Process heat exchanger for SO3 decomposer fabricated with Ni-based alloys surface modified by SiC film deposition and N ion beam bombardment

In the iodine-sulfur (IS) cycle for the hydrogen production using the high temperature gas-cooled reactor (HTGR), one of the important components is the SO3 decomposer which generates SO2 and SO3 gases under high temperature conditions. Since this environment is extremely corrosive, the materials used for the decomposer should meet excellent mechanical properties at the elevated temperature as well as high corrosion resistance in SO2/SO3 atmospheres. In general, ceramics are protective against the corrosion, but metals exhibit limited corrosion resistance. In this work, the ceramic coating on the metallic substrate was studied. We selected SiC as coating materials and Ni-based alloys as the substrate materials. Since the adhesion between the coated layer and the substrate is most crucial in this application, we attempted to develop Ion Beam Mixing (IBM) technique to produce a highly adherent coated layer. For the fabrication of process heat exchange for SO3 decomposer, the diffusion bonding at ∼900 .deg. C is employed because this temperature does not affect the mechanical properties of materials