Ceramic films coatings

In this chapter we look first at an important class of alloys designed to resist corrosion the stainless steels. We then examine a more complicated problem that of protecting the most advanced gas turbine blades from gas attack. The basic principle applicable to both cases is to coat the steel or the blade with a stable ceramic usually Cr203 or AI2O3. But the ways this is done differ widely. The most successful are those which produce a ceramic film which heals itself if damaged - as we shall now describe. 

We have successfully developed a new inorganic ceramic membrane coated with zirconium and alumina. A thin film of alumina and zirconia unsupported membrane was also fabricated. The successful method developed was the sol-gel technique. 

CERAMIC FILMS AND COATINGS edited by John B. Wachtman and Richard A. Haber... 

Hui R, Wang Z, Yick S, Marie R, and Ghosh D. Fabrication of ceramic films for solid oxide fuel cells via slurry spin coating technique. J. Power Sources 2007 172 840-844. 

Wachtman JB, Haber RA (eds.) (1992) Ceramic Films and Coatings, Noyes, Park Ridge... 

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

Abstract. Liquid phase deposition methods are a useful way to create mineral oxide films from aqueous solution under near-ambient conditions. These approaches have been applied to the creation of ceramic coatings on polymers and on polymer-matrix composites. Control has been achieved over the adherence and crystallinity of the solution-deposited thin films based on controlling the composition of both the deposition solution and the substrate surface. The challenge of depositing such films from water, while minimizing film cracking has also been addressed. Crack-free ceramic films of up to 200 nm thickness have been achieved on a variety of polymer substrates. 

Wachtman, J. B. Haber, R. A., Eds. Ceramic Films and Coatings, Noyes Publications Park Ridge, NJ (1993). 

S. Amberg-Schwab, E. Arpac, W. Glaubitt, K. Rose, G. Schottner, U. Schubert, in High Performance Ceramic Films and Coatings (Ed. P. Vincenzini), Elsevier, Amsterdam, 1991, 203. 

E. Cappelli, G. Giunta, A. Parretta, and V. Adoneecchi, High Performance Ceramic Films and Coatings, 1991, p.409. 

The power of laser ablation can be extended as a popular method for trace and bulk analysis in conjunction with ICP-OES and is an invaluable tool in the study of surface behaviour particularly where sensitive surfaces are important. The common area for surface knowledge is in environment, medicines, adhesives, powders, slurries, oil-based samples and liquids. It finds application in the analysis of metallurgical samples, non-conductive polymers, ceramic materials, surface mapping, elemental migration, depth profiling, thin film coatings, biological and clinical specimens, forensic, paint chips, inks, bullets, fabrics, etc. 

Use Electronic and optical applications, starting materials for growing single crystal solid-state lasers, high-temperature dry film lubricants in the form of ceramic-bonded coatings. 

When diffusional relaxation of a suspension brought out of equilibrium by shearing is slow with respect to the time-scale of the process (De number), the suspension is said to be thixotropic. This behaviour is illustrated in Fig. 6.21. Thixotropy is usually imwanted in ceramic membrane support coatings, but does occur for some suspension formulations. The layer thickness obtained in film-coating with the same suspension but with a different shear history can then differ. 

Most liquid films which are formed during film-coating are metastable or instable. This especially involves coating with aqueous suspensions. With ceramic membrane support coatings with a wet coating as thin as 1000 nm, instability can already occur at relatively low contact angles. 

Two main groups of lyogel film formation mechanisms can be distinguished (i) film coating, and (ii) slip casting. In the film-coating process, capillary forces in pores do not play a role and this process can be used also on dense, non-porous substrates. The slip cast process is widespread in the production of bulk ceramics but has only been recently applied to the production of membranes [3,9]. In this process capillary forces play a dominant role. 

Ceramic coatings on fibers and powders have a variety of uses. For example, porous ceramic coatings on nanoscale metallic or ceramic particles can improve the catalytic properties of a powder. Also, the carbon fibers used as reinforcement in metallic matrices can be coated with a thin ceramic film (such as SiC or TiN) to reduce the rate of interdiffusion that may occur between the matrix materials and the fibers, and enhance the wetting of the fiber surface by metals. ... 

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