Reactively sintered TiB2-based heteromodulus UHT ceramics with in-situ formed graphene for machinable concentrated solar light absorbers

The paper encompasses deeper understanding of sintering, properties and applications of nanostructured refractory ceramics with "hard"/"soft" ceramic phase combinations. TiB2–SiC–C Ultra High Temperature Ceramics in heteromodulus form with the in-situ formed nanostructured carbon were sintered via reactive route. It is shown that the green body compositions should account for zirconia contamination introduced during green body milling process. SEM and Raman spectroscopy showed that the in-situ segregating carbon forms platelets with structure of highly defected graphene multilayers and amorphous inclusions. Silicon carbide in the ceramics is present in 2H polytype form. The crack resistance of the ceramics is maximised at 8.4 MPa∙m1/2 for the material with 16 vol% of carbon. Ceramic drilling rate theory is developed and it is shown that the material removal for heteromodulus composite should account for soft phase shapes and distribution and hard phase removal in cascade pull-out events. The model explains significant machinability increase as the soft phase content rises above 20 vol%. The model also demonstrates how hard hetero-modulus material can be drilled with softer than the ceramic drills. Light absorption of the TiB2–SiC–C ceramics was analyzed and it is shown that the presence of high carbon content only reduces light absorption by approximately 10%. Final light absorption remains at above value for the most of concentrated solar energy absorbers. It is concluded that TiB2–SiC–C ceramic can be used as an effective concentrated solar light receiver.