Ceramic Tiles or Ceramic Coatings?
Are you coating your metal components with ceramic to increase its wear-resistance? Why not try using ceramic tiles instead? CeTZP ceramic tiles could be mechanically anchored or fastened onto a metal component (e.g. using a tongue-in-groove configuration) and held in place with adhesives.
Thicker ceramic tiles could take advantage of the mechanical and thermal properties of a ceramic more fully than thinner ceramic coatings.
Also, mechanical interlocking of ceramic tile with metal component enables the joint to be disassembled readily whenever a cracked ceramic tile needs to be replaced.
Ceramic tiling is not new. It is not even a novel concept. Tiles made from traditional ceramics have been used on floors, walls and bathrooms since Roman times or even longer. Tiles made from advanced ceramics have been used in engineering applications (e.g. US Space Shuttles) since the 1970s and are replaceable if damaged. There is also a wealth of knowledge available on the methods of anchoring and fastening.
The actual method of anchoring or fastening of the ceramic tiles to the metal substrate requires careful consideration or the consequences could be dire. In other words it is the details of the design and the details in the method of fastening and joining that are important and could define the difference between success and failure.
Fastening or joining of the ceramic tiles onto a metal base or substrate needs to take account of the unique combination of properties that engineering ceramics possess as well as the differential behaviour between the ceramic and the metal substrate (e.g. crystallographic lattice mismatch). Stress and failure probability analyses need to be used to generate component/material iterations that would lead to improvements in order to meet the hash and severe requirements of an application under operational conditions.
An Application - Using Ceramic Tiles in Engines
Metal engines operate at temperatures too low (< 500 C) for fuel to be burnt completely. Also, metal engines waste a lot of the heat generated during combustion to its surroundings because metals are good conductors of heat (about one-third of the thermal energy generated is lost to the coolant or radiator water). Therefore insulating the internal surfaces of an internal combustion engine with a thermal barrier is clearly a desirable objective.
Making the combustion chamber of an IC engine entirely out of zirconia ceramic or else insulating the surface of the combustion chamber with zirconia ceramic tiles should improve the engine's combustion characteristics and reduce heat loss. This could lead to higher engine performance and lower exhaust emissions.
Also, as the thermal expansion coefficients of zirconia ceramics, cast iron and some steels are similar (~ 9 - 15 x 10E-6/K), thermal mismatch between these materials are likely to be minimal. Many internal combustion engines are made out of cast iron or steel; therefore the combustion surfaces of these engines could be tiled with zirconia-based ceramics without causing thermal stresses through a mismatch of the materials.
The thicker the ceramic thermal barrier the better the insulation and the lesser the heat loss. Ceramic tiles can be made thick enough (e.g. several millimetres) to take advantage of the essential properties of the ceramic. Ceramic coatings, by contrast, are usually too thin (e.g. several microns) to fully take advantage of the ceramic properties. Moreover, ceramic coatings, usually thicker ones, are prone to cracking and being pealed off the metal substrate (e.g. spalling).
Tiling a metal surface with zirconia ceramic should enable the essential properties of the ceramic to be utilised without having to make the whole engine structure out of expensive ceramic. Tiling should also enable the metal-ceramic joint to be disassembled whenever a cracked ceramic tile needs to be replaced. By contrast, an engine made completely in ceramic could be ruined if a crack renders the engine inoperable.
For more about a ceramic rotary engine, please click here.
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