Gaseous metals, sources

It should be emphasized that although in principle one could determine Dq for aqua complexes in this way, it is highly impractical. First, hydration enthalpies of this magnitude are not known to high accuracy. Second, there is not a ready source of +2 gaseous metal ions, and it would also involve determining small differences between large numbers, the heats of hydration of metal ions. As a result, this is not a practical type of measurement. 

The reaction of metal hydrides MH2 with acidic hydrocarbons seems an attractive way to prepare the target compound since a commercially available metal source can be utilized. Moreover, the formation of only gaseous byproducts ensures a facile work-up (equation 13). However, only few compounds have been prepared using this route owing to the low reactivity of the hydrides caused by their polymeric, insoluble nature. Moreover, the unreliable purity of the commercial hydrides poses significant problems. As such, rather acidic ligands and enforced reaction conditions are required for the reaction to proceed. 

One may apply the gas-phase technique to make large amounts of supported metal oxides by the following procedure. The powder of a metal oxide support may be confined as a fixed bed with the gaseous metal acetylacetonate (sublimed from a source at 180-200°C) transported through the bed by an inert carrier gas at a temperature sufficiently high to cause the reaction (>250°C). The extent of reaction between the metal source and the metal oxide support can be determined by monitoring the composition of pentanedione in the gas phase. The... 

In the original work methane was used as the gaseous carbon source. It will now be shown that using ethane as the carbon source results in the formation of metal carbides with higher surface areas than those produced by TPR with methane. Further, the use of ethane allows the carbiding reaction to proceed in a topotactic manner and provides a potential method for synthesising a variety of carbide phases. 

Three-dimensionally ordered macroporous crystalline Ti02 could be obtained by using titanium alkoxides as a metal source. Various titanium alkoxides [Ti(OEt)4, Ti(0 Pr)4, Ti(OBu)4] can be used in alcoholic solutions or neat.f " After the titanium alkoxides have infiltrated the voids of the template, they can be solidified by drying in air (sometimes heated at ca 50 °C) by a sol-gel process. Another titanium source, ammonium lactate titanium dihydroxide, can be used. A gaseous Ti source, TiCE, can be used. Gaseous TiCU was deposited on a SiOi template, and then TiCU was hydrolysed with vaporous H2O. This two-step deposition of Ti02 on the template was repeated to deposit Ti02 in the voids of the template. ... 

Some instruments have been developed for both atomic absorption and atomic fluorescence. However, a powerful source e.g. a laser is required for the latter spectrometry. In principle, when a gaseous metal atom is excited by absorption of radiation, it emits fluorescence radiation when it reverts to the ground state. This can be recorded in a monochromator/detector set up, not unlike atomic absorption. (J.Chem. Educ., 59, 1982,909 895 AnalChem., 53,1981,332A 1448A 54, 1082, 553, 1006A). 

Impurities that can negatively affect the physical and electrical properties of the metallisation layer can originate from several sources, particularly the deposition source and the gaseous environment. Impurities stemming from the source bombard the surface of the growing film and get trapped in the metal layer. 

Exothermic Decompositions These decompositions are nearly always irreversible. Sohds with such behavior include oxygen-containing salts and such nitrogen compounds as azides and metal styphnates. When several gaseous products are formed, reversal would require an unlikely complex of reactions. Commercial interest in such materials is more in their storage properties than as a source of desirable products, although ammonium nitrate is an important explosive. A few typical exampes will be cited to indicate the ranges of reaction conditions. They are taken from the review by Brown et al. ( Reactions in the Solid State, in Bamford and Tipper, Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980). 

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

In addition to assessing a fire s flame cliaracteristies to detennine tlie cause and effect of a fire, knowledge of tlie fire accident type will provide insight into its ignition source and possible fire protection and prevention methods. Electrical, chemical, and metal fires can occur in a solid, liquid, or gaseous pliase. Section 7.3 presents a detmled discussion of tliese fires and tlieir ignition sources. 

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