The Adsorption of Cesium on Tungsten Using Thermionic Emission

The Adsorption of Cesium on Tungsten Using Thermionic Emission 

The study of the adsorption of cesium on tungsten is particularly fruitful because the rate of adsorption and the amount adsorbed can be measured easily and also because it is possible to measure the rate of evaporation of electrons, atoms, and positive ions from the same surface. From these data also can be deduced the nature of the adsorbed species and the forces between the adsorbed species and the tungsten atoms (3,4). 

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 

= A X electronic charge in coulombs X tungsten surface area (1) 

It is convenient to define a quantity 8 as the fraction of the surface covered by an adsorbate. The surface will be said to be covered with a monolayer, and 6 will be equal to 1.00 when every available site is occupied. The number of available sites per square centimeter will differ from one crystallographic plane to the next it will also depend on the size 

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III. The Adsorption of Cesium on Tungsten Using Thermionic Emission. 141... 

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