When 3:30 PM - 4:30 PM Apr 16, 2007
Where 1504 GG Brown
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Amorphous Grain Boundary Films in Ceramics


Manfred Rühle, Max-Planck-Institut für Metallforschung, 2007 Van Vlack Lecture Series

Amorphous grain boundary films (AGFs) exist in several ceramics such as Si3N4, a-Al2O3, ZrO2, and SrTiO3. About 25 years ago, detailed studies of the AGFs started worldwide; T.Y.Tien played a key role within these activities. It was recognized soon that the AGFs possess a thickness of about 1nm and contain atoms which were added to the material as sintering aids. The IGFs control not only the grain growth but also the strength and toughness of the materials. Detailed High-Resolution Transmission Electron Microscopy (HRTEM) studies revealed that an equilibrium thickness exists and that the average composition of the IGFs is also constant (in a good approximation). Recently, detailed theoretical simulations, on an atomic as well as on a continuum thermodynamic scale, and also experimental studies were done within the frame of NANOAM, a research programme supported by the US/NSF and the EC. The result of this work will be summarized shortly. With the advent of a new generation of TEMs, containing elements for correcting the spherical aberration, Cs, details of the atomic structure of the IGFs could be identified. Good agreement exists between the experimental observations of the segregation of the additives to the interface between the IGF and the adjacent crystal and the corresponding quantum mechanical calculations. Results for different ceramic systems will be reported and discussed. Further challenging work will be described.