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These are sprayed on ceramic kiln interiors to improve heat, corrosion and wear resistance.
Key phrases linking here: refractory ceramic coatings - Learn more
Refractory ceramic coatings are sprayed onto the insides of kilns and on elements to achieve several goals. Coated electric kiln elements are claimed to last up to 10 times longer. Coated kiln interiors are more efficient, last longer and are resistant to corrosion and erosion (wetting by molten metals). The coating seals cracks (and thus heat or pressure loss). Fiber surfaces can be spray-coated to greatly improve lifetime and durability. Coatings can be heat-reflective. Coating technology has been developed into successful commercial products.
Coatings obviously need to be very refractory, so that necessitates the use of expensive materials. Fortunately there are many (like zircon, alumina oxide, SiC, non-oxides like boron nitride and titanium diboride, even exotic materials like yttrium, hafnium and tantalum oxides and carbides). Zircon is a commonly available material in ceramics (used as a glaze opacifier) and it is amoung the most heat resistant materials known to man. You can make your own RCC by plasticizing zircon using a hectorite or smectite clay (e.g. VeeGum, Bentone). As little as 3% can produce a paintable or sprayable product. The degree of powdering after firing can be controlled by the addition or a ball clay or kaolin (these will produce a harder fired surface).
Aremco Refractory Coatings page has good explanation of different types available
UltraMet ceramic protective coatings page - very educational
|By Tony Hansen|
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