Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the inte...Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the interface,further growth of hydrate due to the suction of water in the capillary system formed between the wall of the cuvette and the end boundary of the hydrate layer occurs.Most probably,substantial effects on the formation of this capillary system may be caused by variations in reactor wall properties,for example,hydrophobic-hydrophilic balance,roughness,etc.We found,that the rate of CO_(2) hydrate film growth on the surface of the humic acid aqueous solution is 4-fold to lower in comparison with the growth rate on the surface of pure water.We suppose that this is caused by the adsorption of humic acid associates on the surface of hydrate particles and,as a consequence,by the deceleration of the diffusion of dissolved carbon dioxide to the growing hydrate particle.展开更多
In the present work we studied the induction periods of hydrate formation of natural gas in pure water, aqueous solutions of surfactants, and in the presence of surfactant together with aluminum oxide nanopowder, the ...In the present work we studied the induction periods of hydrate formation of natural gas in pure water, aqueous solutions of surfactants, and in the presence of surfactant together with aluminum oxide nanopowder, the activity of which as hydrate formation inducer was studied previously. Sodium dodecyl sulfate（SDS） or neonol AF-9-12 were used as the surfactants. It was demonstrated that the addition of either surfactants or aluminum oxide powder under our experimental conditions causes a decrease in the induction period of hydrate formation from;05 min for pure water to 30–35 min for water with additives. In the case of the simultaneous presence of surfactants and aluminum oxide powder in the system, induction period decreased to;0 min. So, the synergistic effect of the combination of surfactant and oxide powder on gas hydrate nucleation was demonstrated. Possible reasons of this effect have been discussed.展开更多
The results on a dissociation behavior of propane hydrates prepared from ＂dry water＂ and contained unreacted residual water in the form of ice inclusions or supercooled liquid water（water solution of gas） were pre...The results on a dissociation behavior of propane hydrates prepared from ＂dry water＂ and contained unreacted residual water in the form of ice inclusions or supercooled liquid water（water solution of gas） were presented for temperatures below 273 K.The temperature ramping or pressure release method was used for the dissociation of propane hydrate samples.It was found that the mechanism of gas hydrate dissociation at temperatures below 273 K depended on the phase state of unreacted water in the hydrate sample.Gas hydrates dissociated into ice and gas if the ice inclusions were in the hydrate sample.The samples of propane hydrates with inclusions of unreacted supercooled water only（without ice inclusions） dissociated into supercooled water and gas below the pressure of the supercooled water-hydrate-gas metastable equilibrium.展开更多
Gas hydrates and wax are the major flow assurance problems for the transportation of produced hydrocarbons through pipelines.However,in most research works both these two problems are studied separately.Although simul...Gas hydrates and wax are the major flow assurance problems for the transportation of produced hydrocarbons through pipelines.However,in most research works both these two problems are studied separately.Although simultaneous precipitation or deposition of these compounds in pipelines can lead to different mitigation/prevention strategies,the investi-gations in which both these problems are considered simultaneously appeared only recently.There is no information in the literature on the texture/composition and features of decomposition process of mixed wax/hydrate plugs.At the same time,this information could be useful to understand how to treat the problem of formation of these plugs.In this work,three wax/gas hydrate plugs were collected at quasi-static conditions from a water-in-oil emulsion to study their texture,composition and the features of decomposition process.Powder X-ray diffraction and IR(infrared spectroscopy)analyses showed that the plugs consisted of wax and gas hydrate.Thermovolumetric and DSC(Differential Scanning Calorimetry)experiments showed that the main part of gas hydrate in the plugs at the ambient pressure started to decompose at about 268 K.This temperature was higher than the equilibrium temperature of carbon dioxide hydrate at this pressure,indicating that the gas hydrate in the plugs could be effectively preserved at temperatures below the ice melting point(273.2 K).It was found through observation of the hydrate decomposition process in the plugs under the microscope that the gas in the samples released in small bubbles,while the hydrate particles were not visible at this magnification,indicating that the hydrate was indeed highly dispersed in the samples.A residual wax was jelly-like after decomposition of hydrate in all the cases.Rheological experiments showed that the plugs residues after decomposition of the hydrates had higher yield points and viscosities than the initial waxy crude oil origi-nally used for the experiments.展开更多
Modern but not entirely coordinated foundations of quantum physics are described in the book “The Quantum Challenge”. The difficulties and philosophical problems of this area of science are discussed. Discussions of...Modern but not entirely coordinated foundations of quantum physics are described in the book “The Quantum Challenge”. The difficulties and philosophical problems of this area of science are discussed. Discussions of many great scientists who paved the foundations of the physics of micro-world are described. These discussions are still urgent. The diversity of interpretations of the wave function, light interference, uncertainty principle, complementarity and completeness of micro-world description are stressed in this book. Difficulties and problems of quantum mechanics described in this book allowed the author of the present communication to propose a new approach based on the infinitely small metrics The difference of infinitesimals in two geometries allows one to explain W. Heisenberg’s uncertainty principle. Interconnection of the images in these geometries is possible with the help of Weierstrass integral transform. This approach allows one to describe the interference of light behind the screen with slits as a sum of the corpuscular component (Weierstrass transform) and the wave component (Fourier transform).展开更多
A novel geometric approach is proposed for the development of the wave-particle notions. This approach is based on a comparison of the two geometries with different sizes of an infinitesimal point. It is assumed that ...A novel geometric approach is proposed for the development of the wave-particle notions. This approach is based on a comparison of the two geometries with different sizes of an infinitesimal point. It is assumed that the smaller is object mass, the larger is the size of the infinitesimal point in comparison with the point of the geometry of macro world. Within this approach, the smaller is object mass, the larger is the uncertainty of its position from the viewpoint of macro objects (macro geometry). This approach provides a natural ex-planation of Heisenberg’s indeterminancy principle. Formally, this approach appears as an unusual operation with an infinitesimal value (point). However, it should be noted that unusual operations (though with infinitely large values) are already known in physics. These are unattainability of the absolute zero of temperature and unattainability of the maximal velocity of movement. Interconnection of the two geometries with different sizes of infinitesimal values is possible with the help of the direct and inverse Weierstrass transformation. At present, diffraction effects are described using the wave notions about the light and Fourier transform. The diffraction of light is usually registered at a distance not less than 1 - 3 metres between the screens in one of which there is a slit or several slits. This distance is about 106 times longer than the wavelength of the radiation. In the present work, an approach is proposed that allows one to describe the light fluxes at short distances between the screens with the help of Fourier and Weierstrass transforms.展开更多
Results? are presented on synthesis?? and crystal growth of? Gd2S3-Dy2S3 solid solution sulfides and study of their thermoelectric properties in the range of temperatures 80-400 K. Gd0.2Dy0.8S1.48 composition has the ...Results? are presented on synthesis?? and crystal growth of? Gd2S3-Dy2S3 solid solution sulfides and study of their thermoelectric properties in the range of temperatures 80-400 K. Gd0.2Dy0.8S1.48 composition has the best values of thermoelectric efficiency 0.39 x 10-3/K at 400 K.展开更多
Achievable supercooling for the formation of methane hydrate from water emulsions was studied in seven different crude oils and in decane. The experiments were performed under constant rate cooling from + 20 to-15 ...Achievable supercooling for the formation of methane hydrate from water emulsions was studied in seven different crude oils and in decane. The experiments were performed under constant rate cooling from + 20 to-15 °C and a pressure of methane of 12 MPa. It was demonstrated that the shapes and positions of the resulting survival curves depend on the density, viscosity and dispersive power of oil samples used in the experiments, as well as on the degree of oil oxidation. In addition, results of the experiments on ice freezing under the same emulsions are presented. The results obtained in the work allowed us to discuss the possibility and features of primary and secondary nucleation of the hydrate and ice in the systems under consideration.展开更多
Methane and carbon dioxide hydrates are one of the possible forms in which these gases exist in natural coal(for more detailed discussion see Refs [1,2]). In this work, the decomposition of carbon dioxide hydrate in f...Methane and carbon dioxide hydrates are one of the possible forms in which these gases exist in natural coal(for more detailed discussion see Refs [1,2]). In this work, the decomposition of carbon dioxide hydrate in five samples of natural coal differing from each other in metamorphism degree was investigated experimentally. Carbon dioxide hydrate dispersed in coals was synthesized from water adsorbed in these coals. During a linear temperature rise in an autoclave with the coal + hydrate sample the hydrate decomposition manifests itself as a step of increase in gas pressure, accompanied by a decrease/stabilization of the temperature of coal sample. The dependencies of the amount of hydrate formed on initial coal humidity and on gas pressure during hydrate formation were studied. It was demonstrated that each coal sample is characterized by its own humidity threshold below which hydrate formation in natural coal is impossible. With an increase in gas pressure, the amount of water transformed into hydrate increases. For the studied coal samples, the decomposition of carbon dioxide hydrates proceeds within a definite temperature and pressure range, and this range is close to the curve of phase equilibrium for bulk hydrate.展开更多
A series of Ln（Ⅲ） dipivaloylmethanates Ln（dpm）3 has been obtained. The crystalstructures of Tm（dpm）3 （1） and Yb（dpm）3 （2） were determined by X-ray analysis at 200（2） K（Pmn2b Z = 2; a = 17.7509（8）, b ...A series of Ln（Ⅲ） dipivaloylmethanates Ln（dpm）3 has been obtained. The crystalstructures of Tm（dpm）3 （1） and Yb（dpm）3 （2） were determined by X-ray analysis at 200（2） K（Pmn2b Z = 2; a = 17.7509（8）, b = 10.5805（4）, c = 9.8380（4） A, V = 1847.7（1） A3 for （1） and a =17.7272（6）, b = 10.5882（3）, c = 9.8440（3） A, V= 1847.7（1） A^3 for （2））. These data complete thestructural evaluation of lanthanoid tris-dipivaloylmethanates. Compounds 1 and 2 are isostructuralto the complexes Ln（dpm）3 （Ln -- Er and Lu）. It is demonstrated that the volatility of tris-dipivaloylmethanates of rare earth elements increases from the complex of Lu to that of La.展开更多
The growing demand for luminescent nanomaterials intended for various applications increases the necessity to develop and improve approaches to the creation of highly efficient nanosized phosphors.In current study,an ...The growing demand for luminescent nanomaterials intended for various applications increases the necessity to develop and improve approaches to the creation of highly efficient nanosized phosphors.In current study,an approach to enhancing the efficiency of red luminescence of monoclinic Y_(2)O_(3):Eu^(3+)with the particle size of~20 nm by creating the oxygen-enriched environment during the gas-phase synthesis was developed.To investigate the effect of oxygen amount during the synthesis on characteristics of the phosphor,a series of nano structured Y_(2)O_(3):Eu^(3+)with the addition of 0-40 vol%O_(2) to the main buffer gas Ar was synthesized by laser vaporization.It is shown that the amount of added O_(2) exerts virtually no effect on the phase composition and particle size,but significantly improves the luminescent characteristics of Y_(2)O_(3):Eu^(3+).Thus,the addition of 30 vol%O_(2) leads to virtually a 20-fold growth in the photoluminescence(PL)intensity caused by ^(5)D_(0)→^(7)F_(0-4) transitions in Eu^(3+)and an increase in the absolute PL quantum yield from 3%to 53%(λex=395 nm)compared to the sample synthesized without O_(2).The addition of oxygen also improves the emission color coordinates from(0.571,0.320)to(0.630,0.322)due to the removal of a considerable fraction of oxygen vacancies.The synthesized nanopowders are shown to be highly stable:upon storage under ambient conditions for two years.Quantum yield(QY)of the samples decreases by less than 2%.It is expected that the key features underlying the proposed approach will be useful for various methods used to synthesize oxide nanophosphors.展开更多
LaxHf1-xOy thin films with various concentrations of La, homogeneous and nonhomogeneous distributions of elements throughout the films thickness was purposefully grown by CVD. The composition of the films and their ch...LaxHf1-xOy thin films with various concentrations of La, homogeneous and nonhomogeneous distributions of elements throughout the films thickness was purposefully grown by CVD. The composition of the films and their chemical structures were characterized throughout the films thickness by X-ray photoelectron spectroscopy （XPS） and energy-dispersive X-ray spectrometry （EDXA）. A full picture of the film crystallinity was provided by the combination of grazing incidence X-ray diffraction （GIXRD） synchrotron radiation （SR） and high resolution transmission electron microscopy （HR TEM）. It was shown that La acted as ＂molar volume modulator＂ and stabilized the nonequilibrium at T≤1300 ℃ cubic phases. The samples with La content in range of 7 at.%〈CLa〈22 at.% were materials with fluorite-type （Fm-3m） structure. The pyroehlore phase formation was observed at -18 at.% La content. The correlation between the La-doped content and the films microstructure was revealed.展开更多
It is known that simple adding of wood allows one to accelerate the ignition of powder mixtures compared to the situation when pure coal is used.This study focuses on testing the hypothesis about the effect of co-mill...It is known that simple adding of wood allows one to accelerate the ignition of powder mixtures compared to the situation when pure coal is used.This study focuses on testing the hypothesis about the effect of co-milling coal and wood on their co-firing:is the case of composite powdered fuels should ensure the maximum possible efficiency of heat and mass transfer?Firstly,we will show that co-milling of coal and wood leads not independent size reduction of two materials but gives composite powder-coal-covered wood.For the composite fuel further reduction of the ignition delay time of air suspension and reduction of the limit volume concentration required for flame propagation have demonstrated.Obtained synergy also manifests in thermogravimetry.Here we propose a simple method for analyzing the mass loss curves.For any coal-to-wood sawdust ratio,combustion of the composites and mixtures both can be viewed as a weighted sum of the curves of individual components.But only in the case of composites calculated sawdust content is higher than the actual one:the mass loss is redistributed towards the stage occurring at lower temperatures due to geometry of wood/coal contact.展开更多
Dimensionality and orientation of hexagonal boron nitride(h-BN)nanosheets are promising to create and control their unique properties for diverse applications.However,low-temperature deposition of vertically oriented ...Dimensionality and orientation of hexagonal boron nitride(h-BN)nanosheets are promising to create and control their unique properties for diverse applications.However,low-temperature deposition of vertically oriented h-BN nanosheets is a significant challenge.Here we report on the low-temperature plasma synthesis of maze-like h-BN nanowalls(BNNWs)from a mixture of triethylamine borane(TEAB)and ammonia at temperatures as low as 400℃.The maze-like BNNWs contained vertically aligned stacks of h-BN nanosheets.Wavy h-BN nanowalls with randomly oriented nanocrystalline structure are also fabricated.Simple and effective control of morphological type of BNNWs by the deposition-mperature is demonstrated.Despite the lower synthesis temperature,thermal stability and oxidation resistivity of the maze-like BNNWs are higher than for the wavy nanowalls.The structure and oxidation of the nanowalls was found to be the critical factor for their thermal stability and con trolled luminescence properties.Cytotoxic study dem on strated sign ificant antibacterial effect of both maze-like and wavy h-BN nanowalls against E.coli.The reported results reveal a significant potential of h-BN nanowalls for a broad range of applications from electronics to biomedicine.展开更多
基金supported by the Russian Science Foundation(23-29-00830).
文摘Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the interface,further growth of hydrate due to the suction of water in the capillary system formed between the wall of the cuvette and the end boundary of the hydrate layer occurs.Most probably,substantial effects on the formation of this capillary system may be caused by variations in reactor wall properties,for example,hydrophobic-hydrophilic balance,roughness,etc.We found,that the rate of CO_(2) hydrate film growth on the surface of the humic acid aqueous solution is 4-fold to lower in comparison with the growth rate on the surface of pure water.We suppose that this is caused by the adsorption of humic acid associates on the surface of hydrate particles and,as a consequence,by the deceleration of the diffusion of dissolved carbon dioxide to the growing hydrate particle.
文摘In the present work we studied the induction periods of hydrate formation of natural gas in pure water, aqueous solutions of surfactants, and in the presence of surfactant together with aluminum oxide nanopowder, the activity of which as hydrate formation inducer was studied previously. Sodium dodecyl sulfate（SDS） or neonol AF-9-12 were used as the surfactants. It was demonstrated that the addition of either surfactants or aluminum oxide powder under our experimental conditions causes a decrease in the induction period of hydrate formation from;05 min for pure water to 30–35 min for water with additives. In the case of the simultaneous presence of surfactants and aluminum oxide powder in the system, induction period decreased to;0 min. So, the synergistic effect of the combination of surfactant and oxide powder on gas hydrate nucleation was demonstrated. Possible reasons of this effect have been discussed.
基金supported by the Council for Grants of the President of the Russian Federation(Grant NSh–3929.2014.5)the Basic Research Programs of the RAS(Program No.8,and Program the Arctic)the Siberian Branch of the RAS(Interdisciplinary Project No.144)
文摘The results on a dissociation behavior of propane hydrates prepared from ＂dry water＂ and contained unreacted residual water in the form of ice inclusions or supercooled liquid water（water solution of gas） were presented for temperatures below 273 K.The temperature ramping or pressure release method was used for the dissociation of propane hydrate samples.It was found that the mechanism of gas hydrate dissociation at temperatures below 273 K depended on the phase state of unreacted water in the hydrate sample.Gas hydrates dissociated into ice and gas if the ice inclusions were in the hydrate sample.The samples of propane hydrates with inclusions of unreacted supercooled water only（without ice inclusions） dissociated into supercooled water and gas below the pressure of the supercooled water-hydrate-gas metastable equilibrium.
文摘Gas hydrates and wax are the major flow assurance problems for the transportation of produced hydrocarbons through pipelines.However,in most research works both these two problems are studied separately.Although simultaneous precipitation or deposition of these compounds in pipelines can lead to different mitigation/prevention strategies,the investi-gations in which both these problems are considered simultaneously appeared only recently.There is no information in the literature on the texture/composition and features of decomposition process of mixed wax/hydrate plugs.At the same time,this information could be useful to understand how to treat the problem of formation of these plugs.In this work,three wax/gas hydrate plugs were collected at quasi-static conditions from a water-in-oil emulsion to study their texture,composition and the features of decomposition process.Powder X-ray diffraction and IR(infrared spectroscopy)analyses showed that the plugs consisted of wax and gas hydrate.Thermovolumetric and DSC(Differential Scanning Calorimetry)experiments showed that the main part of gas hydrate in the plugs at the ambient pressure started to decompose at about 268 K.This temperature was higher than the equilibrium temperature of carbon dioxide hydrate at this pressure,indicating that the gas hydrate in the plugs could be effectively preserved at temperatures below the ice melting point(273.2 K).It was found through observation of the hydrate decomposition process in the plugs under the microscope that the gas in the samples released in small bubbles,while the hydrate particles were not visible at this magnification,indicating that the hydrate was indeed highly dispersed in the samples.A residual wax was jelly-like after decomposition of hydrate in all the cases.Rheological experiments showed that the plugs residues after decomposition of the hydrates had higher yield points and viscosities than the initial waxy crude oil origi-nally used for the experiments.
文摘Modern but not entirely coordinated foundations of quantum physics are described in the book “The Quantum Challenge”. The difficulties and philosophical problems of this area of science are discussed. Discussions of many great scientists who paved the foundations of the physics of micro-world are described. These discussions are still urgent. The diversity of interpretations of the wave function, light interference, uncertainty principle, complementarity and completeness of micro-world description are stressed in this book. Difficulties and problems of quantum mechanics described in this book allowed the author of the present communication to propose a new approach based on the infinitely small metrics The difference of infinitesimals in two geometries allows one to explain W. Heisenberg’s uncertainty principle. Interconnection of the images in these geometries is possible with the help of Weierstrass integral transform. This approach allows one to describe the interference of light behind the screen with slits as a sum of the corpuscular component (Weierstrass transform) and the wave component (Fourier transform).
文摘A novel geometric approach is proposed for the development of the wave-particle notions. This approach is based on a comparison of the two geometries with different sizes of an infinitesimal point. It is assumed that the smaller is object mass, the larger is the size of the infinitesimal point in comparison with the point of the geometry of macro world. Within this approach, the smaller is object mass, the larger is the uncertainty of its position from the viewpoint of macro objects (macro geometry). This approach provides a natural ex-planation of Heisenberg’s indeterminancy principle. Formally, this approach appears as an unusual operation with an infinitesimal value (point). However, it should be noted that unusual operations (though with infinitely large values) are already known in physics. These are unattainability of the absolute zero of temperature and unattainability of the maximal velocity of movement. Interconnection of the two geometries with different sizes of infinitesimal values is possible with the help of the direct and inverse Weierstrass transformation. At present, diffraction effects are described using the wave notions about the light and Fourier transform. The diffraction of light is usually registered at a distance not less than 1 - 3 metres between the screens in one of which there is a slit or several slits. This distance is about 106 times longer than the wavelength of the radiation. In the present work, an approach is proposed that allows one to describe the light fluxes at short distances between the screens with the help of Fourier and Weierstrass transforms.
文摘Results? are presented on synthesis?? and crystal growth of? Gd2S3-Dy2S3 solid solution sulfides and study of their thermoelectric properties in the range of temperatures 80-400 K. Gd0.2Dy0.8S1.48 composition has the best values of thermoelectric efficiency 0.39 x 10-3/K at 400 K.
基金the Federal Agency for Scientific Organizations for funding
文摘Achievable supercooling for the formation of methane hydrate from water emulsions was studied in seven different crude oils and in decane. The experiments were performed under constant rate cooling from + 20 to-15 °C and a pressure of methane of 12 MPa. It was demonstrated that the shapes and positions of the resulting survival curves depend on the density, viscosity and dispersive power of oil samples used in the experiments, as well as on the degree of oil oxidation. In addition, results of the experiments on ice freezing under the same emulsions are presented. The results obtained in the work allowed us to discuss the possibility and features of primary and secondary nucleation of the hydrate and ice in the systems under consideration.
基金supported by the project №18 "Study of the physicochemical properties of hydrate-containing rocks for the development of remote sensing methods and the characteristics of natural accumulations of gas hydrates" of the Integrated Basic Research Program of the Siberian Branch of the Russian Academy of Sciences.
文摘Methane and carbon dioxide hydrates are one of the possible forms in which these gases exist in natural coal(for more detailed discussion see Refs [1,2]). In this work, the decomposition of carbon dioxide hydrate in five samples of natural coal differing from each other in metamorphism degree was investigated experimentally. Carbon dioxide hydrate dispersed in coals was synthesized from water adsorbed in these coals. During a linear temperature rise in an autoclave with the coal + hydrate sample the hydrate decomposition manifests itself as a step of increase in gas pressure, accompanied by a decrease/stabilization of the temperature of coal sample. The dependencies of the amount of hydrate formed on initial coal humidity and on gas pressure during hydrate formation were studied. It was demonstrated that each coal sample is characterized by its own humidity threshold below which hydrate formation in natural coal is impossible. With an increase in gas pressure, the amount of water transformed into hydrate increases. For the studied coal samples, the decomposition of carbon dioxide hydrates proceeds within a definite temperature and pressure range, and this range is close to the curve of phase equilibrium for bulk hydrate.
文摘A series of Ln（Ⅲ） dipivaloylmethanates Ln（dpm）3 has been obtained. The crystalstructures of Tm（dpm）3 （1） and Yb（dpm）3 （2） were determined by X-ray analysis at 200（2） K（Pmn2b Z = 2; a = 17.7509（8）, b = 10.5805（4）, c = 9.8380（4） A, V = 1847.7（1） A3 for （1） and a =17.7272（6）, b = 10.5882（3）, c = 9.8440（3） A, V= 1847.7（1） A^3 for （2））. These data complete thestructural evaluation of lanthanoid tris-dipivaloylmethanates. Compounds 1 and 2 are isostructuralto the complexes Ln（dpm）3 （Ln -- Er and Lu）. It is demonstrated that the volatility of tris-dipivaloylmethanates of rare earth elements increases from the complex of Lu to that of La.
基金Project supported by Russian Science Foundation(22-73-00106)partly by NIIC project(121031700313-8,M.Rakhmanova,PL kinetics study)。
文摘The growing demand for luminescent nanomaterials intended for various applications increases the necessity to develop and improve approaches to the creation of highly efficient nanosized phosphors.In current study,an approach to enhancing the efficiency of red luminescence of monoclinic Y_(2)O_(3):Eu^(3+)with the particle size of~20 nm by creating the oxygen-enriched environment during the gas-phase synthesis was developed.To investigate the effect of oxygen amount during the synthesis on characteristics of the phosphor,a series of nano structured Y_(2)O_(3):Eu^(3+)with the addition of 0-40 vol%O_(2) to the main buffer gas Ar was synthesized by laser vaporization.It is shown that the amount of added O_(2) exerts virtually no effect on the phase composition and particle size,but significantly improves the luminescent characteristics of Y_(2)O_(3):Eu^(3+).Thus,the addition of 30 vol%O_(2) leads to virtually a 20-fold growth in the photoluminescence(PL)intensity caused by ^(5)D_(0)→^(7)F_(0-4) transitions in Eu^(3+)and an increase in the absolute PL quantum yield from 3%to 53%(λex=395 nm)compared to the sample synthesized without O_(2).The addition of oxygen also improves the emission color coordinates from(0.571,0.320)to(0.630,0.322)due to the removal of a considerable fraction of oxygen vacancies.The synthesized nanopowders are shown to be highly stable:upon storage under ambient conditions for two years.Quantum yield(QY)of the samples decreases by less than 2%.It is expected that the key features underlying the proposed approach will be useful for various methods used to synthesize oxide nanophosphors.
基金supported by the Russian Foundation for Basic Research(12-03-00131)
文摘LaxHf1-xOy thin films with various concentrations of La, homogeneous and nonhomogeneous distributions of elements throughout the films thickness was purposefully grown by CVD. The composition of the films and their chemical structures were characterized throughout the films thickness by X-ray photoelectron spectroscopy （XPS） and energy-dispersive X-ray spectrometry （EDXA）. A full picture of the film crystallinity was provided by the combination of grazing incidence X-ray diffraction （GIXRD） synchrotron radiation （SR） and high resolution transmission electron microscopy （HR TEM）. It was shown that La acted as ＂molar volume modulator＂ and stabilized the nonequilibrium at T≤1300 ℃ cubic phases. The samples with La content in range of 7 at.%〈CLa〈22 at.% were materials with fluorite-type （Fm-3m） structure. The pyroehlore phase formation was observed at -18 at.% La content. The correlation between the La-doped content and the films microstructure was revealed.
文摘It is known that simple adding of wood allows one to accelerate the ignition of powder mixtures compared to the situation when pure coal is used.This study focuses on testing the hypothesis about the effect of co-milling coal and wood on their co-firing:is the case of composite powdered fuels should ensure the maximum possible efficiency of heat and mass transfer?Firstly,we will show that co-milling of coal and wood leads not independent size reduction of two materials but gives composite powder-coal-covered wood.For the composite fuel further reduction of the ignition delay time of air suspension and reduction of the limit volume concentration required for flame propagation have demonstrated.Obtained synergy also manifests in thermogravimetry.Here we propose a simple method for analyzing the mass loss curves.For any coal-to-wood sawdust ratio,combustion of the composites and mixtures both can be viewed as a weighted sum of the curves of individual components.But only in the case of composites calculated sawdust content is higher than the actual one:the mass loss is redistributed towards the stage occurring at lower temperatures due to geometry of wood/coal contact.
文摘Dimensionality and orientation of hexagonal boron nitride(h-BN)nanosheets are promising to create and control their unique properties for diverse applications.However,low-temperature deposition of vertically oriented h-BN nanosheets is a significant challenge.Here we report on the low-temperature plasma synthesis of maze-like h-BN nanowalls(BNNWs)from a mixture of triethylamine borane(TEAB)and ammonia at temperatures as low as 400℃.The maze-like BNNWs contained vertically aligned stacks of h-BN nanosheets.Wavy h-BN nanowalls with randomly oriented nanocrystalline structure are also fabricated.Simple and effective control of morphological type of BNNWs by the deposition-mperature is demonstrated.Despite the lower synthesis temperature,thermal stability and oxidation resistivity of the maze-like BNNWs are higher than for the wavy nanowalls.The structure and oxidation of the nanowalls was found to be the critical factor for their thermal stability and con trolled luminescence properties.Cytotoxic study dem on strated sign ificant antibacterial effect of both maze-like and wavy h-BN nanowalls against E.coli.The reported results reveal a significant potential of h-BN nanowalls for a broad range of applications from electronics to biomedicine.
