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Pressure P (pressure + p)
Selected AbstractsMolecular simulation of complete phase diagrams for binary mixturesAICHE JOURNAL, Issue 7 2001Monica H. Lamm Vapor-liquid, vapor-solid and liquid-solid coexistence lines are calculated for binary mixtures of Lennard-Jones spheres using Monte Carlo simulation and the Gibbs-Duhem integration technique. Complete phase diagrams showing equilibrium between vapor, liquid and solid phases are constructed for binary Lennard-Jones mixtures with diameter ratios ranging from ,11 /,22 = 0.85,1.0 and attractive well-depth ratios ranging from ,11/,22 = 0.625,1.6, at a reduced pressure P*,P,/,11 = 0.002. The Lorentz-Berthelot combining rules are used to calculate the cross-species interaction parameters ,12 and ,12. The variation in the shape of the complete phase diagrams change as a function of the diameter ratio ,11 /,22 and well-depth ratio ,11 /,22 is systematically explored. The phase diagrams found here resemble those found experimentally for argon-methane, iodine-sulfur, water-sodium chloride, water-silver nitrate, water-potassium nitrate, and p-dichlorobenzene-p-dibromobenzene. [source] First-principles calculations of transition phase and thermodynamic properties of CdOPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008Liping Yao Abstract The transition phase of CdO from NaCl-type (B 1) structure to CsCl-type (B 2) structure is investigated by ab initio plane-wave pseudopotential density-functional theory, and the thermodynamic properties of the B 1 and B 2 structures under high pressure and temperature are obtained through the quasiharmonic Debye model. The transition phase from B 1 structure to B 2 structure occurs at a pressure of 83.1 GPa, which agrees well with other calculated values. Moreover, the relationship of the relative volume V /V0, and the Debye temperature , and the heat capacity CV with the pressure P and temperature T are also successfully obtained. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low-temperature electrical conductivity of heavily boron-doped diamond single crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007V. D. Blank Abstract Single crystal diamonds 0.2,0.7 cm large doped with boron concentration 1019,1020 cm,3 were grown by temperature gradient method on the seed under pressure P = 5.5 GPa, temperature T = 1650 K. Temperature dependence of electrical resistance had been measured in the range of 0.5,297 K. Boltzmann activation type of conductivity and Mott's VRH law observed in samples in the temperature ranges ,200,297 K and ,70,297 K respectively. The temperature rise of conductivity in the range of ,0.5,50 K for most heavily doped crystals was proportional to T1/2. This rule indicates the vicinity of the electronic system to metal,insulator transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature-induced phase transition in simulated amorphous Al2O3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2006Vo Van Hoang Abstract Our previous simulation studies indicated the existence of pressure-induced phase transition in liquid and amorphous Al2O3. In the current paper, we present the structural transformation of simulated amorphous Al2O3 from an octahedral to a tetrahedral network structure by heating from the high-density amorphous (hda) model at constant pressure P = 0 GPa. The structure of the models was analyzed through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Furthermore, significant differences in structural characteristics of low-density amorphous (lda) models obtained by heating from the hda one and by cooling from the low-density melt have been found and are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study on surface morphology and selectivity of precipitated iron catalysts of FTSASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Wang Xingjun Abstract The precipitated iron catalyst was prepared by co-precipitation. The surface morphology of the catalyst was investigated under different reduction conditions by SEM (S-250, USA). Under H2 -reduction, the surface morphology of the catalyst had the obvious changes, which the diameter reduced, adhered together, came into being wads considered as a group. But the surface morphology of the catalyst had almost no change under CO reduction. The crystal structure of the catalyst was studied under different reduction conditions by X-ray diffraction (XRD) (Rigaku D/max, Japanese). It was found that the catalyst was reduced completely with H2, but it was reduced partly with CO. The crystal structure of the catalyst converted into the metallic phase with H2 reduction. However, most of the iron converted into iron oxide (Fe3O4) with CO reduction. And the predominant phase in a sample of a mature catalyst is ,-Fe5C2, which is the active phase in the Fischer-Tropsch synthesis (FTS). The experimental results showed that CO conversion and H2 conversion increase with the change of reaction temperature from 260 to 300 °C, under the conditions of pressure P = 2.6 MPa, space velocity = 0.86 Nl h,1 g-Fe,1, n(H2)/n(CO) = 2/3, and most of the hydrocarbon products are C5,11 which hold half of the hydrocarbon products. The next content is C2,4 which holds the quarter of hydrocarbon products. Then it is C12+, which is equal to 18%. And the last is C1, which is equal to 7%. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Synthesis and characterization of compounds LixMn1+xFe2,2xO4 with spinel structure in the quasiternary system "LiO0,5 , MnOx , FeOx"CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006C. Wende Abstract The thermal decomposition of freeze-dried Li-Mn(II)-Fe(III)-formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions LixMn1+xFe2,2xO4 (0 , x , 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O2) during the synthesis are required. Because of the high reactivity of the freeze-dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li-Mn-ferrites were studied by chemical analysis, X-ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A-sites of the spinel lattice AB2O4, while at small x-values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An iterative defect-correction type meshless method for acousticsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2003V. Lacroix Abstract Accurate numerical simulation of acoustic wave propagation is still an open problem, particularly for medium frequencies. We have thus formulated a new numerical method better suited to the acoustical problem: the element-free Galerkin method (EFGM) improved by appropriate basis functions computed by a defect correction approach. One of the EFGM advantages is that the shape functions are customizable. Indeed, we can construct the basis of the approximation with terms that are suited to the problem which has to be solved. Acoustical problems, in cavities , with boundary T, are governed by the Helmholtz equation completed with appropriate boundary conditions. As the pressure p(x,y) is a complex variable, it can always be expressed as a function of cos,(x,y) and sin,(x,y) where ,(x,y) is the phase of the wave in each point (x,y). If the exact distribution ,(x,y) of the phase is known and if a meshless basis {1, cos,(x,y), sin, (x,y) } is used, then the exact solution of the acoustic problem can be obtained. Obviously, in real-life cases, the distribution of the phase is unknown. The aim of our work is to resolve, as a first step, the acoustic problem by using a polynomial basis to obtain a first approximation of the pressure field p(x,y). As a second step, from p(x,y) we compute the distribution of the phase ,(x,y) and we introduce it in the meshless basis in order to compute a second approximated pressure field p(x,y). From p(x,y), a new distribution of the phase is computed in order to obtain a third approximated pressure field and so on until a convergence criterion, concerning the pressure or the phase, is obtained. So, an iterative defect-correction type meshless method has been developed to compute the pressure field in ,. This work will show the efficiency of this meshless method in terms of accuracy and in terms of computational time. We will also compare the performance of this method with the classical finite element method. Copyright © 2003 John Wiley & Sons, Ltd. [source] Influence of Hydrogen Plasma on the Defect Passivation of Polycrystalline Si Thin Film Solar CellsPLASMA PROCESSES AND POLYMERS, Issue S1 2009Benjamin Gorka Abstract Hydrogen passivation (HP) of polycrystalline silicon (poly-Si) thin film solar cells was performed in a parallel plate radio-frequency (rf) plasma setup. The influence of hydrogen pressure p and electrode gap d on breakdown voltage Vbrk is presented showing that the minimum in Vbrk shifts with higher pressures towards higher p,·,d values. Cell test structures provided by CSG Solar AG were used to examine the influence of p and d on the open circuit voltage VOC. The highest VOC's were achieved for p,·,d values that correspond to a minimum in Vbrk. HP strongly improved the VOC. After the hydrogen plasma treatment the VOC improved significantly by a factor of 2 and amounted to 450 mV. Optimized parameters were then applied to different poly-Si solar cells prepared by electron beam evaporation. [source] A New Oxide Ion Conductor: La3GaMo2O12CHINESE JOURNAL OF CHEMISTRY, Issue 8 2006Tian Xia Abstract A new oxide ion conductor, La3GaMo2O12, with a bulk conductivity of 2.7×10,2 S·cm,1 at 800 °C in air atmosphere was prepared by the traditional solid-state reaction. The room temperature X-ray diffraction data could be indexed on a monoclinic cell with lattice parameters of a=0.5602(2) nm, b=0.3224(1) nm, c=1.5741(1) nm, ,=102.555(0)°, V=0.2775(2) nm3 and space group Pc(7). Ac impedance measurements in various atmospheres further support that it is an oxide ion conductor. This material was stable in various atmospheres with oxygen partial pressure p(O2) ranging from 1.0×105 to 1.0×10,7 Pa at 800 °C. A reversible polymorphic phase transition occurred at elevated temperatures as confirmed by the differential thermal analysis and dilatometric measurement. [source] Quasilocal vibrations and the Boson peak in glassesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004D. A. ParshinArticle first published online: 16 NOV 200 Abstract The problem of the low-frequency harmonic excitations and of the Boson peak in glasses is reviewed in the scope of recent theoretical developments. It is shown that the Boson peak inevitably appears in the reduced density of states g(,)/,2 of quasilocal vibrations in glasses which are additional to phonons harmonic excitations. We show that the same physical mechanism is fundamental for such seemingly different phenomenon as formation of the two-level systems in glasses. The fundamental reason for the Boson peak and two-level system formation is an instability of the spectrum of quasilocal harmonic modes weakly interacting with the high frequency surrounding and with each other. The instability controlled by the anharmonicity creates a new stable universal spectrum of harmonic vibrations with a Boson peak feature. We show that under pressure the Boson peak in glasses is always shifted to higher frequencies. For high enough pressures P the Boson peak frequency ,b , P1/3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The magnetic moments and their long-range ordering for Fe atoms in a wide variety of metallic environmentsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010A. Ayuela Abstract The magnitudes of Fe magnetic moments, together with their long-range ordering when appropriate, are compared and contrasted in a variety of metallic environments. Thus, Fe, in its stable body-centered-cubic (bcc) phase under ambient conditions, is considered under pressures p, which can yield different crystal structures at high p, including fcc. The modification of the ferromagnetism in bcc Fe is surveyed as one passes through a bc-tetragonal lattice to the fcc form. In the latter, evidence is presented, both from theory and experiment, that the ordering is antiferromagnetic in character. Then, binary metallic alloys with Fe atoms as the majority component are considered, Fe,Co and Fe,Ga being focal points in both ordered and disordered materials. Finally, some discussion is given, involving again both experiment and theory, of the possible spin polarization of neighboring Cs atoms when Fe impurity atoms are inserted into the low conduction electron density characterizing this heavy alkali metal under ambient conditions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] | |||||||||||||