Arrhenius-type temperature

In all the above three-component models as well as in the four-component models presented next, an Arrhenius-type temperature dependence is assumed for all the kinetic parameters. Namely each parameter k, is of the form A,erJc>(-El/RT). 

This behavior is in between that of a liquid and a solid. As an example, PDMS properties obey an Arrhenius-type temperature dependence because PDMS is far above its glass transition temperature (about — 125°C). The temperature shift factors are... 

However, one should be cautious about overinterpreting the field and temperature dependence of the mobility obtained from ToF measurements. For instance, in the analyses of the data in [86, 87], ToF signals have been considered that are dispersive. It is well known that data collected under dispersive transport conditions carry a weaker temperature dependence because the charge carriers have not yet reached quasi-equilibrium. This contributes to an apparent Arrhenius-type temperature dependence of p that might erroneously be accounted for by polaron effects. 

Equations (1.194) and (1.195) can be accepted, within reason, because both the chemical equilibrium constants and the hole mobility for semiconductors have an Arrhenius-type temperature dependence. It has been shown, by a least-square fitting of the electrical conductivity data of Maruenda et al. to eqn (1.193), that 85 per cent of the data points are within 1.5 per cent of the calculated values, as shown in Fig. 1.58. This indicates that the model proposed here gives an accurate description of the data. The fitting parameters are listed in Table 1.5. 

Furthermore, recent radiotracer experiments have shown that metals such as Cu, Ag, and Au can diffuse into various polymers including polyimides and polycarbonates at elevated temperatures. Arrhenius type temperature dependences are not always found. This is not unexpected considering the distribution of saddle-point energies in amorphous polymers [F. Faupel, R. Willecke (1994)]. 

By assuming an Arrhenius type temperature relation for both the diffusional jumps and r, we can use the asymptotic behavior of /(to) and T, as a function of temperature to determine the activation energy of motion (an example is given in the next section). We furthermore note that the interpretation of an NMR experiment in terms of diffusional motion requires the assumption of a defined microscopic model of atomic motion (migration) in order to obtain the correct relationships between the ensemble average of the molecular motion of the nuclear magnetic dipoles and both the spectral density and the spin-lattice relaxation time Tt. There are other relaxation times, such as the spin-spin relaxation time T2, which describes the... 

Because the consecutive stacked film layers are miscible, it is expected that a typical two-layer sample can be represented morphologically, as shown on Fig. El 1.2a. The thickness of the interface layer, <5/, increases with time, provided that the adjacent layers are molten, as is the case during the residence in the die (220°C), as well as during the time of thermal conditioning and stretching in the RME (140°C). Assuming an Arrhenius-type temperature dependence of the diffusivity (57),... 

As mentioned above, the frequency dependence of the complex dielectric permittivity (e ) of the main relaxation process of glycerol [17,186] can be described by the Cole-Davidson (CD) empirical function [see (21) with a = 1, 0 < Pcd < 1], Now Tcd is the relaxation time which has non-Arrhenius type temperature dependence for glycerol (see Fig. 23). Another well-known possibility is to fit the BDS spectra of glycerol in time domain using the KWW relaxation function (23) < )(t) (see Fig. 24) ... 

According to the adsorption-site theory, the model constants should follow an Arrhenius-type temperature relationship. An Arrhenius-type plot of the adsorption model constants is shown in Figure 3. The rate constant, ko, increases with an increase in temperature, and the adsorption constants decrease with an increase in temperature. These opposing effects are in agreement with a physically realistic model. The activation energies found from these data are 29.3 kcal/mole for reaction, —28.9 kcal/mole for hydrocarbon adsorption, and —35.4 kcal/mole for hydrogen adsorption. 

Many models use an apparent reaction rate [59], with an Arrhenius-type temperature dependence and, as a result, consider the diffusion and reaction on the interior surface of the catalyst only under certain restrictive assumptions. It is important to incorporate mass transfer effects within the washcoat in the model to give a realistic description of the processes in the monolith [54,60]. 

These approximated functions are considered applicable only to low Mw DGEBA oligomers. An Arrhenius-type temperature dependence has been also... 

The Ostwald and Ubbelohde viscometers, a series of glass bulbs which connected to a standard capillary, and the proportionality between t and r made relative measurements of viscosity under conditions of low shear rate fairly easy, particularly as thermostatting the whole device was simple (viscosity shows an Arrhenius-type temperature dependence, r = with typical E... 

The starting temperature for the NO decomposition lies in the range between 340-360°C. On increasing the temperature an Arrhenius type temperature dependence has been observed up to 450 C with an apparent activation energy of about 90 kJ mole . Between 500-550°C there was a maximum in the NO conversion followed by a marked decrease above 600°C. The highest conversion of about 50% was observed for the Cu-ZSM-5 Si/Al = 24 Cu/Al = 0.5 catalyst. The highest conversions for the other Cu ZSM-5 and Cu-clinoptilolite catalysts were about 10 % and 8 %, respectively. 

The decay law also follows an Arrhenius-type temperature dependence. 

It is important to note that there is significant structure in the bands when compared with rotational tunneling lines in other H2 complexes where molecular disorder is not known to be present. This structure may therefore be attributed to the effect of interactions between the two ij2-H2. As the temperature is increased the rotational tunneling peaks shift to lower energy and broaden in the usual manner, where the width shows an Arrhenius-type temperature dependence with an activation energy of 0.4 kcal/mol (Figure 6.6). In addition, a broad quasi-elastic feature... 

On the basis of the above hypotheses, the estimated parameters obtained by data fitting with the kinetic model (4) assume a correct chemico-physical meaning. In particular, it is worthwhile to look at Arrhenius-type temperature dependence of the three parameters... 

The secondary f)-relaxation is also observed in a-chitin from 80 °C to the onset of thermal degradation ( 210°C). It exhibits a normal Arrhenius-type temperature dependence with activation energy of 113 3 kJ/mol. 

The well-known secondary a-relaxation often associated with proton mobility is also observed in CS (neutralized and nonneutralized) from 80 °C to the onset of degradation. On minimum moisture content conditions, this relaxation process could be noticed in the whole temperature range before the onset of thermal degradation. It is strongly affected by moisture content for dry samples by water effects, the activation energy shifts to lower values when compared to dry annealed samples. The nonneutralized CS showed an easier mobility in this ion motion process. This relaxation process exhibits a normal Arrhenius-type temperature dependence with activation energy of 80-90 kJ/mol. 

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