Summary: | 碩士 === 逢甲大學 === 材料科學與工程學系 === 105 === In this study, the ZK60 alloy was refined by equal channel angular pressing (ECAP) and differential speed rolling(DSR) with rolling speed ratios of 6:3and 9:3. The alloys became metal filings by mechanical method, and the alloy powders were prepared by adding 5wt% carbon and various amounts of palladium, silver and zirconium, respectively, in ball milling for 20 hrs, to explore the microstructure of the alloy, low temperature hydrogen absorption / high temperature hydrogen desorption measurement, low temperature hydrogen absorption rate and H2S poisoning on hydrogen storage characteristics. The experimental results showed that the dendritic structure of the cast alloy is completely destroyed and the grain and grain boundary form after the ZK60 is mechanically deformed by ECAP and DSRs. The grain size of the ZK60 alloy after 9: 3 DSR is larger than 6:3 DSR, because of its larger amount of plastic deformation, leading to the earlier occurrence of recrystallization and grain growth. A microstructure of three-dimensional network formed by intermetallic compounds is observed by FESEM under 100KX magnification for ZK60 alloy after ECAP and DSRs.
In the 320oC hydrogen desorption, after ECAP and DSRs followed by ball milling with additions of 5C0.5Pd, 5C0.5Ag and 5C1Zr respectively, the amount of hydrogen absorption of the alloy for 5 cycles at 200oC are (1) more than 5wt%, more than 4wt% and more than 5wt% for 6: 3DSR, (2) more than 5 wt%, more than 5 wt% and more than 6 wt% for 9: 3DSR, and (3) about 6 wt%, more than 6 wt% and more than 5 wt% for ECAP. For hydrogen absorption at 200oC for 10 minutes (with respect to 60 minutes), the percentage is 69.9%, 71.4% and 61.4% for 6:3 DSR, 70.3%, 73.5% and 74.7% for 9:3 DSR, and 93.6%, 95.6% and 86.5% for ECAP, respectively. In addition, the hydrogen absorption percentage is less than 50% for alloys after 6:3 and 9:3 DSRs at 120oC,140oC and 160oC. However, it is less than 50% for alloys after ECAP only at 120oC.
In the poisoning of ZK60 alloys after ECAP, 6: 3DSR and 9: 3DSR followed by ball milling with 5C0.5Pd, 5C0.5Ag and 5C1Zr respectively, the degree of poisoning is also different with the increase of H2S concentration. In pure hydrogen, the amount of hydrogen absorption in the first 5 cycles is almost constant. Once H2S is introduced, it decreases with increasing the number of cycles, which shows the cumulative effect of H2S poisoning. For ZK60 after ECAP and ball milling with 5C1Zr, the introduction of 500 ppm CO into pure hydrogen leads to hydrogen absorption degradation to less than 1wt%, showing that the poisoning effect is very serious. It is because CO has two dangling bonds and can be effectively adsorbed on the surface of the alloy to effectively prevent the hydrogen from diffusing into the interior of the alloy. The poisoning ability of H2S is weaker than that of CO. It is adsorbed on the surface of the alloy only by van der Waals' force, so the poisoning effect on the hydrogen absorption of the ZK60 alloy is less significant.
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