General processing considerations

The purpose of this chapter is to provide some insight into several areas of importance to the desigaer or practitioner of separation processes. 

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Though the total degrees of freedom is seen to be (C + 4) some of the variables will normally be fixed by general process considerations, and will not be free for the designer to select as design variables . The flash distillation unit will normally be one unit in a process system and the feed composition and feed conditions will be fixed by the upstream processes the feed will arise as an outlet stream from some other unit. Defining the feed fixes (C + 2) variables, so the designer is left with ... 

There are four principal factors that are paramount in selecting the best separation technique. They are the energy required for the separation, the capital required for the equipment used in the separation, the efficiency/effectiveness of the separation, and the vitality of the catalyst after the separation. General process considerations include ... 

Chemical vapor deposition (CVD) of thin solid films from gaseous reactants is reviewed. General process considerations such as film thickness, uniformity, and structure are discussed, along with chemical vapor deposition reactor systems. Fundamental issues related to nucleation, thermodynamics, gas-phase chemistry, and surface chemistry are reviewed. Transport phenomena in low-pressure and atmospheric-pressure chemical vapor deposition systems are described and compared with those in other chemically reacting systems. Finally, modeling approaches to the different types of chemical vapor deposition reactors are outlined and illustrated with examples. 

General Process Considerations. To be useful, a CVD process must produce thin films with reproducible and controllable properties including purity, composition, film thickness, adhesion, crystalline structure, and surface morphology. The growth rates must be reasonable, and the deposition must not have significant impact on the microstructures already formed in the substrate. The deposition time must be sufficiently short, and the temperature has to be low enough so that dopant solid-state diffusion does not smear the results of previous processing steps. 

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