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In the given article, a thermodynamic theory for nanodispersed powders of ferroelectrics of various structures, including KDP crystals as potential hydrogen sorbents, is presented. The article presents the statistical theory of KDP crystals developed on the basis of molecular-kinetic concepts, which allows determining, explaining and substantiating their physical properties. The temperature dependence of the order parameter, which is proportional to the degree of spontaneous polarization and deformation, is determined, and the conditions, under which a phase transition in KDP crystals turns out to be a second-order phase transformation close to a first-order one, are elucidated. The Curie temperature of the phase transition is estimated, and the dependences of the order parameter on the intensity of an external electric field or external oriented mechanical stress are established. The configurational heat capacity, its temperature dependence and jumps at the phase-transition point are estimated. The temperature dependences of the direct and inverse permittivities (or susceptibility) are determined. The validity of the Curie–Weiss law for KDP crystals is verified. [ABSTRACT FROM AUTHOR]

The proposed work considers: hydrogen sorption properties of systems of magnesium intermetallic compounds with a complex cubic structure C15b, as promising, reliable, reversible hydrogen accumulators. Considered thermal processes. A statistical theory is proposed for the cubic structure C15b of composition MgRT4Hx, where R = Ce, La, Nd, Pr, Y; T = Co, Ni; 0 ≤ x ≤ 6 at phase transitions in the process of hydrogenation, taking into account pressure. The concentration dependences of the maximum values of the order parameter and a priori probabilities are established. Hydrogen solubility isopleths and isotherms are calculated and considered, and a graphical concentration dependence of the hydrogen atom ordering temperature in MgCeCo4-type crystals is created. The order-disorder transition is considered with allowance for temperature, and the process of absorptiondesorption of hydrogen by the C15b structure is also studied. The equation of thermodynamic equilibrium with the calculation of free energy is derived. And also considered the graphical dependence of the value of the order parameter on temperature and pressure. The temperature dependence of hydrogen solubility in the α, β phases for the MgCeCo4 crystal is considered. The configurational heat capacity of a crystal of the MgSnCu4Hx type structure has been studied, taking into account the temperature and the order parameter. A graph of hydrogen absorption-desorption of the MgCeCo4Hx crystal has been constructed. A comparative analysis of the experimental and practical results of the absorption-desorption of hydrogen by the working fluid of the composition MgRT4Hx has been carried out. [ABSTRACT FROM AUTHOR]

The goal of the research work was the pyrolytic synthesis of straight and spiral carbon nanotubes of approximately the same diameter, as well as their comprehensive analysis. To solve the given problem, a new installation for the pyrolytic synthesis of carbon nanostructures (CNS) with a fusion reactor, which for each fusion process can have its own angle relative to the classical horizontal position of the reactor axis. This reactor made it possible to develop a method for obtaining conglomerates of spiral-shaped multi-walled carbon nanotubes with a diameter of 15–60 nm and to synthesize straight multi-walled carbon nanotubes with a diameter of 5 to 60 nm. The research of pyrolytic synthesis of carbon nanostructures in a vertical reactor allows to work out the technology of purposeful synthesis of nanotubes that have a spiral shape with a certain diameter and pitch of the turn. As part of the work, a new mechanism for the formation of spiral multi-walled carbon nanotubes is also considered and proposed, which is important for their further industrial synthesis and their use in related composites. A scheme is proposed of conditions for the synthesis of carbon nanostructures by the pyrolytic method. Thermal analysis was carried out in the work, which recorded the presence of two different structures with low thermal stability (probably amorphous carbon and higher hydrocarbons). When using scanning and transmission electron microscopy, the formation of spiral nanofibers with a diameter of 15–60 nm in the vertical position of the reactor was recorded, and in the horizontal position of the reactor, the formation of straight and slightly curved MWCTs with a diameter of nanofibers from 5 to 60 nm was found. Raman spectroscopy confirms the presence of multi-layered carbon tubular formation, i.e. MWCT, in both synthesis products. [ABSTRACT FROM AUTHOR]

Several methods of electrochemical synthesis of nickel (Ni) nanopowder are investigated. As shown, the most efficient and cost-effective method is the electrolysis of nickel sulphate (NiSO4) with appropriate impurities of nickel chloride II (NiCl2), boric acid (H3BO3) and thiourea ((NH4)2CS) using the P-5848 potentiostat as a power source. Ultrahigh-purity aluminium (Al) is used as the cathode, and a platinum plate is served as the anode. The synthesis is performed at temperatures of 45–65°C. After two hours of electrolysis at a current density of 1.0–3.3 A/dm², nickel nanopowder with an average scale size (scaly particles) of 55 nm is obtained that is confirmed by high-resolution electron microscopy and Raman spectroscopy of high resolution, as well as modern adsorption methods. Electrochemical reactions take place at the cathode (Ni2++2e=Ni) and at the anode (2H2O=O2↑+4H++4e). Dendritic copper nanoparticles with high dispersion are also obtained with the possibility of regulating the synthesis of copper nanopowder with a bulk density of 0.4 g/cm³. For this purpose, electrolysis of an electrolyte solution with a relatively low copper content and a high sulphuric acid content is performed at a high cathode current density and a relatively low temperature of a copper sulphate solution (CuSO4). At the same time, a significant amount of copper sludge is removed from the cell by means of the periodic shocks, and the copper anode is shed to the bottom of the bath after 13.3 ampere-hours of current per 1 dm² of the anode plane. The electrolysis process is continued at a current density of 15.6 A/dm², and the direction of the current is changed every 20 minutes. In our case, the most appropriate mode of electrolysis is when the cathodes (copper plates) are placed at a distance of 0.8 cm from each other in the electrolyte with 45% H2SO4, 4% CuSO4 and 8% Na2SO4, and the current density at the cathode is of 15.3 A/dm² at the temperature of 54° C and at the voltage between two copper plates of 0.775 V. [ABSTRACT FROM AUTHOR]

Carbon nanostructures (CNS) of different types (carbon nanotubes, fullerenes and fullerene-like structures) are obtained by the method of electricarc evaporation of graphite grades, namely, SIGE (special impregnated graphite electrodes) and FGDG-7 (fine grained dense graphite with a density of 7), within the inert gas (He). A comparative analysis of synthesizedCNS characteristics is performed. The optimal technological conditions for the synthesis of CNS from graphite anode electrodes of comparable grades (SIGE and FGDG-7) are determined. Deposits of plasma chemical synthesis are studied. The structure of the synthesized carbon materials is studied by scanning and transmission electron microscopies, and as shown, carbon nanotubes are formed during the evaporation of SIGE brand graphite even without the use of a catalyst. Differential-thermal, thermogravimetric and differential thermogravimetric analyses are performed, according to the results of which the temperatures of the beginning of interaction of the formed CNS with air oxygen are established. According to the data of the photospectral analysis of the synthesis products, calculations are performed, and it is shown that the fullerene component obtained by evaporation of SIGE brand graphite contains 10–12% of the C60 and C70 fullerenes that is not inferior to similar indicators of FGDG-7 brand graphite. Taking into account the cheapness of SIGE brand graphite compared to FGDG-7 graphite brand, it can be argued that carbon nanostructures synthesized from SIGE brand graphite have a lower cost. This fact is important for the synthesis of carbon nanostructures as filler for state-of-the-art composites. In addition, the synthesis of much cheaper fullerene and fullerene-like molecules is a great advantage for their study and using in state-of-the-art materials, because today, new state-of-the-art nanotechnologies on the base of fullerenes are beginning to be created. [ABSTRACT FROM AUTHOR]

A review of more than 100 contemporary literary works of domestic and foreign researchers on the issues of electric arc synthesis (EAS) of various carbon nanostructures (CNS) has been performed. EAS CNScan be performed in both gaseous and liquid media. EAS in a gaseous medium has a number of advantages, such as high productivity and velocity of the condensation process, as well as ease of control.But this method of synthesis also has disadvantages: it requires a complex vacuum and cooling system, which makes the installation very cumbersome.In addition, this method does not solve the problem of agglomeration of synthesized CNS and has a by-product of synthesis in the form of growth (deposit) on the electrode. EAS in a liquid medium is more compact equipment, as it does not require systems of vacuum (the process takes place at atmospheric pressure) and cooling (liquid medium plays the role of heat dissipation).This method of synthesis uses different types of dielectric liquids – from distilled water (H2O), liquid nitrogen (N2) to hydrocarbon solvents, which can serve as a source of carbon in the synthesis zone.By changing the composition of the liquid phase, it is possible to achieve the synthesis of different types of CNS.Also, this method involves the use of metal electrodes, which, in addition to long service life, can act as catalysts.The metal particles can be encapsulated ANS, forming composites with different magnetic properties.In some studies, it has been shown that mixtures of metal carbides can be formed when metal electrodes are used in the EAS process in a liquid medium.The liquid medium after EASCNS is also of scientific interest. Probably, the liquid medium contains new modifications of soluble organic compounds, which are being researched by researchers around the world.Thus, scientists have found that after EAS in a liquid medium using graphite electrodes, the working solution (C6H6) changed its color.This indicates the formation of soluble organic compounds in it. In the literature review on the basis of literature data the table of modes for industrial synthesis of single-walled CNS is created.Also, a list of modes for the creation of defective CNS as a method of increasing the area of adsorption in nanoparticles. The solution of important problems of the EAS method is recorded: agglomeration of CNS; the problem of forming a deposit; increase productivity. [ABSTRACT FROM AUTHOR]

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Carbon nanomaterials (СNM) containing platinum: fullerenes, nanocomposites, graphenes, single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are created by the method of plasma-chemical synthesis of MPG-7 graphite in helium environment with using the catalyst (Pt). Studies of the morphology and structure of materials formed at the cathode at the micro- and nanoscales have been carried out, and the influence of platinum vapours on the mechanisms of nanostructure formation has been studied. The content of platinum and its distribution in each of the components of the received deposit and in the wall soot is determined by the method of X-ray microanalysis. Differential-thermal analysis of synthesized CNMs in air by TG, DTG, DTA methods is performed, and the composition of synthesis products is identified by differences in heat resistance values. Preliminary results show that such synthesized platinum-containing carbon nanostructures are suitable for 3D-printing CJP technology (ceramic printing) and allow creating electrodes for the fuel cell of the hydrogen cycle without applying a layer of platinum (Pt) catalyst. Today it is the key to creating cheap fuel cells for hydrogen energy. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)