本研究主旨在探討在循環吸放氫作用下，鎂鎳合金儲氫罐壁上的應變在不同位置和方向的變化。實驗用鎂鎳合金儲氫罐是由AISI 316不銹鋼所製成，實驗條件的吸氫壓力為3 MPa，放氫壓力則為真空，吸放氫皆在300oC下完成，並利用SEM觀察Mg2Ni合金粉末在活化前和實驗結束後之形態與大小。 結果顯示，在實驗的後半段，罐壁切線方向應變不論在1/10或3/10瓶高處，由於Mg2Ni粉末結塊的關係，應變累積現象都有消失的時候。然而在1/10瓶高消失的時間比在3/10瓶高消失的時間早5個循環，是因為罐體底部結塊的粉體高度越來越高所導致。就吸放氫循環中的應變增量而言，切線方向應變增量在後期的循環數中驟降到零，但是軸向應變增量從頭至尾則是緩慢遞減。這是因為在罐體底部已結塊的粉體吸氫活動越來越少所致。由SEM的觀察中可以得知，粉碎化不僅可以鈍化Mg2Ni粉末鋒利的外型，還可以讓顆粒大小由活化前的74 ?m縮小到實驗結束後的1 ?m。 在增加足夠的氫氣量之後，Mg2Ni的吸氫量的確有明顯的上升，且不同高低位置的切線方向應變幾乎是隨循環數增加而呈現線性遞增的現象。Mg2Ni粉末的結塊可以有效降低切線方向的應變增量，換言之，粉末的結塊化可以降低由Mg2Ni粉末吸氫之後所造成的體積膨脹量。 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.
