Oxygen diffusion, activation energy for

Based on literature sources and assuming an Arrhenius-type equation to hold, values of D (31) and Cq (32) at 20 and 30 C have been used to estimate the apparent activation energies for oxygen diffusion and solubility to be... 

TABLE 5-6. Difiusion parameters and activation energy for oxygen diffusion in rare earth sesquioxides. (Reprinted with permission from ret 65. Copyright 1968 American Ceramic Society.)... 

The overall activation energy for both processes is about 60 kJ/mol which is one half of the value for the activation energy of oxygen diffusion into the crystalline region of HDPE [65]. The lower values of activation energy for oxidation of allyl radicals show on the participation of reactions of such macroradicals which are in the close proximity of amorphous regions. 

One example of the use of molecular mechanics is in investigating the mechanism of oxygen diffusion in albite, NaAlSisOg, a mineral related to zeolites. Experiments indicate that diffusion of oxygen in albite is faster in the presence of water. Molecular mechanics calculations show that the activation energy for OH- diffusing through the solid is lower than that for diffusion for O2-. 

D]- thus increases with decreasing oxygen pressure. The activation energy for the diffusion is in this case given by... 

The permeation kinetic parameters Dy, k, and can be determined by regressing the experimental oxygen fluxes measured at different conditions with the above permeation model. Table 5.1 lists the expressions of permeation parameters for the Lao.jSro4Coo2Feo803 j perovskite membrane. The diffusion coefficients of oxygen vacancies in other perovskite membranes were also studied by the isotopic method, as summarized in Table 5.2. The activation energy for oxygen vacancy diffusion is in the range of 77 21 kj mol" [20]. 

Fig. XVIII-15. Oxygen atom diffusion on a W(IOO) surface (a) variation of the activation energy for diffusion with d and (b) variation of o- (From Ref. 136. Reprinted with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

On the other hand, the low temperature dependance of the rate constants with activation energies around 5 kcal/mole indicates a diffusion limited reaction rate which could refer to diffusion of oxygene into the fibers of the board, i.e. into the fiberwalls. The corresponding negative activation energy for the groundwood based hardboard and the effect of fire retardants there upon are difficult to understand. 

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