Tungsten vapor pressure

Tungsten hexafluoride is shipped as a Hquid under its own vapor pressure in nickel or steel cylinders in quantities of 45 kilograms per cylinder or less however, it has been shown that the purity of WF packaged in steel cylinders can degrade over time (21). It is classified as a corrosive Hquid by the... 

Another high-temperature cell (Fig. 8 g, up to 2400 °C, can be produced from tungsten. Tungsten Knudsen cells are used primarily for high-temperature vapor pressure measurements, e.g. for metal oxides. They are suitable also for metals when graphite linings are applied to the inner surface. The vapor pressure can be determined... 

This vapor pressure can be deduced from kinetic theory and the rate of arrival of Cs atoms per square centimeter per second (3,4). This arrival rate. A, can be calculated from the measured value of the saturation positive ion current. Langmuir first showed that if the tungsten is hot enough every cesium atom that strikes the surface evaporates off as a positive ion of cesium. This saturated positive ion current, i.p, can be measured easily with a medium sensitive galvanometer when the collector is negative. It is related to A by the equation... 

Suppose the vapor pressure is adjusted so that the arrival rate. A, is about 2.6 X 10 cesium atoms/cm.Vsec. If the temperature of the tungsten filament is about 550°K., the surface will be covered with more... 

Fi(i. 13. Distribution of thermionic electron emission of a tungsten-monocrystal wire in cesium vapor in the [Oil] zone at A 2,000°, B 900°, C 850°K. Cesium vapor pressure corresponds to room temperature [according to Johnson and Shockley (35)]. 

Tungsten hexachloride has not been studied as extensively as the fluoride for tungsten deposition, since the chloride is a solid at room temperature and must be heated to 170°C to achieve a reasonable vapor pressure. Of course, all... 

Table 1(d) on vapor pressure of the metals shows the results of the calculations for the metals tungsten, chromium, iron, and magnesium. 

With the exception of tungsten and zirconium (not calculated) the metals are volatile at elevated temperatures in vacua of the order of 10-10 atm. At 1000°C. the vapor pressure of chromium is 10-8-61 atm., that of iron 10-8-8 atm., and that of magnesium 10-1-5 atm. Thus at 1000°C. the vaporization of chromium and iron is appreciable. 

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