323 research outputs found
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
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