Browsing by Author "Ivanova D.I."

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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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    Effect of the potential on the film composition and the stress corrosion cracking of mild steel in ammonium nitrate solutions
    (2018-01-01) Ivanova D.I.; Fachikov L.B.
    The relation between the film composition and the susceptibility of mild steel (0.17% C) to stress corrosion cracking (SCC) in ammonium nitrate solutions at different potentials has been studied. The susceptibility to SCC is evaluated by constant slow strain rate tests under potentiostatic conditions (-0.5 V - 1.5 V, SCE). The composition of the surface film is identified by Mossbauer spectroscopy. It is found that in the region of the highest susceptibility to SCC (0 V - 0.8 V, SCE) the film is composed mainly of fine particles of FeOOH as well as some quantity of γ-Fe2O3. However at potentials outside this region, where the resistance of the steel to SCC increases considerably, the film is composed exclusively by oxides with a spinel structure Fe3O4 and γ-Fe2O3. It is suggested that the conditions which favour the formation of a spinel structure film may lead to an increased resistance of the steel to SCC.
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    Influence of the support on the morphology of Co-Sn, Ni-Sn, Co-Ni nanoparticles synthesized through a borohydride reduction method applying a template technique
    (2018-01-01) Markova I.N.; Piskin M.B.; Zahariev I.Z.; Hristoforou E.; Milanova V.L.; Ivanova D.I.; Fachikov L.B.
    Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles have been synthesized through a borohydride reduction with NaBH4 in aqueous solutions of the chloride salts of Co, Ni, Sn at room temperature using a template technique with a carbon support. As a result nanocomposite materials have been obtained in situ. The ratio of the metallic components has been chosen according the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn=35:65, Ni:Sn=45:55, Co:Ni=50:50. As carbon supports have been used graphite and carbon powder. To avoid the nanoparticle's aggregation β-cyclodextrin has been added to the reaction solutions. To study the influence of the supports used on the morphology, specific surface area, elemental and phase composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites SEM, EDS, BET, and XRD investigation techniques have been used. The particle's morphology varies with the different supports, but in the all cases it is typical for alloyed materials. The nanoparticles are different in shape and size and exhibit a tendency to aggregate. The last-one is due to the unsaturated nanoparticle's surface and the existing magnetic forces. Regardless of the elemental composition, the nanosized particles are characterized by a relatively high specific surface area (SSA). The Ni-Sn nanoparticle have the largest SSA (80 m2/g), while the Co-Sn particles have the lowest SSA (69 m2/g). The use of a carrier modifies the SSA of the resulting nanocomposites differently depending on the size and shape of the carrier's particles. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that the particle's morphology, size, and specific surface area for the different supports are suitable for use as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.
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    Influence of the support on the morphology of Co-Sn, Ni-Sn, Co-Ni nanoparticles synthesized through a borohydride reduction method applying a template technique
    (2018-01-01) Markova I.N.; Piskin M.B.; Zahariev I.Z.; Hristoforou E.; Milanova V.L.; Ivanova D.I.; Fachikov L.B.
    Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles have been synthesized through a borohydride reduction with NaBH4 in aqueous solutions of the chloride salts of Co, Ni, Sn at room temperature using a template technique with a carbon support. As a result nanocomposite materials have been obtained in situ. The ratio of the metallic components has been chosen according the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn=35:65, Ni:Sn=45:55, Co:Ni=50:50. As carbon supports have been used graphite and carbon powder. To avoid the nanoparticle's aggregation β-cyclodextrin has been added to the reaction solutions. To study the influence of the supports used on the morphology, specific surface area, elemental and phase composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites SEM, EDS, BET, and XRD investigation techniques have been used. The particle's morphology varies with the different supports, but in the all cases it is typical for alloyed materials. The nanoparticles are different in shape and size and exhibit a tendency to aggregate. The last-one is due to the unsaturated nanoparticle's surface and the existing magnetic forces. Regardless of the elemental composition, the nanosized particles are characterized by a relatively high specific surface area (SSA). The Ni-Sn nanoparticle have the largest SSA (80 m2/g), while the Co-Sn particles have the lowest SSA (69 m2/g). The use of a carrier modifies the SSA of the resulting nanocomposites differently depending on the size and shape of the carrier's particles. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that the particle's morphology, size, and specific surface area for the different supports are suitable for use as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.