Anisotropic Hydrogen Permeation in Nano/Poly Crystalline-Nickel Membranes
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Anisotropic Hydrogen Permeation in Nano/Poly Crystalline-Nickel Membranes Y. Cao, H. Li, J. A. Szpunar and W. T. Shmayda1 Department of Metals and Materials Engineering, McGill University, Montreal, PQ, H3A 2B2, Canada 1 Lab for Laser Energetics, University of Rochester, Rochester, NY, 14623-1299, USA Keywords: Hydrogen Permeation, Nanocrystalline, Nickel, Bilayer Membranes ABSTRACT Bilayer nickel membranes have been prepared using electrodeposition to grow polycrystalline nickel on a nanocrystalline nickel substrate. When hydrogen is charged from the nano-Ni side of the nano-Ni and poly-Ni composite membrane, the permeation current increases rapidly, then the membrane releases hydrogen faster during decay. When hydrogen is charged from the poly-Ni side of the same composite membrane, the permeation current rises gradually and takes a longer time to reach steady state. Also the permeability of nano-poly-Ni membrane is eight times higher than that of poly-nano-Ni membrane. The diffusivity for the nano-Ni side charging in a nano-poly-Ni membrane is two times higher than that of poly-Ni side charging of the same membrane. The diffusivity and permeability of nano-poly-Ni membranes are smaller than those for nano-Ni membranes, but larger than those for poly-Ni membranes. Using this anisotropic behavior, one can manipulate hydrogen permeation through composite membranes. A hydrogen permeation model for bilayer membranes is proposed to simulate diffusion in a nano-Ni and poly-Ni bilayer membrane in two-directions of charging. The experimental data is in good qualitative agreement with the model. INTRODUCTION Multilayer membranes consist of several laminated layers, which include at least two different kinds of membranes. By using the behaviors of different layers, various combinations have been used to achieve different properties for a wide variety of applications [1-4]. Oxide and palladium composite films, deposited an oxide layer onto a Pd foil, are an effective tool to study hydrogen permeation through brittle oxides because a pure oxide sample is easily broken. The Pd foil in the entrance side not only acts as a support, but also as a hydrogen absorber [3]. Palladium metal-oxide-semiconductor (Pd-MOS) devices are used in sensitive hydrogen sensors. The hydrogen adsorbed at the Pd surface of the Pd/SiO interface gives a fast response. The outer and inner surface of the Pd film had similar hydrogen adsorption properties [4]. Thin palladium deposited on pore ceramics seems to offer promise for enough hydrogen permeability and lower cost [5]. In a new approach, polycrystalline nickel has been deposited on a nanocrystalline nickel substrate to get a bilayer membrane with anisotropical hydrogen permeation characteristics [6]. Because each layer of a multilayer membrane has different characteristics of hydrogen permeation and is separated from another by an interface, these structural factors may have special influences on hydrogen permeation through the membrane. The effect of interfaces in the
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