Microstructure of Ceramic Materials: Proceedings of a Symposium, April 27-28, 1963 (Classic Reprint) - Softcover

Standards, United States Bureau Of

Softcover

ISBN 10: 152822115X ISBN 13: 9781528221153

Verlag: Forgotten Books, 2017

Inhaltsangabe

Excerpt from Microstructure of Ceramic Materials: Proceedings of a Symposium, April 27-28, 1963

In all materials, the physical and even the chemical properties of a polycrystal line body are not exactly the same as those of a single crystal of the same materials. Many materials are anisotropic their properties depend upon the orientation of the measuring system with respect to the crystallographic axes and the polycrystalline properties are some form of an average over the crystal directions. Thus the di electric constant, elastic constants, index of refraction, magnetic susceptibility, and many other bulk properties depend to some extent on the microstructure of the specimen.

Beyond this, some properties depend on the motion of various entities through the material - transport of atoms and ions in diffusion, transport of phonons in ther mal conduction and electrons and ions in electrical conduction, motion of dislocations and other defects in plastic deformation and of domain walls in ferromagnetic and ferroelectric switching, and even the propagation of cracks in fracture. In these transport processes, the grain boundaries between the crystals in a polycrystalline body behave differently from the bulk material, and their presence markedly affects the resulting properties. Diffusion is usually faster at grain boundaries, especial ly at low temperatures, so that diffusion is enhanced in polycrystalline bodies. Electrons and phonons are scattered by grain boundaries, so that electrical and ther mal conduction tends to be lower in the polycrystals. The movements of dislocations across grain boundaries are impeded, so that plastic deformation is inhibited by their presence, and polycrystalline bodies tend to be stiffer and less ductile than the corresponding single crystals.

Finally, the presence of grain boundaries not only modifies the behavior, but sometimes even introduces new elements. Thus in brittle fracture the grain bounda ries provide sources of cracks, making polycrystals weaker in general than single crystals. The presence of strain and of impurities at grain boundaries raises the local free energy, so that chemical effects, such as etching rates, are enhanced.

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Details zur Ausgabe

• Verlag: Forgotten Books
• Erscheinungsdatum: 2017
• Sprache: Englisch
• ISBN 10: 152822115X
• ISBN 13: 9781528221153
• Einband: Taschenbuch
• Anzahl der Seiten: 116
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