Preparation and characterization of mullite-silicon carbide heat absorbing ceramics for solar thermal tower plant

Abstract

The in-situ synthesized mullite bonded SiC ceramics for solar thermal tower plant were prepared from Silicon carbide (SiC), manufactured aluminum hydroxide (Al(OH)₃) and Suzhou kaolin via semi-dry pressing and pressureless firing. The results indicate that sample B3 (designed mullite content 15 wt%) fired at 1 400 °C exhibited optimal performance with a bending strength of 97.41 MPa. Sample B3 can withstand 30-cycles thermal shock without cracking (wind cooling from 1 100 °C to room temperature), and the bending strength after thermal shock decreased by 17.92%. When the service temperature is 600 °C, the thermal diffusivity, specific heat capacity, thermal conductivity and heat capacity are 6.48×10⁻² cm²·s⁻¹, 0.69 kJ·kg⁻¹· K⁻¹, 9.62 W·m⁻¹·K⁻¹ and 977.76 kJ·kg⁻¹, respectively. The XRD and SEM results show that SiC, mullite, α-quartz, and tridymite are connected closely, which gives the material a good bending strength. After 30-time thermal shock cycles, the structure of samples becomes loose. SiC grains are intersectingly arranged with rodshape mullite, exhibiting a favorable thermal shock resistance. The addition of Al(OH)₃ and Suzhou kaolin can accelerate the synthesis of mullite, thus to reduce the firing temperature effectively. The volume effect of tridymite is relatively small, improving the thermal shock resistance of materials. A higher designed mullite content yields a lower loss rate of bending strength. The mullite content should not be more than 15 wt% or else the bending strength would be diminished.

Keywords

heat absorbing materials / mullite-SiC composite ceramics / thermal shock resistance / thermal properties

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