Method for producing magnesium hydride

Abstract

To provide a method for producing magnesium hydride capable of hydrogenation even under a hydrogen gas atmosphere of 5 atmospheres or less.SOLUTION: There is provided a method for producing magnesium hydride which comprises: a pulverization step of pulverizing magnesium; and a hydrogenation step of subjecting the pulverized magnesium to hydrogenation treatment by heating the magnesium to a temperature of 140°C or more and less than the decomposition temperature of magnesium hydride under a hydrogen gas pressure of 500 Pa or more and 5 atmospheres or less, wherein the amount of a fatty acid added in the pulverization step is 5 mass% or more in the total mass of magnesium and the fatty acid and the pulverized magnesium is not allowed to contact with oxygen until the hydrogenation step has been completed.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for producing magnesium hydride. [Background technology]

[0002] In recent years, hydrogen has been attracting attention as an energy source, and one method for storing this hydrogen is to use magnesium hydride.

[0003] Patent Document 1 discloses a method for producing a magnesium-based hydride from a raw material powder, which is mainly composed of magnesium, by holding the raw material powder in a hydrogen gas atmosphere sealed in a sealed container, maintaining the pressure of the hydrogen gas atmosphere in the sealed container at a predetermined pressure, raising the temperature of the hydrogen gas atmosphere in the sealed container from room temperature, and maintaining the temperature of the hydrogen gas atmosphere in the sealed container at a temperature higher than the temperature corresponding to the predetermined pressure on the equilibrium curve for the reaction in which elemental magnesium and hydrogen molecules combine to produce magnesium hydride, and the reverse reaction, and at a temperature within 100°C of the temperature corresponding to the predetermined pressure on the equilibrium curve, for a predetermined first period, thereby removing the coating on the raw material powder surface, and then maintaining the temperature of the hydrogen gas atmosphere in the sealed container at a temperature lower than the temperature corresponding to the predetermined pressure on the equilibrium curve and within 100°C of the temperature corresponding to the predetermined pressure on the equilibrium curve, without returning it to room temperature, for a predetermined second period, thereby producing a magnesium-based hydride from the raw material powder.

[0004] In other words, the first feature of Patent Document 1 is that the temperature is maintained for a predetermined first period at a temperature higher than the temperature corresponding to a predetermined pressure on the equilibrium curve for the reaction in which elemental magnesium and hydrogen molecules combine to produce magnesium hydride and the reverse reaction, and the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve is within 100°C.

[0005] According to Patent Document 1, this first feature promotes the thermal decomposition of magnesium hydroxide (Mg(OH)2) formed on the surface of magnesium (Mg), and the reduction of magnesium oxide (MgO) formed by this thermal decomposition with hydrogen molecules also progresses, thereby removing the coating on the magnesium surface and enabling it to quickly react with hydrogen (H2).

[0006] Furthermore, Patent Document 1 has a second feature in that the temperature of the hydrogen gas atmosphere is maintained for a predetermined second period at a temperature lower than the temperature corresponding to the predetermined pressure on the equilibrium curve, without being returned to room temperature, and within 100°C of the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve.

[0007] Due to this second feature, Patent Document 1 claims that it is possible to obtain high-purity magnesium hydride (MgH2) with less input energy than conventional techniques that require activation treatment in which hydrogen is repeatedly absorbed and released by repeated heating and cooling. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-044832 Summary of the Invention [Problem to be solved by the invention]

[0009] Incidentally, in Patent Document 1, the examples show that the hydrogen gas pressure during hydrogenation treatment is 10 atmospheres (approximately 1 MPa) or more.

[0010] Patent Document 1 also explains that in order to produce magnesium hydride within a realistic time range, the pressure should be at least 6 atmospheres or more.

[0011] In this way, when the pressure of hydrogen gas during hydrogenation treatment is high, the container structure for causing the reaction must be pressure-resistant, and therefore the container must be thick, which results in poor heat conduction for heating the inside of the container.

[0012] The present invention has been made in view of the above circumstances, and has as its object to provide a method for producing magnesium hydride that can perform hydrogenation even in a hydrogen gas atmosphere of 5 atmospheres or less, for example. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention is realized by the following configuration. (1) The method for producing magnesium hydride of the present invention comprises a crushing step of crushing magnesium by adding a fatty acid, and a hydrogenation step of hydrogenating the crushed magnesium by heating it to a temperature of 140°C or higher, lower than the decomposition temperature of magnesium hydride, under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower, wherein the amount of the fatty acid added in the crushing step is 5 mass% or higher of the total mass of the magnesium and the fatty acid, and the crushed magnesium is not exposed to oxygen until the end of the hydrogenation step.

[0014] (2) In the above configuration (1), the hydrogenation step includes a heat treatment step of heating the crushed magnesium while evacuating the atmosphere before the hydrogenation treatment.

[0015] (3) In the above configuration (1) or (2), the amount of the added magnesium is 15% by mass or less of the total mass of the magnesium and the fatty acid.

[0016] (4) In any one of the above (1) to (3), the pulverization and hydrogenation step, which is a series of steps from the pulverization step to the hydrogenation step, is carried out multiple times. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a method for producing magnesium hydride that allows hydrogenation even in a hydrogen gas atmosphere of 5 atmospheres or less, for example. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view of a pulverizer used in a pulverization step of a first embodiment according to the present invention. FIG. [Figure 2] 1 is a perspective view of a crushing unit of a crusher according to a first embodiment of the present invention. FIG. [Figure 3] FIG. 2 is an exploded perspective view of the crushing unit of the first embodiment according to the present invention. [Figure 4] FIG. 1 is a diagram showing the configuration of a device for a pulverization step according to a first embodiment of the present invention. [Figure 5] 3 is a flowchart showing the procedure of a pulverization step in the first embodiment according to the present invention. [Figure 6] 1 is a side view showing a hydrogenation furnace according to a first embodiment of the present invention. [Figure 7] 1 is a flowchart showing the procedure of a hydrogenation step according to a first embodiment of the present invention. [Figure 8] 3 is a graph showing the effect of adding a fatty acid in the grinding step of the first embodiment according to the present invention. [Figure 9] 1 is a graph showing the decomposition and production boundary line of magnesium hydride obtained by thermodynamic calculation. [Figure 10] FIG. 10 is a perspective view of a pulverizer used in a pulverization step of a third embodiment according to the present invention. [Figure 11] FIG. 10 is a perspective view showing a state in which the hood of a crusher according to a third embodiment of the present invention is open. [Figure 12] FIG. 10 is a perspective view of a grinding container according to a third embodiment of the present invention. [Figure 13] FIG. 10 is an exploded perspective view of a grinding container according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the accompanying drawings. It should be noted that the same elements are denoted by the same reference numerals throughout the description of the embodiments.

[0020] (First embodiment) The method for producing magnesium hydride according to the first embodiment of the present invention includes a crushing step of crushing magnesium by adding a fatty acid, and a hydrogenation step of hydrogenating the crushed magnesium by heating it in a hydrogen gas atmosphere to a temperature at which magnesium hydride can be produced, i.e., a temperature below the decomposition temperature of magnesium hydride.

[0021] Therefore, the equipment used is a pulverizer 1 (see Figure 1) for carrying out the pulverization process and a hydrogenation furnace 8 (see Figure 6) for carrying out the hydrogenation process. Therefore, the pulverizer 1 will be explained first, followed by the pulverization process, then the hydrogenation furnace 8, followed by the hydrogenation process.

[0022] (Crusher) FIG. 1 is a perspective view of a crusher 1 used in a crushing process of a first embodiment according to the present invention, FIG. 2 is a perspective view of a crushing section 3 of the crusher 1 of the first embodiment according to the present invention, and FIG. 3 is an exploded perspective view of the crushing section 3 of the first embodiment according to the present invention.

[0023] As shown in Figure 1, the crusher 1 used in the first embodiment comprises a crusher main body 2 which incorporates a motor for rotating the stirring and crushing teeth 41 of the crushing section 3 and is equipped with a push button 21 for turning the drive power on and off, and a crushing section 3 which is removably attached to the crusher main body 2 and which contains the material to be crushed (not shown).

[0024] Figure 2 is an oblique view showing only the crushing unit 3, with the crushing unit 3 removed from the crusher main body 2. When the crushing unit 3 is attached to the crusher main body 2, the rotating shaft of the agitating and crushing teeth 41 of the crushing unit 3 engages with the rotating shaft of the motor provided in the crusher main body 2. When the push button 21 (the push button 21 marked "ON" in Figure 1) that turns on the drive power is pressed, the motor rotates, which rotates the agitating and crushing teeth 41 of the crushing unit 3 and crushes the material to be crushed (not shown) contained in the crushing unit 3.

[0025] As shown in Figure 3, the crushing unit 3 comprises a crushing unit main body 4 to which stirring and crushing teeth 41 are rotatably attached, and a lid portion 5 which is removably attached so as to cover the upper side of the crushing unit main body 4 and prevents the material to be crushed (not shown) from scattering.

[0026] Specifically, the lid part 5 can be attached to the pulverizer main body 4 by screwing together the threaded groove 42 formed on the inside of the pulverizer main body 4 and the threaded thread 51 formed on the outside of the lower part of the lid part 5.

[0027] The grinder 1 used in the first embodiment is a household mill that is also used in ordinary households to powder tea leaves, coffee beans, etc., and in this embodiment, a grinder manufactured by Zojirushi Corporation is used as the grinder 1.

[0028] The crushing process of the first embodiment is carried out using such a crusher 1, but if the object to be crushed is magnesium, static electricity or the like can become an ignition source, and there is a risk that the magnesium that has been crushed into fine powder will cause a dust explosion.

[0029] For this reason, when carrying out the crushing process, the crusher 1 is placed in an airtight booth to prevent the intrusion of air, and measures are taken to create an argon gas atmosphere inside the airtight booth, and the crushing process is carried out by this.Next, we will explain the crushing process, including the details of these measures.

[0030] (Crushing process) FIG. 4 is a diagram showing the configuration of a device for a pulverization step according to the first embodiment of the present invention. As shown in FIG. 4, the pulverization step is carried out by placing the pulverizer 1 described above in a commercially available airtight booth called a vacuum desiccator 6.

[0031] This vacuum desiccator 6 comprises a square-shaped container body 61 with an open top, a square-shaped lid portion 62 that closes the opening at the top, and a gasket that is placed on the edge of the opening side of the container body 61 and ensures airtightness between the container body 61 and the lid portion 62, and is structured so that the container body 61 and the lid portion 62 can be detachably fixed in place with multiple snap locks 63 provided around the circumference.

[0032] The lid 62 also includes a pressure gauge 621 that displays the pressure inside the vacuum desiccator 6, and two intake and exhaust ports 622 and 623 that can be opened and closed by needle valves.

[0033] The intake / exhaust port 622 is connected to a gas supply line from a high-pressure gas cylinder B1 of argon gas (Ar) decompressed to 0.2 MPa by a pressure reducing valve (not shown), and the intake / exhaust port 623 is connected to a T-shaped pipe (also called a three-way pipe), one side of which is connected to a pipe connected to a vacuum pump P1, and the other side of which is equipped with a needle valve N.

[0034] Although not visible in FIG. 4, the vacuum desiccator 6 is provided with an internal power supply port at a position on the rear side of the crusher 1 of the container body 61 for connecting a 100V power supply.

[0035] Although not shown in the figure, in order to ensure airtightness, the gap with the container body 61 is filled with putty, a switch with a timer function is connected to the electrical wiring of the internal power supply port that is pulled out to the outside, and the electrical wiring of the switch is connected to the power supply port of the 100V power supply inside the room.

[0036] Therefore, by pressing the push button 21 (the push button 21 marked "ON" in Figure 1) that turns on the driving power supply of the crusher main body 2, setting the crusher 1 inside the vacuum desiccator 6 in the ON state, and connecting the outlet of the crusher 1 to the internal power port of the vacuum desiccator 6, the operation and stopping of the crusher 1 can be controlled by a switch with a timer function located outside the vacuum desiccator 6.

[0037] Furthermore, in order to ensure that the grinding process is carried out without entraining air, a battery-powered oxygen concentration meter 7 is installed inside the vacuum desiccator 6.

[0038] Next, the specific procedure of the pulverization step will be described. FIG. 5 is a flowchart showing the procedure of the pulverization step in the first embodiment according to the present invention. Before starting the work, the grinder body 2 of the grinder 1 and the oxygen concentration meter 7 are set inside the vacuum desiccator 6, and the lid 62 of the vacuum desiccator 6 is removed from the container body 61.

[0039] (Step 1) First, the material to be crushed is placed in the crushing section 3 of the crusher 1 (S1). In order to prevent air from entering the crushing section 3 during this placement process, this process is carried out in an airtight work box, commonly sold as a glove box, under an argon gas atmosphere.

[0040] During this grinding process, fatty acids are added to the magnesium to be ground, so a mixture of magnesium and fatty acids is placed inside the grinding section 3. The specific amount of fatty acid to be added (quantity to be added) will be explained later.

[0041] (Step 2) Next, the crushing unit 3 containing the material to be crushed is attached to the crusher main body 2 installed in the vacuum desiccator 6 (S2). After installing the crushing unit 3, do not forget to press the push button 21 (the push button 21 marked "ON" in Figure 1) that turns on the driving power supply for the crusher main body 2, and turn it on. However, unless you start the switch with the timer function described above, no power will be supplied, and the crusher 1 will not operate at this point.

[0042] (Step 3) Next, the lid 62 of the vacuum desiccator 6 is fixed to the container body 61 with a snap lock 63, and with the intake / exhaust port 622 closed, the intake / exhaust port 623 open, and the needle valve N closed, the vacuum pump P1 is driven to draw a vacuum inside the vacuum desiccator 6 (S3).

[0043] The crushing section 3 has a relatively airtight structure to prevent leakage of fine dust particles and the like, and when there is no pressure difference between the inside and outside, it can prevent the ingestion of air from the outside to a certain extent for a while. However, when the vacuum is drawn and the external pressure is reduced, the argon gas inside the crushing section 3 is also sucked out little by little in accordance with the pressure difference, and a vacuum state is created in this step.

[0044] As a guideline for vacuuming, the needle indicating the pressure on the pressure gauge 621 should have moved to the vacuum limit, and as the pressure reduction progresses, the oxygen concentration displayed on the oxygen concentration meter 7 also approaches 0%, so the guideline was set to the time when the oxygen concentration displayed on the oxygen concentration meter 7 reached 0%.

[0045] (Step 4) Once sufficient evacuation has been achieved, the intake / exhaust port 623 is closed, and then the intake / exhaust port 622 is opened, and argon gas is filled into the vacuum desiccator 6 (S4). Then, when this filling operation starts, the vacuum pump P1 is stopped and the needle valve N is left open.

[0046] When supplying argon gas, the opening of the needle valve of the intake / exhaust port 622 may be adjusted so that an appropriate amount of argon gas is supplied.

[0047] Furthermore, when filling with argon gas, the pressure inside the vacuum desiccator 6 becomes higher than that inside the crushing section 3, which has already been placed in a vacuum state due to the previous evacuation, and this pressure difference causes argon gas to fill the inside of the crushing section 3 as well.

[0048] Then, when the pressure inside the vacuum desiccator 6 rises to the point where the pressure gauge 621 of the vacuum desiccator 6 indicates a slightly positive pressure side compared to atmospheric pressure, the needle valve of the intake / exhaust port 623 is opened slightly, allowing for weak positive pressure control with argon gas blowing in, and the filling of the vacuum desiccator 6 with argon gas is completed.

[0049] In this way, by maintaining a weak positive pressure state with the argon gas streamer, it is possible to reliably prevent air from being drawn into the vacuum desiccator 6 during pulverization.

[0050] (Step 5) Once the filling of argon gas has been completed and there is no risk of air being drawn into the pulverizer 1, the pulverizer 1 is put into operation (S5) to pulverize the object to be pulverized.

[0051] Specifically, the operation of starting the switch having the timer function described above, operating the grinder 1 for a predetermined time, and then stopping the operation of the grinder 1 for a predetermined time was repeated until the total operating time of the grinder 1 reached approximately 12 hours. In other words, crushing is performed until the actual operating time of the crusher 1 reaches 12 hours, not including the time when the crusher 1 is stopped, and then crushing by the crusher 1 is terminated.

[0052] The reason why the operation of the grinder 1 is intermittent, with repeated starts and stops, is that, as mentioned earlier, the grinder 1 in the first embodiment is a commercially available mill used in ordinary households, etc., and would break down if operated continuously for a long period of time.However, if it were an industrial mill that is allowed to operate for a long period of time, there would be no need to take any downtime.

[0053] (Step 6) After the object to be pulverized has been pulverized, the pulverized material (pulverized powder) is removed (S6). Immediately after the pulverizer 1 is stopped, the temperature of the pulverized powder is slightly elevated.

[0054] Therefore, while preventing the inclusion of air in the argon gas stream, the temperature of the pulverized powder is waited to drop, and then the pulverizing section 3 of the pulverizer 1 is quickly removed from the vacuum desiccator 6 and transferred to the same airtight work box used to store the material to be pulverized in the pulverizing section 3. Then, under an argon gas atmosphere, the pulverized powder is transferred to an airtight bottle that can prevent the inclusion of air, completing the pulverization process.

[0055] Furthermore, since the process of transferring the crushed powder into the airtight bottle is carried out under an argon gas atmosphere, the bottle is filled with argon gas. By storing it in this state, it is possible to prevent the crushed magnesium from coming into contact with the atmosphere (mainly oxygen) and causing oxidation and deterioration until the next step, the hydrogenation step, is carried out, thereby suppressing a decrease in hydrogenation efficiency.

[0056] On the other hand, here, the airtight bottle is sealed with argon gas to prevent the crushed magnesium from deteriorating, but it has been confirmed that as long as it is stored at room temperature for at least one week, the crushed magnesium will not deteriorate to the extent that it affects hydrogenation, even when stored in a nitrogen atmosphere from a commercially available nitrogen generator that generates nitrogen with 99.9% purity from air.

[0057] Therefore, after the crushed magnesium has cooled to room temperature, it may be stored in a container or booth filled with nitrogen from a nitrogen generator until the hydrogenation process is carried out, and in this case too, it can be prevented from coming into contact with oxygen and causing oxidation and deterioration.

[0058] Next, the hydrogenation step will be described, but first, the hydrogenation furnace 8 for carrying out the hydrogenation step will be described.

[0059] (hydrogenation furnace) FIG. 6 is a side view showing the hydrogenation furnace 8 of the first embodiment according to the present invention. For ease of understanding, FIG. 6 illustrates the heating furnace 81 in a cross section. Also, for ease of understanding, FIG. 6 only shows the mounting position of clamp 824 with a dotted line, and what is actually used is a commercially available clamp that clamps NW standard flanges.

[0060] As shown in Figure 6, the hydrogenation furnace 8 comprises a reaction vessel 82 in which the reaction to hydrogenate the crushed magnesium takes place, a heating furnace 81 that can detachably receive the reaction vessel 82 and heat the temperature inside the reaction vessel 82 to a temperature suitable for hydrogenation, and a pressure adjustment tank 83 that is controlled to maintain the pressure of hydrogen gas at a predetermined pressure and is connected to the reaction vessel 82 via a flexible gas piping FGP so that the hydrogen gas can be supplied to the reaction vessel 82.

[0061] The reaction vessel 82 has a flange portion 8211 that is supported by the heating furnace 81 on its outer periphery at a midpoint in the vertical direction, and is equipped with a reaction vessel main body 821 that is open at the top so that it can contain crushed magnesium, a lid portion 822 for closing the top opening, an O-ring 823 that is placed on the edge of the opening side of the reaction vessel main body 821 and is sandwiched between the reaction vessel main body 821 and the lid portion 822 to ensure airtightness, and a clamp 824 that secures the O-ring 823 by pressing it with the reaction vessel main body 821 and the lid portion 822.

[0062] The cover 822 also has an intake / exhaust port 8221 to which a detachable needle valve N1 is attached to a flexible gas pipe FGP, and which can be opened and closed by operating the needle valve N1.

[0063] The heating furnace 81 comprises an insulated housing 811 having an opening for receiving the reaction vessel body 821, a heater section 812 provided inside the insulated housing 811, and a temperature regulator (not shown) that controls the heater section 812 to maintain a set temperature, and the opening for receiving the reaction vessel body 821 is set to have an inner diameter slightly smaller than the outer diameter of the flange section 8211 so as to be able to support the flange section 8211 of the reaction vessel body 821.

[0064] However, the opening for receiving the reaction vessel main body 821 is set to have an inner diameter larger than the outer diameter of the body of the reaction vessel main body 821 so that the reaction vessel main body 821 can be received.

[0065] The temperature regulator includes a temperature measurement unit (e.g., a thermocouple) that measures the temperature of the heater unit 812, and a power control unit that controls the power supplied to the heater unit 812 based on the results of the temperature measurement to maintain the set temperature.

[0066] The pressure adjustment tank 83 is a stainless steel tank with an airtight structure that traps gas, and is equipped with: an attachment port PT1 for attaching a digital pressure gauge DP for measuring the pressure inside the tank; a hydrogen gas receiving port PT2 for receiving hydrogen gas and having an on-off valve OCB2 attached; an argon gas receiving port PT3 for receiving argon gas and having an on-off valve OCB3 attached; a gas supply port PT4 for connecting a needle valve N2 and a flexible gas piping FGP for sending gas inside the tank to the reaction vessel 82; and an exhaust port PT5 for connecting a vacuum pump P2 used to replace the gas inside the tank and having an on-off valve OCB5 attached.

[0067] The hydrogen gas is supplied to the pressure adjustment tank 83 in such a manner that the hydrogen gas is reduced in pressure to 0.2 to 0.3 MPa, which is the operating pressure of the mass flow controller, by the pressure reducing valve of the high-pressure hydrogen gas cylinder B2, and then supplied via the hydrogen gas mass flow controller MFC-H, which is connected to the hydrogen gas receiving port PT2 via piping.

[0068] In addition, argon gas is supplied to the pressure adjustment tank 83 in such a manner that the argon gas is reduced in pressure to 0.2 to 0.3 MPa, which is the operating pressure of the mass flow controller, by the pressure reducing valve of the high-pressure argon gas cylinder B3, and then supplied via the argon gas mass flow controller MFC-A, which is connected to the argon gas receiving port PT3 via piping.

[0069] To control the gas supply, a sequencer PLC, which is a controller capable of building control programs, is used. In FIG. 6, the dashed lines connecting the sequencer PLC with the digital pressure gauge DP, the hydrogen gas mass flow controller MFC-H, and the argon gas mass flow controller MFC-A indicate that they are connected by signal lines that transmit input and output signals.

[0070] The control program for the sequencer PLC has two modes: a direct input mode in which the mass flow controller to be operated and the flow rate are specified on the LCD screen of the sequencer PLC, and the specified mass flow controller (hydrogen gas mass flow controller MFC-H, argon gas mass flow controller MFC-A) is operated to supply that flow rate; and a pressure control mode in which the mass flow controller to be operated and the upper and lower pressure limits are specified on the LCD screen of the sequencer PLC, and when the output value of the digital pressure gauge DP falls below the lower pressure limit, the specified mass flow controller is operated to supply gas at the preset flow rate.

[0071] In the pressure control mode, when the output value of the digital pressure gauge DP reaches the upper pressure limit due to the supply of gas, the operation of the mass flow controller is stopped and the supply of gas is stopped.

[0072] (Hydrogenation process) Next, the specific procedure of the hydrogenation step will be described. FIG. 7 is a flowchart showing the procedure of the hydrogenation step according to the first embodiment of the present invention. Prior to explaining the procedure of the hydrogenation process, it is assumed that argon gas at atmospheric pressure is filled from the pressure adjustment tank 83 to the reaction vessel 82, and that the opening and closing valves OCB2, OCB3, and OCB5 attached to the hydrogen gas receiving port PT2, the argon gas receiving port PT3, and the exhaust port PT5 are in a closed state. Also, the intake / exhaust port 8221 of the cover 822 and the needle valves N1 and N2 attached to the gas supply port PT4 are also in a closed state.

[0073] (Step 11) First, the reaction vessel 82 is removed from the hydrogenation furnace 8 (S11). Specifically, the needle valve N1 attached to the intake / exhaust port 8221 of the lid portion 822 is disconnected from the flexible gas pipe FGP, and the reaction vessel 82 is removed from the hydrogenation furnace 8.

[0074] By disconnecting the flexible gas piping FGP, the atmosphere will enter the flexible gas piping FGP, but the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 of the reaction vessel 82 is in a closed state, so the atmosphere will not enter the reaction vessel 82. Similarly, the needle valve N2 is also closed, so that the air does not enter the pressure adjustment tank 83.

[0075] (Step 12) Next, the removed reaction vessel 82 is placed in the same airtight work box used to store the material to be crushed in the crushing section 3 as described above in the crushing process, and the crushed material (specifically, crushed magnesium) crushed in the crushing process is stored in the reaction vessel 82 under an argon gas atmosphere (S12).

[0076] Specifically, the clamp 824 of the reaction vessel 82 is removed in an airtight work box, the lid 822 is removed from the reaction vessel main body 821, and the crushed magnesium is placed into the reaction vessel main body 821 through the opening on the top side of the reaction vessel main body 821. Next, the lid 822 is placed to close the upper opening of the reaction vessel body 821, and a clamp 824 is attached to create a sealed state in which outside air does not enter the reaction vessel 82.

[0077] The process of placing the crushed magnesium in the reaction vessel 82 is carried out in an argon gas atmosphere inside an airtight work box, so the reaction vessel 82 containing the crushed magnesium is filled with argon gas.

[0078] (Step 13) Next, the reaction vessel 82 containing the crushed magnesium is attached to the heating furnace 81 again (S13). Specifically, as shown in Figure 6, the reaction vessel 82 filled with argon gas is installed so that the flange portion 8211 of the reaction vessel body 821 is supported by the insulated housing 811, and the needle valve N1 attached to the intake / exhaust port 8221 of the lid portion 822 is connected to the flexible gas piping FGP.

[0079] (Step 14) Next, the atmosphere mixed in the flexible gas piping FGP, the pressure adjustment tank 83, and the argon gas in the reaction vessel 82 are exhausted, and a vacuum is drawn to create a state in which hydrogen gas can be filled (S14).

[0080] First, the vacuum pump P2 is driven, and the on-off valve OCB5 attached to the exhaust port PT5 is opened to start exhausting the argon gas from the pressure adjustment tank 83.

[0081] Next, the needle valve N2 attached to the gas supply port PT4 is opened to exhaust the air mixed in the flexible gas pipe FGP.

[0082] Then, wait for a while in this state until the air mixed in the flexible gas piping FGP is completely discharged.

[0083] After sufficient evacuation has been performed in this manner (for example, after evacuation has been performed to about several Pa), the needle valve N1 attached to the intake / exhaust port 8221 of the lid portion 822 is slowly turned to the open position.

[0084] The needle valve N1 attached to the intake / exhaust port 8221 is slowly turned to the open position in order to slowly exhaust the argon gas from the reaction vessel 82 so that the crushed material (crushed magnesium) in the reaction vessel 82 is not sucked in.

[0085] (Step 15) Once the inside of the reaction vessel 82 is in a vacuum state, a hydrogenation treatment is carried out in which the pulverized material (pulverized magnesium) is heated to a temperature at which hydrogenation proceeds in a hydrogen gas atmosphere (S15).

[0086] First, before actually supplying hydrogen gas to perform hydrogenation treatment, the heater part 812 of the heating furnace 81 is turned on while continuing to evacuate, and heating of the pulverized material (pulverized magnesium) is started. The set temperature of the heater section 812 may be a temperature at which the pulverized material (pulverized magnesium) is heated to a temperature suitable for hydrogenation.

[0087] Specifically, when the pressure of the hydrogen gas is about 90 KPa (approximately 0.9 atmospheres), the heating temperature for hydrogenation should be set to 140°C or higher, because the hydrogenation reaction slows down rapidly if the temperature falls below 140°C.Since a range of about 220°C ± 40°C provides relatively good hydrogenation efficiency, in the first embodiment, the set temperature of the heater section 812 is set to a temperature that heats the crushed material (crushed magnesium) to 220°C.

[0088] In this way, by starting heating under vacuum conditions, excess fatty acids added during the grinding process that adhere to the surface of the ground material (ground magnesium) can be removed, preventing a decrease in hydrogenation efficiency due to the influence of the fatty acids.

[0089] However, if the amount of fatty acid added is not large, the heat treatment of heating the pulverized material (pulverized magnesium) while evacuating the material may be omitted. That is, the supply of hydrogen gas may be started first, and then heating may be started.

[0090] Next, the on-off valve OCB5 attached to the exhaust port PT5 is closed to stop the operation of the vacuum pump P2, and then the on-off valve OCB2 attached to the hydrogen gas receiving port PT2 is opened to start the pressure control mode of the sequencer PLC.

[0091] In the first embodiment, the pressure of the hydrogen gas is controlled to approximately 90 KPa (approximately 0.9 atmospheres), so the upper and lower limits of the controlled pressure are set to a lower limit of 89 KPa and an upper limit of 91 KPa, respectively. When the output value of the digital pressure gauge DP reaches 91 KPa, the operation of the hydrogen gas mass flow controller MFC-H stops, and the supply of hydrogen gas stops.

[0092] As the hydrogenation proceeds, hydrogen gas is taken into the crushed magnesium, causing the pressure in the pressure adjustment tank 83 to drop, and the output value of the digital pressure gauge DP becomes 89 KPa.

[0093] This causes the hydrogen gas mass flow controller MFC-H to operate again, and hydrogen gas is supplied until the output value of the digital pressure gauge DP reaches 91 KPa.

[0094] In this way, while maintaining the pressure of the hydrogen gas atmosphere at approximately 90 KPa, the crushed material (crushed magnesium) is heated to approximately 220°C and hydrogenation treatment is carried out for a predetermined time, after which the heater part 812 of the heating furnace 81 is turned off and the pressure control mode of the sequencer PLC is ended, thereby completing the hydrogenation treatment.

[0095] (Step 16) After the hydrogenation process is completed, the hydrogenated material (magnesium hydride) is removed. However, since the pressure adjustment tank 83 and the reaction vessel 82 are filled with hydrogen gas, the gas is first replaced with argon gas (S16).

[0096] Specifically, after closing the on-off valve OCB2 attached to the hydrogen gas receiving port PT2, the vacuum pump P2 is driven and the on-off valve OCB5 attached to the exhaust port PT5 is opened.

[0097] After sufficient evacuation, the on-off valve OCB5 attached to the exhaust port PT5 is closed, the vacuum pump P2 is stopped, and the on-off valve OCB3 attached to the argon gas receiving port PT3 is opened to supply argon gas until atmospheric pressure is reached.

[0098] When the pressure adjustment tank 83 and the reaction vessel 82 have been filled with argon gas until the pressure reaches atmospheric pressure, the supply of argon gas is stopped and the opening / closing valve OCB3 attached to the argon gas receiving port PT3 is closed.

[0099] At this time, the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 of the reaction vessel 82 and the needle valve N2 attached to the gas supply port PT4 of the pressure adjustment tank 83 are closed, thereby completing the gas replacement operation.

[0100] (Step 17) After the gas exchange is completed, the magnesium hydride, which is the hydrogenated material, is finally removed (S17). Since magnesium hydride is relatively stable in the atmosphere unless exposed to moisture, it is not necessary to carry out the process in an airtight work box used when placing the crushed material (crushed magnesium) in the reaction vessel 82.

[0101] However, in the first embodiment, just as when the crushed material (crushed magnesium) is stored in the reaction vessel 82, the removal work is also carried out inside an airtight work box, and the magnesium hydride is stored in an airtight bottle filled with argon gas. The removal process is essentially the same as the process of placing the crushed material (crushed magnesium) in the reaction vessel 82, except that it is the reverse process (placing the material from the reaction vessel 82 into an airtight bottle), so detailed explanation will be omitted.

[0102] In this way, once the hydrogenated material, magnesium hydride, has been removed from the reaction vessel 82, the hydrogenation process is completed.

[0103] Next, the effect of adding a fatty acid in the grinding step will be described. FIG. 8 is a graph showing the effect of adding fatty acids during the milling process. The graph in Figure 8 shows the results after hydrogenation of three samples, the only difference between these samples being the amount of fatty acid added during the grinding process.

[0104] Fatty acids that can be suitably used include, for example, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, icosanoic acid, henicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, and triacontanoic acid; octadecanoic acid is used here.

[0105] Specifically, for all samples, the magnesium used before grinding was from the same manufacturer with an average particle size of approximately 500 μm, and the amount of magnesium used in the grinding process was standardized to 50 g.

[0106] As can be seen from the horizontal axis of the graph, one sample was subjected to the grinding process with the amount of fatty acid added set to 0 wt % (0 mass %), that is, without adding any fatty acid.

[0107] In another sample, approximately 1.55 g of octadecanoic acid (fatty acid) was added to 50 g of magnesium, so that approximately 3 wt% (approximately 3 mass%) of the total mass of magnesium and fatty acid combined (approximately 51.55 g) was octadecanoic acid (fatty acid). That is, the amount of octadecanoic acid (fatty acid) added in the pulverization step was adjusted to about 3 mass % of the total mass.

[0108] Furthermore, for the remaining sample, approximately 2.63 g of octadecanoic acid (fatty acid) was added per 50 g of magnesium, so that approximately 5 wt% (approximately 5 mass%) of the total mass of magnesium and fatty acid (approximately 52.63 g) was octadecanoic acid (fatty acid). That is, the amount of octadecanoic acid (fatty acid) added in the pulverization step was adjusted to about 5% by mass of the total mass.

[0109] The grinding process and hydrogenation process were as described above, and in the grinding process, the grinder 1 was operated intermittently for the same amount of time in all samples, and grinding was carried out for 12 hours in actual operation.

[0110] In addition, the hydrogenation process was carried out by setting the temperature to heat the crushed magnesium to 220°C, which is suitable for hydrogenating the crushed magnesium, and turning on the heater unit 812 while the vacuum was still drawn.The vacuum state was maintained until the set temperature was reached, and once the set temperature was reached, hydrogen gas was supplied and heating (hydrogenation treatment) was carried out for 8 hours while maintaining the pressure of the hydrogen gas atmosphere at approximately 90 KPa (approximately 0.9 atmospheres).

[0111] Then, when 8 hours have passed since the pressure of the hydrogen gas reached approximately 90 KPa, the heater unit 812 is turned off, and after the temperature has dropped to room temperature, the crushed magnesium after hydrogenation is taken out.

[0112] The hydrogenated crushed magnesium was then sieved, and only those with sizes of 53 μm or less were subjected to an X-ray diffraction device (XRD device) to determine the hydrogenation rate, i.e., the content (wt%) of magnesium hydride in the hydrogenated crushed magnesium. It is believed that the hydrogenation efficiency depends on particle size. However, as explained above, the grinding process is carried out using a commercially available grinder 1 for home use, which results in a large variation in particle size. Therefore, the crushed magnesium after hydrogenation is sieved and analyzed in a state where the particle size is relatively uniform, thereby eliminating the particle size-dependent variation.

[0113] As shown in FIG. 8, when magnesium was crushed without adding octadecanoic acid, the hydrogenation rate was only 3.47 wt% even after 8 hours of hydrogenation treatment.

[0114] However, when the amount of octadecanoic acid added was increased, the hydrogenation rate rose to 14.9 wt% when the amount of octadecanoic acid added was 3 wt%, and further, when the amount of octadecanoic acid added was increased to 5 wt%, the hydrogenation rate rose to 43.3 wt%, indicating a significant improvement in hydrogenation efficiency.

[0115] As described above, the first embodiment uses a mill that is commonly used in households and that grinds an object to be ground while stirring it with the rotation of rotating teeth.

[0116] In the case of such a mill, hard balls to promote pulverization are not used, as are ball mills and bead mills used to produce fine powders. Therefore, the magnesium particles are not repeatedly stretched and pressed together to become one during the pulverization process, but are simply pulverized into fragments when they rub against each other or collide with the rotating teeth. Therefore, it is presumed that the added octadecanoic acid is only present on the surface of the pulverized magnesium and is not kneaded into the interior.

[0117] From this, it is speculated that the mechanism by which the hydrogenation efficiency is improved is that octadecanoic acid has some effect on the surface of magnesium. For example, fatty acids have carboxyl groups, and these react with the oxygen in metal oxides (for example, the oxygen in the oxide film formed on the surface of magnesium) to form metal soaps that have significantly lower melting points, boiling points, and hardness than metal oxides. Therefore, it is surmised that octadecanoic acid has some effect on the surface of magnesium. It is believed that fatty acids also react with metals themselves to form metal soaps.

[0118] Furthermore, when looking at the hydrogenation rate of pulverized magnesium without adding octadecanoic acid, when the pressure of the hydrogen gas atmosphere is low as in the first embodiment, it is difficult to increase the hydrogenation rate in a realistic time, as described in prior art documents.

[0119] However, if octadecanoic acid is added to magnesium during the crushing process, it becomes possible to carry out hydrogenation even in a low-pressure hydrogen gas atmosphere, where it has previously been considered difficult to increase the hydrogenation rate in a realistic amount of time.

[0120] Naturally, the hydrogenation of magnesium proceeds from the surface towards the centre, and it is believed that when the reaction has progressed to the centre, the hydrogenation rate reaches 100%.

[0121] This suggests that the hydrogenation reaction can be completed quickly by reducing the particle size of the magnesium and shortening the distance to the center through which hydrogen must penetrate. As explained above, all of the samples analyzed this time were sieved to determine whether they were 53 μm or smaller, but even when they were sieved through a finer sieve that was able to pass 30 μm particles, no fine particles passed through the sieve.

[0122] This shows that even for particles with a size of 30 μm to 53 μm, if approximately 5 wt% (5 mass%) of octadecanoic acid is added during the crushing process, a hydrogenation rate of over 40 wt% can be achieved after 8 hours of hydrogenation treatment.

[0123] For example, in the case of a 30 μm particle, hydrogenation is thought to have progressed to a depth of approximately 2 μm from the surface in order for 40 wt% to be hydrogenated. If the particle is crushed to a depth of approximately 4 μm during the crushing process, it is expected that an extremely high hydrogenation rate close to 100% can be achieved, even in such a low-pressure hydrogen gas atmosphere, which has traditionally been considered difficult to increase in a realistic amount of time. Furthermore, it can be said that even magnesium, which is soft and difficult to turn into fine powder, can be sufficiently pulverized to such a particle size.

[0124] Therefore, if the amount of octadecanoic acid (fatty acid) added in the grinding process is 5 mass% or more of the total mass of magnesium and octadecanoic acid (fatty acid), it is expected that an extremely high hydrogenation rate can be obtained within a realistic range of ground particle size and in a realistic hydrogenation time, even in a low-pressure hydrogen gas atmosphere, where it is considered difficult to increase the hydrogenation rate in a realistic time.

[0125] However, because such crushed magnesium has a significantly increased reactivity, it is subject to rapid oxidation and deterioration by oxygen, which prevents the hydrogenation reaction from occurring. Therefore, it is important to keep the crushed magnesium from coming into contact with oxygen until the end of the hydrogenation process.

[0126] On the other hand, as can be seen from the description of the first embodiment, this method does not require maintaining magnesium hydride at a high temperature that would decompose it in a high-pressure hydrogen gas atmosphere, as shown in prior art documents.

[0127] FIG. 9 is a graph showing the decomposition boundary line BL of magnesium hydride obtained by thermodynamic calculation, and the advantages of this method in terms of temperature will be explained with reference to this graph. The temperature on this decomposition boundary line may be called the decomposition boundary temperature. The graph shown in Figure 9 shows the pressure of the hydrogen gas atmosphere (unit: Pa) on the vertical axis and the temperature (unit: °C) on the horizontal axis, and was created by determining the lowest temperature at which magnesium hydride begins to decompose at each pressure and graphing it.

[0128] In other words, on the right side (high temperature side) of the magnesium hydride decomposition boundary line BL, magnesium hydride decomposes into magnesium and hydrogen gas, while on the left side (low temperature side), no decomposition of magnesium hydride occurs, and if magnesium and hydrogen gas are present, the generation reaction to form magnesium hydride proceeds.

[0129] In the hydrogenation example described above, the pressure of the hydrogen gas atmosphere is set to approximately 90 kPa, which is slightly lower than 100,000 Pa (100 kPa), and the temperature on the decomposition formation boundary line BL of magnesium hydride is around 280°C.

[0130] However, since the actual heating temperature is about 220°C, it is sufficient to set the temperature to about 60°C lower than the temperature on the decomposition boundary line BL of magnesium hydride.

[0131] For this reason, for example, if the treatment is performed in a hydrogen gas atmosphere of 5 atm (5 atmospheres), as shown by the dotted line on the graph, the temperature on the decomposition boundary line BL of magnesium hydride is approximately 350°C, so the actual heating temperature can be considered to be 300°C or less.

[0132] On the other hand, as shown in prior art documents, if treatment is carried out at a temperature about 50°C higher than the temperature on the decomposition boundary line BL of magnesium hydride, heating will be required to a temperature of 400°C or higher, in which case radiant heat will become dominant.

[0133] Generally, the reactor vessel 82 is made of a metal material such as stainless steel. However, when stainless steel is used, radiant heat is reflected, which reduces the heat transfer efficiency and increases energy loss. Therefore, by performing processing at a low temperature where radiant heat is not dominant, as in the present method, it is possible to perform hydrogenation processing with high energy efficiency.

[0134] Furthermore, with this method, processing can be performed at relatively low pressure, so there is no need to increase the thickness of the reaction vessel 82 to ensure pressure resistance, which allows for good heat conduction and makes it possible to heat the crushed magnesium efficiently, which is thought to be energy efficient.

[0135] On the other hand, thermodynamic calculations show that magnesium hydride can exist stably even at low temperatures, but thermodynamic calculations do not take into account the reaction rate factor, and as mentioned earlier, when the heating temperature of the magnesium falls below 140°C, the decrease in pressure seen in the hydrogenation process due to the absorption of hydrogen gas into the magnesium slows down significantly.

[0136] For this reason, it is preferable to heat magnesium to a temperature of 140° C. or higher in the hydrogenation treatment in the hydrogenation step.

[0137] Specifically, the dashed line in the graph of Figure 9 is 500 Pa (0.5 kPa), and in this case, the temperature on the decomposition boundary line BL of magnesium hydride is approximately 150°C, so if the pressure of the hydrogen gas atmosphere is made 500 Pa or higher, magnesium hydride will not decompose at a temperature of 140°C.

[0138] Therefore, it is preferable to carry out the hydrogenation treatment in the hydrogenation step by heating the crushed magnesium to a temperature of 140°C or higher, below the decomposition temperature of magnesium hydride, under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower.This allows treatment to be carried out at a temperature 50°C or higher lower than 400°C, at which the influence of radiant heat becomes strong, and also allows for good heat conduction and energy-efficient treatment, as there is no need to increase the thickness of the reaction vessel 82. In addition,

[0139] For example, if the hydrogen gas pressure in the hydrogenation process is less than 0.2 MPa, even regular inspections are not required by law, and in order to promote hydrogenation, a high pressure, for example, 30 kPa (approximately 0.3 atmospheres) or more is preferable, so it is more preferable to heat and treat the crushed magnesium under a hydrogen gas pressure of 30 kPa or more and less than 0.2 MPa in the hydrogenation process.

[0140] (Second embodiment) In the first embodiment, octadecanoic acid is used as the fatty acid, but in the second embodiment, a case where dodecanoic acid is used as the fatty acid will be described. In the second embodiment, dodecanoic acid was also added to the magnesium in the grinding process so that the amount of dodecanoic acid added was approximately 5 wt% (approximately 5 mass%: 2.63 g) of the total mass of magnesium and dodecanoic acid combined for 50 g of the same magnesium used in the first embodiment, and grinding was carried out.

[0141] The pulverizer 1 and the pulverization conditions using the pulverizer 1 are the same as those in the first embodiment, and the hydrogenation furnace 8 in which the hydrogenation step was carried out is also the same as that in the first embodiment.

[0142] The crushed magnesium was then divided into two, and one of the two was subjected to a hydrogenation process under the same conditions as in the first embodiment.The crushed magnesium after hydrogenation was sieved, and only those with sizes of 53 μm or less were subjected to an X-ray diffraction device (XRD device) to determine the magnesium hydride content (wt%). As a result, the hydrogenation rate was 51.3 wt%, which was better than that of octadecanoic acid, indicating that the fatty acid added during the grinding process does not have to be octadecanoic acid.

[0143] However, if the alkyl chain is short, the hydrophobicity will be weaker and the fatty acid will be more likely to absorb moisture, so it must be handled carefully to prevent it from absorbing moisture. Conversely, if the alkyl chain is long, the melting point will be higher, and the rise in temperature during the grinding process will not cause the fatty acid to melt, making it difficult to add it to the surface of the magnesium.

[0144] For this reason, it is considered that fatty acids with a total carbon number of approximately 7 to 30, such as heptanoic acid (carbon number 7), octanoic acid (carbon number 8), nonanoic acid (carbon number 9), decanoic acid (carbon number 10), dodecanoic acid (carbon number 12), tetradecanoic acid (carbon number 14), pentadecanoic acid (carbon number 15), hexadecanoic acid (carbon number 16), heptadecanoic acid (carbon number 17), octadecanoic acid (carbon number 18), icosanoic acid (carbon number 20), henicosanoic acid (carbon number 21), docosanoic acid (carbon number 22), tetracosanoic acid (carbon number 24), hexacosanoic acid (carbon number 26), octacosanoic acid (carbon number 28), and triacontanoic acid (carbon number 30), are more suitable.

[0145] On the other hand, for the remaining crushed magnesium, after evacuating the reaction vessel 82, hydrogen gas was filled to 90 kPa before turning on the heater unit 812, and then the heater unit 812 was turned on and hydrogenation treatment was carried out for 8 hours once the set temperature was reached. That is, the difference is that hydrogen gas is supplied before the heater unit 812 is turned on, and the rest is the same.

[0146] In addition, even in the case where hydrogen gas was supplied and hydrogenation treatment was performed before turning on the heater unit 812, the crushed magnesium after hydrogenation was sieved and only those with a size of 53 μm or less were subjected to an X-ray diffraction device (XRD device) to determine the magnesium hydride content (wt%).The hydrogenation rate was a somewhat low value of 29.8 wt%.

[0147] For this reason, it is preferable that the hydrogenation step includes a heat treatment in which the pulverized magnesium is heated while being evacuated before the hydrogenation treatment.

[0148] (Third embodiment) In the first and second embodiments, the grinder 1 is a household mill that is commonly used in homes to pulverize tea leaves, coffee beans, and the like. Unlike industrial mills, this home mill will break down if overloaded. As a result, the fatty acids melt as the temperature rises during grinding, making the material highly viscous. However, if the amount of fatty acid added exceeds 5 wt%, and the viscosity becomes extremely high, the material may become immobile.

[0149] Therefore, in the third embodiment, in order to see whether the hydrogenation efficiency improves even when a larger amount of fatty acid is added, a case where pulverization is performed using a planetary ball mill manufactured by Fritsch will be described.

[0150] (Crusher) FIG. 10 is a perspective view of a grinder S1 used in a grinding process of the third embodiment according to the present invention, FIG. 11 is a perspective view showing the hood S3 of the grinder S1 of the third embodiment according to the present invention in an open state, FIG. 12 is a perspective view of a grinding container S4 of the third embodiment according to the present invention, and FIG. 13 is an exploded perspective view of the grinding container S4 of the third embodiment according to the present invention.

[0151] As shown in Figures 10 and 11, the crusher S1 used in the third embodiment includes a crusher main body S2 that controls the rotation of a crushing container S4 (see Figure 11) that is removably fixed, and a hood S3 that is connected to the crusher main body S2 with a hinge structure that allows it to be opened and closed, and that can cover and conceal the crushing container S4.

[0152] As shown in FIG. 10, the crusher main body S2 includes a condition input section S21 for inputting conditions for controlling the rotation of the crushing container S4, and an emergency stop button S22.

[0153] As shown in Figures 12 and 13, the grinding container S4 comprises a bottomed grinding container body S41 with an upper opening that forms a storage section for storing the grinding material (not shown) and spherical grinding media (not shown) that promotes grinding, and a lid section S42 that closes the upper opening of the grinding container body S41.

[0154] As shown in FIG. 13, the grinding container body S41 has a groove S411 on the edge of the upper opening side for placing an O-ring S5, and a screw threading hole S412 formed radially outward from the groove S411 and into which a screw is threaded. A total of four screw holes S412 are provided at 90-degree intervals in the circumferential direction.

[0155] On the other hand, the cover portion S42 has a through hole S421 with a counterbore for accommodating the head of a screw on its outer surface (see FIG. 12). In addition, this through hole S421 is a through hole S421 for passing the threaded portion of the screw through to the grinding container body S41 side when screwing the lid portion S42 to the grinding container body S41, so the position (distance from the center, etc.) of the through hole S421 corresponds to the screw threading hole S412 of the grinding container body S41.

[0156] Then, the grinding material (not shown) and spherical grinding media (not shown) that promote grinding are placed in the grinding container body S41, and a screw (not shown) is threaded into the screw-engaging hole S412 of the grinding container body S41 through the through hole S421 from the lid portion S42 side so that the lid portion S42 presses the O-ring S5 toward the grinding container body S41. As a result, the grinding material (not shown) and the spherical grinding media (not shown) that promote grinding are placed inside the grinding container S4 in a completely sealed state.

[0157] After the grinding material (not shown) and spherical grinding media (not shown) that promotes grinding are placed inside the grinding container S4 in this manner, the grinding container S4 is fixed to the grinder main body S2 as shown in FIG. 11, the hood S3 is closed as shown in FIG. 10, the condition input unit S21 is operated to input the conditions for controlling the rotation of the grinding container S4, and the grinding start button is pressed to start grinding.

[0158] Specifically, when the grinding start button is pressed, the grinding container S4 itself begins to rotate, and within the sealed grinding container S4, the rotational force vigorously mixes the magnesium to be ground with hard balls (e.g., 5 mmφ high-hardness balls (SUS440C, chrome steel)) that promote grinding, and the grinding process progresses.

[0159] The grinding container S4 corresponds to the grinding section 3 of the grinder 1 in the first and second embodiments, and the basic work procedures for the grinding process and the hydrogenation process are almost the same as those in the first and second embodiments, so below we will explain the differences and may omit explanations of the similarities.

[0160] As can be seen from the above description, the planetary ball mill device, which is the crusher S1 of the third embodiment, is configured to simply rotate the crushing vessel S4 itself for crushing. Therefore, the grinding vessel S4 is configured so that there is no mechanical stirring structure inside the grinding vessel S4, and the grinding vessel body S41 and the lid portion S42 are completely airtight by the O-ring S5. Therefore, there is no risk of outside air being drawn into the grinding container S4 during the grinding operation.

[0161] For this reason, the process of placing the steel balls and the magnesium (including the fatty acid to be added) to be ground into the grinding container S4 for grinding, and the process of removing the ground magnesium, are carried out in an argon gas atmosphere in an airtight work box, as in the first and second embodiments, but grinding is carried out with the planetary ball mill device itself placed in the indoor atmosphere.

[0162] Next, a specific example of the third embodiment will be described. In the third embodiment, magnesium used for pulverization has an average particle size of approximately 180 μm.

[0163] The crushing conditions were as follows: 5 mm diameter hard balls made of high-hardness stainless steel (SUS440C) were placed in the crushing closed vessel S4 so that they occupied one-third of the vessel's internal volume; and 70 g of magnesium was also placed in the vessel so that they occupied one-third of the vessel's internal volume. As the fatty acid, octadecanoic acid was placed in the grinding vessel S4 in an amount that accounted for approximately 13 wt % of the total mass of magnesium and fatty acid. Then, the operation of operating at a rotation speed of 330 rpm for one hour and stopping for one hour was repeated 24 times, so that the time during which the grinding vessel S4 rotated for grinding was 24 hours.

[0164] The reason for stopping the machine for one hour after one hour of operation is to prevent the temperature of the grinding container S4 from rising too high, and the manufacturer recommends that the temperature not exceed 100°C.

[0165] In this way, pulverized magnesium was prepared by adding 13 wt % (13 mass %) of octadecanoic acid, and the pulverized magnesium was used to carry out the hydrogenation step. Specifically, the hydrogenation step is the same as that of the first embodiment, but whereas the hydrogenation treatment was carried out for 8 hours in the first embodiment, the hydrogenation treatment was carried out for 4 hours in the third embodiment.

[0166] Then, as in the first embodiment, the crushed magnesium after hydrogenation was sieved, and only those measuring 53 μm or less were subjected to an X-ray diffraction device (XRD device) to determine the hydrogenation rate, i.e., the content (wt%) of magnesium hydride in the crushed magnesium after hydrogenation, which was found to be 39.5 wt%.

[0167] In the third embodiment, a hydrogenation rate of about 40 wt % was obtained, which is comparable to the first embodiment in which octadecanoic acid was added at 5 wt % (5 mass %). Considering that the hydrogenation treatment time in the third embodiment is half that of the first embodiment, the result of the third embodiment is clearly better than the first embodiment in which octadecanoic acid was added at 5 wt % (5 mass %).

[0168] On the other hand, if too much fatty acid is added, a thick layer of fatty acid may form on the surface of the crushed magnesium, which may inhibit hydrogenation, so it is considered best to limit the amount of fatty acid added to approximately 15 mass% or less of the total mass of magnesium and fatty acid combined.

[0169] In planetary ball mills, the smaller the diameter of the hard balls used for grinding, the smaller the limit particle size that can be ground. Therefore, although high-hardness balls of 5 mmφ were used in the third embodiment, it is believed that if high-hardness balls of 3 mmφ or 1.5 mmφ were used for grinding, the particle size of the magnesium after grinding could be made even smaller.

[0170] Furthermore, considering that the hydrogenation time in the third embodiment is half that of the first embodiment, it can be said that the third embodiment produces even better results than the first embodiment, and similar to the first embodiment, it is expected that an extremely high hydrogenation rate can be obtained within a fully realistic range of crushed particle size and for a realistic hydrogenation time.

[0171] In addition, the amount of fatty acid added to magnesium during the grinding process is considered to be more preferably 6 wt% or more, 7 wt% or more, 8 wt% or more, 9 wt% or more, 10 wt% or more, 11 wt% or more, and 12 wt% or more of the total mass of magnesium and fatty acid combined, in that order. However, since excessive addition is expected to have adverse effects, it is considered best to limit the amount of fatty acid added to magnesium during the grinding process to 15 wt% or less, or 14 wt% or less, of the total mass of magnesium and fatty acid combined.

[0172] Although specific embodiments have been described above, the present invention is not limited to these specific embodiments. For example, in the specific explanation, a method for increasing the hydrogenation rate was described in which the pulverized particle size of magnesium in the pulverization process was reduced, but the pulverization process and the hydrogenation process may also be carried out repeatedly.

[0173] After the initial crushing step and hydrogenation step, the crushed magnesium has been hydrogenated from the surface to a certain depth, forming a layer of magnesium hydride. Furthermore, since the magnesium hydride layer is a layer in which demetallization has progressed, it is easily pulverized, and after a short period of pulverization, the magnesium hydride layer becomes powder, revealing the metallic magnesium portion inside.It is thought that this metallic magnesium portion is then further pulverized, thereby efficiently pulverizing the magnesium into a fine powder.

[0174] Therefore, if crushed magnesium that has already been hydrogenated is subjected to a crushing process again, the crushed state will be further advanced, and if hydrogenation is performed on the crushed magnesium in this more advanced state, magnesium hydride with a higher hydrogenation rate can be obtained.

[0175] In this second grinding process, the magnesium hydride layer is removed by grinding, and fine powder of metallic magnesium is produced, which is a more highly ground product. However, by carrying out the grinding process with the addition of fatty acid, it is thought that the fine powder of metallic magnesium becomes more susceptible to hydrogenation. Therefore, it is desirable to add a fatty acid in the second or subsequent grinding steps.

[0176] In this second grinding process, magnesium containing a magnesium hydride portion is ground, and in this case, the amount of fatty acid added is considered sufficient if it is 5% by mass or more of the total mass of magnesium (mass of magnesium excluding the magnesium hydride portion) and fatty acid.

[0177] On the other hand, the crushed magnesium after hydrogenation has a layer of magnesium hydride formed on the surface, which is expected to prevent the metallic magnesium inside, which is not yet hydrogenated, from being oxidized by oxygen in the air. However, the crushed magnesium immediately after the second crushing process is no longer protected by the magnesium hydride layer, so it is still important to prevent the crushed magnesium after the second crushing process from coming into contact with oxygen until the end of the second hydrogenation process in order to proceed with the hydrogenation reaction.

[0178] Therefore, the method for producing magnesium hydride comprises a crushing step in which fatty acid is added and magnesium is crushed, and a hydrogenation step in which the crushed magnesium is heated to a temperature of 140°C or higher, below the decomposition temperature of magnesium hydride, under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower, to perform hydrogenation.The crushing and hydrogenation step, which combines the steps from the crushing step to the hydrogenation step as a series, may be performed multiple times.Even in this case, it is preferable that the amount of fatty acid added in each crushing and hydrogenation step be 5 mass% or more of the total mass of magnesium and fatty acid combined, and that the crushed magnesium is not exposed to oxygen until the hydrogenation step in each crushing and hydrogenation step is completed.

[0179] As such, the present invention is not limited to specific embodiments, and appropriate modifications and improvements are also included within the technical scope of the present invention, which will be clear to those skilled in the art from the description of the claims. [Explanation of symbols]

[0180] 1. Crusher 2 Crusher body 21 Push Button 3. Crushing section 4 Crushing unit body 41 Agitating and grinding teeth 42 Threaded groove 5 Lid 51 Spiral Mountain 6. Vacuum desiccator 61 Container body 62 Lid 621 Pressure Gauge 622, 623 Intake and exhaust ports 63 Snap Lock 7. Oxygen concentration meter 8 Hydrogenation Furnace 81 Heating furnace 811 Insulated housing 812 Heater section 82 Reaction vessel 821 Reaction vessel body 8211 Flange part 822 Lid 8221 Intake and exhaust port 823 O-ring 824 Clamp 83 Pressure Regulating Tank B1 High-pressure gas cylinder B2 Hydrogen gas cylinder B3 Argon gas cylinder BL decomposition production boundary line DP Digital Pressure Gauge FGP gas piping MFC-A Argon Gas Mass Flow Controller MFC-H Mass Flow Controller for Hydrogen Gas N, N1, N2 needle valves OCB2, OCB3, OCB5 shut-off valve P1, P2 vacuum pumps PLC sequencer PT1 mounting port PT2, PT3 receiving ports PT4 gas supply port PT5 exhaust port S1 Crusher S2 Crusher body S21 Condition input section S22 Emergency Stop Button S3 Hood S4 Grinding container S41 Grinding container body S411 Groove S412 screw hole S42 Lid S421 through hole S5 O-ring

Claims

1. A method for producing magnesium hydride, comprising the steps of: a grinding step of grinding the magnesium by adding a fatty acid; A hydrogenation step of heating the pulverized magnesium under a hydrogen gas pressure of 500 Pa or more and 5 atm or less to a temperature of 140° C. or more and less than the decomposition temperature of magnesium hydride, The amount of the fatty acid added in the grinding step is 5% by mass or more based on the total mass of the magnesium and the fatty acid; A method for producing magnesium hydride, wherein the ground magnesium is not exposed to oxygen until the end of the hydrogenation step.

2. The method for producing magnesium hydride according to claim 1 , wherein the hydrogenation step includes a heat treatment step of heating the pulverized magnesium while performing evacuation before the hydrogenation treatment.

3. The method for producing magnesium hydride according to claim 1 or 2, wherein the amount of the added magnesium is 15 mass % or less of the total mass of the magnesium and the fatty acid.

4. The method for producing magnesium hydride according to any one of claims 1 to 3, wherein a pulverization and hydrogenation step, which is a series of steps from the pulverization step to the hydrogenation step, is carried out a plurality of times.

5. The number of carbon atoms of the fatty acid is 7 or more and 30 or less. The method for producing magnesium hydride according to any one of claims 1 to 4.

6. In the grinding step, the oxide film of the magnesium is scraped off to expose the magnesium surface. The method for producing magnesium hydride according to any one of claims 1 to 5.

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