Hydrogen permeation through steel coated with erbium oxide by sol–gel method Zhenyu Yao a, * , Akihiro Suzuki a , Denis Levchuk b , Takumi Chikada a , Teruya Tanaka c , Takeo Muroga c , Takayuki Terai a a Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan b Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstrasse 2, D-85748 Garching, Germany c Fusion Engineering Research Center, National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan abstract Er 2 O 3 coating is formed on austenitic stainless steel 316ss by sol–gel method. The results showed good crystallization of coating by baking in high purity flowing-argon at 973 K, and indicated that a little oxy- gen in baking atmosphere is necessary to crystallization of coating. The best baking temperature could be thought as 973 K, to get good crystallization of coating and avoid strong oxidation of steel substrate. The deuterium permeation test was performed for coated and bare 316ss, to evaluate the property of Er 2 O 3 sol–gel coating as a potential tritium permeation barrier. In this study, the deuterium permeability of coated 316ss is about 1–2 orders of magnitude lower than that of bare 316ss, and is about 2–3 orders of magnitude than the referred data of bare Eurofer97 and F82H martensitic steel. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction For the concept of fluid/steel blanket, in liquid Pb–Li [1] and Fli- be [2] the tritium solubility is quite low, in reduced activation mar- tensitic (RAM) steel as Eurofer97 [3] and F82H [4] the tritium permeability is higher about one order of magnitude than that of austenitic stainless steel 316ss [5]. Even for 316ss as a common structural material for fusion blanket, the tritium permeation level still cannot be accepted. Thus one of remaining critical issues is the permeation of tritium through the structure wall of metal duct, which once produced in fluid under neutron irradiation. This issue induces the loss of fuel and harm to environment. The promising way to solve this issue is to use coating as tritium permeation bar- rier (TPB) on metal duct [6]. To produce TPB coating on steel, some oxides were chosen as candidate materials. From original idea, Er 2 O 3 coating has been studied widely as insulator to mitigate magneto-hydrodynamic (MHD) pressure drop for Li/V blanket [7]. However in coincidence, Er 2 O 3 coating produced by filtered arc deposition method was found to have quite low deuterium permeability [8]. Therefore Er 2 O 3 coating has potential to act as both TPB and insulator for var- ious kinds of blanket. Among many fabrication methods to produce Er 2 O 3 coating, sol–gel is a candidate method which has advantages of high homo- geneity and single composition for coating, controllable procedure and simple device for process [9]. Especially sol–gel method has possibility to produce coating on the wall of component with com- plex shape. In this study, the fabrication process and characterization of Er 2 O 3 coating by sol–gel method were described. The permeation reduction factor (PRF) of Er 2 O 3 coating acting as potential TPB was estimated by measuring deuterium permeability of coated and bare 316ss. 2. Experimental The sol–gel method has two branch techniques to produce coat- ing, one is spin-coating (for plate shape substrate) and one is mov- ing dipping (for pipe or wire shape substrate). In this study, for the basic research of sol–gel coating the spin-coating technique was applied to disc-shape substrate. The substrate was 316ss disc with size of U 20  0.5 mm. Before deposition, the samples were polished to mirror surface, and clean in acetone and ethanol by ultrasonic bath. The spin-coating pro- cesses could be divided by three steps normally. At first, the coat- ing was performed by spin-coater with droplet of metal organic deposition solvent, in air at room temperature (RT). The composi- tions of dip-coat precursor are erbium carboxylic acid, turpentine, n-butyl acetate, ethyl acetate and some stabilizer and viscosity adjustor. The equivalent content of erbium oxide in solvent is about 3%. The rotary speed of spin-coater was 500–2000 rpm for 10–30 s, in this step the coating shows as wet-sol. At second, the coating was dried in a dry-oven in air at 393 K for 10 min, in this step the wet-sol change to dry-sol then to dry-gel. To get thicker coating, the first and second steps need to be repeated alternately several times. At third, the coating was baked in various 0022-3115/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2008.12.286 * Corresponding author. Tel./fax: +81 3 5841 7420. E-mail address: yaozy401@hotmail.com (Z. Yao). Journal of Nuclear Materials 386–388 (2009) 700–702 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat