Sublimation Pressure Research Articles

The solubility of solids in compressed gases

The density series virial equation of state truncated at the third virial coefficient has been evaluated for describing the fluid nonideality of systems of pure solids in equilibrium with near-critical C0 2 including systems with cosolvents. The function [In ( z φ 1)]/ ϱ is found to be linear with p for pressures up to 400 bar for 16 solutes, eleven of which also involved 8 different cosolvents for temperatures from 300 to 523 K. As required, when the virial series is applicable, the zero-density intercepts obtained from high-pressure data agree with those from low-pressure data. The method shows how cosolvent contributions via composition and density can be explicitly separated. Prediction of second cross virial coefficients along with fitting the third virial to a single data point on the isotherm can be at least as successful as other models. Sensitivity to variations in sublimation pressure, solid molar volume, and fluid density has been tested.

International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance

In order to define the phase boundary between the solid phase (ice) and the fluid phase (liquid and gas) of ordinary (light) water substance in pressure-temperature coordinates, correlation equations for the pressure along the melting curve of the various modifications of ice as well as for the pressure along the sublimation curve are presented. The five equations for the melting pressure of the ice phases, ice I, ice III, ice V, ice VI, and ice VII, which only contain one to three fitted coefficients, cover the pressure range from the ‘‘normal’’ triple point to 20000 MPa. In this entire range the equations represent the selected measurements of the melting pressure within their experimental uncertainty. The 2-coefficient equation for the sublimation pressure covers the temperature range from 190 K to the triple point (273.16 K). The equations correspond to the new International Temperature Scale of 1990 (ITS-90). All these equations form the basis of the revised release on the pressure along the melting and sublimation curves of ordinary water substance. A verbatium copy of this release is presented in the Appendix of this paper. §

The thermodynamic properties to the temperature 700 K of naphthalene and of 2,7-dimethylnaphthalene

Measurements leading to the calculation of the standard thermodynamic properties of the gases are reported for naphthalene (Chemical Abstracts registry number [91-20-3]) and 2,7-dimethylnaphthalene (registry number [582-16-1]). Experimental methods included adiabatic heat-capacity calorimetry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). The critical temperature was determined experimentally for each compound, and the critical pressure and critical density were derived from fitting procedures. Vapor-pressure measurements reported in the literature were compared with the results obtained in this research. Enthalpies of vaporization and sublimation were derived from the experimental measurements and compared with literature results. New self-consistent equations for the variation of sublimation pressure with temperature for naphthalene and 2,7-dimethyl-naphthalene were derived. For each compound, literature values for entropies and enthalpies of the liquid phase and the energy of combustion were combined with the present results to derive standard entropies, enthalpies, and Gibbs free energies of formation for the gaseous phase for temperatures between 298.15 K and 700 K. The standard properties for naphthalene(g) were compared with values obtained using statistical mechanics with various fundamental vibrational-frequency assignments available in the literature. A scheme to estimate the standard thermodynamic functions for gaseous alkylnaphthalenes was updated. the size of the barrier to methyl-group rotation in 2,7-dimethylnaphthalene was shown to be of about the same size as that for toluene. Values for standard entropies for 2-methylnaphthalene(g) in the temperature range 300 K to 700 K were estimated.

The thermal properties of four allotropes of carbon

The heat capacities of diamond, graphite, and the fullerenes C 60 and C 70 are compared and linked to their approximate vibrational spectra. Because all the allotropes have the chemical composition C, their ultimate heat capacity is the Dunlog-Petit value 3 R = 24.9J K −1mol −1. At low temperatures (0–50 K), the fullerenes have a much higher heat capacity than the other two allotropes. As the temperature is increased, graphite and the fullerenes approach approximately equal heat capacities. Up to 1000 K, diamond has a lower heat capacity, but then, because of its weaker C-C bonds compared to the conjugated double bonds in graphite and the fullerenes, it exceeds the heat capacities of the latter. Fullerenes have crystal to plastic-crystal transitions in the region 250–350 K with entropies in agreement with the orientational entropy increase derivable from Walden's rule. Their sublimation pressures reach atmospheric pressure at about 1500 K, and the entropies of transition, when corrected for the entropy of fusion (Richards' rule), obey Trouton's rule. Carbon is thus a textbook example for the differences in thermal behavior possible as a function of chemical bonding and structure.

Free energy of formation of Cs 3PuCl 6 and CsPu 2Cl 7

The free energy, enthalpy and entropy of formation of the compounds Cs 3PuCl 6 and CsPu 2Cl 7 have been determined by measuring the sublimation pressures for the reactions CsCl( s) / ai CsCl( g), 2 5 Cs 3PuCl 6(s) /ai 1 5 CsPu 2Cl 7(s) + CsCl(g) , and CsPu 2 Cl 7( s) / ai 2 PuCl 3( s) + CsCl( g). The pressures are measured using Knudsen effusion mass spectrometry over the temperature range 600 to 850 K. For the formation of Cs 3PuCl 6 from CsCl and PuCl 3, ΔG 0 298 = −77.3 ± 8.5 kJ/ mol, ΔH 0 298 = −82.1 ± 7.8 kJ/ mol, and ΔS 0 298 = −16.2 ± 10.9 J/ K mol. For CsPu 2Cl 7, ΔG 0 298 = −39.4 ± 3.5 kJ/ mol, ΔH 0 298 = −40.8 ± 3.2 kJ/ mol, and ΔS 0 298 = −4.6 ± 4.2 J/ K mol.

Mass spectrum and sublimation pressure of sodium oxide vapor: Stability of the superoxide molecule NaO2

The total sublimation pressure of Na2O(c) has been measured in the range 1000–1050 K by the torsion-effusion method, and the mass spectra of vapors over Na2O(c) and Na2O2(c) have been examined in order to resolve several issues regarding the thermochemical stability of the superoxide molecule NaO2. Measured torsion-effusion pressures are completely consistent with the primary sublimation process Na2O(c)=2Na(g)+0.5 O2(g) and set an upper limit of 200 kJ mol−1 for the bond strength D0(Na–O2). The ionization efficiency curves of Na+ and O2+ in the mass spectrum of vapor over Na2O(c) show no evidence for fragmentation contributions from NaO2. In addition, the absence of a detectable Na+/NaO2 fragment ion signal in vapor over Na2O2(c) can be used to derive an even tighter upper bound of 180 kJ mol−1 for D0(Na–O2). These results are in conflict with various kinetic analyses yielding D0(Na–O2) values of 202 to 243 kJ mol−1, but are in accord with rigorous theoretical calculations giving values near 160 kJ mol−1.

Determination of sublimation pressures of a fullerene (C60/C70) solid solution

The sublimation pressures in equilibrium with a polycrystalline C 60 /C 70 solid solution have been measured with a quartz crystal microbalance (QCM) and by transpiration methods, in the temperature range 772-857 and 806-929 K, respectively. The results from the two independent methods show good agreement. The solid solution was found to have a total vapor pressure of 8.1×10 -4 Torr at 800 K. It is estimated that the total vapor pressure of the C 60 /C 70 solid solution could reach 1 atm at ca. 1523 K

Trends and anomalies in the thermodynamics of gaseous thorium and uranium halides

Abstract

The thermodynamic properties of dibenzothiophene

Measurements leading to the calculation of the ideal-gas thermodynamic properties for dibenzothiophene are reported. Thermochemical and thermophysical properties were determined by adiabatic heat-capacity calorimetry, differential-scanning calorimetry (d.s.c.), comparative ebulliometry, and inclined-piston manometry. A literature value for the energy of combustion was selected and combined with the results to calculate standard entropies, standard enthalpies, and standard Gibbs energies of formation for the ideal-gas at selected temperatures from 298.15 K to 800 K. The critical temperature and critical density were measured with the d.s.c., and a value for the critical pressure was derived. Sublimation pressures from 298.15 K to the triple-point temperature (371.8 K) were derived. All measured and derived properties were compared with literature values.

Sublimation pressures of hydrogen chloride

New measurements of the sublimation pressure of HCl have been carried out between 120 K and 150 K. They appear more reliable than previously published results, at least below 140 K. From our results and the heat capacities of Chihara and Inaba, (9) we derive for the molar cohesion energy of HCl at T = 0 a value of −(20222 ± 20) J · mol −1.

石炭液化油成分の蒸気圧ならびに臨界定数

Coal liquids have received much attention recently as useful raw materials since they contain polycyclic aromatic compounds and heterocyclic compounds. Supercritical gas extraction is expected as one of the successful separation techniques to separate and purify them.In design of such a separation process, physical properties of coal-derived components, i.e., sublimation pressures, solid molar volumes, critical temperatures, critical pressures, critical molar volumes, the Pitzer's acentric factors, and the Stiel's polar factors are needed. The authors surveyed these properties from literature and handbooks. If no experimental critical properties are reported, they are estimated by the Lydersen's group-contribution method. Solubility parameters that are useful to evaluate molecular interaction are also compiled.

Permanency of boric acid used as a fire retardant in cellulosic insulation

The rate of loss of the chemical fire retardant, boric acid, from loose-fill cellulosic insulation due to sublimation has been determined. Apparent sublimation pressures for boric acid have been measured as a function of temperature and relative humidity using a flow system. A direct determination was also made of the rate of mass transfer of boric acid in cellulosic insulation to the air above the insulation. These data were used in a numerical model to show that the loss of boric acid from cellulosic insulation is insignificant at 70 °C and relative humidity near 100%. The redistribution of boric acid and borax in a commercial cellulosic insulation due to vibration was studied by analyzing specimens taken from the top and bottom of horizontally applied material. Long periods of vibration failed to result in statistically significant chemical redistribution.

Niflumic acid-morniflumate phase diagram: I. Study of the components

Niflumic acid and morniflumate have been studied using X-ray diffraction, DTA, DSC and TG techniques. Their solubilities in various solvents at 296 K have also been determined. Neither niflumic acid nor morniflumate significantly decompose at temperatures less than 476 K. They melt at 476 K (Δ fus H = 38 kJ mol −1) and 351 K (Δ fus H = 38 kJ mol −1) respectively. The heat capacities for the solid and liquid phases of both compounds have been determined in the 100–500 K range. The sublimation pressure for niflumic acid may be neglected. The two species easily form glasses. Only niflumic acid recrystallizes at 298 K. All these data will be used in a future study of the phase diagram of these compounds.

ChemInform Abstract: Enthalpies of Sublimation and Vapor Pressures of 8‐Alkyl Derivatives of 9‐Methyladenine.

ChemInform Abstract: Enthalpies of Sublimation and Vapor Pressures of 8‐Alkyl Derivatives of 9‐Methyladenine.

Analytical study of vacuum-sublimation in an initially partially filled frozen porous medium with recondensation

Analytical solutions are developed for vacuum-sublimation in an initially partially filled, frozen, semi-infinite porous medium. Since the porous medium is partially filled, the vapor generated at the sublimation interface will convect into both the dried and frozen regions. The mass transfer of vapor through the porous medium is modeled by the application of Darcy's and Fick's laws. Recondensation of vapor occurs when the vapor convects into the frozen region. The sublimation interface temperature, pressure and vapor concentration are obtained in addition to the interface position. Moreover, the effects of vapor recondensation and the significant system parameters on the non-dimensional interface position are studied. The results show the increased sublimation rate when the vapor recondenses in the frozen region.

The parametric analysis of self-freezing in an initially wet porous medium

The problem of freeze-drying during the self-freezing of a wet porous medium where the freezing and sublimation drying processes occur simultaneously is studied. Analytical solutions of self-freezing in an initially wet semi-infinite porous region are developed by the similarity variable method. The sublimation interface temperature, pressure, and vapor concentration are determined in addition to the positions of the freezing and sublimation interfaces. The vapor transfer in the dried region is modeled by the application of Darcy's and Fick's laws coupled with an additional model for the pressure in this region. For the self-freezing process, the freezing rate is found to be much faster than the sublimation rate. Also, the effects of significant parameters on the sublimation and freezing interface constants are presented for in-depth understanding and application of self-freezing process.

EFFECT OF MASS CONVECTION ON VACUUM-SUBLIMATION IN AN INITIALLY PARTIALLY FILLED FROZEN POROUS MEDIUM

ABSTRACT Exact analytical solutions of vacuum-sublimation in an initially partially filled, frozen, porous medium are developed by the similarity variable technique. The sublimation interface temperature, pressure and vapor concentration are obtained in addition to the position of the sublimation interface. Two theoretical models corresponding to the two-region model which allows for vapor transfer in both the frozen region and dried region and the one-region model accounting for vapor transfer in the dried region only are considered. The comparison between these two models and the effect of mass convection into the frozen region are studied. The results show the significant discrepancies in the interface positions predicted by these two models for some values of the important parameters.

Sublimation-controlled oxidation of antimony trioxide

Previous investigators noted that a mixture of dimorphic Sb 2O 3 oxidizes to orthorhombic Sb 2O 4 more rapidly than each dimorph separately. It was hypothesized that Sb 2O 3(c) sublimes to low-energy nucleation sites on Sb 2O 3(o) to oxidize. In this study thermodynamic calculations indicated that the driving force for oxidizing a sublimed species is much greater than that for nonsublimed Sb 2O 3. The hypothesis was validated experimentally using small-particle-size (10–20 μm) Sb 2O 3 to achieve appreciable sublimation rates. It was found that the oxidation rates of both Sb 2O 3(c) and Sb 2O 3(o) are linearly correlated to the equilibrium sublimation pressure of each dimorph. Also, the apparent activation energy of oxidation was determined to be 42.6–45.9 kcal/mole, approximating the enthalpy of sublimation for Sb 2O 3 (∼43–47 kcal/mole). These observations strongly support the hypothesis that Sb 2O 3 oxidation is sublimation controlled.

Solubility of monocrotaline in supercritical carbon dioxide and carbon dioxide—ethanol mixtures

The solubility of monocrotaline, a chemotherapeutic drug precursor, in supercritical carbon dioxide and carbon dioxide—ethanol mixtures has been measured from 308.15 to 328.15 K and from 8.86 to 27.41 MPa. The solubility ranges from 6.0 × 10 −6 to 2.21 × 10 −4 mol fraction increasing up to 25-fold with the addition of ethanol. A new method for the estimation of the sublimation pressure of monocrotaline was developed based on the measured solubilities of monocrotaline in water. The sublimation pressure was then used in the compressed gas model to correlate the behavior of carbon dioxide—monocrotaline and carbon dioxide—ethanol—monocrotaline systems with reasonable success.

Mechanism and Thermodynamics of the Vaporization of K 2CrO4

The vacuum vaporization behavior of was studied over the range 1075–1240 K, which is just below the melting point of the material. Both molecular vaporization of and decomposition to K(g), , and contribute to the total vaporization flux. Vapor composition and sublimation thermodynamics were studied by Knudsen cell mass spectrometry, while total vapor pressure and vapor molecular weight were determined by the torsion‐effusion method. Composition data inferred from the mass spectrum, the vapor molecular weight data, and comparison of calculated decomposition pressure with measured total pressure are all in close accord in showing the molecular chromate to account for 83% of the total sublimation pressure. This indicates a high degree of thermodynamic stability for the gaseous chromate. The enthalpy of sublimation of at 1200 K was determined to be from second law slope measurements, from which the standard sublimation enthalpy at 298 K was derived as . An absolute entropy value for derived from the sublimation data is about 12.5 J · K−1 · mol−1 higher than one calculated from fragmentary spectroscopic data, indicating some need for further revision of the molecular constants. Results are compared with those from several other studies and the reasons for similarities and differences are discussed. It appears, that gaseous alkali chromates could play an important role in the hot corrosion of superalloys.