Coating processes – Electrical product produced – Metallic compound coating
Reexamination Certificate
1999-05-12
2001-06-26
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Metallic compound coating
C427S115000, C427S421100, C427S453000
Reexamination Certificate
active
06251473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for fabrication of ceramic thin films, in particular, both dense and porous ceramic thin films, utilizing spray coating. Fabrication of thin (less than or equal to about 10 microns) non-porous (dense) electrolyte layers is a key process in the fabrication of reduced-temperature (less than or equal to about 800° C.) solid oxide fuel cells and other solid state devices. This invention is an economical, scaleable and reliable method for the fabrication of non-porous ceramic films such as electrolyte layers used in solid oxide fuel cells as well as porous ceramic thin films suitable for use in, for example, ultra-filtration applications.
2. Description of Related Art
Practical applications of solid oxide electrochemical devices at temperatures below about 800° C. require a thin film sold electrolyte. Such films are currently produced utilizing a chemical vapor deposition method as taught, for example, by U.S. Pat. No. 5,145,720 to Toshio et al., an electrochemical vapor deposition method as taught by U.S. Pat. No. 4,609,562 to Isenberg et al., and sputter deposition as taught by U.S. Pat. No. 5,656,387 to Barnett et al. Chemical vapor deposition and electrochemical vapor deposition and sputter deposition are limited by long process times and high cost.
A number of additional methods have been used to fabricate oxide thin films at low cost. U.S. Pat. No. 5,085,742 to Dollard et al. teaches a method using thermoplasma spraying of yttria stabilized zirconia on doped lanthanum manganite air electrode tubes to provide an electrolyte layer. However, an additional electrochemical vapor deposition is required in order to fill the pores of the plasma spray coated layer.
U.S. Pat. No. 5,358,735 to Kawasaki et al. teaches a method in which a solid oxide powder is sprayed onto a substrate and then impregnated by a salt solution, thereby filling the pores of the spray coated layer. The thin film is then subjected to a high temperature treatment to improve air tightness of the solid oxide thin film formed on the substrate. The heat treatment temperature is between about 1300-1500° C. dependent upon the composition of the impregnated salt solution.
U.S. Pat. No. 5,585,136 to David et al. teaches a sol-gel process for fabricating solid oxide thin films on a substrate. U.S. Pat. No. 5,368,667 to Minh et al. teaches a calender rolling method and Souza et al., Journal of the Electrochemical Society, Volume 144, No. 3 (1997) reports a method for fabricating yttria stabilized zirconia thin films by dipcoating. The thin films of both of these methods are subjected to a high temperature (1400-1600° C.) sintering for airtightness, but quality control, composition-gradient coatings, surface roughness modification and large coating areas are problematic with these methods.
SUMMARY OF THE INVENTION
It is one object of this invention to provide an inexpensive, low temperature (less than about 1300° C.) sintering fabrication process for producing dense oxide thin films.
It is another object of this invention to provide a method for producing porous ceramic thin films having uniform pore sizes and low fabrication cost, which films are required in a variety of applications such as ultra-filtration and gas separation.
These and other objects of this invention are addressed by a method for fabrication of solid ceramic thin films in which a porous or dense supporting substrate is spray coated with at least one oxide powder/solvent suspension resulting in formation of a coated supporting substrate. The coated supporting substrate is then sintered at an elevated temperature, forming a solid ceramic film on the supporting substrate. Such films are suitable for use in fuel cells, gas permeation membrane reactors, sensors, ultra-filtration and gas separation processes. Dense solid oxide thin films produced in accordance with the method of this invention can be either a homogeneous composition or a gradient composition. For porous thin films produced in accordance with the method of this invention, pore size is controlled by particle size of the oxide powder and sintering temperature. In accordance with one preferred embodiment of this invention, the oxide powder has a particle size in the range of about 0.005 microns to about 2.0 microns.
The solid ceramic film produced in accordance with the method of this invention has a thickness in the range of about 0.5 microns to about 50 microns, more particularly in the range of about 2.0 microns to about 15.0 microns.
The temperature at which the coated supporting substrate is sintered is in the range of about 300° C. to about 1600° C. In order for the ceramic thin film to be porous, the sintering temperature is preferably in the range of about 300° C. to about 1100° C. In order to densify the ceramic thin film so as to form a substantially non-porous thin film, the coated supporting substrate is preferably sintered at a temperature in the range of about 1000° C. to about 1600° C.
REFERENCES:
patent: 4609562 (1986-09-01), Isenberg et al.
patent: 5085742 (1992-02-01), Dollard et al.
patent: 5145720 (1992-09-01), Hirai et al.
patent: 5332598 (1994-07-01), Kawasaki et al.
patent: 5358735 (1994-10-01), Kawasaki et al.
patent: 5368667 (1994-11-01), Minh et al.
patent: 5585136 (1996-12-01), Barrow et al.
patent: 5656387 (1997-08-01), Barnett et al.
patent: 5968673 (1999-10-01), Aizawa et al.
Selamr de Souza et al.: Reduced-Temperature Solid Oxide Fuel Cell Based on YSZ Thin-Film Electrolyte,J. Electrochem. Soc.,L35-L37, vol. 144, No. 3, Mar. 1997.
Wang Conghua
Worrell Wayne L.
Pauley Petersen Kinne & Fejer
Talbot Brian K.
The Trustees of the University of Pennsylvania
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