Myroslav Karpets

Bio: Myroslav Karpets is an academic researcher from National Academy of Sciences of Ukraine. The author has contributed to research in topics: Alloy & Solid solution. The author has an hindex of 15, co-authored 122 publications receiving 733 citations. Previous affiliations of Myroslav Karpets include National Academy of Sciences & Russian Academy of Sciences.

Electrolytic synthesis of carbon nanotubes from carbon dioxide in molten salts and their characterization

Abstract: Carbon nanotubes (CNTs) were synthesized from CO2 dissolved in molten salts using the novel electrolytic method developed by the authors. The electrolysis were carried out under current and potential controls. To establish the actual current and potential ranges, the electroreduction of carbon dioxide dissolved in the halide melts under an excess pressure up to 15 bar was studied by cyclic voltammetry on glassy-carbon (GC) electrode at a temperature of 550 °C. The electrochemical–chemical–electrochemical mechanism of CO2 electroreduction was offered for explanation of the obtained results. The structure, morphology, and electronic properties of the CNTs obtained were studied using SEM, TEM, X-ray and electron diffraction analysis, Raman and ESR spectroscopy. It was found that the majority of the CNTs are multi-walled (MWCNTs), have curved form, and most often agglomerate into bundles. Almost all CNTs are filled partly with electrolyte salt. Except MWCNTs the cathode product contains carbon nanofibers, nanographite, and amorphous carbon. The dependences of CNT's yield, their diameter, and structure peculiarities against the electrolysis regimes were established.

Thermal Stability of Superhard Nitride Coatings from High-Entropy Multicomponent Ti–V–Zr–Nb–Hf Alloy

Abstract: Nitride coatings with high hardness (600–650 GPa) are produced from a high-entropy multicomponent single-phase alloy containing five nitride-forming elements by vacuum arc deposition with application of pulsed implantation These high values of hardness are characteristic of metals in the equiatomic alloy only in nanostructured state The mechanical properties of the coatings annealed in the temperature range up to 1200 °C are studied It is established that the coatings are solid solutions of high-entropy nitride with fcc lattice The vacuum coatings inherit the same type of crystal lattice as that of the target (bcc) The crystal lattice of high-entropy vacuum coatings is formed through the mechanism revealed in the cast alloys The parameter of this lattice is close to that calculated by Vegard’s rule

Nanostructural inhomogeneities acting as pinning centers in bulk MgB2 with low and enhanced grain connectivity

Abstract: Regularly distributed structural inhomogeneities in the MgB2 matrix, such as nano-areas with a high concentration of boron (MgBx) and impurity oxygen (Mg?B?O nano-layers or inclusions), are observed in all materials independently of the preparation method, pressure (0.1?MPa?2?GPa) and temperature (600?1100??C), and in materials with different connectivity (18?98%) and density (55?99%). Such inhomogeneities can act as pinning centers in MgB2 because the variation of their size and distribution are well correlated with variations of the critical current density, jc. The decrease in size of MgBx inclusions, the transformation of 15?20?nm thick Mg?B?O nano-layers into separated inclusions, and the localization of impurity oxygen are accompanied by an increase in critical current density in low and medium magnetic fields. The efficiency of these defects is evidenced by a shift from grain-boundary pinning to point pinning.

Production and mechanical properties of high-entropic carbide based on the TiZrHfVNbTa multicomponent alloy

Abstract: The possibility of producing coatings of high entropic carbide by scattering multicomponent alloy in plasma of compressed vacuum–arc discharge has been shown. It is defined that the hardness of coatings from high-entropic carbide based on TiZrHfVNbTa multicomponent alloy is 43–48 GPa and exceeds the hardness of monocarbides of metals that enter into the composition of the alloy. The friction coefficient for the carbide high-entropic coating based on the TiZrHfVNbTa alloy at the loads 2.2 to 5.2 N is 0.14–0.16.

High-entropy ceramics

Abstract: Disordered multicomponent systems, occupying the mostly uncharted centres of phase diagrams, were proposed in 2004 as innovative materials with promising applications. The idea was to maximize the configurational entropy to stabilize (near) equimolar mixtures and achieve more robust systems, which became known as high-entropy materials. Initial research focused mainly on metal alloys and nitride films. In 2015, entropy stabilization was demonstrated in a mixture of oxides. Other high-entropy disordered ceramics rapidly followed, stimulating the addition of more components to obtain materials expressing a blend of properties, often highly enhanced. The systems were soon proven to be useful in wide-ranging technologies, including thermal barrier coatings, thermoelectrics, catalysts, batteries and wear-resistant and corrosion-resistant coatings. In this Review, we discuss the current state of the disordered ceramics field by examining the applications and the high-entropy features fuelling them, covering both theoretical predictions and experimental results. The influence of entropy is unavoidable and can no longer be ignored. In the space of ceramics, it leads to new materials that, both as bulk and thin films, will play important roles in technology in the decades to come. The valuable combination of disorder and non-metallic bonding gives rise to high-entropy ceramics. This Review explores the structures and chemistries of these versatile materials, and their applications in catalysis, water splitting, energy storage, thermoelectricity and thermal, environmental and wear protection.

Processing and Properties of High-Entropy Ultra-High Temperature Carbides

Abstract: Bulk equiatomic (Hf-Ta-Zr-Ti)C and (Hf-Ta-Zr-Nb)C high entropy Ultra-High Temperature Ceramic (UHTC) carbide compositions were fabricated by ball milling and Spark Plasma Sintering (SPS). It was found that the lattice parameter mismatch of the component monocarbides is a key factor for predicting single phase solid solution formation. The processing route was further optimised for the (Hf-Ta-Zr-Nb)C composition to produce a high purity, single phase, homogeneous, bulk high entropy material (99% density); revealing a vast new compositional space for the exploration of new UHTCs. One sample was observed to chemically decompose; indicating the presence of a miscibility gap. While this suggests the system is not thermodynamically stable to room temperature, it does reveal further potential for the development of new in situ formed UHTC nanocomposites. The optimised material was subjected to nanoindentation testing and directly compared to the constituent mono/binary carbides, revealing a significantly enhanced hardness (36.1 ± 1.6 GPa,) compared to the hardest monocarbide (HfC, 31.5 ± 1.3 GPa) and the binary (Hf-Ta)C (32.9 ± 1.8 GPa).

High-entropy ceramics: Present status, challenges, and a look forward

Abstract: High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Although in the infant stage, the emerging of this new family of materials has brought new opportunities for material design and property tailoring. Distinct from metals, the diversity in crystal structure and electronic structure of ceramics provides huge space for properties tuning through band structure engineering and phonon engineering. Aside from strengthening, hardening, and low thermal conductivity that have already been found in high-entropy alloys, new properties like colossal dielectric constant, super ionic conductivity, severe anisotropic thermal expansion coefficient, strong electromagnetic wave absorption, etc., have been discovered in HECs. As a response to the rapid development in this nascent field, this article gives a comprehensive review on the structure features, theoretical methods for stability and property prediction, processing routes, novel properties, and prospective applications of HECs. The challenges on processing, characterization, and property predictions are also emphasized. Finally, future directions for new material exploration, novel processing, fundamental understanding, in-depth characterization, and database assessments are given.

Microstructures and properties of high-entropy alloy films and coatings: a review

Abstract: In the past 14 years, as a branch of high-entropy alloy (HEA) materials, HEA films and coatings have exhibited the attractive and unique properties, relative to the conventional film and coating ma...