Hydrogen Degradation Property of Electrochemically Charged Aluminum
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Hydrogen Degradation Property of Electrochemically Charged Aluminum Hiroshi Suzuki, Daisuke Kobayashi, Kenichi Takai, and Yukito Hagihara Dept. Mechanical Engineering, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, 102-8554, Japan ABSTRACT Degradation property of aluminum due to hydrogen is studied. Hydrogen is introduced by electrolysis charge in aqueous solution with addition of 0.1 mass % NH4SCN as a hydrogen recombination poison. The amount of hydrogen and its existing state in the material is analyzed by hydrogen desorption curves measured by the thermal desorption spectroscopy. The hydrogen desorption curves of charged aluminum showed two peaks, one at less than 100 °C and the other around 400 °C. The existing state of hydrogen relate to each peaks are identified as weakly trapped solute hydrogen to vacancy and free hydrogen molecule located in cavities that exists in the bulk of the material. Tensile properties are obtained to determine degradation property of the material due to hydrogen. The effect of hydrogen on degradation of charged aluminum is analyzed in terms of interaction between hydrogen and vacancy or dislocation. Solute hydrogen and cavities are found to affect ductility of aluminum, whereas hydrogen molecule in cavities has no effect. INTRODUCTION Aluminum and its alloys are one of the candidate materials to be used in hydrogen storage system and as a candidate for hydrogen storage that absorb hydrogen. Although A6061 type aluminum alloy has been used in storage container, the effect of hydrogen to the mechanical properties of aluminum is not well established especially under high pressure of hydrogen that will be utilized in the fuel-cell vehicle of the coming age. For this purpose, full understanding of the state of hydrogen in aluminum is required. A safe and efficient method to introduce hydrogen into aluminum is also needed to access the material in the application. Birnbaum et al. [1] introduced high amount of hydrogen into high-purity aluminum by means of electrochemical method. They accessed various method to introduce hydrogen into aluminum [2], and examined the state of hydrogen by using XAFS, SIMS and TEM observation, concluding hydrogen exists in bubbles that situated near the surface of the material [3]. In this study, we chose the electrolytic charging method to introduce hydrogen into commercial pure aluminum. The existing state of hydrogen is examined by hydrogen desorption curves measured by the thermal desorption spectroscopy. Tensile property is used to determine degradation property due to hydrogen.
EXPERIMENT Experimental procedure Commercial pure aluminum (99%) of thickness 0.2 mm is used as a testing material to examine hydrogen absorption properties. The material is cut into specimen of 20x50 mm, annealed at 400 °C for 30min prior to charging. Hydrogen is introduced by electrolysis charge in 90 °C aqueous environments. The electronic potential against the standard hydrogen electrode and the pH of the solution are chosen from -2.5 to 1.0 V and 2.5 to 10
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