A method for the preparation of magnesium hydride

Abstract

The application relates to the technical field of hydrogen storage materials, and provides an efficient preparation method of magnesium hydride as a hydrogen storage medium. In the method, elemental magnesium powder and hard particles such as silicon carbide are uniformly mixed under the protection of argon; then the mixture is placed in a ball milling device, mechanical ball milling is carried out under a specific hydrogen pressure environment, and finally the target material magnesium hydride is collected. The core of the method is to introduce hard particles such as silicon carbide as a micro-processing medium. In the ball milling process, the particles can effectively cut the dense magnesium hydride layer formed on the surface of magnesium particles from the microscale, so that a large number of defects such as crystal lattice vacancies and dislocations are introduced into the material. The defects significantly enhance the diffusion dynamics of hydrogen atoms, provide an efficient channel for the continuous combination of hydrogen and unreacted magnesium, fundamentally accelerate the progress of the hydrogenation reaction, and significantly improve the generation efficiency of magnesium hydride. The method is simple in process and low in cost, and is suitable for large-scale application.

Description

Technical Field

[0001] This application relates to the field of hydrogen storage materials and their preparation technology, specifically to a method for preparing magnesium hydride. Background Technology

[0002] Hydrogen, as a clean and renewable energy source, is considered one of the most promising energy carriers. Among numerous hydrogen storage materials, magnesium hydride (MgH2) has attracted much attention due to its excellent hydrogen storage capacity, with a specific density of 7.6 wt% and a bulk density of 107 kg·H2 / m³. 3 Both of these figures indicate its enormous potential in energy storage. Current research mainly focuses on the hydrogen desorption modification of magnesium hydride, while research on its synthesis is relatively limited. However, the research needs of laboratories and the applications of magnesium hydride in energy, agriculture, medicine, environmental science, and other fields all necessitate the exploration of low-cost, high-efficiency synthesis methods.

[0003] Among the many existing synthesis methods, ball milling is undoubtedly one of the most feasible and safest. It is widely used in the synthesis and modification of magnesium-based hydrogen storage materials. This method can reduce particle size to the submicron level and ensure uniform distribution of the catalyst in the matrix, thereby improving the hydrogen storage performance of magnesium-based materials.

[0004] Currently, the ball milling process for synthesizing magnesium hydride faces two main problems: 1. Long synthesis cycle: Numerous experiments have shown that the production cycle for ball milling magnesium hydride exceeds 48 hours. This is primarily due to the high kinetic energy barrier of the reaction between magnesium and hydrogen, requiring sufficient external energy to overcome this barrier. 2. Low product purity: Ball milled magnesium hydride has a capacity limit; even with indefinitely extended milling time, the product capacity cannot reach the theoretical hydrogen absorption capacity. Analysis suggests that during ball milling, hydrogen first reacts with magnesium atoms on the particle surface to form a magnesium hydride phase, which grows and surrounds the entire particle. Subsequently, the magnesium hydride phase grows into the particle interior. However, the compressive stress generated by the ball milling collisions makes the magnesium hydride on the particle surface extremely dense, hindering hydrogen atom diffusion and ultimately preventing the achievement of the theoretical hydrogen absorption capacity.

[0005] Some studies have attempted to autocatalyze the synthesis of magnesium hydride by adding magnesium hydride itself, but this still fails to reach the theoretical capacity. Furthermore, ball milling can improve the purity of the magnesium hydride product, but the synthesis cycle still exceeds 48 hours.

[0006] Despite the advantages of ball milling technology, including good safety, excellent sample performance, and low equipment cost, its low throughput and high production time significantly limit its industrialization. Furthermore, large industrial ball mills operate at relatively low speeds. Achieving magnesium hydride synthesis at even lower speeds is another challenge that needs to be overcome in the ball milling process. Summary of the Invention

[0007] The technical problem to be solved by this application is to provide a method for preparing magnesium hydride as a hydrogen storage medium, wherein magnesium metal can be hydrogenated by ball milling at low speed to obtain magnesium hydride, which aims to improve the production efficiency of magnesium hydride.

[0008] This application is achieved through the following technical solution: (1) Mix elemental magnesium powder with hard particles under argon atmosphere and load them into a ball mill jar; (2) Use a vacuum pump to remove the argon from the ball mill jar and fill it with hydrogen at a certain pressure; (3) Perform mechanical ball milling on the mixture under set parameters; (4) Take out the ball-milled material under argon atmosphere to obtain magnesium hydride.

[0009] The hard particles are one of silicon carbide, silicon nitride, and tungsten carbide.

[0010] The hard particles are powders with a diameter of 0.04 to 20 µm. Preferably, the particle size of the hard particles is 0.04 to 10 µm; more preferably, it is 0.04 to 2 µm.

[0011] The average particle size of the hard particles is smaller than the initial average particle size of the magnesium powder used.

[0012] The hard particles have a hardness HV≥1500.

[0013] The added hard particles account for 2.0% to 5.0% of the total weight.

[0014] The hydrogen pressure is 10–20 bar.

[0015] The ball milling parameters are: rotation speed 200-300 r / min, time 8-24 h, and ball-to-material ratio 50:1-200:1.

[0016] In the synthesis method described in this invention, the mechanical ball milling process provides crucial energy for the combination of magnesium (Mg) powder and hydrogen (H2) to overcome the kinetic energy barrier of the reaction. However, in the initial reaction stage, a dense layer of magnesium hydride (MgH2) product rapidly forms on the surface of the magnesium particles. This MgH2 surface layer acts as a diffusion barrier, severely hindering the further diffusion and penetration of hydrogen into the interior of the magnesium particles. This makes it difficult for unreacted magnesium inside to continue hydrogenation, limiting the overall hydrogenation efficiency and the final hydrogen storage capacity. This is the core bottleneck problem faced by traditional pure magnesium hydrogenation ball milling processes. Existing research mainly focuses on adding catalysts (such as Ni, TiO2, etc.) to increase the diffusion rate of hydrogen atoms in magnesium hydride, thereby shortening the time required for hydrogen atoms to cross the existing magnesium hydride layer and thus improving the efficiency of the hydrogenation reaction.

[0017] This invention effectively alleviates the aforementioned diffusion barrier problem by introducing specific hard particles as a grinding aid, thereby continuously disrupting the existing magnesium hydride layer. Its mechanism of action is mainly reflected in the following two synergistic and crucial aspects: 1. Physical damage and inhibition of the surface hydride layer: Under the intense collision and shear stress generated by high-speed ball milling, hard particles (such as SiC) continuously perform micro-mechanical cutting and impact peeling on the surface of magnesium / magnesium hydride composite particles. This action can effectively break, remove, or significantly weaken the initially formed dense MgH2 surface layer, eliminate or greatly reduce its inhibitory effect on hydrogen diffusion into the magnesium matrix, and keep the fresh magnesium surface continuously exposed to the hydrogen atmosphere.

[0018] 2. Defect Engineering Promotes Hydrogen Diffusion: The introduction of hard particles not only acts on the surface, but their micro-cutting action also introduces high-density lattice defects (such as dislocations and vacancies) and plastic deformation in the near-surface region of Mg / MgH2 particles. These microstructural changes (especially the significant increase in dislocation density) provide a large number of low-energy "fast channels" for the diffusion of hydrogen atoms into the magnesium matrix, greatly accelerating the penetration rate and reaction kinetics of hydrogen atoms into the particle interior.

[0019] The effects of the two aspects mentioned above—(1) eliminating diffusion physical barriers and (2) constructing a fast hydrogen diffusion channel—are not simply superimposed, but rather achieve a synergistic enhancement effect through the ball milling process. The continuous action of the hard particles ensures that the surface of the magnesium particles remains in an activated state throughout the entire ball milling reaction, significantly reducing the internal hydrogen diffusion resistance, thereby achieving an efficient conversion of magnesium powder into magnesium hydride.

[0020] Meanwhile, the added hard particles (especially SiC) exhibit excellent chemical stability and structural integrity under the ball milling conditions and hydrogen atmosphere. They function solely as physical grinding aids and defect introducers, without undergoing significant chemical reactions with magnesium or hydrogen. Therefore, the introduction of hard particles does not introduce impurity phases or consume active hydrogen storage components, thus ensuring that the final magnesium hydride product has high purity and excellent hydrogen storage performance. This is also one of the important reasons why this invention can significantly improve hydrogen storage capacity.

[0021] The beneficial results of this application are as follows: Mild and efficient reaction conditions, high product purity: This invention successfully overcomes the dependence of traditional direct hydrogenation of magnesium powder on harsh conditions of high temperature and high pressure. By optimizing the mechanical ball milling process and introducing the synergistic effect of hard particles (such as SiC), efficient and deep hydrogenation of magnesium powder can be achieved in just 24 hours at a hydrogen pressure of about 10-20 bar and a relatively low rotation speed of about 200 r / min. This invention overcomes the problems of long reaction time and low product purity of traditional ball milling methods, significantly reduces equipment requirements and operational risks (avoiding the safety hazards caused by high rotation speed, high temperature, and high pressure), and contains only MgH2 and inert hard particle phase, directly ensuring its excellent hydrogen storage capacity (up to about 7.5 wt%).

[0022] The selection of hard particles is flexible and reliable: the selected hard particles (especially silicon carbide SiC) are widely available, relatively low in cost, and easy to obtain, facilitating large-scale applications. For example, XRD characterization ( Figure 3 As confirmed by [the study], these hard particles exhibit excellent chemical stability and structural integrity during the ball milling hydrogenation process, and do not chemically react with the reactants (Mg, H2). They function solely as physical grinding aids and defect engineering mediators, without introducing impurity phases or consuming effective hydrogen storage components into the final product. This ensures that the intrinsic hydrogen storage performance of the material is not damaged or even improved, and does not adversely affect any subsequent application stages of the material.

[0023] The process is simple and controllable, and easily scalable: the entire process flow is concise (mixing-ball milling hydrogenation-removal), convenient to operate, and has low equipment requirements. The hydrogen pressure range (10–20 bar) and ball milling speed (200 r / min) used are within the parameter range that can be achieved by modifying conventional equipment, without the need for specially customized high-pressure or ultra-high-speed equipment. Combined with the stability of hard particles and mild reaction conditions, this invention has excellent scalability and industrial production potential, providing a practical technical route for the large-scale preparation of high-performance magnesium hydride hydrogen storage materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 These are schematic diagrams of X-ray diffraction tests for Embodiments 1 and 4 of this application; Figure 2This is a programmed temperature rise desorption experiment curve of the ball-milled samples of Examples 1, 2 and Comparative Example 1 of this application; Figure 3 These are SEM morphology diagrams of the ball-milled samples of Example 1 and Comparative Example 1 of this application; Figure 4 This is a schematic diagram comparing the surface roughness of ball-milled samples of Comparative Example 1 and Example 3 of this application under an atomic force microscope; Figure 5 This is a programmed temperature rise desorption experiment curve of the ball-milled samples of Example 1 and Comparative Example 2 of this application; Figure 6 This is a programmed temperature rise desorption experiment curve of the ball-milled samples of Example 1 and Comparative Example 3 of this application; Figure 7 This is a programmed temperature rise desorption experiment curve of the ball-milled samples of Example 1 and Comparative Example 4 of this application; Figure 8 This is a programmed temperature rise desorption experiment curve of the ball-milled samples of Example 1 and Comparative Example 5 of this application. Detailed Implementation

[0026] Magnesium hydride, as a highly promising solid-state hydrogen storage material, has relatively low raw material costs (magnesium powder and hydrogen). However, existing industrial production processes for magnesium hydride heavily rely on harsh conditions of high temperature and high pressure, resulting in large equipment investments, high operational risks, and persistently high production costs (commercial price approximately 3600 RMB / kg), thus limiting its large-scale application. Developing a mild, safe, and low-cost magnesium hydride preparation technology is a crucial issue that urgently needs to be addressed.

[0027] Mechanical ball milling is widely studied for the preparation of magnesium hydride due to its safety and ease of scale-up. However, traditional magnesium powder ball milling processes are inefficient at lower rotational speeds (e.g., 200–300 r / min) and mild hydrogen pressures (e.g., 10–20 bar), failing to yield high-purity magnesium hydride. The core bottleneck lies in the fact that the dense magnesium hydride (MgH2) surface layer formed in the initial stage of the reaction severely hinders the diffusion of hydrogen into the magnesium particles, making it difficult for the internal magnesium to continue hydrogenation, resulting in insufficient product purity.

[0028] To overcome the aforementioned technical challenges, this invention provides an innovative method for preparing magnesium hydride. Its core lies in introducing specific hard particles as reaction promoters during the ball milling and hydrogenation process of magnesium powder. The basic principle is to utilize the high hardness of the hard particles to exert continuous micro-mechanical action on the surface of Mg / MgH2 particles during ball milling. This action effectively disrupts the initial MgH2 surface layer that hinders hydrogen diffusion and introduces high-density lattice defects (such as dislocations) in the near-surface region, thereby synergistically promoting the diffusion and reaction of hydrogen into the particle interior. This achieves high-purity, high-capacity magnesium hydride under relatively mild process conditions (low rotation speed, moderate hydrogen pressure).

[0029] To achieve the above objectives, this application provides a method for preparing magnesium hydride as a hydrogen storage medium, wherein magnesium metal is hydrogenated by ball milling at low speed to obtain magnesium hydride.

[0030] The preparation method includes the following steps: (1) mixing elemental magnesium powder with hard particles under argon atmosphere protection; (2) using a vacuum pump to remove argon from the ball mill jar and filling it with hydrogen at a certain pressure; (3) mechanically ball milling the mixture under set parameters; (4) taking out the ball-milled material under argon atmosphere to obtain magnesium hydride.

[0031] Specifically, commercially available magnesium powder and hard particles are mixed in a ball mill jar under an argon atmosphere, filled with a certain amount of hydrogen, and then placed on a planetary ball mill for grinding. The resulting material is magnesium hydride.

[0032] The hard particles are one of silicon carbide, silicon nitride, and tungsten carbide.

[0033] The selection of hard particles requires sufficient hardness, and the size of the hard particles can be selected within the range of 0.04 to 20 µm. Preferably, the particle size is no greater than 10 µm; more preferably, it is no greater than 2 µm. If the particle size is too large, such as approaching or exceeding the particle size of the original magnesium powder, an effective micro-cutting effect cannot be achieved. Instead, steric hindrance will hinder the effective action of the ball milling media on the magnesium powder, reducing the production efficiency of magnesium hydride.

[0034] The average particle size of the hard particles is smaller than the initial average particle size of the magnesium powder used, for the following reasons: (1) Enhanced mechanical crushing effect. The main function of hard particles is as a medium for transmitting mechanical force during ball milling. When the average particle size of hard particles is smaller than the initial average particle size of the magnesium powder used, the relative impact force between particles is greater. Smaller hard particles will collide and rub more with magnesium powder particles, effectively transferring mechanical energy to the magnesium powder particles, improving crushing efficiency, and thus accelerating the crushing and refining process of magnesium powder. Smaller hard particles can produce a more delicate and efficient crushing effect during ball milling, promoting a more uniform and in-depth hydrogenation reaction of magnesium powder. At the same time, if the particle size of hard particles is large, it may cause the gaps between magnesium powder particles to increase, thereby reducing the friction between particles during ball milling and affecting the crushing effect. Smaller hard particles can effectively avoid this problem, making the crushing and hydrogenation of magnesium powder more uniform.

[0035] (2) Increasing the contact area between magnesium powder and hydrogen. During ball milling, hard particles not only break down the magnesium powder but also help disperse the magnesium powder particles. The average particle size of the hard particles is smaller than the initial average particle size of the magnesium powder used, which can more effectively refine the magnesium powder, increase its surface area, and thus provide more active sites for hydrogen reaction. By refining the magnesium powder particles, more contact area and reaction sites can be provided, which helps the reaction between hydrogen and magnesium powder to proceed more fully, enhances the efficiency of the hydrogenation reaction, and thus accelerates the formation of magnesium hydride.

[0036] (3) Reduce wear and grinding force waste. When the average particle size of hard particles is larger than the initial average particle size of the magnesium powder used, their friction and collision forces may be concentrated in a single location during ball milling, leading to excessive wear in local areas and affecting the uniformity of the ball milling process. When the average particle size of hard particles is smaller than the initial average particle size of the magnesium powder used, the hard particles can be more evenly distributed during the ball milling process, ensuring that the wear is uniform throughout the entire ball milling process.

[0037] (4) Avoid uneven grinding. If the average particle size of the hard particles is larger than the initial average particle size of the magnesium powder used, it may lead to strong local wear, which may prevent the magnesium powder in some areas from receiving effective mechanical action, thus affecting the uniformity of the reaction. Smaller particles help maintain the uniformity of the ball milling process.

[0038] (5) Optimize the relative motion between hard particles and magnesium powder. Hard particles with a smaller diameter than magnesium powder have more flexible relative motion with magnesium powder, which can generate more collisions and friction. This rapid and efficient relative motion can effectively promote the crushing of magnesium powder particles and better transfer hydrogen to the surface of magnesium powder particles, thereby accelerating the hydrogenation reaction.

[0039] (6) Prevent magnesium powder agglomeration. Hard particles with a particle size larger than that of magnesium powder may cause magnesium powder to agglomerate during ball milling. Smaller hard particles can effectively disperse magnesium powder through continuous friction and collision, thus avoiding agglomeration and maintaining the dispersed state of magnesium powder, which helps hydrogen gas to contact magnesium powder better.

[0040] The hard particles have a hardness of HV≥1500 to ensure effective micro-cutting of the magnesium matrix during ball milling, fully promote hydrogen diffusion and reaction, and improve hydrogenation efficiency.

[0041] The amount of hard particles added is 2.0% to 5.0% of the total weight of the mixture of elemental magnesium powder and hard particles. Too high a proportion will result in a loss of mass in the generated magnesium hydride, while too low a proportion will result in minimal cutting effect on the magnesium powder / magnesium hydride, and will not have a positive impact on the formation efficiency of magnesium hydride.

[0042] The hydrogen pressure is 10–20 bar for the following reasons: (1) Increase hydrogen concentration: The higher the hydrogen pressure, the higher the hydrogen molecule density, the greater the chance of contact with magnesium powder, which in turn promotes the adsorption of hydrogen and the increase of reaction rate.

[0043] (2) Reaction equilibrium: Based on the nature of gaseous reactions, hydrogen can react more effectively with magnesium powder under higher pressure, thereby promoting the hydrogenation process. Under low pressure conditions, the reaction may be slower or even stop.

[0044] (3) Avoid overpressure damage: If the hydrogen pressure is too high, it may cause excessive pressure on the ball mill jar, affecting the safety and stability of the equipment. Therefore, setting a reasonable hydrogen pressure range (10-20 bar) can balance the reaction rate and safety.

[0045] Optionally, the ball milling parameters are a rotation speed of 200–300 r / min and a time of 8–24 h. Too low a rotation speed or time provides limited mechanical stress, which cannot reach the energy barrier for the transformation of magnesium to magnesium hydride, resulting in incomplete reaction; too high a speed will cause particle agglomeration, affecting the subsequent hydrogen release performance.

[0046] The ball-to-material mass ratio in ball mills is 50:1 to 200:1. The reasons are as follows: (1) Impact on crushing effect and reaction rate: A higher ball-to-material mass ratio can increase the impact force of the ball milling media on the sample, thereby accelerating the crushing of magnesium powder and exposing more active sites on the surface of magnesium powder, which is conducive to the reaction between magnesium and hydrogen. Therefore, controlling the ball-to-material mass ratio within an appropriate range can help improve the efficiency of hydrogenation reaction and the purity of the product.

[0047] (2) Controlling heat generation: Heat is generated during ball milling. A higher ball-to-material mass ratio helps to effectively disperse mechanical energy and avoid the adverse effects of local overheating on the reaction. An excessively high ball-to-material mass ratio may lead to excessive friction and excessive heat accumulation, thereby affecting the hydrogenation reaction of magnesium powder.

[0048] (3) Uniformity and reactivity: An appropriate ball-to-material mass ratio helps to ensure uniform dispersion of the sample, ensures sufficient contact between magnesium powder and hydrogen, and promotes the formation of magnesium hydride. If the ratio is too low, the sample may not be subjected to enough impact during ball milling, resulting in insufficient reaction; if the ratio is too high, it may lead to excessively long ball milling time, thereby reducing efficiency.

[0049] To ensure that the above-described implementation details and operations of this application can be clearly understood by those skilled in the art, the above technical solutions are illustrated below through multiple embodiments.

[0050] Example 1

[0051] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were added to a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was then added to the jar, and the glove box was sealed. After evacuating the jar of argon gas using a vacuum pump, the jar was filled with hydrogen gas at a pressure of 20 bar and ball-milled on a planetary ball mill. The ball mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box. Figure 1 As shown, the X-ray powder diffraction pattern of the ball-milled material was determined, confirming it as magnesium hydride.

[0052] The product obtained by the above preparation method was subjected to a programmed temperature-controlled desorption test. The specific parameters were: temperature increased from room temperature to 500 °C over 30 min, held at 500 °C for 80 min, and a dehydrogenation curve was plotted. Figure 2 As shown, the dehydrogenation rate can reach 7.5%, which is equivalent to a MgH2 formation rate of over 98%.

[0053] Example 2

[0054] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 2 µm, HV=2500) was then added to the jar, and the glove box was sealed. After evacuating the jar of argon gas using a vacuum pump, the jar was filled with hydrogen gas at a pressure of 20 bar and ball-milled on a planetary ball mill. The ball mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0055] The product obtained by the above preparation method was subjected to a programmed temperature-controlled desorption test. The specific parameters were: temperature increased from room temperature to 500 °C over 30 min, held at 500 °C for 80 min, and a dehydrogenation curve was plotted. Figure 2 As shown, the dehydrogenation rate can reach 6.9%, which is equivalent to a MgH2 formation rate of about 91%.

[0056] Example 3

[0057] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 588 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 12 mg of silicon carbide powder (2% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box. Figure 1 As shown, the X-ray powder diffraction pattern of the ball-milled material was determined, confirming it as magnesium hydride.

[0058] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount could reach 6.7%, which is equivalent to a MgH2 formation rate of more than 88%.

[0059] Example 4

[0060] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder mixed with silicon nitride, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-material ratio of 100:1. 30 mg of silicon nitride powder (5% by mass, average particle size 0.04 µm, HV=1500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box. Figure 1 As shown, the X-ray powder diffraction pattern of the ball-milled material was determined, confirming it as magnesium hydride.

[0061] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount could reach 6.5%, which is equivalent to a MgH2 formation rate of more than 85%.

[0062] Example 5

[0063] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 300 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0064] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount reached 7.51%, which is equivalent to a MgH2 formation rate of over 98%.

[0065] Example 6

[0066] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-material ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 16 hours at a speed of 300 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0067] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount reached 6.56%, which is equivalent to a MgH2 formation rate of more than 86%.

[0068] Example 7

[0069] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-material ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 8 hours at a speed of 300 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0070] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount could reach 5.4%, which is equivalent to a MgH2 formation rate of more than 71%.

[0071] Example 8

[0072] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 1140 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 50:1. 60 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box. Figure 1 As shown, the X-ray powder diffraction pattern of the ball-milled material was determined, confirming it as magnesium hydride.

[0073] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount could reach 7.1%, which is equivalent to a MgH2 formation rate of more than 93%.

[0074] Example 9

[0075] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 285 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-material ratio of 200:1. 15 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box. Figure 1 As shown, the X-ray powder diffraction pattern of the ball-milled material was determined, confirming it as magnesium hydride.

[0076] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount reached 7.52%, which is equivalent to a MgH2 formation rate of over 99%.

[0077] Example 10

[0078] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder with silicon carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon carbide powder (5% by mass, average particle size 0.04 µm, HV=2500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 10 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0079] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount could reach 6.3%, which is equivalent to a MgH2 formation rate of more than 82%.

[0080] Example 11

[0081] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder mixed with silicon nitride, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon nitride powder (5% by mass, average particle size 2 µm, HV=1500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0082] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount reached 7.4%, which is equivalent to a MgH2 formation rate of over 97%.

[0083] Example 12

[0084] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder mixed with tungsten carbide, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-powder ratio of 100:1. 30 mg of silicon nitride powder (5% by mass, average particle size 10 µm, HV=1500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0085] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min, holding at 500℃ for 80 min, and plotting the dehydrogenation curve. The dehydrogenation amount reached 7.25%, which is equivalent to a MgH2 formation rate of over 95%.

[0086] Example 13

[0087] A method for preparing magnesium hydride as a hydrogen storage medium, comprising the steps of ball milling magnesium powder mixed with silicon nitride, and the preparation method including: In a high-purity argon glove box, stainless steel balls and approximately 570 mg of commercially available magnesium powder were placed in a 60 ml stainless steel ball milling jar at a ball-to-material ratio of 100:1. 30 mg of silicon nitride powder (5% by mass, average particle size 20 µm, HV=1500) was added to the jar, and the glove box was sealed. The jar was then filled with hydrogen gas at 20 bar and ball-milled on a planetary ball mill. The mill was set to rotate forward and backward for 15 minutes each, with a 5-minute pause between rotational changes, for a total milling time of 24 hours at a speed of 200 rpm. After milling, the contents were removed from the jar in an inert gas glove box.

[0088] The product obtained by the above preparation method was subjected to programmed temperature desorption. The specific parameters were: heating to 500℃ in 30 min and holding at 500℃ for 80 min. The dehydrogenation curve was plotted, and the dehydrogenation amount reached 6.94%, which is equivalent to a MgH2 formation rate of more than 91%.

[0089] Comparative Example 1 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that: the commercially available magnesium powder is not mixed with any other substances before ball milling, while the remaining preparation steps and parameters remain unchanged.

[0090] To verify the progressiveness of the embodiments of this application, the following performance tests were performed on the magnesium hydride prepared in Embodiment 1 and Comparative Example 1 of this application: (1) Based on programmed temperature rise desorption, such as Figure 2The figure shows a comparison of the programmed temperature rise desorption curves for Comparative Example 1 and Example 1. As shown, the amount of magnesium hydride produced without silicon carbide hard particles (5.1 wt%) is significantly lower than that produced by ball milling with added silicon carbide hard particles (7.5 wt%). This confirms that doping with silicon carbide hard particles improves the production efficiency of magnesium hydride.

[0091] (2) Scanning electron microscopy (SEM) was performed on the hydrogen storage materials in Comparative Example 1 and Example 1 to study the microscopic characteristics of the materials ball-milled with doped silicon carbide. The test results are as follows: Figure 3 As shown. Among them. Figure 3 (a) SEM image of the sample of pure magnesium powder subjected to hydrogen pressure ball milling in Comparative Example 1 and Figure 3 (b) SEM morphology of ball-milled sample with silicon carbide doping size of 0.04 μm. It can be clearly seen from the figure that the surface roughness of the ball-milled sample after adding silicon carbide is greater, which confirms that the addition of silicon carbide has the effect of micro-cutting.

[0092] (3) Atomic force microscopy was performed on the hydrogen storage materials in Comparative Example 1 and Example 1. The test results are as follows: Figure 4 As shown, where Figure 4 (a) Surface morphology of the sample obtained by hydrogen-pressure ball milling of pure magnesium powder in Comparative Example 1. Figure 4 (b) Surface morphology of the ball-milled sample doped with 0.04 μm silicon carbide. The image clearly shows that the sample image after ball milling with silicon carbide exhibits a higher surface undulation (approximately 250 nm), indicating that ball milling with silicon carbide increases the surface roughness of the sample. This roughness helps to provide more reaction surface area, thereby promoting the formation of magnesium hydride. The sample surface without silicon carbide ball milling is relatively smooth, with a maximum height change of only about 90 nm. This confirms that the addition of silicon carbide has a micro-machining effect.

[0093] Comparative Example 2 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that the doped silicon carbide powder has a size of 74 µm, which is larger than the upper limit of hard particles (20 µm) claimed in this invention and exceeds the average particle size of commercially available magnesium powder. The remaining preparation steps and parameters remain unchanged.

[0094] Furthermore, to verify the progressiveness of the embodiments of this application, the magnesium hydride prepared in Embodiment 1 and Comparative Example 2 of this application were subjected to the following performance tests: According to programmed temperature rise desorption, such as Figure 5The figure shows a comparison of the programmed temperature rise desorption curves for Comparative Example 2 and Example 1. As shown, the amount of magnesium hydride produced by ball milling with 74 µm silicon carbide doping is significantly lower than that produced by ball milling with 0.04 µm silicon carbide hard particles, and even lower than that produced by ball milling without silicon carbide doping. This confirms that the size of the silicon carbide hard particles has a decisive influence on the production efficiency of magnesium hydride. When the particle size is too large (such as 74 µm in this comparative example), it not only fails to provide an effective micro-cutting effect to promote hydrogen diffusion, but also forms a physical barrier between the ball milling media and the magnesium powder due to its excessive volume, severely hindering the collision deformation of the magnesium powder and the diffusion and penetration of hydrogen, ultimately leading to a significant reduction in the hydrogenation reaction efficiency. This comparative result conversely confirms the necessity and scientific basis of selecting the upper limit of the hard particle size in this invention.

[0095] Comparative Example 3 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that the doped hard particle powder is magnesium oxide (HV = 400), while the other preparation steps and parameters remain unchanged.

[0096] To verify the progressiveness of the embodiments of this application, the magnesium hydride prepared in Example 1 and Comparative Example 3 of this application were subjected to the following performance tests: According to programmed temperature rise desorption, such as Figure 6 The figure shows a comparison of the programmed temperature rise desorption curves for Comparative Example 3 and Example 1. As shown, the sample doped with low-hardness magnesium oxide (HV = 400) produced significantly less magnesium hydride than the magnesium hydride produced by ball milling with high-hardness silicon carbide (HV = 2500), and even less than the undoped sample. This comparison demonstrates that the hardness of the hard particles is a key factor determining the magnesium hydride formation efficiency. When the particle hardness is too low (such as the magnesium oxide with HV = 400 in this comparative example), it cannot effectively achieve microscopic cutting of the magnesium matrix during ball milling, making it difficult to fully promote hydrogen diffusion and reaction, ultimately leading to a decrease in hydrogenation efficiency.

[0097] Comparative Example 4 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that the ball milling time is 2 hours, while the other preparation steps and parameters remain unchanged.

[0098] To verify the progressiveness of the embodiments of this application, the magnesium hydride prepared in Example 1 and Comparative Example 4 of this application were subjected to the following performance tests: According to programmed temperature rise desorption, such as Figure 7The figure shows a comparison of the programmed temperature rise desorption curves for Comparative Example 4 and Example 1. As shown, the sample ball-milled for 2 hours produced significantly less magnesium hydride than the sample ball-milled for 24 hours. This comparison demonstrates that ball milling time is a key factor affecting magnesium hydride formation efficiency. When the ball milling time is too short (such as 2 hours in this comparative example), the ball milling process cannot achieve sufficient microscopic cutting of the magnesium matrix, and at the same time, the solid-phase reaction between magnesium and hydrogen is incomplete, resulting in a large amount of magnesium not being converted into magnesium hydride, ultimately leading to a low hydrogenation efficiency. This result confirms the necessity of setting a longer ball milling time (8–24 h) in this invention.

[0099] Comparative Example 5 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that the ball milling speed is 150 r / min, while the other preparation steps and parameters remain unchanged.

[0100] To verify the progressiveness of the embodiments of this application, the magnesium hydride prepared in Embodiment 1 and Comparative Example 5 of this application were subjected to the following performance tests: According to programmed temperature rise desorption, such as Figure 8 The figure shows a comparison of the programmed temperature rise desorption curves for Comparative Example 5 and Example 1. As shown, the sample with a ball milling speed of 150 r / min produced significantly less magnesium hydride than the sample with a ball milling speed of 200 r / min. This comparison illustrates that the ball milling speed is another key parameter determining the magnesium hydride formation efficiency. When the ball milling speed is too low (such as 150 r / min in this comparative example), the kinetic energy of the milling media is insufficient, making it difficult to effectively achieve microscopic cutting of the magnesium matrix and continuous exposure of the fresh surface, resulting in incomplete reaction between magnesium and hydrogen, ultimately leading to a decrease in hydrogenation efficiency. This result confirms the necessity of controlling the ball milling speed to achieve better preparation results in this invention.

[0101] Comparative Example 6 A method for preparing magnesium hydride as a hydrogen storage medium differs from Example 1 in that the content of added hard silicon carbide particles is 10%, while the other preparation steps and parameters remain unchanged.

[0102] To verify the progressiveness of the embodiments of this application, the magnesium hydride prepared in Example 1 and Comparative Example 6 of this application were subjected to the following performance tests: According to programmed temperature-progression desorption, the sample with 10% added hard silicon carbide particles produced less magnesium hydride than the sample with 5% silicon carbide. This comparison shows that excessive addition of hard particles not only failed to improve the conversion efficiency of Mg to MgH2, but also had a negative effect. Excessive hard particles reduce the content of effective products and enhance particle agglomeration during ball milling. Conversely, if the amount of hard particles added is too low, it is difficult to exert effective micro-cutting and activation effects. These results confirm the necessity and preference of controlling the amount of hard particles added within the range of 2-5% in this application.

[0103] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A process for the preparation of magnesium hydride, characterized in that, The process includes the following steps: (1) Mixing elemental magnesium powder with hard particles under an argon atmosphere and loading them into a ball mill jar; (2) Using a vacuum pump to remove the argon from the ball mill jar and filling it with hydrogen at a certain pressure; (3) Performing mechanical ball milling on the mixture under set parameters; (4) Removing the ball-milled material under an argon atmosphere to obtain magnesium hydride. The hard particles are one of silicon carbide, silicon nitride, and tungsten carbide.

2. The method of claim 1, wherein: The average particle size of the hard particles is 0.04–20 µm.

3. The method for preparing magnesium hydride as described in claim 1, characterized in that: The average particle size of the hard particles is smaller than the initial average particle size of the magnesium powder used.

4. The method for preparing magnesium hydride as described in claim 1, characterized in that: The hard particles have a hardness HV≥1500.

5. The method for preparing magnesium hydride as described in claim 1, characterized in that: The amount of hard particles added is 2.0 to 5.0% of the total weight of the mixture of elemental magnesium powder and hard particles.

6. The method for preparing magnesium hydride as described in claim 1, characterized in that: The hydrogen pressure is 10–20 bar.

7. The method for preparing magnesium hydride according to claim 1, characterized in that: The ball milling parameters are a rotation speed of 200–300 r / min and a time of 8–24 h.

8. The method for preparing magnesium hydride as described in claim 1, characterized in that: In step (2), the ball-to-material mass ratio in the ball mill is 50:1 to 200:1.

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