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In this study it was suggested a heat treatment of a cylindrical bamboo to prevent from cracking accompanied drying. Theoretical evaluation for the changes of the strain and the residual stress arisen from drying showed that cracking could be produced due to the difference of strains between the inner and outer surfaces and would be harder at a high temperature than at a low temperature because a plastic accommodation would be significant at a high temperature whereas it would be negligible at a low temperature. In addition, it was known that if crack was not found during cooling and very early time after heat treatment (high temperature drying) crack would not be produced thereafter. In order to conform these theoretical predictions the heat treatments of cylindrical bamboos were carried out at 200°C for 0.5~3 hours and the heat treated and the untreated were kept at 60°C to see crack formation. As the result, the heat treated bamboos were not cracked whereas all of the untreated were cracked. The changes of the artificial cracks formed after heat treatment showed that the compressive residual stress was produced by absorption of moisture from air on the outer surface of bamboo 5 days after the heat treatment.
In this paper it has been compared briefly the hydrogen storage using hydrogen storage alloys with other technologies and introduced the general properties of hydrogen storage alloys. The recent research trends and activities related to hydrogen storage alloys were given here.
The pulverization and alloy degradation phenomena in Nd_(15)Fe_(77)B_8 and Nd_(12)Fe_(70)Co_(10)B_7Ga₁ alloys upon the hydrogen absorption and desorption cycling have been investigated by measuring hydrogen solubility changes, microstructure observation and DSC thermal analysis. The cycling was performed by varing the temperature from 25℃ to 400℃ at a constant hydrogen pressure. As the number of cycles increased upto 15 cycles, the hydrogen solubility decreased markedly implying severe alloy degradations in both alloys, whereas the pulverization progressed small. The degadation could be attributed to the segregation of Nd or the precipitation of Nd-rich phases on the alloy surface and to the oxidation of those phases.
The volume expansions of Ti0.95Zr0.05V0.4Mn1.45Fe0.1Cr0.05 alloy during hydrogenation with various conditions have been investigated. The theoretical volume expansion measured with XRD for this alloy with hydrogenation was 21%. The apparent volume expansion of this alloy ingot with hydrogenation was composed of two effects. One is a hydrogenation and the other is a pulverization. The apparent volume of free alloy powder was 1.8 times greater than that of an ingot, implying the pulverization effect on the apparent volume expansion is 80%. The apparent volume expansion of the alloy ingot with hydrogenation under a unconstrained condition was about 80 (±15)%, much smaller than that of free alloy powder which expected as 118%. In addition, The apparent volume expansion of the alloy ingot with hydrogenation under a constrained condition(Al container) was about 50%, much smaller than that of the unconsrained. This reduced apparent volume expansion of the alloy ingot could be attributed to an arrangement of alloy powder keeping its original shape of the ingot even after hydrogenation.