Knudsen effusion apparatus

Twin Knudsen Effusion Apparatus for Small Samples of Radioactive... 

At Los Alamos a new Knudsen effusion apparatus has been constructed to take specific advantage of the principles described. 

Figure 3. Cross-sectional view of UHV target-mass spectrometer Knudsen effusion apparatus...

Ferro et al. (67) used a coupled torsion-Knudsen effusion apparatus to measure the vapor pressures of o-. m. and p-chlorobiphenyls. The apparatus, as shown in Figure 3.37, consists of a conventional torsion-Knudsen effusion... 

Figure 3.37. Coupled torsion-Knudsen effusion apparatus of Ferro el a). 16). A, electro-balance B. tungsten torsion wire C. reflecting, mirror D. braking disc E. torsion cell F. twin cell G. thermostatic sand bath.

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. 

The apparatus and the special accessories necessary for this work are schematically illustrated in the Fig. 22. The reaction chamber used for the Knudsen effusion method is positioned above the balance. The reaction chamber is thermostatically controlled and connected with a cold trap. Both of them are protected from outside temperature effects by an insulating material. This protection leads to a more constant temperature and a straight line in the recorded loss in weight. 

Hastie [131] coupled for the first time a quadrupole mass spectrometer with a Knudsen cell. One of the quadrupole mass spectrometer - Knudsen cell systems used at our laboratory is shown in Fig. 4. The system has been developed to study small alkali metal clusters under equilibrium conditions (see Sect. 3.2). Broad-band photoionization by a 1 kW Hg/Xe lamp is used for the first time in Knudsen effusion mass spectrometry to reduce fragmentation. Other quadrupole mass spectrometer - Knudsen cell systems have for example been developed by Hilpert [132, 133], Fraser and Rammensee [134], Plante [135], Ono et al. [136], Kematick et al. [137], and Edwards et al. [138]. Cryogenic pumping is used in the device by Hilpert to reduce mercury background ion intensities for the study of amalgams [132], The instruments described in Refs. 134,135 use a chopper to modulate the molecular beam from the Knudsen cell. Interfering background ion intensities can, thereby, be subtracted. The apparatus developed by the authors of Refs. 137, 138 renders possible the simultaneous application of Knudsen effusion mass spectrometry and the mass-... 

The vaporization studies of the actinide/noble-metal compounds RujU, Ir2Pu as well as those of the Rh-Pu and Pt-Pu systems (see Table 7) were carried out by an apparatus combining Knudsen effusion mass spectrometry... 

The incongruent vaporization of the compounds of the Ta-Al system and of WSCj (see Table 7) was studied by an apparatus combining Knudsen effusion mass spectrometry and mass-loss measurements. Schiffman et al. [240] obtained an enthalpy change of AH298 = 311 3 kJmoP for the reaction of evaporation 1/2 WSe Cs) 1/2 W(s) -h Se(g). 

Figure 3.36. Apparatus used by Wiedemann (60) for Knudscn effusion vapor-pressure measurements. A, Knudsen cell B, cold trap C. ionization gauge D. balance and housing E, diffusion pumps F. thermostatically controlled reaction chamber.

The Knudsen and torsion-effusion methods have been combined in a single apparatus, for example by Lindscheid and Lange. In this work the torsion cell was suspended from a microbalance, thus enabling simultaneous observations of mass loss and cell rotation to be made. The values of vapour pressure calculated from the two sets of results can be combined through the Knudsen and torsion-effusion equations to obtain the molar mass of the vapour species. Lindscheid and Lange carried out such measurements for Fe, Co, and Ni, and for Ni + Co alloys. 

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