scholarly journals Theoretical Prediction of CHn Crystal Structures under High Pressures

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1499
Author(s):  
Tao Yang ◽  
Jinjia Liu ◽  
Xiaotong Liu ◽  
Xiulei Liu ◽  
Ning Li
Keyword(s):  
Evolutionary Algorithms ◽  
High Pressures ◽  
Ambient Pressure ◽  
Total Density ◽  
Potential Candidate ◽  
Elevated Pressures ◽  
Graphene Synthesis ◽  
Pressure Region ◽  
Total Density Of States ◽  
High Pressure Region

CHn is the precursor unit for graphene synthesis. We have theoretically predicated a series of CHn structures with n = 1, 2, 4, 6, 8, 10, and 12 at elevated pressures (ambient pressure, 50, 100, 200, 300, 350, and 400 GPa) using evolutionary algorithms. The predicted CH and CH2 structures are graphane-type and polyethylene over the whole considered pressure range, respectively. The molecular crystalline methane is predicted for the stoichiometry of CH4. The combination of methane and H2 for CH6, CH8, CH10, and CH12 up to 300 GPa are obtained. At 400 GPa, the mixture of polymer and H2 for CH6, CH10, and CH12 comes into play. From the computed enthalpy, higher pressure and more hydrogen concentration contributed to the decomposition (to carbon and H2) of CHn systems. The total density of states for these CHn structures show that only the CH12 phase is metallic above 300 GPa. The rotational properties are traced in H2 and the CHn structures. The CH4 rotation is more sensitive to the pressure. The H2 units are nearly freely rotational. Other structures of CHn, including fcc-type and experimentally known structures, are not competitive with the structures predicted by evolutionary algorithms under high pressure region. Our results suggest that the CHn (n > 4) system is a potential candidate for hydrogen storage where H2 could be released by controlling the pressure.

scholarly journals Pressure Prediction of Electronic, Anisotropic Elastic, Optical, and Thermal Properties of Quaternary (M2/3Ti1/3)3AlC2(M = Cr, Mo, and Ti)

2016 ◽  
Vol 2016 ◽  
pp. 1-18 ◽  
Author(s):  
Liang Sun ◽  
Yimin Gao ◽  
Yangzhen Liu ◽  
Guoliang Wang ◽  
Yiran Wang ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Ambient Pressure ◽  
Relative Volume ◽  
Ultraviolet Region ◽  
Total Density ◽  
Covalent Bonds ◽  
Optical Functions ◽  
Anisotropic Elastic ◽  
The One ◽  
Total Density Of States

The electronic, mechanical, anisotropic elastic, optical, and thermal properties of quaternary (M2/3Ti1/3)3AlC2(M = Cr, Mo, and Ti) under different pressure are systematically investigated by first-principles calculations. The bonding characteristics of these compounds are the mixture of metallic and covalent bonds. With an increase of pressure, the heights of total density of states (TDOS) for these compounds decrease at Fermi level. The highest volume compressibility among three compounds is Mo2TiAlC2for its smallest relative volume decline. The relative bond lengths are decreasing when the pressure increases. The bulk and shear modulus of the one doped with Cr or Mo are larger than those of Ti3AlC2with pressure increasing. With an increase of pressure, the anisotropy of these compounds also increases. Moreover, Mo2TiAlC2has the biggest anisotropy among the three compounds. The results of optical functions indicate that the reflectivity of the three compounds is high in visible-ultraviolet region up to ~10.5 eV under ambient pressure and increasing constantly when under pressure. Mo2TiAlC2has the highest loss function. The calculated sound velocity and Debye temperature show that they all increase with pressure.CVof the three compounds is also calculated.

scholarly journals Pressure effect of the mechanical, electronics and thermodynamic properties of Mg–B compounds A first-principles investigations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
GuoWei Zhang ◽  
Chao Xu ◽  
MingJie Wang ◽  
Ying Dong ◽  
FengEr Sun ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Boron Content ◽  
Structural Parameters ◽  
Debye Model ◽  
Total Density ◽  
First Principle ◽  
Volume Deformation ◽  
Temperature And Pressure ◽  
Total Density Of States

AbstractFirst principle calculations were performed to investigate the structural, mechanical, electronic properties, and thermodynamic properties of three binary Mg–B compounds under pressure, by using the first principle method. The results implied that the structural parameters and the mechanical properties of the Mg–B compounds without pressure are well matched with the obtainable theoretically simulated values and experimental data. The obtained pressure–volume and energy–volume revealed that the three Mg–B compounds were mechanically stable, and the volume variation decreases with an increase in the boron content. The shear and volume deformation resistance indicated that the elastic constant Cij and bulk modulus B increased when the pressure increased up to 40 GPa, and that MgB7 had the strongest capacity to resist shear and volume deformation at zero pressure, which indicated the highest hardness. Meanwhile, MgB4 exhibited a ductility transformation behaviour at 30 GPa, and MgB2 and MgB7 displayed a brittle nature under all the considered pressure conditions. The anisotropy of the three Mg–B compounds under pressure were arranged as follows: MgB4 > MgB2 > MgB7. Moreover, the total density of states varied slightly and decreased with an increase in the pressure. The Debye temperature ΘD of the Mg–B compounds gradually increased with an increase in the pressure and the boron content. The temperature and pressure dependence of the heat capacity and the thermal expansion coefficient α were both obtained on the basis of Debye model under increased pressure from 0 to 40 GPa and increased temperatures. This paper brings a convenient understanding of the magnesium–boron alloys.

scholarly journals Experimental and computational study on roles of WOx promoting strong metal support promoter interaction in Pt catalysts during glycerol hydrogenolysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tinnakorn Saelee ◽  
Poonnapa Limsoonthakul ◽  
Phakaorn Aphichoksiri ◽  
Meena Rittiruam ◽  
Mongkol Lerdpongsiripaisarn ◽  
...  
Keyword(s):  
Density Of States ◽  
Design Guidelines ◽  
Total Density ◽  
High Electron ◽  
Metal Support Interaction ◽  
Metal Support ◽  
Glycerol Hydrogenolysis ◽  
The Stability ◽  
Total Density Of States ◽  
Promoter Interaction

AbstractBiodiesel is of high interest due to increased demand for energy with the concern regarding more sustainable production processes. However, an inevitable by-product is glycerol. Hence, the conversion of this by-product to higher-value chemicals, especially 1,3-propanediol (1,3-PDO) via glycerol hydrogenolysis reaction, is one of the most effective pathways towards a profitable process. In general, this process is catalyzed by a highly active Pt-based catalyst supported on γ-Al2O3. However, its low 1,3-PDO selectivity and stability due to surface deactivation of such catalysts remained. This led to the surface modification by WOx to improve both the selectivity by means of the increased Brønsted acidity and the stability in terms of Pt leaching-resistance. Hence, we applied experimental and density functional theory (DFT)-based techniques to study the fundamentals of how WOx modified the catalytic performance in the Pt/γ-Al2O3 catalyst and provided design guidelines. The effects of WOx promoter on improved activity were due to the shifting of the total density of states towards the antibonding region evident by the total density of states (TDOS) profile. On the improved 1,3-PDO selectivity, the main reason was the increasing number of Brønsted acid sites due to the added WOx promoter. Interestingly, the stability improvement was due to the strong metal-support interaction (SMSI) that occurred in the catalyst, like typical high leaching-resistant catalysts. Also, the observed strong metal-support-promoter interaction (SMSPI) is an additional effect preventing leaching. The SMSPI stemmed from additional bonding between the WOx species and the Pt active site, which significantly strengthened Pt adsorption to support and a high electron transfer from both Pt and Al2O3 to WOx promoter. This suggested that the promising promoter for our reaction performed in the liquid phase would improve the stability if SMSI occurred, where the special case of the WOx promoter would even highly improve the stability through SMSPI. Nevertheless, various promoters that can promote SMSPI need investigations.

Molecular Dynamics Simulations on Melting of Aluminum

2013 ◽  
Vol 423-426 ◽  
pp. 935-938 ◽  
Author(s):  
Ji Feng Li ◽  
Xiao Ping Zhao ◽  
Jian Liu
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Molecular Dynamics Simulations ◽  
High Pressures ◽  
Ambient Pressure ◽  
Initial Porosity ◽  
Equilibrium Melting Point ◽  
Porosity Effect ◽  
Dynamics Simulations ◽  
Experimental Melting Point

Molecular dynamics simulations were performed to calculate the melting points of perfect crystalline aluminum to high pressures. Under ambientpressure, there exhibits about 20% superheating before melting compared to the experimental melting point. Under high pressures, thecalculated melting temperature increases with the pressure but at a decreasing rate, which agrees well with the Simon's melting equation. Porosity effect was also studied for aluminum crystals with various initial porosity at ambient pressure, which shows that the equilibrium melting point decreases with the initial porosity as experiments expect.

HYDROGEN — ZERO CARBON FOOTPRINT

2021 ◽  
Vol 7 (1) ◽  
pp. 10-25
Author(s):  
Mikhail V. Gordin ◽  
Valery I. GUROV ◽  
Anton N. Varyukhin ◽  
Alexander V. Geliev ◽  
Elena V. SHCHERBAKOVA
Keyword(s):  
Power Systems ◽  
The Past ◽  
Long Term Storage ◽  
Strategic Direction ◽  
Pressure Region ◽  
Zero Carbon ◽  
World Class ◽  
High Pressure Region ◽  
Term Storage

This article presents Russia’s main achievements of over the past 65 years in the development of an advanced scientific and technical groundwork for the introduction of hydrogen as a fuel in various energy systems. On the basis of the obtained world-class results, the authors argue for the necessity of creating a Center for Hydrogen Innovative Development (CVIR) with the decisive participation of enterprises with real experience in obtaining liquid hydrogen (H2l) with the possibility of its long-term storage. A concept has been formulated for the development of breakthrough technological solutions for the widespread use of hydrogen as an efficient and environmentally friendly (without the formation of carbon oxides) fuel in various power systems within the framework of the CVIR. In particular, the strategic direction of the CVIR project was developed in order to create a developed infrastructure for the reliable provision of vehicles with the required amount of fuel in a limited period of time. This can be achieved by applying the method of cryogenic filling of transport cylinders, taking into account the real properties of hydrogen in the ultra-high pressure region (70 MPa and above). The results have revealed possibilities for further building up the advanced scientific and technical groundwork for the broad promotion of hydrogen in the energy complex of Russia, which is presented in the CVIR project. In addition, the authors have compared the developed technologies with foreign analogues.

scholarly journals Pressure-Dependent Clustering in Ionic-Liquid-Poly (Vinylidene Fluoride) Mixtures: An Infrared Spectroscopic Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2099
Author(s):  
Teng-Hui Wang ◽  
Wei-Xiang Wang ◽  
Hai-Chou Chang
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Vinylidene Fluoride ◽  
Ambient Pressure ◽  
Infrared Spectroscopic Study ◽  
Research Attention ◽  
Nanoscale Structures ◽  
Local Structures ◽  
Poly Vinylidene Fluoride ◽  
Hydrogen Bonded

The nanostructures of ionic liquids (ILs) have been the focus of considerable research attention in recent years. Nevertheless, the nanoscale structures of ILs in the presence of polymers have not been described in detail at present. In this study, nanostructures of ILs disturbed by poly(vinylidene fluoride) (PVdF) were investigated via high-pressure infrared spectra. For 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HEMIm][TFSI])-PVdF mixtures, non-monotonic frequency shifts of the C4,5-H vibrations upon dilution were observed under ambient pressure. The experimental results suggest the presence of microheterogeneity in the [HEMIm][TFSI] systems. Upon compression, PVdF further influenced the local structure of C4,5–H via pressure-enhanced IL–PVdF interactions; however, the local structures of C2–H and hydrogen-bonded O–H were not affected by PVdF under high pressures. For choline [TFSI]–PVdF mixtures, PVdF may disturb the local structures of hydrogen-bonded O–H. In the absence of the C4,5–H⋯anion and C2–H⋯anion in choline [TFSI]–PVdF mixtures, the O–H group becomes a favorable moiety for pressure-enhanced IL–PVdF interactions. Our results indicate the potential of high-pressure application for designing pressure-dependent electronic switches based on the possible changes in the microheterogeneity and electrical conductivity in IL-PVdF systems under various pressures.

scholarly journals Ultrasonography-guided botulinum toxin injection to the cricopharyngeus muscle: a case report and technical notes

2020 ◽  
Vol 22 (3) ◽  
pp. 345 ◽  
Author(s):  
Yi-Chian Wang ◽  
Chueh-Hung Wu ◽  
Shaw-Gang Shyu ◽  
Ming-Yen Hsiao ◽  
Tyng-Guey Wang
Keyword(s):  
Botulinum Toxin ◽  
Botulinum Toxin Injection ◽  
Food Passage ◽  
Cricopharyngeus Muscle ◽  
Lateral Medullary Syndrome ◽  
Pressure Region ◽  
Effective Choice ◽  
High Pressure Region ◽  
Common Target

Dysphagia associated with the cricopharyngeus muscle (CPm) dysfunction negatively influences the quality of life. This high-pressure region must relax and the lumen must open for smooth food passage. The CP muscle is therefore a common target of chemodenervation with botulinum toxin (BTX). Here we presented a patient with severe left lateral medullary syndrome and non-relaxation of the CPm. We described how to localize the CPm in the transverse and longitudinal views under ultrasonography and offered a video demonstrating ultrasonography-guided BTX injection. Ultrasonography-guided CPm injection with BTX may serve as a reliable, rapid, and effective choice for treatment of cricopharyngeal dysphagia.

scholarly journals THE PHONON SPECTRUM OF THE OCTAGONAL TILING

1993 ◽  
Vol 07 (06n07) ◽  
pp. 1505-1525 ◽  
Author(s):  
J. LOS ◽  
T. JANSSEN ◽  
F. GÄHLER
Keyword(s):  
Specific Heat ◽  
Density Of States ◽  
Phonon Spectrum ◽  
Low Frequency ◽  
Debye Model ◽  
Square Lattice ◽  
Total Density ◽  
Unit Cells ◽  
Linear Behaviour ◽  
Total Density Of States

A study of the phonon spectrum of the octagonal tiling is presented, by calculating and analysing the properties of the spectrum of perfect and randomized commensurate approximants with unit cells containing up to 8119 vertices. The total density of states, obtained by numerical integration over the Brillouin zone, exhibits much structure, and in the low frequency range of the spectrum there is deviation from the normal linear behaviour in the form of pseudogaps. For randomized approximants these pseudogaps disappear and the density of states is globally smoothened. It turns out that the widths of the gaps in the dispersion vanish in the low frequency limit. Therefore the scaling behaviour of the lowest branches tends to the behaviour of an absolutely continuous spectrum, which is not the case at higher frequencies. As an application, the vibrational specific heat of the different tiling models is calculated and compared to the specific heat of a square lattice and of a Debye model.

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