Effusion method, vapor pressures

Samples were analyzed by gas chromatography (GC). Water solubility was determined by equilibration of analytical grade material with water at constant temperature. Equilibrium was approached from both under and super saturation conditions and samples were analyzed by GC. Vapor pressures were determined by the Knudsen effusion method. 

De Pablo, R.S. (1976) Determination of saturated vapor pressure in range 10-1—10 torr by effusion method. J. Chem. Eng. Data 21, 141-143. 

Swan, T.H., Mack, Jr., E. (1925) Vapor pressures of organic crystals by an effusion method. J. Am. Chem. Soc. 47, 2112-2116. Swann, R.L., Laskowski, D.A., McCall, P.J., Vander Kuy, K., Dishburger, H.J. (1983) A rapid method for the estimation of the environmental parameters octanol/water partition coefficient, soil sorption constant, water to air ratio, and water solubility. Residue Rev. 85, 17-28. 

For measuring low vapor pressures within the range from 1 to 10-6 torr, the well-known Knudsen effusion method was applied (see Section 2.2.). The alumina Knudsen cell was used for vapor pressure measurements of gold and of sodium chloride. The orifice is located in the center of the lid. 

Ideally, the Knudsen effusion method can be applied for determination of vapor pressures if molecular flow is verified (p < 10 3 torr). Precise measurement of vapor... 

Da Silva and Monte [5] have measured the vapor pressure of crystalline benzoylacetone by the Knudsen mass-loss effusion method over the temperature range, 292-302°C. One set of their data is given in Table 8.5. As the vapor pressure is low, and the temperature range is small, use the... 

Goodman, M.A. Vapor pressure of agrochemicals by the Knudsen effusion method using a quartz crystal microbalance, J. Chem. Eng. Data, 42(6) 1227-1231, 1997. 

The vapor pressure of liquid EuC12 was measured by a target-collection Knudsen effusion method. For the congruent vaporization the pressure of EuCla(g) may be represented over the temperature range 1135-1569 K by the equation... 

Li, X.-W, Shibata, E., Kasai, E., Nakamura, T. (2002) Vapor pressure determination for dibenzo-p-dioxin, dibenzofuran, octachlo-rodibenzo-p-dioxin and octachlorodibenzofuran using a Knudsen effusion method. Mater. Transact. 43, 2903-2907. 

Cubicciotti et al.5 used a torsion-effusion method to determine decomposition pressures in the range 723 to 767 K and found only S02 in the vapor. They surmised that the salt is in metastable equilibrium with respect to disproportionation below 775 K. 

Vapor pressures at ambient temperatures of a number of pesticides can be determined by using a du Pont 900 differential thermal analyzer to measure boiling points for a series of pressures down to 10 mm., or by using an effusion method for compounds having vapor pressures from 10 3 to 10 7 mm. Less than 100 mg. of the sample are required in either case. Accuracy can be determined by comparison with direct measurements available in the literature. Vapor pressures for phenoxy herbicide esters are lower than values reported in the literature. 

Vapor pressures obtained by the Knudsen effusion method are shown in Table II. The precision of the determinations is indicated by the 95% confidence interval computed either from an average of experimental determination or from the standard deviation of the regression equation. 

Table II. Comparison of Vapor Pressures by the Effusion Method with Literature Results...

Table III. Vapor Pressures of Esters of Phenoxyacetic Acid Herbicides by the Knudsen Effusion Method...

Corrections in Knudsen Effusion Method. Two corrections must be applied in the Knudsen effusion method to prevent large errors correction for (1) finite thickness of the orifice plate and (2) pressure drop owing to loss of vapor through the orifice. The first correction is necessary because the Knudsen effusion equation shown below is derived from an orifice with negligible thickness. Orifices whose thicknesses are an appreciable fraction of their diameter have collimating action that diminishes their effective area. A correction factor attributed originally to Clausing... 

Plante, E. R. "Vapor Pressure Measurements of Potassium Over K20-Si02 Solutions by a Knudsen Effusion Mass Spectrometric Method", 1979 p. 265, ibid, (8). 

Metals. Kruglikh, et al. (104) measured saturated vapor pressures of erbium, samarium, and ytterbium by the Knudsen effusion method, and standard (average) sublimation entropies of 18.4, 20.7, and 25.6 cal./(gram atom °K.) were derived. Nesmeyanov, et al. (146) studied the vapor pressure of yttrium by an integral variant of the effusion technique. Similar studies at higher temperatures by Herrick (70) on samarium metal have been interpreted in good accord by both first and second law methods. Ideal gas thermodynamic functions have been derived from 100 °K. to 6000°K. at 100° intervals for both actinide and lanthanide elements by Feber and Herrick (45). 

The enthalpy of formation of YF3 was determined by Rudzitis, Feder, and Hubbard 164) using fluorine bomb calorimetry. NdCla was done by solution methods (179), and the enthalpies of formation of LaFs and PrFa were determined by Polyachenok 161) who employed an indirect equilibration technique. A recent torsion-effusion study of the vapor pressure of CeFs 115) yields second and third law values for the enthalpy of sublimation. The thermodynamics of the chlorination of rare earths with gaseous chlorine have also been investigated 144). Gibbs energies of formation were determined for CeClg by solid-state electromotive force techniques 41). 

Peterson and Hutchison (1, 2) have measured vapor pressures (1114-1304 K) for liquid SrBrg by the Knudsen effusion method. Results of 2nd and 3rd law analysis of these pressures are tabulated below. We assume that the dlbromlde monomer was the only vapor species present. Mass spectra for some of the other alkaline earth dlhalldes (3) Indicate that the saturated vapor consist predominantly of the metal dlhallde monomer which agrees with predictions which were made by Brewer et al. (4) for the dlhallde molecules. Included in the table Is a value for a H derived from a 3rd law analysis of a single vapor pressure point determined by Stock and Heynemann (5) and tabulated by Brewer et al. (4). 

Mass spectrometer Boiling Point Torsion-effusion Torsion-effusion "Bell" method (total vapor pressures)... 

The total vapor pressures of KF(g) and K F Cg) over KF(cr, t) have been determined by many investigators using the boiling point (1, 2, 5), Knudsen-effusion (3), transpiration ( ), and torsion-effusion (6) methods. A method of trial and error is employed to select the appropriate values for Ag H (KF, cr, 298.15 K) and t, 298.15 K) such that by use of these... 

---