away from purely macroscopic phenomena. Moreover, numerous new synthetic techniques have made it possible to fabricate nanometer-scale structures that exhibit new physical phenomena, which in turn can form the basis for new technologies. Increasingly, the properties and performance of materials are determined by the nanostructure of the materials, and society is using more of these materials each year. Development of such materials represents a scientific frontier with technological importance to many industries.

SYNTHESIS AND PROCESSING

Synthesis and processing are terms that refer to the building of new arrangements of atoms, molecules, and molecular aggregates; the control of structure at all levels from the atomic to the macroscopic; and the development of processes to produce materials and components effectively and competitively. Synthesis is often used alone to refer to the physical and chemical means by which atoms and molecules are assembled. Processing may be used in a similar way, for example, in the phrase electronic materials processing. Processing may also imply changes on a larger scale, including materials manufacturing. It is often applied to such macroscopic manipulations as ingot solidification, mechanical modification, sintering, and joining. These macroscopic manipulations, of course, also cause important structural changes at the levels of atoms and grains.

In materials science and engineering, the distinctions between synthesis and processing have become increasingly blurred in recent years. The fabrication of artificially structured materials, which involves synthesis of materials on the atomic scale, is typically referred to as processing. The preparation of ceramics, which in the past generally involved sintering of mixtures of mineral-derived oxides, now involves considerable synthetic chemistry in some instances. Broadly, it may be stated that synthesis and processing form a continuous range of activities in which assemblages of atoms, molecules, and molecular aggregates are transformed into useful products.

Synthesis and processing research is evolving to the point that, in some cases, new materials can be tailored, atom by atom, to achieve a desired set of properties or to obtain new and sometimes unexpected phenomena. Synthesis and processing encompass a comprehensive array of techniques and technologies as diverse as rolling of sheet steel, pressing and sintering of ceramic powders, ion implantation of silicon, creation of artificially structured materials, ladle-refining of steel, sol-gel production of fine ceramic powders, pouring of polymer-modified concrete, shaping by machining or chip processes, thermomechanical processing of alloys, preparation of polymers by chemical reactions, coating of turbine blades for corrosion resistance, zone refining of silicon, growth of gallium arsenide crystals, and laying-up of composite materials. Some of these technologies are quite new and may,



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