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Miscibility Gap (miscibility + gap)
Selected AbstractsMiscibility Gap in the System Cesium Amide/Ammonia, CsNH2/NH3 , Thermodynamic Investigations.CHEMINFORM, Issue 26 2003Dieter Peters Abstract For Abstract see ChemInform Abstract in Full Text. [source] Aliovalent Substitutions in Olivine Lithium Iron Phosphate and Impact on Structure and PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Nonglak Meethong Abstract Lithium transition metal phosphate olivines are enabling a new generation of high power, thermally stable, long-life rechargeable lithium batteries that may prove instrumental in the worldwide effort to develop cleaner and more sustainable energy. Nanoscale (<100,nm) derivatives of the olivine family LiMPO4 (M,=,Fe, Mn, Co, Ni) are being adopted in applications ranging in size scale from hybrid and plug-in hybrid electric vehicles to utilities-scale power regulation. Following the previous paradigm set with intercalation oxides, most studies have focused on the pure ordered compounds and isovalent substitutions. In contrast, even the possibility for, and role of, aliovalent doping has been widely debated. Here, critical tests of plausible defect compensation mechanisms using compositions designed to accommodate Mg2+, Al3+, Zr4+, Nb5+ ions on the M1,and/or M2 sites of LiFePO4 with appropriate charge-compensating defects are carried out, and conclusive crystallographic evidence for lattice doping, e.g., up to at least 12 atomic percent added Zr, is obtained. Structural and electrochemical analyses show that doping can reduce the lithium miscibility gap, increase phase transformation kinetics during cycling, and expand Li diffusion channels in the structure. Aliovalent modifications may be effective for introducing controlled atomic disorder into the ordered olivine structure to improve battery performance. [source] Level-set based numerical simulation of a migrating and dissolving liquid drop in a cylindrical cavityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004Edmondo Bassano Abstract In the present paper the dissolution of a binary liquid drop having a miscibility gap and migrating due to thermo-solutal capillary convection in a cylindrical cavity is studied numerically. The interest in studying this problem is twofold. From a side, in the absence of gravity, capillary migration is one of the main physical mechanisms to set into motion dispersed liquid phases and from the other side, phase equilibria of multi-component liquid systems, ubiquitous in applications, often exhibit a miscibility gap. The drop capillary migration is due to an imposed temperature gradient between the cavity top and bottom walls. The drop dissolution is due to the fact that initial composition and volume values, and thermal boundary conditions are only compatible with a final single phase equilibrium state. In order to study the drop migration along the cavity and the coupling with dissolution, a previously developed planar two-dimensional code is extended to treat axis-symmetric geometries. The code is based on a finite volume formulation. A level-set technique is used for describing the dynamics of the interface separating the different phases and for mollifying the interface discontinuities between them. The level-set related tools of redistancing and off-interface extension are used to enhance code resolution in the critical interface region. Migration speeds and volume variations are determined for different drop radii. Copyright © 2004 John Wiley & Sons, Ltd. [source] Thermodynamic Properties and Phase Diagram for the System MoO2,TiO2JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008K. Thomas Jacob The activity of molybdenum dioxide (MoO2) in the MoO2,TiO2 solid solutions was measured at 1600 K using a solid-state cell incorporating yttria-doped thoria as the electrolyte. For two compositions, the emf was also measured as a function of temperature. The cell was designed such that the emf is directly related to the activity of MoO2 in the solid solution. The results show monotonic variation of activity with composition, suggesting a complete range of solid solutions between the end members and the occurrence of MoO2 with a tetragonal structure at 1600 K. A large positive deviation from Raoult's law was found. Excess Gibbs energy of mixing is an asymmetric function of composition and can be represented by the subregular solution model of Hardy as follows The temperature dependence of the emf for two compositions is reasonably consistent with ideal entropy of mixing. A miscibility gap is indicated at a lower temperature with the critical point characterized by Tc (K)=1560 and. Recent studies indicate that MoO2 undergoes a transition from a monoclinic to tetragonal structure at 1533 K with a transition entropy of 9.91 J·(mol·K),1. The solid solubility of TiO2 with rutile structure in MoO2 with a monoclinic structure is negligible. These features give rise to a eutectoid reaction at 1412 K. The topology of the computed phase diagram differs significantly from that suggested by Pejryd. [source] Inhomogeneous Phase Transition upon Hydrogenation of Nanocluster Pd FilmsCHEMPHYSCHEM, Issue 3 2009Marcel Di Vece Dr. Abstract Phased out: A combination of electrochemical and optical techniques is used to study the interaction of hydrogen with palladium nanoclusters. Hydrogen pressure-composition isotherms reveal the reduced presence of the , phase in palladium nanoclusters. Hydrogen extraction transients relate the reduced miscibility gap to a core-shell phase transformation in the palladium nanoclusters (see picture). [source] On the Validity of Stokes,Einstein and Stokes,Einstein,Debye Relations in Ionic Liquids and Ionic-Liquid MixturesCHEMPHYSCHEM, Issue 13 2008Thorsten Köddermann Abstract Stokes,Einstein (SE) and Stokes,Einstein,Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt,% IL). The deviations from both relations could be related to dynamical heterogeneities described by the non-Gaussian parameter ,(t). If ,(t) is close to zero, at a concentration of 1 wt,% IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids. [source] The Role of Surface and Interface Energy on Phase Stability of Nanosized Insertion CompoundsADVANCED MATERIALS, Issue 25-26 2009Marnix Wagemaker Thermodynamic theory reveals the impact of surface and interface energies on the equilibrium properties and solubility limits of interstitial ions in nanosized crystallites. Applied to LixFePO4 especially interface energy contributions play important roles, and their effect explains observations of the narrowing of electrochemically measured miscibility gaps in nanostructured electrodes. [source] Liquid,liquid miscibility gaps and hydrate formation in drug,water binary systems: Pressure,temperature phase diagram of lidocaine and pressure,temperature,composition phase diagram of the lidocaine,water systemJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2010René Ceolin Abstract The pressure,temperature (P,T) melting curve of lidocaine was determined (dP/dT,=,3.56,MPa,K,1), and the lidocaine,water system was investigated as a function of temperature and pressure. The lidocaine,water system exhibits a monotectic equilibrium at 321,K (ordinary pressure) whose temperature increases as the pressure increases until the two liquids become miscible. A hydrate, unstable at ordinary pressure, was shown to form, on increasing the pressure, from about 70,MPa at low temperatures (200,300,K). The thermodynamic conditions of its stability were inferred from the location of the three-phase equilibria involving the hydrate in the lidocaine,water pressure,temperature,mole fraction (P,T,x) diagram. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2756,2765, 2010 [source] Thermochemistry of Glasses in the Y2O3 -Al2O3 -SiO2 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Yahong Zhang Enthalpies of drop solution in molten 2PbO-B2O3 at 1078 K were measured for glasses along the 2YAlO3 -3SiO2 and return ˝Y3Al5O12 -3SiO2 joins. The onset glass transition temperature increases slightly with increasing silica content and Y/Al. Enthalpies of mixing were calculated on the basis of amorphous end members. Strongly negative heats of mixing support the absence of miscibility gaps except possibly for very high silica content, consistent with experimental phase analyses, which indicate much narrower miscibility gaps compared with the phase diagrams calculated on the basis of previous data and the CALPHAD formalism. [source] | |||||||||||||