26 Matching Results

Search Results

Advanced search parameters have been applied.

Equations of state of SiO/sub 2/ and H/sub 2/O mixtures

Description: Equations of state (EOS) of silicon dioxide--water mixutes were developed to allow realistic computer simulations of surface and underground nuclear explosions of different yields to be conducted. Beacuse the amount of water contained in silicate rocks affects the size of craters and cavities formed by nuclear explosions, this factor must therefore be included in calculations of the EOS data of silicon cioxide--water mixtures. EOS were tabulated for mixtures containing three different concentrations of water at densities between 10/sup -5/ and 140 Mg/m/sup 3/ and temperatures between 0.025 and 25,000 eV. The calculations were performed by using an improved mixture model based on earlier EOS data of silicon dioxide and water. The improved model makes allowances for a nonequilibrium dynamic effect that occurs more slowly than does the polymorphic phase change of silicate rocks. These data were used in an attempt to simulate the behavior of water-containing rocks during nuclear explosions. 17 figures, and 7 tables.
Date: December 1, 1978
Creator: Ree, F.H.
Partner: UNT Libraries Government Documents Department

New approach to multiphase equilibria: application to high-pressure physics problems

Description: A multiphase, multicomponent equation-of-state (EOS) model based on first principles of statistical mechanics is described. The model has been used to study fluid-fluid phase separations in binary (H/sub 2/-He, Ar-Ne, Xe-He, and N/sub 2/-H/sub 2/O) and ternary or more complex systems involving species with C, H, N, and O atoms. Results of these calculations and a brief description of a new theory which can simultaneously describe both solid and fluid EOS properties are given. 26 refs., 4 figs.
Date: June 1, 1985
Creator: Ree, F.H.
Partner: UNT Libraries Government Documents Department

Chemical equilibrium calculations for the high pressure and temperature dissociation of liquid nitrogen

Description: Calculations are reported for the equation-of-state properties of shock-compressed liquid nitrogen. The statistical mechanical, chemical equilibrium calculations, which allow for the simultaneous presence of both the diatomic and monatomic forms of nitrogen, show good agreement with recent dynamic experiments.
Date: July 1, 1987
Creator: Hamilton, D.C. & Ree, F.H.
Partner: UNT Libraries Government Documents Department

Electrical conductivity and equation of state measurements on planetary fluids at high pressures and temperatures

Description: Hugoniot equation-of-state, shock temperature, and electrical conductivity measurements are reported for fluids believed to be the primary constituents of the planets Uranus and Neptune. The equation-of-state results are compared with calculations performed using a statistical mechanical, chemical equilibrium computer code and electrical conductivities are discussed in terms of the recently measured magnetic field of Uranus. 4 refs., 2 figs., 1 tab.
Date: July 1, 1987
Creator: Hamilton, D.C.; Nellis, W.J.; Holmes, N.C.; Radousky, H.B.; Ree, F.H. & Nicol, M.
Partner: UNT Libraries Government Documents Department

Three phase carbon EOS model with electronic excitation

Description: A simple and rapid way for computing EOS data of multiphase solids with a liquid phase is described with emphasis on carbon. The method uses a scaling model for the liquid phase and includes a provision for electronic effects. The free energy minimum determines the stable phase.
Date: July 1, 1987
Creator: van Thiel, M.; Ree, F.H. & Grover, R.
Partner: UNT Libraries Government Documents Department

A new perturbation theory of solids and fluids and its applications to high-pressure melting problems

Description: A statistical mechanical theory that can describe both solids and fluids in a self-consistent way is described. This theory utilizes a optimized reference potential whose repulsive range shrinks with density. A unique feature of the new theory is that solid- and fluid-phase thermodynamic properties are both computed within a single theoretical framework. Hence, it allows us to study melting phenomena in a self-consistent manner. For solids, the new theory treats both harmonic and anharmonic effects in thermodynamic properties on equal footing. Applications to several model and rare gas systems show that the new theory can accurately predict fluid, solid, and fluid-solid transition properties. Effective pair potentials inferred from the analysis of krypton and xenon isotherms contain short- and long-range modifications to the Aziz-Slaman pair potential. The long-range correction is repulsive and originates from the Axilrod-Teller three-body force, while the short-range correction probably originates from many-body forces. Using the computed melting curves of krypton and neon, we discuss the range of validity of the corresponding states principle for rare gas systems. 68 refs., 8 figs., 6 tabs.
Date: May 1, 1990
Creator: Ree, F.H.
Partner: UNT Libraries Government Documents Department

Multiphase carbon and its properties in complex mixtures

Description: We describe some key features of a carbon three-phase equation of state and a high-pressure high temperature mixture model in which it is used. Electronic terms in the carbon model have been investigated with INFERNO (atom in a cell model). The Lindeman criterion for melting is rederived for the anisotropic structure of the graphite lattice. The curvature of the graphite melting line is constrained by the evidence for the positive slope of the diamond melting line. The importance of carbon is apparent from various experiments on shock generated mixtures. The model allows us to estimate the energy of carbon clusters produced in a detonating mixture. A cluster model with specific surface structure is used to predict this energy. 41 refs., 7 figs., 4 tabs.
Date: September 1, 1990
Creator: van Thiel, M. & Ree, F.H.
Partner: UNT Libraries Government Documents Department

Effective like- and unlike-pair interactions at high pressure and high temperature

Description: We describe how information on effective interactions of chemical species involving C, O, and N atoms at high pressure and high temperature may be inferred from available shock wave data of NO and CO. Our approach uses a modern statistical mechanical theory and a detailed equation of state (EOS) model for the condensed phases of carbon.
Date: May 1, 1991
Creator: Ree, F.H. & van Thiel, M.
Partner: UNT Libraries Government Documents Department

The significance of interaction potentials of water with other molecules in the EOS of high explosives products

Description: The chemical equilibrium and thermodynamic properties of detonated explosive mixtures at high temperature (T) and pressure (P) depend critically on all interactions between the major products. Improvements in the homomolecular interaction of nitrogen, carbon-dioxide, and condensed carbon have had significant effects on detonation properties of LX-14 (an HMX formulation). Extensive work on O, N, and C products also showed the importance of including high temperature unstable species in determining the potential-constant of the major products of detonation. That work also showed the need to improve the unlike pair interaction constants in our statistical mechanical chemical equilibrium theory (CHEQ). Thirdly, a recent comparison of experimental and theoretical detonation velocities (D) indicated that the original set of interaction potentials used contains canceling errors that limit the overall effectiveness of the code as a predictor of high P and T properties of reactive mixtures. This study proceeds from explosives with simple product mixtures, RX-23-AB, HNB, and PETN, to HMX-like mixtures. The present set of potential constants is compared to the experimental EOS used for a number of experimental systems that use LX-14.
Date: July 1, 1993
Creator: van Thiel, M.; Ree, F. H. & Haselman, L. C. Jr.
Partner: UNT Libraries Government Documents Department

Unlike pair interactions in N{sub 2}-H{sub 2}O mixtures

Description: Statisical-mechanical chemical equilibrium calculations have been performed to determined the deviation of the unlike species potential from that predicted by the Lorentz-Berthelot rule. The potentials of the water-water and nitrogen-nitrogen interactions have been reexamined in the light of remaining deviations from experiment. The resulting deviation of the constant from one (1), in the extended Lorentz-Berthelot rule, is determined from the best exp-6 potentials for nitrogen and water with consideration of possible deviations of the measured detonation velocity of RX-23-AB from its ideal equilibrium value.
Date: July 1, 1993
Creator: van Thiel, M. & Ree, F. H.
Partner: UNT Libraries Government Documents Department

Accurate determination of pair potentials for a C{sub w}H{sub x}N{sub y}O{sub z} system of molecules: A semiempirical method

Description: Statistical mechanical chemical equilibrium calculations of the properties of high-pressure high-temperature reactive C,H,N,O mixtures are made to derive an accurate self-consistent set of inter-molecular potentials for the product molecules. Previous theoretical efforts to predict such properties relied in part on Corresponding States theory and shock wave data of argon. More recent high-pressure Hugoniot measurements on a number of elements and molecules allow more accurate determination of the potentials of these materials, and explicit inclusion of additional dissociation products. The present discussion briefly reviews the previous analysis and the method used to produce a self-consistent set of potentials from shock data on N{sub 2}, O{sub 2}, H{sub 2}, NO, an N{sub 2} + O{sub 2} mixture, carbon, CO{sub 2}, and CO, as well as some simple explosive product mixtures from detonation of hexanitrobenzene, PETN, and a mixture of hydrazine nitrate, hydrazine and water. The results are tested using the data from an HMX explosive formulations. The effect of the non-equilibrium nature of carbon clusters is estimated using data for TNT as a standard to determine a nonequilibrium equation of state for carbon. The resulting parameter set is used in a survey of 27 explosives. For the subset that contains no fluorine or two-phase carbon effects the rms deviation from experimental detonation velocity is 1.2%.
Date: March 1, 1995
Creator: Thiel, M. van; Ree, F.H. & Haselman, L.C.
Partner: UNT Libraries Government Documents Department

Equilibrium and nonsequlibrium properties of bulk and nanosize clusters of carbon

Description: The detonation behavior of carbon-rich high explosives is affected by a slow coagulation of carbon atoms by diffusion and their possible transformation from one chemical bonding type to another. We have examined the applicabilityof the Brenner potential at high pressure and high temperature by molecular dynamics simulations and the stability and barrier height between graphitic and diamond clusters as a function of cluster size by quantum chemical calculations. The diffusion kinetics of carbon clusters have been examined by including a time-dependent surface correction to the Gibbs free energy of these clusters.
Date: August 1997
Creator: Ree, F. H.; Glosli, J. & Winter, N.
Partner: UNT Libraries Government Documents Department

Supercritical fluid phase separations induced by chemical reactions

Description: Our statistical mechanical studies predict that a chemically reactive system containing species composed of C, H, N, O atoms can exhibit a phase separation into a N{sub 2}-rich and a N{sub 2}-poor phase. The preset work is concerned with the effect of the fluid phase separation upon addition of F atoms in the system. Our study shows that F atoms mainly appear as a constituent of HF in a N{sub 2}-poor fluid phase up to a certain pressure beyond which they occur as CF{sub 4} in a N{sub 2}-rich phase and that the phase separation may be abrupt in thermodynamic sense. The pressure at the phase boundary can occur at about 30 GPa at 3000 K and about 10 GPa to 20 GPa at 1000 K.Some of these ranges maybe accessible by present-day experimental high-pressure techniques. We discuss implications of this study to detonation physics.
Date: November 1997
Creator: Ree, F. H.; Viecelli, J. A. & van Thiel, M.
Partner: UNT Libraries Government Documents Department

Insensitive HE EOS

Description: A typical insensitive high explosive such as LX-17 has a large carbon-content and produces hydrogen fluoride (HF) as a detonation product. It is also characterized by slow energy release as indicated by a large curvature of the detonation front. We analyze these new physics issues which are needed to predict the performance of a insensitive high explosive. (U)
Date: December 1, 1997
Creator: Ree, F.H.; Viecelli, J. & van Thiel, M.
Partner: UNT Libraries Government Documents Department

Thermodynamic and structural properties of strongly coupled plasma mixtures from the perturbative HNC-equation

Description: Recently, we developed the perturbative hypernetted-chain (PHNC) integral equation which can predict reliable thermodynamic and structural data for a system of particles interacting with either short range or long range (Coulomb) potential. The present work extends this earlier work to mixtures. This is done by employing a reference potential which is designed to satisfy a thermodynamic consistency on the isothermal compressibility as described in the next section. We test the present theory in Sec. III by applying it to plasma mixtures interacing with either an unscreened or a screened Coulomb potential. We made comparisons of results from the present theory with those from the best available theory, i.e., Rosenfeld`s density functional theory (DFT). The DFT was shown to give internal energy with three to five fignre accuracy compared to a wide range of Monte Carlo data. Meanwhile, small deviations of excess internal energy from the so-called ``liner mixing rule`` (LMR) are better predicted by a less sophiscated theory like the hypernetted- chain (HNC) equation. This rule relates thermodynamics of an unscreened mixture to those for individual components in a strongly coupled regime where the potential energy of a constituent particle is much larger than its kinetic energy. We also apply the present theory to a H{sub 2} + H mixture interacting with Morse potentials. For this sytem, comparison of thermodynamic properties and radial distribution functions from the present theory will be made with those from another successful theory of dense fluid, i.e., the HMSA equation of Zerah and Hansen.
Date: December 1, 1997
Creator: Kang, H.S. & Ree, F.H.
Partner: UNT Libraries Government Documents Department

Kinetics and thermodynamic behavior of carbon clusters under high pressure and high temperature

Description: Physical processes that govern the growth kinetics of carbon clusters at high pressure and high temperature are: (a) thermodynamics and structural <i>sp</i>?-to-<i>sp</i>? bonding) changes and (b) cluster diffusion. Our study on item (a) deals with <i>ab initio</i> and semi-empirical quantum mechanical calculations to examine effects of cluster size on the relative stability of graphite and diamond clusters and the energy barrier between the two. We have also made molecular dynamics simulations using the Brenner bond order potential. Kesults show that the melting line of diamond based on the Brenner potential is reasonable and that the liquid structure changes from mostly <i>sp</i>-bonded carbon chains to mostly <i>sp</i>?-bonding over a relatively narrow density interval. Our study on item (b) uses the time-dependent clustor size distribution function obtained from the relevant Smoluchowski equations. The resulting surface contribution to the Gibbs free energy of carbon clusters was implemented in a thermochemical code.
Date: May 4, 1998
Creator: Glosli, J N; Ree, F H & Winter, N W
Partner: UNT Libraries Government Documents Department

Equation of state of insensitive high explosives

Description: Detonation of an insensitive high explosive formulated with a fluorine containing binder produces a large amount of condensed carbon and gaseous HF product, which transforms into CF{sub 4} as the pressure is increased. The former (carbon condensation) is characterized by slow energy release, while the latter (HF) has no shockwave data. We have identified that these two items are the key factors, which make reliable prediction of the performance of an insensitive high explosive very difficult. This paper describes physical models to address these issues and apply the models to analyze experimental data of LX-17.
Date: August 12, 1998
Creator: Ree, F H; Van Thiel, M & Viecelli, J A
Partner: UNT Libraries Government Documents Department

Hugoniots of aerogels involving carbon and resorcinol formaldehyde

Description: Recently, a first-order phase transition is predicted in liquid carbon using atomistic simulation and Brenner's bond order potential. There are also experimental data suggesting a possibility for a first-order phase transition. In light of this, a thermochemical equilibrium code (CHEQ) is used to provide guidance to experiments to find a liquid-liquid phase change in carbon foam and carbon-rich aerogel, resorcinol formaldehyde. Isotherms and Hugoniots were computed based on the previous analysis by van Thiel and Ree. The present calculations predict the liquid-liquid-graphite triple point to be at 5000 K and 5.2 GPa and its critical point to be at 6000 K and 8.8 GPa. The present Hugoniot calculations suggest that the liquid-liquid phase transition may be detected by performing a shock experiment with initial density of approximately 0.15 gm/cm{sup 3}.
Date: June 24, 1999
Creator: Hrubesh, L H; Ree, F H; Schmidt, R D; Shon, J; Van Thiel, M; Vantine, H C et al.
Partner: UNT Libraries Government Documents Department

Modeling high-pressure and high-temperature phase changes in bulk carbon

Description: The phase diagram of carbon is not experimentally well known at high pressure and/or high temperature. We have determined the phase diagram of carbon by means of Monte Carlo and molecular dynamics simulations methods using the Brenner bond order potential. The melting line of diamond was found to have a positive slope with the graphite-diamond-liquid triple point in agreement with an estimated value based on experiment. The present calculation predicts a first-order phase transition in liquid carbon terminated by a critical point and by a triple point on the graphite melting line. The low-density liquid is predominantly sp bonded with little sp{sup 3} character. The high-density liquid is mostly sp{sup 3} bonded with little sp character.
Date: July 1, 1999
Creator: Glosi, J N & Ree, F H
Partner: UNT Libraries Government Documents Department

Equations of state of nonspherical fluids by spherical intermolecular potentials

Description: The equilibrium properties of anisotropic molecular fluids can be in principle calculated in a statistical mechanics framework, but the theory is generally too cumbersome for many practical applications. Fortunately, at high densities and temperatures the anisotropy can be averaged-out by means of a density and temperature independent potential (the median) that produces reliable thermodynamics [1,2]. The proposal of Shaw and Johnson [1], which turns out to be the so-called median potential [2], is very successful in predicting the thermodynamics of simple fluids such as N{sub 2} and CO{sub 2} at reasonable high pressures and temperatures [3]. Lebowitz and Percus [2] pointed out some time ago that the success of this approximation could perhaps be understood in terms of a simple theory that treats the asphericity as a perturbation. The median appears to be the best choice for hard nonspherical potential [4], which may explain its success for fluids at high densities, where the hard core contribution is known to be dominant.
Date: August 16, 1999
Creator: Bastea, S & Ree, F H
Partner: UNT Libraries Government Documents Department