Vol 52, No 7 (2016)

Methods of optical in situ microscopy and scanning reflectometry were used to determine that localized corrosion defects (pitting) emerging on a pipe steel in a neutral solution simulate a neutral underfilm solution. The initial stages of this process were studied. The density, mean radius,and dimensions of corrosion spots (or pits) were determined. It was shown that the defects grew mainly into a depth that exceeded 100 μm after several hours and attained 600 μm after 33 days of corrosion tests. Similar behavior may lead to corrosion cracking under the cyclic mechanical stresses. The stress intensity factors realizable in steel in the event of localized corrosion defects were calculated, and the possibility of determining the danger of corrosion cracking initiation under stress of pipe steel was determined on the basis of both optical and electrochemical data.

Using the method of recording anode potentiodynamic curves in neutral and mildly alkaline borate buffer solutions, the corrosion and electrochemical behavior of iron-armco samples bombarded with oxygen ions is studied. It is shown by the method of X-ray photoelectron spectroscopy that, during such bombardment, implantation of oxygen into the surface layers of iron occurs. Therein, iron oxides of variable composition and various forms of adsorbed and absorbed oxygen are formed. These oxygen formations contribute to transfer of the iron surface to a more corrosion-resistant, passive state.

It has been shown that copper nanomarkers can be used for revealing microcracks and regions of microdamage on the surface of pipelines and parts of oil and gas machinery. The synthesis of copper nanoparticles by hydrazine-induced reduction from aqueous salt solutions in the presence of surface active agents (SAAs) and their silicon-dioxide stabilization, which is needed to prevent surface oxidation processes, are described. Testing of the deposition of optical nanomarkers on a metal surface has been performed. It has been discovered that copper nanoparticles become trapped in microcracks on the surface of metal samples and stay there after the surplus substance is removed from the surface. It has been shown that synthesized copper nanoparticles can be detected in microcracks and regions of microdamage by irradiating metal surfaces of constructional materials with a femtosecond laser.

Atmospheric corrosion stability of metals can be achieved by coating their surfaces with superthin nanoscale layers. The scientific principles of inhibiting metal corrosion have been under development for many years, but a new direction of progress has emerged recently. The main achievement of research in this new direction is the possibility of covering metals in nanoscale films that, despite their extreme thinness, ensure high corrosion resistance of the metals under various atmospheric conditions. To this end, methods are suggested for producing such coatings from volatile organic compounds that can adsorb on metal surfaces from the gaseous phase. Increasing the irreversibility of adsorption of volatile corrosion inhibitors is necessary to strengthen the protective effect of the nanolayers they form on the surface. Nanolayer-coating protection has a number of fundamental advantages, including retention of article dimensions, a lack of a need for special utilization and degreasing methods, and affordability.

The results of a study of anticorrosion performance of low carbon containing tungsten-based hard chemical vapor deposition (CVD) coatings with microhardness from 5 to 17 GPa are presented in this work. Their high corrosion resistance in hydrochloric acid and hydrogen sulfide solutions is noted, as their corrosion rate does not exceed 6 μm per year in hydrochloric acid solution and 15 μm per year in hydrochloric acid solution saturated with hydrogen. The open circuit potentials correspond to tungsten (VI) oxide formation so the corrosion process supposedly runs in passive state. Taking into account the low porosity of the CVD layers, which is lower than 0.02%, these coatings are promising for application as anticorrosion wear-resistant coatings for chemical and oil and gas apparatus responsible units.

The possibility of increasing the thickness of a magnetite coating (MC) and its heterogeneity due to successive oxidation of low-carbon steel in two bathes based on ammonium nitrate solutions has been shown. Results are shown of a comparative corrosion test of steel with an MC obtained during single- or two-step oxidation in nitrate solutions, with further passivation by the IFKhAN-39U composition, which show the advantages of oxidation in two bathes.

Coatings obtained in solutions of permanganates are known alternatives to thin chromate conversion coatings on aluminum alloys. However, permanganate ion is an insufficiently effective corrosion inhibitor for aluminum in the acidic medium, and, therefore, modified additives are introduced into converting solutions based on it. The present research is devoted to studying the corrosive characteristics of coatings produced by chemical oxidation in the IFKhANAL-2 permanganate composition and its modifications on AMg-3 aluminum alloy. It is shown that iron and nickel salts are most effective as modified additives and subsequent filling of produced coatings in corrosion inhibitor solutions increases their protective properties up to the level of standard chromate coatings. The researched coatings provide protection for 1.5 years under conditions of a humid tropical climate.

Paint and lacquer coatings (PLCs) are most commonly used when one needs to impart an aesthetic appeal to metal surfaces and protect them from the effects of the environment. Priming paint and lacquer compositions, which are dispersions of anticorrosion pigments in film-forming materials possessing a high adhesion to the surface that is being coated, are rather widespread among the variety of paint and lacquer corrosion- protection materials. The use of a fluorine-containing film-forming material to produce a PLC is rather promising. In this work, we have studied the protective properties of coatings that are based on epoxy varnish and a fluorine-containing polymer and filled with chromate and chromate-free anticorrosion pigments. The protective properties of PLCs have been evaluated by express tests in a salt spray chamber. The PLC structure has been analyzed by scanning-electron and atomic-force microscopy.

Chemical modification of the surface of basalt glass fiber has been considered, including diffusion-mode oxidation without formation of new crystalline phases and ion-exchange lithium enrichment. The effect of such a modification on the appearance of new surface formations during the hardening of composites that consist of the modified fiber and model nonorganing binding materials (mixtures of Ca₃SiO₅ and Ca₃Al₂O₆ with water) has been analyzed. It has been shown that both ion-exchange lithium enrichment and diffusion-mode oxidation change the composition and the morphology of hydrosilicate and hydroaluminate particles that are formed on the surface from “individual hydraulically active phase–water” mixtures. They have also been shown to change the morphology of the very fiber that is in contact with the liquid phase of the binding material.

The effect of reactive oxygen intermediates, such as superoxide radical and hydrogen peroxide, on the initiation of biological zinc corrosion is demonstrated. A correlation between the amounts of formed hydrogen peroxide and the corrosive activity of the studied bacteria is revealed.

The results of industrial application of a matrix eddy-current probe in studying local corrosion in heat-exchanger tubes are considered. Local corrosion of several heat exchangers that were used under various conditions has been analyzed by eddy-current techniques. Statistical analysis has confirmed the effect of polymer coatings on local corrosion suppression and prevention. Using an original eddy-current probe, the rate of scale formation on the tubes of a thermal power station condenser has been measured for heat-exchanger tubes that were protected from inside by a polymer coating.