Chemical vapour transport reactions

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

Vapour phase reactions also yield solid products in many instances. In chemical vapour transport reactions, a gaseous reagent acts as a carrier to transport a solid by transforming it into the vapour state ... 

Chemical vapour transport has been used to grow magnetite crystals using the reaction of magnetite with hydrogen chloride gas ... 

Crystals of silica can be grown using the chemical vapour transport method with hydrogen fluoride as a carrier gas. The reaction involved is ... 

Growth by reversible reaction (chemical vapour transport)... 

CUjTaSe is formed by the reaction of Cu, Ta and Se in the presence of gaseous I. In Table 2.1, we list a few examples of the chemical transport system. Table 2.2 lists some crystals grown by the chemical vapour transport method. 

Thus the addition of an inert gas which does not intervene chemically in the transport reaction but adds to the density of the gas, reduces the segregation due to thermal diffusion. An example of this is the reduction of thermal separation in a mixture of H2 and H20 by the addition of Hg vapour (Dastur and Chipman, 1948). 

The presence of oxygen may also cause other relevant effects as exemplified by an endothermic reaction, as given by platinum, and which may result in a chemical vapour phase transport PU,. + 02 Pt02 gas. At a temperature around 1200°C,... 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

Chemical vapour deposition (CVD) In CYD (see Section 4.2.1) process reactant vapours (e.g. metal chlorides) are transported to the substrate where they are adsorbed on the surface, the reaction and subsequent crystal growth occurring on the substrate surface. Deposition rates typically lie in the 1-10 pmhrx. 

Chemical transport reactions are those in which a solid (or liquid) substance A reacts with a gas to form a vapour phase product. The reverse reaction then occurs in a different part of the system with the reformation of substance A... 

Chemical vapour infiltration (CVI) is an extension of CVD processes only when a CVD process occurs on an internal surface of a porous substrate (especially for the fibre preform). As compared with CVD, the CVI process for ceramics is much more effective and important because it is the optimal technique to fabricate fibre reinforced ceramics and particularly carbon fibre reinforced carbon and advanced ceramic matrix composites. Both CVI and CVD techniques share some common features in overall chemistry, however, the CVI is much more complex than the CVD process in mass transport and chemical reactions. 

Chemical vapour deposition (CVD) is the delivery (by uniform mass transport) of a volatile precursor or precursors to a heated surface on which reaction takes place to deposit a thin film of the solid product the surface must be hot enough to permit reaction but cool enough to allow solid deposition. Multilayer deposition is also possible. Metal-organic chemical vapour deposition (MOCVD) refers specifically to use of metal-organic precursors. 

In this contribution, the interaction between surface and gas-phase reactions and their coupling by molecular transport is investigated nmnerically. Two examples are discussed more detailed heterogeneous ignition and diamond formation by chemical vapour deposition. 

Heterogeneous reaction systems are modelled by detailed chemical kinetics and transport models and numerically simulated for two simple configurations, an cataJytically active wire and disk. As special case for the latter configuration, chemical vapour deposition of diamond is simulated. Elementary reaction mechanisms are applied in the gas phase and on the surface, and the coupling of the catalytic surface with the surrounding reactive fiow is accounted for by a detailed transport model. 

Numerous teclmiques have been developed for depositing films from vapours, ranging from straightforward evaporation to advanced chemical transport in which reactions are activated by heat, light or plasma. These have been surveyed in two comprehensive reviews [8, 9] and two popular interdisciplinary textbooks [K), H]. The tliree most widely used chemically based teclmiques are ... 

It was found that the reaction rate could be significantly enhanced if a fluorspar addition is made to the briquette with the objective of producing a small amount of a liquid phase at the operating temperature. There is a eutectic in the Ca0-Si02-CaF2 system at a temperature of 1398K. These studies show the importance of the role of a vapour species to transport chemical potentials in a solid-solid reaction, and also the desirability of introducing a small quantity of a liquid. 

In this paper a transfer model will be presented, which can predict mass and energy transport through a gas/vapour-liquid interface where a chemical reaction occurs simultaneously in the liquid phase. In this model the Maxwell-Stefan theory has been used to describe the transport of mass and heat. On the basis of this model a numerical study will be made to investigate the consequences of using the Maxwell-Stefan equation for describing mass transfer in case of physical absorption and in case of absorption with chemical reaction. Despite the fact that the Maxwell-Stefan theory has received significant attention, the incorporation of chemical reactions with associated... 

The mass and heat transport model should be able to predict mass and energy fluxes through a gas/vapour-liquid interface in case a chemical reaction occurs in the liquid phase. In this study the film model will be adopted which postulates the existence of a well-mixed bulk and a stagnant transfer zone near the interface (see Fig. 1). The equations describing the mass and heat fluxes play an important role in our model and will be presented subsequently. 

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