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.

Description

FIELD OF THE INVENTIONThis invention relates to the production of thick ceramic films, including composite films, on selected substrates, using a sol-gel coating technique. More particularly this invention relates to a technique for depositing polycrystalline ceramic films such as lead zirconate titanate and partially stabilized zirconia, in thicknesses greater than 10 .mu.m.BACKGROUND OF THE INVENTIONCeramic coatings can be prepared by thermal or plasma spraying and physical vapour deposition (PVD) techniques. In plasma spray, a bulk powder is passed through a plasma and directed towards a substrate where it cools on contact. Films up to 10 mm thick can be produced in this way but usually need post-deposition heating as the deposited film tends to be porous (10% porosity is considered good). Another drawback of the plasma spray technique is that only line of sight geometries can be successfully coated. In PVD, expensive vacuum systems are required to coat high quality ceramic films...

AI Technical Summary

Benefits of technology

An object of the present invention is to provide an improved method for applying adherent ceramic films to metallic substrates in thicknesses greater than 5 .mu.m and at least up to 200 .mu.m without cracking.

Problems solved by technology

Another drawback of the plasma spray technique is that only line of sight geometries can be successfully coated.

In PVD, expensive vacuum systems are required to coat high quality ceramic films of less than 10 .mu.m.

In addition this technique is also limited to line of sight geometries.

Clearly a 10 .mu.m film made 0.1 .mu.m at a time is a very time consuming and laborious process.

Sol Gel films are, however, very susceptible to substrate interaction, defects and stresses within the film.

Solvents and organics can escape from 0.1 .mu.m layers relatively easily but for thicker layers this is not so resulting in defects which can act as nucleation centres for crack propagation.

Sol gel films are also substrate dependent and most films are limited to metallized silicon or other highly polished substrates.

Conventional sol gel technology cannot, therefore, be used to produce thick, large area sol gel films.