Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Heating – annealing – or sintering
Patent
1992-09-18
1995-03-28
Lieberman, Paul
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Heating, annealing, or sintering
505742, 505782, 505501, 252518, 252521, H01B 1200, H01L 3912
Patent
active
054017122
ABSTRACT:
A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa.sub.2 Cu.sub.3 O.sub.x indicates that sintering kinetics are enhanced at reduced p(O.sub.2) and that because of second phase precipitates, grain growth is prevented. The density of specimens sintered at 910.degree. C. increased from 79 to 94% theoretical when p(O.sub.2) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O.sub.2) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910.degree. C resulted in a fine-grain microstructure, with an average grain size of about 4 .mu.m. Post sintering annealing in a region of stability for the desired phase converts the second phases and limits grain growth. The method of pinning grain boundaries by small scale decompositive products and then annealing to convert its product to the desired phase can be used for other complex asides. Such a microstructure results in reduced microcracking, strengths as high as 230 MPa and high critical current density capacity.
REFERENCES:
patent: 5024992 (1991-06-01), Morris
patent: 5106829 (1992-04-01), Quadri
patent: 5149684 (1992-09-01), Woolf
patent: 5232907 (1993-08-01), Matsuhiro
patent: 5244868 (1993-09-01), Jin
patent: 5250509 (1993-10-01), Hettich
Chen Nan
Goretta Kenneth C.
Poeppel Roger B.
Singh Jitrenda P.
Kopec M.
Lieberman Paul
University of Chicago
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