Thesis - Oztek_Muzaffer_T_200508_MA

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The existing phases and their compositions for different pressures and temperatures are represented in the diagram. With the initial introduction of hydrogen to the metal, the solid solution phase (α) is formed. As pressure is increased, the α-phase becomes saturated with H, after which the hydride phase (β) starts to form. In the plateau region, both phases co-exist. At H/M ratios high enough to correspond to the completion of α to β conversion, only β-phase exists. Hysteresis is a phenomenon that is commonly observed in metal-hydrogen systems. It is the observation of lower decomposition plateau pressure compared to formation plateau pressure. Hysteresis is not a desired property for practical applications and should be considered when designing an application. Despite the many publications about the degree of hysteresis in specific systems, it is risky to use these data for hydride device design because hysteresis is not a unique materials property and is dependent on history of the sample and the test method used [18]. Other problems, such as heat transfer, may arise when scaling up a hydride system. In that case, heat must be provided to decompose these compounds and release the hydrogen, while heat is liberated when the compounds are formed and must be removed to allow the hydriding reactions to proceed to completion [19]. The desired characteristics of hydrides for practical applications are [18] • High hydrogen capacity • Moderate hydriding temperature and pressure • Moderate dehydriding temperature • High rate of hydriding • Low susceptibility to capacity loss by cycling 8
• Insensitivity to poisoning by impurities • Low manufacturing costs Hydride formers usually do not possess the above characteristics in their pure form. Nevertheless, hydride formers can be improved by various methods, such as the addition of one or more new elements to form alloys or intermetallic compounds, changing the sample preparation method, applying activation procedures, or employing protective/catalytic surface treatment. For example, alloying is a common method to decrease the stability of hydrides of pure metals so that hydrogen is recoverable at moderate temperatures [20]. Combining different metals can form either alloys or intermetallic compounds. Alloys are physical mixtures; however, intermetallics (AB x ) are compounds. Intermetallics are composed of an intermediate phase between A and B with different structure from both the parent elements and the terminal solid solutions. Within the domain of homogeneity of an intermetallic, various structural defects and antiphase boundaries might exist. In an intermetallic system, experimental reproducibility is harder to attain and impurities may play a greater role in effecting the stability of the phase, compared to elemental materials, since they are not well defined materials. Impurities may play an important role in the degree of shift of composition between the surface layers and the bulk [21]. Generally the properties of intermetallic compound hydrides have little or no resemblance to those of the constituent metal hydrides [22]. 9
Page 1 and 2: RECOVERY OF HYDROGEN AND HELIUM FRO
Page 3 and 4: ABSTRACT Waste streams of hydrogen
Page 5 and 6: I dedicate this work to my family m
Page 7 and 8: I also would like to cheer for my f
Page 9 and 10: 2.2.2.1. Hydriding and Dehydriding
Page 11 and 12: LIST OF FIGURES Figure 1. Pressure-
Page 13 and 14: Figure 34. Pressure profiles under
Page 15 and 16: 1. INTRODUCTION The focus of this s
Page 17 and 18: ecause of the difference in partial
Page 19 and 20: hydrides by dissolving large amount
Page 21: hydrogen storage alloy has a specif
Page 25 and 26: hydrogen capacity was not reproduci
Page 27 and 28: showed the lowest plateau pressure
Page 29 and 30: grain boundaries increases the tota
Page 31 and 32: These parameters are generally inte
Page 33 and 34: Figure 4. CaCu5-type P6/mmm structu
Page 35 and 36: In this study, the addition of Al t
Page 37 and 38: 2. EXPERIMENTAL 2.1.Chemicals and R
Page 39 and 40: Figure 5. The high energy Spex 8000
Page 41 and 42: 2.2.1.1. Hydriding and Dehydriding
Page 43 and 44: approximately 5 atm, and heating th
Page 45 and 46: determined by the start and end of
Page 47 and 48: 450 400 coating thickness (Å) 350
Page 49 and 50: 3. RESULTS AND DISCUSSIONS 3.1. Hyd
Page 51 and 52: DSC 111 heat flow/mW Exo 300 Figure
Page 53 and 54: The thermogram associated with the
Page 55 and 56: total time was broken into three 30
Page 57 and 58: The VTiNi sample was subjected to d
Page 59 and 60: solid solution of hydrogen rather t
Page 61 and 62: DSC 111 Heat Flow/mW 180 Exo Figure
Page 63 and 64: 100 rpm setting, the milling vial w
Page 65 and 66: BPR, 400 rpm, 5 minutes) did not re
Page 67 and 68: Table 1: Effects of various milling
Page 69 and 70: Due to the fast kinetics observed a
Page 71 and 72: The mole % Al after milling was les
Page 73 and 74:
Figure 24: Percent hydrogen capacit
Page 75 and 76:
the start of the heating period, wh
Page 77 and 78:
However, it was noted that the part
Page 79 and 80:
percent hydrogen was decreased. The
Page 81 and 82:
3.2.2.4. AuPd and Pt Coating on LaN
Page 83 and 84:
1.0 0.8 (a) (b) Wt. % H absorbed 0.
Page 85 and 86:
After dehydriding by the sample, th
Page 87 and 88:
19 18 P (atm) 17 16 15 14 0.74 %Al
Page 89 and 90:
GC output, arbitrary units 0 5 10 1
Page 91 and 92:
sample was LaNi 5 . This may indica
Page 93 and 94:
30 min. 15 min. Intensity (arb. uni
Page 95 and 96:
After milling the percentages of Al
Page 97 and 98:
4. CONCLUSIONS This study has been
Page 99 and 100:
16. Van-Vucht, J.H.N., Kuijpers, F.
Page 101 and 102:
47. Suryanarayana, C., Progress in
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Thesis - Oztek_Muzaffer_T_200508_MA

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