Простой метод изготовления нанопроволок карбида кремния

In this work, we introduce a simple and convenient approach for growing SiC nanowires (SiCNWs) directly on carbon source from graphite. The commercial SiO powder and the cheap common graphite were used as the source materials. SiCNWs have been synthesized during holding time less than 60-80 min at 1450-1500 C by using a simple and low-cost method in an industrial furnace with a resistant heater.У даній роботі представлено простий і зручний підхід для вирощування нанодротів карбіду кремнію (SiCNWs) безпосередньо на джерело вуглецю з графіту. У якості вихідних матеріалів були використані промисловий порошок SiO і дешевий звичайний графіт. SiCNWs були синтезовані за допомогою простого і недорогого методу під час витримки в промисловій печі зі стійкими нагрівачем 60-80 хв при температурі 1450-1500 С.В данной работе представлен простой и удобный подход для выращивания нанопроволок карбида кремния (SiCNWs) непосредственно на источнике углерода из графита. В качестве исходных материалов были использованы промышленный порошок SiO и дешевый обычный графит. SiCNWs были синтезированы с помощью простого и недорогого метода во время выдержки в промышленной печи с устойчивыми нагревателем 60-80 мин при температуре 1450-1500 С

Off-diagonal quark distribution functions of the pion within an effective single instanton approximation

We develop a relativistic quark model for pion structure, which incorporates the non-trivial structure of the vacuum of Quantum Chromodynamics as modelled by instantons. Pions are boundstates of quarks and the strong quark-pion vertex is determined from an instanton induced effective lagrangian. The interaction of the constituents of the pion with the external electromagnetic field is introduced in gauge invariant form. The parameters of the model, i.e., effective instanton radius and constituent quark masses, are obtained from the vacuum expectation values of the lowest dimensional quark and gluon operators and the low-energy observables of the pion. We apply the formalism to the calculation of the pion form factor by means of the isovector nonforward parton distributions and find agreement with the experimental data.Comment: LaTeX; altered version; references and figures added. Published: paper has been accepted for publication in Nucl. Phys.

Carbon ceramics from plants: Graphitization of biomorphic matrixes

Properties of matrixes obtained from plants at various pyrolysis temperatures have been discussed. The article is devoted to graphitization of carbon matrixes obtained from plants. All stages of production, starting from preparation of the precursors up to high-temperature pyrolysis, have been considered together with some specific properties of matrixes at each stage. Previously unexplored new structural surface changes have been found. The use of potassium-doped wooden precursors showed the graphitization property of the matrix surfaces and allowed to form the matrix capillary wall coating with layers of crystalline graphite as well as graphene flakes and films with a low number of defects. New possibilities to apply these matrixes as examples of ultracapacitor, power unit filter electromagnetic interference and audio power amplifier antiresonance element have been discussed as well

Simple method for SiC nanowires fabrication

In this work, we introduce a simple and convenient approach for growing SiC nanowires (SiCNWs) directly on carbon source from graphite. The commercial SiO powder and the cheap common graphite were used as the source materials. SiCNWs have been synthesized during holding time less than 60-80 min at 1450-1500 °C by using a simple and low-cost method in an industrial furnace with a resistant heater

Biomorphous SiC ceramics prepared from cork oak as precursor

Porous ceramic materials of SiC were synthesized from carbon matrices obtained via pyrolysis of natural cork as precursor. We propose a method for the fabrication of complex-shaped porous ceramic hardware consisting of separate parts prepared from natural cork. It is demonstrated that the thickness of the carbon-matrix walls can be increased through their impregnation with Bakelite phenolic glue solution followed by pyrolysis. This decreases the material's porosity and can be used as a way to modify its mechanical and thermal characteristics. Both the carbon matrices (resulted from the pyrolysis step) and the resultant SiC ceramics are shown to be pseudomorphous to the structure of initial cork. Depending on the synthesis temperature, 3C-SiC, 6H-SiC, or a mixture of these polytypes, could be obtained. By varying the mass ratio of initial carbon and silicon components, stoichiometric SiC or SiC:C:Si, SiC:C, and SiC:Si ceramics could be produced. The structure, as well as chemical and phase composition of the prepared materials were studied by means of Raman spectroscopy and scanning electron microscopy

Biomorphic SiC from peas and beans

Biomorphic porous SiC ceramics produced by impregnation with liquid or vapor silicon of carbon matrices derived from peas (Pisum sativum L.) and beans (Phaseolus) precursors were investigated. Optical and scanning electron microscopy was used to study the structure of ceramics. It was shown that SiC ceramics made from endosperm of peas and beans seeds has inherited the alveolate structure and possesses many hierarchical pores with diameters varying between 20 to 100 µm. Raman spectroscopy investigations showed that the 3C polytype is formed at a synthesis temperature of about 1550 ⁰C, and that both 3C and 6H-SiC are formed at temperatures of about 1800 ⁰C. It is shown possibilities of production of ceramic articles of various forms from seeds

Effect of macrostructure on the thermoelectric properties of biomorphous SiC/Si ceramics

In this work, effect of porous macrostructure on the thermoelectric properties of biomorphous SiC/Si ceramics prepared by the liquid silicon infiltration process has been investigated. Temperature dependences of the conductivity and thermal e.m.f. have been measured within the range 20-700 °C. It has been shown that electrical resistivity of the samples decreases drastically as temperature increases over the entire temperature range, indicating semiconductor behavior. All the samples demonstrate a negative thermal e.m.f. confirming the electronic mechanism of charge transfer. It is ascertained that anisotropy of porous macrostructure of the ceramics influences considerably on their electric and thermoelectric properties. The figure of merit maximum value of 1.2×10⁻⁵ K⁻¹ at 700 °C was obtained

Mechanical properties of biomorphous ceramics

Mechanical properties: The Vickers hardness and bending strength of porous biomorphic SiC (bioSiC) ceramics fabricated from different natural hardwoods were investigated. It has been found that these parameters are highly dependent on the geometrical densities of ceramics, and Vickers hardness values can be well described using the Ryskevitch-type equation. It has been shown that the data of geometrical density bio-SiC ceramics can be used to estimate mechanical parameters such as bending strength. Materials with advanced properties appropriate for surgical applications are being designed. Further ways to improve the mechanical properties of ceramics and ceramic products have been discusse

X-ray diffraction investigation of GaN layers on Si(111) and Al₂O₃ (0001) substrates

Methodical approaches to the analysis of X-ray data for GaN films grown on various buffer layers and different substrates are presented in this work. Justification of dislocation structure investigation by various methods was analyzed and approaches for evaluation of deformation level and relaxation are discussed. Clarity and accuracy of obtained structure characteristics of nitride films are under discussion. Optimization methods for experimental data processing are shown. Structural properties were obtained using high resolution X-ray diffraction with two types of scans and reciprocal space maps. Microscopic nature of spatial inhomogeneities in these structures (deformations and dislocation density) and influence of the buffer layer thickness on properties of GaN layer were discussed with account of obtained results

Investigation of luminescent properties inherent to SrTiO₃:Pr³⁺ luminophor with Al impurity

The red-emitting SrTiO₃:Pr³⁺,Al luminophors that can be used for the white light emitting diodes (LEDs) were prepared using the sol-gel method. The starting materials were SrCl₂, Ti (O – i – C₃H₇)₄, Al(NO₃)₃·9H₂O and PrCl₃. The reaction between them results in a mixture of compounds that transform into single-phase SrTiO₃:Pr³⁺,Al after annealing in air. Displacement of Ti out of the SrTiO₃ lattice caused by substitution with Al and formation of individual crystalline TiO₂ phase (rutile) were observed. PL spectra show the high-intense red peak (λ = 617 nm), the same high-intense peak with the full width at half maximum (FWHM) 20 nm was found in cathodoluminescence spectra. The increase of the aluminium concentration from 0 up to 15 mol.% leads to approximately two-fold increase in the luminance. The latter increases from 180 up to 350 cd/m² at the anode voltage 10 kV and current density 30 μA/cm²