Materials processing industry

In the materials processing industry, size reduction or comminution is usually carried out in order to increase the surface area because, in most reactions involving solid particles, the rate of reactions is directly proportional to the area of contact with a second phase. Thus the rate of combustion of solid particles is proportional to the area presented to the gas, though a number of secondary factors may also be involved. For example, the free flow of gas may be impeded because of the higher resistance to flow of a bed of small particles. In leaching, not only is the rate of extraction increased by virtue of the increased area of contact between the solvent and the solid, but the distance the solvent has to penetrate into the particles in order to gain access to the more remote pockets of solute is also reduced. This factor is also important in the drying of porous solids, where reduction in size causes both an increase in area and a reduction in the distance... 

What we have covered in this chapter barely scratches the surface of a vast area of applications of colloidal phenomena in chemical and materials processing industries and in environmental and other operations. There are many fundamental, as well as practical, problems in the above topics (especially ones involving polymers, polyelectrolytes, and polymer-colloid and polymer-surfactant mixtures) that are currently areas of active research in engineering, chemistry, physics, and biology. Some of the references cited at the end of this chapter contain good reviews of topics that are extensions of what we have covered in this chapter (see, e.g., Elimelech et al. 1995, Hirtzel and Rajagopalan 1985, Israelachvili 1991, Gregory 1989, and O Melia 1990). 

It is well established (elucidated in several articles in this encyclopedia) that the production of integrated circuits (ICs) requires manufacturing techniques of extreme precision and sophistication, The purity of materials used is also far higher than experienced by most other materials-processing industries. It has been observed by Howard, Jackel, Mankiewich. and Skocpol (AT T Bell Laboratories), m a 1986 paper, that a singlecrystal silicon wafer 15 cm or more in diameter can be obtained with concentrations of undesired dopants at less than 1 part in 10 billion and with only about one defect per square centimeter. Accuracy m recent years is in terms of a few nanometers, and feature sizes in commercial circuits are down to 1 micrometer (micron) and getting smaller, Thus, it is no surprise... 

Small time scales also play an important role in energy transport mechanisms. For example, ultra-short (pico-second and femto-second) pulse lasers are extremely useful for material processing industry. Here the tiny time scales permit localized laser-material interaction beneficial for high energy deposition and transport. 

Storage batteries Motor vehicles Material processing Industrial plants... 

Constraints of Plant Design. The potential hazards encountered in the uranium feed materials processing industry include many that are common to the heavy chemicals industry. However special problems present themselves owing to direct radiation, the possibility of inhalation and ingestion of radioactive dusts and gases, nuclear safety, and more unusual chemical hazards. 

The materials processing industry receives diverse raw materials to be transformed directly from the primary sector, either for direct consumption as... 

Compressibility can be defined as the compaction of a powder by tapping or mechanical compression. These processes can occur either unintentionally as a result of handling or transporting, or intentionally as when producing tablets or agglomerates. In the materials processing industry, unintentional compression is normally undesirable, while operations aimed at obtaining defined shapes are usually required in some processes. The former will be... 

The state of being fluidized, called "fluidization" as already done, turns out to be advantageous in numerous operations of the materials processing industry run, normally, by practicing chemical engineers. 

In fluidized beds there are favorable conditions for rapid heat and mass transfer between the solids and the fluid. Very rapid mixing of the solids generally occurs so that the coefficients for the transfer of heat to boimdary surfaces are quite high. Fluidized beds are, therefore, used both as heat exchangers and chemical reactors particularly where close control of temperature is required and where large amounts of heat must be added to, or removed from the system. There are, of course, many other relevant applications of fluidized beds in the materials processing industry. A proper knowledge of the flow patterns of both fluid and particles is, therefore, necessary. 

A number of unit operations have as fundamental purpose the separation of two or more components within a system. Mixtures and multiphase fluids previously mentioned are varied in the materials processing industries and include solutions, suspensions, dispersions, and solid blends. The components within these systems may include any of the three common states of matter (i.e., solid, liquid, or gas), and so different combinations are possible. There are many criteria used to determine the most suitable strategy to... 

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