The Vapor Pressures of Inorganic Substances. I. Beryllium¹

Abstract

The need for more complete data on the vapor pressure and thermodynamic properties of many elementary substances has prompted us to determine the vapor pressure of solid beryllium over a wide temperature range. For these measurements both the Langmuir and Knudsen methods were used and the data obtained by these two methods are in good agreement. Intercomparison of these data affords a means of determining the value of the condensation coefficient for this substance. The theory and use of these methods are described by other investigator^.^,^^^^In Langmuir's method the vapor pressure of a substance is determined by the relationship where m is the rate a t which the material evaporates into a vacuum per unit area of surface, P is the vapor pressure, M is the molecular weight of the evaporating particle, R is the gas constant per mole, T is the absolute temperature and a is the condensation ~oefficient.~ The necessary relationship for determining the vapor pressure of a substance by Knudsen's method iswhere m is the rate at which the vapor under its equilibrium pressure will effuse through an orifice, and the other symbols have the same meaning as before. ExperimentalThe measurements consisted in the measurement of the rate a t which a metal surface evaporates into a vacuum (Langmuir method) and the determination of the rate a t which metal vapor a t its equilibrium pressure effuses through an orifice (Knudsen method). For the former measurements the samples were in the form of either cylinders or annular rings; for the latter the finely divided material was placed inside buckets constructed of sheet molybdenum. The annular rings were approximately 2.8 cm. 0.d. X 1.3 cm. i.d. X 1.0cm. thick; the cylinders were approximately 2.5cm. long X 2.3 cm.diameter. Themolybdenum buckets were approximately 1.9 cm. long X 1.9 cm. diameter andhadeffusion holes0.318cm.and0.398cm. in dia., respectively. Since the solid samples changed size due to evaporation they were measured between runs. The areas were corrected to take into account the increase due to thermal expansion.The beryllium samples used were of two sorts : vacuum(1) This work was carried out under contract between the Office of Naval Research and the Ohio State University Research Foundation. The coefficient, u, is the condensation coefficient-sometimes called the accommodation coefficient; however, since this is ambiguous in that the term has been preempted for the thermal accommodation, we feel that the more descriptive term "condensation coefficient" is preferable. (4a) Johnston and Marshall, ibid., 62, 1382 (1940).cast and experimentally sintered. Both of these materials were used for the Langmuir type measurements whereas for the Knudsen measurements the vacuum cast material was used exclusively. All of the vacuum cast material used was of high purity. The analysis of the material used in the Langmuir runs is A1 0.06%, Cr O.Ol%, Cu O.Ol%, F e 0.07%, Mg O.Ol%, Ni O.Ol%, Si 0.03%, together mth entirely negligible amounts of several other impurities, and Cr O.Ol%, Cu...

The Kinetics of the Reactions of Beryllium with Oxygen and Nitrogen and the Effect of Oxide and Nitride Films on its Vapor Pressure

“…Excellent agreement is found with the results of Holden, Speiser, and Johnston (12). The effect of oxide and nitride films on the vapor pressure was also studied.…”

“…An energy of activation of 75,000 cal per mole was calculated over the temperature range of 725 ~ to 925~ This is to be compared to an energy of activation of 50,300 cal per mole for the oxidation reaction. The value of 75,000 cal per mole was the highest energy of activation that we ob- served and is close to the value of AH0 ~ for the evaporation of beryllium (12).…”

“…During the course of this study, it became necessary to determine the vapor pressure of beryllium for our particular apparatus although a careful study of the vapor pressure of beryllium has been made recently by Holden, Speiser, and Johnston (12).…”

Sulfur “concrete” for lunar applications – Sublimation concerns

“…Also known as a ''sticking'' coefficient, a v is a measure of the difficulty for atoms to either attach to or be released from a surface, and ascertaining its value is fraught with difficulty (McEachern and Sandoval, 1973). Values of a v % 1 were reported for tungsten (Langmuir, 1913b), copper and iron (Marshall et al, 1937), nickel and nickel oxide (Johnston and Marshall, 1940), and beryllium (Holden et al, 1948).…”

EFFECTS OF LIQUID PROPELLANT EXPLOSIONS ON NUCLEAR ROCKET ENGINES. Final Report.

“…Vaporization rates as a function of surface temperature are shown in Figure 4. Data for this plot were obtained under vacuum conditions (11). In the presence of oxygen or nitrogen, the rate of evaporization is considerably reduced due to the formation of protective coatings (9).…”