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 Art

[0002] In recent years, hydrogen has attracted attention as an energy source, and there is a method that uses magnesium hydride as a method for storing the hydrogen.

[0003] And in Patent Document 1, a raw material powder mainly composed of magnesium is held in a hydrogen gas atmosphere sealed in a sealed container, the pressure of the hydrogen gas atmosphere in the sealed container is maintained at a predetermined pressure, the temperature of the hydrogen gas atmosphere in the sealed container is raised from room temperature, and the temperature of the hydrogen gas atmosphere in the sealed container is higher than the temperature corresponding to the predetermined pressure on the equilibrium curve of the reaction in which elemental magnesium and hydrogen molecules combine to form 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. By maintaining at a temperature for a predetermined first period, the film on the surface of the raw material powder is removed. Next, the temperature of the hydrogen gas atmosphere in the sealed container is not returned to room temperature, but is lower than the temperature corresponding to the predetermined pressure on the equilibrium curve, and the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve is within 100 ° C. By maintaining at a temperature for a predetermined second period, a method for producing a magnesium-based hydride for producing a magnesium-based hydride from a raw material powder is disclosed.

[0004] That is, in Patent Document 1, the first feature is to maintain for a predetermined first period at a temperature higher than the temperature corresponding to the predetermined pressure on the equilibrium curve of the reaction in which elemental magnesium and hydrogen molecules combine to form 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 characteristic allows for 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 by hydrogen molecules, thereby removing the coating on the magnesium surface and enabling it to react quickly with hydrogen (H2).

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

[0007] This second characteristic makes it possible to obtain high-purity magnesium hydride (MgH2) with less energy input compared to conventional techniques that require an activation process involving repeated heating and cooling to absorb and release hydrogen. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2008-044832 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] By the way, in Patent Document 1, the examples show that the hydrogen gas pressure during the hydrogenation treatment is set to a pressure atmosphere of 10 atmospheres (approximately 1 MPa) or higher.

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

[0011] Thus, when the hydrogen gas pressure during hydrogenation is high, the container structure required for the reaction needs to have pressure resistance, which necessitates increasing the thickness of the container. This, in turn, results in poor heat transfer for heating the inside of the container.

[0012] This invention has been made in view of these circumstances, and aims to provide a method for producing magnesium hydride that can be hydrogenated even in a hydrogen gas atmosphere of 5 atmospheres or less. [Means for solving the problem]

[0013] To achieve the above objective, the present invention is understood by the following configuration. (1) The present invention provides a method for producing magnesium hydride, comprising: a grinding step of grinding magnesium with the addition of a fatty acid; and a hydrogenation step of hydrogenating the ground magnesium by heating it to a temperature of 140°C or higher and below 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 grinding step is 5% by mass or more of the total mass of the magnesium and the fatty acid combined, and the ground magnesium is not exposed to oxygen until the end of the hydrogenation step.

[0014] (2) In the configuration of (1) above, the hydrogenation step includes a heat treatment step in which the crushed magnesium is heated while vacuuming is performed before the hydrogenation treatment.

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

[0016] (4) In any one of the configurations (1) to (3) above, the grinding and hydrogenation process, which combines the processes from the grinding process to the hydrogenation process as a series, is performed multiple times. [Effects of the Invention]

[0017] According to the present invention, for example, even in a hydrogen gas atmosphere of 5 atm or less, a method for producing magnesium hydride capable of being hydrogenated can be provided.

Brief Description of the Drawings

[0018] [Figure 1] It is a perspective view of the crusher used in the crushing process of the first embodiment according to the present invention. [Figure 2] It is a perspective view of the crushing part of the crusher of the first embodiment according to the present invention. [Figure 3] It is an exploded perspective view of the crushing part of the first embodiment according to the present invention. [Figure 4] It is a diagram showing the device configuration of the crushing process of the first embodiment according to the present invention. [Figure 5] It is a flowchart showing the procedure of the crushing process of the first embodiment according to the present invention. [Figure 6] It is a side view showing the hydrogenation furnace of the first embodiment according to the present invention. [Figure 7] It is a flowchart showing the procedure of the hydrogenation process of the first embodiment according to the present invention. [Figure 8] It is a graph showing the effect of adding fatty acid in the crushing process of the first embodiment according to the present invention. [Figure 9] It is a graph showing the decomposition generation boundary line of magnesium hydride obtained by thermodynamic calculation. [Figure 10] It is a perspective view of the crusher used in the crushing process of the third embodiment according to the present invention. [Figure 11] It is a perspective view showing the state where the hood of the crusher of the third embodiment according to the present invention is opened. [Figure 12] It is a perspective view of the crushing container of the third embodiment according to the present invention. [Figure 13] It is an exploded perspective view of the crushing container of the third embodiment according to the present invention.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings. Throughout the description of the embodiments, the same elements are denoted by the same reference numerals.

[0020] (First Embodiment) The first embodiment of the present invention provides a method for producing magnesium hydride, comprising a grinding step of grinding magnesium by adding a fatty acid, and a hydrogenation step of hydrogenating the ground magnesium by heating it in a hydrogen gas atmosphere to a temperature at which magnesium hydride can be produced, that is, a temperature below the decomposition temperature of magnesium hydride.

[0021] Therefore, the apparatus used consists of a pulverizer 1 (see Figure 1) for the pulverization process and a hydrogenation furnace 8 (see Figure 6) for the hydrogenation process. We will explain the pulverizer 1 first, then the pulverization process, and then the hydrogenation furnace 8 first, followed by the hydrogenation process.

[0022] (Crusher) Figure 1 is a perspective view of the pulverizer 1 used in the pulverization process of the first embodiment of the present invention, Figure 2 is a perspective view of the pulverization section 3 of the pulverizer 1 of the first embodiment of the present invention, and Figure 3 is an exploded perspective view of the pulverization section 3 of the first embodiment of the present invention.

[0023] As shown in Figure 1, the pulverizer 1 used in the first embodiment comprises a pulverizer body 2 which has a built-in motor for rotating the stirring and grinding teeth 41 of the grinding section 3 and a push button 21 for turning the drive power ON and OFF, and a grinding section 3 which is detachably attached to the pulverizer body 2 and contains the material to be ground (not shown).

[0024] Figure 2 is a perspective view showing only the grinding unit 3 after it has been removed from the main body of the grinder 2. When the grinding unit 3 is attached to the main body of the grinder 2, the rotation shaft of the stirring and grinding teeth 41 of the grinding unit 3 fits together with the rotation shaft of the motor provided in the main body of the grinder 2. When the push button 21 that turns on the drive power (the push button 21 labeled "ON" in Figure 1) is pressed, the motor rotates, causing the stirring and grinding teeth 41 of the grinding unit 3 to rotate and grinding the material to be ground (not shown) contained within the grinding unit 3.

[0025] As shown in Figure 3, the grinding unit 3 comprises a grinding unit body 4 to which stirring and grinding teeth 41 are rotatably attached, and a lid 5 that is detachably attached to cover the upper side of the grinding unit body 4 and prevents the material to be ground (not shown) from scattering.

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

[0027] The grinder 1 used in the first embodiment is a household mill commonly used in homes to grind tea leaves, coffee beans, etc., and in this embodiment, a grinder manufactured by Zojirushi Corporation is used as grinder 1.

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

[0029] Therefore, when carrying out the crushing process, measures are taken to place the crusher 1 inside an airtight booth to prevent the intrusion of air, and to maintain an argon gas atmosphere inside the airtight booth. Next, the crushing process will be explained, including the details of these measures.

[0030] (Grinding process) Figure 4 shows the apparatus configuration for the grinding process of the first embodiment according to the present invention. As shown in Figure 4, the grinding process is carried out by installing the grinder 1, which was described earlier, inside a commercially available airtight booth called a vacuum desiccator 6.

[0031] This vacuum desiccator 6 comprises a rectangular container body 61 with an open top, a rectangular lid 62 that closes the top opening, and a packing positioned on the open side edge of the container body 61 to ensure airtightness between the container body 61 and the lid 62. The container body 61 and the lid 62 can be detachably secured by a plurality of snap locks 63 provided circumferentially.

[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 with needle valves.

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

[0034] Although not visible in Figure 4, this vacuum desiccator 6 has an internal power port for connecting a 100V power supply located behind the crusher 1 on the container body 61.

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

[0036] Therefore, by pressing the push button 21 (the push button 21 labeled "ON" in Figure 1) to turn on the power supply of the main body of the crusher 2, setting the crusher 1 inside the vacuum desiccator 6 while it is ON, and connecting the power 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 timer switch located outside the vacuum desiccator 6.

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

[0038] Next, I will explain the specific steps of the grinding process. Figure 5 is a flowchart showing the procedure of the grinding process according to the first embodiment of the present invention. Before commencing the work, the main body 2 of the pulverizer 1 and the oxygen concentration meter 7 are set inside the vacuum desiccator 6, and the lid 62 of the vacuum desiccator 6 is detached from the container body 61.

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

[0040] During this grinding process, fatty acids are added to the magnesium, which is the material to be ground. This involves placing a mixture of magnesium and fatty acids into the grinding unit 3. The specific amount of fatty acids 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 main body unit 2 of the crusher, which is installed inside the vacuum desiccator 6 (S2). After installing the crushing unit 3, be sure to press the push button 21 (the push button 21 marked "ON" in Figure 1) to turn on the power supply of the crusher main unit 2. However, since power will not be supplied unless the switch with the timer function explained earlier is started, the crusher 1 will not operate at this point.

[0042] (Step 3) Next, the lid 62 of the vacuum desiccator 6 is secured 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 create a vacuum inside the vacuum desiccator 6 (S3).

[0043] The crushing section 3 has a relatively airtight structure to suppress leakage of fine dust and other particles, and under conditions where there is no pressure difference between the inside and outside, it can suppress the intrusion of outside air to some extent for a while. However, when vacuuming is performed and the external pressure decreases, the argon gas inside the crushing section 3 is gradually drawn out in proportion to the pressure difference, and a vacuum is created in this step.

[0044] As a guideline for vacuuming, the pressure gauge 621 needle should move to its limit towards vacuum. In addition, as the pressure decreases, the oxygen concentration display on the oxygen concentration meter 7 will also approach 0%, so the vacuuming process was continued until the display on the oxygen concentration meter 7 showed 0%.

[0045] (Step 4) Once sufficient vacuuming is complete, the intake / exhaust port 623 is closed, then the intake / exhaust port 622 is opened, and argon gas is filled into the vacuum desiccator 6 (S4). Then, once the filling process has begun, the vacuum pump P1 is stopped and the needle valve N is opened.

[0046] Furthermore, when supplying argon gas, the opening degree of the needle valve in the intake / exhaust port 622 should be adjusted to ensure an appropriate supply amount.

[0047] Furthermore, during the argon gas filling process, the pressure inside the vacuum desiccator 6 increases relative to the pulverization section 3, which is under vacuum due to the aforementioned vacuuming process. This pressure difference causes the argon gas to fill the pulverization 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 is slightly positive above atmospheric pressure, the needle valve of the intake / exhaust port 623 is opened slightly to allow for weak positive pressure control with argon gas flowing, and the argon gas filling process inside the vacuum desiccator 6 is completed.

[0049] In this way, by maintaining a weakly positive pressure state with an argon gas blower, it is reliably prevented that air will be drawn into the vacuum desiccator 6 during the grinding process.

[0050] (Step 5) Once the argon gas filling is complete and there is no risk of air being drawn into the pulverizer 1, the pulverizer 1 is started (S5) to pulverize the material to be pulverized.

[0051] Specifically, the operation of the switch with the timer function described above was started, the crusher 1 was operated for a predetermined time, and the operation of the crusher 1 was stopped for a predetermined time, and this process was repeated until the total operating time of the crusher 1 reached approximately 12 hours. In other words, the crushing process is continued until the actual operating time of the crusher 1 reaches 12 hours, excluding the time it is stopped, at which point the crushing process in the crusher 1 is terminated.

[0052] The reason why the pulverizer 1 is operated intermittently, repeatedly starting and stopping, is, as mentioned earlier, because the pulverizer 1 in the first embodiment is a commercially available mill machine used in typical households, and would malfunction if operated continuously for a long period of time. If it were an industrial mill machine that is permitted to operate for long periods of time, there would be no need to include stopping time.

[0053] (Step 6) Once the crushing of the material to be crushed is complete, the crushed material (crushed powder) is removed (S6). However, immediately after stopping the crusher 1, the temperature of the crushed powder has risen slightly.

[0054] Therefore, while preventing the inclusion of air with an argon gas blower, the crushing powder is allowed to cool down. Then, the crushing unit 3 of the crusher 1 is quickly removed from the vacuum desiccator 6 and transferred to the same airtight working box in which the material to be crushed was placed. The crushed powder is then transferred to an airtight bottle that prevents the inclusion of air under an argon gas atmosphere, thus completing the crushing process.

[0055] Furthermore, since the transfer of the crushed magnesium powder into the airtight bottle is carried out under an argon gas atmosphere, the inside of the airtight bottle is filled with argon gas. Storing the powder in this state prevents the crushed magnesium from coming into contact with the atmosphere (mainly oxygen) and undergoing oxidative degradation until the next hydrogenation process is carried out, thereby suppressing a decrease in hydrogenation efficiency.

[0056] On the other hand, in this case, the airtight bottle is filled with argon gas to prevent deterioration of the crushed magnesium. However, it has been confirmed that if stored at room temperature for at least one week, the crushed magnesium does not deteriorate to the point of affecting hydrogenation even when stored in a nitrogen atmosphere using a commercially available nitrogen generator that produces 99.9% pure nitrogen from the atmosphere.

[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, thereby preventing oxidative degradation due to contact with oxygen.

[0058] Next, I will explain the hydrogenation process, but first, I will explain the hydrogenation furnace 8 used for the hydrogenation process.

[0059] (Hydrogenator) Figure 6 is a side view showing a hydrogenation furnace 8 of the first embodiment according to the present invention. Figure 6 shows the heating furnace 81 as a cross-sectional view for easier understanding of the explanation. Furthermore, in Figure 6, for the sake of clarity, the mounting position of clamp 824 is only indicated by a dotted line; the clamp 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 for carrying out the hydrogenation reaction of pulverized magnesium, 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 regulating 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 it.

[0061] The reaction vessel 82 has a flange portion 8211 supported by the heating furnace 81 on its outer circumference at an intermediate position in the vertical direction, and comprises a reaction vessel body 821 with an opening at the top to accommodate crushed magnesium, a lid portion 822 for closing the upper opening, an O-ring 823 positioned on the edge of the opening side of the reaction vessel body 821 and sandwiched between the reaction vessel body 821 and the lid portion 822 to create an airtight seal, and a clamp 824 for fixing the O-ring 823 so as to be pressed by the reaction vessel body 821 and the lid portion 822.

[0062] Furthermore, the lid portion 822 is equipped with an intake / exhaust port 8221 that can be opened and closed by operating the needle valve N1, which is attached to the flexible gas piping FGP.

[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 controller (not shown) that controls the heater section 812 to maintain a set temperature. 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 support the flange section 8211 of the reaction vessel body 821.

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

[0065] The temperature controller includes a temperature measuring unit (for example, 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 regulating tank 83 is a stainless steel tank with a sealed structure for containing gas, and is equipped with a mounting port PT1 for mounting a digital pressure gauge DP for measuring the pressure inside the tank, a hydrogen gas receiving port PT2 for receiving hydrogen gas and equipped with an on / off valve OCB2, an argon gas receiving port PT3 for receiving argon gas and equipped with an on / off valve OCB3, a gas supply port PT4 for which a needle valve N2 is installed and to which a flexible gas pipe FGP is connected for sending the gas inside the tank to the reaction vessel 82, and an exhaust port PT5 for which an on / off valve OCB5 is installed and for connection to a vacuum pump P2 used when replacing the gas inside the tank.

[0067] Furthermore, the hydrogen gas supply to the pressure adjustment tank 83 is configured such that the hydrogen gas, which has been reduced to a pressure of 0.2 to 0.3 MPa (the operating pressure of the mass flow controller) by the pressure reducing valve of the high-pressure hydrogen gas cylinder B2, is supplied via the hydrogen gas mass flow controller MFC-H, which is connected by piping to the hydrogen gas receiving port PT2.

[0068] Furthermore, the supply of argon gas to the pressure adjustment tank 83 is configured such that argon gas, which has been reduced to a pressure of 0.2 to 0.3 MPa (the operating pressure of the mass flow controller) by the pressure reducing valve of the high-pressure argon gas cylinder B3, is supplied via the argon gas mass flow controller MFC-A, which is connected by piping to the argon gas receiving port PT3.

[0069] Furthermore, a sequencer PLC, a controller capable of building control programs, is used to control the gas supply. In Figure 6, the dashed lines connecting the sequencer PLC, 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 includes a direct input mode in which the sequencer PLC controls the operation of a specified mass flow controller (hydrogen gas mass flow controller MFC-H, argon gas mass flow controller MFC-A) by specifying the mass flow controller and flow rate on the sequencer PLC's LCD screen, and a pressure control mode in which the sequencer PLC controls the operation of a specified mass flow controller and upper and lower pressure limits by specifying the mass flow controller and upper and lower pressure limits on the sequencer PLC's LCD screen, 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 a preset flow rate.

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

[0072] (Hydrogenation process) Next, I will explain the specific steps of the hydrogenation process. Figure 7 is a flowchart showing the procedure of the hydrogenation process according to the first embodiment of the present invention. Prior to explaining the hydrogenation process procedure, it should be assumed that the reaction vessel 82 is filled with argon gas at atmospheric pressure from the pressure adjustment tank 83, and that the on / off 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 the closed position. Furthermore, the intake and exhaust ports 8221 of the lid 822 and the needle valves N1 and N2 attached to the gas supply port PT4 are assumed to be 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 822 and the flexible gas piping FGP are disconnected, and the reaction vessel 82 is removed from the hydrogenation furnace 8.

[0074] Although disconnecting the connection would allow air to enter the flexible gas piping FGP, the reaction vessel 82 is not able to receive air because the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 is closed. Similarly, since the needle valve N2 is also closed, no air enters the pressure regulating tank 83.

[0075] (Step 12) Next, the removed reaction vessel 82 is placed in the same airtight work box used earlier in the process of placing the material to be ground into the grinding section 3, as described in the grinding process, and the grinding material (specifically, the ground magnesium) ground in the grinding process is placed into the reaction vessel 82 under an argon gas atmosphere (S12).

[0076] Specifically, the clamps 824 of the reaction vessel 82 are removed inside the airtight work box, the lid 822 is removed from the reaction vessel body 821, and the crushed magnesium is placed into the reaction vessel body 821 through the opening on the top of the reaction vessel body 821. Next, the lid 822 is installed to close the upper opening of the reaction vessel body 821, and the clamp 824 is attached to create a sealed state that prevents outside air from entering the reaction vessel 82.

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

[0078] (Step 13) Next, the reaction vessel 82 containing the crushed magnesium is reattached to the heating furnace 81 (S13). Specifically, as shown in Figure 6, the reaction vessel 82, filled with argon gas, is installed such 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 air mixed in the flexible gas piping FGP, the pressure adjustment tank 83, and the argon gas in the reaction vessel 82 are evacuated, and a vacuum is created to prepare the system for filling with hydrogen gas (S14).

[0080] First, the vacuum pump P2 is activated, and the on / off valve OCB5 attached to the exhaust port PT5 is opened to begin evacuating the argon gas from the pressure regulating tank 83.

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

[0082] Then, we wait in this state for a while until all the air mixed in with the flexible gas pipeline FGP is completely expelled.

[0083] After sufficiently evacuating the system (for example, to a few Pa), the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 is slowly turned to the open position.

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

[0085] (Step 15) Once the reaction vessel 82 is under vacuum, a hydrogenation treatment is carried out by heating the pulverized material (pulverized magnesium) to a temperature at which hydrogenation can proceed under a hydrogen gas atmosphere (S15).

[0086] First, before actually supplying hydrogen gas and performing the hydrogenation treatment, the heater section 812 of the heating furnace 81 is turned ON while the vacuum is still being maintained, and the heating of the crushed material (crushed magnesium) is started. The set temperature of the heater section 812 may be any temperature suitable for heating the crushed material (crushed magnesium) to a temperature suitable for hydrogenation.

[0087] Specifically, when the hydrogen gas pressure is around 90 kPa (approximately 0.9 atmospheres), the hydrogenation reaction slows down rapidly below 140°C, so it is desirable to keep the heating temperature above 140°C. A range of approximately 220°C ± 40°C provides relatively good hydrogenation efficiency. Therefore, in the first embodiment, the set temperature of the heater section 812 is set to the temperature at which the pulverized material (pulverized magnesium) is heated to 220°C.

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

[0089] However, if the amount of fatty acid added is not large, the heat treatment of heating the crushed material (crushed magnesium) while vacuuming can be omitted. In other words, it is also possible to supply hydrogen gas first and then start heating.

[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 hydrogen gas pressure is controlled to approximately 90 kPa (approximately 0.9 atmospheres). The upper and lower limits of the controlled pressure are set to 89 kPa and 91 kPa, respectively. When the output value of the digital pressure gauge DP reaches 91 kPa, the hydrogen gas mass flow controller MFC-H stops operating, and the hydrogen gas supply is halted.

[0092] As hydrogenation progresses, hydrogen gas is incorporated into the pulverized magnesium, causing the pressure in the pressure adjustment tank 83 to decrease, and the output value of the digital pressure gauge DP becomes 89 kPa.

[0093] Then, the hydrogen gas mass flow controller MFC-H is activated 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 hydrogen gas atmosphere pressure at approximately 90 kPa, the hydrogenation treatment is performed for a predetermined time while heating the pulverized material (pulverized magnesium) to approximately 220°C. Then, the heater section 812 of the heating furnace 81 is turned OFF, and the pressure control mode of the sequencer PLC is terminated, ending the hydrogenation treatment.

[0095] (Step 16) After the hydrogenation process is complete, 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 started and the on / off valve OCB5 attached to the exhaust port PT5 is opened.

[0097] After sufficient vacuuming is performed, the on / off valve OCB5 attached to the exhaust port PT5 is closed to stop the operation of the vacuum pump P2, 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] Once the pressure in the pressure adjustment tank 83 and the reaction vessel 82 has been filled with argon gas until the pressure reaches atmospheric pressure, the supply of argon gas is stopped and the on / off 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, and the gas replacement operation is completed.

[0100] (Step 17) After the gas exchange is complete, the final step is to remove the magnesium hydride, which is the material after hydrogenation (S17). Since magnesium hydride is relatively stable in the atmosphere as long as it is not exposed to moisture, it is not necessary to carry out the process of placing the crushed material (crushed magnesium) into the reaction vessel 82 in the airtight working box used for this purpose.

[0101] However, in the first embodiment, just as when the crushed material (crushed magnesium) was placed in the reaction vessel 82, the removal operation is also carried out in an airtight working box, and the magnesium hydride is stored in an airtight bottle filled with argon gas. The removal process is almost identical to the process of placing the crushed material (crushed magnesium) into the reaction vessel 82, simply by reversing the procedure (placing the material from the reaction vessel 82 into the airtight bottle). Therefore, a detailed explanation will be omitted.

[0102] Thus, once the magnesium hydride, the material after hydrogenation, has been removed from the reaction vessel 82, the hydrogenation process is complete.

[0103] Next, we will explain the effects of adding fatty acids during the grinding process. Figure 8 is a graph showing the effect of adding fatty acids during the grinding process. The graph in Figure 8 shows the results after hydrogenation for three samples. The only difference between these samples is the amount of fatty acid added during the grinding process.

[0104] Suitable fatty acids 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, eicosanoic acid, henicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, triacontanoic acid, etc., and in this case, octadecanoic acid is used.

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

[0106] As can be seen on the horizontal axis of the graph, one sample was processed using 0 wt% (0 mass%) of fatty acids, meaning the grinding process was carried out without any addition.

[0107] In another sample, approximately 1.55 g of octadecanoic acid (fatty acid) was added to 50 g of magnesium, so that octadecanoic acid (fatty acid) accounted for approximately 3 wt% (approximately 3 mass%) of the total mass of magnesium and fatty acid combined (approximately 51.55 g). In other words, the amount of octadecanoic acid (fatty acid) added during the grinding process is set to approximately 3% by mass of the total mass.

[0108] Furthermore, for the remaining sample, approximately 2.63g of octadecanoic acid (fatty acid) was added to 50g of magnesium, so that octadecanoic acid (fatty acid) constituted approximately 5 wt% (approximately 5 mass%) of the total mass of magnesium and fatty acid combined (approximately 52.63g). In other words, the amount of octadecanoic acid (fatty acid) added during the grinding process is set to approximately 5% by mass of the total mass.

[0109] The grinding process and the hydrogenation process were as previously described. In the grinding process, the intermittent operation time of the grinder 1 was kept the same for all samples, and the grinding was performed for a total of 12 hours of actual operation time.

[0110] Furthermore, in the hydrogenation process, the heater unit 812 was turned ON while the system was under vacuum, with a temperature setting of 220°C, which is suitable for hydrogenating the pulverized magnesium. The vacuum state was maintained until the set temperature was reached, at which point hydrogen gas was supplied, and the hydrogen gas atmosphere pressure was maintained at approximately 90 kPa (approximately 0.9 atmospheres) while heating (hydrogenation treatment) was carried out for 8 hours.

[0111] Then, after the hydrogen gas pressure reaches approximately 90 kPa and 8 hours have passed, the heater unit 812 is turned OFF, and after the temperature has dropped to room temperature, the hydrogenated pulverized magnesium is removed.

[0112] Subsequently, the hydrogenated pulverized magnesium was sieved, and only particles smaller than 53 μm were subjected to X-ray diffraction (XRD) to determine the hydrogenation rate, that is, the content (wt%) of magnesium hydride in the hydrogenated pulverized magnesium. Although hydrogenation efficiency is thought to be particle size dependent, as explained earlier, the grinding process is carried out using a commercially available grinder 1 used in households, resulting in large variations in particle size. Therefore, the particle size-dependent variations are eliminated by sieving the ground magnesium after hydrogenation and analyzing it in a state where the particle size is relatively uniform.

[0113] As shown in Figure 8, magnesium ground without the addition of octadecanoic acid only achieves a hydrogenation rate of 3.47 wt% even after 8 hours of hydrogenation treatment.

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

[0115] In the first embodiment, as described above, a mill machine is used that grinds the material to be ground while stirring it with the rotation of rotating blades, which are commonly used in households.

[0116] In the case of this type of mill, unlike ball mills or bead mills used to produce fine powders, rigid balls are not used to promote grinding. Therefore, the grinding process does not involve the magnesium being repeatedly stretched and pressed together to form a single mass. Instead, the magnesium is simply pulverized into fragments when it rubs against itself or collides with the rotating teeth. Consequently, it is presumed that the added octadecanoic acid exists only on the surface of the ground magnesium and is not incorporated into the interior.

[0117] From this, it can be inferred that the mechanism by which hydrogenation efficiency is improved is due to some effect of octadecanoic acid on the surface of magnesium. For example, fatty acids have carboxyl groups, and these carboxyl groups 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, which have significantly lower melting points, boiling points, and hardness than metal oxides. Thus, it is presumed that octadecanoic acid is exerting some kind of effect on the surface of magnesium. Furthermore, fatty acids are thought to react with metals themselves, forming metal soaps.

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

[0119] However, by adding octadecanoic acid to magnesium during the grinding process, hydrogenation becomes possible even in a low-pressure hydrogen gas atmosphere, where it has traditionally been difficult to increase the hydrogenation rate in a realistic timeframe.

[0120] Naturally, the hydrogenation of magnesium proceeds from the surface towards the center, and it is thought that the hydrogenation rate reaches 100% when the reaction progresses to the center.

[0121] This suggests that by reducing the particle size of magnesium and shortening the distance to the center where hydrogen needs to penetrate, the hydrogenation reaction can be completed more quickly. As explained earlier, all the samples analyzed in this study were sieved to contain particles smaller than 53 μm. Furthermore, even when the samples were passed through a finer sieve that allows 30 μm particles to pass through, no fine particles were found to have passed through that sieve.

[0122] This indicates that even with particles ranging in size from 30 μm to 53 μm, adding approximately 5 wt% (5 mass%) of octadecanoic acid during the grinding process allows for a hydrogenation rate exceeding 40 wt% after 8 hours of hydrogenation treatment.

[0123] For example, considering a 30 μm particle, for 40 wt% to be hydrogenated, hydrogenation is thought to progress to a depth of about 2 μm from the surface. If the grinding process progresses to about 4 μm, it is expected that an extremely high hydrogenation rate close to 100% can be obtained, even in a low-pressure hydrogen gas atmosphere, which has conventionally been considered difficult to achieve a high hydrogenation rate in a realistic time. Furthermore, grinding to that particle size is sufficient to adequately grind even magnesium, which is soft and difficult to turn into a fine powder.

[0124] Therefore, if the amount of octadecanoic acid (fatty acid) added in the grinding process is 5% by 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 grinding particle size and within 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 pulverized magnesium is highly reactive, it undergoes rapid oxidative degradation by oxygen, which can prevent the hydrogenation reaction from occurring. Therefore, it is important to keep the pulverized magnesium from coming into contact with oxygen until the hydrogenation process is complete.

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

[0127] Figure 9 is a graph showing the decomposition boundary line BL for magnesium hydride, determined by thermodynamic calculations. The advantages of this method in terms of temperature will be explained with reference to this graph. The temperature at this decomposition boundary is sometimes referred to as the decomposition boundary temperature. The graph shown in Figure 9 shows the pressure of a hydrogen gas atmosphere (in Pa) on the vertical axis and the temperature (in °C) on the horizontal axis. It graphs the lowest temperature at which magnesium hydride decomposition begins at each pressure.

[0128] In other words, on the right side (high temperature side) of the magnesium hydride decomposition and formation boundary line BL, magnesium hydride decomposes into magnesium and hydrogen gas, while on the left side (low temperature side), decomposition of magnesium hydride does not occur, and if magnesium and hydrogen gas are present, the formation reaction to produce magnesium hydride proceeds.

[0129] In the hydrogenation example explained earlier, the hydrogen gas atmosphere pressure is set to approximately 90 kPa, which is slightly lower than 100,000 Pa (100 kPa). As a result, the temperature at the magnesium hydride decomposition boundary line BL is around 280°C.

[0130] However, since the actual heating temperature is around 220°C, it is sufficient to use a temperature approximately 60°C lower than the temperature at the magnesium hydride decomposition boundary line BL.

[0131] From this, for example, in the case of processing in a hydrogen gas atmosphere of 5 atm (5 atmospheres) as shown by the dotted line on the graph, the temperature on the magnesium hydride decomposition and formation boundary line BL is approximately 350°C, so it can be considered that the actual heating temperature can be 300°C or lower.

[0132] On the other hand, as shown in prior art literature, if the process is carried out at a temperature about 50°C higher than the temperature on the magnesium hydride decomposition boundary line BL, the temperature will have to be heated to over 400°C, in which case radiant heat will be dominant.

[0133] While reaction vessel 82 is typically made of metal materials such as stainless steel, using stainless steel reflects radiant heat, which is thought to reduce heat transfer efficiency and increase energy loss. Therefore, by performing processing in the low-temperature range where radiant heat is not dominant, as in this method, it is possible to perform a more energy-efficient hydrogenation process.

[0134] Furthermore, since this method allows processing at relatively low pressure, there is no need to increase the thickness of the reaction vessel 82 for pressure resistance. This allows for good heat transfer and efficient heating of the pulverized magnesium, resulting in energy efficiency.

[0135] On the other hand, thermodynamic calculations suggest that magnesium hydride can exist stably even at low temperatures. However, thermodynamic calculations lack a reaction rate factor, and as mentioned earlier, when the heating temperature of magnesium falls below 140°C, the pressure decrease observed in the hydrogenation process due to the absorption of hydrogen gas into magnesium slows down considerably.

[0136] Therefore, in the hydrogenation process, it is preferable to heat the magnesium to a temperature of 140°C or higher.

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

[0138] Therefore, the hydrogenation process is preferably carried out by heating the pulverized magnesium to a temperature of 140°C or higher and below the decomposition temperature of magnesium hydride under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower. This allows the process to be carried out at a temperature range 50°C or higher below 400°C, where the effect of radiant heat becomes strong, and also eliminates the need to increase the thickness of the reaction vessel 82, resulting in good heat transfer and an energy-efficient process. In addition,

[0139] For example, if the hydrogen gas pressure in the hydrogenation process is less than 0.2 MPa, there is no legal requirement for periodic inspections. Furthermore, since higher pressures, such as 30 kPa (approximately 0.3 atmospheres) or more, are preferable for promoting hydrogenation, it is more preferable to heat and process the pulverized 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 was used as the fatty acid, but in the second embodiment, we will describe the case in which dodecanoic acid is used as the fatty acid. In the second embodiment, as in the first embodiment, dodecanoic acid was added to the magnesium during the grinding process so that the amount of dodecanoic acid added to the total mass of magnesium and dodecanoic acid combined was approximately 5 wt% (approximately 5% by mass: 2.63 g) for 50 g of magnesium.

[0141] Furthermore, the pulverizer 1 and the pulverizing conditions using the pulverizer 1 are the same as in the first embodiment, and the hydrogenation furnace 8 in which the hydrogenation process was carried out is also the same as in the first embodiment.

[0142] The pulverized magnesium was then divided into two portions. One portion was subjected to a hydrogenation process under the exact same conditions as in the first embodiment. The hydrogenated pulverized magnesium was then sieved, and only the particles smaller than 53 μm were subjected to an X-ray diffractometer (XRD) to determine the magnesium hydride content (wt%). As a result, the hydrogenation rate was 51.3 wt%, which was a better result than that obtained with octadecanoic acid. This indicates that the fatty acid added during the grinding process does not necessarily have to be octadecanoic acid.

[0143] However, shorter alkyl chains result in weaker hydrophobicity and increased water absorption, requiring careful handling to prevent water absorption. Conversely, longer alkyl chains increase the melting point, preventing the fatty acids from melting during the pulverization process and making it difficult to add them to the magnesium surface.

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

[0145] Meanwhile, for the remaining half of the crushed magnesium, after evacuating the reaction vessel 82, hydrogen gas was filled to 90 kPa before turning on the heater unit 812. Then, the heater unit 812 was turned on, and a hydrogenation treatment was carried out for 8 hours once the set temperature was reached. In other words, the only difference is that hydrogen gas was supplied before turning on the heater unit 812; everything else is the same.

[0146] Furthermore, in the case where hydrogen gas was supplied before turning on the heater unit 812 to perform the hydrogenation treatment, the pulverized magnesium after hydrogenation was sieved, and only those particles smaller than 53 μm were subjected to an X-ray diffractometer (XRD) to determine the magnesium hydride content (wt%). The hydrogenation rate was a somewhat low 29.8 wt%.

[0147] Therefore, it is preferable that the hydrogenation process includes a heat treatment in which the crushed magnesium is heated while under vacuum before the hydrogenation treatment.

[0148] (Third embodiment) In the first and second embodiments, the case in which a household mill machine, commonly used in ordinary households, is used as the grinder 1 to powder tea leaves, coffee beans, etc. was shown. Unlike industrial mills, this home-use mill will break down if it is overloaded. Therefore, when the temperature rises during grinding, the fatty acids dissolve and become highly viscous. However, if the amount of added fatty acids exceeds 5 wt%, the viscosity becomes extremely high, which can cause the material to become immobile.

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

[0150] (Crusher) Figure 10 is a perspective view of the pulverizer S1 used in the pulverization process of the third embodiment according to the present invention, Figure 11 is a perspective view showing the hood S3 of the pulverizer S1 of the third embodiment according to the present invention in an open state, Figure 12 is a perspective view of the pulverization container S4 of the third embodiment according to the present invention, and Figure 13 is an exploded perspective view of the pulverization 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 body S2 that controls the rotation of a detachably fixed crushing container S4 (see Figure 11), and a hood S3 that is connected to the crusher body S2 by a hinge structure so as to be openable and closable and capable of covering the crushing container S4.

[0152] As shown in Figure 10, the main body S2 of the crusher includes a condition input unit 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, which constitutes a storage section for grinding material (not shown) and spherical grinding media (not shown) that promote grinding, and a lid S42 that closes the upper opening of the grinding container body S41.

[0154] Furthermore, as shown in Figure 13, the grinding container body S41 is provided with a groove S411 on the upper opening edge for positioning an O-ring S5, and a screw thread hole S412 formed radially outward from the groove S411 for screwing. Furthermore, there are a total of four screw threading holes S412, spaced at 90-degree intervals in the circumferential direction.

[0155] On the other hand, the lid portion S42 has a through hole S421 on its outer surface (see Figure 12) which has a counterbore for accommodating the head of a screw. Furthermore, this through-hole S421 is a through-hole S421 for passing the threaded portion of the screw through to the grinding container body S41 when screwing the lid S42 to the grinding container body S41. Therefore, the position of the through-hole S421 (distance from the center, etc.) corresponds to the screw threaded 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 screwed into the screw threading hole S412 of the grinding container body S41 through the through hole S421 from the lid S42 side, so that the lid S42 presses the O-ring S5 toward the grinding container body S41 side, and the grinding material (not shown) and spherical grinding media (not shown) that promote grinding are placed inside the grinding container S4 in a completely sealed state.

[0157] After placing the grinding material (not shown) and spherical grinding media (not shown) that promote grinding into the grinding container S4, as shown in Figure 11, the grinding container S4 is fixed to the grinder body S2, as shown in Figure 10, the hood S3 is closed, the condition input unit S21 is operated to input 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 starts rotating, and within the sealed grinding container S4, the rotational force vigorously agitates the rigid balls (for example, 5mmφ high-hardness balls (SUS440C, chromium steel)) that promote grinding and the magnesium to be ground, causing the grinding to proceed.

[0159] Furthermore, since the grinding container S4 corresponds to the grinding section 3 of the grinder 1 in the first and second embodiments, and the basic operating procedures for the grinding process and the hydrogenation process are almost the same as in the first and second embodiments, the differences will be explained below, and explanations of similar points may be omitted.

[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 container S4 itself for crushing. Therefore, the grinding container S4 does not have a mechanical stirring structure inside, and the grinding container S4 is configured such that a complete airtight seal is achieved between the grinding container body S41 and the lid S42 by an O-ring S5. Therefore, there is no need to worry about outside air being drawn into the grinding container S4 during the grinding operation.

[0161] Therefore, the process of placing the rigid balls and the magnesium to be ground (including the fatty acid for addition) into the grinding container S4 for grinding, and the process of removing the ground magnesium, are carried out in an argon gas atmosphere inside an airtight work box, as in the first and second embodiments. However, the planetary ball mill device itself is placed in the ambient air while grinding is performed.

[0162] Next, we will describe a specific example of the third embodiment. In the third embodiment, magnesium with an average particle size of approximately 180 μm was used for grinding.

[0163] For the grinding conditions, rigid balls made of high-hardness stainless steel (SUS440C) with a diameter of 5 mm were placed so as to occupy 1 / 3 of the internal volume of the closed grinding container S4, and similarly, 70 g of magnesium was placed so as to occupy 1 / 3 of the internal volume. As for the fatty acids, octadecanoic acid in an amount equivalent to approximately 13 wt% of the total mass of magnesium and fatty acids was placed in the grinding container S4 for grinding. Then, the machine was operated at a rotation speed of 330 rpm for one hour, followed by a one-hour stop, and this cycle was repeated 24 times, so that the total time the grinding container S4 was rotating for grinding was 24 hours.

[0164] The reason for the one-hour shutdown after one hour of operation is to suppress the temperature rise of the grinding container S4 used for grinding, and the manufacturer recommends using it so that the temperature does not exceed 100°C.

[0165] In this way, 13 wt% (13 mass%) of octadecanoic acid was added to produce pulverized magnesium, and the hydrogenation process was carried out using this pulverized magnesium. Specifically, the hydrogenation process is similar to that of the first embodiment, but while the first embodiment involved an 8-hour hydrogenation treatment, the third embodiment involved a 4-hour hydrogenation treatment.

[0166] Then, similar to the first embodiment, the hydrogenated pulverized magnesium was sieved, and only those particles smaller than 53 μm were subjected to an X-ray diffractometer (XRD apparatus) to determine the hydrogenation rate, that is, the content (wt%) of magnesium hydride in the hydrogenated pulverized magnesium. The result was 39.5 wt%.

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

[0168] On the other hand, adding too much fatty acid may cause a thick layer of fatty acid to form on the surface of the crushed magnesium, potentially inhibiting hydrogenation. Therefore, it is considered best to limit the amount of fatty acid added to about 15% by mass or less of the total mass of magnesium and fatty acid combined.

[0169] In planetary ball mill devices, generally, the smaller the diameter of the rigid balls used for grinding, the smaller the limit particle size that can be ground. Therefore, although 5 mmφ high-hardness balls were used in the third embodiment, it is thought that the particle size of magnesium after grinding can be further reduced by using 3 mmφ high-hardness balls or 1.5 mmφ high-hardness balls for grinding.

[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 yields even better results than the first embodiment. It is expected that, similar to the first embodiment, an extremely high hydrogenation rate can be obtained within a sufficiently realistic range of pulverized particle size and within a realistic hydrogenation time.

[0171] Furthermore, the amount of fatty acid added to magnesium during the grinding process is considered to be more preferable in the following order: 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, relative to the total mass of magnesium and fatty acids combined. However, since excessive addition can lead to adverse effects, it is considered best to limit the amount of fatty acids 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 acids 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, it was further described that reducing the particle size of the magnesium in the grinding process is a method to increase the hydrogenation rate, but the grinding process and hydrogenation process may also be carried out repeatedly.

[0173] After the initial grinding and hydrogenation processes, the ground magnesium undergoes hydrogenation to a certain depth from the surface, forming a layer of magnesium hydride. Furthermore, since the magnesium hydride layer is a layer where demetallation has progressed, it is easily pulverized. With short-time pulverization, the magnesium hydride layer becomes a powder, exposing the metallic magnesium portion inside. It is believed that further pulverization of this metallic magnesium portion efficiently leads to the fine powderization of magnesium.

[0174] Therefore, if the pulverized magnesium that has already undergone hydrogenation treatment is subjected to the pulverization process again, it will be further pulverized. By performing hydrogenation treatment on this further pulverized magnesium, magnesium hydride with a higher hydrogenation rate can be obtained.

[0175] In this second grinding process, the magnesium hydride layer is removed by grinding, resulting in a finer powder of metallic magnesium that has undergone further grinding. It is believed that adding fatty acids during the grinding process makes the metallic magnesium powder more susceptible to hydrogenation. Therefore, it is desirable to add fatty acids in the second and subsequent grinding processes as well.

[0176] In this second grinding process, the magnesium, including the magnesium hydride portion, is ground. In this case, it is considered sufficient to add fatty acids if they are 5% or more of the total mass, which is the sum of the mass of magnesium (mass of magnesium excluding the magnesium hydride portion) and the mass of fatty acids.

[0177] On the other hand, since a layer of magnesium hydride is formed on the surface of the pulverized magnesium after hydrogenation treatment, it is expected to have the effect of preventing the unhydrogenated metallic magnesium inside from being oxidized by oxygen in the atmosphere. However, since the magnesium pulverized immediately after the second pulverization process is not protected by such a layer of magnesium hydride, it is important to prevent the magnesium pulverized after the second pulverization process from coming into contact with oxygen until the end of the second hydrogenation process in order to promote the hydrogenation reaction.

[0178] Therefore, the method for producing magnesium hydride may include a grinding step in which a fatty acid is added and the magnesium is ground, and a hydrogenation step in which the ground magnesium is heated to a temperature of 140°C or higher and below the decomposition temperature of magnesium hydride under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower to hydrogenate it. The grinding and hydrogenation steps may be combined into a series and repeated multiple times. However, even in this case, the amount of fatty acid added in the grinding step of each grinding and hydrogenation step should be 5% by mass or more of the total mass of magnesium and fatty acid combined, and the ground magnesium should not be exposed to oxygen until the end of the hydrogenation step in each grinding and hydrogenation step.

[0179] Thus, the present invention is not limited to specific embodiments, and modifications and improvements made as appropriate 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 main body 21 Push Buttons 3. Grinding section 4. Grinding Unit Body 41 Agitation and grinding teeth 42 Threaded grooves 5 Lid 51. Raigōzan 6. Vacuum Desiccator 61 Container body 62 Lid 621 Pressure Gauge 622, 623 Intake and exhaust ports 63 Patching Tablets 7. Oxygen concentration meter 8 Hydrogen reactor 81 Heating furnace 811 Insulated enclosure 812 Heater section 82 Reaction vessel 821 Reaction vessel body 8211 Flange section 822 Lid 8221 Intake and Exhaust Ports 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 valves P1, P2 Vacuum Pumps PLC (Programmable Logic Controller) PT1 mounting port PT2, PT3 receiving ports PT4 gas supply port PT5 Exhaust Port S1 Crusher S2 Crusher main body S21 Condition Input Section S22 Emergency Stop Button S3 Hood S4 Grinding container S41 Grinding container body S411 Groove S412 Screw thread hole S42 Lid S421 Through hole S5 O-ring

Claims

1. A method for producing magnesium hydride, A grinding process in which fatty acids are added and magnesium is ground, The invention comprises a hydrogenation step in which the pulverized magnesium is heated to a temperature of 140°C or higher and below the decomposition temperature of magnesium hydride under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower, thereby undergoing hydrogenation treatment. The amount of the fatty acid added in the grinding step is 5% by mass or more of the total mass of the magnesium and the fatty acid combined. The aforementioned fatty acid is a straight-chain fatty acid having 7-30 carbon atoms. A method for producing magnesium hydride, wherein the pulverized magnesium is kept from coming into contact with oxygen until the end of the hydrogenation step.

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

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

4. A method for producing magnesium hydride according to any one of claims 1 to 3, wherein the grinding and hydrogenation steps, which are combined as a series of steps from the grinding step to the hydrogenation step, are performed multiple times.

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

6. In the aforementioned grinding process, the magnesium surface is exposed. A method for producing magnesium hydride according to any one of claims 1 to 5.

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