Browsing by Author "Marcheva Y."

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    Effect of H3Po3 and Nah2Po2 in the electrolyte on the composition and microstructure of Ni-Co-P alloys
    (2019-01-01) Ignatova K.; Alakushev M.; Kozhukharov S.; Marcheva Y.; Vladimirova S.; Avdeev G.
    The effect of two phosphorus-containing additives (phosphorous acid, H3PO3 and sodium hypophosphite, NaH-2PO2) in modified Watt's electrolyte (pH = 2; 80°S) on the deposition kinetics, morphology, component and phase composition of Ni-Co-P coatings was studied. When only one of the studied additives is present in the solution, the P content in the coatings reaches maximum of 15 % and their structure is amorphous. The P and Ni incorporation in the coatings is facilitated when the electrolytes with prevailing concentrations of H3PO3 are used. The maximal P content (over 30 %) in the coatings was reached when both additives were present in the electrolyte. These coatings possess mixed structure with nano-dimensional amorphous phase and crystal hexagonal phase of solid solutions Ni2P and Ni2P-Co2P. The increasing of the current density causes P content decrement and the resulting crystal phase is tetragonal, composed by solid solutions of Ni3P and Ni3P-Co3P.
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    Kinetics of electrodeposition of NiP, CoP and NiCoP coatings depending on sodium hypophosphite concentration
    (2018-01-01) Ignatova K.; Marcheva Y.
    The effect of NaH2PO2 concentration in the electrolyte (pH = 2) on the kinetics of NiP, CoP and NiCoP alloys electrodeposition at room temperature was studied. It was established that at concentration of NaH2PO2 about 0,2 M the deposition rate of NiP alloys decreases; the deposition rate of CoP alloys increases but at the same time the quality of the coating becomes bad. In both cases it was observed a depolarizing effect on the deposition. With increasing of the content of NaH2PO2, the phosphorus content in NiCoP alloys increases to approximately 7 % and the current efficiency of electrodeposition (CEE) goes over 100 %. The comparison of the kinetic data with those of CEE of NiCoP coatings showed that the mechanism of deposition is mixed chemical-electrochemical.