Faculty of Engineering and Natural Sciences

 

FENS SEMINARS

 

 Glass in and on Oxides

Prof. Dr. Barry Carter

 

University of Minnesota

Department of Ch. E. & Materials Science, University of Minnesota, Minneapolis, MN

Abstract:

 

The wetting of ceramic surfaces and interfaces by a secondary phase is so ubiquitous that we often take if for granted. Classic liquid-phase sintering (LPS) relies on the wetting of the ceramic powder compact by a glass-forming additive with a lower melting point. Wetting of clays by water-based solvents and the application of glazes are, of course, encountered everyday in the pottery industry. We are investigating the wetting and dewetting of glasses on ceramic substrates using a combination of microscopy techniques. We know that surface structure and morphology can influence dewetting behavior and the geometry of the dewet droplets, but just how the secondary phase wets the crystalline ceramic at processing temperatures is less clear. This talk will emphasize two model systems: anorthite on sapphire and silica on rutile. Thin films (100 nm) of the second phase (anorthite or silica) are deposited onto a single-crystal substrate of sapphire or rutile by pulsed-laser deposition (PLD). The specimens are then heat-treated in air at high temperature (1400°C-1650°C). The second phase may dewet or continue to wet the surface; which process occurs may be very sensitive to the actual processing temperature. The relationship between dissolution and reprecipitation of the crystalline material is key to many processes, including the interplay between surfaces and grain boundaries, and grain-boundary migration. Particular attention will be paid to considering the importance of kinetics in these processes, and how they combine to control the wetting process. Special thanks go to my past and present colleagues, Shelley R. Gillis, N. (Ravi) Ravishankar, Nicole Munoz and Jessica Riesterer. This research is supported by the US DOE under grant No. DE-FG02-01ER45883.

May 5^th, 2005-13:40, FENS L 047