Density and phase equilibrium for ice and structure I hydrates using the Gibbs–Helmholtz constrained equation of state

A new, rigorous framework centered around the multi-scale GHC equation of state is presented for predicting bulk density and phase equilibrium for light gas–water mixtures at conditions where hexagonal ice and structure I hydrate phases can exist. The novel aspects of this new framework include (1) the use of internal energies of departure for ice and empty hydrate respectively to determine densities, (2) contributions to the standard state fugacity of water in ice and empty hydrate from lattice structure, (3) computation of these structural contributions to standard state fugacity from compressibility factors and EOS parameters alone, and (4) the direct calculation of gas occupancy from phase equilibrium. Numerical results for densities and equilibrium for systems involving ice and/or gas hydrates predicted by this GHC-based framework are compared to predictions of other equations of state, density correlations, and experimental data where available. Results show that this new GHC-based EOS framework accurately predicts the densities of hexagonal water ice and structure I gas hydrates as well as phase equilibrium for methane–water and CO₂–water mixtures.     

Investigation on hydrate growth at the oil–water interface: In the presence of asphaltene

Natural gas hydrates can readily form in deep-water oil production processes and pose a great threat to the oil industry. Moreover, the coexistence of hydrate and asphaltene can result in more severe challenges to subsea flow assurance. In order to study the effects of asphaltene on hydrate growth at the oil–water interface, a series of micro-experiments were conducted in a self-made reactor, where hydrates nucleated and grew on the surface of a water droplet immersed in asphaltene-containing oil. Based on the micro-observations, the shape and growth rate of the hydrate shell formed at the oil–water interface were mainly investigated and the effects of asphaltene on hydrate growth were analyzed. According to the experimental results, the shape of the water droplet and the interfacial area changed significantly after the formation of the hydrate shell when the asphaltene concentration was higher than a certain value. A mechanism related to the reduction of the interfacial tension caused by the absorption of asphaltenes on the interface was proposed for illustration. Moreover, the growth rate of the hydrate shell decreased significantly with the increasing asphaltene concentration under experimental conditions. The conclusions of this paper could provide preliminary insight how asphaltene affect hydrate growth at the oil–water interface.     

The effect of metal–solvent properties on the alteration of specific zones on a carbon phase diagram

In this work Fe–Sb and Fe–Ge alloys (up to 10 wt.% Sb, Ge) were used as a solvent-catalyst for diamond synthesis at pressures of 5–6 GPa and temperatures of 1800–1900 K. Carbon solubility, capillary properties and synthesis performance of alloys were investigated. When using alloys with additive content up to 10 wt.%, rapid graphite to diamond transformation was observed. In spite of identical P,T-conditions and identical composition of a solvent–catalyst, different crystal morphology on the top and on the bottom sides of a diamond polycrystalline layer was formed, although their habit type {111} was identical. Thermodynamic and kinetic aspects of these phenomena are discussed.     

EMMS-based modeling of gas–solid generalized fluidization: Towards a unified phase diagram

Hydrodynamic features of gas-solid generalized fluidization can be well expressed in the form of phase diagrams, which are important for engineering design. Mesoscale structure presents almost universally in generalized fluidization and should be considered in such phase diagrams. However, current phase diagrams were mainly proposed for cocurrent upward flow according to experimental data or empirical correlations with homogeneous assumption. The energy-minimization multiscale (EMMS) model has shown the capability of capturing mesoscale structure in generalized fluidization, so EMMS-based phase diagrams of generalized fluidization were proposed in this article, which describe more reasonable global hydrodynamics over all regimes including the important engineering phenomena of choking and flooding. These characteristics were also found in discrete particle simulation under various conditions. For wider range of application, the typical hydrodynamic parameters of the phase diagrams were correlated to non-dimensional numbers reflecting the effects of material properties and operation conditions. This study thus shows a possible route to develop a unified phase diagram in the future.     

Experimental study of the SnO2–ZrO2 phase diagram

The study of the SnO₂–ZrO₂ phase diagram in the 1230–1750 °C temperature range has shown the existence of an immiscibility gap, leading to two (Zr_1−xSn_x)O₂ and (Sn_1−yZr_y)O₂ limited solid solutions. Four compositions were synthesised for each solid solution, leading to pure phases, which were characterised by room-temperature and high-temperature X-ray diffraction. The unit-cell parameters of tetragonal (Sn_1−yZr_y)O₂, monoclinic (Zr_1−xSn_x)O₂ and tetragonal (Zr_1−xSn_x)O₂ were determined and correlated with the content of the substituted atom. The monoclinic to tetragonal and reverse reactions for the (Zr_1−xSn_x)O₂ series were also characterised (transition temperatures) when varying the tin mole fraction.     

Addition of malodorants to lighter gas – The phase equilibrium properties of mixtures of lighter gas and selected substances

Relevant thermodynamic and phase behavior of mixtures created by adding malodorants to lighter gas to discourage its abuse have been studied. The influence of physical factors such as temperature, pressure and concentration of the selected substances with lighter gas is studied. This work represents one component in a larger study examining the feasibility of adding malodorants to lighter gas and focuses on the physical chemistry or chemical engineering aspects of the problem. An initial set of 27 compounds was selected based on deterrent effect (odor) in order to find suitable additives to lighter gas components. The aim is to find substances that not only have the correct physiological effect (discourage abuse) but also the correct physical behavior upon addition to lighter gas (solubility, phase behavior). Specifically the way the malodorant partitions between the vapor and liquid phase is modeled. Furthermore, addition of the malodorants should not affect the normal use of the lighter. Thus of the 27 initial components chosen, nine were found that could be suitable additives. In this work we used the thermodynamic models COSMOtherm – an activity coefficient model – and Cubic-Plus-Association (CPA) – an equation of state – to model the fluid phase and solubility behavior of the mixtures formed by the various additives with butane.     

Studying the structure of the vapor–liquid equilibrium diagram of the butyl propionate–propionic acid–butyl butyrate–butyric acid system

This article deals with specific structural features of the vapor–liquid equilibrium diagram of the butyl propionate–propionic acid–butyl butyrate–butyric acid four-component system, which is of industrial importance and contains biazeotropic ester–acid constituents. The positions of some isomanifolds in the concentration tetrahedron and in its constituents are reported.     

Influence of novel shrinkage-reducing polycarboxylate superplasticizer on the nature of calcium–silicate–hydrates

Currently, a novel shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) is used to control cementitious shrinkage. To clarify its mechanism when applied in cementitious materials, the influence of SR-PCA on the composition, morphology, and structure of synthetic calcium–silicate–hydrate (C–S–H), together with the interaction between SR-PCA and C–S–H at the atomic level, is investigated. For comparison, a commercial polycarboxylate superplasticizer (PCA) is also employed. The results show PCA and SR-PCA can adsorb on the C–S–H surface rather than intercalate into the layers. Compared with PCA, SR-PCA has a milder impact on C–S–H crystallinity. SR-PCA refines the pore structure of C–S–H drastically, whereas PCA loosens the structure by increasing the mesopore volume. In addition, the adsorption effect of SR-PCA on the C–S–H surface is less significant than that of PCA. At the atomic level, this less adsorption of SR-PCA is attributed to the lower adhesion energy of the C–S–H/SR-PCA interface due to the weaker Ca–O bond strength.     

Effect of a sweeping air stream and gas–phase aspect ratio of an isothermal Stefan diffusion column on the experimental estimation of binary gas diffusivities

The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, D_AB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect D_AB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, D_AB,exp, by nonlinear regression. For Re < 600, the D_AB,exp errors relative to D_AB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the D_AB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate D_AB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.     

Thermochemistry of the ZrO2–SrO System: From enthalpies of formation and heat capacities of the compounds to the phase diagram

The thermodynamics of the ZrO₂–SrO system is of interest for the optimization of synthesis and applications of functional materials and high-temperature structural ceramics. Earlier data on phase relationships and thermodynamic properties of the system are unfortunately scattered and inconsistent. In this study, the compounds Sr_n+1Zr_nO_3n+1 (n = 3, 2, and 1) were prepared by solid-state reaction. Their heat capacities from 573 to 1273 K were measured by differential scanning calorimetry and their enthalpies of formation from component oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. The CALPHAD method was used to assess the ZrO₂–SrO system, using both available literature data and our new measurements. A self-consistent thermodynamic database and the calculated phase diagram of the ZrO₂–SrO system are provided. This work is a prerequisite for accurate predictions of the relationships among the composition, temperature, and microstructure of complex functional and structural materials containing ZrO₂ and SrO.     

Effect of the injection-nozzle geometry on the interaction between a gas–liquid jet and a gas–solid fluidized bed

In industrial fluid cokers, bitumen is first mixed with steam in a premixer, and then fed to the atomization nozzle. The objective of this work was to evaluate the impact of both the premixer and the nozzle geometrical configuration on the quality of the liquid–solid contact resulting from injections of liquid into a gas–solid fluidized bed. To assess the quality of the liquid–solid contact a method based on electric conductance measurements of the bed material previously developed by the authors [9] was used. Liquid atomization efficiency in open air, spray geometry, and spray stability were also characterized to evaluate their effects on the nozzle spraying performance within the fluidized bed. This study indicated that spray stability is highly beneficial to the liquid–solid contact efficiency. In particular, fluid constrictions such as the series of converging and diverging sections within the nozzle have a stabilizing effect on the spray. Future optimization of the existing liquid-injection systems should consider alternative gas–liquid premixers and nozzle geometries to enhance the jet stability.     

Structure of the phase diagram of the 2-methyl-1,3-butadiene–2-methyl-2-butene–acetonitrile–water system

The structure of the liquid–liquid–vapor diagram of the industrially important four-component system 2-methyl-1,3-butadiene–2-methyl-2-butene–acetonitrile–water has been determined. A model of the phase equilibrium has been derived from experimental data. The evolution of the three-phase immiscibility region in the concentration simplex has been investigated.     

Flow characteristics of gas–liquid two phase plunging jet absorber–gas holdup and bubble penetration depth

A gas-liquid two phase plunging jet is formed through a gas sucking type multi-jet ejector nozzle. In this study, the effects of various conditions in the multi-jet ejector nozzle, the column diameter, and the liquid jet length on penetration depth of air bubblesl _B and gas holdup h_G in a gas-liquid two phase plunging jet absorber were studied experimentally. Consequently, empirical equations concerningl _B and h_G were obtained, respectively. These equations agree with the experimental data with an accuracy of ±20% forl _B and ±25% for h_G.     

Mapping distributions of mechanical properties and formation ability on the ternary B―C―N phase diagram

Based on first-principles calculations, we present the distributions of mechanical properties and formation ability of amorphous B_xC_yN_z solids on the ternary B-C-N phase diagram. Along the C-BN isoelectronic line, the formation energy shows symmetric distributions; the Young's modulus and ratio of bulk modulus and shear modulus (B/G) show zonal distributions. Amazingly, for some peculiar compositions (B: 13-17 at.%; C: 48-52 at.%; N: 33-35 at.%), B-C-N solids exhibit certain ductile characteristic that is comparable to metals. On the phase area (B: 15-30 at.%; C: 50-60 at.%; N: 20-30 at.%), B-C-N solids possess both excellent hardness and good formation ability. These theoretical results provide valuable guidance for intentionally synthesizing B_xC_yN_z materials with desirable mechanical properties.     

Effect of Storage Conditions and Antioxidants on the Oxidative Stability of Sunflower–Chia Oil Blends

The mixture of different proportions of sunflower with chia oil provides a simple method to prepare edible oils with a wide range of desired fatty acid compositions. Sunflower–chia (90:10 and 80:20 wt/wt) oil blends with the addition of rosemary (ROS), ascorbyl palmitate (AP) and their blends (AP:ROS) were formulated to evaluate the oxidative stability during storage at two temperature levels normally used, cool (4 ± 1 °C) and room temperature (20 ± 2 °C) for a period of 360 days. Peroxide values (PV) of the oil blends with antioxidants stored at 4 ± 1 °C showed levels ≤10.0 mequiv O₂/kg oil; the lowest levels of PV were found for blends with AP:ROS. Values higher than 10.0 mequiv O₂/kg were observed between 120–240 days for oil blends stored at 20 ± 2 °C. Similar trends were observed with p-anisidine and Totox values. The oxidative stability determined by the Rancimat method and differential scanning calorimetry showed a greater susceptibility of the oils to oxidative deterioration with increasing unsaturated fatty acids content. The addition of antioxidants increased the induction time and decreased the Arrhenius rate constant, indicating an improvement in the oxidative stability for all the oil blends. Temperature had a strong influence on the stability of these blends during storage.     

Stability of the δ-TeO2 phase in the binary and ternary TeO2 glasses

The stability of δ-TeO₂ phase was studied in binary TeO₂–WO₃, TeO₂–CdO and ternary TeO₂–WO₃–CdO glasses. The samples were prepared by heating high purity powder mixtures of TeO₂, WO₃ and/or CdO to 800 °C in a platinum crucible with a closed lid, holding for 30 min and quenching in water bath. Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the thermal, phase and microstructural properties of the δ-TeO₂ phase. The addition of CdO into the tellurite glasses increased the stability range of the δ-TeO₂ phase up to higher temperature values and expanded the compositional δ-TeO₂ formation range. The formation of δ-TeO₂ phase in the binary systems was observed for samples containing 5–10 mol% WO₃ and 5–15 mol% CdO. However, for the ternary TeO₂–WO₃–CdO system the formation of δ-TeO₂ phase was determined in a wider compositional range.     

A study on the growth mechanism and gas diffusion barrier property of homogeneously mixed silicon–tin oxide by atomic layer deposition

SiO₂ and SnO₂ films were deposited using plasma-enhanced atomic layer deposition (PEALD) at low temperature (100 °C), and homogeneously mixed structure (HMS) films consisting of Si, Sn, and O were deposited through a “1st precursor dose – 2nd precursor dose – oxidation”, a new ALD process method for mixing two elements. For a deep consideration of the growth mechanism during the HMS film deposition process, density functional theory (DFT) calculations of the adsorption reactions of the precursors on the surface were conducted. The properties of the thin films such as density, atomic composition, crystallinity, surface roughness, optical transmittance and the water vapor diffusion barrier property were analyzed by XRR, XPS, XRD, AFM, UV-VIS and the electrical Ca test.By changing the dose sequence of the two precursors in the HMS process, various physical/chemical characteristics of the films could be controlled. Also, by adjusting the appropriate amount of Sn in the HMS films, the shortcomings of SnO₂ were compensated by the mixed SiO₂; and through this process, excellent gas diffusion barrier properties of WVTR ∼ 1.33 × 10⁻⁴ g/m²day were secured.     

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

Tantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high-performance photonic and photoelectric components. However, successful attainment of feature control in tantalum-doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro- and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li₂O–Ta₂O₅–SiO₂ ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li₂O–Ta₂O₅–SiO₂ ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO₆ octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta⁵⁺ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li₂O–Ta₂O₅–SiO₂ ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials.     

Synthesis of hybrid compounds apatite–alendronate by reactive milling and effects on the structure and morphology of the apatite phase

The preparation of apatite–alendronate hybrid materials by reactive milling is proposed in this work. Calcium phosphate compounds of various compositions have been associated to bisphosphonates and found suitable for local application with release kinetics of the drug compatible with the inhibition of bone resorption. Hybrid compounds have been obtained by reactive milling. The compositions used were: AP(X-100), Alendronate(X) where X=7 and X=15. An interaction between the hydroxyl group of the apatite and the amine group of alendronate can be identified with FTIR and enables to confirm the formation of the hybrids. The incorporation of the alendronate hinders the growing of the apatite crystals resulting in smaller coherent domains of diffraction for the apatite phase.