1958 年 27 巻 2 号 p. 83-88
Effect of adsorption in producing and measuring vacuum usually becomes predominant at the vacuum higher than 10-3mmHg, and its significance is revealed by the recent developments in ultra high vacuum techniques. This paper is divided into Part 1 and Part 2.
In Part 1, it is shown that approximate treatments of gas flow in high vacuum as of a kind of diffusion problem give some equations, which are useful to clarify the effect of adsorption in non-stationary gas flow problems. Diffusion constant is expressed including terms of the sticking probability, the time of adsorption and the roughness factor as well as the usual geometrical factor. As a rule, the rate of migration of a molecule is determined by two terms. One of which is the average time spent by a molecule to terminate a flight from a point on the wall to the next point on it, and the other the time spent on the wall, the duration of which should be correlated with the characteristics of adsorption. Calculations give that the average time spent during the stay on the wall is longer in some cases than the time of flight.
As to geometrical factors, the effect of adsoption depends, of course, to surface to volume ratio as evidenced by the flow of gas through a narrow pipe or a fine pin-hole.