Slow thermal treatments

The decomposition described in Equation (146) takes place at relatively low temperatures hence, thermal treatment at a relatively slow temperature rate can be sufficient in order to significantly reduce fluorine levels in the final oxides. Nevertheless, treatment at a high temperature rate can lead to another mechanism of ammonium fluoride decomposition yielding gaseous ammonia and molten ammonium hydrofluoride according to the following scheme ... 

Many studies on template thermal degradation have been reported on zeolites of industrial interest including ZSM5 [1-5], silicalite [1], and beta [6-8], as well as surfactant-templated mesostructured materials [9-13]. The latter are structurally more sensitive than molecular sieves. Their structure usually shrinks upon thermal treatment. The general practice is slow heating at 1 °C min (N2/air) up to 550 °C, followed by a temperature plateau. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

Cryomicroscope studies have the advantage of showing pictures of the structural changes and the frozen product can be freeze-dried in most instruments. The pro duct layer is very thin and the product is quickly frozen. The behavior of the product during warming and drying therefore corresponds exactly only to a quickly frozen product. To simulate a thermal treatment is difficult because of the thin layer. However, experience shows, that critical temperatures taken from such studies are valuable, especially if they are supported by e.g. ER data of a more slowely frozen product. 

Yb-Au-Sb. The LiGaGe type was established for the YbAuSb compound (a = 0.4635, c = 0.7765) by Merlo et al. (1990) by means of powder and single crystal diffraction method on a sample obtained by melting stoichiometric amounts of the components in iron or in tantalum crucibles and arc welded shut under an argon atmosphere. After slow cooling, no further thermal treatments were applied. The purities of the metals were Yb 99.9%, Au and Sb 99.999%. The crystal structure was confirmed by Flandorfer et al. (1997) by X-ray powder diffraction. 

Compound 50c was obtained in ca. 25% yield as a precipitate from the acid-catalyzed condensation of pyrogallol and isovaleraldehyde. No evidence of any hexamer was found in the solid material. To convert this material into the hexamer (50c)6, the original precipitate can be dissolved in Et20, acetone, or methanol, with a few drops of nitrobenzene or o-dinitrobenzene, followed by crystallization upon slow evaporation. The hexamer may also be obtained by thermal treatment of the initial precipitate or the initial filtrate. The product in the initial filtrate may be converted into hexamer by extraction in Et20, followed by evaporation to dryness with subsequent dissolution in methanol. The methanol solution is then heated to 120-150 °C for at least 12 h. Methanol may be removed under vacuum to yield a red-brown solid. Colorless hexameric spherical capsules are obtained from this solid utilizing the crystallization procedure described for the initial precipitate. 

The unique phosphine-carbon dioxide complex Cp2Ti (C02)PMe3 is prepared by treatment of Cp2Ti(PMc3)2 with dry CO2 at -180°C (equation 50). Slow thermal decomposition of Cp2Ti(C02)PMc3 at room temperature leads principally to Cp2Ti(CO)2. ... 

However, interchange reactions appear to be rather slow at temperatures below Tm(15). We(50) observed that thermal treatment of some of liquid crystalline, aromatic copolyesters at the temperatures substantially lower than Tm did not lead to any changes in the comonomer sequence even after a prolonged period of time. A copolyester especially of 4-hydroxybenzoic acid, however, can undergo a special type of sequence changes below Tm, which is called the crystallization induced reaction(51). 

We observe threshold effects at different temperatures both for the slow decay constants r2 and in the fraction of surviving carbynes after the thermal treatment Rq. This has a value of roughly 29% after the metastable decay at RT, it drops at 15% at lOO C remaining constant up to 150°C. We observe another drop to 8% at 200°C. This suggests the presence of two activated processes with energy barriers situated between 25 and 40meV. 

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