Effusion rates, vapor pressure determination

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... 

To determine the effect of orifice size on vapor pressure, five different orifices were used to measure the effusion rates at 25 °C. of one compound, 2-chlorcMt-aminopyrimidine. Carson, Cooper, and Stranks (6) have shown that the net rate of effusion is directly proportional to the flux (rate of effusion per unit area) if other factors are constant. That is, a graph of... 

If even at the lowest heating rate only decomposition occurs (no change of TG signal if different carrier gases are used), the vapor pressure caimot be determined by ambient pressure TGA, and complimentary HV effusion... 

Knudsen effusion cells are used to determine vapor pressures of high-temperature materials. For example, a Knudsen cell is filled with tungsten and heated to 4500 K in a vacuum. Measurements show that the cell loses mass— assumed to be W vapor—at the rate of 2.113 grams per hour out of a hole that is 1.00 mm in area. Calculate the vapor pressure of W at 4500 K. 

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