Halide Processes

Photopolymerization processes have been known since the. 1820s when a permanent photographic image was obtained using a coating of bitumen on glass (B-71MI11404). Since then photopolymerization systems have received almost as much attention as silver halide processes, but only a few have been used as substitutes for the latter in information... 

Instant photography (e.g. of the Polaroid type) also relies indirectly on the silver halide process but here the reduced Ag (metallic silver) acts as a reducing agent to modify the solubility properties of a dye. The dye is linked covalently to a molecule such as a quinone (Figure 6.5), which is insoluble in water. When this is reduced to hydroquinone, it becomes soluble in alkaline solutions. The principle of this photographic process is the following ... 

B. H. Carroll, G. C. Higgins, and T. H. James, Introduction to Photographic Theory, The Silver Halide Process, John Wiley Sons, Inc., New York, 1980. 

Fluorination with Metal Fluorides. The majority of organic fluorides produced today are still made by the antimony halide process, starting with hydrogen fluoride and antimony pentachloride ... 

Organo halide Process parameters RMgCI yield... 

Figure 12.21 A schematic diagram of the halide process for volatilization of Ga using an AsCb source and H2 and subsequent deposition of GaAs in the lower temperature zone. Note that the etch reaction 4GaAs + 12 HCl —> dGaCb + AS4 + 6H2 is endothermic and runs forward at 825°C in the presence of excess HCl and in reverse (i.e. as deposition of GaAs) at 750°C in the presence of excess H2, hence the downstream supply of H2.

Figure 20.22 A schematic diagram of the growth of GaAs by the halide process. In this approach Ga is volatilized by reaction with HCI to form GaCl3. The reaction rate is controlled both by the various reactor zone temperatures and by the partial pressure of H2, a reactant, and HCI, a product.

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