Browsing by Author "Ilieva G.P."

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    CHARACTERIZATION OF CONTAINING MOLYBDENUM PHOSPHATE COATINGS ELECTROCHEMICALLY FORMED ON ALUMINUM SURFACES
    (2021-01-01) Ilieva G.P.; Ivanova D.I.; Fachikov L.B.
    Results on the influence of different factors on the morphology, the composition, the color characteristics and the contact angle of wettability of aluminium surfaces related to electrochemically formed coating processes have been reported. The coatings have been formed by cathodic polarization of aluminum (99.5 %) suaces in solutions containing ammonium and sodium phosphates, MoO42- promoting ions, buffers, softeners, inorganic activators, as well as surfactants. The coating thicknesses have raised by increasing in temperature and cathodic current density upon other equal conditions. SEM and AFM analyzes have been used to reveal that the surfaces of the treated aluminum samples have been coated by homogenous dense films with different roughness.
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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.