Vapour phase decomposition

Solymosi, F. et al., Proc. 14th Combust. Symp., 1309-1316, 1973 The mixed oxide (copper chromite) was the most effective of several catalysts for the vapour-phase decomposition of perchloric acid, decomposition occurring above 120°C. 

The following data refer to the vapour phase decomposition of ethylene oxide at 414 °C ... 

Woolley, J.F. PTFE apparatus for vapour-phase decomposition of high-purity materials. Analyst 100, 896-898 (1975)... 

Matusiewicz, H. PTFE microsampling device for acid-vapour-phase decomposition in Teflon digestion bomb. Chem. Anal. (Warsaw) 33, 173-175 (1988)... 

The thermal vapour phase decomposition of nitroglycerin in the temperature range 140-165° C obeys a first order rate law, but appears to have both homogeneous and heterogeneous components . 

It is of interest that the above mentioned IMC s, based on La, Ni, and Co, are very stable and active catalysts for the vapour phase decomposition of methanol into hydrogen and carbon monoxide (Klabunovskii et al. ). 

Burning of plastics generally begins with the flash-over of vapour-phase decomposition products. The visible sign of the gas-phase combustion is the flame. 

Neumann, C., Eichinger, P. (1991) Ultra-trace analysis of metaUic contaminations on silicon wafer surfaces by vapour phase decomposition/total reflection X-ray fluorescence (VPD/TXRF). Spectrochimica Acta Part B Atomic Spectroscopy, 46,1369-1377. 

Interstellar silicon carbide grains contain the five noble gases in non-solar isotopic and elemental abundances, but of similar composition to values calculated for the helium-burning shell of low mass carbon stars . Silicon carbide is deposited on vapour phase decomposition of cyclic carbosilanes, the spectrum of SiC free radicals is determined, and SiCH present in reionisation... 

Nasibulin, A.G., Shurygina, L.l. and Kauppinen, E.l. (2005) Synthesis of nanoparticles using vapour-phase decomposition of copper(ll) acetylacetonate. Colloid Journal, 67,... 

Br20 a dark-brown solid moderately stable at —60° (mp —17.5° with decomposition), prepared by reaction of Bt2 vapour on HgO (cf. CI2O p. 846) or better, by low-temperature vacuum decomposition of BrOa. The molecule has C2v symmetry in both the solid and vapour phase with Br-O 185 1pm and angle BrOBr 112 2° as determined by EXAFS (extended X-ray absorption fine structure). It oxidizes I2 to I2O5, benzene to 1,4-quinone, and yields OBr in alkaline solution. 

Much of the early work on alkyl radicals of short life was, as we have seen (p. 301), carried out in the vapour phase through decomposition of metal alkyls, e.g. (23) ... 

Applications involving ring transfer or loss. The kinetic lability, volatility, and Lewis acidity of heavy alkaline earth metallocenes have been the properties most important to their applications. The gas-phase decomposition of volatile metallocenes is useful in the preparation of thin films of alkaline earth-containing materials and in doping semiconductors. Reviews are available on the use of group 2 organometallic compounds as precursors for chemical-vapour deposition (CVD).2 3... 

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

To account for this behaviour, it is generally assumed that the coal "molecule" breaks down much more drastically when very rapidly raised to decomposition temperatures, and that repoly-merlzatlon of the radical fragments Is Inhibited by their fast discharge from the coal. Some support for this thesis can be seen In the fact that. In a coke oven, "primary" tars will aromatize the more the longer they are In Intimate contact with the hot coke. But a necessary corollary Is, obviously, that the fragments must be supposed to stabilize themselves In the vapour-phase by Internal disproportionation. 

In this example, the volatile precursor compounds were heated to obtain the product. Other energy sources are also used, notably electromagnetic radiation. An example of vapour phase deposition involving photo-decomposition is given in the next section on vapour phase epitaxy. 

Mercury telluride (HgTe) was first made by vapour phase epitaxy in 1984. This preparation illustrates the use of ultraviolet radiation as the energy source for decomposition. Diethyltellurium ((C2H5)2Te) vapour in a stream of hydrogen carrier gas... 

In general, dehydration means loss of water molecules from chemical substances, irrespective of their structure. Even if all cases where water is bonded in hydrate form are excluded, a number of reactions remain which also include formation of nitriles from amides, lactones from hydroxy acids etc. However, the present treatment will concentrate on the heterogeneous catalytic decomposition of alcohols in the vapour phase, which can be either olefin-forming or ether-forming reactions, and on the related dehydration of ethers to olefins. 

The thermal decomposition of 2-azidoacetic acid (N3CH2CO2H) in the vapour phase has been shown, by photoelectron and matrix isolation infrared spectroscopy, to involve simultaneous formation of CO2 and methanimine (CH2NH) with concerted ejection of N2.52 No evidence was found for formation of intermediate nitrene (NCH2CO2H) or the imine (HNCHCO2H) to which it could be converted by 1,2-hydrogen shift. 

Thermal decompositions (pyrolyses) and catalysed reactions in the vapour phase are widely used large-scale industrial techniques. These vapour phase reactions often lead to more economic conversions than the smaller batchwise laboratory methods, because relatively inexpensive catalyst preparations (compared to the often expensive reagents required in laboratory procedures) may be used, and because the technique lends itself to automated continuous production. In undergraduate laboratory courses the technique has not achieved widespread use. The discussion below of the various apparatus designs, to meet a range of experimental conditions, may be regarded as an introduction to this topic. 

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