Decomposition in vacuum

Zirconium i dride. Zirconium hydride [7704-99-6] ZrH2, is a britde, metaUic-gray soHd that is stable in air and water, and has a density of 5.6 g/cm. The chemical properties of ZrH2 closely resemble those of titanium hydride. Thermal decomposition in vacuum (1 mPa (7.5 x 10 //mHg)) begins at 300°C and is nearly complete at 500—700°C. It is prepared in the same manner as T1H2. 

Several methods are described for the production of tantalum and niobium metal. Metals can be obtained by reduction of pentachlorides with magnesium, sodium, hydrogen or by thermal decomposition in vacuum [24,28]. Oxides can be reduced using carbon, aluminum, calcium, magnesium [28, 537, 538] or alkali and rare earth metals [539]. 

Reference to the decomposition of KMn04 has already been made in the discussion of chain branching reactions (Chap. 3, Sect. 3.2) in which the participation of a highly reactive intermediate was postulated. This work provided a theoretical explanation of the Prout—Tompkins rate equation [eqn. (9)]. Isothermal decomposition in vacuum of freshly prepared crystals at 473—498 K gives symmetrical sigmoid a time curves which are described by the expression... 

In the reverse WGS reaction, hydrogen promoted both decomposition paths of the formate to H2+C02 and H20+CO, and the decomposition selectivity did not change. Thus, the mechanism of hydrogen promotion is different from that of electron donors in the WGS reaction. COz not only blocks the adsorption sites of H2 but also suppresses the decomposition of the formate intermediate. The rate constant for the steady-state reaction is higher than that obtained from the formate decomposition in vacuum, but it is smaller than that for the formate decomposition under the ambient H2. As a result, the reverse WGS reaction proceeds with a balance of H2 promotion and C02 suppression. 

Thermal decomposition in vacuum produces iron(II) oxide ... 

Synthetic cryptomelane or OMS-2 has a composition of KMn8Oi0-nH2O. In this case, there is no substitution of the framework with K+ or other ions such as the Mg2- - incorporation with OMS-1. The average oxidation state of OMS-2 is about 3.9. The framework is primarily composed of Mn4 ions, however, some Mn3+ ions are found. The thermal stability of OMS-2 is about SOO C for decomposition in vacuum or in N2 and up to about 900<>C when decomposition is done in the presence of O2. In both OMS-1 and OMS-2, the presence of 02 leads to healing of the structure by O atoms. Defect sites are believed to be oxygen vacancies that are formed during thermal treatment. 

Decomposition in vacuum between 724 and 749 K was shown [44] to fit the contracting volume equation (f, = 311 kJ mol ) and the reaction rate decreased in the presence of an inert gas. Instantaneous nucleation was followed by rapid surface growth. 

The rate of decomposition in vacuum at 575 K was increased [78] by preliminary reactor irradiation and, following such pretreatment, the ar-time ciuwes were fitted by the power law with n = 2. From the kinetic analysis, it was concluded that there is preferred nucleation along tracks of radiation damage in the crystal followed by cylindrical growth of product nuclei. 

Le Van et al. [117] concluded, from X-ray studies of the decomposition of nickel malonate in an inert atmosphere, that finely divided nickel was the first formed residual product and this was subsequently carbonized by carbon monoxide. The shapes of the ur-time curves for decomposition in vacuum and in the presence of water vapour [116] or oxygen [118] were closely comparable, although the values of E, (and the reaction products) were significantly changed (179, 137 and 157 kJ mol , respectively for the reactions mentioned). 

It is insoluble in water, ammonia, hydrochloric, and sulfuric acid, but is decomposed by nitric acid. Reaction with oxygen occurs at 650-700 °C and thermal decomposition in vacuum starts at 600-620 °C. 

When analyzing gaseous product of PVA decomposition in vacuum it was stated that main volatile products are H2O was defined quantitatively by the reaction with calcium hydride and by gasochromatography determination of hydrogen, being released during the reaction ... 

Figure 31. Detonation velocity in lead azide films following decomposition in vacuum at 523 K (137).

Oxidizes Instantly in air, evolving heat. Evolves hydrogen on thermal decomposition in vacuum, forming Bordeaux red M0s07(0H)a. This is also the main product obtained in the reaction of aerated water with MOg05(OH)xo. 

Decomposition in Vacuum Substitution of the quantities P and Pg into Eqs. 3.14 and 3.16 yields the final expressions for calculation of the absolute rates of decomposition. Thus, for the decomposition of reactant R into volatile gaseous products A and B in accordance with reaction (3.10) ... 

Ewing J, Bemto D, Searcy AW (1979) Nature of CaO produced by caldte powder decomposition in vacuum and in CO2. J Am Ceram Soc 62 580-584... 

Polystyrene is, however, a relatively ideal case. In Fig. 4.199, data on the isoconversion of decomposition of a segmented polyurethane are reproduced. Only the first 10% of decomposition in vacuum give parallel lines with activation energies between 145 and 170 kJ mol". Perhaps it may still be possible to describe this early decomposition as a single process. At higher conversion, the kinetics is much more complex and no interpretation is possible with thermogravimetry alone. 

Foaming due to excessively high temperatures (vacuum decomposition) in vacuum service, or very high-viscosity liquids in vacuum service, or high-boiling aromatic fractions used as absorption oils in absorbers. Mist extractors are not of much help for these services. 

Molybdenum oxy-carbide species were synthesized in the supercage of NaY zeolite by adsorption of Mo(CO)g vapor followed by thermal decomposition in vacuum at 573 K [265]. The structure of the encaged species was fidly characterized by TPD, EXAFS, XPS, and XRF. The decomposition of methanol at 573 K on the oxy-carbide species yielded H2, CH4, and CO2 in an approximate ratio of2 l l. 

Despite having outstanding and desirable properties, MAX phases are very prone to thermal decomposition in vacuum or inert atmosphere when exposed to elevated temperatures. Above 1400 °C, MAX phases decomposed to binary carbide(e.g.,TiC ) or binary nitride (e.g., TiN ), primarily through the sublimation of A-elements such as A1 or Si, which results in a porous surface layer of MX being formed. Positive activation energies were determined for the decomposition of MAX phases except for TijAlCj where negative activation energy of 71.9 kJ moF was obtained due to... 

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