Design, development and optimization of the ceramic absorber material

The present Technical Report includes the activities within the WP3 of project E2PHEST2US that concerns the design, development and ptimization of the ceramic absorber material. According to previous analyses the best candidate material for the present application should possess a combination of properties including appropriate absorbance, good electrical conductivity and good thermal stability. The characterizations performed so far have identified SiC-based materials and the ternary composites based on AlN-SiC-MoSi2 as the most promising. These composite materials offer the possibility to tailor microstructure and properties through an appropriate choice of composition. They also proved to have superior oxidation resistance thanks to the development of a silica-based protective layer. Optical measurements evidenced that the amount of MoSi2 should be minimal because it increases the material's reflectance. On the other hand, MoSi2 content should be high enough (around 30 vol%) to obtain an electrically conductive composite, which is another requirement for the kind of absorber designed. These requirements can be fulfilled designing a graded composite, constituted of at least two different compositions as follows: - the side that works as the receiver contains a low amount of MoSi2 (typically 10 vol%); - the opposite side that works as emitter (with a suitable diamond coating), contains a high amount of MoSi2 (typically 30 vol%). On these bases, the activity was concentrated on the design of optimized pellets with a double composition: compositions based on SiC and ternary composites containing 10 vol% of MoSi2 were coupled to compositions containing 30 vol% of MoSi2 to combine the beneficial effect of low amount of reflective phase in the external surface and a conductive material in the inner surface. Additional pellets of best performing materials, SAYM10 and ASMY30 were also produced to carry out further tests with diamond deposition