Adsorption sticking ratio

CigTAC behaves very differently from CieTAB. There is no increase in sticking ratio at the cmc, either with or without KCl. A lack of direct involvement of micelles in the adsorption process may be a consequence of the decreased level of ion... 

Sticking coefficient is the ratio of the rate of adsorption to the rate at which the adsorptive strikes the total surface, i.e., covered and uncovered. It is usually a function of surface coverage, of temperature and of the details of the surface structure of the adsorbent. 

This section considers the traditional description of the process where a molecule approaches a solid surface and eventually is trapped by the potential. A convenient way to gain access to this problem is through the consideration of the rate of adsorption. In the most simple case, the rate of adsorption is proportional to the number of molecules impinging per unit time on the surface, the so-called particle flux, and to the (dimensionless) efficiency with which an impinging particle actually sticks to the surface, i.c. the so called sticking probability. The initial sticking coefficient. vu is the ratio of the number of adsorbed particles rrs and the number of impinging particles for the uncovered surface. Therefore,... 

The sticking factor gives the ratio of the number of activated collisions divided by the total number of collisions, whereas in Eq. (9.65) gives the rate of adsorption (in mol cm s" ), with an activation energy Ea for adsorption at the external surface, the other parameters having their usual meaning. 

At the same time it is clear that such a setting makes accurate rate measurements difficult. The sticking coefficient is determined by [NJN — 1] and for N0jN 1 this ratio would have to be known with great accuracy. In the other extreme, when SF SE we can approximate a closed system. This maximizes the pressure drop in the cell on adsorption, but brings with it all the evils of a closed system. In practice, the adjustment of SE/SF must therefore be varied to suit each system. 

Sticking probability Ratio of the rate of adsorption to the rate of collision of the gaseous molecule with the surface. 

A H2 molecule impinging on the surface can be physisorbed or dis-sociatively chemisorbed or rejected. In order to stick on the surface and to dissociate the molecule has to dissipate its kinetic, rotational and vibrational energy by the excitation of phonons and possibly of electron-hole pairs in the substrate. Thus, the metal lattice and possibly the conduction electrons serve as a heat bath in the adsorption (and desorption) process. The ratio of the number of molecules which stick on the surface to those which impinge on the surface is called sticking coefficient s. It depends on Jthe coverage 0. The initial sticking coefficient for 0 = 0 is of the order of 0.2 to 0.5 for H2 on clean transi-... 

---