as corrosion inhibitor formulations for mild steel in hydrochloric Acid: Experimental and computational studies

Three hydrazinecarboxamides, namely, 2-cyclohexylidenehydrazinecarboxamide (SCYHEX), 2-(pentan-3-ylidene)hydrazinecarboxamide (SP3ONE) and 2-(pentan-2-ylidene)hydrazinecarboxamide (SP2ONE) were tested as inhibitors of acid corrosion of mild steel both without and with addition of iodide ions. The formulated inhibitor solutions showed excellent corrosion inhibition efficiency as they suppressed steel to the tune of 82% without KI additive, and up to 97% with KI additive. The shifts in corrosion potentials recorded from polarization measurements were anodic and ranged from 25 mV to 55 mV (without KI) relative to the uninhibited electrolyte, suggesting that the Schiff bases are mixed-type corrosion inhibitors with prominent effects on anodic dissolution of steel. The inhibitors adsorb at steel/electrolyte interface as reveled by the AC impedance measurements that showed more than 5 times increase in the charge transfer resistance and equivalence decrease in double layer capacitance of the inhibitor-containing solutions compared to the blank. Theoretical density functional theory (DFT) calculations suggested possible covalent interactions between the Schiff bases molecules and Fe with Fe---N and Fe---C bond lengths ranging from 1.87 Å to 1.96 Å. Experimentally derived synergistic parameters for Schiff bases-iodide ions interactions were generally greater than 1 and a strong H---I bond of ca. 2.3 Å length was observed in what appeared to be first time theoretical modelling of inhibitor-iodide ion synergistic interactions. DFT derived reactivity indices of protonated Schiff bases molecules correlated with the observed strengths of corrosion inhibition. Monte Carlo simulations study also confirmed the tendency of the inhibitor molecules to adsorb on mild steel surface and displace corrosive ions from the steel surface.

Influence of Non-metallic Inclusions on Corrosive Properties of Polar Steel

Polar steel requires excellent toughness and corrosion resistance for breaking icy surfaces in low-temperature seawater environments. In this study, the effect of inclusions on the corrosion resistance of polar steel was examined. In the experiments conducted, the composition and morphology of the inclusions in steel were controlled using different deoxidation methods during steel refining. The morphology and composition of the corrosion-resistant active inclusions were analyzed using scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of polar steel was determined by measuring the saturation current density of the anodic dissolution of steel in a corrosive medium via an electrochemical method. The corrosion resistance under simulated seawater was also investigated under laboratory conditions. It was found that as the ratio of Al/Mg approaches the stoichiometric composition of the spinel (2.3–2.5), the inclusions become less active; as the ratio increases further, the corrosion-resistant activity increases due to the formation of MgAl2O4⋅CaO complexes, leading to an increase in local stress around the inclusions. If steel is deoxidized with Zr–Ti, small Zr–Ti complex oxides form in the steel, providing nucleation particles for the precipitation of spheroidized and uniformly distributed MnS. Therefore, steel deoxidized with Zr–Ti has better seawater corrosion resistance than Al-deoxidized steel.

Specificity of carbon diffusion during plasma electrolytic treatment of steel

This work is devoted to evaluation of the diffusion coefficient of carbon using the thickness of the martensitic layer after plasma electrolytic carburising in various electrolytes followed by quenching. The effective diffusion coefficients of carbon in the structure of mild steel containing oxide and martensitic layers are determined. The maximum diffusion coefficient at a carburising temperature of 900 °C is 23.6. 10−8 cm2/s for treatment in an acetone-based electrolyte for 1 min. The obtained values were comparable with the calculation results for the thickness of the pearlite layer after anodic plasma electrolytic carburising as well as data of measurements of the distribution of carbon concentration in the carburised layer after cathodic saturation. The influence of the oxide layer inhibiting the diffusion of carbon and the possibility of controlling its thickness by varying the concentration of ammonium chloride, which provides anodic dissolution of steel, were confirmed.

Phosphate coatings as a way to protect steel reinforcement from corrosion

Phosphate coatings are successfully applied as a method of protecting steel products and structures from corrosion. Phosphate coatings mechanically prevent the entry of aggressive particles, such as chloride ions, to the surface of steel reinforcement. The parameters of corrosion rate of reinforcing steel in aggressive environment are determined by graphical method. The analysis of corrosion diagrams allows us to judge the effect of protective phosphate coatings on the kinetics of the corrosion process of steel reinforcement in environments of varying degrees of aggressiveness. The tests of the protective properties of phosphate coatings by contact corrosion method show that films with a finer crystal structure, as in modified phosphate coatings, are more resistant to anodic dissolution of steel. In parallel to determination of iron ions content in solutions the potential of steel reinforcement samples was measured. In samples protected by phosphate films, the potential change is not as sharp as in samples without coating, and the “dilution” of steel is slower. The study of anodic behavior of steel reinforcement of reinforced concrete, experimental study of the mass transfer mechanism of electrolyte supply to the surface of reinforced steel allow to develop practical recommendations to improve corrosion resistance and ensure the durability of reinforced concrete building materials.

The Effect of Chemiadsorbed Layers of Nitrilotris–Methylenephosphonate Complexes of Lead(II) with Bridging and Chelate Coordination on the Electrochemical Behavior of a Steel 20 Surface. Thermochemical Induction of Secondary Inhibition

The effect of the chemiadsorbed layers of two lead(II) complexes of nitrilotris–methylenephosphonic acid, differing from one another in coordination of the Pb(II) atom, on the corrosion-electrochemical behavior of a Steel 20 surface in neutral aqueous medium with natural aeration, after deposition of the adsorption layers of the complexes and their heat treatment in air, was investigated. The adsorption layer of the complex with a bridging structure weakly retards the anodic dissolution of steel, and the heat treatment has almost no effect on the protective effectiveness. The adsorption layer of a complex with a chelate structure at medium temperatures also has a weak effect on the kinetics of anodic process; however, the change of the structure of the surface layer after heat treatment at 300°C results in a sharp decrease in the anode current and to refining of the steady-state corrosion potential. The conclusion was drawn that heat treatment induces chelate decomplexation and results in secondary inhibition of the surface of steel by products of the thermochemical transformation.

Voltampermetric investigation of peculiarities of anodic processing of biomedical stainless steel AISI 304 in ethaline: temperature and additional water influence

It is shown that deep eutectic solvent Ethaline is an environmentally friendly and highly efficient medium for electropolishing of AISI 304 stainless steel that is widely used for medical products. The obtained voltammograms allow choosing optimal conditions for anodic treatment of AISI 304 steel samples in Ethaline at different temperature conditions (from 20 to 50°C) and with water additives (up to 10 %). It is established that high efficiency of Ethaline as an electrolyte for anodic treatment is primarily associated with its unique physicochemical properties: significant viscosity and, at the same time, relatively high, as for ionic liquids, electrical conductivity. The high viscosity of the Ethaline solvent causes slow diffusion of the products of anodic dissolution of steel, which achieve the formation of a viscous electrode layer and provide a high efficiency of the polishing process. It has been shown that with an increase in electrolyte temperature and water content in Ethaline the anodic dissolution rate of steel increases and this allows the use of high anode current densities for electropolishing in galvanostatic mode or lower potentials in the potentiostatic mode.

Contact Displacement of Copper at Copper Plating of Carbon Steel Parts

The process of the contact displacement of copper by the carbon steel surface in a low-concentrated sulfate electrolyte and in electrolytes containing copper complexes with glycine, tartrate, and ethylenediaminetetraacetate is studied. The method of analyzing the particular reactions of interaction between a steel surface and copper-containing electrolytes in the absence of current is applied. The parameters of the contact exchange kinetics are determined with computer processing of the arrays of the coordinates of the particular polarization dependences of cathodic copper deposition in the electrolytes and the anodic dissolution of steel in the corresponding background solutions, as well as of the chronopotentiograms of steel samples in the electrolytes under study. The values of the contact exchange current density and the relation between the areas of the cathode and anode surface sections are calculated as a function of the steel substrate potential and the steel–electrolyte contact time. The influence of the nickel sublayer thickness on the kinetics of the contact exchange in a low-concentrated sulfate electrolyte is shown.

The inhibition of mild steel corrosion in acidic medium by 1-methyl-3-pyridin-2-yl-thiourea

The effect of 1-methyl-3-pyridin-2-yl-thiourea on the corrosion resistance of mild steel in H 2SO 4 solution was investigated by different techniques. The results show that the inhibition efficiency increases with the increase of inhibitor concentration. This compound affects both the anodic dissolution of steel and the hydrogen evolution reaction in 0.5 M H 2SO 4. The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm. From the adsorption isotherm, value of the Δ G ads for the adsorption process was calculated. From the corrosion rate obtained at 25–45 ± 1 °C E a, Δ H a and possible mechanism have been proposed.

Plant extracts as corrosion inhibitors of mild steel in HCl solutions

The effects of various plant extracts on the dissolution of mild steel in HCl solutions were studied. The additives investigated were Papaia, Poinciana pulcherrima, Cassia occidentalis and Datura stramonium seeds and Papaia, Calotropis procera B, Azydracta indica and Auforpio turkiale sap. Weight-loss determinations and electrochemical measurements were performed. It was found that all extracts except those of Auforpio turkiale and Azydracta indica reduced the corrosion of steel with an efficiency of 88%–96% in 1 N HCl and with a slightly lower efficiency in 2 N HCl. Both the cathodic evolution of hydrogen and the anodic dissolution of steel are inhibited. We believe that the inhibition action is mostly due to the products of the hydrolysis of the protein content of these plants.