Browsing by Author "Sknar, Irina V."

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Determination of the Efficiency and Selectivity of Anodic Dissolution of a Heat-Resistant Rhenium-Containing Superalloy in Chloride-Containing Media With Sulfuric or Methanesulfonic Acids
(Eastern-European Journal of Enterprise Technologies, 2025) Kotok, Valerii Е.; Sknar, Yuri Е.; Butyrina, Tetyana Е.; Sknar, Irina V.; Sukha, Irina V.; Demchyshyna, Oksana
ENG: Тhe object of this study is the elec-trochemical anodic dissolution of a heat-resistant nickel-based superalloy containing rhenium and other alloying elements in acidic electrolytes containing sodium chloride. The investi-gated alloy was obtained from scrap of high-temperature equipment. The anodic dissolution of the superalloy was studied in two acidic media: sulfuric and methanesulfonic acids. A comparative analysis of cyclic voltammetry and galvanostatic experiments was carried out. In sulfuric acid electrolyte, anodic processes proceed more vigorously, as indicated by higher cur-rent densities. However, this method records not only the dissolution currents of metals but also side processes such as anodic oxygen evolution and reoxidation of dissolved ions. Under galvanostatic conditions, which allow direct determination of alloy mass loss, it was shown that methanesulfonic acid with sodium chloride pro-vides a higher dissolution rate despite the medium's lower conductivity. This effect is explained by the higher solubility and stability of the methane-sulfonates of the alloying components (Cr, Al, Nb, Ta, Re), which reduce the tendency of the surface to repassivate. In the H2SO4 + NaCl medium, dissolution proceeds more uniformly but at lower mass efficiency, attributed to the formation of poorly soluble sulfates. In the methanesulfonate electrolyte, within the current density range of 1.5–2.5 A•dm-2, the ratios of Ni, Cr, Co, W, and Re were closest to those in the original alloy, while rhenium was detected in solution, unlike in the sulfuric medium. The obtained results can be applied to optimize the initial stage of superalloy recycling and to develop electrochemical technologies for the recovery of strategically important metals from industrial waste.
Determination of the Electrochemical Dissolution Feasibility of a Superalloy Used in Turbine Components in Alkaline Solutions With Additives
(Eastern-European Journal of Enterprise Technologies, 2025) Kotok, Valerii Е.; Sknar, Yuri Е.; Butyrina, Tetyana Е.; Sknar, Irina V.; Demchyshyna, Oksana; Chasova, Ella
ENG: The object of this study was an electro-chemical anodic dissolution of a heat-re-sistant nickel-based superalloy (≈62 wt.%),recovered from destroyed components of spe-cial-purpose equipment, which contains valu-able metals such as Re (≈4 wt.%), Co, W, Mo, Ta, Nb, and others. The research addressed the problem of the lack of an effective elec-trochemical method for selectively extract-ing these components, particularly rhenium and other valuable elements, from such an alloy in alkaline media. The anodic behav-ior of the alloy was experimentally studied in 0.5 M NaOH in the presence of various com-plexing and activating additives (NaCl, cit-ric acid, EDTA salt, and Na2H2P2O7). It was shown that none of the additives provided a significant acceleration of anodic dissolu-tion. This was demonstrated by the fact that the increase in the average specific charge calculated for five cyclic voltammetry scans that contributed to alloy dissolution did not exceed 8%. In other cases, the values were sig-nificantly lower than in the base solution con-taining only alkali. It was established that the anodic dissolution process has a surface-selec-tive nature: Ni, Co, Cr, Re, and Al are leached into the electrolyte, while a residual surface layer enriched in W, Ta, Nb, and Mo forms, hindering further dissolution. X-ray fluores-cence analysis data confirmed changes in the chemical composition(Ni content decreased to ≈48 wt.%, W increased from ≈9to≈20wt.% on the surface). Theoretical justification of the results is provided, based on the physico-chemical properties of compounds that may form during anodic dissolution in the pres-ence of additives. The absence of an activating effect from the additives suggests the need for further studies on pure NaOH. The obtained data are of practical importance for the selec-tive separation of superalloy elements before further processing.
Electrochemical Discharge of Nickel With Low Internal Stresses
(Oles Honchar Dnipro National University, Dnipro, 2025) Sknar, Yuri; Sknar, Irina V.; Butyrina, Tetiana E.
ENG: The work is devoted to the current topic of electrochemical separation of nickel with low voltages from sulfate electrolytes of electroextraction. Scrap processing of strategic nickel-containing superalloys with electroextraction of nickel is an urgent task today. Electrochemically deposited nickel is characterized by high internal tensile stresses, which leads to its delamination from the cathode surface. To reduce the internal stresses of nickel deposits obtained in such systems, it is proposed to use sulfur-containing organic compounds of sodium allylsulfonate, sodium orthoarylsulfonate, and sodium propynylsulfonate. It was established that allylsulfonate and orthoarylsulfonate practically do not affect the kinetics of nickel release. Propynyl sulfonate with a concentration of more than 5 mmol/l significantly inhibits the process of electrodeposition of nickel, which is related to the adsorption capacity of this compound with the triple bond present in the molecule. It is shown that due to the presence of a sulfo group in the composition of the molecules, the used organic additives contribute to the reduction of the internal stresses of nickel deposits. It was established that allyl sulfonate and orthoaryl sulfonate are the most promising reagents that contribute to reducing the internal stresses of electrodeposited nickel. Lowstress nickel deposits can be obtained in the range of current densities from 2 to 7 A/dm2 at a concentration of these additives from 15 to 30 mmol/l.
Study of the Influence of Synthesis Parameters on the Structural and Magnetic Properties of Cobalt Ferrite
(Oles Gonchar Dnipro National University, Dnipro, 2024) Frolova, Liliya A.; Sknar, Irina V.
ENG: The synthesis of cobalt ferrite by plasma chemical method was studied in the work. The influence of pH of the reaction medium, temperature and duration of treatment on magnetic properties, intensity of peaks on X-ray diffraction, average size of crystallites, value of dislocation density was determined using the central composite rotatable planning of the experiment, which is based on the results obtained by X-ray phase analysis, vibrational magnetometry, and electron microscopy. Statistical analysis made it possible to quantitatively assess the influence of the synthesis parameters on the selected response functions. The results showed that the pH of the reaction medium is the parameter that shows the greatest influence both on the growth of cobalt ferrite powder crystallites and on the magnetic properties of the samples obtained by the plasma chemical method.