JP2004083967A - Method for producing hydrogen storage material and hydrogen storage material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a low-cost hydrogen storage material which has a high hydrogen storage content at a low temperature, and has excellent mass-productivity, and to provide a hydrogen storage material. <P>SOLUTION: Either Mg or Mg alloy, and either Nb or Nb-V alloy are stacked to form a stacked body (steps S1 to S4); the stacked body is subjected to machining so as to be a fine wire shape or a sheet shape, and also so as to control the average thickness of the Mg layer formed of Mg or Mg alloy to ≤1 [μm] (steps S5 to S15); and the stacked body after the machining is subjected to heat treatment so as to rearrange the crystal orientation of the Mg layer (a step S16). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a hydrogen storage material and a hydrogen storage material, and more particularly to a method for producing a linear or sheet-shaped hydrogen storage material and a hydrogen storage material.
[0002]
[Prior art]
In the development of fuel cells for vehicles, methods for directly mounting hydrogen as a fuel include:
(1) High-pressure hydrogen cylinder (2) Two hydrogen storage alloys are promising.
[0003]
Among them, the hydrogen storage alloy has a larger number of hydrogen atoms per unit volume than liquid hydrogen, and the hydrogen storage tank can be made compact.
[0004]
Further, since hydrogen release is an endothermic reaction, safety is high.
[0005]
As a typical hydrogen storage alloy currently in practical use, a LaNi5-based hydrogen storage alloy that exhibits a stable hydrogen absorption / desorption reaction at around room temperature is known, and is widely used as a negative electrode material for Ni-H batteries. I have. The LaNi5-based hydrogen storage alloy is also mounted on a trial fuel cell vehicle.
[0006]
As other hydrogen storage alloys, hydrogen storage alloys such as Mg-based, Ti-Fe-based, and Ti-V-based have been studied.
[0007]
[Problems to be solved by the invention]
The above-mentioned conventional hydrogen storage alloys are roughly classified into the following problems (1) to (5).
[0008]
{Circle around (1)} Although the hydrogen storage alloy is a metal and is compact, despite its compactness, the weight increases, so that the amount of hydrogen storage per weight in LaNi5 is reduced to about 1.3 [wt%]. there were. For this reason, an Mg-based hydrogen storage alloy having a low weight density (light) has been proposed. According to this Mg-based hydrogen storage alloy, 3 to 6 wt% of hydrogen can be stored. However, the Mg-based hydrogen storage alloy has a new problem that a heat source is required because the hydrogen absorption / desorption reaction occurs at a temperature of about 250 [° C.] or more, resulting in poor energy efficiency. .
[0009]
{Circle around (2)} Since LaNi ₅ contains a rare earth element, there is a problem that the raw material cost and the production cost are increased. On the other hand, the Ti—Fe-based hydrogen storage alloy is a hydrogen storage alloy that can be reduced in cost as compared with LaNi _5, and has many prototypes and examples after LaNi ₅ .
[0010]
However, absorption and release properties of hydrogen, such as showing a hysteresis occlusion and release of hydrogen disadvantageously inferior LaNi _5.
[0011]
{Circle around (3)} LaNi ₅ and TiFe-based alloys have low thermal conductivity, and when stored in a large amount in a tank, it takes time to heat and cool the alloy, resulting in a long time to occlude / release hydrogen. was there.
[0012]
{Circle around (4)} When a hydrogen storage alloy stores hydrogen, its lattice constant increases and the crystal size increases. Most hydrogen-absorbing alloys are brittle, and as hydrogen is repeatedly absorbed and released, the powder becomes finer, the intermolecular force between powders (van der Waals force) increases, and the internal pressure of the tank storing the alloy increases. There was a problem that would.
[0013]
{Circle around (5)} As described above, Mg-based alloys have a large hydrogen storage capacity per unit weight. Particularly, Mg alone shows the highest hydrogen storage capacity of 6 [wt%], but is heated to 300 [° C.] or more. Otherwise, there was no hydrogen storage / release reaction.
[0014]
By the way, a multilayer thin film in which Pd and Mg, which are metals that occlude and release hydrogen at 100 ° C. or less, are alternately stacked in the order of submicron or less. Has been found to be occluded and has attracted attention.
[0015]
Although the details of the hydrogen absorption and release phenomena by the Pd / Mg multilayer thin film are unknown, it is described in principle as a cooperative phenomenon of Pd and Mg.
[0016]
In other words, Pd that has absorbed hydrogen has an increased lattice constant and expands in the plane direction. It is considered that the very thin interface of the Mg layer in contact with this also increases the lattice constant and absorbs hydrogen. On the other hand, when hydrogen is released, it is considered that hydrogen is first released from Pd, so that it contracts in the plane direction, compressive stress is applied to Mg, and hydrogen is released.
[0017]
By the way, Pd for forming the Pd / Mg multilayer thin film is a noble metal which is at least as expensive as Pt. As a method for manufacturing a Pd / Mg multilayer thin film, a PVD method is used. Therefore, there has been a problem in both mass productivity and manufacturing cost.
[0018]
Accordingly, an object of the present invention is to provide a method of manufacturing a hydrogen storage material which has a large amount of hydrogen storage at a low temperature, is low in cost, and is excellent in mass productivity, and a hydrogen storage material.
[0019]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a method for producing a hydrogen storage material includes a laminating step of laminating either one of Mg or an Mg alloy and one of Nb or an Nb-V alloy to form a laminate. A machining process of forming the body into a thin line or sheet shape, and performing machining to reduce the average thickness of the Mg layer formed of the Mg or Mg alloy to 1 [μm] or less; A heat treatment step of subjecting the laminated body to a heat treatment for rearranging the crystal orientation of the Mg layer.
[0020]
In this case, in the laminating process, either one of Mg and the Mg alloy and one of Nb or the Nb-V alloy may be laminated in a sheet state or a pipe state.
[0021]
Further, the machining may include at least one of extrusion, wire drawing, and rolling.
[0022]
Further, in the heat treatment process, the heat treatment may be performed at a temperature of 500 ° C. or more and 800 ° C. or less.
[0023]
Furthermore, the ratio R between the thickness TMg of the Mg or Mg alloy layer and the thickness TNb of one of the Nb and Nb-V alloy layers in the laminate may satisfy the following equation. Good.
[0024]
2.7 ≦ R ≦ 8
Here, R = TMg / TNb
The method may further include a metal coating step of applying a metal coating to the laminate before the machining step, and a coating removing step of chemically or mechanically removing the metal coating after the heat treatment step.
[0025]
Further, any of Cu, Cu alloy, Al and Al alloy may be used as the metal coating.
[0026]
In addition, the hydrogen storage material includes a Mg layer made of Mg or an Mg alloy, and an Nb layer made of Nb or an Nb-V alloy, wherein the Mg layer and the Nb layer have a multilayer structure. It is characterized in that the average thickness of the Mg layer is 1 [μm] or less.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a preferred embodiment of the present invention will be described.
[1] Principle of Embodiment Prior to detailed description of the embodiment, the principle of the embodiment will be described.
[0028]
In the present embodiment, a Mg sheet or Mg alloy sheet having a high hydrogen storage amount at a temperature of 250 to 300 [° C.] or higher, and Nb or Nb absorbing hydrogen at a temperature of 100 [° C.] or lower but having a low hydrogen storage amount. The hydrogen storage capacity is improved by combining the Nb-V alloy sheets to form a multilayer structure, thinning the wire, and setting the average thickness of the Mg layer made of Mg or Mg alloy to 1 [μm] or less.
[0029]
In this case, the reason why the average thickness of the Mg layer is 1 [μm] or less is that the cooperation between the Mg layer and the Nb layer composed of the Nb or Nb-V alloy layer in the storage / release of hydrogen is as follows. This is because it does not occur unless the thickness of the Mg layer is on the order of submicron or less.
[0030]
Further, Mg has a weight density of 1.74 [g / cc] and an amount capable of actually occluding / releasing hydrogen is 6 [wt%]. On the other hand, the Nb0.9V0.1 alloy, which is an Nb-V alloy, has a weight density of 8.3 [g / cc] and an amount capable of actually storing / releasing hydrogen is 1.2 [wt%]. Therefore, when the ratio of the Nb-V alloy having a low hydrogen storage amount per unit weight increases, the hydrogen storage amount per unit weight in the entire composite material also decreases.
[0031]
Here, assuming that the hydrogen storage capacity of the Mg / Nb-V composite material (composite) is satisfied by the combined rule of the hydrogen storage capacities of the individual hydrogen storage materials, the final hydrogen storage capacity is 3 [wt]. %], The thickness ratio between the Mg layer and the Nb layer needs to be about 2.6 or more. On the other hand, considering that Mg causes occlusion / release of hydrogen at a low temperature due to the influence of Nb or Nb-V alloy that occludes / releases hydrogen at room temperature, the influence of the Nb layer on the Mg layer extends to the entire Mg layer. Therefore, the ratio of the thickness of the Mg layer to the thickness of the Nb layer must not be too large.
[0032]
As a guide, when comparing the thermal expansion coefficients of Mg and Nb, the thermal expansion coefficient of Mg at 20 [° C.] = 24.8 × 10 −6 / K, whereas the thermal expansion coefficient of Nb = 7.1 × 10-6, which means that Mg is about three times easier to expand.
[0033]
Therefore, considering the thermal stress strain in the metal composites having different coefficients of thermal expansion, the ratio of the thickness TMg of the Mg layer to the thickness TNb of the Nb layer is as follows.
TMg: TNb = 1: 8
In this case, the stress strain at the central portion of the Mg layer becomes negligibly small compared to the strain at the interface between the Mg layer and the Nb layer, and it is considered that the hydrogen storage reaction due to the cooperative phenomenon disappears.
[0034]
Therefore, in the present embodiment, the thickness ratio (TMg / TNb) between the Mg layer and the Nb layer is set to 8 or less.
[0035]
The crystal orientation of Mg particles in the Mg layer after wire drawing and rolling is random due to repeated plastic deformation. By the way, the condition for hydrogen absorption is that the Mg layer has a structure in which the thickness direction of the layer and the c-axis direction of the crystal orientation coincide with each other, and the hexagonal crystal grows in the layer direction). Therefore, after the wire drawing, heat treatment is performed at a temperature of 500 ° C. or more to alleviate the crystal distortion due to the working, and in addition, the temperature (650 ° C.) to 800 ° C. near or above the melting point (660 ° C.). [° C.]), the crystal orientation is rearranged by heat treatment so that the Mg layer has a structure in which the thickness direction of the layer matches the c-axis direction of the crystal orientation.
[2] Method of Manufacturing Hydrogen Storage Wire Next, a method of manufacturing the hydrogen storage wire of the embodiment will be described.
[0036]
FIG. 1 is a diagram showing a process of manufacturing a hydrogen storage material. FIG. 2 is an explanatory diagram of a manufacturing state of the jelly roll.
[0037]
First, a pure Mg sheet 11 having a predetermined thickness and width, an Nb-V alloy sheet 12, and a Mg columnar mandrel 13 having a predetermined diameter are prepared (steps S1, S2, S3). ).
[0038]
Next, the pure Mg sheets 11 are stacked so as to be inside when wound. That is, an Mg / Nb-V structure is adopted.
[0039]
Then, a sheet having a Mg / Nb-V structure overlapped on a cylindrical columnar mandrel 13 made of Mg is wound in a laver winding shape, so that a jelly having a predetermined diameter, which is a cylinder having a (Mg / Nb-V) multilayer structure, is obtained. A roll (laminate) 15 (see FIG. 3) is formed (Step S4).
[0040]
Then, as shown in FIGS. 3 and 4, a jelly roll 15 having a (Mg / Nb-V) multilayer structure is inserted into an Nb-V pipe 16 having predetermined inner and outer diameters (step S5). The Nb-V pipe is inserted into a Cu pipe (metal coating) 17 having a predetermined inner diameter and outer diameter (step S6).
[0041]
Subsequently, while the jelly roll 15 and the Cu pipe 17 in which the Nb-V pipe 16 is inserted are heated to a predetermined temperature, hydrostatic extrusion is performed to a predetermined diameter (step S7).
[0042]
Next, the obtained extruded material is drawn and thinned (step S8), and is made into a hexagonal line having a predetermined opposite side distance in a final step of thinning (step S9).
[0043]
Further, the shape of the obtained hexagonal wire is corrected and cut into hexagonal wires 20 having a predetermined length (step S10). FIG. 5 shows an enlarged sectional view of the hexagonal wire 20.
[0044]
Next, 61 hexagonal wires and a Cu pipe (metal coating) 21 having a predetermined inner diameter capable of accommodating the 61 hexagonal wires 20 are prepared (steps S11 and S12). Here, the number of the hexagonal wires 20 is set to 61 because the hexagonal wires 20 are arranged in a hexagonal column shape, and five layers of hexagonal columns (one, six, twelve, eighteen, twenty-four, for each layer) are used. This is because the number is necessary for forming in the form of the above) and arranging them without gaps. Therefore, in the case of less than five layers or six or more layers, the number is determined according to the number of layers.
[0045]
FIG. 6 is a schematic cross-sectional view of the multi billet.
[0046]
Then, as shown in FIG. 6, 61 hexagonal wires 20 are inserted into the Cu pipe 21 (step S13). In FIG. 6, the number of hexagonal wires is not accurately drawn for simplification of the drawing.
[0047]
Subsequently, the Cu pipe 21 into which the hexagonal wire is inserted is subjected to hydrostatic extrusion so as to have a predetermined diameter while being heated to a predetermined temperature (step S14).
[0048]
Next, the obtained extruded material was drawn to be thinned to a predetermined diameter, specifically, a diameter of 1 [mm] (step S15). In this state, the average thickness of the Mg layer portion is set to 1 [μm] or less.
[0049]
Subsequently, the material after the wire drawing is subjected to a heat treatment in an Ar gas to relax crystal distortion and rearrange the crystal orientation (step S16). Specifically, heat treatment is performed at 650 ° C. for one hour.
[0050]
Next, Cu which is a metal coating is removed with nitric acid (Step S17).
[0051]
Subsequently, the bundle of the washed and dried filaments is heat-treated in a vacuum (Step S18). Specifically, heat treatment is performed at 450 [° C.] for one hour.
[0052]
Then, a hydrogen storage initial activation process is performed to obtain a hydrogen storage material (step S19).
[3] Effects of Embodiment According to the hydrogen storage material according to the manufacturing method of this embodiment, the amount of hydrogen storage per unit weight can be increased as compared with the conventional hydrogen storage alloy, so that the hydrogen storage material can be used once for a vehicle. Range can be extended by hydrogen supply.
[0053]
Further, since the hydrogen storage material of the present embodiment is a composite of a ductile metal, the internal pressure of the container does not increase due to fine powder due to repetition of hydrogen storage and release, which is observed in a conventional hydrogen storage alloy.
[0054]
In addition, since the hydrogen storage material of the present embodiment is constituted by a composite wire of Mg having relatively high thermal conductivity, the followability of temperature control in the container is higher and faster than other alloys. Hydrogen filling becomes possible.
[4] Modification of Embodiment In the above description, the thickness of the Mg layer is set to 1 [μm] or less, that is, on the order of submicron by using a multi-bilette, but the Mg sheet and the Nb- By reducing the thickness of the V-sheet and increasing the diameter of a single billet, it is possible to obtain a submicron-order Mg layer without using a multi-bilette. According to the adoption of this large single billet, the number of processing steps can be reduced, and the processing cost can be significantly reduced.
[0055]
In the above description, the hydrogen storage alloy conventionally used as a powder is made into a wire, but as a modified example, a number of Mg / Nb-V laminated sheets are used instead of a laver-wrapped cylindrical shape in the manufacturing process. It is also possible to form a hydrogen storage sheet formed in a multilayered sheet shape by repeating rolling in a state in which the sheet is formed by alternately stacking the sheets.
[0056]
In the above description, a sheet prepared by preparing a pure Mg sheet and an Nb-V alloy sheet and superimposing the Mg / Ti / Fe-Ni structure on an Mg cylindrical mandrel having a predetermined diameter is prepared. A jelly roll (laminated body) having a predetermined diameter, which is a cylindrical column having a (Mg / Nb-V) multilayer structure, was formed by winding in a laver winding shape. However, an Nb sheet was used instead of the Fe-Ni alloy. It is also possible to configure so as to form a jelly roll (laminate).
[0057]
In the above description, the case where the Cu pipe is used as the metal coating has been described. However, it is also possible to use a Cu alloy pipe, an Al pipe, or an Al alloy pipe.
[0058]
In the above description, the case of a fuel cell for a vehicle has been described as an example. However, the invention can be applied to a heat pump without refrigerant by utilizing the fact that the hydrogen storage / release reaction is an exothermic / endothermic reaction. In this case, higher heat conductivity can be expected to contribute to the responsiveness and energy efficiency of the heat pump as compared to a heat pump using a conventional hydrogen storage alloy.
[0059]
【Example】
Next, specific examples will be described.
[0060]
When a pure Mg sheet is formed by winding a pure Mg sheet having a thickness of 0.2 [mm] and a width of 100 [mm] and an Nb-V alloy sheet having a thickness of 0.05 [mm] and a width of 100 [mm]. And a pure Mg sheet and an Nb-V sheet in this order. That is, an Mg / Nb-V structure is adopted.
[0061]
Then, a (Mg / Nb-V) multi-layered cylinder is formed by winding a sheet laminated on the Mg / Nb-V structure on a Mg-made cylindrical mandrel having a diameter of 7 [mm] in a laver winding shape. I do.
[0062]
Then, the winding is performed until the outer diameter of the (Mg / Nb-V) multilayered cylinder becomes 22.7 [mm].
[0063]
Subsequently, a (Mg / Ti / Fe-Ni) multilayer cylinder is inserted into an Nb-V alloy pipe having an inner diameter of 23 [mm] and an outer diameter of 24 [mm]. Further, this Nb-V alloy pipe was inserted into a Cu pipe having an inner diameter of 24.2 [mm] and an outer diameter of 28 [mm], and a Cu plug was attached to one end of the Cu pipe and an Fe plug was attached to the other end to form a single billet. .
[0064]
Subsequently, while the single billet was heated to 300 ° C., it was subjected to hydrostatic extrusion to a diameter of 10 mm to obtain a single billet extruded material.
[0065]
Next, the obtained single billet extruded material is drawn into a thin line by wire drawing. In the final step of thinning, the hexagonal wire has an opposite side distance of 2.6 [mm], and after being straightened straight, has a length of 100 [mm]. Hexagonal wire.
[0066]
Next, 61 cut hexagonal wires are inserted into a Cu pipe having an inner diameter of 23 [mm] and an outer diameter of 28 [mm], and a Cu plug is inserted into one end (front end) of the Cu pipe, and Fe is inserted into the other end (rear end). A plug was attached to form a multi billet.
[0067]
Subsequently, the multi billet was extruded with a hydrostatic pressure to a diameter of 10 mm while the multi billet was heated to 300 ° C. to obtain a multi billet extruded material.
[0068]
Next, the obtained multi-billet extruded material was drawn and thinned to a diameter of 1 [mm].
[0069]
Further, the extruded multi-billet material after the thinning was heat-treated at 650 [° C.] in Ar gas for 1 hour to relax the crystal distortion and rearrange the crystal orientation.
[0070]
Thereafter, the extruded multi-billette material after the thinning was immersed in a nitric acid solution having a predetermined concentration to dissolve and remove Cu, thereby forming a bundle of 61 filaments, washed with water, and dried in vacuum.
[0071]
The dried bundle of filaments having a diameter of 75 [μm] was heat-treated in Ar gas at 600 [° C] for 1 hour.
[0072]
At this time, the calculated thickness of the Mg layer was 0.625 [μm], and the thickness of the Nb-V layer was 0.156 [μm].
[0073]
Further, as an initial hydrogen activation treatment, 1000 [mg] filament was put in a stainless steel high pressure vessel having an internal volume of 1000 [cc], and the following processes (1) to (4) were repeated three times.
[0074]
(1) evacuation of the stainless steel high-pressure vessel (2) pressurization of hydrogen gas to 2 [MPa] (3) holding the stainless steel high-pressure vessel heated to 100 [° C] for 3 hours [4] 20 [° C] After the above-mentioned initial activation treatment in which the pressure of the stainless steel high-pressure vessel is set to the atmospheric pressure, the hydrogen gas is reduced to 0.5 [MPa] at room temperature while keeping the bundle of filaments in the stainless steel high-pressure vessel. In a pressurized state, the vessel was heated to 140 ° C. and maintained for 1 hour, then returned to room temperature and depressurized to atmospheric pressure.
[0075]
In this state, the weight of the filament taken out of the container was measured. As a result, a weight increase of 1025 [mg] was confirmed.
[0076]
From the experimental results, it was confirmed that the filament using the hydrogen storage wire of the present example stored 2.5 [wt%] of hydrogen.
[0077]
This value is about twice or more higher than the hydrogen storage amount (about 1 [wt%]) of the Nb-V alloy alone or 1.3 [wt%] of LaNi ₅ which is practically used. Met.
[0078]
【The invention's effect】
According to the present invention, the hydrogen storage amount per unit weight can be increased as compared with the conventional hydrogen storage alloy, so that the cruising distance can be extended by one hydrogen supply for a vehicle.
[0079]
In addition, since the metal composite is ductile, the internal pressure of the container does not increase due to fine powder due to repetition of hydrogen storage and release, which is observed in a conventional hydrogen storage alloy.
[0080]
In addition, since it is constituted by a composite wire of Mg, which is relatively high in thermal conductivity, the followability of temperature control in the container is higher than that of other alloys, and faster hydrogen filling is possible.
[Brief description of the drawings]
FIG. 1 is a manufacturing process diagram of a hydrogen storage material.
FIG. 2 is an explanatory diagram of a manufacturing state of a jelly roll (laminate).
FIG. 3 is a schematic cross-sectional view of a single billet.
FIG. 4 is a perspective view illustrating the structure of a single billet.
FIG. 5 is an enlarged schematic sectional view of a hexagonal wire.
FIG. 6 is a schematic sectional view of a multi billet.
[Explanation of symbols]
11 Pure Mg sheet 12 Nb-V alloy sheet 13 Mg mandrel 15 Jelly roll (Jerry roll)
16 Nb-V pipe 17 Cu pipe (metal coating)
20 hexagonal wire 21 Cu pipe (metal coating)

Claims (8)

A laminating process of laminating any one of Mg or Mg alloy and one of Nb or Nb-V alloy to form a laminate;
A machining process of forming the laminate into a thin wire or sheet shape, and performing machining to reduce the average thickness of the Mg layer formed of the Mg or Mg alloy to 1 μm or less;
Performing a heat treatment for rearranging the crystal orientation of the Mg layer on the laminated body after the mechanical processing. The method for producing a hydrogen storage material according to claim 1,
In the laminating process, any one of Mg and Mg alloy and one of Nb and Nb-V alloy are laminated in a sheet state or a pipe state. The method for producing a hydrogen storage material according to claim 1 or 2,
The method for producing a hydrogen storage material, wherein the machining includes at least one of extrusion, drawing, and rolling. The method for producing a hydrogen storage material according to any one of claims 1 to 3,
The method for producing a hydrogen storage material, wherein the heat treatment is performed at a temperature of 500 ° C. or more and 800 ° C. or less. The method for producing a hydrogen storage material according to any one of claims 1 to 4,
The ratio R of the thickness TMg of the Mg or Mg alloy layer to the thickness TNb of one of the Nb and Nb-V alloys in the laminate satisfies the following equation: The method of manufacturing the material.
2.7 ≦ R ≦ 8
Here, R = TMg / TNb The method for producing a hydrogen storage material according to any one of claims 1 to 5,
A metal coating step of performing metal coating on the laminate before the machining step;
A method of chemically or mechanically removing the metal coating after the heat treatment step. The method for producing a hydrogen storage material according to claim 6,
A method for producing a hydrogen storage material, wherein any one of Cu, Cu alloy, Al and Al alloy is used as the metal film. A Mg layer composed of Mg or a Mg alloy;
An Nb layer composed of Nb or an Nb-V alloy,
The Mg layer and the Nb layer have a multilayer structure,
The hydrogen storage material, wherein the average thickness of each Mg layer is 1 [μm] or less.

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