Knudsen effusion method

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. 

The most usual effusion methods are based on equilibration of a substance in a Knudsen cell. A small fraction of the vapour molecules effuse through a small effusion orifice in the lid of the cell (diameter from 0.1 to 1 mm), ideally without... 

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. 

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. 

In the Knudsen effusion method a substance is enclosed in a sealed container into which a very small hole is drilled. This hole must be knife-edged and the mean free path of the vapour must be 10 times the diameter of the hole. In its simplest form an experiment proceeds as follows. The Knudsen cell, with sample in it, is carefully weighed and then heated in a vacuum at the requisite temperature for a set time. The cell is then re-weighed and the weight loss is measured. However, it is now more usual to continuously measure the weight of the cell. If the molecular weight and surface area of the sample is known the vapour pressure can be found. 

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. 

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