Abstract
A process combining the pyrolysis of a lignocellulosic structure and reactive gas treatments has been developed to prepare porous TiC-SiC ceramics for solar receivers. The natural micro-porosity of balsa was complemented by a high open macro-porosity by laser cutting a periodical arrangement of parallel channels. The lignocellulosic structure was first pyrolysed into carbon. This reactive carbon material was then converted into TiC by Reactive Chemical Vapor Deposition (RCVD) using TiCl4/H2. After controlling the absence of cracks due to volume changes, the TiC structure was finally infiltrated by the Chemical Vapor Infiltration (CVI) of SiC using CH3SiCl3/H2. The density, porous structure, elemental and phase compositions, oxidation behavior and crushing strength were assessed after pyrolysis, RCVD and CVI. The SiC CVI coating significantly improves the compressive strength, the oxidation resistance and the thermal properties. The SiC layer is no longer fully protective at high temperature but the mechanical properties remain reasonably high.
Highlights
The increasing problem of CO2 emissions and energy security concerns such as nuclear safety, radioactive waste management and resource dependence, have given interest in alternative sources of energy
The change in macroscopic dimensions is about -20% along the fiber axis and -30% in the perpendicular direction, leading to an overall volume shrinkage around 60% and a nearly 40% decrease of the apparent density
Despite the strong weight loss and anisotropic shrinkage observed during this stage [38], the microstructure of the material is remarkably preserved at all scales (Fig. 5)
Summary
The increasing problem of CO2 emissions and energy security concerns such as nuclear safety, radioactive waste management and resource dependence, have given interest in alternative sources of energy. Volumetric receivers with a proper choice of porous structure and solid constituent can collect a solar radiation power that is significantly higher than tubular receivers [5]. These high open porosity and specific surface materials can be for instance monolith honeycomb structures [6,7], isotropic reticulated foams [7,8,9,10,11] or non-extrudable 3D periodic lattices [10].
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