STRESS ON A REACTION VESSEL BY THE SWELLING OF A HYDROGEN ABSORBING ALLOY

There is a possibility that hydrogen absorbing alloys will generate un expected stress in an alloy bed and deform or destroy the vessel becau se the alloys expand when they absorb hydrogen. Thy amount of stress g enerated on the vessel surface by alloy swelling was measured with the object of elongating the life time of the reaction vessel in heat uti lization systems that use hydrogen absorbing alloys. As a result, it w as found that 1) localized stress is generated at the bottom of the ve ssel due to hydrogen ab-/desorption cycles with an alloy packing fract ion of 50 vol %, and this stress not only increases with each cycle, b ut also continues to increase even after plastic deformation of the ve ssel, 2) stress accumulation depends on the amount of hydrogen ab-/des orption and on the initial packing fraction, and 3) the mechanism for stress accumulation can be estimated as a two-step process in which ag glomeration between the hydride particles occurs when the packing frac tion of hydride is higher than 61 vol % in the initial cycles (Step 1) , and then fine powder generated by pulverization during the cycles fa lls in gaps at the bottom of the vessel and causes the hydride packing fraction at the bottom of the vessel to gradually increase (Step 2). (C) 1998 Elsevier Science S.A.