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SUMMARY INHIBITORS INFLUENCE ON THE STEEL CORROSION PRODUCTS Kristina Saulėnienė Graduation thesis for Master degree has been carried out at the department of Chemistry of Vilnius Pedagogical University and at the Institute of Chemistry Research adviser: prof. habil. dr. R. Ramanauskas Concrete normally provides reinforcing steel with exellent means of protection against corrosion, while carbon dioxide and chlorides penetrate through the pores of the concrete and catalyse the steel corrosion. The most effective inhibitors of the steel corrosion in alkaline environment are the nitrites (anodic inhibitors which help to form more solid oxide film), therefore in this scientific work their influence on the steel corrosion products (oxides) was researched. Fe oxides were formed by anodic polarization of steel in the alkaline solution and then analised influence of the chloride ions and nitrites to their formation. For electrochemical measurement the solution of 0,1 M NaOH was chosen, because its pH (12,6) is almost the same as one of the electrolyte being found in the pores of concrete. The measurements of the polarization curves were started after the reduction of the oxide film of the electrode surface, e.g. starting the spreading of the potentials from the negative values (~ -1,2 V Ag/AgCl). Analysing the influence of the chloride ions on the steel polarization in the alkaline environment, we were interested in the amounts of the forming Fe (II) and Fe (III) oxides, which... [to full text]

There is an increasing interest in exploring the use of conductive polymers for protecting metals from corrosion. The corrosion resistance of steel coated with the conductive polymer polypheneylenevinylene (PPV) is studied. The corrodant used is deaerated 1% w/w NaCl(aq). / The PPV coating is deposited by a homemade spinning coater. The effect of substrate microstructure and surface treatment on PPV coating morphology is investigated. The morphology and surface roughness of the coating are measured by Atomic Force Microscopy (AFM). The PPV coating thickness and substrate surface roughness are measured by profilometer. / Open Circuit Potential (OCP), electrochemical impedance spectroscopy (EIS), linear potentiodynamic voltammetry (Tafel) and optical microscopy were used to characterize the structure and properties of the coatings. The correlation between the coating thickness, the surface treatment of the steel substrate prior to coating, and the corrosion behaviour of PPV coated steel was investigated. / Under the condition of our studies, the level of pH in the solution used for corrosion testing has the strongest effect on the corrosion behaviour of PPV coated steel.

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The present work represents an attempt to study the inhibition of corrosion of mild steel in acid media by seventeen furan derivatives, at 17 to 30 different inhibitor concentrations, from 0 up to 20 mMole per liter. / One of the techniques used to correlate the inhibitive action of organic compounds is based on the Linear Free Energy Relationship (LFER). The relationship is used to elucidate the mechanism of inhibition, by studying the effects of physico-chemical characteristics of the inhibitor molecules, such as functional group, polar function electron density, steric effects, and (pi)-orbital character of the donating electrons on the corrosion inhibition of mild steel in acid solution. / The results show that furfuryl alcohol, 2,5-furan dimethanol, and 2-furonitrile act as excellent inhibitors over the entire concentration range covered in this study, whereas the remaining investigated compounds exhibit substantial fluctuations in the inhibitive action with concentration. Frequent maxima and minima of inhibitive action have been observed. This behaviour can be explained on the basis of the different reaction mechanisms of the absorbed intermediate inhibitor complex at the metal surface. / The results of the study suggest that the inhibitive action of ortho-substituted compounds is influenced by steric effect. Although LFER is a valuable tool for comparing inhibitive actions of various compounds, other criteria should be considered. These criterion or special effects include polymerization, (pi)-orbital electrondelocalization, and mesomeric effects. Such effects could cause a compound to act as a good inhibitor, irrespective of considerations relating to electron affinity.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

In applications where resistance to localised corrosion is required, stainless steel alloys containing molybdenum are generally used thanks to their superior resistance to localised attack in aggressive environments. For ferritic stainless steels, vanadium additions have been found to also have a beneficial effect on the resistance to localised corrosion. In this study vanadium and molybdenum were compared directly as alloying elements in 18% chromium ferritic stainless steel as far as their effect on increasing the resistance to localised corrosion is concerned. Pitting potentials in a neutral chloride solution were used as the criterion for qualifying resistance to localised corrosion and it was shown that vanadium gave similar or slightly higher pitting potentials at addition levels of up to 4% (weight percent). It was subsequently found that the mechanism by which the molybdenum and the vanadium increase the resistance to localised corrosion, are not the same. The experimental data for the molybdenum containing alloys corresponded well with other work done in this field. The positive effect of molybdenum additions on the pitting resistance of these alloys could be explained through its effect in lowering the dissolution rate in the active dissolution region by enriching on the dissolving surface. The vanadium additions to these alloys were shown not to have an effect on the active dissolution kinetics. The effect of these two alloying elements on the initiation of metastable pits were examined, but no meaningful advantage for the vanadium containing alloys over the rest could be found. It is suggested that vanadium play a role in changing the dissolution kinetics of the salt film, which forms during the growth of a metastable pit. A delayed dissolution of salt film remnants would lead to a loss of the enriched pit solution, which would cause the metastable pit to repassivate. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

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A thesis submitted to the Faculty of Engineering and the Built Environment, University of Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy (Engineering), 2017 / Chromium oxide provides an inexpensive and practical means of increasing the corrosion resistance of austenitic stainless steel in most environments. However, the oxide is prone to dissolve in reducing acids and in chloride containing solutions, which compromises the durability and effective operation of structures made of austenitic stainless steel. This research project explored the use of thin ruthenium surface alloys produced by ion implantation, RF sputtering and pulsed electrodeposition (PED) to improve the corrosion resistance of AISI 304L austenitic stainless steel in reducing acids and chloride solutions via a technique known as cathodic modification. The properties of the alloyed 304L stainless steel were evaluated using a number of tools including X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), potentiodynamic polarisation, and electrochemical impedance spectroscopy (EIS). Preliminary tests in 1 M sulphuric acid showed that the ruthenium surface alloys sufficiently raised the corrosion potential of 304L stainless steel to ranges where the stability of chromium oxide is guaranteed. Surface alloys produced by RF sputtering and PED were associated with the best corrosion resistance, and protection efficiencies of at least 85%, but they spalled during corrosion exposure rendering them unsuitable for corrosion application. The corrosion of the ruthenium implanted surface alloys exhibited a strong dependence on the surface roughness of the stainless steel, with the least corrosion rates achieved on rough 304L stainless steel samples implanted with 1016 Ru/cm2 at 50 keV. Corrosion characterisation of these ruthenium implanted surface alloys was studied in various corrosive media including sulphuric acid, sodium chloride, magnesium chloride and simulated fuel cell solutions. Their corrosion rates in sulphuric acid decreased with increase in acid concentration, and exhibited non-Arrhenius behaviour in the acid solutions; corrosion rates were unaffected by increasing exposure temperature from 25 to 50°C. In 3.5 wt% sodium chloride, addition of ruthenium via ion implantation changed pit morphology from elongated to circular, indicating a diminished tendency for pits to initiate at manganese sulphide stringers. Corrosion rates of the ruthenium implanted stainless steels in the simulated fuel cell solutions were at least 69% lower than the target corrosion rate for use in polymer electrode membrane fuel cells (PEMFCs), thus presenting a possible practical application of ruthenium surface alloyed austenitic stainless steel. / CK2018