Browsing by Author "Fachikova D.I."

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    APPLICATION OF ORGANIC COATINGS ON AMORPHOUS PHOSPHATED ZINC SURFACES
    (2023-01-01) Liubenova T.L.; Fachikova D.I.
    The phosphating of zinc surfaces, increasing their roughness and surface tension, provides high adhesion and a significant increase in the protective ability of subsequently applied organic coatings. This paper presents the results obtained in a study of combined coatings, including the formation of amorphous phosphate films on galvanized steel surfaces, followed by the application of layers of three type paints and varnishes. By means of gravimetric and physical-analytical methods, the influence of various factors such as concentration and temperature on the formation, composition and properties of the coatings obtained on zinc surfaces in phosphating solutions have been investigated. Coatings obtained at pH 4.0 are distinguished with best homogeneity and color density. The thickness of the coatings grows with increasing of temperature, at other conditions being equal. Тhe composition, structure, roughness and probable compounds of the obtained phosphate coatings have been determined by physical analytical methods. The phosphate coatings contain such elements as oxygen, phosphorus, zinc, molybdenum, nickel, which are probably combined as phosphate and oxide compounds.The phosphate films are X-ray amorphous, with indefinite habit and very well expressive relief. Using physico-mechanical methods, the adhesion, elasticity and impact strength of paint and varnish coatings on phosphated and non-phosphated zinc surfaces were measured.
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    CORROSION BEHAVIOR OF MILD AND LOW ALLOYED CARBON STEELS IN MINING CONDITIONS
    (2022-01-01) Fachikova D.I.; Ilieva G.P.; Fachikov L.B.
    This communication addresses corrosion behaviors of two steels employed as construction elements in underground mining, precisely mild steel st.25 (0.23 % C) and low alloyed carbon steel KP-355 (0.19 % C, 0.96 % Cr, 0.36 % Cu). Tests were carried out in representative synthetic media containing chlorides and sulphates in different ratios and various pH. The concentration of the chloride and sulphate ions, as well the values of pH were relevant to the ranges of variations observed in real mining waters. The studies were performed by physical (optical microscopy) and electrochemical (potentiodynamic polarization) methods. The microstructures of both steels are almost identical, that is, they are ferrite-perlite in nature. The mechanical characteristics, the yield strength limit, Re, 0.2, MPa and tensile strength, Rm, MPa are higher to the alloyed steel respectively with about 30 % and 20 %. The polarization relationships allow obtaining the main parameters characterizing the corrosion process - the corrosion potential, Еcorr, V (SCE) and the corrosion current density, icorr, A сm-2. The latter are processed by the methods of mathematical statistics.
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    ELECTROCHEMICAL EXTRACTION AND CHARACTERIZATION OF A RECOVERY TIN
    (2023-01-01) Fachikova D.I.; Fachikov L.B.
    Statistics on the production of а secondary tin show that its use in many countries reaches a significant amount. One of the most important sources of secondary tin is a scrap of white sheet metal formed by stamping various products, waste from used cans, and other obsolete tin products. In the present work, using chemical, electrochemical and physical methods, a technology for dissolving tin from used cans in alkaline solutions with the addition of p-nitroaniline and its electroextraction from solutions is proposed. The optimal conditions of dissolution and extraction (concentration and temperature of the medium, current density, current yield), as well as the chemical composition of the obtained metal tin, are determined.
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    Kinetics and Characterization of Phosphate Coatings Prepared on Aluminum Surfaces
    (2025-01-01) Djumailieva Z.K.; Fachikova D.I.; Ilieva G.P.; Liubenova T.L.
    The electrochemical formation of phosphate thin coatings on aluminum alloy АА1050 has been studied. The mass/thick-nesses of the films were determined by gravimetrical measurements at different conditions: concentration of the working solutions 2.0-11.0 vol.%; duration of the processes 1.0-10.0 min; temperature in the range of 20.0-70.0°С; cathodic current densities 0.1-0.5 Adm–2. The chemical elements containing in the phosphate coatings were determined by EDX-analysis. The morphology and topography of the coatings were studied by SEM. The corrosion behavior and the protective ability of the phosphate coatings are investigated by potentiodynamic polarization method (PDPM) and by electrochemical impedance spectroscopy (EIS). It has been found that as the concentration, temperature and density of the polarizing cathode current density rises, the mass of the phosphate films increases – the thinner ones being dense and uniform, while the thicker ones are cracked. Mainly phosphorus, oxygen, molybdenum and nickel exist in the coatings and their amounts increase with temperature of the phosphating bath is raised while the Al content in the coatings reduces at the same conditions. The corrosion of the phosphated specimens increase slightly with a rise in the temperature of the solutions during their phosphating, when the cracks in the coatings and resp. the bare metal of the substrate increases. The uncoated specimen has lower barrier ability, while the phosphated has higher barrier ability in the corrosion medium.