CELLULAR CERAMICS MADE OF SILICON CARBIDE CERAMICS FOR BURNER TECHNOLOGY

Cellular ceramics have been of increased interest for applications in burner technology. High power density of the burners up to some MWm(-2) raises the load on the materials regarding thermal shock and temperature. Silicon carbide (SiC) ceramics is favoured for such applications, because it combines low CTE. high thermal conductivity and emissivity as well as good stability at high temperatures. Nevertheless cellular ceramics have a high inner surface and lower strength compared to the bulk. This results in problems with crack resistance and long time oxidation stability. Manufacturing of cellular ceramic components needs special efforts to find a good compromise between shaping method and material properties. To tackle these problems the following methods were used to enhance stability of burner components: (1) thermomechanical simulation, (2) model experiments to calculate long time oxidation resistance, (3) optimisation of materials, cellular structure and manufacturing technology and (4) experiments in laboratory burner equipment for validation Open cell foams made of siliconized SiC provide highest strength but limited operating temperature because of the melting of the free silicon. Burners with intermediate heat load can use such foams for a very long time, because of a stable passivation layer. Sintered or recrystallized SiC foams resist higher temperatures than SiSiC but exhibit limited long time oxidation stability only, if they contain open microporosity. Special designed IR-emitter plates with aligned cells possess high durability against thermals shock. A special developed sintered SiC has been used showing good oxidations resistance which allows the prediction of a 3-5 years lifetime at least.