Browsing by Author "Fachikov L."

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    Corrosion of high nitrogen stainless steel in sodium orthophosphate solutions
    (2014-01-01) Loukaycheva M.; Tzaneva B.; Fachikov L.
    The corrosion behavior of Cr18Mn12N (0.61% N) and Cr18Ni9 steels in water solutions of sodium orthophosphates (NaH2PO4, Na2HPO4 u Na3PO4)-0.1 M, with sodium chloride addition (0.5M) have been investigated by potentiostatic and galvanostatic methods. Galvanostatic results reveal that both steels exhibit almost identical behaviors. The increase in the current density does not affect the value of the stationary potentials reached after 1 hour of polarization. In solutions of NaH2PO4 and Na2HPO4 both steels develop pitting corrosion. In Na3PO4 with added chloride, the steels show passive behavior at the applied current densities; there are indications of pitting occurrence on the chrome-nickel steel surface that subsequently repassivate. The potentiostatic dependencies provide a basis to determine the values of the pitting formation potentials, Epit and the incubation time, ti of the pitting nucleation. The recorded Epit for the nitrogen steel have more negative values than those obtained with the classical stainless steel. However, the nickel free steel demonstrates 5-10 times lower speed of pitting nucleation and growth compared to Cr18Ni9. In Na3PO4 solutions in presence of NaCl, the Cr18Mn12N steel shows better corrosion resistance-more positive Epit and longer incubation time.
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    Ftir spectroscopy method for investigation of Co-Ni nanoparticle nanosurface phenomena
    (2017-01-01) Zahariev I.; Piskin M.; Karaduman E.; Ivanova D.; Markova I.; Fachikov L.
    The Co-Ni nanoparticles examined are synthesized through a borohydride reduction with NaBH4 in aqueous solutions of chloride salts containing a different ratio of Co and Ni (1:1, 4:1 and 1:4, correspondingly) and also in the course of a template synthesis with graphite as a support in presence of β-cyclodextrin. The morphology, the elemental and phase composition of the synthesized Co-Ni nanoparticles are studied by SEM, EDS and XRD analyses. FTIR spectroscopy investigations carried out provide to elucidate the atom /molecule groups formed in the Co-Ni nanoparticles and their carbon-containing nanocomposites. The different shape and position of the bands of absorption at the relevant wavenumber [cm-1] identify the mode of vibrations (symmetric and asymmetric stretching and bending vibrations) of the created chemical bonds arising at the nanoparticle surface such as C-OH, CO-OH, C-H2, C=O, BO3, BO4, free OH, H-OH (H2O), CoO, NiO. The FTIR spectra reported illustrate also the effect of the different Co:Ni ratios studied and that of the support used. The data obtained show that FTIR spectroscopy is a sensitive method suitable for studying Co-Ni nanoparticles and their carbon-containing nanocomposites surface phenomena.
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    SEM and EDX Study of Stainless Steels, Suggested as Human Body Implants
    (2018-06-12) Simitchiiska R.; Ivanova D.; Fachikov L.
    The most important requirement for any material used as an implant is to be biocompatible and not to cause undesirable effects in the human body. Corrosion of implants is included in the topic of biocompatibility because it is a determining factor in their sustainability and seamless fulfillment of their functional purpose. The work presents the results obtained in the comparative study of two austenitic stainless steels (Cr18Ni9 and Cr18Mn12N) in two models of artificial saliva, accepted as environments for testing the corrosion behavior of materials for these aims. The nature of the corrosion attack, the composition of the corrosion products at 37°C and the pH 5.5 and pH 6.75 of the model media were determined using physical methods such as SEM and EDX of investigation and analysis. It was found that Cr18Mn12N steel (0.61 % N), exhibits higher corrosion resistance.
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    SEM and EDX Study of Stainless Steels, Suggested as Human Body Implants
    (2018-06-12) Simitchiiska R.; Ivanova D.; Fachikov L.
    The most important requirement for any material used as an implant is to be biocompatible and not to cause undesirable effects in the human body. Corrosion of implants is included in the topic of biocompatibility because it is a determining factor in their sustainability and seamless fulfillment of their functional purpose. The work presents the results obtained in the comparative study of two austenitic stainless steels (Cr18Ni9 and Cr18Mn12N) in two models of artificial saliva, accepted as environments for testing the corrosion behavior of materials for these aims. The nature of the corrosion attack, the composition of the corrosion products at 37°C and the pH 5.5 and pH 6.75 of the model media were determined using physical methods such as SEM and EDX of investigation and analysis. It was found that Cr18Mn12N steel (0.61 % N), exhibits higher corrosion resistance.
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    Spectroscopic study of the template synthesized intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles with a carbon support
    (2018-01-01) Markova I.; Piskin M.; Zahariev I.; Ivanova D.; Fachikov L.; Christoforou E.
    Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles are synthesized through a borohydride reduction in a mixture of aqueous solutions of CoCl2.6H2O, NiCl2.6H2O and SnCl2.2H2O salts at room temperature applying a template technique. A carbon support is used. As a result nanocomposite materials are obtained in situ. The ratio of the metallic components is chosen on the ground of 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. Graphite and carbon powders are used as a carbon support. To avoid the nanoparticle's aggregation β-cyclodextrin is added to the reaction solutions. EDS and XPS investigation methods are applied to study the surface composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites. A particle's morphology is typical for the alloyed materials. The nanoparticles are characterized by a relatively high specific surface area. Both the elemental and phase composition of the investigated particles and their carbon composites do not alter with the change of the carbon support. They depend only on the ratio between the respective metal components set in the starting reaction solutions according to the phase diagrams of the corresponding binary systems. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that they are suitable to be used as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.