Vapor transport synthesis

Cadmium chromium(III) selenide can be prepared by the direct combination of the elements or by the reaction of cadmium selenide with chromium(III) selenide. Crystals of cadmium chro-mium(III) selenide have been prepared by flux growth1 in cadmium chloride, by vapor transport,2 and by a liquid-transport method3 with a platinum metal catalyst. The synthesis given... 

The synthesis of black, pyrite type of silicon diphosphide was first accomplished at high pressure1 (15-50 kb.). It has since been prepared by vapor-transport techniques.2 3 A low-pressure, red form of SiP2 is produced by sublimation from 900-500°C. in a... 

Polycrystalline zeolite membranes consist of inter-grown zeolite crystals with no apparent cracks or pinholes (Fig. lA). These films are composed of only zeolite (i.e., there are no non-zeolite components such as amorphous silica or polymer). They are normally supported on a substrate although free-standing films have also been synthesized. Membranes can be prepared on different substrates such as silicon wafer, quartz, porous alumina, carbon, glass, stainless steel (SS), gold, etc. Polycrystalline films are primarily prepared by hydrothermal synthesis methods including in situ crystallization, seeded growth,and vapor transport, " and have potential use in all of the applications discussed in this entry. 

An important way of overcome the diffusion barrier in solid state synthesis is the technique of vapor transport, where an agent is added to the reactants to produce a volatile intermediate in a sealed tube. For example the formation of A12S3 is slow even at 800°C where A1 is liquid and S... 

Almost every conceivable solid compound can be made from the gas phase by chemical reactions between gases. The synthesis of single crystal by vapor transport is the subject of Section 8.4.1. The preparation of powders, layers, and fibers from gaseous precursors is dealt with in Section 8.4.2-S.4.4. The following four methods are described. 

Vapor transport solids are transported through the gas phase in a closed vessel using a reactive gas that is not consumed in the process. This method is used for crystal growth, reactive sintering, and synthesis of solids. 

Several methods have been developed to synthesize inorganic fullerenes and nanotubes based on layered MS2 [45-50]. They include arc discharge, laser ablation techniques, electron beam irradiation of MS2 crystals, chemical transport reaction, and precursor synthesis approach [50,54-58]. The chemical vapor transport method, which was discussed earlier, has also been used to synthesize both M0S2 and WS2 nanotubes. 

The present review of zeolite membrane technology covers synthesis and characterization methods as well as the theoretical aspects of transport and separation mechanisms. Special attention is focused on the performance of zeolite membranes in a variety of applications including liquid-liquid, gas/vapor and reactive... 

This CVD procedure is somewhat different from that used to deposit semiconductor layers. In the latter process, the primary reaction occurs on the substrate surface, following gas-phase decomposition (if necessary), transport, and adsorption. In the fiber optic process, the reaction takes place in the gas phase. As a result, the process is termed modified chemical vapor deposition (MCVD). The need for gas-phase particle synthesis is necessitated by the slow deposition rates of surface reactions. Early attempts to increase deposition rates of surface-controlled reactions resulted in gas-phase silica particles that acted as scattering centers in the deposited layers, leading to attenuation loss. With the MCVD process, the precursor gas flow rates are increased to nearly 10 times those used in traditional CVD processes, in order to produce Ge02-Si02 particles that collect on the tube wall and are vitrified (densified) by the torch flame. 

Zhang, Y. W., Okubo, T. and Ogura, M. Synthesis of mesoporous aluminosilicate with zeolitic characteristics using vapor phase transport, Chem. Commun. 2005, 2719-2720. 

Ceramic and semiconductor thin films have been prepared by a number of methods including chemical vapor deposition (CVD), spray-coating, and sol-gel techniques. In the present work, the sol-gel method was chosen to prepare uniform, thin films of titanium oxides on palladium Titanium oxide was chosen because of its versatility as a support material and also because the sol-gel synthesis of titania films has been clearly described by Takahashi and co-workers (22). The procedure utilized herein follows the work of Takahashi, but is modified to take advantage of the hydrogen permeability of the palladium substrate. Our objective was to develop a reliable procedure for the fabrication of thin titania films on palladium, and then to evaluate the performance of the resulting metalloceramic membranes for hydrogen transport and ethylene hydrogenation for comparison to the pure palladium membrane results. 

Most relevant for the oxygen transport should be the defective crystal structure of both catalyst components. The defective structure and the intimate contact of crystallites of the various phases are direct consequences of the fusion of the catalyst precursor and are features which are inaccessible by conventional wet chemical methods of preparation. Possible alternative strategies for the controlled synthesis of such designed interfaces may be provided by modem chemical vapor deposition (CVD) methods with, however, considerably more chemical control than is required for the fusion of an amorphous alloy. 

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