The adsorption of hydrogen on tungsten

Abstract

When a gas atom or molecule strikes a solid surface it may either rebound, the collision being accompanied by an interchange of energy, or it may be adsorbed. In order to obtain a satisfactory interpretation of either type of phenomenon it is necessary to know the nature of the atoms concerned. This is comparatively easy for the gas, but the solid requires closer attention. The essential condition is that the surface of the solid is completely freed from adsorbed films of impurity before the experiment starts and remains free. In the earlier papers in which an account of the development of the present work on this problem has been given, it has been shown that the average interchange of energy when gas atoms strife and rebound from a slightly hotter metal surface is very markedly affected by the presence of such adsorbed films. The accommodation coefficient is a quantitative measure of the efficiency of this interchange and for neon with a tungsten surface the removal of all adsorbed films caused the accommodation coefficient to change almost by an order of magnitude (0.6 for an ordinary surface covered with adsorbed films of impurity and about 0.07 or 0.08 for a bare tungsten surface). This suggested that the accommodation coefficient of neon could be used as an indicator in studying the adsorption on bare tungsten of known gases mixed with the neon. The application to the study of the adsorption of hydrogen of the method that has been developed with this idea as a basis is described in 2.

A Kinetic Approach to the Inactivation of Zinc by Various Soil Constituents.

“…The first evidence for this was obtained by Roberts (1935). He measured heats of adsorption of hydrogen on tungsten surface that was considered to be quite homogeneous.…”

“…Langmuir (1918), Paneth and Vorwerk (1922) and Roberts (1935) have shown that a definite adsorption limit occurs, beyond which further molecules cannot be adsorbed readily. When the surface area is known, the limit is found to correspond to the existence of a unimolecular layer.…”

The friction of clean metals and the influence of adsorbed gases. The temperature coefficient of friction

“…The work of Roberts (1935) and Van Cleave (1938) has shown th at both these gases form chemisorbed films on tungsten, but it seems that such films can possess little or no frictional properties on the metals. This result is in harmony with the observations of Holm and Kirschstein (1936) th a t oxygen de creased the adhesion between metals, while hydrogen and nitrogen did not.…”

“…However, in the case of tungsten some information is available. Langmuir and Villars (1931) have shown th a t the oxide film on this metal begins to evaporate a t 1500° K. Later, Roberts (1935) made a thorough study of the conditions under which the surface of this metal may be cleaned, and found th at a tungsten wire had to be heated in excess of 2000° K before the oxide film was completely removed. Bosworth and Rideal (1937) have observed th a t the fraction of a tungsten surface which remains covered by adsorbed oxygen a t 1600° K is only 0*3.…”

“…The friction could only be restored to its initial high value by evacuating the apparatus and reheating the metals to a high temperature. Roberts (1935) has shown th a t if oxygen is admitted at a low pressure (10-3 to 10~4 mm.) to a clean tungsten surface at room temperature, the surface is immediately covered by the gas.…”