scholarly journals Phase Behaviour of Methane Hydrates in Confined Media

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 201
Author(s):  
Hao Bian ◽  
Lu Ai ◽  
Klaus Hellgardt ◽  
Geoffrey C. Maitland ◽  
Jerry Y. Y. Heng
Keyword(s):  
Phase Behaviour ◽  
Methane Hydrates ◽  
Scanning Calorimetry ◽  
Macroporous Silica ◽  
Interfacial Energies ◽  
Temperature Method ◽  
Hydrate Phase ◽  
Dissociation Temperature ◽  
Confined Media ◽  
Decomposition Behaviour

In a study designed to investigate the melting behaviour of natural gas hydrates which are usually formed in porous mineral sediments rather than in bulk, hydrate phase equilibria for binary methane and water mixtures were studied using high-pressure differential scanning calorimetry in mesoporous and macroporous silica particles having controlled pore sizes ranging from 8.5 nm to 195.7 nm. A dynamic oscillating temperature method was used to form methane hydrates reproducibly and then determine their decomposition behaviour—melting points and enthalpies of melting. Significant decreases in dissociation temperature were observed as the pore size decreased (over 6 K for 8.5 nm pores). This behaviour is consistent with the Gibbs–Thomson equation, which was used to determine hydrate–water interfacial energies. The melting data up to 50 MPa indicated a strong, essentially logarithmic, dependence on pressure, which here has been ascribed to the pressure dependence of the interfacial energy in the confined media. An empirical modification of the Gibbs–Thomson equation is proposed to include this effect.

scholarly journals Double-Chain Cationic Surfactants: Swelling, Structure, Phase Transitions and Additive Effects

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3946
Author(s):  
Rui A. Gonçalves ◽  
Yeng-Ming Lam ◽  
Björn Lindman
Keyword(s):  
Phase Transitions ◽  
Phase Behaviour ◽  
Double Chain ◽  
Scanning Calorimetry ◽  
Alkyl Chains ◽  
X Ray Scattering ◽  
Amphiphilic Compounds ◽  
Liquid Phases ◽  
Lamellar Phases ◽  
Water Layers

Double-chain amphiphilic compounds, including surfactants and lipids, have broad significance in applications like personal care and biology. A study on the phase structures and their transitions focusing on dioctadecyldimethylammonium chloride (DODAC), used inter alia in hair conditioners, is presented. The phase behaviour is dominated by two bilayer lamellar phases, Lβ and Lα, with “solid” and “melted” alkyl chains, respectively. In particular, the study is focused on the effect of additives of different polarity on the phase transitions and structures. The main techniques used for investigation were differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). From the WAXS reflections, the distance between the alkyl chains in the bilayers was obtained, and from SAXS, the thicknesses of the surfactant and water layers. The Lα phase was found to have a bilayer structure, generally found for most surfactants; a Lβ phase made up of bilayers with considerable chain tilting and interdigitation was also identified. Depending mainly on the polarity of the additives, their effects on the phase stabilities and structure vary. Compounds like urea have no significant effect, while fatty acids and fatty alcohols have significant effects, but which are quite different depending on the nonpolar part. In most cases, Lβ and Lα phases exist over wide composition ranges; certain additives induce transitions to other phases, which include cubic, reversed hexagonal liquid crystals and bicontinuous liquid phases. For a system containing additives, which induce a significant lowering of the Lβ–Lα transition, we identified the possibility of a triggered phase transition via dilution with water.

scholarly journals Thermodynamic Modelling and Microstructural Study of Z-Phase Formation in a Ta-Alloyed Martensitic Steel

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1332
Author(s):  
Florian Riedlsperger ◽  
Bernadette Gsellmann ◽  
Erwin Povoden-Karadeniz ◽  
Oriana Tassa ◽  
Susanna Matera ◽  
...  
Keyword(s):  
Special Focus ◽  
Scanning Calorimetry ◽  
Transmission Electron Microscopy Analysis ◽  
Computational Framework ◽  
Mobility Data ◽  
Interfacial Energies ◽  
Transmission Electron ◽  
Size Number ◽  
Electron Microscopy Analysis ◽  
Microscopy Analysis

A thermokinetic computational framework for precipitate transformation simulations in Ta-containing martensitic Z-steels was developed, including Calphad thermodynamics, diffusion mobility data from the literature, and a kinetic parameter setup that considered precipitation sites, interfacial energies and dislocation density evolution. The thermodynamics of Ta-containing subsystems were assessed by atomic solubility data and enthalpies from the literature as well as from the experimental dissolution temperature of Ta-based Z-phase CrTaN obtained from differential scanning calorimetry. Accompanied by a comprehensive transmission electron microscopy analysis of the microstructure, thermokinetic precipitation simulations with a wide-ranging and well-documented set of input parameters were carried out in MatCalc for one sample alloy. A special focus was placed on modelling the transformation of MX into the Z-phase, which was driven by Cr diffusion. The simulation results showed excellent agreement with experimental data in regard to size, number density and chemical composition of the precipitates, showing the usability of the developed thermokinetic simulation framework.

SAXS Study of Selected Cationic Surfactant Influence on the DSPC-Based Model Phospholipid System

2007 ◽  
Vol 130 ◽  
pp. 257-262
Author(s):  
Maciej Kozak ◽  
Ludwik Domka ◽  
Stefan Jurga
Keyword(s):  
Phase Transition ◽  
Differential Scanning Calorimetry ◽  
Small Angle ◽  
Phase Behaviour ◽  
Lamellar Phase ◽  
Scanning Calorimetry ◽  
X Ray ◽  
X Ray Scattering ◽  
Hydrocarbon Chains ◽  
Main Transition

The phase behaviour of lipid bilayer systems prepared with 1,2-distearoyl-sn-glycero-3- phosphocholine (DSPC) with dodecyldimethyl(benzyloxymethyl)ammonium chloride (BzMDDAC) (at concentrations 0.1, 1 and 5%) has been studied by small angle X-ray scattering and differential scanning calorimetry. The SAXS and DSC results of the hydrated 10% DSPC revealed one typical phase transition corresponding to melting of the hydrocarbon chains at 55 °C. In the system of 10% DSPC - 0.1 % BzMDDAC the main transition was somewhat shifted towards lower temperatures, while at 1% concentration of BzMDDAC in the mixture, the lamellar phase disappeared, as evidenced by SAXS and DSC. The increase in BzMDDAC concentration to 5% in the mixture with 10% DSPC resulted in formation of a new lamellar phase.

The Study of Oxidative Stability of Castor Oil Based Biodiesel

2013 ◽  
Vol 724-725 ◽  
pp. 334-337 ◽  
Author(s):  
Yun Feng Yang ◽  
Guo Sheng Hu ◽  
Yin Jie Chen
Keyword(s):  
Differential Scanning Calorimetry ◽  
Oxidative Stability ◽  
Constant Temperature ◽  
Castor Oil ◽  
Acid Value ◽  
Scanning Calorimetry ◽  
Accelerated Oxidation ◽  
Temperature Method ◽  
Pressure Differential Scanning Calorimetry ◽  
Activity Energy

The oxidative stability of castor oil based biodiesel, added different antioxidant, was studied systematacially through pressure differential scanning calorimetry (PDSC), accelerated oxidation test, constant temperature method, programmed temperature method. The result shows after adding antioxidant in castor oil, the generation of hyperoxide and acid value were suffocated for the biodiesel. When the content of antioxidant 300 was 0.6 wt.%, the initiation oxide temperature raised to 197.7°C, the acid value reduced to 1.41, the solubility of oxide reduced to 1.40mg/100mL, and the activity energy of oxidation was 48.18kJ/mol.

scholarly journals Phase Transitions of Binary Lipid Mixtures: A Combined Study by Adiabatic Scanning Calorimetry and Quartz Crystal Microbalance with Dissipation Monitoring

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
P. Losada-Pérez ◽  
N. Mertens ◽  
B. de Medio-Vasconcelos ◽  
E. Slenders ◽  
J. Leys ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Quartz Crystal Microbalance ◽  
Quartz Crystal ◽  
Phase Behaviour ◽  
Scanning Calorimetry ◽  
Departure Point ◽  
Peltier Element ◽  
Adiabatic Scanning Calorimetry ◽  
Lipid Mixtures

The phase transitions of binary lipid mixtures are studied by a combination of Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D). pASC, a novel type of calorimeter, provides valuable and unambiguous information on the heat capacity and the enthalpy, whereas QCM-D is proposed as a genuine way of determining phase diagrams by analysing the temperature dependence of the viscosity. Two binary mixtures of phospholipids with the same polar head and differing in the alkyl chain length, DMPC + DPPC and DMPC + DSPC, are discussed. Both techniques give consistent phase diagrams, which compare well with literature results, showing their capability to map the phase behaviour of pure lipids as well as lipid mixtures. This work can be considered as a departure point for further investigations on more complex lipid mixtures displaying relevant phases such as the liquid-ordered phase and solid-lipid interfaces with biologically functional importance.

Tautomeric polymorphism of the neuroactive inhibitor kynurenic acid

2019 ◽  
Vol 75 (6) ◽  
pp. 793-805
Author(s):  
Dorota Pogoda ◽  
Jan Janczak ◽  
Sylwia Pawlak ◽  
Michael Zaworotko ◽  
Veneta Videnova-Adrabinska
Keyword(s):  
Solid State ◽  
Kynurenic Acid ◽  
Variable Temperature ◽  
Neurological Diseases ◽  
Crystal Form ◽  
Phase Behaviour ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray

Kynurenic acid (KYN; systematic name: 4-hydroxyquinoline-2-carboxylic acid, C10H7NO3) displays a therapeutic effect in the treatment of some neurological diseases and is used as a broad-spectrum neuroprotective agent. However, it is understudied with respect to its solid-state chemistry and only one crystal form (α-KYN·H2O) has been reported up to now. Therefore, an attempt to synthesize alternative solid-state forms of KYN was undertaken and six new species were obtained: five solvates and one salt. One of them is a new polymorph, β-KYN·H2O, of the already known KYN monohydrate. All crystal species were further studied by single-crystal and powder X-ray diffraction, thermal and spectroscopic methods. In addition to the above methods, differential scanning calorimetry (DSC), in-situ variable-temperature powder X-ray diffraction and Raman microscopy were applied to characterize the phase behaviour of the new forms. All the compounds display a zwitterionic form of KYN and two different enol–keto tautomers are observed depending on the crystallization solvent used.

The phase behaviour of lipid X at high water concentration

1990 ◽  
Vol 68 (1) ◽  
pp. 345-351 ◽  
Author(s):  
G. Lipka ◽  
H. Hauser
Keyword(s):  
Differential Scanning Calorimetry ◽  
Hexagonal Phase ◽  
Water Concentration ◽  
Critical Micellar Concentration ◽  
High Water ◽  
Phase Behaviour ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Repeat Distance ◽  
X Ray

The phase behaviour of lipid X at high water concentrations (> 60%) is studied using mainly differential scanning calorimetry (DSC) and X-ray diffraction. The critical micellar concentration (CMC) decreases from 8 × 10−5 M at −2 °C to 4 × 10−5 M at 20 °C. The critical micellar temperature (CMT) is 0 °C and decreases slightly with increasing lipid X concentration. Above the CMC and below the CMT, lipid X forms a lamellar gel phase (Lβ). Above 0 °C and at concentrations ranging from the CMC up to about 0.2 M (20%), lipid X forms small micelles. At even higher concentrations there is a transition to a hexagonal phase, probably hexagonal I. Addition of excess NaCl to lipid X dispersions at concentrations < 0.2 M (20%) has several effects on the phase behaviour of lipid X. (i) The lamellar phase is stabilized up to temperatures of ≈20 °C at [NaCl] ≥ 0.7 M. (ii) NaCl induces a tighter packing of the hydrocarbon chains. (iii) At concentrations > 0.7 M NaCl, the bilayer repeat distance decreases to about 43 Å (1 Å = 0.1 nm).Key words: lipid X, phase behaviour, effects of NaCl, differential scanning calorimetry, X-ray diffraction.

Clathrate hydrate equilibrium modeling: Do self-consistent cell models provide unique equilibrium solutions?

2015 ◽  
Vol 93 (8) ◽  
pp. 826-830
Author(s):  
Patrick G. Lafond ◽  
R. Gary Grim ◽  
Amadeu K. Sum
Keyword(s):  
Solid Phase ◽  
Mean Field ◽  
Melting Behavior ◽  
Multiple Equilibrium ◽  
Stability Field ◽  
Equilibrium Solutions ◽  
Scanning Calorimetry ◽  
Cell Potential ◽  
Hydrate Phase ◽  
The Stability

When clathrate hydrates of xenon gas are formed deep within the stability field, anomalous melting behavior is readily observed in differential scanning calorimetry (DSC). In the DSC thermograms, multiple dissociation events may be observed, suggesting the presence of more than one solid phase. Following a suite of diffraction and NMR measurements, we are only able to detect the presence of simple structure I hydrate. Recognizing that hydrates are nonstoichiometric compounds, we look back to how the molar composition of a hydrate phase is determined. Making a mean-field improvement to current equilibrium models, we find that some conditions yield multiple solutions to the cage filling of the hydrate phase. Though the solutions are not truly stable, they would result in a kinetically trapped system. If such a case existed experimentally, this could explain the dissociation behavior observed for xenon hydrates. More importantly, this raises the question of how well defined the equilibrium condition is for a cell potential model, and whether or not multiple equilibrium solutions could exist.

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