Communication Compatibility of Lead-Bismuth Eutectic with SiC-Coated Graphite at Elevated Temperature POULAMI CHAKRABORTY, ABHIJIT GHOSH, and GAUTAM KUMAR DEY Uniform coating of b-silicon carbide (b-SiC) was formed over a graphite pellet through slurry-based silicon coating followed by in situ reaction at 1873 K (1600 °C). The coated pellet was exposed to molten lead-bismuth eutectic (LBE) at 1173 K (900 °C) in static condition for 200 h. Weight loss measurement, X-ray diffraction, and secondary electron microscopy–energy-dispersive spec- troscopy confirmed that the SiC coating could effectively prevent molten LBE from attacking the inner graphite material. DOI: 10.1007/s11663-016-0763-1 Ó The Minerals, Metals & Materials Society and ASM International 2016 In order to meet the growing energy demands and to counter the negative atmospheric effects arising due to usage of fossil fuels, hydrogen has emerged as a clean, reliable, and sustainable energy source. [1] In this regard, Bhabha Atomic Research Centre (BARC) is engaged in developing a prototype Compact High Temperature Reactor (CHTR), which aims at the production of industrially usable hydrogen by splitting of water. [1,2] The CHTR uses U-233- and thorium-based carbide as fuel (TRISO-coated particle) compacted in a graphite matrix. [3] Cylindrical fuel compacts are packed in fuel bores located at the walls of each graphite fuel tube. The arrangement of the fuel tube placed along with the BeO moderator is shown in Figure 1. The core heat is removed by natural circulation of lead-bismuth eutectic alloy [44.5 wt pct Pb + 55.5 wt pct Bi], which enters the fuel tube at 1173 K (900 °C) at the lower plenum, takes the reactor heat, and leaves the tube at 1273 K (1000 °C) from the upper plenum. Thus, maintenance of long-term integrity of the graphite fuel tube in the presence of lead-bismuth eutectic (LBE) in the temper- ature range of 1173 K to 1273 K (900 °C to 1000 °C) is an important factor in deciding the feasibility of this process. LBE is found to be substantially corrosive toward various structural materials like austenitic stainless steels. [4,5] Moreover, experiments to study the compat- ibility of graphite with LBE at 1073 K (800 °C) have revealed the formation of a lead-carbon reaction layer over the graphite surface that had an estimated growth rate of 61.3 lm/year. [6,7] Considering this aspect, a protective oxidation- and corrosion-resistant coating of silicon carbide (SiC) has been proposed over the graphite fuel tubes. Nevertheless, obtaining a uniform and adherent SiC coating over graphite material is a major challenge. Although SiC is a relatively hard and inert material, compatibility of the same with LBE at the high working temperatures of CHTR remains another important area of investigation. [8,9] With this view, a layer of SiC was formed on a graphite pellet through the slurry-based silicon coating followed by in situ reaction at an elevated temperature. Later, the corrosion behav- ior of the coated pellet with molten LBE was studied in static condition for 200 hours at 1173 K (900 °C). Commercially available graphite pellets of 17 mm diameter (5 mm thickness) were coated with silicon (Si) slurry prepared in-house. The pellets were initially manufactured from nuclear grade graphite material and had a density of 1.8 gm/cc. The coating of silicon over the graphite pellet was carried out by simple brush painting method. Silicon-coated samples were subse- quently heat treated at 1873 K (1600 °C) for 3 hours in argon atmosphere to form the SiC coating on graphite surface. Figure 2 shows the photograph of the SiC- coated graphite pellet. Afterwards, the surface of one sample was investi- gated through X-ray diffraction (XRD). Later, the cross section of the same sample was analyzed through secondary electron microscopy (SEM). The rests of the samples were kept intact for use in compatibility studies. The compatibility study was performed in a retort fabricated with 50NB Inconel 625 pipe, which was closed at the bottom with a 10-mm-thick Inconel 625 plate. The 250-mm-long retort was provided with flanged connection at the top. A 5-mm-thick, 90-mm-long graphite crucible having an inside diameter of 40 mm was placed inside the Inconel retort. This graphite crucible was used to contain the LBE. The schematic of the completely assembled test facility equipped with online sample replacement mechanism is shown in Figure 3. On the other hand, the sample holder was made of a small molybdenum cup having 20 mm inner diameter and 35 mm length. Holes were drilled through the sides POULAMI CHAKRABORTY, Scientific Officer-E, is with the Fusion Reactor Materials Section, Bhabha Atomic Research Centre, Trombay, Mumbai, 400085, Maharashtra, India. Contact emails: poulamic@barc.gov.in; myworld.pc@gmail.com. ABHIJIT GHOSH, Scientific Officer-G, is with the Glass and Advanced Materials Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400085, Maharashtra, India. GAUTAM KUMAR DEY, Distin- guished Scientist, is with the Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400085, Maharashtra, India. Manuscript submitted April 11, 2016. Article published online August 29, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B VOLUME 48B, FEBRUARY 2017—1