Chemical processes etching

Rotameters The rotameter, an example of which is shown in Fig. 10-21, has become one of the most popular flowmeters in the chemical-process industries. It consists essentially of a plummet, or float, which is free to move up or down in a vertical, slightly tapered tube having its small end down. The fluid enters the lower end of the tube and causes the float to rise until the annular area between the float and the wall of the tube is such that the pressure drop across this constriction is just sufficient to support the float. Typically, the tapered tube is of glass and carries etched upon it a nearly linear scale on which the position of the float may be visually noted as an indication of the flow. 

Surface features can also be revealed by etching, which permits identification of points of intersection of line dislocations with the surface, and this is valuable in determining the role of these imperfections in chemical processes [45,214] and, in particular, nucleus formation. Smaller topographical details can be rendered visible by the evaporation of a thin (<0.5 nm) film of gold onto the surface [215,216]. Heights and depths of surface features can be determined by interferometry [203—205]. Microcinematography has also been used [217] to record the progress of solid phase reactions. 

Crystallization processes are very important in chemical processes whenever there are solid products in a reactor. We saw in Chapter 9 that crystallization and dissolution particle sizes could be handled with the same equations as chemical vapor deposition and reactive etching. We note here that crystallization reactions can be handled with the same equations as polymerization. 

Heterogeneous reaction at the interface between a solid surface and the adjacent gas is central to many chemical processes. Examples include deposition or etching of materials, atmospheric corrosion, combustion of solids, and heterogeneous catalysis. 

Symyx, one of the pioneers in combinatorial screening, presented a chemical processing microsystem in 2000 for the screening of 256 catalysts on a silicon or quartz glass wafer [44]. The reactant flow was distributed by a microstructured manifold etched into a silicon wafer (see Bergh, Chapter 3). 

Coating of polymer surfaces with thicker metal layers (10-30 pm) is a much more complicated operation. Several pre-treatment steps are required first the polymer surface has to be modified in such a way that, by a chemical process, a layer of copper or nickel can be deposited. With ABS use is made of the circumstance that it is a two-phase system, consisting of a hard matrix in which rubber particles are dispersed. The rubber particles present at the surface, are etched away, leaving a rough, porous surface, which offers a good adhesion to the chemically deposited copper or nickel. Thereafter the application by electrolysis of further layers of other metals (e.g. chromium) is simple. Also for PP, PMMA and polyamides, methods have been developed for chemical deposition of the first metal layer. 

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