The Dynamics of Adsorption Micromeritics（吸附微粒学的动力）.pdf

The Dynamics of Adsorption In typical environments where gas molecules and solid surfaces coexist, a vast number of col- lisions between the two occur each second. However, the interaction between a molecule and a solid surface at the point of collision may not be exactly what you imagine. When a molecule approaches a surface from an arbitrary direction and strikes the surface, one of two things happens. Either the molecule rebounds like a billiard ball striking the cushion of a billiard table or the molecule sticks to the surface. Those that stick remain for a short time, then fly off at an angle unrelated to the angle at which they arrived. The latter phenomenon is the more normal one. As molecules strike repeatedly upon the solid surface and linger for a time, there develops a higher concentration of gas molecules at this surface than in the bulk of the gas. This is somewhat analogous to the fact that you will find a higher concentration of automobiles at an intersection with a stop sign compared to the concentration of autos along comparable section of street leading to the intersection. In the case of gas molecules, the phenomenon is called adsorption. You may expect to find adsorption of molecules in every case where a surface is exposed to a gas. Closely examining the surface upon which the molecules are adsorbing reveals that both the molecules composing the solid material and the adsorbed molecules are vibrating. These vibrations are expected since we know that the average kinetic energy (motion) of molecules is zero only at the temperature of absolute zero. The absorbed gas molecule attaches to an adsorption site and rides the “bucking” surface until thrown off to rejoin the chaos in the gas phase. It may happen that before being ejected free of the surface, the adsorbed molecule will be bumped around to many other adsorption sites. The intensity and frequency of the surface motion are directly related to the temperature of the soli