Desoiption kinetics

Siuface rheology has to be taken into account when describing siuface movement and adsorption/desoiption kinetics. Some brief information on surface rheology is given in Section 3.2. The rate of normal and lateral surfactant transport and dynamic surface tension response on external disturbances depends on relaxation properties, into which Section 3.1. introduces. 

It is shown how the new approadi to adsoiption/desoiption kinetics based on the Statistical Rale Theory can be successfully applied to describe the kinetics of dissociative gas cbemisorplion on solids. 

Abstract. In the paper we consider the problems with moving bound that model the kinetics of hydrogen desorption from hydrides of metals. Change of phase, desoiption processes and size reduction effect are taken into consideration. Equations are derived at various assumptions for the experimental method of thermal desoiption spectrometry. As the high-temperature TDS-spectra peaks are considered, the diffusion may be assumed to be fast. Therefore ordinary differential equations are sufficient. We present the results of numerical experiments for the models with bulk and surface desorption. 

Figure 3. Determination of adsorption kinetics fiom desoiption mns after varied adsorption periods. (Schematic).

Ashida, M. et al.. Kinetics of proton adsorption-desoiption at TiO -HjO interface by means of pressure-jump technique, J. Colloid Intetf. Sci.. (ft. 219. 1978. 

Wu. Ch.H. et al.. Modeling competitive adsorption of molybdate, sulfate, and selenate on y-ALO, hy the triple-layer model, J. Colloid Interf. Sci., 233, 259, 2001. Hachiya. K. et al.. Static and kinetic studies of adsorption-desorption of metal ions on y-ALO, siuface. 1. Static study of adsorption-desoiption, J. Pltys. Chem., 88, 23, 1984. Tamiu a, H.. Katayama. N., and Furuichi, R.. Modeling of ion-exchange reactions on metal oxides with the Frumkin isotherm. 1. Acid-base and charge characteristics of MnO,. TiO,. Fe,O4. and ALO, surfaces and adsorption affinity of alkali metal ions. Environ. Sci. Technol.. 30. 1198. 1996. 

During tire studies caiiied out on tliis process some unusual behavior has been observed. Such results have led some autliors to the conclusion that SSP is a diffusion-controlled reaction. Despite tliis fact, the kinetics of SSP also depend on catalyst, temperature and time. In the later stages of polymerization, and particularly in tire case of large particle sizes, diffusion becomes dominant, with die result tliat tire removal of reaction products such as EG, water and acetaldehyde is controlled by tire physics of mass transport in the solid state. This transport process is itself dependent on particle size, density, crystal structure, surface conditions and desoiption of the reaction products. 

As a prelude to the development of kinetic rate expressions for heterogeneous chemical reactions, if A reacts with B, for example, then the next step in the mechanism is ha + Ba, forming an activated complex on the snrface. Each reversible step in the seqnence above is characterized by a forward rate constant adsoiption for adsoiption, with units of mol/area time atm, and a backward rate constant A ,desoiption for desorption, with units of mol/area time. The ratio of these rate constants adsorption/ h, desoiption defines the adsorption/desorption equi-... 

Finally, if the rate constants of the two desoiption reactions B and B are approximately the same, the two branches proceed with similar rates, and a vqh" between 1 and 2 characterizes the kinetics. 

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