Packing Of Layers Research Articles

Structure Formation of Hexagonal Diamond: Ab Initio Calculations

The formation of structure of hexagonal diamond from graphite and cubic diamond is simulated with the density functional theory. Orthorhombic AB graphite transforms into hexagonal diamond under uniaxial compression at pressures above 61 GPa. The pressure should be higher than 57 GPa to form hexagonal diamond from AA graphite. Another possible way to obtain hexagonal diamond is uniaxial compression of cubic diamond under pressures from 300 to 380 GPa. The theoretical calculations were used to interpret the diffraction data obtained after X-ray diffraction and electron microscopic analysis of natural and synthetic diamond-like materials. We found that there are no crystals with ideal cubic and hexagonal structures in diamond-like carbon materials, and their structure is characterized by random packing of molecular layers.

Effect of the Anomeric Configuration on the Micellization of Hexadecylmaltoside Surfactants.

The self-assembly of the two anomeric forms of n-hexadecyl-d-maltopyranoside (denoted α-C16G2 and β-C16G2) has been studied in dilute aqueous solution by means of surface tension measurements, scattering methods (dynamic light scattering, static light scattering, and small-angle X-ray and neutron scattering), and cryo-transmission electron microscopy at different surfactant concentrations and temperatures. Surface tension measurements demonstrate differences in the surfactant adsorption at the air-water interface, where α-C16G2 shows a lower CMC than β-C16G2. Similarly, micelle morphology was found to profoundly depend on anomerism. β-C16G2 preferentially forms very elongated micelles with large persistence lengths, whereas α-C16G2 assembles into smaller micelles for which the structure varies with concentration and temperature. The differences between the two surfactant anomers in terms of self-assembly can be attributed to the interaction between neighboring headgroups. Specifically, β-C16G2 allows for a closer packing in the palisade layer, hence reducing the micelle curvature and promoting the formation of more elongated micelles. Strong intermolecular headgroup interactions may also account for the observed rigidity of the micelles.

Mesomorphic and Dielectric Properties of Supramolecular 3,5-Diamino-1-dodecyl-1,2,4-triazole

The formation of a thermotropic smectic phase in 3,5-diamino-1-dodecyl-1,2,4-triazole was revealed by polarizing microscopy and DSC. Depending on heating and cooling conditions, transitions between different types of layered packings occur, which was evidenced by dielectric measurements. Quantum-chemical simulation established that the mesomorphism of 1,2,4-triazole derivatives is associated with the formation of supramolecules with a higher polarizability anisotropy. The calculation results confirmed the possibility of lateral hydrogen bonding which favors layered smectic packing.

Simple model for the stripe phase in compounds with bent-core molecules which exhibit a lower-temperature ferroelectric smectic-A phase.

Bent-core (BC) molecules usually exhibit polar packing in smectic layers in which the long or bow axes tilt with respect to the layer normal. In many compounds, the tilt angle goes to zero, and typically the polarization (P) of neighboring layers has an antiferroelectric order (SmAP_{AF}). A careful molecular engineering has led to the discovery of the ferroelectric SmAP_{F} phase in a few BC compounds. Detailed experimental studies [Zhu et al., J. Am. Chem. Soc. 134, 9681 (2012)10.1021/ja3009314] have shown that one of the compounds undergoes a weak first order transition to a striped phase (SmAP_{Fmod}), in which the repolarization switching occurs at a threshold electric field, the latter increasing with temperature. The main optical birefringence of the SmAP_{Fmod} phase increases rapidly with the field at lower temperatures of its range. A small (<10%) fraction of the BC molecules can be expected to have less bent conformations in excited states (ESs), and we argue that the ES conformers rotate freely about the bow axes, and aggregate to form regions without any polar order to gain rotational entropy. In turn, a favorable divP term leads to the formation of stripes in the polarized regions made of ground state conformers. Based on this physical picture, we develop a simple phenomenological model to reproduce all the experimental trends qualitatively. In sample cells with insulating layers neighboring stripes prefer to have an antiparallel orientation of the mean P direction. The dielectric constant of the stripe phase increases with a dc bias electric field, a trend which is opposite to that in other ferroelectric liquid crystals.

Novel hydroxy polyamine surfactant N-(2-hydroxyethyl)-N-dodecyl-ethanediamine: Its synthesis and flotation performance study to quartz

A novel hydroxy polyamine surfactant N-(2-hydroxyethyl)-N-dodecyl-ethanediamine (NHDE) was designed by introducing the hydroxyethyl into diamines collector, and synthesized in the paper. The structure of NHDE was characterized by Fourier transform infrared spectroscopy (FTIR), 1H NMR and liquid chromatography mass spectrometry (LC/MS). NHDE was originally introduced as the collector in the flotation system of quartz and hematite to verify the desiliconization performance. The tests of micro-flotation, zeta potential, FTIR, and X-ray photoelectron spectroscopy (XPS) were used to study the flotation performance and adsorption mechanism of NHDE on the quartz surface. Micro-flotation results showed that NHDE exhibited outstanding performance for collecting quartz, and the efficient flotation separation of quartz from its mixture with hematite could be conducted under pH 4.5–9.5. The analysis results of zeta potential, FTIR, and XPS indicated that the adsorption of NHDE on quartz surface were due to the combination of electrostatic attractive force and the multiform hydrogen bonding. The multiform hydrogen bond not only enhanced the adsorption of NHDE on quartz surface, but also made NHDE form the stable packing layer on the quartz surface to strengthen the hydrophobic of quartz surface.

3-D structure of the discharging zone of the Daginsky hydrothermal system (Sakhalin Island) according to the ground penetrating radar method and well logs

The paper presents the results of a comprehensive analysis of GPR data and geophysical well survey data (gamma-ray logging and self-polarization potentials) to study the 3-D spatial structure of the Daginsky hydrothermal system discharging zone (Sakhalin Island) and its hydrogeological situation. According to the GPR method, the paleo-valleys were identified, the morphology of which indicates the presence of runoff hollows, the accumulation of sandy-aleurite-clay sediments covered with peat formations. It can be concluded that the caprock in this area consists of a pack of water layers and permeable zones. Based on the data of geophysical studies in wells, three zones can be distinguished, each of which is characterized by the corresponding values of gamma activity and changes in the potentials of its own polarization. All this helps in identifying permeable thermally conductive zones. The data obtained are of practical importance.

Calculation of Hydrodynamic Characteristics of Combined Apparatuses with a Regular-Suspended Packing

The analysis of operation of heat and mass transfer apparatuses and dust collectors with a mobile packing (MP) has allowed creating the designs of apparatuses with a combined regular- suspended packing, which allow using the advantages of vortex interaction of flows in the layer of a regular packing with mechanical cleaning of deposits in the chaotic motion of suspended discrete contact elements. The studies of the hydraulic resistance and the retained liquid amount have been performed in the apparatuses with a tubular- suspended and tubular-fountaining packing and their comparative analysis. In order to calculate the hydraulic resistance, the retained liquid amount and the layer gas content, the calculated dependences are presented, taking into account the vortex interaction of gas and liquid flows.

Chloranilato-Based Layered Ferrimagnets with Solvent-Dependent Ordering Temperatures

We report the synthesis and the characterization of six new heterometallic chloranilato-based ferrimagnets formulated as (NBu4)[MnCr(C6O4Cl2)3]·nG with n = 1 for G = C6H5Cl (1), C6H5I (3), and C6H5CH3 (4); n = 1.5 for G = C6H5Br (2) and n = 2 for G = C6H5CN (5) and C6H5NO2 (6); (C6O4Cl2)2− = 1,3-dichloro,2,5-dihydroxy-1,4-benzoquinone dianion. The six compounds are isostructural and show hexagonal honeycomb layers of the type [MnCr(C6O4Cl2)3]− alternating with layers containing the NBu4+ cations. The hexagons are formed by alternating Mn(II) and Cr(III) connected by bridging bis-bidentate chloranilato ligands. The benzene derivative solvent molecules are located in the hexagonal channels (formed by the eclipsed packing of the honeycomb layers) showing π-π interactions with the anilato rings. The six compounds behave as ferrimagnets with ordering temperatures in the range 9.8–11.2 K that can be finely tuned by the donor character of the benzene ring and by the number of solvent molecules inserted in the hexagonal channels. The larger the electron density on the aromatic ring and the larger the number of solvent molecules are, the higher Tc is. The only exception is provided by toluene, where the formation of H-bonds might be at the origin of weaker π-π interactions observed in this compound.

Simulation of spatial ordering of powder mixture particles when packed in square matrices using an example of monodisperse balls

The peculiarities of self-ordering of large particles of powder mixture components with layer-by-layer pressing of long billets used in material production by the method of self-propagating high-temperature synthesis (SHS) are studied using the example of structure formation at compaction of thin layers of a model system of monodisperse calibrated solid balls (1 mm in diameter). In unilateral axial compaction, the case of packing of thin layers of balls (containing 1–5 monolayers) in a square matrix (with a ratio of the transverse dimension of the matrix to the diameter of the ball ∼14) is considered at low pressures that do not cause significant deformation of the balls. In the disperse system under study, a structural ordering of the particles occurs with a characteristic stepped view of the curve of the compact height dependence on the number of balls in the initial charge of balls. With an increase in the number of balls in the charge, the density of thin layers changes periodically during the compaction. In the compacts, fragments of structures in which the particles are arranged orderly like regular packing of ideal balls appear. The square shape of the matrix provides the formation of fragments of rhombohedral and cubic packing. The influence of nonuniform distribution of the initial charge of balls inside the matrix on the structuring of thin layers during compaction is considered.

Comparative assessment of different image processing methods to determine the gas–liquid interfacial area in froth regimes of sandwich packings from ultrafast X-ray tomography image data

Sandwich packings consist of alternatingly stacked structured packing layers of different specific surface area. In such packings froth two-phase flow appears when the packing is operated between the loading limits of the layers. For this highly agitated flow regime, there is a lack of hydrodynamic data, in particular on gas-liquid interfacial area. Ultrafast X-ray tomography, a cross-sectional imaging technique with a frame rate of more than 1000 cross-sectional images per second, is applied to visualize the gas-liquid flow and to extract the gas–liquid interfacial area data via image post-processing methods. For that, we assessed different segmentation methods, that are, level set and gray level contour techniques.

Establishment and efficiency analysis of a single-stage denitrifying phosphorus removal system treating secondary effluent

For advanced phosphorus and nitrogen removal, denitrifying phosphorus removal (DPR) was used to treat secondary effluent of sewage plants based on alternating anoxic/anaerobic process within single-stage biofilter. Under the hydraulic load of 3 m3/(m2·h), average removal rates of TP and TN in the system were 61.05% and 90.54%. 82.7% of the NO3–-N removal occurred in the upper of the packing layer. TP removal occurred in upper and lower of the packing layer, accounting for 42.02% and 57.98% of the total removal, respectively. Biomass and bioactivity decreased proportional to the height incensement of packing layer. Nitrogen and phosphorus removal rates increased with anaerobic time while decreased with hydraulic load. 16S rDNA sequencing results showed dominant DNPAOs in the system included Acinetobacter and Dechloromonas, while dominant denitrifying bacteria included Flavobacterium, Comamonadaceae, Hydrogenophaga, Thauera and Azospira. The study further provided an effective and feasible way for advanced wastewater treatment.

First germanium doped titanium disulfide polytypes: Crystal structure and metal–metal interactions

Single crystals of Ge-doped TiS 2 polytypes, 1T, (4H) 2 , 12R, and their corresponding new a √3 × a √3 superstructure were grown by chemical vapor transport method. The crystals were characterized by combining X-ray diffraction and transmission electron microscopy techniques. The structures of these polytypes are all based on close packing layers of sulfur of CdI 2 -type structure. Except in the 1T polytype, the germanium atoms are observed to be equally distributed over both partial and complete occupancy layers. A significant distortion of the metal–sulfur distances is observed in the superstructure polytypes, as a consequence of metal–metal corrugated layers. The 12R- a √3 × a √3 superstructure is revealed by both electron diffraction and X-ray diffraction by the presence of satellite reflections. Electron diffraction patterns from the 12R polytype show highly structured diffuse scattering surrounding the main spots. These diffuse segments, which are arranged in triangles sharing vertices, correspond to a 2 a * × 2 a * superstructure and are attributed to the short-range order of metal atoms in the partially filled layers. La croissance des monocristaux des polytypes de TiS 2 dopés au germanium, 1T, (4H)2, 12R, et de sa nouvelle superstructure a √3 × a √3 correspondante a été réalisée par la méthode du transport chimique en phase vapeur (CVT). Les cristaux ont été caractérisés en combinant les techniques de diffraction des rayons X (DRX) et de la microscopie électronique à transmission (MET). La structure de ces polytypes est basée sur des couches compactes de soufre de type CdI2. À l'exception du polytype-1T, les atomes de germanium sont répartis de manière équitable à la fois dans les couches partiellement ou totalement occupées. Une importante distorsion est observée dans les distances métal–soufre des polytypes à superstructure, résultat de l'ondulation des couches métal–métal. La superstructure 12R- a √3 × a √3 a été identifiée à la fois par diffraction des rayons X et par microscopie électronique par la présence de réflexions satellites. Les clichés de diffraction électronique du polytype 12R montrent une diffusion diffuse très structurée entourant les taches ( spots ) de diffraction principales. Cette diffusion en forme de segments triangulaires se partageant des sommets correspond à une superstructure 2 a * × 2 a * et est attribuée à un ordre à courte distance (SRO) des atomes métalliques dans les couches métalliques partiellement occupées.

Development of a mesoscale model for the gas phase fluid dynamics in structured packings based on fundamental experiments and CFD investigations

This paper presents a new mesoscale model simulating the gas phase fluid dynamics and concentration distribution in structured packings, used in absorption and distillation columns. The model describes the structured packing as an arrangement of triangular channel sections and is implemented with an own developed mesoscale simulation code (StructuPack). The velocity field is stored at the cell faces and is driven by pressure, inertial and viscous forces. The coupled continuity and momentum equations are solved with the SIMPLE-algorithm, that is usually applied in CFD solvers. The development of the model is based on fundamental investigations with CFD simulations and experiments, described in the first part of the paper. Particularly, the concentration distribution in a representative geometry of structured packings, a single crisscrossing junction of triangular channels, is analysed. As one result of the fundamental investigations the CFD solver could be validated as a predictive tool with respect to concentration distribution for the laminar regime in structured packings. In the second part, the mesoscale model is described in detail and validated with a scenario of tracer distribution in a packing layer. By means of comparison with CFD simulations of the same scenario it was shown that the mesoscale model has the ability to yield good representations of concentration, pressure and velocity profiles in a structured packing. Thereby the mesoscale computational performance was three orders of magnitudes more efficient with respect to CFD. At the advent of high-performance computing this means that models at intermediate scale are a viable tool to simulate scenarios like maldistribution effects in industrial sized structured packings of distillation and absorption columns.

Microscopic characterization of xenon adsorption in wedge pores

We explored the possibility of using xenon as a molecular probe to characterize graphitic non-uniform pores in activated carbon (AC), and studied its isotherms with a Grand Canonical Monte Carlo (GCMC) simulation. To model non-uniform pores, we used a wedge pore model, a better description of the pore space in AC, and studied the effects of the pore length, the wedge angle and the temperature on the behaviour of the adsorption and desorption isotherms. For temperatures below the triple point, the isotherm exhibits two distinct regions: in the region of low loadings it shows a step-wise behaviour as the adsorption progresses from the tip of the wedge, followed by the second region of gradual increase in the adsorbed density with pressure. A distinct feature is the possible existence of multiple hysteresis loop in the first region and the reversibility of the isotherm in the second region. The hysteresis is due to the commensurate packing of molecular layers across the pore to form domains along the axial direction of the pore and the number of layers is incremented by one as we move from one domain to the next. We have found that the hysteresis disappears when either the wedge angle is greater than a critical value or the temperature is greater than the so-called bifurcation temperature. The second region of reversibility is due to the formation of the condensate separated from the gas phase with a concave interface whose radius of curvature is found to satisfy the Kelvin equation.

H2O2-based selective oxidations by divanadium-substituted polyoxotungstate supported on nitrogen-doped carbon nanomaterials

Abstract In this work, we present a new methodology for the preparation of highly active, selective, leaching-tolerant and recyclable catalysts on the basis of polyoxometalates (POM) and nitrogen-doped carbon nanomaterials. A divanadium-substituted γ-Keggin phosphotungstate [γ-PW10O38V2(μ-O)(μ−OH)]4− (PV2), was immobilized on two types of supports – N-doped carbon nanofibers (N-CNFs) having herring-bone packing of graphite layers and bamboo-like N-doped carbon nanotubes (N-CNTs). Two series of catalysts have been prepared and characterized by elemental analysis, N2 adsorption, TEM, XPS and FTIR techniques. Their catalytic performance was assessed in the liquid-phase selective oxidation of two representative organic substrates, 2,3,6-trimethylphenol and cyclohexene, with aqueous H2O2 as the green oxidant. The presence of nitrogen in the supports ensures strong binding and quasi-molecular dispersion of POM on the carbon surface, which is crucial for the catalytic performance and catalyst stability. The catalysts reveal truly heterogeneous nature of the catalysis and can be easily recovered and reused without loss of the catalytic performance. The morphology of the support has a significant impact on the catalytic performance: the supported PV2 catalysts prepared using N-CNTs are more active and, in general, more selective than the catalysts prepared with N-CNFs.

To the Theory of Electronic States of an Epitaxial Graphene Bilayer

The energy spectrum of an epitaxial graphene bilayer is investigated. The most general case of spontaneous breaking of the P symmetry within and between the layers is considered. The influence of the gate voltage on the energy spectrum is studied. It is shown that a general profile of this influence substantially depends on the ratio between bandgaps corresponding to different layers. At a certain value of the Coulomb potential caused by the transition of a charge from the substrate, the bandgap collapses. These studies are carried out for two types of layer packing in the bilayer, namely, the AB and AA packings.

Formulation of carbon black-ionomer dispersions for thin film formation in fuel cells

The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer. The interactions between the ionomer, carbon black particles, and solvent affect the suspension properties and thus the layer morphology. We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics. Highly branched carbon blacks with a high surface area tend to form less cracked layers. As less branched carbons can pack together more closely, a smaller pore size results in a larger capillary pressure during drying and thus more cracks. The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles. The carbon black aggregates are thus smaller, resulting in closer packing and thinner layers. Moreover, the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer, preventing crack formation. An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.

Решение обратной задачи метода потенциалов самопроизвольной поляризации в пачке пластов с зоной проникновения (терригенный разрез)

Решение обратной задачи метода потенциалов самопроизвольной поляризации в пачке пластов с зоной проникновения (терригенный разрез)

Формирование структуры гексагонального алмаза: ab initio расчеты

Modeling of the structure formation of hexagonal diamond from graphite and cubic diamond was performed using the density functional theory method. The transformation of orthorhombic AB graphite into hexagonal diamond can occur as a result of uniaxial compression at pressures above 61 GPa. For the formation of hexagonal diamond from AA graphite, the pressure must exceed 57 GPa. Another possible way to obtain hexagonal diamond is uniaxial compression of cubic diamond at pressures from 300 to 380 GPa. The data of theoretical calculations were used to interpret the diffraction data obtained as a result of X-ray diffraction and electron microscopic analysis of natural and synthetic diamond-like materials. It was found that crystals with the ideal cubic and hexagonal structure are not contained in diamond-like carbon materials, and their structure is characterized by random packing of molecular layers.

Dibenzochrysene enables tightly controlled docking and stabilizes photoexcited states in dual-pore covalent organic frameworks.

Covalent organic frameworks (COFs), consisting of covalently connected organic building units, combine attractive features such as crystallinity, open porosity and widely tunable physical properties. For optoelectronic applications, the incorporation of heteroatoms into a 2D COF has the potential to yield desired photophysical properties such as lower band gaps, but can also cause lateral offsets of adjacent layers. Here, we introduce dibenzo[g,p]chrysene (DBC) as a novel building block for the synthesis of highly crystalline and porous 2D dual-pore COFs showing interesting properties for optoelectronic applications. The newly synthesized terephthalaldehyde (TA), biphenyl (Biph), and thienothiophene (TT) DBC-COFs combine conjugation in the a,b-plane with a tight packing of adjacent layers guided through the molecular DBC node serving as specific docking site for successive layers. The resulting DBC-COFs exhibit a hexagonal dual-pore kagome geometry, which is comparable to COFs containing another molecular docking site, namely 4,4',4'',4'''-(ethylene-1,1,2,2-tetrayl)-tetraaniline (ETTA). In this context, the respective interlayer distances decrease from about 4.6 Å in ETTA-COFs to about 3.6 Å in DBC-COFs, leading to well-defined hexagonally faceted single crystals sized about 50-100 nm. The TT DBC-COF features broad light absorption covering large parts of the visible spectrum, while Biph DBC-COF shows extraordinary excited state lifetimes exceeding 10 ns. In combination with the large number of recently developed linear conjugated building blocks, the new DBC tetra-connected node is expected to enable the synthesis of a large family of highly correlated and ordered 2D COFs with promising optoelectronic properties.