First-principles density functional theory (DFT) is employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga2O3 crystals. Hybrid exchange–correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga2O3. Based on the results of our calculations, we predict that an oxygen vacancy in β-Ga2O3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga2O3. On the other hand, all types of charge states of gallium vacancies are sufficiently deep acceptors with transition levels more than 1.5 eV above the valence band of the crystal. Due to high formation energy of above 10 eV, they cannot be considered as a source of p-type conductivity in β-Ga2O3.
Purpose: The purpose of this investigation is to substantiate by means of numerical simulation
the expedience of high-temperature utilization of used tires with subsequent methanation of fuel
gases and separation of multicomponent hydrocarbon mixtures to drain the liquefied methane.
Design/methodology/approach: The investigation was carried out by means of numerical
simulation. In mathematical description of gas processes relations of thermodynamics and
heat and mass transfer were used. To determine the coefficients of thermal and physical
parameters of working bodies the Peng-Robinson equation of state was used through the
computer program REFPROP. The system of equations is represented as the interrelations
between the functional elements according to the principle "output from the element A – input
into the element B". Its solution was obtained by the method of successive approximations,
namely by the Newton-Raphson iteration method. Using this method we have determined
the values of temperature, pressure, mass flow rate and mass content of the hydrocarbon
gas mixture components in each reference cross-section of the power facility.
Findings: As a result of numerical simulation, it is determined that when the multicomponent
hydrocarbon mixtures are separated, three flows of energy resources may be obtained: with
a high mass content of methane of 91.5% and 83.4%, which may be used as motor fuel, and
a gas flow suitable for maintaining the process of waste gasification. However, to remove
heat in the condenser of the rectification column, it is necessary to use expensive liquid
nitrogen. The cost of methane production may be reduced if the condenser is removed from
the rectification column. However, such approach reduces the overall yield of commercial
products almost in four times and significantly reduces the methane with the third product
(molar percentage of 35%).
Research limitations/implications: The investigation was carried out for the material of
used tires without a metal frame.
Practical implications: The implementation of the technology of high-temperature recycling
of used tires gives the opportunity to use the generated synthetic gas to maintain the process
of utilization, and gives the opportunity to produce liquefied methane, suitable for storage.
Originality/value: The main problem of high-temperature recycling of tires is the emission
of toxic gas to the atmosphere. It is proposed to allocate methane energy resource from this
gas. For the first time an attempt was made to justify the expedience of the technology of
high-temperature utilization of tires for liquefied methane production.
The samples of porous InP were grown up by a method of anode etching on a substrate (100) InP n-type. The samples were characterized by SEM and photoluminescence (PL) where a blue shift was observed in PL. To remove surface oxides from the surface of porous InP using the thermal cleaning of the samples in a stream of high purity hydrogen. Size of walls between pores which makes 3 - 11nm.
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