Analysis of Wall Strain on the Reaction Vessel of Mg2Ni Alloy During Cyclic Hydriding/Dehydriding Processes

• Main Authors: Yu-Hao Jhang, 張育豪
• Other Authors: Chih-Kuang Lin
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/11733591969566871696

碩士 === 國立中央大學 === 機械工程研究所 === 96 === The purpose of this study is to investigate the wall strain variation on the reaction vessel of Mg2Ni alloy at various combinations of location and direction during cyclic hydriding/dehydriding processes. The reaction vessel was made of AISI 316 stainless steel. The pressure conditions for the absorption and desorption steps were set at 3 MPa and vacuum, respectively, at 300 oC. The particle morphology of the Mg2Ni alloy before activation and after a 45-cycle test was analyzed with scanning electron microscopy (SEM). Results showed that the strain accumulation phenomenon in the hoop strain disappeared at the later hydriding/dehydriding cycles due to agglomeration of the Mg2Ni alloy powders no matter at the location of 1/10 or 3/10 height of the vessel. The cycle number at the disappearance of the strain accumulation phenomenon in the hoop strain at the location of 1/10 height of the vessel was smaller than that of the 3/10 height by 5 cycles. This was ascribed to a continuous increase in the height of an agglomerated disk formed at the bottom of the reaction vessel. With regard to the strain increment in a hydriding/dehydriding cycle, the hoop strain increment was drastically reduced toward zero at the later testing cycles while the axial strain increment was gradually reduced in a smaller rate throughout the test. This could be attributed to less and less absorption activities taking place in the continuously growing agglomerated Mg2Ni alloy disk formed at the bottom of the reaction vessel. The SEM observations showed that a pulverization mechanism caused not only the corners of the Mg2Ni alloy powders to change from sharp to smooth and round but also the particle size of the Mg2Ni powders to decrease from 74 to 1 ?m after activation and a 45-cycle test. After supplying sufficient hydrogen gas, the hoop strain on vessel wall was increased linearly with progressive cycles throughout the testing period. When the Mg2Ni alloy powders were agglomerated, the hoop strain increment was reduced. It indicates that the volume expansion induced by the Mg2Ni hydride powders was reduced by agglomeration.