Résumé
TiC/SiC nanocomposites have been prepared and fully characterized at various length scales before exploring their spectral selectivity for their exploitation as solar selective absorbers. The full design process consists of (i) performing the reaction between a polysilazane, namely Durazane (R) 1800, and tetrakis(dimethylamino)titanium, (ii) shaping the as-synthesized polymer into pellets, (iii) pyrolyzing in flowing argon the raw pellets in order to achieve the conversion of the polymer into a single-phase ceramic and (iv) performing a heat-treatment at higher temperature to generate nanocomposite structures while developing the porosity of the pellets. The evolutive material is characterized at each step of the process via a combination of complementary techniques including FTIR and solid-state NMR spectroscopies, elemental analyses, thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The optical properties (0.25-25 mu m wavelength range) of the materials have been explored as a function of the temperature at which the final material has been isolated (1000-1800 degrees C). The material prepared at 1800 degrees C made of TiC nanocrystals in situ immobilized in a highly crystallized SiC matrix with an open porosity of 56% exhibited a boosted room temperature spectral selectivity of 1.91 which has been so far the highest referenced among SiC-based materials.