Magnesium hydride composite hydrogen storage briquette and mechanical strength strengthening method thereof

Abstract

The invention belongs to the technical field of hydrogen storage materials, and relates to a magnesium hydride composite hydrogen storage briquette and a mechanical strength strengthening method thereof. Comprising the following steps: mixing expanded graphite powder, magnesium hydride powder and a substance A to form a mixture, and carrying out cold pressing treatment on the mixture to form an initial pressing block; carrying out hot pressing treatment on the initial pressing block, and cooling to form a magnesium hydride composite hydrogen storage pressing block; the melting point temperature range of the substance A is 350-450 DEG C, and the temperature of the hot pressing treatment is not lower than the melting point temperature of the substance A and not higher than 450 DEG C. The technical problem that in an existing cold pressing technology, after repeated hydrogen absorption and desorption, the pressing block is broken and even collapses, and consequently enhanced heat transfer fails can be solved, and the mechanical strength of the magnesium hydride composite hydrogen storage pressing block is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen storage materials, and relates to a magnesium hydride composite hydrogen storage briquette and a method for strengthening its mechanical strength. Background Art

[0002] As an efficient solid-state hydrogen storage material, metal hydrides have broad application prospects in the field of hydrogen energy storage and utilization. Their core advantage lies in the rapid absorption and release of hydrogen through reversible gas-solid reactions, and the reaction kinetics performance of this process directly determines the actual application efficiency of the hydrogen storage system. However, the thermodynamic characteristics of metal hydrides impose strict requirements on the reaction process, that is, the heat released or absorbed during the hydrogen absorption or desorption process must be transferred in a timely manner, otherwise the reaction will spontaneously stop due to heat accumulation or insufficient supply. This unique thermodynamic-kinetic coupling characteristic makes the heat transfer performance a key factor restricting the development of metal hydride hydrogen storage technology. In practical applications, if efficient heat management cannot be achieved, even metal hydrides with excellent intrinsic properties are difficult to continuously exert their advantages of rapid hydrogen absorption and desorption. Therefore, how to effectively strengthen the heat transfer performance of the metal hydride bed has become a scientific problem that needs to be solved urgently by researchers in this field.

[0003] To address this technical bottleneck, the development of composite hydrogen storage briquettes provides an effective solution. This technology cold-presses metal hydride powder and high thermal conductivity materials (such as metal foam, expanded graphite, etc.) in a mold to construct a heat transfer enhanced structure with a three-dimensional thermal conductivity network. The introduction of high thermal conductivity materials significantly improves the equivalent thermal conductivity of the composite briquette, creating favorable conditions for the rapid transfer of reaction heat; secondly, the cold pressing process ensures the uniform distribution of metal hydride particles in the high thermal conductivity matrix, effectively avoiding powder agglomeration; more importantly, this uniformly dispersed structure can relieve the internal stress generated by the volume expansion of the material during hydrogen absorption, preventing mechanical damage to the hydrogen storage tank due to local stress concentration. Compared with the traditional powder-packed bed, the composite hydrogen storage briquette can improve its heat transfer efficiency by more than an order of magnitude while maintaining good mass transfer performance, which lays a solid foundation for the rapid cycling operation of the metal hydride hydrogen storage system.

[0004] However, although the cold pressing technology commonly used in the industrial sector currently has the advantages of simple process and low cost, obvious limitations have emerged during long-term cyclic use. As a representative of typical metal hydrides, magnesium hydride undergoes a volume change of approximately 30% during the hydrogen absorption and desorption cycle. This periodic expansion - contraction behavior poses a severe challenge to the mechanical stability of the compact structure. The composite compacts prepared by the single cold pressing method often exhibit problems such as the initiation and propagation of microcracks and even overall collapse after dozens of cycles due to the lack of sufficient structural toughness. This structural failure not only leads to the destruction of the high - thermal - conductivity network, resulting in a sharp decline in heat transfer performance, but also may cause the leakage and agglomeration of metal hydride powders, further deteriorating the hydrogen storage performance of the system. More seriously, the fine powders generated by the crushing of the compacts may block the hydrogen channels, increasing the mass transfer resistance and forming a vicious cycle of double deterioration of heat transfer and mass transfer. The existence of these problems severely restricts the practical application of cold - pressed composite hydrogen storage compacts in long - cycle hydrogen storage systems. Summary of the Invention

[0005] The purpose of the present invention is to provide a magnesium hydride composite hydrogen storage compact and its mechanical strength strengthening method to solve the technical problem in the existing cold pressing technology that the compact cracks or even collapses after repeated hydrogen absorption and desorption, resulting in the failure of enhanced heat transfer, and to improve the mechanical strength of the magnesium hydride composite hydrogen storage compact.

[0006] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a mechanical strength strengthening method for a magnesium hydride composite hydrogen storage compact, including the following steps: Mix expanded graphite powder, magnesium hydride powder and substance A to form a mixture, and subject the mixture to cold pressing to form an initial compact; subject the initial compact to hot pressing and then cool it to form a magnesium hydride composite hydrogen storage compact; the melting point temperature range of substance A is 350 - 450 °C, and the temperature of the hot pressing is not lower than the melting point temperature of substance A and not higher than 450 °C.

[0007] Preferably, substance A is zinc fiber, zinc powder, alloy powder or alloy fiber.

[0008] Preferably, the alloy is zinc - aluminum alloy.

[0009] Preferably, when substance A is powder, its particle size is 200 - 1000 μm.

[0010] Preferably, when substance A is fiber, its diameter is 100 - 1000 μm and its length is 1 - 30 mm.

[0011] Preferably, substance A accounts for 3% - 15% of the mass of the mixture.

[0012] Preferably, the expanded graphite powder accounts for 5% - 25% of the mass of the mixture.

[0013] Preferably, in the cold pressing treatment, the cold pressing pressure is 50 - 200 MPa; the duration of the cold pressing treatment is 1 - 60 s.

[0014] Preferably, the hot pressing pressure is 0 - 50 MPa; the duration of the hot pressing treatment is 1 - 60 s.

[0015] In a second aspect, the present invention provides a magnesium hydride composite hydrogen storage briquette.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Through the synergistic effect of cold pressing and hot pressing, and by defining the temperature range of the melting point of substance A to be higher than the operating temperature of magnesium hydride but lower than its sintering temperature range, by controlling the hot pressing temperature, it not only ensures that substance A fully melts and flows during the hot pressing stage, forming a strong interfacial bond with the expanded graphite powder and magnesium hydride particles, but also avoids the thermal decomposition of magnesium hydride at high temperatures, thereby improving the mechanical strength of the magnesium hydride composite hydrogen storage briquette while maintaining the stability of the hydrogen storage capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a flowchart of a method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage briquette of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the following will generally explain and define the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art for the present invention. When there are conflicting situations, the definition in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0021] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0022] In this text, unless otherwise specified, the terms "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0023] In this text, for the sake of concise description, not all possible combinations of all technical features in each embodiment or example are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as being within the scope described in this specification.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings: The first object of the present invention is to provide a method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage briquette, as Figure 1 shown, which includes the following steps: Mix expanded graphite powder, magnesium hydride powder, and substance A to form a mixture, and cold-press the mixture at 50 - 200 MPa for 1 - 60 s to form an initial briquette; hot-press the initial briquette at 0 - 50 MPa for 1 - 60 s, and after cooling, form a magnesium hydride composite hydrogen storage briquette; the melting point temperature range of substance A is 350 - 450 °C, and the temperature of the hot-pressing treatment is not lower than the melting point temperature of substance A and not higher than 450 °C.

[0025] In the preparation process of magnesium hydride composite hydrogen storage compacts, the flexible control of the hot pressing process has a crucial impact on the performance of the final product. According to the actual application requirements, two different hot pressing methods can be adopted: one is not to apply additional pressure when substance A reaches the molten state, and only rely on the capillary action of the molten metal to achieve natural bonding between particles; the other is to heat synchronously to above the melting point of substance A during the cold pressing process, and achieve the effects of fusion welding and pressure welding through the synergistic action of pressure and temperature. These two treatment methods have their own advantages. The former pays more attention to maintaining the pore structure and hydrogen storage activity of the material, while the latter emphasizes obtaining a densified high-strength structure. In actual operation, the precise control of process parameters is particularly important. The selection of temperature needs to strictly match the melting point characteristics of substance A. By regulating these key process parameters, magnesium hydride composite hydrogen storage compacts with different performances can be prepared, from porous structures that focus on buffering performance to dense products that emphasize load-bearing capacity, meeting the diverse needs of different application scenarios. Especially in application scenarios that require high cycle stability, a multi-step composite process, such as a combined treatment of cold pressing - melt infiltration - secondary hot pressing, can achieve the goals of high strength and high durability at the same time.

[0026] Through the synergistic action of cold pressing and hot pressing in the method of the present invention, and the melting point temperature range of substance A is 350 - 450 °C (a temperature range higher than the operating temperature of magnesium hydride but lower than its sintering temperature), it not only ensures its full melting and flowing in the hot pressing stage, forming a strong interfacial bond with expanded graphite powder and magnesium hydride particles, but also avoids the thermal decomposition of magnesium hydride at high temperatures (MgH 2 The decomposition temperature is about >300 °C), thereby maintaining the stability of the hydrogen storage capacity while strengthening the mechanical properties. Secondly, the alternating process design of cold pressing and hot pressing optimizes the compact structure. Cold pressing realizes the preliminary densification of the mixed material, and during the hot pressing process, the molten substance A penetrates into the particle gaps through capillary action to form a three-dimensional network bonding structure. In addition, the expanded graphite powder not only acts as a skeleton to inhibit the agglomeration of magnesium hydride and provide gas diffusion channels, but its layered structure can also form an interlocking interface with the molten substance A, improving the compressive strength and crack resistance toughness; at the same time, the uniform distribution of substance A can buffer the volume strain during the hydrogen absorption and desorption cycle, delay the interfacial peeling, and extend the cycle life of the compact.

[0027] The substance A is zinc fiber / powder (melting point 420°C), alloy powder or alloy fiber. The dense coating layer formed by the zinc melt or alloy melt at the interface can isolate the direct contact between magnesium hydride and the external environment, inhibit oxidation and disproportionation reactions during high-temperature treatment, and cooperate with the porous gas-conducting structure of expanded graphite to maintain dynamic stability of the compact in the hydrogen absorption and desorption cycle and reduce the capacity attenuation rate. During the hot pressing process, the zinc fiber / powder or alloy fiber / powder can form a uniform liquid flow inside the compact after melting, penetrate into the pores and interfaces of magnesium hydride and expanded graphite through capillary action, and form a continuous metal bonding phase after cooling, which significantly enhances the mechanical interlocking and load transfer efficiency between particles, improves the compressive strength of the compact, and the bridging effect of the zinc fiber can effectively inhibit crack propagation and improve toughness.

[0028] Exemplarily, the alloy is a zinc-aluminum alloy, such as ZA-27 and ZA-8, both of which have melting points of 431°C and 385°C, respectively. The introduction of zinc-aluminum alloy not only inherits the low-temperature melting bonding advantage of pure zinc, but its aluminum element can also form a Mg-Al-Zn transition layer at the interface, enhance the chemical compatibility with magnesium hydride particles, and inhibit interface peeling at high temperatures. In addition, the solid solution strengthening effect of aluminum can significantly improve the hardness and wear resistance of the alloy after solidification, and improve the anti-powdering ability of the compact during the cyclic absorption and desorption of hydrogen. At the same time, the fluidity of the ZA series alloy is better than that of pure zinc, and it can more fully fill the interlayer pores of expanded graphite to form a three-dimensional interpenetrating structure of "graphite-alloy-magnesium hydride", taking into account high thermal conductivity (promoting thermal management of hydrogen absorption and desorption) and compressive strength, and has both process controllability, cost-effectiveness and performance adjustability, providing a reliable path for the engineering application of hydrogen storage compacts.

[0029] When the substance A is a powder, its particle size is 200~1000 μm, and the powder can be densified by melting and filling micropores to reduce hydrogen permeation path defects. When the substance A is a fiber, its diameter is 100~1000 μm and its length is 1~30 mm. It can construct a three-dimensional mesh reinforcement skeleton and absorb energy through plastic deformation. In addition, the ductility of the fiber / powder makes it difficult to break during the cold pressing stage, ensuring the uniformity of mixing.

[0030] The substance A accounts for 3% to 15% of the mass of the mixture. An appropriate amount of substance A can form a continuous and dense metal bonding network in a molten state. This network structure is like a steel skeleton at the microscopic level, which not only significantly enhances the overall compressive strength of the pressed block, making it exhibit excellent stability when subjected to external pressure, but also gives the pressed block excellent impact toughness, effectively resisting structural damage caused by external impact force; at the same time, it can effectively prevent magnesium hydride from being over-wrapped, thereby ensuring that the hydrogen storage material can maintain an efficient hydrogen storage capacity during the process of hydrogen absorption and desorption, and maintain its excellent hydrogen storage performance.

[0031] The expanded graphite powder accounts for 5% - 25% of the mass of the mixture. The unique layered structure of expanded graphite endows it with excellent electrical and thermal conductivity. In the mixture, it constructs an efficient three-dimensional conductive / thermal network, which not only accelerates the heat transfer during the hydrogen absorption and desorption processes, promotes the uniform progress of the reaction, but also significantly improves the overall thermal management efficiency of the compact. In addition, when magnesium hydride undergoes volume expansion, the layered structure of expanded graphite can effectively buffer stress like a spring, reducing the internal cracks and pulverization phenomena in the material caused by volume changes. Thus, while maintaining a high hydrogen storage density, it extends the service life of the material and improves its cycle stability.

[0032] The present invention uses a solid-state metallurgical bonding mechanism to strengthen the structure of the magnesium hydride matrix. By precisely controlling the hot pressing temperature, a perfect balance between the selective melting of substance A and the stable structure of the magnesium hydride matrix is achieved. The lower limit of the hot pressing temperature range is set as the melting point temperature of substance A (such as 420 °C for zinc or 385 °C for ZA-8 alloy), ensuring that the bonding phase fully melts and flows; the upper limit is strictly controlled below the starting temperature of magnesium hydride sintering (about 450 °C), effectively avoiding the abnormal sintering and growth of matrix particles. During the hot pressing process, the molten substance A forms a continuous three-dimensional network strengthening structure at the interface of magnesium hydride particles through capillary action, achieving both the high-strength characteristics similar to metal matrix composites and completely retaining the original microscopic hydrogen mass transfer channel network in the magnesium hydride matrix. Secondly, through the melting-solidification phase change process of substance A, a composite interface structure with both mechanical interlocking and metallurgical bonding characteristics is constructed between magnesium hydride particles: on the one hand, the solidified metal phase effectively inhibits the relative displacement of magnesium hydride particles during the hydrogen absorption and desorption cycles through mechanical anchoring; on the other hand, the locally formed transition layer (Mg-Zn or Mg-Al-Zn) significantly enhances the interface bonding strength. The present invention simultaneously solves the two major technical problems of insufficient mechanical strength and poor cycle stability of hydrogen storage materials for the first time under the condition of a temperature lower than the thermal decomposition temperature of magnesium hydride through precise interfacial metallurgical engineering, providing a new material solution for the development of a new generation of high-performance solid-state hydrogen storage devices.

[0033] The following further elaborates the present invention in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0034] In the following examples, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. In the following examples, various raw materials are used. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0035] Example 1 Mix 5 parts of expanded graphite powder, 92 parts of magnesium hydride powder, and 3 parts of zinc-aluminum alloy powder (ZA-27) by mass ratio to form a mixture. Cold press the mixture at 50 MPa for 60 s to form an initial briquette; hot press the initial briquette at 0 MPa for 60 s and cool to form a magnesium hydride composite hydrogen storage briquette; the temperature of the hot pressing treatment is 431 °C.

[0036] Example 2 Mix 25 parts of expanded graphite powder, 72 parts of magnesium hydride powder, and 3 parts of zinc-aluminum alloy powder (ZA-27) to form a mixture. Cold press the mixture at 100 MPa for 40 s to form an initial briquette; hot press the initial briquette at 10 MPa for 40 s and cool to form a magnesium hydride composite hydrogen storage briquette; the temperature of the hot pressing treatment is 450 °C.

[0037] Example 3 Mix 5 parts of expanded graphite powder, 80 parts of magnesium hydride powder, and 15 parts of zinc-aluminum alloy fiber (ZA-8) to form a mixture. Cold press the mixture at 150 MPa for 20 s to form an initial briquette; hot press the initial briquette at 25 MPa for 20 s and cool to form a magnesium hydride composite hydrogen storage briquette; the temperature of the hot pressing treatment is 450 °C.

[0038] Example 4 Mix 25 parts of expanded graphite powder, 60 parts of magnesium hydride powder, and 15 parts of zinc powder to form a mixture. Cold press the mixture at 200 MPa for 10 s to form an initial briquette; hot press the initial briquette at 40 MPa for 10 s and cool to form a magnesium hydride composite hydrogen storage briquette; the temperature of the hot pressing treatment is 420 °C.

[0039] Example 5 Mix 10 parts of expanded graphite powder, 80 parts of magnesium hydride powder, and 10 parts of zinc fiber to form a mixture. Cold press the mixture at 200 MPa for 1 s to form an initial briquette; hot press the initial briquette at 50 MPa for 1 s and cool to form a magnesium hydride composite hydrogen storage briquette; the temperature of the hot pressing treatment is 450 °C.

[0040] Comparative Example Mix 5 parts of expanded graphite powder and 92 parts of magnesium hydride powder (ZA-27) by mass ratio to form a mixture, and cold press the mixture at 50 MPa for 60 s to form an initial compact; hot press the initial compact at 0 MPa for 60 s, and cool it to form a magnesium hydride hydrogen storage compact; the temperature of the hot pressing treatment is 431 °C.

[0041] Conduct mechanical property tests on the hydrogen storage compacts prepared in Example 1 and the comparative example, and the results are shown in Table 1: Table 1 Mechanical property test results

[0042] As can be seen from Table 1, the compressive strength of the hydrogen storage compact prepared in Example 1 of the present invention is increased from 150 MPa in the control example to 195 MPa, an increase of 30%; the fracture toughness is increased from 5.2 MPa·m 1 / 2 to 6.8 MPa·m 1 / 2 , an increase of 31%.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact, characterized in that: The following steps are involved: Expanded graphite powder, magnesium hydride powder and substance A are mixed to form a mixture, and the mixture is subjected to cold pressing to form an initial compact; the initial compact is subjected to hot pressing, and after cooling, a magnesium hydride composite hydrogen storage compact is formed; the melting point temperature range of the substance A is 350-450°C, and the temperature of the hot pressing treatment is not lower than the melting point temperature of the substance A and not higher than 450°C.

2. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 1, characterized in that: The substance A is zinc fiber, zinc powder, alloy powder or alloy fiber.

3. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 2, characterized in that: The alloy is a zinc-aluminum alloy.

4. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 2, characterized in that: When the substance A is powder, its particle size is 200-1000 μm.

5. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 2, characterized in that: When the substance A is a fiber, its diameter is 100-1000 μm and its length is 1-30 mm.

6. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 1, characterized in that: The substance A accounts for 3% to 15% of the mixture mass.

7. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 1, characterized in that: The expanded graphite powder accounts for 5% to 25% of the mass of the mixture.

8. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 1, characterized in that: The cold pressing pressure in the cold pressing process is 50-200 MPa; and the cold pressing time is 1-60 seconds.

9. The method for strengthening the mechanical strength of a magnesium hydride composite hydrogen storage compact according to claim 1, characterized in that: The hot pressing pressure is 0-50 MPa; and the hot pressing treatment time is 1-60 s.

10. A magnesium hydride composite hydrogen storage compact, characterized in that: The invention is prepared by the mechanical strength strengthening method according to any one of claims 1 to 9.

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