Please cite this article in press as: Y. Xu, et al., Effect of water vapor and hydrogen treatments on the surface structure of Ni 3 Al foil, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.02.144 ARTICLE IN PRESS G Model APSUSC-27360; No. of Pages 6 Applied Surface Science xxx (2014) xxx–xxx Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Effect of water vapor and hydrogen treatments on the surface structure of Ni 3 Al foil Ya Xu a,∗ , Yan Ma b , Junya Sakurai a , Yuden Teraoka c , Akitaka Yoshigoe c , Masahiko Demura a , Toshiyuki Hirano a a Hydrogen Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan b North China Electric Powder University, 2 Beinong Road, Huilongguan, Changping District, Beijing 102206, China c Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan a r t i c l e i n f o Article history: Received 30 December 2013 Received in revised form 22 February 2014 Accepted 24 February 2014 Available online xxx Keywords: Ni3Al foil catalyst Synchrotron radiation X-ray photoemission spectroscopy Water vapor treatment Hydrogen reduction a b s t r a c t We have developed a water vapor treatment followed by hydrogen reduction to modify the surface structure of Ni 3 Al foils in order to obtain high catalytic activity. The Ni 3 Al foils were heat treated in water vapor at 873 K for 1 h followed by H 2 reduction at 873 K for 1 h. The effects of the water vapor treatment and the H 2 reduction on the surface structure of the Ni 3 Al foils were investigated by means of scanning electron microscopy and synchrotron radiation X-ray photoemission spectroscopy. Both Ni and Al in the surface layer of the Ni 3 Al foil were oxidized during the water vapor treatment; fine NiO particles with a high density were formed on the outermost surface, accompanied by the formation of oxide layers of Al(OH) 3 and NiAl 2 O 4 /Al 2 O 3 beneath the NiO particles. The NiO particles were reduced to metallic Ni and the Al(OH) 3 was decomposed to Al 2 O 3 , whereas the NiAl 2 O 4 and Al 2 O 3 remained unchanged during the subsequent H 2 reduction, forming a Ni-enriched porous structure on the surface layer of NiAl 2 O 4 /Al 2 O 3 . © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Ni 3 Al intermetallic compound is known as a promising high-temperature structural material because of its excellent high- temperature strength and corrosion/oxidation resistance [1–3]. However, its poor room-temperature ductility has been a serious problem. We have overcome this problem and successfully devel- oped thin foils of Ni 3 Al with a thickness of less than 30 m by cold rolling unidirectionally solidified ingots [4–6]. Recently, we investigated the catalytic properties of the Ni 3 Al foils for methanol decomposition in the temperature range from 513 to 793 K and found that such flat foils show high catalytic activity and selectiv- ity for methanol decomposition into H 2 and CO, despite the small surface area of the foils, demonstrating that the Ni 3 Al foils can be used as plate type catalysts [7], and thus serve both functionali- ties of catalytic and structural materials, by which one can make a more efficient reactor for hydrogen production [8,9]. The high cat- alytic activity for methanol decomposition was attributed to the formation of fine Ni particles on the foil surface through a selective ∗ Corresponding author at: Hydrogen Materials Unit, National Institute for Mate- rials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. Tel.: +81 298592573; fax: +81 298592501. E-mail address: XU.Ya@nims.go.jp (Y. Xu). oxidation and/or hydroxylation of Al by the small amount of H 2 O produced during the reaction [9,10]. This result suggests that water vapor oxidation is effective for modifying the surface morphology and enhancing the catalytic activity of Ni 3 Al foils. Many studies have been carried out on the oxidation of Ni 3 Al in air or pure O 2 [11–17], whereas there have been very few studies on the oxidation of Ni 3 Al in water vapor [18,19]. Schumann et al. [18] studied the oxidation behavior of Ni 3 Al single crystals under low oxygen partial pressure realized by exposing the Ni 3 Al in a flow- ing H 2 /H 2 O mixture at 1223 K. Fine Ni particles were observed on the surface of the Ni 3 Al after being exposed for 1 min, accompanied by formation of a continuous thin -Al 2 O 3 oxide scale. Continued oxidation resulted in thickening of the -Al 2 O 3 scale and coalesc- ing of the Ni particles. However, they did not report the effect of water vapor at temperatures lower than 1223 K and at high water vapor partial pressures. Garza et al. [19] studied the interaction of an oxide film on Ni 3 Al with the water vapor, and they revealed that the water vapor can significantly affect the oxide film even at low H 2 O pressures. However, they did not mention the oxidation behavior of Ni 3 Al caused by water vapor. In this study, we carried out a water vapor treatment of Ni 3 Al foils at 873 K, followed by H 2 reduction at 873 K, which is com- monly used as a pre-reduction process for Ni 3 Al catalysts [20,21]. The effect of the water vapor treatment and H 2 reduction on the surface structure of the Ni 3 Al foils was investigated by means of http://dx.doi.org/10.1016/j.apsusc.2014.02.144 0169-4332/© 2014 Elsevier B.V. All rights reserved.