Thermal trap effect

M. H. Cobble, Irradiation into Transparent Solids and the Thermal Trap Effect, J. Franklin Inst. 278, pp. 383-393,1964. 

Two examples of path-dependent micromechanical effects are models of Swegle and Grady [13] for thermal trapping in shear bands and Follansbee and Kocks [14] for path-dependent evolution of the mechanical threshold stress in copper. 

So, for given strain rate s and v (a function of the applied shear stress in the shock front), the rate of mixing that occurs is enhanced by the factor djhy due to strain localization and thermal trapping. This effect is in addition to the greater local temperatures achieved in the shear band (Fig. 7.14). Thus we see in a qualitative way how micromechanical defects can enhance solid-state reactivity. 

Thermal insulation effects by limiting the substrate and membrane temperature to prevent thermal damage and (3) Reduce permeation of corrosive fluid to the substrate, thus minimizing its corrosion rate. CRM linings, such as acid brick and monolithic cements, also prevent "wash", which is the removal of the membrane or substrate corrosion products by the circulating medium. Even when the fluid eventually reaches the membrane or substrate surface, the amount is relatively small, thus limiting chemical attack, and any corrosion products are trapped beneath the masonry shield. 

The presence of SO2 deactivated the trap as shown in Figure 7. The trap was initially treated with 1000 vppm NOx in background gas (minus the SO2) for 15 minutes. The desorption profile generated by injection of 6500 vppm C, as propylene, is shown as the fresh catalyst. After aging in 150 vppm SO2 in air and 10% H2O at 500 C for 24 hours the trap effectively loses all of its NOx adsorption/desorption capacity. Even with a calcination at 800 C in sulfur free air only about 30% of the initial capacity could be recovered. The absence of regeneration is primarily due to retained SOx which occupies NOx adsorption sites although some thermal deactivation at 800 "C also occurs. 

Characteristics - trapping efficiency - ease of separation from the final product - solubility in crude monomer, raw material and coproducts - thermal stability - volatility - degradability - toxicity - ease of handling - price - trapping effectiveness - color formation - solubility - ease of handling - ease of removal or ability to override - toxicity... 

In order for the trapping rate of vacancies by solute atoms to be important with respect to the thermal release in determining the bounded vacancy concentration, vs > 5i T [17], which in the present case gives T < 524 K. This means that the trapping effect is more dominant in stage 1 than in stage 2. 

It has been found that the Tg of PMMA-silica nanocomposites [152] increased with silica content. Also the thermal properties were enhanced. Thus, the degradation temperature at 10% weight loss was about 30 °C higher than that of pristine PMMA. The results could be due to the trapping effect . 

Like in any porous insulation material, the total heat losses are the sum of the skeletal conduction (phonons), gas conduction (collisions between gas molecules), and radiation contributions. The particular mesoscopic structure of aerogels leads to a considerable reduction of the gas-phase conduction contribution due to a trapping effect of the pore gas. For most terrestrial applications, the thermal conductivity at ambient temperature and pressure is relevant, which although well studied, is still a challenge to determine accurately [203], primarily due to the lack of large-area homogeneous aerogel specimens. 

Other. Because a foam consists of many small, trapped gas bubbles, it can be very effective as a thermal insulator. Usually soHd foams are used for insulation purposes, but there are some instances where Hquid foams also find uses for insulation (see Eoamed plastics Insulation, thermal). Eor example, it is possible to apply and remove the insulation simply by forming or coUapsing the foam, providing additional control of the insulation process. Another novel use that is being explored is the potential of absorbing much of the pressure produced by an explosion. The energy in the shock wave is first partially absorbed by breaking the bubbles into very small droplets, and then further absorbed as the droplets are evaporated (53). 

Scheme 6 depicts a typical penicillin sulfoxide rearrangement (69JA1401). The mechanism probably involves an initial thermal formation of a sulfenic acid which is trapped by the acetic anhydride as the mixed sulfenic-acetic anhydride. Nucleophilic attack by the double bond on the sulfur leads to an episulfonium ion which, depending on the site of acetate attack, can afford either the penam (19) or the cepham (20). Product ratios are dependent on reaction conditions. For example, in another related study acetic anhydride gave predominantly the penam product, while chloroacetic anhydride gave the cepham product (7lJCS(O3540). The rearrangement can also be effected by acid in this case the principal products are the cepham (21) and the cephem (22 Scheme 7). Since these early studies a wide variety of reagents have been found to catalyze the conversion of a penicillin sulfoxide to the cepham/cephem ring system (e.g. 77JOC2887).

It is obvious, and verified by experiment [73], that above a critical trap concentration the mobility increases with concentration. This is due to the onset of intertrap transfer that alleviates thermal detrapping of a carrier as a necessary step for charge transport. The simulation results presented in Figure 12-22 are in accord with this notion. The data for p(c) at ,=0.195 eV, i.e. EJa—T), pass through a minimum at a trap concentration c—10. Location of the minimum on a concentration scale depends, of course, on , since the competition between thermal detrapping and inter-trap transport scales exponentially with ,. The field dependence of the mobility in a trap containing system characterized by an effective width aeff is similar to that of a trap-free system with the same width of the DOS. 

The thermal decomposition reactions of KN3, T1N3, and AgN3 have been studied in the corresponding halide matrices [301]. The formation of NCCT from trapped C02 was described and labelling with ISN established that only a single end-N atom of the azide ion was involved in NCO formation. The photodecomposition of PbN6 and the effects of dopants have been followed [302] by the changes produced in the near and the far infrared. 

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