Isothermal decay

The thermal decay of trapped electrons in linear polyethylene has been investigated by Keyser et al. [210]. The results for isothermal decay at temperatures ranging from 77 to 127°K are given in Fig. 36. At a given temperature, an initially rapid decrease in concentration is followed by a much slower decay. A limiting or very slowly decreasing concentration is obtained after a long period. The same type of behaviour has been... 

There are, however, more subtle thermal stability requirements for the electro-optic materials described here. The electro-optic response in these polymers arises from a non-centrosymmetric orientation created during the process of poling and subsequent cooling. Thus the structures are thermodynamically unstable and are subject to reorientation with corresponding loss of response. This "depoling phenomenon" has been studied by a number of workers. The rates for this process increase dramatically as the temperature approaches Tg. For example. Fig. 5a shows on a log-log plot isothermal decay of the electro-optic response at 815 nm for MAI (32%) poled at 0.5 MV/cm for 5 minutes at T, (127 C). It is clear that the kinetics are very complex, but we may define a "half-life" for the response and plot this versus inverse temperature (°K) on a traditional Ahrennius scale as shown in Fig. 5b. This plot does appear linear. If we can extrapolate these results to lower temperatures, these data suggest a half-life of about 1... 

The surface potential isothermal decay for the positive corona charge maintained initial potential in the porous film in the progress for 3h, but was the decrement of approximately 4% with both solid films. 

Figure 3.11. Isothermal decay of pressure difference as a function of time.

In order to illustrate the method, we can refer to the measurements of the isothermal decay of nonlinear d33 proportional to the square root of the SHG intensity, of DR19 in a polyimide films [71]. Polyimides are good candidates for NLO devices since they offer high thermal and good chemical stability. The second order nonlinear coefficient d33 have been fitted with a double exponential function ... 

Fig. 15 Isothermal decay of quasistatic J33 coefficient for fluorocarbon polymer films, made fi om compact PTFE and FEP layers by using a mesh-controlled fusion bonding process, and PP films as a function of time at 90 °C (Reprinted from Zhang et al. (2007) with permission)...

Reactor type Sampling and analysis Isothermality Solid contact Fluid- decaying catalyst Ease of construction... 

When a jet is supplied at some distance from the surface, the attachment occurs when the distance between the outlet and the surface is below a critical distance otherwise the jet will propagate as a free jet. If the jet attaches to the surface, the flow downstream of the attached point is similar to that of a wall jet. For a compact isothermal jet, the critical distance for jet attachment to the surface is = 6Aq For < 6Al - the velocity decay coefficient Kj... 

Fig. 1. Generalized a—time plot summarizing characteristic kinetic behaviour observed for isothermal decompositions of solids. There are wide variations in the relative significance of the various stages (distinguished by letter in the diagram). Some stages may be negligible or absent, many reactions of solids are deceleratory throughout. A, initial reaction (often deceleratory) B, induction period C, acceleratory period D, point of inflection at maximum rate (in some reactions there is an appreciable period of constant rate) E, deceleratory (or decay) period and F, completion of reaction.

Gholami Y., Azin R., et al. Prediction of carbon dioxide dissolution in bulk water under isothermal pressure decay at different boundary conditions. 2015 Journal of Molecular Liquids 202 23-33. 

Recently, we have shown that non-isothermal chemiluminescence measurements for oxidized cellulose provide the same rate constants of cellulose degradation as may be measured from experiments on the decay of polymerization degree determined by viscometry. This may be also taken as indirect evidence that the light emission is somehow linked with the scission of polymer chains [29]. 

When the samples were etched mildly, the anomalous increase upon annealing was not observed. In an isothermal annealing experiment performed at 423 K for As—H complexes, the exponential decay given by Eq. (3) was verified for a 50 times reduction in concentration. In Fig. 11 the results of a series of 30 min isochronal anneals are shown for each of the donor-H complexes. The curves are given by Eq. (3) with an assumed attempt frequency of 1013 s-1 and binding energies of 1.32 eV for P—H and 1.43 eV for As—H and Sb—H. 

These solutions Ca(t) are plotted in Figure 5-6. Several features of these curves are worth noting. First, the adiabatic reactor requires a much shorter z to attain complete conversion than does the isothermal reactor. Second, the shapes of the curves are quite different, with the isothermal reactor exhibiting the standard exponential decay but the adiabatic reactor exhibiting an acceleration in rate as the reaction proceeds because the temperature increases. 

Except for radioactive decays, other reaction rate coefficients depend on temperature. Hence, for nonisothermal reaction with temperature history of T(t), the reaction rate coefficient is a function of time k(T(t)) = k(t). The concentration evolution as a function of time would differ from that of isothermal reactions. For unidirectional elementary reactions, it is not difficult to find how the concentration would evolve with time as long as the temperature history and hence the function of k(t) is known. To illustrate the method of treatment, use Reaction 2A C as an example. The reaction rate law is (Equation 1-51)... 

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