Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 27 TUESDAY AFTERNOON
JS1-TuA-INV.10 DECORATIVE COATINGS ON ENAMEL CERAMICS DEPOS-
ITED BY PVD TECHNIQUES. A. Alberdi. Fundación Tekniker. Avda. Otaola, 20. 20600
Eibar, Spain..F. Lucas, A. Belda. Fritta S.L. CV-20 Km 8, 12200 Onda (Castellón), Spain.Mª
José Orts. Instituto de Tecnología Cerámica (ITC). Campus Universitario Riu Sec, 12006 Castellón,
Spain
Ceramic tiles - floor tiles, wall tiles and other decorative articles - are usually made by firing a ceramic
backing, which is coated with a consolidated layer of frits and crystalline materials that glaze
after the baking process. The ceramic backing may be raw, as when the single-fire method is used,
or else baked, when the double-fire method is used.
Obviously, ceramic glazed products must have technical and decorative qualities that make them
suitable for the use to which they are to be put, such as hardness, resistance to cracking, wear and
scratching, imperviousness and insolubility in water and in those acids and alkalis with which they
may enter into contact in normal use. Decorative effects are created depending on the finishing
process used, for example, gloss or matt, opaque or transparent, smooth or granulated, polished, etc.
Modern decorative trends ask for conferring the tile a metallic appearance.
Current ceramic metallizing techniques normally consist of adding a given amount of metal to the
baked tiles, but prior to glazing or final enamelling, so their finishes have very low scuff and
scratching resistance, being impossible to use on floors or facades, and they are not resistant to
chemical attack. Furthermore, the gloss of current finishes does not exceed 200‰ at angle of incidence
of 60º.
Recently, new metallizing techniques have been developed using Physical Vapour Deposition
(PVD) methods. The authors set up a novel procedure to metallise enamelled products. Under vacuum
and after degassing the tile backing, a metallic coating grows on the enamelled tile surface by
bombardment with metallic ions and neutral atoms of titanium, zirconium, tantalum or chromium.
These atomic species are generated by a high intensity arc discharge (in the range 50-250 A) between
an electrode made of the metal of interest, normally a rod, pipe or plate, and an auxiliary cooper
electrode. Apart from pure metal films, nitrides and carbo-nitrides of these metals can be also
deposited on the tile surface by adding nitrogen and hydro carbide gases in the vacuum chamber.
Using this new procedure, enamelled tiles coated with 0.3 microns thick decorative films were produced,
which show attractive colours and metal appearance. Finishing colours depended on the
chemical nature of the film: golden (zirconium, titanium and tantalum nitrides), metallic grey (chromium
nitride, and pure Ti, Zr or Cr), reddish brown or purple (titanium carbo-nitrides). Apart from
the attractive colour, these decorative surfaces exhibit an outstanding metallic gloss (ZrN 736‰ at
angle of incidence of 60º), and excellent resistance to acids and alkaline substances.
Key words: Ceramic tiles, decorative coatings, physical vapour deposition.
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