Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiCsandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ∼10 cm/s and 550 °C, with and without a 1.8-2T magnetic field, were performed to materials coated with a 200-400-µm-thick dense SiC layer, obtaining promising results.

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h i g h l i g h t s • A wide range of porous SiC materials with different properties were produced. • The produced 50% porous SiC has k ≈ 5 W/m K at 700 • C and ≈ 3 10 −5 S/m at 550 • C. • The produced 50% porous SiC has a flexural strength in the range 50-80 MPa. • A 200 m dense CVD-SiC coating offers reliable protection against static PbLi corrosion. a b s t r a c t Flow Channel Inserts (FCIs) are key elements in a DCLL blanket concept for DEMO, since they provide the required thermal insulation between the He cooled structural steel and the hot liquid PbLi flowing at ≈700 • C, and the necessary electrical insulation to minimize MHD effects. In this work a SiC-based sandwich material is proposed for FCIs, consisting of a porous SiC core covered by a dense CVD-SiC layer. A method to produce the porous SiC core is presented, based on combining a starting mixture of SiC powder with a spherical carbonaceous sacrificial phase, which is removed after sintering by oxidation, in such a way that a microstructure of spherical pores is achieved. Following this technique, a porous SiC material with low thermal and electrical conductivities, but enough mechanical strength was produced. Samples were covered by a 200 m thick CVD-SiC coating to form a SiC-sandwich material. Finally, corrosion tests under static PbLi were performed, showing that such a dense layer offers a reliable protection against static PbLi corrosion.

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This paper discusses the characteristics of ZnO and ZnO:Ga ceramics fabricated by uniaxial hot pressing. The short-wavelength transmission limit of zinc oxide ceramics is in the 370-nm region; the long-wavelength limit is determined by the free-charge-carrier concentration and lies in the interval from 5 to 9 μm. The total transmittance of such ceramics in the visible and near-IR regions is about 70% when the sample is 0.5 mm thick. The luminescence spectrum is represented by a broad emission band with maximum at 580 nm, having a defect nature. The introduction of 0.03-0.1 mass % gallium into the zinc oxide structure inhibits grain growth and increases the free-charge-carrier concentration to 3.44 × 10 19 cm −3. As the gallium concentration increases in the range 0.05-0.1 mass % in a ceramic of composition ZnO:Ga, the defect luminescence band is suppressed and a characteristic exciton luminescence is formed with a maximum corresponding to 389 nm and a damping time constant of 1.1 ns.