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HYDROGEN ECONOMY Hydrogen production methods
ALLOYS FOR HYDROGEN SEPARATION, RECOVERY AND PURIFICATION
M. D. Hampton , D. K. Slattery*, M. T. Oztek
Deputy-Editor-in-Chief
Department of Chemistry, University of Central Florida, Orlando, FL 32816, USA * Florida Solar Energy Center, Cocoa, FL, USA
Education
Undergraduate: B. S., 1975
Graduate: Ph.D., 1980
University of Florida, Gainesville, Florida Chemistry Major, Mathematics Minor
Texas Tech University, Lubbock, Texas Analytical Chemistry Major, Biochemistry Minor Dissertation: "Synthesis, Crystal Structure, and Reactivity of a 12-Crown-4 Sandwich Complex of Manganese(II)"
Michael Douglas Hampton
Postdoctoral
Fall, 1980-Spring, 1981
Texas Tech University, Lubbock, Texas Dr. Jerry L. Mills, Inorganic Chemistry "Synthesis of Trimethyl Borane" Employment History
University of Central Florida, Department of Chemistry
• Full Professor, April, 2003 to Present.
• Associate Professor, August, 1987 to March, 2003.
• Assistant Professor, August, 1981 to July, 1987.
Texas Tech University, Department of Chemistry and Biochemistry
• Visiting Assistant Professor, Fall, 1980 through Spring, 1981.
• Graduate Teaching and Research, Fall, 1975 through Spring, 1980. Honors and Awards
• Faculty Fellow, Faculty Center for Teaching and Learning, 2005-present.
• University of Central Florida Teaching Incentive Program (TIP) Award, 1994, 1997, and 2006.
• 2003 Excellence in Undergraduate Teaching Award, College of Arts & Sciences, UCF, April, 2003.
• Outstanding 4-Year College Teacher Award, Orlando Section American Chemical Society, 2002.
• Certificate of Recognition for Research Contributions made through the 2001 NASA summer faculty fellowship program at the John F. Kennedy Space Center, 2000 and 2001.
• Certificate of Appreciation, from NASA and John F. Kennedy Space Center, for outstanding efforts in assisting NASA's Materials Science Lab by performing xray photoelectron spectroscopy analysis, March 23, 2000.
• 1995 Excellence in Undergraduate Teaching Award, College of Arts & Sciences, UCF, April, 1995.
• Outstanding 4-Year College Teacher Award, Orlando Section American Chemical Society, 1994.
• Inducted into Phi Kappa Phi, April, 1992.
• First Annual Outstanding Chemist Award, Orlando Section American Chemical Society, 1991. University Service (Past 5 Years)
University:
• Chief of GEP Assessment and Committee Chair, 2006-present
• Member, University Assessment Committee, 2006-present
• Member Greater Orlando GK-12 Partnership Advisory Board - 2007
• Member, Common Program Oversight Committee, 2005-present
• Undergraduate Affairs Committee, 2001-2005
• Analytical Award Committee, 1981-2005
• Chair, Instrumentation/OCO Committee, 2001-2004
• Freshman Coordinator, 1985-1998, 2001-2004
• Chair, Instrumentation/OCO Committee, 1995-2002
Лекция профессора Университета Центральной Флориды, доктора М. Д. Хэмптона будет представлена во время торжественной церемонии награждения в Государственной Думе РФ 29 ноября 2008 г. в 1500.
Lecture of professor of University of Central Florida, Dr. M. D. Hampton will be presented during rewarding ceremony in the RF State Duma November 29, 2008 at 1500.
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• Analytical Chemistry Faculty Search Committee, 2000-2002
• Departmental Rep., Orange Co. Public Schools Partners in Ed. Program, 1987-2002
• Sabbatical Leave Committee, 2000-2002
• East Europe Linkage Institute, regularly meet, tour, and host visitors, 1997-2002 College of Arts and Sciences:
• Scholarship and Awards Committee, 2001-present
• Promotion and Tenure Committee, member and secretary, 2004-2005 | • Arts Task Force, 2004
• Chaired several grade dispute hearings, 2004-present ! Department of Chemistry:
_ • Facilities and Safety Committee, 2005-present
'¡L • Executive Committee, 2005-present
£ • Alumni and Industrial Relations Committee, 2005-present
±= • Undergraduate Affairs Committee, 1981-present
g • Analytical Award Committee, 1981-present
• Greivance Committee, chair, 2005-present
0
5 • Instrumentation Committee, Chair, 1995-2005
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Professional Society Service (Past 5 Years)
National American Chemical Society:
• International Chemistry Olympiad Subcommittee, 1985-present
• Chair, Selection Committee for Coach of United States Team at International Chemistry Olympiad, 1994- present
• Local Arrangements Chair, 223rd National Meeting, Orlando, FL, April, 2002 Orlando Section American Chemical Society:
• Orlando Section Chair, 2005
• Orlando Section Chair Elect, 2004
• Orlando Section Executive Committee, 2001-2005
• Florida Award Selection Committee, 1999-2002
Other National and International Professional Experience
• Deputy Editor-in-Chief, International Scientific Journal for Alternative Energy and Ecology, ISSN 16088298, 2001 to present.
• Editor, "NATO Advanced Research Workshop on Hydrogen Materials Science and Chemistry of Metal Hydrides", NATO Science Series, II. Mathematics, Physics and Chemistry - Vol. 71, Kluwer Academic Publishers, 2002. ISBN 1-4020-0730-2. 483 pages., underwritten by NATO, 1999 to present.
• Courtesy appointment, Senior Research Scientist, Florida Solar Energy Center, 2001-2002.
• Materials Engineer, NASA, Materials Testing Branch, Kennedy Space Center, November, 1984 to December, 1988.
• Worked with scientists in former Soviet states to find funding for peaceable research. An example is below (Michael D. Hampton in collaboration with group in All-Russian Institute for Experimental Physics, ISTC project #1580, "Hydrogen Sensors for Vacuum Cryogenic Objects," submitted to International Science and Technology Center, Moscow, Russia. Funded)
Peer Reviewed Publications
1. NATO Advanced Research Workshop on Hydrogen Materials Science and Chemistry of Metal Hydrides, NATO Science Series, II. Mathematics, Physics and Chemistry - Vol. 71, Michael D. Hampton, Editor along with Dmitry V. Schur, Svetlana Yu. Zaginaichenko, and V. I. Trefilov. Kluwer Academic Publishers, 2002. ISBN 1-4020-0730-2. 483 pages.
2. D. Cauceglia, M. D. Hampton, J. K. Lomness, D. K. Slattery, an M. Resan, "Hydrogen Uptake Characteristics of Mechanically Alloyed Ti-V-Ni", Journal of Alloys and Compounds, 417, 159 (2006).
3. Mirna Franjic, Michael D. Hampton, Janice K. Lomness, and and Darlene K. Slattery, "Effect of TixAl ^ Catalysts on Hydrogen Storage Properties of LiAlH4 and NaAlH4", International Journal for Hydrogen Energy, t 30,1417(2005).
§■ 4. M. Resan, M. D. Hampton, J. K. Lomness, and D. K. Slattery, "The Effects of Various Catalysts on
^ Hydrogen Release and Uptake Properties of LiAlH4", International Journal of Hydrogen Energy, 30, 1413 (2005).
1 5. M. D. Hampton, D. K. Slattery, N. Jafari-Mohajery, and J. Lomness, "The Use of Alanates for Hydrogen ^ Storage" // Alternative Energy and Ecology, Special Issue: Collection of theses of the Second International Sym-| posium on Safety and Economy of Hydrogen Transport, 2003, pg. 78.
6 6. Michael D. Hampton, Janice K. Lomness, and Lucille Giannuzzi, "Surface study of liquid water treated g, and water vapor treated Mg2 35Ni alloy", International Journal of Hydrogen Energy, 27, 79 (2002).
7. Janice K. Lomness, Lucille A. Giannuzzi, Michael D. Hampton, "Site Specific TEM Characterization of § Micrometer Sized Particles Using the FIB Lift-Out Technique", Microscopy and Microanalysis, 7(5), 418 (2001). 0 8. Janice K. Lomness, Michael D. Hampton, Lucille A. Giannuzzi, "Hydrogen Uptake Characteristics of
Mechanically Alloyed Mixtures of Ti-Mg-Ni", Int. J. Hydrogen Energy, 27, 915 (2002).
9. Michael D. Hampton, Janice K. Lomness, and Lucille Giannuzzi, "Surface study of liquid water treatated and water vapor treated Mg2 35Ni alloy", International Journal of Hydrogen Energy, 27, 79 (2002).
10. Michael D. Hampton, Rajkumar Juturu, and Janice K. Lomness, "Activation of Mg2Ni for Initial Hydrogen Uptake, by Water Vapor", International Journal of Hydrogen Energy, 24(10), 981 (1999).
11. Michael D. Hampton and Janice K. Lomness, "Water Activation of Mg2Ni for Hydrogen Uptake", International Journal of Hydrogen Energy, 24, 175 (1999).
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12. Gary L. Wood, Christopher Tillman, and Michael D. Hampton, "Synthesis of 1,1,1,3,3,3-hexachloro-2,4-isobutylcyclodiphosphaz(V)anecyclodiphoshpazane. An Inorganic Experiment", J. Chem. Ed., 72(6), 547 (1995).
13. Michael P. McCann and Michael D. Hampton, "Detection of Molecular Hydrogen by Stimulated Raman Emission", Applied Spectroscopy, 48(4), 537 (1994).
14. R. Zidan, D. Slattery, M. D. Hampton, and A Raissi, "Chemical Storage of Hydrogen in Metal Hydrides", Proceedings of the DOE/SERI Program Review, Washington, DC, Jan., 1991.
15. B. J. Lockhart, M. D. Hampton, C. J. Bryan, Symposium on Flammability and Sensitivity of Materials „ in Oxygen-Enriched Atmospheres: Fourth Volume, ASTM STP 1040, J. M. Stoltzfus, F. J. Benz, and J S. 5 Stradling Ed., American Society for Testing and Materials, Philadelphia, PA, 1989.
16. M. D. Hampton, W. Rees, S. Hall, and J. L. Mills, "Trimethyl Borane." Inorganic Syntheses, 29, ~ (1989). &
17. Michael D. Hampton, Darlene K. Slattery, N. Jafafi-Mohajeri, Mirna Franjic, and Janice K. Lomness, | "Complex Hydrides as Hydrogen Storage Media", Symposium P1, "Hydrogen Electrochemistry and Generating "5 Systems", Proceedings of the 203rd Meeting of the Electrochemical Society, Paris, France, April 27-May 2, 2003. y
18. Michael D. Hampton, Darlene K. Slattery, Mirna Franjic, and N. Jafafi-Mohajeri, "Alanates for Hydro- 1 gen Storage", Proceedings of the International Forum - Symposium on Safety and Economy of Hydrogen Storage ° and Transport, Sarov, Russia, Aug. 18 - 21, 2003. g
19. Janice K. Lomness, Michael D. Hampton, and Lucille A. Giannuzzi, "Hydrogen Storage in Titanium- ™ Magnesium-Nickel Mixtures", Materials Research Society Symposium Proceedings, Vol. 53, BB7.9.1, 2003.
20. Darlene K. Slattery, Michael D. Hampton, Janice K. Lomness, Nahid Najafi-Mohajeri and Mirna Fran-jic, "Hydrogen Storage Using Complex Hydrides", Proceedings of the 225th National Meeting of the American Chemical Society, New Orleans, LA, March 24 - 27, 2003.
21. Michael D. Hampton, Janice K. Lomness, and Lucille A. Giannuzzi, "Hydrogen Storage in Titanium-Magnesium-Nickel Mixtures", Symposium BB, "Defect Properties and Related Phenomena in Intermetallic Alloys", Proceedings of the MRS Meeting, Boston, MA, Dec., 2002.
22. Darlene K. Slattery and Michael D. Hampton, "Complex Hydrides for Hydrogen Storage", Proceedings of the 2002 US DOE Hydrogen Program Review, NREL/CP-610-32405, pp. 2002.
23. Orlando Melendez, Martha Williams, Michael Hampton, Gordon Nelson, and Erik Weiser, "Surface Evaluation by X-ray Photoelectron Spectroscopy of High Performance Polyimide Foams After Exposure to Oxygen Plasma", Proceedings of the 43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Denver, CO, April, 2002.
24. Gusev A.L., Hampton M.D., Zolotuchin I.V., Kalinin J.E., Ponomarenko A.T., Travkin V.S., Veziroglu T.N. "Superinsulation: New Effects, Structures, Design Principles", Extended Abstracts of the "Eurofillers' 01" Conference, Juli 9-12, 2001, Technical University of Lodz (Poland), C-10, pp.102/C-10/1-103/C-10/2.
25. Michael D. Hampton, "Surface Evaluation by XPS of High Performance Foams After Exposure to Oxygen Plasma", 2001 Research Reports of the NASA/ASEE Summer Faculty Fellowship Program, NASA CR-2001-210265, pp. 74, E. R. Hosler and C. Black, Editors, October, 2001.
26. Michael D. Hampton, Janice K. Lomness, and Lucille Giannuzzi, "The Role of Water in the Storage of Hydrogen in Metals", 2000 Research Reports, NASA/ASEE Summer Faculty Fellowship Program, NASA CR-2001-210260, E. Ramon Hosler and G. Buckingham Editors, Nov. 2000, pp. 63.
27. Janice K. Lomness, Lucille A. Giannuzzi, Michael D. Hampton, "Site Specific TEM Characterization of Micrometer Sized Particles Using the FIB Lift-Out Technique" in Microscopy and Microanalysis, Volume 6, Supplement 2, Proceedings; Microscopy and Microanalysis 2000, Philadelphia, PA, Aug. 13 - 17, 2000, Springer Verlag, New York Inc, pp 518.
28. M. D. Hampton and J. L. Mills, "Safety of Microscale General Chemistry Experiments", Proceedings of the Safety Considerations in Microscale Chemistry Laboratories Symposium, 197th National Meeting of the American Chemical Society, Dallas, TX, April, 1989.
Hydrogen absorption properties of LaNi5 and LaNi5Alx
intermetallics prepared by mechanical alloying have been investigated as a function of alloy preparation parameters and alloy composition in the range of 0.9 to 33.3 atomic % Al in LaNi5Alx. LaNi5 and its aluminum added derivatives, powdered by mechanical alloying, did not readily interact with H2. Activation has been achieved by thermal treatment of the powdered samples. Interactions were rapid at 193 K and 5 atm. H2 pressure. Hydrogen capacity was reduced slightly with the addition of Al, however the time of completion of the reaction was unaffected. Formation of LaNi4Al has been verified by X-ray diffraction analysis. LaNi5 was tested to selectively react with H2 in a stream of H2-He and it retained H2, producing pure He.
Introduction
Lanthanum nickel, LaNi5 has long been studied as a possible hydrogen storage material. Unfortunately, because of its high mass, the weight content of hydrogen is extremely low, making the material unsuitable for automotive purposes. However, the material forms a hydride at room temperature, or lower, with good kinetics. This makes LaNi5 an excellent candidate for applications that
require rapid uptake under mild conditions. One such use is for the recovery of hydrogen that is lost during the purging of transfer lines, or is lost due to boil-off during the storage of liquid hydrogen.
At NASA's Kennedy Space Center, KSC, hydrogen is used for the space shuttle and other launch vehicles. As a result, huge quantities of liquid hydrogen are transported, transferred and
stored at KSC. During the transfer of the hydrogen from the trucks to the storage dewars, significant quantities of hydrogen are lost during the cooldown of the transfer lines and from flash evaporation as the high pressure cryogenic liquid enters the low pressure dewars. Additionally, during storage, hydrogen is constantly lost because of boil off. Recovery of this lost hydrogen could lead to substantial savings.
In addition to the hydrogen that is lost due to transfer operations and boil off, NASA also loses hydrogen during purge operations. Prior to filling lines with liquid hydrogen, they must be pre-cooled with liquid helium. After an operation, the residual hydrogen is purged, again with helium, in order to safe the systems. Both the hydrogen and helium in these operations is currently not recovered, leading to additional losses.
It was the loss of this hydrogen and helium that led to the study described here. LaNi5 absorbs hydrogen rapidly, reversibly and selectively. As a result, it is capable of not only absorbing hydrogen as it vaporizes during transfer operations, but also is potentially useful for separating hydrogen from the helium purge gas. Selective removal of the hydrogen would allow recovery of helium, in high purity, for future use.
Background
Hydriding alloys of the AB5 type are suitable materials for hydrogen storage applications because of their large hydrogen capacity, easy activation and rapid hydriding/dehydriding rates. One of those representative compounds that has been extensively studied is LaNi5 [1, 2]. It has been used as an electrode in nickel metal hydride batteries and as an absorber for gaseous hydrogen. LaNi5 rapidly reaches equilibrium with hydrogen, even at low pressures and temperatures, and the hydriding and de-hydriding processes are reversible at H2 partial pressures close to atmospheric [3].
Hydriding alloys are of great interest due to the simplicity of tailoring the hydriding properties by a variety of methods. One common method is the partial substitution of one metal for another. For example, the substitution of Ge, Zn or Al for the Ni in LaNi5 was reported to have increased the cycle life of the hydride with a slight decrease in hydrogen capacity [4-6]. Partial substitution of La by rare earth metals, however, deteriorated the hy-driding properties and cycle life [7]. Another option to manipulate the characteristics is to change the sample preparation method. Laboratory scale possibilities include melting, annealing or mechanical alloying, or a combination of several techniques [8]. Further treatment after alloying is also necessary for LaNi5 to readily react with hydrogen.
Hydrogen absorbing alloys reported previously were prepared by arc melting the elements, which were analyzed after size reduction and several hydriding-dehydriding cycles for activation. For example, LaNi5-xAlx samples, prepared by arc melting followed by annealing and size reduction, were activated by hydriding in pure hydrogen gas at 17atm and dehydriding at 363 K three times [6].
Mechanical alloying is a low temperature activation method and has been reported to activate FeTi, Mg2Ni and LaNi5, which are inert to hydrogen prior to milling. For FeTi, milling is believed to give rise to Fe rich clusters on the surface and the generation of new surfaces by cracking [9]. LaNi5 has been formed from elemental La and Ni via milling at room temperature, and partially substituted La0.5Zr0.5Ni5 has been synthesized from an equimolar mixture of LaNi5 and ZrNi5 [10].
In the present study, we had an interest in being able to selectively remove hydrogen from a hydrogen-helium stream, such as is generated when helium is used to purge a system that has carried hydrogen. These purge gases, a hydrogen-helium mixture, are typically vented, resulting in a loss of millions of dollars of resources. The ability to selectively remove and capture the hydrogen would also allow the helium to be reclaimed for further use.
Experimental
Sample preparation. Sample preparation involved the ball milling of LaNi5 that had been pre-alloyed by the manufacturer. Al and LaNi5 were mechanically alloyed in changing proportions using a high energy ball mill. Al content is presented as mole percentages, varying between approximately 0.9 and 33.3 % of the total number of atoms in LaNi5Alx. The results of the effect of the addition of Al to LaNi5 on hydriding capacity and rate was analyzed by differential scanning calor-imetry at 293 K and 5 atm initial H2 pressure. LaNi5 (99.9%, REacton) and Al (99.5%, -325 mesh) were obtained from Alfa Aesar and stored under the Ar atmosphere of a Labconco glove box. The mechanical activation of LaNi5 and LaNi5Alx was done by ball milling in a high energy S5pexx 8000M Mixer/Mill. A 50-mL tungsten carbide grinding vial obtained from Spex Certi Prep Inc., Metuchen, NJ, was used with two 11.11 mm tungsten carbide balls as the high energy ball milling medium. The milling canisters were loaded and unloaded in the glove box to avoid contact with air and moisture. LaNi5 samples were ball milled with the following durations and ball to powder ratios, respectively: 10 minutes, 10:1; 10 minutes, 1:1; 30 minutes, 1:1. Approximately 200 mg of the milled powder was utilized for hydrogen uptake analysis.
LaNi5Alx samples were ball milled for 10 minutes with 10:1 ball to powder ratio and analyzed for hydrogen uptake, followed by elemental analysis. Five LaNi5 samples were milled for 3, 6, 10, 15 and 30 minutes with a ball to powder ratio of 10:1 for x-ray diffraction studies.
LaNi5 samples for use in the larger scale U-tube reactor were prepared using a 50-mL stainless steel grinding vial with two 12.70 mm stainless steel balls. Samples were milled for 30 minutes with a ball-to-powder ratio (BPR) of 1.7:1.
Equipment. Hydriding and dehydriding characteristics of sample materials were determined using a SETARAM DSC-111 Differential Scanning Calorimeter. The DSC furnace was fitted with
sample and reference cells made from 1/4" Hastelloy C-22 seamless tubing. The cells were connected to inlet and exit valves, with quick disconnects for easy access. The inlet and exit valves were needle and globe valves, respectively. The inlet valves were connected to hydrogen and helium cylinders and the exit valves opened to the atmosphere. All components and fittings were made of 316 stainless steel. Pressure was monitored with two Omega type PX602 pressure transducers with a range up to 13.6 atm. Pressure data were acquired with a Dell 4200 PC using LabView software with a National Instruments board. Thermal data were directly transferred to the PC from the DSC and analyzed using Setsoft 2000 software. The amount of hydrogen absorbed or released was calculated and graphed using SigmaPlot software. Sample boats for the DSC were made from 316 stainless steel. The samples loaded into the boat were placed into a hollow glass tube that was sealed at both ends with plastic caps and then transferred from the glove box to the DSC to prevent exposure of the samples to air. Sample cell volume was determined by a water displacement method. Lateral heat loss compensation curves were previously determined.
A U-tube reactor was constructed from a seamless stainless steel pipe, 1 foot long, 1 inch O.D., that was bent into a U-shape to contain samples as large as 300 g. The reactor was fitted with 0.5 micron pore size inline filters and needle valves on each end. The downstream valve was connected to a three neck flask for effluent gas collection. The compositional analysis of the effluent gas was done with a Buck Scientific type 910 gas chromatograph fitted with a Hayesep DB 100/120, 30 ft, 1/8 inch O.D. stainless steel column obtained from Alltech. The GC utilized a TCD detector and the carrier gas was argon. Sample injection was done with a gas tight 100 |L syringe. The GC was connected to a Dell GX110 PC and the data was recorded using PeakSimple chromatography software.
Thermal activation. In the DSC, samples were activated with a thermal cycle following milling. This was done by placing the sample in the DSC in a hydrogen atmosphere at approximately 5 atm, and heating the furnace to 150 °C, followed by cooling to ambient temperature. During this activation step, samples were hydrided to some extent, if not completely. Therefore, these samples were heated up to 150 °C under a minimal flow of argon to ensure no hydrogen was left in the sample.
For study in the U-tube reactor, samples were ball milled in stainless steel vials with lower ball to powder ratios and longer milling times. Approximately 200 grams of milled alloy were placed in a Pyrex petri dish that was then transferred into a 2 L capacity Parr pressure reactor for activation. Samples were heated to 250 °C under a hydrogen pressure of approximately 20 atm. After the system reached equilibrium, it was allowed to cool under hydrogen pressure. After cooling, the system was vented and heated to remove absorbed hydrogen.
Hydriding procedure. Activated samples for hydriding trials in the DSC were prepared by loading 100 to 300 milligrams of sample into sample boats under an argon atmosphere in the glove box. The boats were transferred to the DSC after the furnace temperature had been adjusted to between 20 to 25 °C. The boat was loaded into the cell under a minimal hydrogen flow, which limited air exposure of the samples and avoided blowing the samples out of the boat. After inserting the boat, the exit valves were closed, the system was adjusted to the desired pressure and then the upstream valves and the hydrogen source cylinder valve were closed.
The U-tube reactor was used to determine hy-driding characteristics via continuous operation. The U-tube was disconnected from the rest of the structure by the quick disconnects and filled with approximately 200 g of sample under an argon atmosphere in the glove box. The rest of the structure was then assembled on both ends and the reactor was removed from the glove box. After purging the reactor with argon, a hydrogen/helium mixture was allowed to flow through the reactor. At the same time, samples were injected into the GC continuously with appropriate one minute intervals, determined by the start and end of a hydrogen-helium peak pair. The flow rate through the reactor was monitored with a Fisher Scientific digital flow meter.
Dehydriding was accomplished by heating the reactor to 150 °C under argon flow. The exit stream was analyzed for hydrogen using the GC. As soon as no hydrogen was detected in the stream, the system was allowed cool to room temperature.
Sample Characterization and Analysis. A Rigaku Multiflex x-ray diffractometer using Cu-Ka radiation, was employed to characterize LaNi5 + Al samples. Analysis was done over a 20 range of 20 ° to 80 °. The slit width and scanning speed, respectively, were 0.020 mm and 2.400 degrees per minute. The x-ray generator voltage and current were set to 40 kV and 30 mA, respectively. Samples were supported on a metal sample holder whose bottom was closed by scotch tape and the sample was filled above it. Data were analyzed with Jade analysis software.
Elemental analysis of LaNi5 and Al doped LaNi5 was done by flame emission spectroscopy using a Varian Inc. SpectrAA10 spectrometer. Lanthanum, nickel, and aluminum were determined at 441.7, 341.5 and 396.1 nanometers, respectively. An acetylene/nitrous oxide flame was used with a slit width of 0.2 nm for all elements. Lanthanum standards were prepared by making dilutions from a stock solution of La2O3 dissolved in HNO3. Nickel and aluminum stock solutions were prepared by dissolving pure elements in 1:1 HNO3 and then standards were prepared by making appropriate dilutions. The interference of Ni on Al determination and of Al on the determination of La were accounted for by matching the concentrations of the interferences in the standards to those of samples.
Results and Discussion
During ball milling, it was noted that a significant amount of material always coated the grinding media and the walls of the vial. Because Al was the more malleable component of the two and, therefore, more likely to stick to the media and walls, elemental analysis was run after the samples had been ball milled and used for hydrogen uptake. The composition of LaNi5Alx samples initially and after ball milling are given in Table 1. The mole % Al after milling was less than originally placed in the milling jar for all samples except for Sample 4.. Apparently, during milling the aluminum did coat the milling media and was depleted from the bulk. The increase of Al content in Sample 4 is assumed to be the result of non-homogeneity of the milled product; the sample taken for analysis may not have been representative of the whole.
Table 1
Aluminum content of free powder in milling jar
Sample
1
4
Mole % Al
Initial mixture
0.87
5.26
14.29
33.33
After milling
0.77
4.74
12.00
47.31
LaNi5 samples, prepared with various milling conditions, were reacted with H2 at 293 K and 5 atm H2 in the DSC. None of the samples showed activity towards hydrogen after only ball milling. However, ball milling followed by a single thermal activation cycle resulted in a material that readily reacted with hydrogen. The hydrogen uptake reaction was observed to be rapid in all cases, reaching completion within 10 minutes. On the other hand, the total hydrogen absorption capacity was affected by changes in milling settings. The results are listed in Table 2. When the ball to powder ratio was decreased, a decrease in hydrogen capacity was observed. This effect is believed to be a consequence of the reduced number of collisions between milling media and the particles, resulting in relatively less stress being induced in the particles. This resulted in less activation of the sample. Furthermore, the degree of activation of the sample was independent of the material from which the milling jar and media were made. This indicates that contamination with iron is not a factor in the activation of the samples.
Table 2
Effects of various milling parameters on hydrogen capacity
Milling vial SS1 WC2 WC WC WC
Milling time, min 30 Non milled 10 10 30
Ball to powder ratio 1.7:1 n/a 10:1 1:1 1:1
% H absorbed (wt %) 0.76 0 1.06 0.54 0.66
Stainless steel Tungsten carbide
Using the DSC, reactions between the samples shown in Fig. 1 and hydrogen were carried out at 293 K and 5 atm H2. The weight percent of H absorbed by the LaNi5Alx samples is listed in Table 3 and the uptake curves are given in Fig. 1. The dependence of percent hydrogen absorbed on Al content in LaNi5 is given in Fig. 2. The observed amount of H2 absorbed remained constant at low Al content, and then decreased as Al content increased.
Table 3
% H uptake values for different amounts of Al in LaNi5
Mole % Al
Average Wt % H absorbed
Maximum Wt % H absorbed
0
1.04
1.09
0.77
1.05
1.13
4.74
0.95
0.98
12.00
0.87
0.92
47.31
0.68
0.69
0.8
0.6
0.4
0.2
— 0.77 %
— 4.74 %
— 12.00 %
+ 47.31 %
0 %
500
1000
1500
2000
2500
Time (s)
Fig. 1. Hydrogen uptake curves for LaNi5 samples with various amounts of Al
1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65
-О и -P
0.60
20 30
% Al
Fig. 2. Hydrogen capacity as a function of Al in LaNi5
Four consecutive x-ray diffraction spectra were obtained for a LaNi5 sample, Fig. 3. The spectra were not consistent with each other, yet the elemental analysis proved that the composition of the sample was LaNi5. The inconsistencies may indicate that the LaNi5 from Alfa Aesar was not in its normal crystalline form and the energy from the x-ray beam was inducing changes in the crystal phase.
2
3
After grinding LaNi5 with a mortar and pestle in the glove box, three consecutive XRD scans yielded peaks that were consistent with the reported peak positions of LaNi5. However, the relative intensity of the observed peaks did not match with the reported ratios, and inconsistencies within the spectra were observed.
Five more LaNi5 samples were prepared by ball milling in the Spex8000M for 3, 6, 10, 15 and 30 minutes respectively. The XRD spectra of the samples are given in Fig. 4. As reference, the XRD spectrum of non-milled LaNi5 that most closely matches the expected spectrum is included. The relative intensities of the peaks were observed to approach the reported ratios for LaNi5 as milling duration was increased. This suggests that the normal phase of LaNi5, a CaCu5 phase was formed as the milling proceeded. In contrast, the peaks were observed to lose intensity and broaden, which suggested the formation of an amorphous phase, but the broadening effect could be because of particle size reduction.
Samples of LaNi5 mixed with 5.26, 14.29 and 33.33 mole % Al were examined with x-ray dif-fractometry. The spectrum of LaNi5 with 33 mole % Al is given in Fig. 5. The Bragg peak for LaNi5 at 42.5 ° was identified; as were peaks for Al. However, the intensities of other LaNi5 reflections were not strong enough to be identified.
е .1
, 1 . „1 . . ...A J
с
b
о о rt о § Se S е
20 30 40 50 60 70 80
2-Theta (deg.)
Fig. 3. XRD spectra of LaNi5: a — LaNi5 (reference), b, c, d, e — non-milled sample
44.5 ° ^ LaNi5 + 47.31 %А1
I LaNi5 +12.00 %А1
1 LaNi5+4.74%Al
20
30
40
60
70
40 50 60
2-Theta (deg.)
Fig. 5. XRD spectrum of non-milled LaNi5 with 33 mole % Al
In the XRD spectra of the milled samples, Fig. 6, the intensity of the Al Bragg peak at 38.5 ° increased with the increased Al content; however, its intensity was less than the Bragg peak of LaNi5. The angle of the Bragg peaks also changed from 42.5 ° to 42.0 This suggests the formation of LaNi4Al for which the angle of the Bragg peak is at 42.0 4°. The formation of LaNi4Al would lead to the release of free Ni through LaNi5 + Al ^ LaNi4Al + Ni. The formation of Ni could not be verified because the Bragg peak for Ni, at 45.5 coincides with one of the lines of LaNi5. However, for LaNi4Al, a reflection expected at 44.5 ° was observed for LaNi5 milled with Al, also suggesting the formation of LaNi4Al by ball milling. This peak is indicated with an arrow in the figure.
2-Theta (deg.)
Fig. 4. XRD spectra of LaNi5 milled for various times
50
2-Theta (deg.)
Fig. 6. XRD spectra of milled LaNi5 containing Al
In order to determine the ability to selectively absorb hydrogen, the U-tube was filled with approximately 190 grams of LaNi5 and then the flow of 2 % (v/v) H2:He at about 9 atm was fed into it. The flow out of the reactor was restricted to about 200 mL min-1 by a pressure relief valve. The valve maintained the pressure within the reactor, while allowing a slow flow. The gas chromatogram of multiple injections is given in Fig. 7. The single peaks over the first 20 minutes were assigned to helium as a result of their retention time. Hydrogen was not observed in the effluent because it
Fig.
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7. Chromatograms for hydrogen absorption in the U-tube reactor, circles indicate helium and filled circles indicate hydrogen
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Fig. 8. Effluent gas composition as percent hydrogen (V/V)
was captured by LaNi5. When LaNi5 became saturated with H2, peaks at the retention time for hydrogen began to appear in the gas chromato-grams of samples. The percent hydrogen values in the effluent were calculated using peak area ratios of H2 and He. The breakthrough curve is plotted as a function of time, Fig. 8.
The LaNi5 in the U-tube reactor successfully removed the hydrogen from the H2-He stream and allowed the passage of pure He. The amount of hydrogen retained in the reactor at the time of saturation was calculated from material balance as follows. The amount of helium leaving the system was calculated using flow rate and time, VHe (mL) = flow rate (mL-min-1) x time (min), which was equal to the amount of He that entered the system. Since the composition of the entering gas mixture was known, the amount of H2 entered was calculated using VHydrogen = VHe x (20/80) and converted to the weight percent hydrogen in the LaNi5.
The average percent hydrogen absorbed in four trials with the same feed pressure was calculated as 0.041 %. The low percent hydrogen of LaNi5 was possibly due to the low pressure of H2. To
increase the hydrogen absorption in the continuous system, a higher partial pressure of H2 would be useful. However, in this experiment, the absorption characteristics of the absorbing material were sufficient to remove the hydrogen from the feed stream to levels below the limit of detection of the gas chromatograph.
Conclusions
The alloy, LaNi5, was shown to have the kinetics and capacity needed to remove hydrogen from a flowing stream of hydrogen and helium, thus allowing purification of both gases. Addition of aluminum to the alloy up to a level of 47 mole % provided for an improvement in the kinetics of hydrogen absorption without significantly reducing capacity. This incorporation of aluminum into the lanthanum nickel alloy will enormously reduce the weight and cost of the alloy required to purify hydrogen and helium.
In addition to being used to purify helium and hydrogen, LaNi5 could also be used to capture the hydrogen currently lost to boil-off. The hydrogen recovered could be used to automobiles or buses.
References
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3. Boser O. // Journal of the Less Common Metals, 1976. 46. P. 91-99.
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5. WithamC., Bowman Jr. R. C., Fultz B. // Journal of Alloys and Compounds, 1997. 254. P. 574-578.
6. Nishimura K., SatoK., NakamuraY., InazumiC., Oguro K., Ueharal., Fujitani S., Yonezu I. // Journal of Alloys and Compounds, 1998. 268. P. 207-210.
7. Brundle C. R. // Physical Review Letters, 1978. 40. P.972-975.
8. Percheron-Guegan A., Welter J-M. Preparation of Intermetallics and Hydrides, in Hydrogen in Intermetallic Compounds I / L. Schlapbach, Editor. 1992. Springer-Verlag: Heidelberg.
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10. Msika E., Latroche M., Cuevas F., Perch-eron-Guegan A. // Materials Science and Engineering B, 2004. 108(1-2). P. 91-95.
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