"Tape casting and subsequent lamination of tapes into a high-density green body are two of the key steps in processing multilayer dielectric ceramics. Defects incorporated during these steps such as delaminations, pin holes, and trapped foreign matter can significantly decrease the breakdown strength of the material and hence reduce the reliability of the devices in which it is used. The purpose of this study was to quantitatively characterize and model the tape casting process and lamination behavior of ceramic tapes in order to eliminate or at least reduce the amount and size of defects to an acceptable level.
Dispersions of TiO2 and an X7R dielectric in a commercial polyvinyl butyral (PVB) binder system were chosen for study due to their use in ongoing studies on symmetric Blumleins and ultrahigh gradient insulators. Initial studies focused on optimizing the rheological behavior of slurries containing 50-65 vol% powder by adding dispersants. Green tapes were cast using a doctor blade assembly under clean-room conditions. Microstructural analyses of green and calcined tapes were performed using mercury porosimetry and SEM. From these observations, a model of the binder distribution within a cross-section of the tape was developed.
In order to understand how the tapes deform when laminated, a study was conducted using a dynamic mechanical analyzer (DMA). These stress/strain compression measurements were performed at several temperatures (25°C to 80°C) to determine the effect of cold and hot pressing conditions. The deformation results were related back to the microstructure and composite mechanical behavior of the three phases (binder, powder, and voids).
Further investigations were conducted on cross-sections of sintered laminated parts to determine the effect of pressing conditions on the generation of lamination defects. Electric field modeling was used to determine field enhancement effects generated by these common delamination and tape defects. Finally, electrode configurations to suppress field enhancement in ultra-high gradient insulators were modeled"--Abstract, page iii.
Brow, Richard K.
Waddill, George Daniel
Materials Science and Engineering
M.S. in Ceramic Engineering
University of Missouri--Rolla
xiii, 121 pages
© 2000 Chad Robert Essary, All rights reserved.
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Essary, Chad Robert, "Processing and characterization of ceramic tape layers for ultra-high gradient insulators" (2000). Masters Theses. 1971.
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