Activation energy resistance

In a study of oxidation resistance over the range 1200—1500°C an activation energy of 276 kj/mol (66 kcal/mol) was determined (60). The rate law is of the form 6 = kT + C the rate-controlling step is probably the diffusion of oxygen inward to the SiC—Si02 interface while CO diffuses outwards. 

Endotliermic Decompositions These decompositions are mostly reversible. The most investigated substances have been hydrates and hydroxides, which give off water, and carbonates, which give off CO9. Dehydration is analogous to evaporation, and its rate depends on the moisture content of the gas. Activation energies are nearly the same as reaction enthalpies. As the reaction proceeds in the particle, the rate of reaction is impeded hy resistance to diffusion of the water through the already formed product. A particular substance may have sever hydrates. Which one is present will depend on the... 

PTFE decomposes to TFE with first-order kinetics and a 347.4-kJ/mol activation energy under vacuum pyrolysis conditions It is extremely flame resistant and does not bum in air Its limiting oxygen mdex (LOR, the muumum oxygen content of an atmosphere under ambient conditions that sustams combustion, is 96%, which means that it requires almost pure oxygen for combustion... 

The conclusion regarding the fact that constant current conductivity involves not all microcrystals of the sample is proved by results of measurements of electric conductivity in sintered ZnO films in case of alternating current (Fig. 2.10). The availability of barrier-free ohmic pathways is proved by a low value of initial resistivity in sintered samples ( 1 - 5 kOhm) in addition to exponential dependence of electric conductivity plotted as a function of inverse temperature having activation energy 0.03 - 0.5 eV, which coincides with ionization energy of shallow dope levels. The same value is obtained from measurements of the temperature dependence of the Hall constant [46]. 

Compared with metals, semiconductors have quite high resistivity, as conduction of current requires a supply of activation energy. The conductivity of semiconductors increases with increasing temperature. 

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