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Claire Michel
Abstract
Thermomechanical behaviour and oxidation behaviour of silicon nitride bonded SiC refractories used in waste-to-energy plants
Claire Michel - 16 February 2011
In this work, the microstructure and the thermomechanical
behaviour of two SiC-based refractories are studied. In
waste-to-energy plants, these materials are subjected to severe
sollicitations such as thermal gradients, chemical composition
gradients and corrosion.
SiC-Si3N4 and SiC-SiAlON refractories are composed by SiC
agregates bonded with silicon nitride based phases. A complex
porosity network characterises the bonding phase. Its
microstructure is analysed with Scanning Electron Microscopy
(SEM). The thermomechanical behaviour of each refractory is
characterised with 4-points bending tests and ultrasonic pulse
echo measurement of the Young's modulus.
During the running of waste-to-energy plants, refractories are
exposed to oxidation phenomenons. They are more critical with an
increase of a water content in the air. Thus, the oxidation
behaviour is studied between 800°C and 1200°C under dry air,
ambiant air and humid air. The microstructural evolutions due to
oxidation are influenced by the porosity network, which leads to
two oxidation stages depending on temperature level and
environnemental conditions. Thermomechanical behaviour is also
determined for each oxidation stage. This characterisation
approach permits to establish relationships between the
thermomechanical behaviour and the microstructural evolutions
during oxidation. Phenomenological modellings are
presented. Finally, thermal treatments are proposed in order to
improve the durability of SiC-Si3N4 and SiC-SiAlON refractories
in waste-to-energy plants.
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