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Based on the 4,4'-bipyridine organic linker, metal–organic frameworks of Co 2 (4,4'-bpy) 3 (NO 3 ) 4 ·xH 2 O (CB-MOF) have been prepared. The pressure-dependent structure evolution of CB-MOF has been investigated up to 11 GPa. An isostructural phase transition was observed at about 6 GPa followed by negative compressibility along the b axis.
Mesoporous materials with tailored properties hold great promise for energy harvesting and industrial applications. Here we have synthesized a novel tungsten bronze mesoporous material (K x WO 3 ; x ~ 0.07) having inverse FDU-12 type pore symmetry and a crystalline framework. In situ small angle X-ray scattering (SAXS) measurements of the mesoporous K 0.07 WO 3 show persistence of a highly ordered meso-scale pore structure to high pressure conditions (~18.5 GPa) and a material with remarkable mechanical strength despite having ~35% porosity. Pressure dependent in situ SAXS measurements reveal a bulk modulus κ = 44 ± 4 GPa for the mesoporous K x WO 3 which is comparable to the corresponding value for the bulk monoclinic WO 3 (γ-WO 3 ). Evidence from middle angle (MAXS) and wide angle X-ray scattering (WAXS), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy shows that the presence of potassium leads to the formation of a K-bearing orthorhombic tungsten bronze (OTB) phase within a monoclinic WO 3 host structure. Our ab initio molecular dynamics calculations show that the formation of the OTB phase provides superior strength to the mesoporous K 0.07 WO 3 .
In the present work, the defect properties of oxygen self-diffusion in PuO 2 are investigated over a wide temperature (300–1900 K) and pressure (0–10 GPa) range, by combining molecular dynamics simulations and thermodynamic calculations. Based on the well-established cBΩ thermodynamic model which connects the activation Gibbs free energy of diffusion with the bulk elastic and expansion properties, various point defect parameters such as activation enthalpy, activation entropy, and activation volume were calculated as a function of T and P. Molecular dynamics calculations provided the necessary bulk properties for the proper implementation of the thermodynamic model, in the lack of any relevant experimental data. The estimated compressibility and the thermal expansion coefficient of activation volume are found to be more than one order of magnitude greater than the corresponding values of the bulk plutonia. As a result, the diffusion mechanism is discussed in the context of the temperature and pressure dependence of the activation volume.
MD simulations reveal the origin of anomalous pressure dependence of propane diffusion in silica mesopores.
The dissociation of 2-methyl furan at high temperatures has been studied in a combined experimental and theoretical approach to elucidate the details of this multi-channel unimolecular reaction. Laser schlieren densitometry studies were performed in a diaphragmless shock tube over the range 1600 < T < 2300 K and three pressures 60, 120 and 240 Torr. The theoretical study identified many reaction paths, most of which are initiated by the formation of carbenes. Of these paths, five account for 99% consumption of 2MF, and three account for 95% consumption. Simulations of the experimental results with a model that incorporated the theoretical predictions of reaction paths failed to reproduce the experimental data. This was resolved by increasing the rate of loss of an H-atom from the methyl group in 2-methyl furan by a factor of 2–4. The resulting model provides good simulations of the complete set of experimental data. In conclusion, the branching fractions for the three key reactions are both temperature and pressure dependent.
The high temperature gas phase chemistry of the four butyl radical isomers (n-butyl,sec-butyl, iso-butyl, andtert-butyl) was investigated in a combined experimental and theoretical study. Organic nitrites were used as convenient and clean sources of each of the butyl radical isomers. Rate coefficients for dissociation of each nitrite were obtained experimentally and are at, or close to, the high pressure limit. Low pressure experiments were performed in a diaphragmless shock tube with laser schlieren densitometry at post-shock pressures of 65, 130, and 260 Torr and post-shock temperatures of 700-1000 K. Additional experiments were conducted with iso-butyl radicals at 805 K and 8.7 bar to elucidate changes in mechanism at higher pressures. These experiments were performed in a miniature shock tube with synchrotron-based photoionization mass spectrometry. The mass spectra confirmed that scission of the O-NO bond is the primary channel by which the precursors dissociate, but they also provided evidence of a minor channel (<7.7%) through HNO loss and formation of an aldehyde. These high pressure experiments were also used to determine the disproportionation/recombination ratio for iso-butyl radicals as 0.3. Reanalysis of the lower-temperature literature and the present data yielded rate constants for the disproportionation reaction, iso-butyl + iso-butyl = iso-butene + iso-butane. A chemical kinetics model was developed for the reactions of the butyl isomers that included new paths for highly energized adducts. These adducts are formed by the addition of H, CH 3 or C 2 H 5 to the butyl radicals. Accompanying theoretical investigations show that chemically activated pathways are competitive with stabilization of the adduct by collision under the conditions of the laser schlieren experiments. These calculations also show that at 10 bar and T< 1000 K stabilization is the only important reaction, but at higher temperatures, even at 10 bar, chemically activated product channels should also be considered. Branching fractions and rate coefficients are presented for these reactions. Furthermore, this study also highlights the importance of the radical structure for determining branching ratios for disproportionation and recombination of alkyl radicals, and these were facilitated by theoretical calculations of recombination rate coefficients for the four butyl radical isomers. Overall, the results reveal previously unknown features of butyl radical chemistry under conditions that are relevant to a wide range of applications and reaction mechanisms are presented that incorporate pressure dependent rate coefficients for the key steps.
Spatio-temporal mapping of species in a femtosecond laser induced Zircaloy-4 plasma identified conditions well-suited for the detection and analysis of deuterium across a wide range of concentrations.
Carbon dioxide (CO 2 ) emissions from fossil fuel combustion are a significant source of greenhouse gas, contributing in a major way to global warming and climate change. Carbon dioxide capture and sequestration is gaining much attention as a potential method for controlling these greenhouse gas emissions. Among the environmentally friendly solvents, deep eutectic solvents (DESs) have demonstrated the potential capability for carbon capture. To establish a theoretical framework for DES activity, thermodynamics modeling and solubility predictions are significant factors to anticipate and understand the system behavior. Here, in this study, we combine the COSMO-RS model with machine learning techniques to predict the solubility of CO 2 in various deep eutectic solvents. A comprehensive data set was established comprising 1973 CO 2 solubility data points in 132 different DESs at a variety of temperatures, pressures, and DES molar ratios. This data set was then utilized for the further verification and development of the COSMO-RS model. The CO 2 solubility (ln(x CO 2 )) in DESs calculated with the COSMO-RS model differs significantly from the experiment with an average absolute relative deviation (AARD) of 23.4%. A multilinear regression model was developed using the COSMO-RS predicted solubility and a temperature-pressure dependent parameter, which improved the AARD to 12%. Finally, a machine learning model using COSMO-RS-derived features was developed based on an artificial neural network algorithm. The results are in excellent agreement with the experimental CO 2 solubilities, with an AARD of only 2.72%. The ML model will be a potentially useful tool for the design and selection of DESs for CO 2 capture and utilization.
Enhancing the porosity of metal–organic frameworks (MOFs) typically relies on substituting their organic ligand components. Furthermore, we show that cross-linked terephthalate ligands yield oligoMOF and polyMOF versions of MIL-53(In) in which pressure-dependent phase transformations no longer occur. These materials show enhanced uptakes and CO 2 /N 2 selectivity, while retaining the overall MIL-53 framework.
The operation of solid-state batteries with a lithium metal anode and a high voltage cathode requires solid electrolytes (SEs) that are chemically stable with lithium, have a wide electrochemical window, and accommodate volume changes in the electrodes. Unfortunately, no SE has exhibited satisfactory mechanical and electrochemical properties that fit these requirements to date. Dual solid electrolyte systems that use a different SE for the anolyte and catholyte present a viable solution. Here, we focus on oxyhalide SEs that demonstrate superior ionic conductivity and cathode compatibility, where their lithium metal reactivity and poor reduction stability can be resolved using a lithium garnet (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 , LLZTO) separator. Nonetheless, this imposes a new hetero-electrolyte (H-E) interface at the anolyte|catholyte contact that defines the ion transport across the boundary. We report its promising properties, which are deconvoluted from the electrical measurements of bilayer symmetric cells, for three representative oxyhalide catholytes, LiNbOCl 4 , LiTaOCl 4 , and Li 3 Al 3 O 2 Cl 8 . Pressure-dependent measurements reveal that the relative softness of the oxyhalides (hardness ≤0.4 GPa) enables H-E resistances lower than 150 Ω cm 2 at 2–3 MPa. Mesoscale modelling reveals that the transfer-active contact area of oxyhalides with LLZTO is about 2–3-fold higher than that of argyrodite, Li 6 PS 5 Cl. The low H-E resistance of the LiNbOCl 4 |Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 dual electrolyte enables the cycling of a Li|LiNi 0.82 Mn 0.07 Co 0.11 O 2 full cell with a high discharge capacity (200 mA h g −1 ) at 60 °C and ∼7 MPa. Importantly, we demonstrate a Li-reservoir-free full cell with high Coulombic efficiency (>99.5%) and capacity at 1 MPa using this approach coupled with a garnet-silver interlayer.
Femtosecond pulse laser ablation of aluminum under different ambient air pressures between 1 atm and 4 x 10{sup -4} Pa is investigated using a femtosecond time-resolved shadowgraphic method. It is observed that as the ambient air pressure decreases, the contact front becomes more and more distinct for a certain pressure range, demonstrating that the confinement effect of the ambient air to the ablated target material can play a critically important role in the laser ablation process. It is also found that the concentric and semicircular stripe pattern, which results from the diffraction of the probe beam by the expanding plume of a specific material state and is typically observed in the shadowgraphs for 1-2 ns delay time, gradually blurs and disappears while the ambient air pressure decreases from 1 atm to 7000 Pa. If a prepulse or a relatively large pulse pedestal exists before the main pulse, however, the stripe pattern can still be observed even though the ambient air pressure is 5 x 10{sup -4} Pa. It is thus inferred that what contributes to the formation of the unique stripe pattern is a mixture of the ejected target material and ionized background gas induced by the femtosecond laser ablation.
The study of pressure induced structural phase transition of uranium sulphide, which crystallizes in rock salt (B1) structure, has been performed using the well described three body interaction model (TBIPM). Our present TBIP model consists of long range coulombic interaction, three body interactions, Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals interaction. The present results are in good agreement with the available experimental data on the phase transition pressure (Pt = 80.2 GPa). So it can be considered as an adequate and suitable model to perform high pressure studies.
Results of synchrotron based high pressure x ray diffraction measurements on Heuslar alloys Ni{sub 2}MnGa and Co{sub 2}FeSi are reported up to 30.6 and 24.6 GPa respectively. Pressure volume data for Ni{sub 2}MnGa shows normal compressibility behaviour up to 30.6 GPa with the value of bulk modulus Bo and its pressure derivative B' as 130 GPa and 4.97 respectively. In case of Co{sub 2}FeSi, the P-V data shows normal behaviour upto 5 Gpa and hereafter linear P-V relation. The estimated ambient pressure compressibility based on data up to 5 GPa is 267 GPa (with B' = 4). The fit to linear P-V data above 5 GPa yields a compressibility of 279.5.
We report here the successful synthesis of orthorhombic cubanite using microwave heating and characterization for its orthorhombic phase by powder X-ray diffraction, Micro-Raman, Thermal and high pressure electrical resistivity measurements. The unique physico-chemical conditions prevent successful synthesis under laboratory conditions, however the mineral occurs in nature in its orthorhombic form. A distinct endothermic dip in Differential Thermal Analysis (DTA) at 280 deg. C is in agreement with the DTA data reported for natural cubanite. An irreversible first order phase transformation from orthorhombic to NiAs structure is seen at 4 GPa/200 deg. C. High pressure electrical resistivity and micro-Raman spectroscopic measurements on the synthetic sample exhibit transformation to isocubanite.
Diamond anvil cell (DAC) technique relies on pressure determination based on use of pressure gauges. Fluorescence-based gauges, such as ruby and Sm doped yttrium aluminum garnet (Sm:YAG), are frequently used in the high pressure research. Here we present the results of DAC experiments which allowed extending calibration curves of the fluorescence frequency versus pressure up to 120 GPa at high temperatures up to 700 K for both for ruby and Sm:YAG. Cubic boron nitride was used as the reference gauge.
The bulk modulus of scandia is evaluated by ab initio calculation, based on density functional theory, and compared with bulk modulus measurement on nearly fully dense scandia and with the value attained from the equation of state based on diamond anvil cell measurements. The current results are in the upper range of the bulk moduli results in the literature. The scatter in the literature results might be explained by the differences in the specific volumes of the measured and calculated cases. For the specific volume of 59.65 {+-} 0.07 {angstrom}{sup 3} the average measured isothermal bulk modulus of scandia from the present study and recent literature results is 188 {+-} 10 GPa.
An incompressible Co{sub 54}Ta{sub 11}B{sub 35} bulk metallic glass (BMG) was investigated using in situ high-pressure synchrotron diffraction and nanoindendation. The elastic constants were deduced from the experiments based on the isotropic model. The Vickers hardness was measured to be 17.1 GPa. The elastic moduli and hardness are the highest values known in BMGs. The theoretically calculated elastic properties by density-functional study were well consistent with experimental measurements. The analysis of charge density and bonding character indicates the covalent character of Co-B and B-B bonds, underlying the unusually high elastic modulus and hardness in this material.
A primary dissociation channel of Br{sub 2} elimination is detected following a single-photon absorption of (COBr){sub 2} at 248 nm by using cavity ring-down absorption spectroscopy. The technique contains two laser beams propagating in a perpendicular configuration. The tunable laser beam along the axis of the ring-down cell probes the Br{sub 2} fragment in the B{sup 3}{Pi}{sub ou}{sup +}-X{sup 1}{Sigma}{sub g}{sup +} transition. The measurements of laser energy- and pressure-dependence and addition of a Br scavenger are further carried out to rule out the probability of Br{sub 2} contribution from a secondary reaction. By means of spectral simulation, the ratio of nascent vibrational population for v = 0, 1, and 2 levels is evaluated to be 1:(0.65 {+-} 0.09):(0.34 {+-} 0.07), corresponding to a Boltzmann vibrational temperature of 893 {+-} 31 K. The quantum yield of the ground state Br{sub 2} elimination reaction is determined to be 0.11 {+-} 0.06. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state (COBr){sub 2} via internal conversion. A four-center dissociation mechanism is followed synchronously or sequentially yielding three fragments of Br{sub 2}+ 2CO. The resulting Br{sub 2} is anticipated to be vibrationally hot. The measurement of a positive temperature effect supports the proposed mechanism.