Chemical reaction vapor deposition

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

A vacuum technique closely related to CVD is PVD (physical vapor deposition), in which a solid (metal or compound) is evaporated in a vacuum by heating or by a plasma (called sputtering) and condensed on a substrate to form a coating. Often there is no chemical reaction during deposition—hence the name. PVD is a line-of-sight process, and unlike CVD it suffers from shadowing on profiled surfaces if the substrates are stationary with respect to the source. 

Deposition n. ) Usually referred to in metal treatment as the amount of treatment by weight (mg/ft ). (2) Process of applying a material to a base by means of vacuum, evaporation, sputtering, electrolysis, chemical reaction, vapor methods, etc. 

During the vapor deposition process, the polymer chain ends remain truly aUve, ceasing to grow only when they are so far from the growth interface that fresh monomer can no longer reach them. No specific termination chemistry is needed, although subsequent to the deposition, reaction with atmospheric oxygen, as well as other chemical conversions that alter the nature of the free-radical chain ends, is clearly supported experimentally. 

Germanium difluoride can be prepared by reduction (2,4) of GeF by metallic germanium, by reaction (1) of stoichiometric amounts of Ge and HF in a sealed vessel at 225°C, by Ge powder and HgF2 (5), and by GeS and PbF2 (6). Gep2 has been used in plasma chemical vapor deposition of amorphous film (see Plasma TECHNOLOGY Thin films) (7). 

The epitaxy reactor is a specialized variant of the tubular reactor in which gas-phase precursors are produced and transported to a heated surface where thin crystalline films and gaseous by-products are produced by further reaction on the surface. Similar to this chemical vapor deposition (CVE)) are physical vapor depositions (PVE)) and molecular beam generated deposits. Reactor details are critical to assuring uniform, impurity-free deposits and numerous designs have evolved (Fig. 22) (89). 

In PECVD, the plasma generation region may be in the deposition chamber or precede the deposition chamber in the gas flow system. The latter configuration is called remote plasma-enhanced CVD (RPECVD). In either case, the purpose of the plasma is to give activation and partial reaction/reduction of the chemical precursor vapors so that the substrate temperature can be lowered and still obtain deposit of the same quaUty. 

This reaction, operated at pilot plant scale, has not as of this writing (ca 1997) been commercialized. The same reaction may be used for chemical vapor deposition of titanium boride. 

Titanium carbide may also be made by the reaction at high temperature of titanium with carbon titanium tetrachloride with organic compounds such as methane, chloroform, or poly(vinyl chloride) titanium disulfide [12039-13-3] with carbon organotitanates with carbon precursor polymers (31) and titanium tetrachloride with hydrogen and carbon monoxide. Much of this work is directed toward the production of ultrafine (<1 jim) powders. The reaction of titanium tetrachloride with a hydrocarbon-hydrogen mixture at ca 1000°C is used for the chemical vapor deposition (CVD) of thin carbide films used in wear-resistant coatings. 

Tertiary stibines have been widely employed as ligands in a variety of transition metal complexes (99), and they appear to have numerous uses in synthetic organic chemistry (66), eg, for the olefination of carbonyl compounds (100). They have also been used for the formation of semiconductors by the metal—organic chemical vapor deposition process (101), as catalysts or cocatalysts for a number of polymerization reactions (102), as ingredients of light-sensitive substances (103), and for many other industrial purposes. 

Reactions of boron ttihalides that are of commercial importance are those of BCl, and to a lesser extent BBr, with gases in chemical vapor deposition (CVD). CVD of boron by reduction, of boron nitride using NH, and of boron carbide using CH on transition metals and alloys are all technically important processes (34—38). The CVD process is normally supported by heating or by plasma formed by an arc or discharge (39,40). 

Carbon Composites. In this class of materials, carbon or graphite fibers are embedded in a carbon or graphite matrix. The matrix can be formed by two methods chemical vapor deposition (CVD) and coking. In the case of chemical vapor deposition (see Film deposition techniques) a hydrocarbon gas is introduced into a reaction chamber in which carbon formed from the decomposition of the gas condenses on the surface of carbon fibers. An alternative method is to mold a carbon fiber—resin mixture into shape and coke the resin precursor at high temperatures and then foUow with CVD. In both methods the process has to be repeated until a desired density is obtained. 

Physics and chemistry researchers approach III—V synthesis and epitaxial growth, ie, growth in perfect registry with the atoms of an underlying crystal, differently. The physics approach, known as molecular beam epitaxy (MBE), is essentially the evaporation (14—16) of the elements, as illustrated in Figure 4. The chemistry approach, organometaUic chemical vapor deposition (OMCVD) (17) is exemplified by the typical chemical reaction ... 

The preceeding discussion was confined mostly to the carbon deposition curves as a function of temperature, pressure, and initial composition. Also of interest, especially for methane synthesis, is the composition and heating value of the equilibrium gas mixture. It is desirable to produce a gas with a high heating value which implies a high concentration of CH4 and low concentrations of the other species. Of particular interest are the concentrations of H2 and CO since these are generally the valuable raw materials. Also, by custom it is desirable to maintain a CO concentration of less than 0.1%. The calculated heating values are reported as is customary in the gas industry on the basis of one cubic foot at 30 in. Hg and 15.6°C (60°F) when saturated with water vapor (II). Furthermore, calculations are made and reported for a C02- and H20-free gas since these components may be removed from the mixture after the final chemical reaction. Concentrations of CH4, CO, and H2 are also reported on a C02 and H20-free basis. 

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