Techniques Knudsen effusion

Vapor pressures of phases in these systems were measured by the Knudsen effusion technique. Use of mass spectrometer-target collection apparatus to perform thermodynamic studies is discussed. The prominent sublimation reactions for these phases below 2000 K was shown to involve formation of elemental plutonium vapor. Thermodynamic properties determined in this study were correlated with corresponding values obtained from theoretical predictions and from previous measurements on analogous intermetallics. 

Vapor pressures were determined by using the Knudsen effusion technique. Effusion rates through and orifice contained in each sample cell were measured as a function of temperature by use of a mass spectrometer/target collection... 

Knudsen effusion technique and equation, vapor pressure determination. 100-101... 

Knudsen effusion/thermogravimetry technique, extrapolated Clausius-Clapeyron eq., Oja Suuberg 1998)... 

Malaspina, L., Bardi, G., Gigli, R. (1974) Simultaneous determination by Knudsen-effusion microcalorimetric technique of the vapor pressure and enthalpy of vaporization of pyrene and 1,3,5-triphenylbenzene. J. Chem. Thermodyn. 6, 1053-1064. 

Boehncke, A.. Martin. K.. Muller. M.G., and Cammenga, H.K. The vapor pressure of lindane (Y-l,2,3,4,5,6-hexachlorocyclo-hexane) - A comparison of Knudsen effusion measurements with data from other techniques, /. Chem. Eng. Data, 41 (3) 543-545,1996. 

Two papers reported powder pattern crystallographic results. The paper by Santos et al. (7) stood out from the rest because it presented a collection of more classical physical chemistry experiments. In this paper the authors described the use of micro-combustion calorimetry, Knudsen effusion to determine enthalpy of sublimation, differential scanning calorimetry, X-ray diffraction, and computed entropies. While this paper may provide some justification for including bomb calorimetry and Knudsen cell experiments in student laboratories, the use of differential scanning calorimetry and x-ray diffraction also are alternatives that would make for a crowded curriculum. Thus, how can we choose content for the first physical chemistiy course that shows the currency of the discipline while maintaining the goal to teach the fundamentals and standard techniques as well ... 

Using the Knudsen effusion technique and highly purified samples of lindane [(y-HCH), one of the most widely used and most frequently detected organochlorine pesticides see Willet et al. (1998)], Boehncke et al. (1996) determined the vapor... 

Knudsen-effusion technique, extrapolated from 37-54.92°C, Smith et al. 1964)... 

In the first experiments to measure the vapor pressure of metallic Bk, using Knudsen effusion target-collection techniques, the preliminary data were fitted with a least-squares line to give a provisional vaporization equation for the temperature range 1326-1582 K, and Ai 298 was calculated to be 382 18 kJ/mol (128). The crystal entropy of berkelium metal at 298 K (S s) had been estimated earlier to be 76.2 1.3 J K 1 mol-1 (129), and later, to be 78.2 1.3 J K 1 mol-1 (124). 

Later data on the vapor pressure of berkelium metal over the temperature range 1100-1500 K, obtained by using combined Knudsen effusion mass spectrometric and target collection techniques, have been published in 1982 (124). The vaporization equations obtained were... 

We have developed several new measurement techniques ideally suited to such conditions. The first of these techniques is a High Pressure Sampling Mass Spectrometric method for the spatial and temporal analysis of flames containing inorganic additives (6, 7). The second method, known as Transpiration Mass Spectrometry (TMS) (8), allows for the analysis of bulk heterogeneous systems over a wide range of temperature, pressure and controlled gas composition. In addition, the now classical technique of Knudsen Effusion Mass Spectrometry (KMS) has been modified to allow external control of ambient gases in the reaction cell (9). Supplementary to these methods are the application, in our laboratory, of classical and novel optical spectroscopic methods for in situ measurement of temperature, flow and certain simple species concentration profiles (7). In combination, these measurement tools allow for a detailed fundamental examination of the vaporization and transport mechanisms of coal mineral components in a coal conversion or combustion environment. 

Using separate gravimetric Knudsen effusion and KMS techniques, we have obtained data for the heat of vaporization to form K2S04(g), and detailed results will appear elsewhere ( ). From thermal data, the dissociation pressure, as represented by the reaction,... 

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). 

AjH° is calculated from that of the crystal by means of A H°(298.15 K) = 55.15 0.1 kcal mol". The selected value of sub ° is an average of those obtained by 3rd law analysis of vapor pressures measured by manometry ( ), torsion effusion (4) and entrainment (8-10). Mass-spectrometric data (, 2) are in reasonable agreement and so is the average of two Knudsen-effusion studies (6, 7). Several techniques (2, 4, 6) were used to show that the amount of dimer in the vapor is negligible up to at least 1000 K. JANAF analyses of the vaporization data are summarized as follows ... 

Drowart and co-workers have used the Knudsen effusion-mass spectroraetric technique to determine the vapor equilibrium over the systems SiC-graphite (1 ) and boron-silicon-graphite (2 ). 3rd law analysis of the partial pressures of Si and SiC yields the results summarized below. The adopted value, A.H (298.15 K) 172 8 is the mean of the two results and the uncertainty... 

Peterson and Hutchison (1 ) used a weight loss Knudsen effusion technique to observe vapor pressures of the liquid at 18 temperatures ranging from 1076 K to 1294 K. Our 2nd and 3rd law analyses of these data, after rejection of one point due to... 

Peterson and Hutchison (1, used a weight loss Knudsen effusion technique to observe vapor pressures of the liquid at 20... 

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