Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
• • 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
  • C01B3/0031—Intermetallic compounds; Metal alloys; Treatment thereof
  • C01B3/0047—Intermetallic compounds; Metal alloys; Treatment thereof containing a rare earth metal; Treatment thereof
  • C01B3/0057—Intermetallic compounds; Metal alloys; Treatment thereof containing a rare earth metal; Treatment thereof also containing nickel
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/383—Hydrogen absorbing alloys
• • 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
  • Y02E60/10—Energy storage using batteries
• • 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 present invention is directed to Ca, Mg and Ni-containing alloys. It is also directed to a method for preparing these alloys and to their use for reversibly absorbing hydrogen from a gas phase.
• Hydrogen gas is very light. It can be compressed under high pressure and stored in pressurized vessels. It can also be liquefied and stored in liquid form. Hydrogen also reacts with metal or non-metals to form hydrides. Some metal hydrides called “low temperature metal hydrides” are reversible at ambient temperature and pressure. From a safety point of view, metal hydrides are intrinsically safe since the hydrogen must be released from the hydrides before it can burn or be oxidized. The volumetric density of hydrogen storage in metal hydrides is usually high.
• the most serious shortcomings of the reversible metal hydrides and more particularly the low temperature metal hydrides are their low gravimetric storage density and the high cost.
• the weight of the hydrogen storage tank is not a problem.
• the high cost of conventional low temperature metal hydrides results in too expensive storage devices.
• CaNis is isomorphic to LaNis and has higher storage capacity than that of LaNis based hydrides.
• CaNi ' 2 there are four stable compounds, CaNi ' 2, CaNiX Ca2Mi i7 and CaNis, but only the CaNis has been considered to be of practical interest since the plateau pressures of CaNis are adequate for applications.
• the other three compounds do form very stable hydrides.
• hydrogen can not be extracted at temperatures below 100°C under normal pressure.
• Ca and Mg have very high evaporation rate, it is very hard to produce a stoichiometric Ca-Mg-Ni alloy in large quantity.
• the Mg and Ca alloy in liquid form has to be protected by argon or SF ⁇ because of the rapid oxidization and possible explosion.
• the composition has to be adjusted by trial and error due to evaporation loss of Mg and Ca.
• the so-cast alloys usually have very high macro-segregation and micro-segregation. Homogenization by long annealing treatments is required but adds costs to the alloys.
• the Ca-Mg-Ni alloys were synthesized by liquid phase sintering in closed Ta tubes starting from elemental Mg, Ca and Ni at a temperature below 1250°C. Such a method also needs high temperature and long sintering time to reach complete reaction.
• Mg-Ca-Ni alloys of the AB 3 type have also been synthesized by a powder sintering method.
• Kadir et al disclosed a CaMg2Ni9 ternary alloy prepared by sintering fine powder mixtures of MgNi 2 and CaNis. This paper states that the sintering process involved raising the temperature stepwise to 600°C, 850°C and 990°C (in 0.6MPa Ar gas), with set temperature holds for 2-3h. Several attempts were necessary until an optimum composition was found. A slight excess of CaNis over the stoichiometric composition was necessary in order to compensate for the evaporative loss of Ca.
• Mg and Ca are known to react with all type of ceramic crucible at elevated temperatures and Ni is known to react with refractive metals at high temperatures. Therefore, all the sintering of alloys containing Mg, Ca and Ni were performed so far in Mo or Ta crucible, especially when long sintering times were needed. In practice, this means that the use of this technology would be expensive.
• the present invention as claimed hereinafter relates to new Ca, Mg and Ni-containing alloys of the general formula:
• M is at least one metal selected from the group consisting of Y, Ce, La, Pr, Nd, Th, Nd, Ti, V, Zr, Ta, Hf, Sr, Ba and Misch metals;
• T is at least one element selected from the group consisting of Al, 2n,
• a is an integer equal to 2 or 5 z is a number ranging from 0 to 0.5, and when a is equal to 2, then b, c, d, e are numbers selected so that:
• the alloys according to the invention can be said to be of the AB2 type.
• the alloys according to the invention can be said to be of the A2B5 type.
• the alloys according to the invention can be said to be of the AB5 type.
• the alloys may be single phase or multiphase.
• the invention also relates to a method for preparing the above mentioned alloys, comprising the steps of:
• the invention further relates to the use of the above-mentioned alloys for reversibly absorbing hydrogen from a gas phase.
• Fig. 1-1 shows the XRD (x-ray diffraction) spectra of a sample of composition Cao. Mgo.eNi 2 made by milling a powder mixture of Ca, Mg and Ni powders as a function of milling time.
• Fig.l-3 shows the XRD spectra of a mechanically alloyed Cao.3Mgo.7Ni2 sample annealed for 1 hour at different temperature 600°C, 800°C and 1000°C.
• Fig.l-5 shows PCT (pressure-concentration isotherm) of Ca ⁇ Mg ⁇ -xNi2 alloys measured at 30°C.
• Fig.l-6 shows the XRD spectra of Zn (on the B site) and Mm (on the A site) substituted Cao. Mgo.sNi2 alloy after annealing at 1000°C for 1 h.
• Fig.l-7 shows the XRD spectra of Cu and Fe (on the B site) and Mm (on the
• Fig.l-8 shows the PCT of various (Cao.4-xMgo.6- Y Mmx+ y )Ni2 substituted alloys.
• Fig.l-9 shows the position of the plateau pressures versus the lattice parameters for various CaxMg ⁇ -xN ⁇ 2 alloys and (CaxMgo.7Mm y )Ni 2 .
• the substitution of Ca by Mm does not change much the lattice parameter but increases significantly the plateau pressures.
• Fig.11-1 shows the XRD spectra of (Cao ⁇ Mgo.e ⁇ Nis after ball milling for various time using process A (i.e. starting with a mixture of intermetallics and elemental powders) .
• Fig.ll-3 shows the XRD spectra of (Cao.37sMgo.625)2Nis made by process B
• Fig. H-4 shows the PCT curves measured at 30°C of (Cao.37sMgo.62s)2Nis annealed at various temperatures.
• Fig. H-5 shows the PCT curves of (Cao.37sMgo.62s) 2 Ni5 annealed at 1000°C and measured at various temperatures.
• Fig.ll-6 shows the XRD spectra of various (CaxMgy Nis with various Mg/Ca ratios.
• Fig.ll-7 shows the PCT curves measured at 30°C of the various samples shown in Fig.ll-5.
• Fig. II-8 shows the XRD spectra of various Mm substituted (Cao.375- Mgo.6 2 5-yMm +y)2Ni5 - Substitution on the A site.
• Fig.ll-9 shows the PCT curves of the various substituted alloys shown in Fig.ll-8.
• Fig. H-10 shows the XRD spectra of (Cao.sMgo.37sMmo.i2s)2Ni5 and its hydride.
• Fig.11-1 1 shows the XRD spectra of various A2B5 type alloys with substitution on the B site.
• Fig.11-1 2 shows the PCT curves of various substituted alloys shown in Fig.ll-1 1 .
• alloys of the ABs type With respect to the alloys of the ABs type:
• Fig.lll-1 shows the XRD spectra of CaxMm-i-xNis alloys made by mechanical alloying followed by annealing
• Fig.lll-2 shows the lattice parameters of the CaxMnm-xNis alloys shown in Fig.lll-1 .
• Fig. III-3 shows representative PCT curves of some of the ternary Ca ⁇ Mm ⁇ - ⁇ Ni5 alloys shown in Fig.lll-1 .
• Fig.lll-4 a&b show XRD spectra of ball milled Ca-Mg-Ni ternary alloys before and after annealing treatment and demonstrate that the solubility of Mg in CaNis is very low.
• Fig.lll-5 a&b show XRD spectra of ball milled Mm-Mg-Ni ternary alloys before and after annealing treatment and demonstrate that the solubility of Mg in MmNis is also very low.
• Fig.lll-6 shows XRD spectra of various mechanically alloyed Mm-Ca-Mg-Ni quaternary alloys before annealing treatment.
• Fig.111-7 shows XRD spectra of various mechanically alloyed Mm-Ca-Mg-Ni quaternary alloys after annealing treatment.
• Fig.lll-8 shows the PCT curves of the quaternary alloys shown in Fig.lll-7
• Fig.lll-9 a&b shows the XRD spectra of various Mm-rich quaternary Mm-Ca- Mg-Ni alloys (a) and the corresponding PCT curves (b).
• Fig.lll-10 a&b show the XRD spectra of various Mm-poor quaternary Mm- Ca-Mg-Ni alloys (a) and the corresponding PCT curves (b).
• Fig.lll-1 1 shows the relationship between the plateau pressure and the c/a parameter of various (Mm-Ca-Mg)bNis alloys.
• alloys according to the invention are of the formula:
• These alloys are single or multiphase hydrogen storage compounds of the AB2 type, which are capable of absorbing and desorbing hydrogen from a gas phase at ambient temperature with a flat plateau pressure and a storage capacity larger than 1 .2 wt %.
• These alloys may be prepared by a method comprising the following two steps.
• the first one consists of preparing a powder by milling a mixture of elemental powders and/or pre-alloyed combination of the elemental powders
• the milling can be a conventional ball milling or a more intensive mechanical alloying that can be carried out at room temperature or at high temperatures with or without anti-sticking agents and in various kind of atmosphere.
• the second step consists of annealing and/or sintering the milled powder at elevated temperatures in a crucible made of, for example, stainless steel, for a short period of time in an inert or reactive atmosphere. This is an essential step to achieve a high reversible absorption capacity and a flat plateau.
• the annealing temperature should be higher than 800°C but not higher than 1050°C.
• the invention is based on the discovery that the mechanical alloying of elemental powders (such as powders of Ca, Mg, Ni) and/or of mixtures of intermetallic compounds (such as powders of CaNis, MgNi 2 ) corresponding to the composition of the formula:
• the invention is also based on the discovery that, when a thermal treatment) of the present invention is applied to this mechanically alloyed powder, a substantial improvement in properties is achieved. Indeed, the hydrogen storage properties of the mechanically alloyed Mg-Ca-Ni are substantially improved by annealing the powder at temperatures higher than 800°C for short period of time, typically at 1000°C or slightly higher, for 0.5h to 1 h. Annealing at temperatures lower than 800°C does not improve the hydrogen storage properties very much.
• the ball milling time can vary from a few minutes to several hours. When the milling time is of about 10 hours, then a true alloy is formed between the components (see Fig.1-1 ), i.e. a nanocrystalline ternary intermetallic compound with the CaNi 2 structure (C15-type)). Thus, in that case, the ball milling step is a mechanical alloying. Under these conditions, the post- thermal step becomes an annealing treatment which could be as short as 0.5 to 1 hour as indicated above.
• the powder particles are then only agglomerates of the various constituents.
• the post-thermal step is a sintering treatment which could take a few hours to produce the final alloy product.
• Example 1-1 Compound according to the prior art made by the method according to the invention
• a Mg powder (> 99%, + l OOmesh), Ca granules (> 99.5, ⁇ 2mm in size) and a Ni powder ( ⁇ 99.9%, -325mesh) were used as starting materials.
• Isothermal annealing was performed in a tubular furnace under the protection of argon flow.
• the mechanically alloyed powder was sealed in a stainless steel crucible before annealing. The powder was heated to 1000°C at a heating rate of 30C/min, and held at 1 000°C for 1 hour, then cooled down to room temperature in the furnace.
• Hydrogen absorption/desorption properties were measured by using an automatic Sievert's type apparatus.
• the annealed powder normally needs mild activation treatment, such as heated to 200°C under vacuum and then cooled down.
• EDX analysis shows that the Fe content in the end product less than 0.2 at. %.
• the composition of the end product was close to the nominal composition.
• the activated alloy exhibited a relatively flat plateau and a high capacity.
• Example 1-2 Compound according to the invention made by the method according to the invention
• alloys according to the invention may be of the formula:
• Mg and Ca are present in a Mg/Ca ratio ranging from 0.5 to 2 and more preferably from 1 .5 to 1.75.
• the CaNi 2 -type system (also called AB2) has been the subject of PART I hereinabove.
• the unit cell volume decreases and the plateau pressure increases with increasing the Mg content.
• CaNi3 type alloys have been investigated in great details.
• the intermetallic compound CaN ⁇ 3 can absorb hydrogen readily to form CaNi3H 4 e but cannot release hydrogen under ambient conditions (see reference A).
• the unit cell volume and hydrogen storage properties can be altered by different substitutions for the A, B and C elements.
• the second range of composition encompassed by the present invention is the range where the A/B ratio is between 0.45 and 0.35.
• A means (Cao. 4 -xMgo.6- v Mx+y) and B means (N -zTz). This range corresponds to alloys of the A2B5 type.
• a AB2 phase with a cubic C1 5 structure is formed when the A/B ratio is bigger than 0.45.
• the A/B ratio is less than 0.35, an AB3 phase with the PuNi3 structure is formed.
• the A/B ratio is in the range of 0.35-0.45, a new A ⁇ Bs-type phase with a crystallographic structure which has not yet been identified, is obtained.
• This new alloy is made by the same method as the one discussed previously, which comprises first preparing a powder by milling a mixture of elemental powders and/or pre-alloyed combinations of elemental powders (ex.: Ca, Mg, Ni, CaN ⁇ 2, MgN ⁇ 2 ”) in amounts sufficient to achieve the requested composition, and then annealing and/or sintering the so milled mixture at an elevated temperature of about 1000°C to form the requested hydrogen storage alloy.
• the invention is based on the discovery of new hydrogen storage alloys of the A2B5 type which contains Ca, Mg, Ni and other optional elements. These new alloys are capable of absorbing and desorbing hydrogen from the gas phase at ambient temperature with a flat plateau pressure and a storage capacity larger than 1 .5 wt%.
• These alloys may be prepared by a method comprising two steps.
• the milling can be a conventional ball milling or a more intensive mechanical alloying. It can be carried out at room temperature or at high temperatures with or without anti-sticking agents and in various kinds of atmosphere.
• the second step consists of annealing and/or sintering the milled powder at elevated temperatures in a crucible made of, for example, stainless steel, for a short period of time in an inert or reactive atmosphere. This is an essential step to achieve high reversible capacity and a flat plateau.
• the annealing temperature should be higher than 900°C but not higher than 1080°C.
• the invention is based on the discovery that mechanical alloying of elemental powders (such as Ca, Mg, Ni) and/or mixtures of intermetallic compounds (such as CaNis, MgNi ⁇ ) corresponding to the requested composition (CaxMgi-x Nis leads to a highly disordered structure when the Mg/Ca ratio is between 0.33 and 1.67.
• the so-milled alloy can reversibly absorb and desorb hydrogen at room temperature.
• the reversible capacity is small and the slope of the PCT curves is very big.
• the invention is also based on the discovery that a new A2B5 type phase is formed when the mechanically alloyed (Ca ⁇ Mg ⁇ -x)2Nis is annealed at temperature above 600 °C.
• the formation range of this new phase depends on the Mg/Ca ratio and the (Ca + Mg)/Ni ratio.
• the new phase no longer forms when the Mg/Ca ratio is lower than 0.3. If the Mg/Ca ratio is higher than 1 .75, a large amount of MgNi 2 phase is formed and, as a result, the storage capacity is reduced.
• the Mg/Ca ratio is set at 1 .5, the new phase is formed when the (Mg + Ca)/Ni ratio is between 0.35 and 0.45.
• the invention is further based on the discovery that when a thermal treatment is applied to this mechanically alloyed powder, substantial improvement in properties is achieved. Indeed, the hydrogen storage properties of the ball milled Ca-Mg-Ni are significantly improved by annealing the powder at temperatures higher than 900°C preferably around 1000°C or slightly higher for a short period of time, preferably 0.5 to 1 hour. Annealing at temperatures lower than 900 °C does not improve the hydrogen storage properties very much. It has also been discovered that further improvements are achieved by adding other elements to the basic elements used for preparing the alloys. Such an addition raises the plateau pressure and improves other hydrogen storage properties such as plateau slope and the long term stability .
• Hydrogen absorption/desorption properties were measured by using an automatic Sievert's type apparatus.
• the annealed powder normally needs a mild activation treatment, such as a heating treatment to 200 °C under vacuum followed by a cooling.
• EDX analysis showed that the Fe content in the end product is less than 0.2 at.%.
• the composition of the end product was close to the nominal composition.
• the activated alloy exhibited a relatively flat plateau and a high capacity
• the alloy was annealed in the same manner as in Example 11-1 .
• This alloy had a storage capacity of 1.65wt%. Its plateau pressure was flat and significantly raised as compared to that of Example 11-1 .
• alloys according to the invention may also be of the formula:
• the alloys according to the invention as defined hereinabove are of the ABs type.
• LaNis- and MmNis- based ABs type alloys have been widely investigated as hydrogen storage materials (see reference 1 and 2).
• the La, Mm and Ni atoms can be substituted by many other elements to tailor the hydrogen storage properties for different applications (see reference 3).
• substitution of La by Mg in LaNis has not been successful.
• a second phase with an approximate composition of LaMg1.85Ni9.26 was found with a nickel-rich LaNis+x main phase in a melt casting Mgo.1Lao.9Ni5 sample (see reference 4). The hydrogen storage capacity was reduced due to the formation of this second phase.
• CaNis intermetallic compound represents a category of low cost hydrogen storage materials with a storage capacity up to 1 .9wt. % (see references 5 to 7). However, little attention has been paid so far to such a system, probably due to its well-known bad cycling stability (see reference 8). Improvement of the hydrogen storage properties of CaNis by substitution of Ca or Ni with other elements has been tried (see references 5 to 8; A and K). Ternary CaxMrm-xNis alloys were produced by melt casting and were also investigated (see reference 5). Mm substitution for Ca can raise the plateau pressure of CaNis. However, the plateau slope is big for the as-cast ternary alloys due to segregation. Annealing at elevated temperatures ( > 1000°C) can reduce the slope to some extent.
• the invention is based on the discovery that slight substitution of Mg in the CaNis destroys the ABs structure, and a mixture of AB3 and free nickel is formed.
• the hydrogen storage capacity is also reduced.
• the alloy of the ABs type containing Mg comprises more than 3 elements, the solubility limit can be extended and the plateau can be tailored by the Mg content.
• the plateau slope is also small and the reversible hydrogen storage capacity is bigger in comparison to ternary Ca-Mm-Ni AB5 type alloys.
• the present invention provides new hydrogen storage alloys of the ABs type, which contains Ca, Mg, Ni and M. These alloys are capable of absorbing and desorbing hydrogen from a gas phase at ambient temperature with a flat plateau pressure and a storage capacity larger than 1 .3wt.%.
• the milling can be a conventional ball milling or a more intensive or mechanical alloying which can be carried out at room temperature or at high temperatures with or without anti-sticking agents and in various kinds of atmosphere.
• the second step consists of annealing and/or sintering the mechanically alloyed powder at elevated temperatures in a crucible made of, for example, stainless steel for a short period of time in an inert or reactive atmosphere. This is an essential step to achieve high reversible capacity and a flat plateau.
• the annealing temperature should be higher than 800°C but not higher than 1 100°C.
• the invention is based on the discovery that mechanical alloying of elemental powders (such as Ca, Mm, Ni) and/or mixtures of intermetallic compounds (such as CaNis, MmNis) corresponding to the requested composition CaxMmi-xNis leads to a nanocrystalline ABs type structure.
• elemental powders such as Ca, Mm, Ni
• mixtures of intermetallic compounds such as CaNis, MmNis
• the so-milled alloy can reversibly absorb and desorb hydrogen at room temperature.
• the reversible capacity is small and the slope of the PCT curves is very big.
• the invention is also based on the discovery that when a thermal treatment is applied to this mechanically alloyed powder, substantial improvement in properties is achieved. Indeed, the hydrogen storage properties of the mechanically alloyed Mg-Ca-Ni are substantially improved when the powder is annealed at temperatures higher than 800°C typically at 1000°C or slightly higher, for short period of time, preferably 0.5h-1 h. Annealing at temperatures lower than 800°C does not improve the hydrogen storage properties very much.
• Example III- 1 Compound according to the prior art made by the method according to the invention.
• a Mm powder ( >99%, + l OOmesh), Ca granules ( > 99.5, ⁇ 2mm in size) and a Ni powder ( ⁇ 99.9%, -325mesh) were used as starting materials.
• Isothermal annealing was performed in a tubular furnace under argon.
• the mechanically alloyed powder was sealed in a stainless steel crucible before annealing.
• the powder was heated to 1000°C at a heating rate of 30°C/min, held at 1000°C for 1 hour and then cooled down to room temperature in the furnace.
• Hydrogen absorption/desorption properties were measured by using an automatic Sievert's type apparatus.
• the annealed powder normally needs mild activation treatment, such as a heating treatment to 200 °C under vacuum followed by a cooling.
• EDX analysis shows that the Fe content in the end product is less than 0.3 at.%.
• the composition of the end product was close to the nominal composition.
• the activated Mmo. 4 Cao.6 Nis alloy exhibited a relatively flat plateau and a high capacity.
• Example 111-2 Compound according to the invention made by the method according to the invention

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