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Critical Pressure (critical + pressure)
Selected AbstractsDetermination of cubic equation of state parameters for pure fluids from first principle solvation calculationsAICHE JOURNAL, Issue 8 2008Chieh-Ming Hsieh Abstract A new method for estimation of parameters in cubic equations of state from ab initio solvation calculations is presented. In this method, the temperature-dependent interaction parameter a(T) is determined from the attractive component of solvation free energy, whereas the volume parameter b is assumed to be that of solvation cavity. This method requires only element-specific parameters, i.e., atomic radius and dispersion coefficient, and nine universal parameters for electrostatic and hydrogen-bonding interactions. The equations of state (EOS) parameters so determined allow the description of the complete fluid phase diagram, including the critical point. We have examined this method using the Peng,Robinson EOS for 392 compounds and achieved an accuracy of 43% in vapor pressure, 17% in liquid density, 5.4% in critical temperature, 11% in critical pressure, and 4% in critical volume. This method is, in principle, applicable to any chemical species and is especially useful for those whose experimental data are not available. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] The Effect of Electric Field on Pressure Filtration of Ceramic SuspensionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2009Yoshihiro Hirata The consolidation behavior of Al2O3 and indium tin oxide (ITO, 90% In2O3,10% SnO2) particles 150,200 nm in size was examined using a pressure filtration apparatus at a constant compressive rate under an electric field. The relation of applied pressure (,Pt) with volume of dehydrated filtrate (Vf) was compared with the established filtration theory (theory I) for a well-dispersed suspension and the newly developed filtration theory (theory II) for a flocculated suspension. The experimental results without polyelectrolyte dispersant deviated from theory I when ,Pt exceeded a critical pressure (,Ptc). This deviation is associated with the phase transition from a dispersed suspension to a flocculated suspension at ,Ptc. A good agreement was shown between the developed theory II and experimental results after the phase transition. When a dispersant (polyacrylic ammonium, PAA) was added to alumina, ITO, or Al2O3,ITO mixed powder suspensions, the consolidation behavior of the particles was controlled by the dissociation and amounts of adsorbed and free PAA. The addition of a large amount of highly charged PAA enhanced the repulsive interaction between PAA-adsorbed particles, and the consolidation behavior was explained by theory I. The adsorption of neutral PAA on the particles reduced the repulsive interaction, and the consolidation behavior was well explained by theory II. The phase transition from dispersed to flocculated suspension was very sensitive to the electric field during the pressure filtration. The ,Ptc for the suspension with and without PAA decreased drastically when a low electric field was applied. The final packing density of the flocculated particles was greatly increased by the application of a weak electric field. However, the dense structure under high pressure was relaxed to a low-density structure when the stored elastic strain energy was released. [source] Pressure-induced structural transitions in multi-walled carbon nanotubesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2009Hiroyuki Shima Abstract We demonstrate a novel cross-sectional deformation, called the radial corrugation, of multi-walled carbon nanotubes (MWNTs) under hydrostatic pressure. Theoretical analyses based on the continuum elastic approximation have revealed that MWNTs consisting of more than ten concentric walls undergo elastic deformations at critical pressure , above which the circular shape of the cross-section becomes radially corrugated. Various corrugation modes have been observed by tuning the innermost tube diameter and the number of constituent walls, which is a direct consequence of the core,shell structure of MWNTs. Cross-sectional views of MWNT under high hydrostatic pressure: elliptic deformation with the mode index n,=,2 (left), and radial corrugations with n,=,5 (center), and n,=,6 (right). The index n indicates the circumferential wave number of the deformed cross-section. [source] Phonon instability in nanocrystalline silicon carbidePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006F. Cleri Abstract In recent experiments by a low-pressure, low-temperature technique, stable nanotubules of rocksalt SiC were synthetized in massive amounts. Ab-initio perturbative density-functional theory calculations in the bulk rocksalt phase provide evidence of drastic phonon softening at a critical pressure of about 2 GPa. To explain the exceptional persistence of the rocksalt structure at ambient conditions we propose that the high pressure induced by interfacial curvature may quench the phonon instability in the nanocrystals down to this minimum threshold, corresponding to the observed nanocrystal size of about 2 nm. Below such pressure the onset of mechanical instability forbids further growth and transformation to ordinary SiC. Nanocrystalline rocksalt SiC is a remarkable example of a material whose unstable, high-pressure phase is stabilized at ambient conditions upon reducing the grain size in the nanometre range. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of Scale and Confinement on Gap Tests for Liquid ExplosivesPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 5 2003François-Xavier Jetté Abstract The factors influencing initiation of detonation in gap tests for liquid explosives are investigated experimentally. A calibrated donor charge (nitromethane) and PMMA attenuator disk arrangement are used to transmit shocks of known strength (2,10,GPa) into a test explosive of nitromethane sensitized with 5% diethylenetriamine. The test explosive is contained in capsules of different wall materials (PVC, Teflon, aluminum), and the dimensions of the charges vary from 25,mm to 100,mm in diameter. For the small-scale charges, the presence of the confining wall of the test capsule is seen to have a pronounced effect on the detonation initiation. Certain wall materials (PVC, Teflon) exhibit a multi-valued critical gap thickness, meaning that a weaker shock may result in initiation while a stronger shock does not. The effect of the wall materials could not be correlated with their acoustic or shock impedance, and the only way to eliminate these effects was to make the diameter of the test charge larger than the donor charge. When the size of the donor charge was increased, the critical pressure required for initiation decreased. These results could be correlated to "ideal" shock initiation experiments that use flyer plates as shock sources assuming that lateral rarefactions quench detonation initiation if they reach the central axis of the charge before the onset of detonation is complete. [source] The metal,insulator phase transition in mixed potassium,rubidium electro-sodalitesACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2004Georg K. H. Madsen The collapse under pressure of the antiferromagnetic ground state of the potassium,rubidium electro-sodalite is studied using the linearized augmented plane wave with local orbitals method. Special considerations needed for setting up this basis for systems such as the electro-sodalites are discussed. It is demonstrated that the magnetism collapses at a unit-cell volume similar to potassium electro-sodalite and rubidium electro-sodalite. A critical pressure of 8,GPa is predicted. The mechanism behind the collapse is a mixing of the F -center states with the highly diffuse unoccupied p states of the alkali atoms. [source] A consistent vertical Bowen ratio profile in the planetary boundary layerTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 620 2006M. Hantel Abstract It has recently been suggested that the integrand b=,,,,, of the subgrid-scale conversion rate between available and kinetic energy has a measurable impact upon the Lorenz energy cycle. Here we discuss a technique to estimate this quantity within the lower part of an atmospheric column by relating b to the subgrid-scale fluxes of sensible and latent heat in form of their sum (the total convective heat flux, c, to be diagnosed from the pertinent energy law) and their ratio (a generalized Bowen ratio, ,, to be specified a priori). We focus on the frequently observed case that c vanishes at or above the top of the boundary layer, which implies that , must be minus unity at the same level (referred to as ,critical pressure'). , at the earth's surface is taken as measured. Observations suggest that the vertical curvature of the , profile is negative in the boundary layer. We specify an analytic vertical profile ,(,) that interpolates these pieces of information; , is a non-dimensional vertical coordinate. The pertinent thermodynamic energy law from which the column profile c(,) is gained (referred to here as convection equation) is driven by the (observed) grid-scale budget; the solution c is over most of the boundary layer quite insensitive to ,. It is only in the immediate vicinity of the critical pressure that c(,) becomes sensitively dependent upon ,(,); it actually turns infinite at this level (a ,pole' of the convection equation). We remove the pole through adjusting the critical pressure by a uniquely determined (and actually quite small) amount. This makes the , profile consistent with the convection equation and with the other convective flux profiles, across the entire boundary layer. The remaining open parameter that cannot be fixed by our method is the curvature of the Bowen ratio profile. This exercise has implications for about a third of all atmospheric columns over the globe and thus may be relevant for the quantification of the global energy cycle. Copyright © 2006 Royal Meteorological Society [source] | |||||||||||||