Desorption equation

Equation (88) represents the general adsorption/desorption equation in a multi-component solution system which can be used in the general transport equation... 

The additional aspect of CO desorption, equation (9.1.42), leads to the disappearance of the CO-poisoned state [15] because at every value of Vco adsorbed CO molecules are able to leave the surface. 

In curves 4 the system behaviour is shown under the conditions of curves 3 but now including the effect of A-desorption, equation (9.1.42). In this case we obtain a reactive state. We observe a phase transition of the first order at y — 0.268. For Yco < U the lattice is completely occupied by particles B. A phase transition point y2 does not exist but we obtain a smooth transition over a wide range of kco Due to the desorption the state poisoned by A does not exist. 

So, this is an example of such theoretical treatment when thermodynamic and kinetic characteristics are not self-consistent with each other. The theoretical failure above occurred due to the desorption equation used, that does not allow for the real distribution of the Hg atoms, i.e., the macroscopic equation used does not describe the two-dimensional adspecies condensation appearing in the experiment. It should be taken into account that adspecies are in two coexisting phases, so the total desorption rate is a sum of the desorption rates from these phases [146,152]. 

The preconcentrator is a mechanical system used to concentrate the limited mass of explosive delivered from the sample collection subsystem [8], From the sample collection subsystem airflow, the preconcentrator adsorbs explosives (vapor or particulate). The adsorbing surface is then heated to desorb the explosives into the airflow stream for delivery either to a detector or another preconcentration stage. Concentration of the explosives sample occurs because the explosive contained in the sample collection airflow prior to adsorption is now contained in a smaller volume after desorption. Equation 2 shows the relationship between concentration and volumes related to the preconcentrator. 

The feasibility of this sequence has been dt monstrated by Maitlis and coworkers by a model reaction using the well-characterized binuclcar complex (4). Upon pyroIy7ing this complex at temperatures of 350 C, the following product composition was observed methane (4g ). ethylene (20%), ethane (2%), and propene (30%). The formation of propene is explained by insertion of two methylene groups (Equation (27)) which is followed by (J-elimination and desorption (Equation (28 [157],... 

In order to fully describe the progression of adsorbate coverage during electrodeposition, mass balance is imposed by summing the individual processes,/ adsorption and desorption (Equation 2.2), geometry (Equation 2.4), consumption (Equations 2.5 and 2.6) and reduction (Equation 2.9) ... 

In this way a great deal can be learned from carrying out a desorption experiment and it could be said that this technique has perhaps the greatest information content of any used in surface science. The basic kinetic parameters can be determined, as also can coverage (by integration of the desorption peak), and this is a parameter not so easily (or accurately) found from most other techniques. However, it is rare for desorption experiments to show simple integral order desorption. More typically the desorption equation should be written as follows. 

Like the Edwards line shape analysis, the mathematics involved is fairly complex and for brevity is not repeated in detail here. They began by making the general desorption equation dimensionless, viz. 

Replacing the fugacity by coverage p = (1/T/0 )c ewe arrive at the Langmuir desorption equation, which shows the dependence of the desorption rate on coverage... 

For a protein incorporated in a matrix, the rate of release (i.e., the effective diffusion coefficient and Ft) depends on the molecular weight of the protein, the size of the dispersed particles, the loading, and the molecular weight of the polymer. For example, matrices of EVAc containing dispersed particles of bovine serum albumin (BSA) release protein for an extended period (Figure 9.11). The rate of release from the matrix depends on BSA loading (the number of BSA particles dispersed per unit volume of matrix) and BSA particle size. The rate of release from these matrices can be characterized by an effective diffusion coefficient or tortuosity, which must depend on the characteristics (i.e., particle size and loading) of the device. Tables 9.2 and 9.3 list the tortuosity values calculated from fits of the desorption equation to available literature data of protein release from EVAc slabs. 

The value of the activation energy of desorption strongly depends on a surface coverage ( oh) and increases with decreasing oh- The corresponding desorption equation can be written as follows... 

Analysis of the TPD curves allowed Pokrovskiy and coworkers [15,29,69] to determine the activation energy of desorption Ej) and the pre-exponential factor (k ) for the desorption rate constant in desorption equation, which can be represented as follows [11,15,29,73]... 

Equations T3.5 and T3.6 in Table 4.3 are obtained by considering the activation energy for diffusion as a function of material moisture content. Equations T3.7 through T3.10 are not based on the Arrhenius form. They are empirical and they use complicated functions concerning the discrimination of the moisture and temperature effects (except, of course. Equation T3.7). Equation T3.11 is more sophisticated as it considers different diffusivities of bound and free water and introduces the functional dependence of material moisture content on the binding energy of desorption. Equation T3.12 introduces the effect of porosity on moisture diffusivity. 

For a protein incorporated in the usual slab matrix, the rate of release, and therefore the effective diffusion coefficient and Fx, depend on the molecular weight of the protein, the size of the dispersed particles, the loading, and the molecular weight of the polymer. Tables I and II list the tortuosity values calculated from fits of the desorption equation [Eq. (4) or (5)] to available literature data of protein release from EVAc slabs. 

Equation (7.94) can be applied under the following conditions Homogeneous surface, i.e. all adsorption sites are the same no interaction between adsorbed molecules without re-adsorption during desorption and without new diffusion process after desorption. Equation (7.95) can be only applied to the first order desorption process. 

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