Method for producing thick ceramic films by a sol gel coating process

Abstract

A method for producing thick ceramic films of greater than 10 mu m on selected substrates is described. Conventional sol gel solutions are loaded with up to about 90% by weight of finely divided ceramic particles and mixed. The resulting slurry or paint can be either spun or dip coated or sprayed or painted onto a planar or other substrate, fired to remove the organic materials and to develop a microcrystalline structure. The fired film may then be heated. Composite films are also contemplated.

We claim: 
     
       1. A process for producing a polycrystalline ceramic film on a substrate comprising: (a) mixing a .[.organo-metallic.]. sol-gel solution with up to about 90% by weight of said solution of a ceramic powder .Iadd.selected from the group consisting of oxides, carbides and nitrides .Iaddend.so as to produce a uniform stable dispersion;   (b) applying said stable dispersion to a substrate.Iadd., without a substantial temperature differential therebetween, .Iaddend.so as to provide a coating thereon up to about 6 μm thick; and   (c) firing said coated substrate at a temperature up to about 1000° C. so as to remove organic constituents and produce a stable polycrystalline .[.metallic oxide.]. .Iadd.ceramic .Iaddend.film containing said ceramic powder on said substrate.   
     
     
       2. A process as claimed in claim 1 wherein steps (b) and (c) are repeated at least five times so as to produce a stable .[.crack-free.]. polycrystalline film at least 10 μm thick. 
     
     
       3. A process as claimed in claim 1 including the step of heating said .[.metallic oxide.]. .Iadd.ceramic .Iaddend.film on said substrate at a temperature up to about 1000° C. after said firing. 
     
     
       4. A process as claimed in claim 1 wherein said ceramic powder is selected from the group consisting of .Iadd.yttria .Iaddend.stabilized .[.Zirconia.]. .Iadd.zirconia, ceria.Iaddend., stabilized .[.Zirconia.]. .Iadd.zirconia.Iaddend., PZT, .[.Alumina.]. .Iadd.alumina.Iaddend., .[.Titania.]. .Iadd.titania.Iaddend., .[.Calcium.]. .Iadd.calcium.Iaddend., .[.Zirconate.]. .Iadd.zirconate.Iaddend., .[.Silica.]. .Iadd.silica.Iaddend., .[.Silicon Carbide.]. .Iadd.silicon carbide.Iaddend., .[.Titanium Nitride.]. .Iadd.titanium nitride.Iaddend., .[.Calcium-Hydroxyapatite,.]. and .[.Nickel Zinc Ferrite.]. .Iadd.nickel zinc ferrite.Iaddend.. 
     
     
       5. A process as claimed in claim 4 wherein said sol-gel solution is selected from the group consisting of PZT, .[.Zirconia.]. .Iadd.zirconia.Iaddend., .[.Alumina.]. .Iadd.alumina.Iaddend., .[.Silica.]. .Iadd.silica.Iaddend., .[.Nickel Zinc Ferrite.]. .Iadd.nickel zinc ferrite .Iaddend.and .[.Titania.]. .Iadd.titania .Iaddend.solutions. 
     
     
       6. A process as claimed in claim 1 wherein said film is selected from the group consisting of a.[.,.]. bio-inert film.[.,.]. and a dielectric film. 
     
     
       7. A process as claimed in claim 6 wherein said bio-inert film comprises calcium zirconate. 
     
     
       8. A process as claimed in claim 6 wherein said dielectric film is selected from the group consisting of alumina, calcium-modified zirconia.[...]., and ceria stabilized zirconia. 
     
     
       9. A process as claimed in claim 1 wherein said substrate is selected from the group consisting of stainless steel and carbon steel nuts, carbon steel tubes, carbon steel plates, and aluminum substrates. 
     
     
       10. A process as claimed in claim 9 wherein said substrate is a carbon steel tube and said film is deposited on inside and outside surfaces thereof. .[.11. A process as claimed in claim 1 wherein said film is 
     
     
        crack-free..].12. A process for producing a polycrystalline film selected from the group consisting of zirconia and titania on a substrate selected from the group consisting of aluminum foil and stainless steel, comprising: (a) mixing a sol-gel mixture selected from the group consisting of titania and zirconia and a solution of a metal salt with up to 90% by weight of a .[.yttria stabilized.]. powder selected from the group consisting of titania and .Iadd.yttria stabilized .Iaddend.zirconia in a size range between 0.1 and 10 microns so as to produce a stable dispersion;   (b) applying said stable dispersion to said substrate so as to provide a coating up to 6 μm thick; and   (c) firing said coated substrate at a temperature up to about 500° C. so as to produce a stable polycrystalline film on said substrate.   
     
     
        .[.     A process as claimed in claim 12 wherein said film is 
     
     
        crack-free..].14. A process for producing .Iadd.a .Iaddend.polycrystalline composite ceramic .[.films.]. .Iadd.film .Iaddend.on a substrate comprising: (a) mixing a first .[.organo-metallic.]. sol-gel solution with up to about 90% by weight of .Iadd.said first solution of .Iaddend.a first ceramic powder so as to produce a first uniform stable dispersion;   (b) mixing a second .[.organo-metallic.]. sol-gel solution with up to about 90% by weight of said .Iadd.second .Iaddend.solution of a second ceramic powder so as to produce a second uniform stable dispersion;   (c) applying a first coating of one of said first and second stable dispersions to said substrate.Iadd., without a substantial temperature differential therebetween.Iaddend.;   (d) firing said first coating at a temperature up to about 1000° C. so as to remove organic constituents and produce a stable polycrystalline first .[.metal oxide.]. .Iadd.ceramic .Iaddend.film containing a respective one of said ceramic powders on said substrate;   (e) applying a second coating of the other of said first and second stable dispersions to said first .[.oxide.]. .Iadd.ceramic .Iaddend.film on said substrate; and   (f) firing said second coating at a temperature up to about 1000° C. so as to remove organic constituents and produce a stable .[.crack-free.]. polycrystalline second .[.metal oxide.]. .Iadd.ceramic .Iaddend.film containing the respective other one of said ceramic powders on said first   
     
     
        metal .[.oxide.]. .Iadd.ceramic .Iaddend.film. 15. A process as claimed in claim 14 wherein steps (c), (d), (e) and (f) are repeated so as to produce a composite .[.metal oxide.]. .Iadd.ceramic .Iaddend.layer at least 10 
     
     
        μm thick. 16. A process as claimed in claim 15 wherein said first ceramic powder is silicon carbide and said second ceramic powder is 
     
     
        titanium nitride. 17. A process as claimed in claim 16 wherein said first and second .[.organo-metallic.]. sol gel solutions are the same. .[.18. A process as claimed in claim 14 wherein said films are 
     
     
        crack-free..]..Iadd. 9.  A process as claimed in claim 1, wherein said sol gel solution is organo metallic or a salt. .Iaddend..Iadd.20. A process as claimed in claim 14 wherein said first and second sol gel solutions are organo-metallic or salts. .Iaddend..Iadd.21. A process as claimed in claim 5 wherein said PZT solution is selected from the group consisting of alkoxides, metal salts, carboxylates and ketones. .Iaddend..Iadd.22. A process as claimed in claim 5 wherein said zirconia is selected from the group consisting of alkoxides, metal salts, carboxylates and ketones. .Iaddend..Iadd.23. A process as claimed in claim 5 wherein said titanium is selected from the group consisting of alkoxides, metal salts carboxylates and ketones. .Iaddend..Iadd.24. A process as claimed in claim 20, wherein said sol gel solutions are aqueous, organic or mixtures thereof. .Iaddend..Iadd.25. A process as claimed in claim 5, wherein said sol gel solution is aqueous, organic or a mixture thereof. .Iaddend..Iadd.26. A process as claimed in claim 1 wherein said ceramic powder is calcium hydroxy-apatite. .Iaddend..Iadd.27. A process as claimed in claim 1 wherein said film is crack-free. .Iaddend..Iadd.28. A process as claimed in claim 12 wherein said film is crack-free. .Iaddend..Iadd.29. A process as claimed in claim 14 wherein said films are crack-free. .Iaddend.