Electron localization, high temperature

Powder samples of Y Cs2 exhibited localized-electron behavior both at temperatures above 200 K and temperatures below 90 K, but with different Curie—Weiss curves (Allen, 1998). The Curie—Weiss curve at low temperature corresponded to 0.29(4) electrons per fullerene similar to that of La Cs2/ with a small Curie constant of 2.7(8) K, and to 1.0(1) electrons at high temperature, with an extremely large Curie constant of 280(30) K. This single electron spin clearly agrees with the single impaired electron which is expected, and as observed in solution ESR experiments (see Section 6.1). The high-temperature susceptibility is weakly temperature dependent, and if it arises from a metal then the density of state (DOS) is 10(1) states per molecule per electonvolt at 294 K. 

The problem suggested by these data is whether radiation annealing is due to the local high temperatures in the hot spots or to the enhanced probability of recombination owing to the increased supply of ions, free radicals, or electrons produced hy the radiation. 

Unlike chemical reactions, tribochemical reactions are triggered by frictional force, resulting in wear. Tribochemical wear can be seen as one type of corrosive wear. When the corrosion is activated by mechanical interactions between the contacting surfaces, it produces activated surface sites and localized high temperatures sufficient for chemical reaction. Tribochemical wear involves surface charging of electrons, surface passivation, and surface film removal processes. 

Figure 20. Electronic structure and transport in mixed conducting perovskites. (a) Band picture of electronic structure in the high-temperature metallic phase of Lai- r tCo03-(5. (Reprinted with permission from ref 109. Copyright 1995 Elsevier.) (b) Localized picture of electron/ hole transport in semimetallic Lai- 3r Fe03-(5, involving hopping of electrons and/or electron holes (depending on the oxidation state of iron).

Hydrolysis of acetals yields aldehydes, which are intermediates in the biochemical /3-oxidation of hydrocarbon chains. Acid catalyzed hydrolysis of unsubstituted acetals is generally facile and occurs at a reasonable rate at pH 4-5 at room temperature. Electron-withdrawing substituents, such as hydroxyl, ether oxygen, and halogens, reduce the hydrolysis rate, however [50]. Anionic acetal surfactants are more labile than cationic [40], a fact that can be ascribed to the locally high oxonium ion activity around such micelles. The same effect can also be seen for surfactants forming vesicular aggregates. 

Thus, although it is safe to assume that the 5f states are localized states, excited f states are never far above the Fermi energy. They will, therefore, influence the electronic properties and high temperature phases of Cf and Es (which, with a metal radius R = 2.0 A seem to have attained divalency). 

It is known that initiation of solid TNT to explosion cannot be caused by local heating to high.temperature, unless the material contains some bubbles of gas, such as air, At, etc. This means that the presence of gas bubbles is of importance, although they do not seem to take part in the chem reaction. The luminescence of these gases on shock heating plays the decisive role. By 2-color pyrometry with electronic amplification the temp... 

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