Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0026—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof of one single metal or a rare earth metal; Treatment thereof
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0031—Intermetallic compounds; Metal alloys; Treatment thereof
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0078—Composite solid storage mediums, i.e. coherent or loose mixtures of different solid constituents, chemically or structurally heterogeneous solid masses, coated solids or solids having a chemically modified surface region
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0408—Light metal alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/74—Iron group metals
  • B01J23/745—Iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/024—Multiple impregnation or coating
  • B01J37/0244—Coatings comprising several layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C2202/00—Physical properties
  • C22C2202/04—Hydrogen absorbing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/32—Hydrogen storage

Definitions

• the instant invention relates generally to hydrogen storage materials and more specifically magnesium-based hydrogen storage materials in which hydrogen desorption is catalyzed by materials which are insoluble in said magnesium-based hydrogen storage material.
• the insoluble catalytic material may be in the form of: 1) discrete dispersed regions of catalytic material in a hydrogen storage material bulk; 2) discrete dispersed regions on the surface of particles of the hydrogen storage material; 3) a continuous or semi-continuous layer of catalytic material on the surface of bulk or particulate hydrogen storage material; or 4) combinations thereof.
• Hydrogen may be used, for example, as fuel for internal-combustion engines in place of hydrocarbons. In this case it has the advantage of eliminating atmospheric pollution through the formation of oxides of carbon, nitrogen and sulfur upon combustion of the hydrocarbons. Hydrogen may also be used to fuel hydrogen-air fuel cells for production of the electricity needed for electric motors.
• One of the problems posed by the use of hydrogen is its storage and transportation.
• Hydrogen may be stored under high pressure in steel cylinders, but this approach has the drawback of requiring hazardous and heavy containers which are difficult to handle (in addition to having a low storage capacity of about 1% by weight). Hydrogen may also be stored in cryogenic containers, but this entails the disadvantages associated with the use of cryogenic liquids; such as, for example, the high cost of the containers, which also require careful handling. There are also "boil off" losses of about 2-5% per day. Another method of storing hydrogen is to store it in the form of a hydride, which then is decomposed at the proper time to furnish hydrogen.
• the MgH 2 ⁇ Mg system is the most appropriate of all known metal-hydride and metal systems that can be used as reversible hydrogen-storage systems because it has the highest percentage by weight (7.65 % by weight) of theoretical capacity for hydrogen storage and hence the highest theoretical energy density
• this alloy can be titanium/iron hydride (a typical low-temperature hydride store) which can be operated at temperatures down to below 0 °C.
• These low-temperature hydride alloys have the disadvantage of having a low hydrogen storage capacity. Storage materials have been developed in the past, which have a relatively high storage capacity but from which hydrogen is nevertheless expelled at temperatures of up to about 250 °C.
• these alloys also have the disadvantage that the price of the alloy is very high when metallic vanadium is used.
• U.S. Pat. No. 4,111,689 has disclosed a storage alloy which comprises 31 to 46% by weight of titanium, 5 to 33% by weight of vanadium and 36 to 53% by weight of iron and/or manganese.
• alloys of this type have a greater storage capacity for hydrogen than the alloy according to U.S. Pat. No. 4,160,014, hereby incorporated by reference, they have the disadvantage that temperatures of at least 250 °C. are necessary in order to completely expel the hydrogen. At temperatures of up to about 100 °C, about 80% of the hydrogen content can be discharged in the best case. However, a high discharge capacity, particularly at low temperatures, is frequently necessary in industry because the heat required for liberating the hydrogen from the hydride stores is often available only at a low temperature level.
• magnesium is preferred for the storage of hydrogen not only because of its lower material costs, but above all, because of its lower specific weight as a storage material.
• the hydriding Mg+H 2 ⁇ MgH 2 is, in general, more difficult to achieve with magnesium, inasmuch as the surface of the magnesium will rapidly oxidize in air so as to form stable MgO and/or Mg(OH) 2 surface layers. These layers inhibit the dissociation of hydrogen molecules, as well as the absorption of produced hydrogen atoms and their diffusion from the surface of the granulate particles into the magnesium storage mass.
• magnesium and magnesium alloys can also be enhanced by the addition of materials which may help to break up stable oxides of magnesium.
• Mg 2 Ni in which the Ni appears to form unstable oxides.
• thermodynamic examinations indicated that the surface reaction Mg 2 Ni+0 2 ⁇ " 2MgO+Ni extended over nickel metal inclusions which catalyze the hydrogen dissociation-absorption reaction. Reference may be had to A. Seiler et al., Journal of Less-Common Metals 73, 1980, pages 193 et seq.
• Laid-open Japanese Patent Application No.55- 167401 "Hydrogen Storage Material, " in the name of Matsumato et al, discloses bi or tri-element hydrogen storage materials of at least 50 volume percent amorphous structure.
• the first element is chosen from the group Ca, Mg, Ti, Zr, Hf, V, Nb, Ta, Y and lanthanides, and the second from the group Al, Cr, Fe, Co, Ni, Cu, Mn and Si.
• a third element from the group B, C, P and Ge can optionally be present.
• the amorphous structure is needed to overcome the problem of the unfavorably high deso ⁇ tion temperature characteristic of most crystalline systems.
• a high desorption temperature (above, for example, 150 °C.) severely limits the uses to which the system may be put.
• the material of at least 50% amo ⁇ hous structure will be able to desorb at least some hydrogen at relatively low temperatures because the bonding energies of the individual atoms are not uniform, as is the case with crystalline material, but are distributed over a wide range.
• Matsumoto et al claims a material of at least 50% amo ⁇ hous structure. While Matsumoto et al does not provide any further teaching about the meaning of the term "amo ⁇ hous," the scientifically accepted definition of the term encompasses a maximum short range order of about 20 Angstroms or less.
• disordered hydrogen storage materials characterized by a chemically modified, thermodynamically metastable structure
• the modified hydrogen storage material can be made to have greater hydrogen storage capacity than do the single phase crystalline host materials.
• the bonding strengths between the hydrogen and the storage sites in these modified materials can be tailored to provide a spectrum of bonding possibilities thereby to obtain desired abso ⁇ tion and deso ⁇ tion characteristics.
• Disordered hydrogen storage materials having a chemically modified, thermodynamically metastable structure also have a greatly increased density of catalytically active sites for improved hydrogen storage kinetics and increased resistance to poisoning.
• the synergistic combination of selected modifiers inco ⁇ orated in a selected host matrix provides a degree and quality of structural and chemical modification that stabilizes chemical, physical, and electronic structures and conformations amenable to hydrogen storage.
• the framework for the modified hydrogen storage materials is a lightweight host matrix.
• the host matrix is structurally modified with selected modifier elements to provide a disordered material with local chemical environments which result in the required hydrogen storage properties.
• Another advantage of the host matrix described by Ovshinsky, et al. is that it can be modified in a substantially continuous range of varying percentages of modifier elements. This ability allows the host matrix to be manipulated by modifiers to tailor-make or engineer hydrogen storage materials with characteristics suitable for particular applications.
• the disordered materials are thus capable of more distortion during expansion and contraction allowing for greater mechanical stability during the abso ⁇ tion and deso ⁇ tion cycles.
• One drawback to these disordered materials is that, in the past, some of the Mg based alloys have been difficult to produce. Particularly those materials that did not form solutions in the melt. Also, the most promising materials (i.e. magnesium based materials) were extremely difficult to make in bulk form. That is, while thin-film sputtering techniques could make small quantities of these disordered alloys, there was no bulk preparation technique. Then in the mid 1980's, two groups developed mechanical alloying techniques to produce bulk disordered magnesium alloy hydrogen storage materials.
• compositionally Varied Materials and Method for Synthesizing the Materials the contents of which are inco ⁇ orated by reference.
• This patent disclosed that disordered materials do not require any periodic local order and how spatial and orientational placement of similar or dissimilar atoms or groups of atoms is possible with such increased precision and control of the local configurations that it is possible to produce qualitatively new phenomena.
• this patent discusses that the atoms used need not be restricted to "d band” or "f band” atoms, but can be any atom in which the controlled aspects of the interaction with the local environment and/or orbital overlap plays a significant role physically, electronically, or chemically so as to affect physical properties and hence the functions of the materials.
• Amo ⁇ hicity is a generic term referring to lack of X-ray diffraction evidence of long- range periodicity and is not a sufficient description of a material.
• amo ⁇ hous materials there are several important factors to be considered: the type of chemical bonding, the number of bonds generated by the local order, that is its coordination, and the influence of the entire local environment, both chemical and geometrical, upon the resulting varied configurations.
• Amo ⁇ hicity is not determined by random packing of atoms viewed as hard spheres nor is the amorphous solid merely a host with atoms imbedded at random.
• Amo ⁇ hous materials should be viewed as being composed of an interactive matrix whose electronic configurations are generated by free energy forces and they can be specifically defined by the chemical nature and coordination of the constituent atoms. Utilizing multi-orbital elements and various preparation techniques, one can outwit the normal relaxations that reflect equilibrium conditions and, due to the three-dimensional freedom of the amo ⁇ hous state, make entirely new types of amo ⁇ hous materials-chemically modified materials . . .
• amo ⁇ hicity was understood as a means of introducing surface sites in a film, it was possible to produce "disorder" that takes into account the entire spectrum of effects such as porosity, topology, crystallites, characteristics of sites, and distances between sites.
• Ovshinsky and his team at ECD began constructing "disordered" materials where the desired irregularities were tailor made. See, U.S. Pat. No.4,623,597, the disclosure of which is inco ⁇ orated by reference.
• disordered corresponds to the meaning of the term as used in the literature, such as the following:
• a disordered semiconductor can exist in several structural states. This structural factor constitutes a new variable with which the physical properties of the [material] . . . can be controlled.
• structural disorder opens up the possibility to prepare in a metastable state new compositions and mixtures that far exceed the limits of thermodynamic equilibrium.
• disordered [materials] . . . it is possible to control the short-range order parameter and thereby achieve drastic changes in the physical properties of these materials, including forcing new coordination numbers for elements . . . S. R.
• Ovonic These families of negative electrode materials, individually and collectively, will be referred to hereinafter as "Ovonic.”
• One of the families is the La-Ni 5 -type negative electrode materials which have recently been heavily modified through the addition of rare earth elements such as Ce, Pr, and Nd and other metals such as Mn, Al, and Co to become disordered multicomponent alloys, i.e., "Ovonic".
• the second of these families is the Ti-Ni-type negative electrode materials which were introduced and developed by the assignee of the subject invention and have been heavily modified through the addition of transition metals such as Zr and V and other metallic modifier elements such as Mn, Cr, Al, Fe, etc.
• This second family of Ovonic materials reversibly form hydrides in order to store hydrogen.
• All the materials used in the '400 Patent utilize a Ti-V-Ni composition, where at least Ti, V, and Ni are present with at least one or more of Cr, Zr, and Al.
• the materials of the '400 Patent are generally multiphase polycrystalline materials, which may contain, but are not limited to, one or more phases of Ti-V-Zr-Ni material with C.sub.14 and C.sub.15 type crystal structures.
• Other Ovonic Ti-V-Zr-Ni alloys are described in commonly assigned U.S. Pat. No.
• Venkatesan, Fetcenko, Jeffries, Stahl, and Bennet the disclosure of which is inco ⁇ orated by reference. Since all of the constituent elements, as well as many alloys and phases thereof, are present throughout the metal, they are also represented at the surfaces and at cracks which form in the metal/electrolyte interface. Thus, the characteristic surface roughness is descriptive of the interaction of the physical and chemical properties of the host metals as well as of the alloys and crystallographic phases of the alloys, in an alkaline environment. The microscopic chemical, physical, and crystallographic parameters of the individual phases within the hydrogen storage alloy material are important in determining its macroscopic electrochemical characteristics.
• V-Ti-Zr-Ni type alloys tend to reach a steady state surface condition and particle size.
• This steady state surface condition is characterized by a relatively high concentration of metallic nickel.
• Figure 1 plots the PCT curve of the '432 patents thin film alloy (reference symbol ⁇ ) with that of the present composite hydrogen storage material (reference symbol ⁇ ) .
• the hydrogen storage composite materials of the present invention adsorb more than 4 weight percent of hydrogen, and what is even more remarkable is that this hydrogen can be desorbed at a temperature of 30 °C.
• the present invention uses catalysis to promote hydrogen adso ⁇ tion/deso ⁇ tion in a relatively pure Mg material using insoluble catalytic material and reduces the deso ⁇ tion temperature of the high capacity Mg-based materials by adding some grain grow inhibitors.
• the instant invention provides for a magnesium-based hydrogen storage material including magnesium or a magnesium-based hydrogen storage alloy; and a hydrogen deso ⁇ tion catalyst whcih is insoluble in said magnesium-based hydrogen storage alloy and is in the form of: 1) discrete dispersed regions of catalytic material within the bulk of said magnesium or magnesium-based hydrogen storage alloy; 2) discrete dispersed regions on the surface of particles of said magnesium or magnesium-based hydrogen storage alloy; 3) a continuous or semi-continuous layer of catalytic material on the surface of said magnesium or magnesium-based hydrogen storage alloy which is in bulk or particulate form; or 4) combinations thereof.
• the magnesium-based hydrogen storage alloy includes at least 80 atomic percent magnesium and may include aluminum.
• the hydrogen deso ⁇ tion catalyst includes iron and may further include one or more elements selected from the group consisting of B, Cu, Pd, V, Ni, C, Mn, Zr, Rb, Nb, Ti, U and Sc.
• the instant invention further includes methods of making the magnesium-based hydrogen storage material.
• One such method includes a) mixing powders of the magnesium or magnesium-based hydrogen storage alloy and powders of the hydrogen deso ⁇ tion catalyst; b) pressing the mixed powders into a compact; and c) sintering/annealing said compact at a temperature between 450 °C and 600 °C.
• the sintering/annealing is performed for at least 10 hours.
• Another such method includes a) forming a melt of powders of the magnesium or magnesium- based hydrogen storage alloy and powders of the hydrogen deso ⁇ tion catalyst in a protective atmosphere; b) stirring the melt to insure suspension of the insoluble powders of the hydrogen deso ⁇ tion catalyst within the molten magnesium or magnesium-based hydrogen storage alloy; and c) rapidly quenching the stirred melt such that the suspended insoluble powders of the hydrogen deso ⁇ tion catalyst are well distributed in the solidified magnesium or magnesium-based hydrogen storage alloy.
• Yet another method includes; a) mixing powders of said magnesium or magnesium-based hydrogen storage alloy and powders of said hydrogen deso ⁇ tion catalyst; and b) mechanically alloying the mixture in an attritor such that powder particles of said hydrogen deso ⁇ tion catalyst are embedded in at least the surface of powder particles of said magnesium or magnesium-based hydrogen storage alloy.
• Preferably heptane and carbon powder are used as grinding aids during mechanical alloying of said mixture.
• a further method includes; a) providing bulk or particulate magnesium or magnesium-based hydrogen storage alloy; and b) depositing a continuous or semi-continuous layer of catalytic material onto the surface of said bulk or particulate magnesium or magnesium-based hydrogen storage alloy by vapor deposition, electrolytic coating or electroless coating.
• the coating is formed by evaporation of said catalytic material and is about 100 angstroms thick.
• the catalyst may be distributed in multiple ways by combining the above techniques.
• the bulk or particulate magnesium or magnesium-based hydrogen storage alloy may be produced by; a) forming a melt of said magnesium or magnesium-based hydrogen storage alloy; and b) rapidly quenching said magnesium or magnesium-based hydrogen storage alloy by a bulk quick quenching method.
• Useful bulk quick quenching method includes melt spinning, centrifugal atomization, gas atomization, or water atomization.
• FIGURES Figure 1 is a scanning electron micrograph (SEM) taken in back-scattering mode of a hydrogen storage material of the instant invention made from pure metal powders pressed and sintered at a temperature above 500° C for 22 hours under vacuum;
• Figure 2 is an X-ray diffraction pattern of the material of figure 1 ;
• Figure 3 is a plot of the pressure-concentration-isotherm (PCT) curve for the material of figure 1 measured at 240° C;
• Figure 4 plots the percent hydrogen abso ⁇ tion versus time (i.e. abso ⁇ tion rates) of the material of figure 1 at various temperatures;
• Figure 5 plots the percent of hydrogen desorbed versus time (i.e.
• Figure 6 plots the PCT curves of samples having the same composition as that of figure 1, but sintered/annealed at 570 and 600 °C respectively;
• Figure 7 is an SEM back-scattering micrograph of another material according to the instant invention having the same composition as the material of figure 1 but formed by mechanical alloying;
• Figure 8 is the XRD plot of the material of figure 7;
• Figure 9 is a plot of the PCT curve of the material of figure 7, measured at 240 °C;
• Figure 10 plots the PCT absorption curves of the material of figure 7 at 240 °C, 210 °C, 180 °C, and 150 °C;
• Figure 11 is an SEM backscattered photomicrograph of a cross-section of a melt spun ribbon of a very uniform Mg-Al alloy used to produce a material according to the instant invention;
• Figure 12 shows a PCT plot of a hydrogen storage material according to the instant invention at 150 °C, the material was produced using the
• the present inventors have found that iron and/or other elements which have a very low solubility in Mg, to a Mg based alloy prohibits the grain growth of Mg or Mg-based crystallites within the alloy and catalyze the deso ⁇ tion of hydrogen from such Mg material.
• the instant invention provides for magnesium-based hydrogen storage materials in which hydrogen deso ⁇ tion is catalyzed by iron and/or other elements which are substantially insoluble in said magnesium-based hydrogen storage material.
• the insoluble catalytic material may be in the form of: 1) discrete dispersed regions of catalytic material in a hydrogen storage material bulk; 2) discrete dispersed regions on the surface of particles of the hydrogen storage material; 3) a continuous or semi-continuous layer of catalytic material on the surface of bulk or particulate hydrogen storage material; or 4) combinations thereof.
• the catalytic material can be added during the alloying process by special rapid quenching methods; or by mechanical alloying methods.
• the catalytic material can also be applied to the surface of the magnesium-based alloy by processes such as thermal evaporation, magnetic sputtering, or by electrolytic or electroless plating methods. Elements which have almost no solid solubility in Mg may be used as grain grow inhibitors/deso ⁇ tion catalysts.
• Example 1 Raw materials consisting of pure metal powders of magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), iron (99.9+%,10 micron) and other minor constituents were mixed in an agate mortar-pestle. Ten different compositions were produced, and their compositions in weight percent are listed in Table 1. A hardened steel die was used to press the mixed powders into a pellet of 1 cm diameter and 1 cm long. The pressed pellet was placed in a quartz tube and was sintered at a temperature above 500° C for 22 hours under vacuum.
• Figure 1 is a scanning electron micrograph (SEM) taken in back-scattering mode of an MM-1 sample sintered/annealed at 500°C.
• the SEM indicates phase segregation of Fe and an ALFe j intermetalhc compounds imbedded in the main Mg matrix.
• the Fe and Fe-rich phases are about a few microns in diameter and the proximity is about 10-20 microns.
• Figure 2 is an X-ray diffraction pattern of the sample, which was recorded on a Rigaku Mini Flex. It clearly indicates the co-existence of Fe and FeAl with the main Mg phase.
• Figure 3 is a plot of the pressure-concentration-isotherm (PCT) curve for the same material measured at 240° C.
• PCT pressure-concentration-isotherm
• Example 2 Another MM-1 material was produced by the process described in Example 1 with a change in sintering/annealing temperature.
• Figure 6 plots the PCT curves of samples sintered/annealed at 570 °C and
• Example 3 The mechanically alloyed (MA) powders of MM- 1 were prepared from mixtures of pure elemental magnesium (99.8%, -325 mesh), aluminum (99.5%, -325 mesh), and iron (99.9+%, 10 micron). The milling was carried out in an attritor loaded with Cr-steel grinding balls.
• FIG. 7 is an SEM back-scattering micrograph of this sample. The figure indicates severe phase segregation within the material. Region 1 (bright contrast on the picture) is filled with Fe and Al powder while Region 2 (central darker area) is all magnesium.
• Figure 8 which is the XRD plot of the sample, shows no indication of any amo ⁇ hous intermetallic product formed by this process.
• the MA-MM- 1 powder was pressed onto an expanded nickel metal substrate and then coated on both sides with 100 angstroms of iron as surface catalysis.
• Figure 9 is a plot of the PCT curve measured at 240 ° C for the MA-MM- 1.
• the pressure plateau is higher than that of the sintered MM-1 due to the varied distance between Mg-storage phase and Fe-catalytic phase and shows a spectrum of varying kinetics.
• the maximum hydrogen storage capacity was increased from 5.0 to 5.7% and the hydrogen is fully desorbed at 240 °C.
• Figure 10 plots the PCT abso ⁇ tion curves of the MA-MM-1 sample at 240 °C, 210 °C, 180 °C, and 150 °C.
• the plateau pressure increases with the temperature. This phenomenon is to be expected from thermo-equilibrium considerations. However, the maximum storage capacity decreases with decreasing in temperature.
• thermo-equilibrium model does not fit into the thermo-equilibrium model.
• this abnormality is due to the influence of temperature on the abso ⁇ tion kinetics. That is, the PCT analysis was done within specific time constraints and thus may underestimate the full hydrogen storage capacity at lower temperature. Higher maximum capacities than measured at these lower temperature may have been achieved if more time was available to achieve equilibrium.
• Example 4 Raw material with the designed composition of MM- 1 was put in an air-operated induction furnace with additional flux to isolate surface from the atmosphere and prevent excessive magnesium evaporation from the metal liquid. Extra argon gas was supplied to the crucible as an isolation blanket to prevent oxidation of the molten metal. After melting all ingredients in the crucible, the melt was tilted pour into a mold and slowly cooled to room temperature. The composition of the resulting ingot was examined by induction coupled plasma (ICP) analysis and no trace of iron was detected. From this comparative example, it can be seen that conventional induction melting techniques cannot inco ⁇ orated iron in the Mg bulk. The Mg- Al Ingot from above was placed in a bottom-poured melt-spinning machine.
• ICP induction coupled plasma
• FIG. 11 is an SEM backscattered photomicrograph of the ribbon cross-section which shows a very uniform Mg-Al alloy.
• the ribbon was then chopped into small pieces and was placed into attritor for the same MA process as described in Example 3.
• the ground powder was then pressed onto a Ni expanded metal substrate and coated on both faces with 100 angstroms of Fe.
• the MS+MA-MM- 1 shows very good hydrogen deso ⁇ tion kinetics at relatively low temperatures.
• Figure 12 shows a PCT plot of this sample measured at 150 ° C.
• the abso ⁇ tion/deso ⁇ tion pressure hysteresis observed is due to the low measuring temperature. Nevertheless, a deso ⁇ tion plateau at 250 ton- is very exciting.
• Figure 13 compares the maximum reversible hydrogen storage capacities at various temperatures for the three different processes (i.e. sintering, MA-only, MS + MA).
• the MS + MA process gives the lowest deso ⁇ tion onset temperature (90° C) but also the lowest maximum reversible capacity due to the non-uniform distribution of the Fe phase.
• the MA-only sample shows the highest deso ⁇ tion temperature onset (150° C) but with the highest reversible storage capacity.
• Example 5 Raw materials with the nominal composition of MM-1 were put in an air-operated induction furnace with additional flux to isolate the molten surface from the atmosphere and prevent excessive magnesium evaporation from the liquid metal. Extra argon gas was supplied to the crucible as an isolation blanket to prevent oxidation of the metal. The molten alloy was stirred manually to uniformly suspend immiscible FeAl and Fe phases in the liquid. The liquid was tilt-poured through an argon protected ladle into a water-cooled quenching mold to inco ⁇ orate the Fe and FeAl phases into the final product.
• Figure 1 Raw materials with the nominal composition of MM-1 were put in an air-operated induction furnace with additional flux to isolate the molten surface from the atmosphere and prevent excessive magnesium evaporation from the liquid metal. Extra argon gas was supplied to the crucible as an isolation blanket to prevent oxidation of the metal. The molten alloy was stirred manually to uniformly suspend immiscible FeAl and Fe phases in the liquid. The liquid was tilt-
• FIG. 14 is an SEM micrograph of a cross-section of the resulting ingot which reveals a uniform distribution of FeAl and Fe secondary phase in the Mg host matrix.
• the Fe-inclusion is about 1 micron in size.
• the ICP analysis conformed the existence of Fe and Al in the ingot.
• Other bulk quick quenching methods such as melt spinning, centrifugal atomization, gas atomization, water atomization, with proper stirring in the liquid, such as secondary stirring coil, inert gas bubbling, rotating crucible, etc. may reach similar results.

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• 2003
  • 2003-12-11 US US10/735,240 patent/US20050126663A1/en not_active Abandoned
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