Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique

A high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness

Superconducting joining of melt-textured Y-Ba-Cu-O bulk material

The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO parts. The peculiarities of solidification, phase formation, structure transformations and electromagnetic properties of MT-YBCO soldered with TmBa2Cu3O7-d are discussed.Comment: PS of 6 pages text and 5 figures, presented at ICMC'2000, Brasi

Effects of high pressure on the physical properties of MgB2

The synthesis of MgB2-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8-1.0 \cdot 106 A/cm2 in the self field and 103 A/cm2 in a magnetic field of 8 T at 20 K, 5-3 \cdot 105 A/cm2 in self field at 30 K, the corresponding critical fields being HC2 = 15 T at 22 K and irreversible fields Hirr =13 T at 20 K, and Hirr =3.5 T at 30 K, thermal conduction of 53+/-2 W/(m \cdot \kappa), the Vickers hardness Hv=10.12+/-0.2 GPa under a load of 148.8 N and the fracture toughness K1C = 7.6+/-2.0 MPa m0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that highpressure-prepared materials are promising for application in transformer-type fault current limiters working at 20-30 K.Comment: International Conference on Superconductivity and Magnetism 25-30 April 2010,Antalya, Turkey, in print Journal of Superconductivity and Novel Magnetis

Complex assessment of ukrainian agroholdings' economic security

Retrospective diagnostics of main financial results of activity (profit, earnings and yield of shares); business capital, market capitalization, EBITDA, operating margin and net profit margin, P / E, ROA, ROE, ROC as of 2018 and an average of 5 years; Consideration of Montier C-Score and Piotroski F-Score indicators on financial issues of companies; liquidity of the balance of agroholdings on the criterion of the ratio of assets and liabilities; the coefficient analysis of enterprises and the diagnosis of bankruptcy probabilities using models of multiple discriminant analysis (MDA model), logistic regression (Logit-model) and rating methods (Beaver's indicators and definition of the class of the potential beneficiary of the investment prokect) helped to formulate a generalized conclusion on the probability of bankruptcy according to models and a general assessment of the financial condition of agricultural companies. Based on the analysis, it has been determined that, according to all methods of the agroholding, the sample collectively generates a series from the highest to the lowest: MHP / Kernel, IMC, Agroton and Avangard. In view of this, it is necessary to formulate and continuously improve integrated risk management systems (integrated systems of enterprise economic security), rather than separate procedures at the level of different departments of the compan

Geochemical Indicators of the Carbonate Sedimentation Depositional Environments and Geodynamic Conditions in the East of the Middle Urals in the Kizelovian Time

Изучена геохимия известняков кизеловского горизонта Восточно-Уральской зоны (р. Реж, Средний Урал): изотопный состав углерода и кислорода, концентрации малых элементов, значения редокс-индикаторов. Предполагается, что карбонатные отложения формировались в мелководной, богатой кислородом обстановке в условиях высокой биопродуктивности тепловодной экосистемы в пределах изолированной карбонатной платформы при стабильном погружении территории. Ряд признаков свидетельствует о том, что осадконакопление в кизеловское время могло происходить во внутренней лагуне достаточно крупной атолловидной структуры. Современными аналогами Режевской карбонатной платформы могут быть некоторые атоллы Мальдивского архипелага.Geochemical characteristics of the limestones of Kizelovskian substage of the Eastern Urals zone (Rezh River, Middle Urals), such as carbon and oxygen isotopic composition, concentration of minor and trace elements, and redox value indicators, were studied in details. Based on the results of data interpretation and analysis of lithological features, it was assumed that carbonate deposits formed in shallow oxygen-rich environment with high bioproductivity warm water ecosystem, and within the isolated carbonate platform with a steady sinking territory. Some signs indicate that sedimentation during the Kizelovian time occurred in the inner lagoon of a large atoll. The Maldivian archipelago could be a contemporary analogue of the Rezhevskaya carbonate platform

Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

Friction has a direct relation with the energy efficiency and environmental cleanliness in all moving mechanical systems. To develop low friction coatings is extremely beneficial for preserving not only our limited energy resources but also the earth’s environment. This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation,and thereby it contributes to better controlling the mechanical and tribological properties. Experimental findings and theoretical calculations reveal that high-hardness (18.2 GPa), high-adhesion strength (28 N) as well as low-internal stress (-0.8 GPa) can be achieved by a nanocrystallite/amorphous microstructure architecture for the nc-WC/a-C(Al) carbon-based nanocomposite coating;in particular low friction (~0.05) can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces. This design concept is general and has been successfully employed to fabricate a wide class of low friction carbon-based nanocomposite coating