1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity....1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity.However,fossil methane production and combustion lead to large greenhouse gas emissions,contributing to climate change[1].展开更多
Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The res...Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.展开更多
The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carrie...The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carried out at 273.15K under 4.00 MPa.The key process variables of gas formation rate,gas volume stored in hydrate and separation concentration were closely investigated in twelve THF-SDS-sponge-gas systems to verify the sponge effect in these hydrate-based separation processes.The gas volume stored in hydrate is calculated based on the measured gas pressure.The CH4 mole fraction in hydrate phase is measured by gas chromatography to confirm the separation efficiency.Through close examination of the overall results,it was clearly verified that sponges with volumes of 40,60 and 80 cm 3 significantly increase gas hydrate formation rate and the gas volume stored in hydrate,and have little effect on the CH4 mole fraction in hydrate phase.The present study provides references for the application of the kinetic effect of porous sponge media in hydrate-based technology.This will contribute to CMM utilization and to benefit for local and global environment.展开更多
Study on the microscopic structure of clathrate hydrate has made significant progress in the past decades.This review aims to summarize the state of the art of the experimental characterization of vip molecular occu...Study on the microscopic structure of clathrate hydrate has made significant progress in the past decades.This review aims to summarize the state of the art of the experimental characterization of vip molecular occupancy in clathrate hydrate cages,which is an important area of the microscopic structures.The characterizing method and features of different vip molecular,such as hydrocarbon,carbon dioxide,hydrogen and inhibitor/promoter,in different hydrate cages have been extensively reviewed.A comprehensive use of advanced technologies such as X-ray diffraction,Raman spectroscopy and nuclear magnetic resonance may provide better understanding on the compositions and microscopic mechanisms of clathrate hydrate.展开更多
Using transient plane source technique, we measured THF hydrate thermal conductivity from 243 K to 263 K. The sample THF solution is over saturated in order to avoid the effect of ice. And also to avoid the effect of ...Using transient plane source technique, we measured THF hydrate thermal conductivity from 243 K to 263 K. The sample THF solution is over saturated in order to avoid the effect of ice. And also to avoid the effect of crystal anisotropy, the THF hydrate was crushed to measure. In the test temperature value increases with the temperature increasing.展开更多
Gas hydrate is a new technology for energy gas（methane/hydrogen）storage due to its large capacity of gas storage and safe.But industrial application of hydrate storage process was hindered by someproblems.For methan...Gas hydrate is a new technology for energy gas（methane/hydrogen）storage due to its large capacity of gas storage and safe.But industrial application of hydrate storage process was hindered by someproblems.For methane,the main problems are low formation rateand storage capacity,which can be solved by strengthening mass andheat transfer,such as adding additives,stirring,bubbling,etc.Onekind of additives can change the equilibrium curve to reduce the formation pressure of methane hydrate,and the other kind of additivesis surfactant,which can form micelle with water and increase the interface of water-gas.Dry water has the similar effects on the methanehydrate as surfactant.Additionally,stirring,bubbling,and sprayingcan increase formation rate and storage capacity due to mass transferstrengthened.Inserting internal or external heat exchange also canimprove formation rate because of good heat transfer.For hydrogen,the main difficulties are very high pressure for hydrate formed.Tetrahydrofuran（THF）,tetrabutylammonium bromide（TBAB） andtetrabutylammonium fluoride（TBAF） have been proved to be able todecrease the hydrogen hydrate formation pressure significantly.展开更多
In this study,enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS)solution with different concentrations of suspended graphite nanoparticles(GNPs)were investigated at 6.1-9.0 MPa and 274.1...In this study,enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS)solution with different concentrations of suspended graphite nanoparticles(GNPs)were investigated at 6.1-9.0 MPa and 274.15 K.The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system.At a relatively low pressure of 6.1 MPa,the suspension with 0.4 wt%of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm3·cm-3.However,the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory.At the applied pressure,the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%)of GNPs was more significant than that in the traditional SDS solution.Furthermore,compared with those of the system without GNPs,enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs,and the storage capacities were increased by 3.9%-17.0%.The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.展开更多
N-type Si-based type-Ⅰ clathrates with different Ga content were synthesized by combining the solid-state reaction method,melting method and spark plasma sintering （SPS） method.The effects of Ga composition on high...N-type Si-based type-Ⅰ clathrates with different Ga content were synthesized by combining the solid-state reaction method,melting method and spark plasma sintering （SPS） method.The effects of Ga composition on high temperature thermoelectric transport properties were investigated.The results show that at room temperature,the carrier concentration decreases, while the carrier mobility increases slightly with increasing Ga content.The Seebeck coefficient increases with increasing Ga content. Among all the samples,Ba7.93Ga17.13Si28.72exhibits higher Seebeck coefficient than the others and reaches -135μV·K^-1 at 1000 K.The sample prepared by this method exhibits very high electrical conductivity,and reaches 1.95x 10^5 S·m^-1 for Ba8.01Ga16.61Si28.93 at room temperature.The thermal conductivity of all samples is almost temperature independent in the temperature range of 300-1000 K,indicating the behaviour of a typical metal.The maximum ZT value of 0.75 is obtained at 1000 K for the compound Ba7.93Ga17.13Si28.72.展开更多
A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering （SPS）. X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples e...A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering （SPS）. X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750℃. Lattice contraction recurred when the SPS temperature was further increased in the range of 750-1000℃. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800℃. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT-T curve.展开更多
Four types of nanoparticles,amorphous carbon,ironⅢoxide,SiO2,and amino-coated SiO2,were tested to determine changes in tetrahydrofuran-water(THF-water)clathrate hydrate nucleation and agglomeration.Rates were experim...Four types of nanoparticles,amorphous carbon,ironⅢoxide,SiO2,and amino-coated SiO2,were tested to determine changes in tetrahydrofuran-water(THF-water)clathrate hydrate nucleation and agglomeration.Rates were experimentally found to determine their viability for preventing natural gas hydrates from developing during offshore drilling operations.THF-water clathrates were chosen as a model to represent gas hydrate growth at atmospheric pressure.Concentrations of each nanoparticle between 0.15%and 1.0%by weight were tested as a kinetic inhibitor to hydrate formation.Tests were repeated at various temperatures below the formation temperature of 4.4℃for THF-water clathrate hydrates.Measurements were made to identify how the concentration of THF affects the clathrate hydrates forming under static conditions between20%and 30%by mole of THF.The primary tests in this study were performed using a 20:80 THF/water ratio.Temperature increases during hydrate nucleation for THF-water were measured between-5 and 3℃.The range of ideal nanoparticle concentrations was found to be between 0.15%and 0.45%by weight for optimal static,kinetic inhibition of hydrate nucleation.At approximately 0.3%by weight,the most significant inhibition was observed under static conditions for all four types of nanoparticles tested.We found that functionalized amino-coated SiO2 nanoparticles,across all tests,significantly increased the time required for the formation of THF-water clathrate hydrates compared to the other three non-functionalized nanoparticles.The amorphous carbon and ironⅢoxide nanoparticles performed similarly across each test and were both the least effective in their inhibition of the clathrate hydrates of the four nanoparticles studied compared to a control.展开更多
Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band （below 15...Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band （below 15 meV） and yield correct relative intensity. Based on the results, the uncertain profile at ～6 meV is assigned to anharmonic vip modes coupled strongly to small cages. Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for vip-host coupling that explains the anomalous thermal conductivity of clathrate hydrate.展开更多
Fundamental mechanics of gas hydrates is of importance to evaluating geomechanical and geotechnical properties of gas hydrate deposits,but it remains largely unexplored yet due to insufficient direct experimental tech...Fundamental mechanics of gas hydrates is of importance to evaluating geomechanical and geotechnical properties of gas hydrate deposits,but it remains largely unexplored yet due to insufficient direct experimental techniques and high-quality of gas hydrate samples.Here,classic molecular dynamic(MD)simulations are used to study the fracture mechanics of three main methane clathrate hydrates of sI,sII and sH types.The results show that the mechanical properties of those three methane clathrate hydrates are intrinsically different and are degraded by the presence of nanocracks.They show brittle facture and different fracture toughness.In terms of energy release rate,they are ranked as sH>sI>sII.Moreover,the three methane clathrate hydrates with nanocracks can be explained by a modified Griffith criterion.Moreover,it is intriguingly identified tip amorphization during the crack propagation process of the three methane clathrate hydrates,and sH methane clathrate hydrate with specific nanocrack exhibits slower crack propagation than other two methane clathrate hydrates.展开更多
Lattice dynamical simulations of noble gas hydrate structures I and II have been performed. Potential energies were investigated to study the influence of vip species on the stability of the hydrate structure. Resul...Lattice dynamical simulations of noble gas hydrate structures I and II have been performed. Potential energies were investigated to study the influence of vip species on the stability of the hydrate structure. Results show that when the diameter of inclusion molecules is between 3 A and 4.2 A, such as Ar and Kr, the critical role of the 512 cage in the stabilization of hydrates becomes effective. For Xe hydrates SI and SII, with the help of lattice dynamical calculations, the modes attributions are identified directly. We proposed the resonant effect of the fingerprint frequency at about 7 meV and 10 meV which arise from the coupling of Xe molecules in the 512 cage with the host lattice.展开更多
A cadmium tetracyanoplatinate host clathrate,(MV)[Cd_(2){Pt(CN)_(4)}_(3)]·2(H_(2)O)(1),including a methylviologen dication (MV^(2+)) was synthesized,and the crystal structures,photochromic and photoluminescence p...A cadmium tetracyanoplatinate host clathrate,(MV)[Cd_(2){Pt(CN)_(4)}_(3)]·2(H_(2)O)(1),including a methylviologen dication (MV^(2+)) was synthesized,and the crystal structures,photochromic and photoluminescence properties were investigated.In 1,the alternatively parallel stacking between the MV^(2+)dications as electron acceptors in the channels and the electron donors[Pt1(CN)_(4)]^(2-) units in the host frameworks give a unique donor-acceptor (DA) system.Under UV irradiation,the electron transfer between MV^(2+) and[Pt(CN)_(4)]^(2-) ions generates MV^(·+)radicals with a photochromic behavior from pale-yellow to blue.This process occurs through single-crystal-to-single-crystal (SCSC) transformation and obvious structure variation of viologen cations is successfully observed.Moreover,the spectral overlap between the emission bands of 1 and the absorption around 623 nm for the MV^(·+) radicals leads to a modulation of the photoluminescence.展开更多
A novel supramolecular polysiloxane clathrate, POS/C, has been preparedby in-situ encapsulating rodlike p-butoxybenzylidene-p ' - dodecoxyaniline (BBDA ) , one kindof Schiff base liquid crystal molecule, within th...A novel supramolecular polysiloxane clathrate, POS/C, has been preparedby in-situ encapsulating rodlike p-butoxybenzylidene-p ' - dodecoxyaniline (BBDA ) , one kindof Schiff base liquid crystal molecule, within the pore of polyorganosiloxane (POS) whichis prepared by hydrosilylation coupling reaction of polyvinylsilsesquioxane (Vi- T ) withtetramethyldisiloxane (H-MM). Investigation by polarized light microscopy (PLM), differ-ential scanning calorimetry (DSC), infrared spectroscopy (IR), atomic force microscopy(AFM) and molecular simulation gives a preliminary support to the existence of the titlesupramolecular clathrate.展开更多
We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound（Na8Si46） under pressure using first-principles methods. The obtained dependencies of ...We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound（Na8Si46） under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus,Young＇s modulus, Debye temperature,sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.展开更多
Recently,a new phase C'_(1) H_(2) hydrate was experimentally identified.In this work,the diffusive behaviors of H_(2) in C'_(1)phase clathrate hydrate are explored using classic molecular dynamics(MD)simulatio...Recently,a new phase C'_(1) H_(2) hydrate was experimentally identified.In this work,the diffusive behaviors of H_(2) in C'_(1)phase clathrate hydrate are explored using classic molecular dynamics(MD)simulations.It reveals that the cage occupancy by H_(2) molecule negligibly influences the C'_(1) phase clathrate structure but greatly dictates the diffusion coefficient of H_(2)molecule.Due to the small cage size and small windows connecting the neighboring cages in C'_(1) phase clathrate,nonoccupancy of the neighboring cages is demanded to enable the diffusion of H_(2) molecule that is primarily dominated by hopping mechanism.Moreover,the analysis of diffusive free energy landscape reveals lower energy barrier of H_(2) molecule in C'_(1) phase clathrate hydrate than that of other gases in conventional clathrate hydrates,and that H_(2) molecule travels through the windows between neighboring cages with preferential molecular orientation.This study provides critical physical insights into the diffusion behaviors of H_(2) in the C'_(1) phase clathrate hydrate,and implies that the C'_(1) clathrate hydrate is a promising solid structure for the next-generation H_(2) storage.展开更多
Single-crystal samples of type-VIII BasGa16-xCuxSn30 （x = 0, 0.03, 0.06, 0.15） clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5 × 10^19 cm^-3 for all the s...Single-crystal samples of type-VIII BasGa16-xCuxSn30 （x = 0, 0.03, 0.06, 0.15） clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5 × 10^19 cm^-3 for all the samples, the carrier mobility, μH, increases to more than twice that of BasGa16Sn30 for all the Cu doping samples, and consequently the electrical conductivity is enhanced distinctly from 1.90×10^4 S/m to 4.40 ×10^4 S/m, with the Cu composition increasing from x = 0 to x = 0.15. The Seebeck coefficient,α, decreases slightly with the increases in Cu composition. The values are about 0.72 W/mK at 300 K and are almost invariant with temperature up to 500 K for the samples with x = 0 and x = 0.03. The lattice thermal conductivity, μL, decreases from 0.59 W/InK for x = 0 to 0.50 W/mK for x = 0.03 at 300 K. The figure of merit for x = 0.03 reaches 1.35 at 540 K.展开更多
基金funding from the European Research Council(ERC)under grant agreement no.834134(WATUSO)VLAIO for Moonshot funding(ARCLATH,No.HBC.2019.0110 and ARCLATH2,No.HBC.2021.0254)+3 种基金supported by the Flemish Government as an international research infrastructure(I001321N)infrastructure support by Department EWI via the Hermes Fund(AH.2016.134)the Hercules Foundation(AKUL/13/21)FWO Vlaanderen for an FWO-SB fellowship。
文摘1.Challenges circular methane energy systems In recent decades,methane-based energy systems have rapidly gained traction across the globe because of the increasing availability of low-cost methane production capacity.However,fossil methane production and combustion lead to large greenhouse gas emissions,contributing to climate change[1].
文摘Nitrogen hydrate samples were synthesized using liquid nitrogen and powder ice at 16 MPa and 253 K. Confocal laser Raman spectroscopy was used to investigate the characteristics of nitrogen clathrate hydrates. The results show that the Raman peaks of N-N and O-H stretching vibration in nitrogen hydrates are observed at 2322.4 and 3092.1 cm^-1, respectively, which are very similar to those in natural air clathrate hydrates. For comparison, we measured the Raman peaks of N-N stretching vibration both in liquid nitrogen and nitrogen molecules saturated water, which appear at 2326.6 and 2325.0 cm^-1, respectively. The Raman spectroscopic observations on the dissociation process suggest that nitrogen molecules occupy both the large and small cages in nitrogen clathrate hydrates. However, only one Raman peak is observed for N N stretching vibration because the difference of the environment of nitrogen molecules between large and small cages is too small to be differentiated by Raman spectroscopy.
基金Supported by the National Natural Science Foundation of China （50874040 50904026） the Scientific Research Fund of Heilongjiang Provincial Education Department （11551420）
文摘The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carried out at 273.15K under 4.00 MPa.The key process variables of gas formation rate,gas volume stored in hydrate and separation concentration were closely investigated in twelve THF-SDS-sponge-gas systems to verify the sponge effect in these hydrate-based separation processes.The gas volume stored in hydrate is calculated based on the measured gas pressure.The CH4 mole fraction in hydrate phase is measured by gas chromatography to confirm the separation efficiency.Through close examination of the overall results,it was clearly verified that sponges with volumes of 40,60 and 80 cm 3 significantly increase gas hydrate formation rate and the gas volume stored in hydrate,and have little effect on the CH4 mole fraction in hydrate phase.The present study provides references for the application of the kinetic effect of porous sponge media in hydrate-based technology.This will contribute to CMM utilization and to benefit for local and global environment.
基金Supported by the National Natural Science Foundation of China(51706248,51876222)National Key R&D Program of China(2017YFC0307304)
文摘Study on the microscopic structure of clathrate hydrate has made significant progress in the past decades.This review aims to summarize the state of the art of the experimental characterization of vip molecular occupancy in clathrate hydrate cages,which is an important area of the microscopic structures.The characterizing method and features of different vip molecular,such as hydrocarbon,carbon dioxide,hydrogen and inhibitor/promoter,in different hydrate cages have been extensively reviewed.A comprehensive use of advanced technologies such as X-ray diffraction,Raman spectroscopy and nuclear magnetic resonance may provide better understanding on the compositions and microscopic mechanisms of clathrate hydrate.
文摘Using transient plane source technique, we measured THF hydrate thermal conductivity from 243 K to 263 K. The sample THF solution is over saturated in order to avoid the effect of ice. And also to avoid the effect of crystal anisotropy, the THF hydrate was crushed to measure. In the test temperature value increases with the temperature increasing.
基金supported by the National 863 Program (2007AA03Z229)the Fundamental Research Funds for the Central Universities (2009ZM0185)
文摘Gas hydrate is a new technology for energy gas（methane/hydrogen）storage due to its large capacity of gas storage and safe.But industrial application of hydrate storage process was hindered by someproblems.For methane,the main problems are low formation rateand storage capacity,which can be solved by strengthening mass andheat transfer,such as adding additives,stirring,bubbling,etc.Onekind of additives can change the equilibrium curve to reduce the formation pressure of methane hydrate,and the other kind of additivesis surfactant,which can form micelle with water and increase the interface of water-gas.Dry water has the similar effects on the methanehydrate as surfactant.Additionally,stirring,bubbling,and sprayingcan increase formation rate and storage capacity due to mass transferstrengthened.Inserting internal or external heat exchange also canimprove formation rate because of good heat transfer.For hydrogen,the main difficulties are very high pressure for hydrate formed.Tetrahydrofuran（THF）,tetrabutylammonium bromide（TBAB） andtetrabutylammonium fluoride（TBAF） have been proved to be able todecrease the hydrogen hydrate formation pressure significantly.
基金supported by the National Natural Science Foundation of China(grant numbers 51606125,51802190,21978171,51876130,51674240)the Innovation Program of Shanghai Municipal Education Commission(grant number 13ZZ117)。
文摘In this study,enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS)solution with different concentrations of suspended graphite nanoparticles(GNPs)were investigated at 6.1-9.0 MPa and 274.15 K.The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system.At a relatively low pressure of 6.1 MPa,the suspension with 0.4 wt%of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm3·cm-3.However,the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory.At the applied pressure,the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%)of GNPs was more significant than that in the traditional SDS solution.Furthermore,compared with those of the system without GNPs,enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs,and the storage capacities were increased by 3.9%-17.0%.The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.
基金Project supported by the National Basic Research Program of China (Grant Nos 2007CB607501 and 2007CB607503)Yunnan Natural Science Fund (Grant No 2008CD114)
文摘N-type Si-based type-Ⅰ clathrates with different Ga content were synthesized by combining the solid-state reaction method,melting method and spark plasma sintering （SPS） method.The effects of Ga composition on high temperature thermoelectric transport properties were investigated.The results show that at room temperature,the carrier concentration decreases, while the carrier mobility increases slightly with increasing Ga content.The Seebeck coefficient increases with increasing Ga content. Among all the samples,Ba7.93Ga17.13Si28.72exhibits higher Seebeck coefficient than the others and reaches -135μV·K^-1 at 1000 K.The sample prepared by this method exhibits very high electrical conductivity,and reaches 1.95x 10^5 S·m^-1 for Ba8.01Ga16.61Si28.93 at room temperature.The thermal conductivity of all samples is almost temperature independent in the temperature range of 300-1000 K,indicating the behaviour of a typical metal.The maximum ZT value of 0.75 is obtained at 1000 K for the compound Ba7.93Ga17.13Si28.72.
基金supported by the National Natural Science Foundation of China(No.51072023)the National Science Foundation of US(No.DMR-0821284)the National Aeronautics and Space Administration of US(Nos.NNX10AM80H and NNX07AO30A)
文摘A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering （SPS）. X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750℃. Lattice contraction recurred when the SPS temperature was further increased in the range of 750-1000℃. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800℃. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT-T curve.
文摘Four types of nanoparticles,amorphous carbon,ironⅢoxide,SiO2,and amino-coated SiO2,were tested to determine changes in tetrahydrofuran-water(THF-water)clathrate hydrate nucleation and agglomeration.Rates were experimentally found to determine their viability for preventing natural gas hydrates from developing during offshore drilling operations.THF-water clathrates were chosen as a model to represent gas hydrate growth at atmospheric pressure.Concentrations of each nanoparticle between 0.15%and 1.0%by weight were tested as a kinetic inhibitor to hydrate formation.Tests were repeated at various temperatures below the formation temperature of 4.4℃for THF-water clathrate hydrates.Measurements were made to identify how the concentration of THF affects the clathrate hydrates forming under static conditions between20%and 30%by mole of THF.The primary tests in this study were performed using a 20:80 THF/water ratio.Temperature increases during hydrate nucleation for THF-water were measured between-5 and 3℃.The range of ideal nanoparticle concentrations was found to be between 0.15%and 0.45%by weight for optimal static,kinetic inhibition of hydrate nucleation.At approximately 0.3%by weight,the most significant inhibition was observed under static conditions for all four types of nanoparticles tested.We found that functionalized amino-coated SiO2 nanoparticles,across all tests,significantly increased the time required for the formation of THF-water clathrate hydrates compared to the other three non-functionalized nanoparticles.The amorphous carbon and ironⅢoxide nanoparticles performed similarly across each test and were both the least effective in their inhibition of the clathrate hydrates of the four nanoparticles studied compared to a control.
基金Project supported by the National Natural Science Foundation of China (Grant No 10474085)
文摘Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band （below 15 meV） and yield correct relative intensity. Based on the results, the uncertain profile at ～6 meV is assigned to anharmonic vip modes coupled strongly to small cages. Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for vip-host coupling that explains the anomalous thermal conductivity of clathrate hydrate.
基金This work was supported by the National Natural Science Foundation of China(Grants 11772278,11904300 and 12002350)the Jiangxi Provincial Outstanding Young Talents Program(Grant 20192BCBL23029)。
文摘Fundamental mechanics of gas hydrates is of importance to evaluating geomechanical and geotechnical properties of gas hydrate deposits,but it remains largely unexplored yet due to insufficient direct experimental techniques and high-quality of gas hydrate samples.Here,classic molecular dynamic(MD)simulations are used to study the fracture mechanics of three main methane clathrate hydrates of sI,sII and sH types.The results show that the mechanical properties of those three methane clathrate hydrates are intrinsically different and are degraded by the presence of nanocracks.They show brittle facture and different fracture toughness.In terms of energy release rate,they are ranked as sH>sI>sII.Moreover,the three methane clathrate hydrates with nanocracks can be explained by a modified Griffith criterion.Moreover,it is intriguingly identified tip amorphization during the crack propagation process of the three methane clathrate hydrates,and sH methane clathrate hydrate with specific nanocrack exhibits slower crack propagation than other two methane clathrate hydrates.
基金This project was supported by the National Natural Science Foundation of China(Grant No.10474085).
文摘Lattice dynamical simulations of noble gas hydrate structures I and II have been performed. Potential energies were investigated to study the influence of vip species on the stability of the hydrate structure. Results show that when the diameter of inclusion molecules is between 3 A and 4.2 A, such as Ar and Kr, the critical role of the 512 cage in the stabilization of hydrates becomes effective. For Xe hydrates SI and SII, with the help of lattice dynamical calculations, the modes attributions are identified directly. We proposed the resonant effect of the fingerprint frequency at about 7 meV and 10 meV which arise from the coupling of Xe molecules in the 512 cage with the host lattice.
文摘A cadmium tetracyanoplatinate host clathrate,(MV)[Cd_(2){Pt(CN)_(4)}_(3)]·2(H_(2)O)(1),including a methylviologen dication (MV^(2+)) was synthesized,and the crystal structures,photochromic and photoluminescence properties were investigated.In 1,the alternatively parallel stacking between the MV^(2+)dications as electron acceptors in the channels and the electron donors[Pt1(CN)_(4)]^(2-) units in the host frameworks give a unique donor-acceptor (DA) system.Under UV irradiation,the electron transfer between MV^(2+) and[Pt(CN)_(4)]^(2-) ions generates MV^(·+)radicals with a photochromic behavior from pale-yellow to blue.This process occurs through single-crystal-to-single-crystal (SCSC) transformation and obvious structure variation of viologen cations is successfully observed.Moreover,the spectral overlap between the emission bands of 1 and the absorption around 623 nm for the MV^(·+) radicals leads to a modulation of the photoluminescence.
基金This project is financially supported by NSFC(59483001 & 29574187),Chinese Academy of Sciences(KJ-952-S1-508)and Organic Solids Laboratory,ICCAS.
文摘A novel supramolecular polysiloxane clathrate, POS/C, has been preparedby in-situ encapsulating rodlike p-butoxybenzylidene-p ' - dodecoxyaniline (BBDA ) , one kindof Schiff base liquid crystal molecule, within the pore of polyorganosiloxane (POS) whichis prepared by hydrosilylation coupling reaction of polyvinylsilsesquioxane (Vi- T ) withtetramethyldisiloxane (H-MM). Investigation by polarized light microscopy (PLM), differ-ential scanning calorimetry (DSC), infrared spectroscopy (IR), atomic force microscopy(AFM) and molecular simulation gives a preliminary support to the existence of the titlesupramolecular clathrate.
基金Project supported by National Natural Science Foundation of China(Grant Nos.11347134 and 11304254)the Doctor Foundation of Southwest University of Science and Technology,China(Grant No.13zx7125)
文摘We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound（Na8Si46） under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus,Young＇s modulus, Debye temperature,sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12172314,11772278,and 11904300)the Jiangxi Provincial Outstanding Young Talents Program(Grant No.20192BCBL23029)+2 种基金the Fundamental Research Funds for the Central Universities(Xiamen University:Grant Nos.20720210025 and 20720220023)the Research Council of Norway(Grant No.262644)the 111 project(Grant No.B16029)。
文摘Recently,a new phase C'_(1) H_(2) hydrate was experimentally identified.In this work,the diffusive behaviors of H_(2) in C'_(1)phase clathrate hydrate are explored using classic molecular dynamics(MD)simulations.It reveals that the cage occupancy by H_(2) molecule negligibly influences the C'_(1) phase clathrate structure but greatly dictates the diffusion coefficient of H_(2)molecule.Due to the small cage size and small windows connecting the neighboring cages in C'_(1) phase clathrate,nonoccupancy of the neighboring cages is demanded to enable the diffusion of H_(2) molecule that is primarily dominated by hopping mechanism.Moreover,the analysis of diffusive free energy landscape reveals lower energy barrier of H_(2) molecule in C'_(1) phase clathrate hydrate than that of other gases in conventional clathrate hydrates,and that H_(2) molecule travels through the windows between neighboring cages with preferential molecular orientation.This study provides critical physical insights into the diffusion behaviors of H_(2) in the C'_(1) phase clathrate hydrate,and implies that the C'_(1) clathrate hydrate is a promising solid structure for the next-generation H_(2) storage.
基金Project supported by the National Natural Science Foundation of China(Grant No.50902119)
文摘Single-crystal samples of type-VIII BasGa16-xCuxSn30 （x = 0, 0.03, 0.06, 0.15） clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5 × 10^19 cm^-3 for all the samples, the carrier mobility, μH, increases to more than twice that of BasGa16Sn30 for all the Cu doping samples, and consequently the electrical conductivity is enhanced distinctly from 1.90×10^4 S/m to 4.40 ×10^4 S/m, with the Cu composition increasing from x = 0 to x = 0.15. The Seebeck coefficient,α, decreases slightly with the increases in Cu composition. The values are about 0.72 W/mK at 300 K and are almost invariant with temperature up to 500 K for the samples with x = 0 and x = 0.03. The lattice thermal conductivity, μL, decreases from 0.59 W/InK for x = 0 to 0.50 W/mK for x = 0.03 at 300 K. The figure of merit for x = 0.03 reaches 1.35 at 540 K.
