Condensed phase composition

Vapor pressures and vapor compositions in equilibrium with a hypostoichiometric plutonium dioxide condensed phase have been calculated for the temperature range 1500 I H 4000 K. Thermodynamic functions for the condensed phase and for each of the gaseous species were combined with an oxygen-potential model, which we extended from the solid into the liquid region to obtain the partial pressures of O2, 0, Pu, PuO and Pu02 as functions of temperature and of condensed phase composition. The calculated oxygen pressures increase rapidly as stoichiometry is approached. At least part of this increase is a consequence of the exclusion of Pu +... 

The temperature dependences of the total pressures In equilibrium with the condensed-phase composition PuOj gQ, PuOl.96> and P11O1.994 are compared in Figure 4. The differences shown In Figure 4 are due to the differences In oxygen pressures for the different compositions. 

Another significant comparison between the two systems concerns the partial pressures of the metal dioxide molecules. These pressures are relatively insensitive to the condensed-phase composition and are quite similar in the plutonia and urania systems. Calculated metal dioxide vapor pressures are compared in Table V for 0/M = 1.96. 

Further clarification is obtained from Figure 2 where the relations are depicted by a composition diagram where the vapor phase composition is the ordinate and the condensed phase composition is the abscissa. A straight line with a slope equal to the equilibrium distribution constant KiD is the locus of all equilibrium compositions. The curved line represents a set of nonequilibrium conditions for condensation out of the vapor phase. The departure from equilibrium can be projected on either axis, and the lengths of the projections correspond to the two expressions for potential difference shown above. Refs. 2 and 10 treat the boundary layer in detail. 

FIGURE A.l. Vapor pressures versus condensed-phase composition for completely miscible binary systems. 

Here we introduce models commonly used to represent the composition dependence of excess properties in liquid mixtures. Just as in 4.5 for volumetric equations of state, the models considered here are semitheoretical they may have some limited mathematical or physical basis, but they inevitably contain parameters whose values must be obtained from experimental data. The emphasis here is on the composition dependence of y, because, for condensed phases, composition is the most important variable temperature is next in importance, and pressure is least important. 

System pressures and temperatures, together with gas and condensed phase compositions, are also calculated. The different values obtained will not be presented here, they will only be discussed later in relation to the release and transport of core materials, as this is the subject of interest to this presentation. 

Table 3 shows results obtained from a five-component, isothermal flash calculation. In this system there are two condensable components (acetone and benzene) and three noncondensable components (hydrogen, carbon monoxide, and methane). Henry s constants for each of the noncondensables were obtained from Equations (18-22) the simplifying assumption for dilute solutions [Equation (17)] was also used for each of the noncondensables. Activity coefficients for both condensable components were calculated with the UNIQUAC equation. For that calculation, all liquid-phase composition variables are on a solute-free basis the only required binary parameters are those for the acetone-benzene system. While no experimental data are available for comparison, the calculated results are probably reliable because all simplifying assumptions are reasonable the... 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

In distillation operations, separation results from differences in vapor-and liquid-phase compositions arising from the partial vaporization of a hquid mixture or the partial condensation of a vapor mixture. The vapor phase becomes enriched in the more volatile components while the hquid phase is depleted of those same components. In many situations, however, the change in composition between the vapor and liquid phases in equihbrium becomes small (so-called pinched condition ), and a large number of successive partial vaporizations and partial condensations is required to achieve the desired separation. Alternatively, the vapor and liquid phases may have identical compositions, because of the formation of an azeotrope, and no separation by simple distillation is possible. 

The R s of a fibrous or cellular insulation like those in Table 2 generally decrease as the temperature increases. In the case of closed-cell polymeric foams like polyurethane nr pnlyisncyanurate board, the R may decrease if the insulation temperature drops below the condensation temperature of the blowing agent in the cells. This is because of changes in the gas- phase composition and therefore the gas-phase thermal conductivity. The R of insulations also depends on density when all other factors are constant. The relationship bett een R and density... 

It may reasonably be assumed that the terms in the expression for the entropy which depend on the temperature diminish, like the entropy of a chemically homogeneous condensed phase, to zero when T approaches zero, and the entropy of a condensed solution phase at absolute zero is equal to that part of the expression for the entropy which is independent of temperature, and depends on the composition (Planck, Thennodynamik, 3 Aufi., 279). 

Powling (P7) recently reported on the results of an extensive study of the combustion characteristics of ammonium perchlorate-based composite propellants. The nature of the chemical processes taking place at the solid-gas interface and the possibility of heat release in the condensed phase were considered. Although the evidence is that some heat release is likely to occur within the solid surface, Powling found that the combustion in all pressure regions appears to be dominated by gas-phase reactions. 

It should be emphasized that a survey of the vapor pressure measurements of plutonium-bearing species above bivariant Pu02-x(s) revealed that in general these measurements suffer from a lack of knowledge of the composition of the condensed phase. 

During the course of exploratory experimentation involved in the preparation of 8-242pU203, some limited oxygen potential measurements over Pu02-X fluorite phase were made at 1750 and 2050 K. The transpiration method was used for this study because, for a given temperature, the composition of the condensed phase can be fixed by appropriate choice of oxygen potential (via H2/... 

One of the most Important thermophysical properties of reactor fuel In reactor safety analysis Is vapor pressure, for which data are needed for temperatures above 3000 K. We have recently completed an analysis of the vapor pressure and vapor composition In equilibrium with the hypostolchiometric uranium dioxide condensed phase (1 ), and we present here a similar analysis for the plutonium/oxygen (Pu/0) system. 

In this paper we describe (1) the gas-phase thermodynamic functions (2) the condensed-phase thermodynamic functions (3) the oxygen potential (and the phase boundaries that are consistent with It) and (4) the resulting vapor pressure and composition as functions of temperature and composition of the condensed phase. 

General. The methods we have used to calculate the vapor pressures and vapor compositions at high temperatures are the same as those used previously (1-2) for the U/0 system. The total pressure, p(total), In equilibrium with a Pu02 x condensed phase Is... 

An alternative way to view the oxygen enrichment of the vapor relative to the condensed phase Is to calculate the oxygen-to-plutonium ratio of the gas, R(gas), with Eq. (2). The value of R(gas) exceeds that of the condensed phase with which It Is In equilibrium by a large amount. Like the U/0 system, this oxygen enrichment of the vapor relative to the condensed phase Is Increasing with temperature. One Implication of these results Is that the condensed-phase and vapor-phase compositions will depend upon the extent of vaporization of a sample with overall composition given by 0/Pu = 2 - x. 

Vapor compositions In equilibrium with a PuOj.q condensed phase (top) and a PuOj.go condensed phase (bottom). 

Hydroxysulfate compounds, structure 56-57 Hypostoichiometric Pu dioxide condensed phase, vapor pressures and vapor compositions.124-41... 

Intermolecular forces are responsible for the existence of several different phases of matter. A phase is a form of matter that is uniform throughout in both chemical composition and physical state. The phases of matter include the three common physical states, solid, liquid, and gas (or vapor), introduced in Section A. Many substances have more than one solid phase, with different arrangements of their atoms or molecules. For instance, carbon has several solid phases one is the hard, brilliantly transparent diamond we value and treasure and another is the soft, slippery, black graphite we use in common pencil lead. A condensed phase means simply a solid or liquid phase. The temperature at which a gas condenses to a liquid or a solid depends on the strength of the attractive forces between its molecules. 

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