On the Vapor Pressure of Solid Argon

Abstract

The vapor pressure of solid argon was measured by a precision apparatus with a standard error of ,0.023 Torr in the temperature range from 75.0 to 83.8 K, and that of liquid argon to the same precision from 83.8 to 85.2 K. The data were used to determine the coefficients A and B of the two parameter vapor pressure equation, l o g l o p = A f (BIT), and to locate the triple point of argon by an extrapolation method. The results are in good agreement with those of other workers. The static lattice energy E, of the solid and geometrical mean frequency o, of the vibrational spectrum, corrected for the presence of lattice vacancies, gas imperfection, and finite crystal volume, were also determined from the data. When determined over successive small temperature intervals, E, is found to increase as the temperature increases, as expected. The magnitude of E, agrees with the value obtained from a lattice-sum calculation on the basis of a Lemard-Jones (6-12) potential to within f 0.17%.On a mesure la pression de vapeur de I'argon solide avec unappareil de precision ayant un kcart type de f 0.023 Torr. L'intervalle de temperature s'etendait de 75.0 a 83.8 K pour I'argon solide et de 83.8 a 85.2 K pour I'argon liquide. Les resultats obtenus ont ete utilisks pour determiner les coefficients A et B de I'equation deux parametres de la pression de vapeur (log,, p = A f (BIT)) et pour determiner le point triple de I'argon par une methode d'extrapolation. Les resultats sont en bon accord avec ceux d'autres chercheurs. On a aussi obtenu, a partir de ces mesures, I'energie statique du reseau solide Eo et la moyenne geometrique o, du spectre des frkquences de vibration, en corrigeant pour les vacances dans le reseau, les imperfections de gaz et le volume fini du cristal. Les valeurs de E, obtenues pour de petits intervalles successifs de temperature augmentent comme prevu en fonction de la temperature. La grandeur de E, est en accord, ii mieux que + 0.17%, avec la valeur obtenue a partir d'un calcul de somme de reseau bas6 sur un potentiel de Lennard-Jones. Introductionlattice vibrational spectrum. An attempt was also The vapor pressure of solid argon has been measured by many investigators over the past seventy years. The data have been used to determine such properties of argon as the latent heat, the static lattice energy, and the geometrical mean frequency of the lattice vibrational spectrum. However, these results are observed to vary from one investigator to another. To determine more accurate values of the physical quantities mentioned above, a copious number of accurate data points is required. This is especially true if one wishes to detect the variation of static lattice energy with temperature. To this end a precision vapor pressure assembly was constructed in the form of a modified adiabatic calorimeter.The experimental data were first fitted to the traditional empirical vapor pressure equation and were then compared with those of others. The data were also used to determine the triple point of argon by an extrapolation...

Specific Surface Area of Nanopowders from Argon Adsorption at 77 and 87 K: Zeta Adsorption Isotherm Approach

“…We interpret this adsorption behavior as indicating a phase change of the Ar vapor adsorbate for both of the analyzed substrates, and these results are supported by previous results of ZAI analyses on various substrates. 18,20,24,30,31 Because 77 K is below the triple point of bulk argon 47,48 and corresponds to a solid state, 49,50 we cannot interpret the phase change as a wetting transition, as was done for Ar vapor adsorbate at 87 K. To analyze the nature of the phase, we extrapolate the experimental data of γ LV of Ar reported by Stansfield 45 and compare it with the determined value of γ SV (α −1 ) of silica and carbon black.…”

“…Because 77 K is below the triple point of bulk argon , and corresponds to a solid state, , we cannot interpret the phase change as a wetting transition, as was done for Ar vapor adsorbate at 87 K. To analyze the nature of the phase, we extrapolate the experimental data of γ LV of Ar reported by Stansfield and compare it with the determined value of γ SV (α –1 ) of silica and carbon black.…”

“…As seen in Figure a, the area-specific N 2 adsorption amount is greater than that of the Ar vapor for the entire equilibrium range at 77 K, and both predict finite adsorption at x V equal to unity, with the N 2 isotherm showing a steep increase near saturation. It should also be noted that at 77 K the bulk state of argon would be a solid state, and the corresponding saturation vapor pressure at this state ,, is used in the current study to determine the values of x V . However, some investigations have used − the saturation pressure of a supercooled liquid state at 77 K for bulk argon as the reference pressure.…”

Coexistence behavior of the vapor-liquid-solid equilibrium states for argon

“…A comprehensive literature search for vapor pressure measurements yielded a total of 513 experimental values from 24 sources. These sources (3,(6)(7)(8)(9)(10)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) are presented in Table II. All temperatures in this investigation have been expressed in terms of the International Practical Temperature Scale of 1968.…”

“…Typical saturated-liquid densities are shown in Figure 3. The screened values, which extended up to TR = 2.15 (323 K), were utilized to establish the saturated-liquid relationship pR = 3.0471 7r1/4 + 17.8847r4 exp(-6.54927R) (16) Equation 16 reproduces the selected measurements with an overall average deviation of 0.19% (31 screened points) for liquid densities. The point deviations are well distributed about zero with all but five within ±0.30%.…”