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Advancing Materials Research
the strength of matter, dominated by dislocation movements, challenge still lies ahead. A current study at the Battelle Memorial Institute finds that the fracture of matter and efforts to contain it now cost the United States no less than $119 billion per year. Even the appropriate basic categorizations of overload, brittle fracture, ductile rupture, fatigue, creep, creep rupture, stress corrosion, threading fatigue, thermal shock, buckling, and delamination require more specific scientific description than has yet been applied. The move toward automated manufacture and robotics processing of materials even accents the ignorance of these factors. As noted below, the appropriate control of dislocations may even provide new networks of conductivity and electronic and photonic responses in suitable crystals.
RECOGNITION OF NEW FRONTIERS
Along with these signals of need, there are signals of knowledge, perhaps as beckoning and as rich with meaning as those once heralding the solid-state and materials endeavors themselves. In polymers, we have long known, and technically and scientifically applied, the close coexistence of ordered and disordered phases. Indeed, a single chain can indulge in both, and many do. Whole classes of important materials, such as the Arnel fiber of Celanese Corporation, came from appropriate adjustment of lateral and longitudinal states of order, in that case, in cellulose triacetate. Annealing and heat treatment affecting such order are crucial factors in the performance of nearly all microcrystalline synthetic fibers, plastics, and films.
However, we have been rightly charmed by the beauty and utility of traditional crystallography. Only recently, computer-assisted study of aluminum alloyed with minor components of manganese, iron, and chromium has shown an icosahedral structure imputing 5-fold symmetry. This, of course, displaces atom groupings from the expected unit-cell behavior. On 29 July 1984, Japanese workers reported in the Physical Review Letters about a nickel-chromium alloy that in electron diffraction by small particles seems to exhibit a 12-fold symmetry. This they interpreted as a dodecagon, which indeed would conform to an intermediate structure between the disorder of glass and the regularity of a crystal. Reexamination of what were termed anomalous diffraction patterns of an aluminum-manganese-silicon alloy from AT&T Bell Laboratories offers a complementary example, where a unit cell would require thousands of atoms, but currently can best be interpreted as icosahedral arrays within such “unit cell.” In India similar icosahedra seem to have been formed in magnesium-zinc-aluminum alloys by rapid cooling. There is also the report of a sheet structure with 10-fold symmetry within the sheet, but a periodic stacking of the sheets themselves.
The point is that conventional structure practices are not really sophisticated enough to deal with the growing diversity of materials science and engi-