A heat treatment method for a vanadium-based hydrogen storage alloy

Abstract

The application discloses a heat treatment method of vanadium-based hydrogen storage alloy and belongs to the technical field of vanadium-based hydrogen storage alloy processing, and aims at solving the problems of high activation temperature and difficult crushing and powdering of the vanadium-based hydrogen storage alloy.The vanadium-based hydrogen storage alloy provided by the application comprises the following components in percentage by weight: V: 68-80%, Ti: 7-12%, Cr: 10-20%, and (Fe+Zr+Mn): 0-8%.The application solves the problems of high activation temperature and difficult crushing and powdering by one-step solid solution aging heat treatment in a hydrogen-argon mixed atmosphere with a specific ratio, and cooperatively acts on the microstructure and surface characteristics of the vanadium-based hydrogen storage alloy.

Description

Technical Field

[0001] This invention belongs to the field of vanadium-based hydrogen storage alloy processing technology, and particularly relates to a heat treatment method for vanadium-based hydrogen storage alloys. Background Technology

[0002] Hydrogen energy / storage technology is a necessity for global energy transition and upgrading, and an effective way to achieve the "dual carbon" goal. Hydrogen storage alloys, as reversible hydrogen absorption and desorption materials, are also important energy conversion materials for the development of hydrogen energy / storage technologies. Vanadium-based hydrogen storage alloys have advantages such as high hydrogen storage capacity and good hydrogen absorption / desorption platform characteristics. However, vanadium-based hydrogen storage alloys have a high vanadium content and a dense oxide layer on the surface, requiring activation at 400℃ under vacuum before hydrogen absorption. Furthermore, the high strength and toughness of vanadium-based solid solution hydrogen storage alloys lead to difficulties in crushing and powdering. These factors all affect the application of vanadium-based hydrogen storage alloys in practical working conditions. Summary of the Invention

[0003] In view of the above analysis, the present invention aims to provide a heat treatment method for vanadium-based hydrogen storage alloys to solve at least one of the problems of high activation temperature, crushing and powdering difficulties in existing vanadium-based hydrogen storage alloys.

[0004] The objective of this invention is mainly achieved through the following technical solutions: The present invention provides a vanadium-based hydrogen storage alloy, the chemical composition of which, by weight percentage, includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 0%~8%.

[0005] The present invention provides a vanadium-based hydrogen storage alloy, the chemical composition of which, by weight percentage, includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 0%~8%.

[0006] In one possible design, its chemical composition by weight percentage includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 2%~8%.

[0007] In one possible design, the chemical composition of the aforementioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 70%~80%, Ti: 9%~12%, Cr: 14%~20%, (Fe+Zr+Mn): 4%~8%.

[0008] In one possible design, the chemical composition of the above-mentioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 72%~80%, Ti: 10%~12%, Cr: 16%~20%, (Fe+Zr+Mn): 4%~6%. On the other hand, the present invention also provides a heat treatment method for a vanadium-based hydrogen storage alloy, used to heat treat the above-mentioned vanadium-based hydrogen storage alloy; the heat treatment method includes the following steps: Step 1: Atmosphere alteration and preparation; The vanadium-based hydrogen storage alloy sample was placed in a quartz tube and subjected to inert atmosphere replacement. Step 2: Filling and sealing with mixed gas; After the atmosphere replacement is completed, a mixture of hydrogen and argon in a specific ratio is introduced into the quartz tube so that the vacuum pressure gauge shows -0.02 to -0.04 MPa. Step 3: Staged high-temperature heat treatment; The sealed quartz tube is placed in a heat treatment furnace for two stages of heating and heat preservation. Step 4: Cooling; After the heat treatment is completed, the quartz tube is removed from the heat treatment furnace and cooled to room temperature. Furthermore, in step 1, the vacuum is evacuated for 9-11 minutes to ensure the vacuum level is within the range of 0.01~0.1 Pa; then, inert protective gas is introduced until the vacuum pressure gauge shows -0.05 MPa.

[0009] Furthermore, in step 1, the vacuum is evacuated again for 9-11 minutes to ensure that the vacuum degree is 0.01~0.1 Pa; the inflation-vacuuming process is repeated three times to ensure that the air in the quartz tube is completely expelled.

[0010] Furthermore, in step 2, the volume fraction of hydrogen in the mixed gas of hydrogen and argon is 10% to 20%. After the gas filling is completed, the quartz tube is sealed.

[0011] Furthermore, in step 2, the volume fraction of hydrogen in the hydrogen-argon mixture is 14% to 20%.

[0012] Furthermore, in step 4, after heat treatment and cooling, the alloy is vacuumed for 3000s at an activation temperature ≤80℃, and then hydrogen is absorbed once under hydrogen conditions at 40℃ and 8MPa, thus the vanadium-based hydrogen storage alloy can be fully activated.

[0013] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) On the one hand, the present invention ensures the high hydrogen storage capacity and good plateau characteristics of the alloy through elemental ratio. The V content is set to 68%-80%, as it is the main hydrogen-absorbing element and can maintain the body-centered cubic (BCC) crystal structure to ensure high hydrogen storage capacity. At the same time, Ti (7%-12%) and Cr (10%-20%) are added. They form an infinite solid solution with V, maintain the BCC structure, improve the hydrogen absorption rate, synergistically regulate the cell volume, and precisely adjust the hydrogen absorption and desorption plateau pressure to meet the needs of different solid-state hydrogen storage applications. The adjustable plateau pressure is very important for hydrogen storage and release operations.

[0014] (2) The heat treatment method provided by the present invention can achieve the purpose of reducing the activation temperature of the alloy (such as reducing the activation temperature of the alloy from 400℃ to 40℃), reducing the Vickers hardness of the alloy, and improving the microstructure of the alloy in one step. This is beneficial to the activation and crushing of the alloy, and can improve the hydrogen storage capacity of the alloy to meet its practical application.

[0015] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0016] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1a This is a SEM image of the alloy before heat treatment; Figure 1b This is an SEM image of the alloy after heat treatment. Detailed Implementation

[0017] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0018] Currently, vanadium-based hydrogen storage alloys exhibit excellent comprehensive performance in terms of hydrogen storage capacity, hydrogen absorption / desorption plateau pressure, cycle stability, and manufacturing cost, making them the most promising hydrogen storage alloys for application in the hydrogen energy field. However, the high strength, high hardness, and high toughness of these vanadium-based hydrogen storage alloys make them difficult to crush and pulverize. Furthermore, their activation performance is poor, requiring high activation temperatures and numerous activation cycles. These issues limit their application in the hydrogen storage field.

[0019] To solve the above technical problems, the present invention provides a heat treatment method for a vanadium-based hydrogen storage alloy, wherein the chemical composition of the vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 0~8%.

[0020] In the above-mentioned vanadium-based hydrogen storage alloys, V is the main hydrogen-absorbing element, maintaining the crystal structure and basic hydrogen storage performance of the alloy BCC. When the vanadium content is 68%~80%, the alloy has high cycle stability and great application prospects.

[0021] In the aforementioned vanadium-based hydrogen storage alloys, Ti and Cr can be infinitely dissolved in V, maintaining the BCC crystal structure and increasing the alloy's hydrogen absorption rate. The ratio of Ti to Cr can synergistically regulate the cell volume of the V-based hydrogen storage alloy, adjusting the hydrogen absorption and desorption plateau pressure to meet its application requirements in solid-state hydrogen storage. Simultaneously, Ti and Cr elements can reduce the V content, lowering raw material costs.

[0022] In the aforementioned vanadium-based hydrogen storage alloys, Fe, Zr, and Mn play a role in regulating the hydrogen absorption and desorption plateau characteristics of the alloy, reducing the alloy hysteresis coefficient, which is beneficial to improving the hydrogen desorption efficiency of the alloy, and can also effectively reduce the raw material cost of the alloy.

[0023] In one possible design, the chemical composition of the above-mentioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 2%~8%.

[0024] In one possible design, the chemical composition of the above-mentioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 70%~80%, Ti: 9%~12%, Cr: 14%~20%, (Fe+Zr+Mn): 4%~8%.

[0025] In one possible design, the chemical composition of the above-mentioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 72%~80%, Ti: 10%~12%, Cr: 16%~20%, (Fe+Zr+Mn): 4%~6%.

[0026] In one possible design, the chemical composition of the aforementioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 80%, Ti: 8%, Cr: 12%.

[0027] In one possible design, the chemical composition of the aforementioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 75%, Ti: 8%, Cr: 14%, Fe: 3%.

[0028] In one possible design, the chemical composition of the above-mentioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 70%, Ti: 10%, Cr: 17%, Fe: 3%.

[0029] In one possible design, the chemical composition of the aforementioned vanadium-based hydrogen storage alloy, by weight percentage, includes: V: 75%, Ti: 8%, Cr: 12%, Mn: 5%.

[0030] On the one hand, this invention ensures high hydrogen storage capacity and good plateau characteristics of the alloy through elemental composition. The V content is set at 68%-80%, as it is the main hydrogen-absorbing element and maintains the body-centered cubic (BCC) crystal structure, guaranteeing high hydrogen storage capacity. Simultaneously, Ti (7%-12%) and Cr (10%-20%) are added, forming an infinite solid solution with V to maintain the BCC structure, increase the hydrogen absorption rate, synergistically regulate the cell volume, and precisely adjust the hydrogen absorption / desorption plateau pressure to meet the needs of different solid-state hydrogen storage applications. Adjustable plateau pressure is crucial for hydrogen storage and release operations.

[0031] On the other hand, the present invention introduces trace alloying elements (Fe+Zr+Mn) as composite additives, with the total amount controlled at 0-8% (preferably 2%-8%, or even 4%-6%), to regulate the hydrogen absorption and desorption plateau characteristics of the alloy, reduce the hysteresis coefficient, reduce energy loss, and improve hydrogen desorption efficiency.

[0032] On the other hand, the present invention also provides a heat treatment method for vanadium-based hydrogen storage alloys, for heat treating the aforementioned vanadium-based hydrogen storage alloys, the heat treatment method comprising the following steps: Step 1: Atmosphere alteration and preparation; The vanadium-based hydrogen storage alloy block is placed inside a quartz tube, and a thorough inert atmosphere replacement is performed first. Specifically, the following steps are taken: evacuate for 9-11 minutes (e.g., 10 minutes) to ensure a vacuum level of 0.01~0.1 Pa; then fill with an inert protective gas (e.g., argon) until the vacuum pressure gauge reads -0.05 MPa; evacuate again for 9-11 minutes (e.g., 10 minutes) to ensure a vacuum level of 0.01~0.1 Pa; repeat this filling-evacuation process three times to ensure that the air inside the quartz tube is completely removed, creating a pure reaction environment.

[0033] Step 2: Filling and sealing with mixed gas; After the atmosphere replacement is completed, a mixture of hydrogen and argon in a specific ratio is introduced into the quartz tube so that the vacuum pressure gauge shows -0.02 to -0.04 MPa.

[0034] In step 2 above, the volume fraction of hydrogen in the mixed gas of hydrogen and argon needs to be precisely controlled between 10% and 20%. After the gas filling is completed, the quartz tube should be tightly sealed.

[0035] Compared with the prior art, the present invention controls the volume fraction of hydrogen in the mixed gas within the range of 10% to 20%, thereby ensuring that the alloy can absorb a small amount of hydrogen during the subsequent heat treatment process of the vanadium-based hydrogen storage alloy. After hydrogen absorption, the alloy will exhibit lattice expansion and generate microcracks, which can achieve the goal of alloy breakage and pulverization. At the same time, the microcracks are also conducive to alloy activation, reduce alloy hardness, and thus reduce the difficulty of alloy breakage.

[0036] Step 3: Staged high-temperature heat treatment (one-step solution aging heat treatment); The sealed quartz tube is placed in a heat treatment furnace for a two-stage heating and holding process: First stage of heating: The furnace temperature is rapidly increased to 800℃ at a rate of 10~20℃ / min.

[0037] The second stage of heating and holding: After the furnace temperature reaches 800℃, continue to heat up to the specified temperature of 900℃~1200℃ at a rate of 3~5℃ / min, and hold at this temperature for 10~20 hours.

[0038] In the above-mentioned staged high-temperature heat treatment process, in order to ensure a more uniform temperature distribution of the material during the heating process, the present invention adopts a gradual heating method, so that the elements in the material have more time to diffuse and redistribute.

[0039] This invention involves holding the alloy at a furnace temperature of 900℃~1200℃ for 10~20 hours. The purpose is to allow sufficient time for the migration and transformation of microstructure and compositional segregation within the alloy, resulting in a more uniform microstructure (e.g., ...). Figure 1b (As shown), thereby improving the performance of the hydrogen storage alloy. Additionally, it allows the alloy sufficient reaction time with hydrogen in the mixed gas, thus activating and pulverizing the alloy.

[0040] Step 4: Cooling; After the heat treatment is completed, the alloy is removed from the heat treatment furnace and cooled to room temperature.

[0041] In step 4 above, after the alloy is evacuated for 3000s at an activation temperature ≤80℃, it is subjected to a hydrogen absorption operation once in a hydrogen atmosphere at 40℃ and 8MPa, and the vanadium-based hydrogen storage alloy can be fully activated.

[0042] After heat treatment, the Vickers hardness of the above-mentioned vanadium-based hydrogen storage alloy is ≤220HV.

[0043] After heat treatment, the hydrogen storage capacity of the aforementioned vanadium-based hydrogen storage alloy increased by ≥0.1wt%. This is because heat treatment of the alloy results in a more uniform microstructure, reduced component segregation, improved plateau characteristics, and enhanced hydrogen storage performance.

[0044] The heat treatment method for vanadium-based hydrogen storage alloys provided by this invention is an integrated method that combines activation, powder preparation, and microstructure homogenization. Through a specific heat treatment regime and a one-step heat treatment process, three effects can be achieved: Firstly, it lowers the activation temperature of vanadium-based hydrogen storage alloys, reducing the difficulty of alloy activation.

[0045] Specifically, during high-temperature heat treatment in a mixed atmosphere of hydrogen and argon in a specific ratio, hydrogen reacts with the dense oxide layer on and within the alloy surface. For example, hydrogen can reduce vanadium oxide (V₂O₅) to metallic vanadium, while simultaneously generating water vapor that escapes, thus removing the oxide layer that hinders hydrogen adsorption. Furthermore, at high temperatures, hydrogen in the mixed atmosphere can penetrate the alloy lattice, interacting with active metal atoms such as vanadium to form the initial structure of metal hydrides, laying the foundation for subsequent rapid activation. This pretreatment eliminates the need for high-temperature vacuuming to break down the stubborn oxide layer and initiate initial hydrogen absorption during the subsequent hydrogen absorption process, thus significantly reducing the temperature required for the alloy to reach full activation.

[0046] Secondly, it reduces the hardness of the alloy, making it easier to break.

[0047] Specifically, during high-temperature heat treatment, the atoms inside the alloy gain sufficient diffusion kinetic energy, causing the originally unevenly distributed precipitates to dissolve and redistribute. Simultaneously, prolonged holding at high temperatures allows for a certain degree of grain growth, relatively reducing the number of grain boundaries and alleviating stress concentration at these boundaries. Furthermore, the mixed atmosphere of hydrogen and argon at high temperatures promotes the movement and annihilation of dislocations within the alloy, reducing its dislocation density. These changes in microstructure work together to reduce the overall hardness of the alloy, making it easier to break during subsequent powder preparation, thus reducing the energy consumption and time required for crushing.

[0048] Third, it makes the alloy's microstructure more homogeneous, thereby improving the alloy's hydrogen storage capacity. The following explains the specific mechanism by which this improves the alloy's hydrogen storage capacity: Specifically, during the high-temperature heat treatment process, the alloy is held at 900℃~1200℃ for 10~20 hours, allowing the atoms within the alloy sufficient diffusion energy and time. Regions of compositional segregation that might have previously existed are effectively improved through long-range atomic diffusion, resulting in a more uniform distribution of constituent elements within the alloy matrix (e.g., Figure 1b(As shown). This homogenization of composition avoids the loss of hydrogen storage active sites or blockage of hydrogen storage channels caused by local compositional imbalances. Simultaneously, prolonged high-temperature treatment promotes the dissolution, recombination, and uniform distribution of precipitated phases within the alloy, reducing the crowding out of hydrogen storage space by coarse or irregular precipitates. More importantly, the homogenized microstructure makes the alloy's lattice structure more regular, with more consistent cell parameters, providing a more unified and stable lattice environment and sufficient interstitial sites for the adsorption, diffusion, and storage of hydrogen atoms. Furthermore, the microcracks formed during heat treatment also provide channels for the rapid penetration and diffusion of hydrogen, enabling the alloy to accommodate more hydrogen atoms, ultimately increasing the hydrogen storage capacity by ≥0.1wt%.

[0049] Compared to traditional methods that employ multiple steps to achieve activation, powdering, and microstructure homogenization, this invention simplifies the process, reduces energy and time costs, and improves production efficiency. Furthermore, the single-step high-temperature heat treatment process ensures continuity and stability, preventing adverse effects of multi-step process parameter fluctuations on alloy properties. This makes the vanadium-based hydrogen storage alloy easier to control in quality and more stable and reliable in performance, facilitating its large-scale application and promotion in the field of solid-state hydrogen storage.

[0050] In summary, this invention reduces the activation temperature of a vanadium-based hydrogen storage alloy from 400°C to below 80°C and significantly lowers the Vickers hardness to below 220 HV by placing the alloy in a hydrogen-argon mixed gas at a specific ratio and subjecting it to a one-step solution-aging heat treatment. Compared with alloys that have not undergone mixed gas treatment and heat treatment, the alloy exhibits improved microstructure uniformity and a significantly increased hydrogen storage capacity.

[0051] like Figure 1a As shown in Figure 1b, the vanadium-based hydrogen storage alloy without the heat treatment described in this invention exhibits significant compositional segregation in its microstructure. The boundaries of enriched regions for different elements are clearly defined, the grain size distribution is uneven, and some coarse grains are present. However, the alloy treated by the heat treatment method described in this invention, which integrates activation, powder preparation, and microstructure homogenization, shows a significant improvement in compositional segregation in its microstructure. The distribution of each element is more diffuse and uniform, the grains are finer and their size distribution is more regular, the previously clear boundaries of enriched regions become blurred, and the overall microstructure exhibits a high degree of homogenization. This optimization of the microstructure is a crucial microscopic basis for improving the alloy's hydrogen storage performance, reducing the activation temperature, and decreasing its hardness.

[0052] Example 1 In the heat treatment method for vanadium-based hydrogen storage alloys that integrates activation, powder preparation, and microstructure homogenization provided in this embodiment, the composition of the hydrogen storage alloy, expressed as a weight percentage, is shown in Table 1 below: Table 1. Composition table of sample 1 of the hydrogen storage alloy in this embodiment.

[0053] The heat treatment process in this embodiment specifically includes the following steps: Step 1: Insert the vanadium-based hydrogen storage alloy block into the quartz tube, evacuate for 10 minutes until the vacuum gauge reads below 0.1 Pa, then fill with inert protective gas argon until the vacuum pressure gauge reads -0.05 MPa. Evacuate again for 10 minutes until the vacuum gauge reads below 0.1 Pa. Fill with inert gas three times and purge completely to ensure that the air inside the quartz tube is completely replaced.

[0054] Step 2: Fill the quartz tube with a mixture of hydrogen and argon gas until the vacuum pressure gauge reads -0.03 MPa. The hydrogen volume in the mixture should account for 12% of the total volume. Seal the quartz tube. Place the sealed quartz tube into a heat treatment furnace and heat it to 800℃ at a rate of 10℃ / min. After reaching 800℃, continue heating to 1050℃ at a rate of 3℃ / min. Hold at this temperature for 12 hours and then cool to room temperature.

[0055] Step 3: Take samples before and after heat treatment, crush them separately, and take 1g of each sample to place in a hydrogen storage alloy PCT tester to test its activation temperature and hydrogen storage capacity. Take the block sample and cut it into 1cm×1cm×1cm blocks by wire cutting, grind and polish the surface, and place it in a Vickers hardness tester for Vickers hardness testing.

[0056] Testing in this embodiment demonstrated that a heat treatment process using a hydrogen-argon mixture with a hydrogen volume ratio of 12% and a two-stage heating process (first increasing the temperature to 800°C at 10°C / min, then to 1050°C at 3°C / min) followed by a 12-hour holding period successfully reduced the activation temperature of the vanadium-based hydrogen storage alloy from 400°C to 40°C and the Vickers hardness from 285HV to 213HV, while simultaneously increasing the hydrogen storage capacity by 0.1wt%. This indicates that the heat treatment method effectively solves the problems of high activation temperature and difficulty in crushing and pulverizing vanadium-based hydrogen storage alloys, and improves their hydrogen storage performance.

[0057] Example 2 The heat treatment method for vanadium-based hydrogen storage alloys, which integrates activation, powder preparation, and microstructure homogenization, provided in this embodiment, has the following components and their weight percentages: Table 2 below. Table 2. Composition table of sample 2 of the hydrogen storage alloy in this embodiment.

[0058] The heat treatment process in this embodiment specifically includes the following steps: Step 1: Insert the vanadium-based hydrogen storage alloy block into the quartz tube, evacuate for 10 minutes until the vacuum gauge reads below 0.1 Pa, then fill with inert protective gas argon until the vacuum pressure gauge reads -0.05 MPa, then evacuate for 10 minutes until the vacuum gauge reads 0.05 Pa. Repeat the process of filling with inert gas three times and then purging it completely to ensure that the air inside the quartz tube is completely replaced.

[0059] Step 2: Fill the quartz tube with a mixture of hydrogen and argon gas until the vacuum pressure gauge reads -0.04 MPa. The hydrogen volume in the mixture should account for 17% of the total volume. Seal the quartz tube. Place the sealed quartz tube into a heat treatment furnace and heat it to 800℃ at a rate of 10℃ / min. After reaching 800℃, continue heating to 1050℃ at a rate of 4℃ / min. Hold at this temperature for 16 hours and then cool to room temperature.

[0060] Step 3: Take samples before and after heat treatment, crush them separately, and take 1g of each sample to place in a hydrogen storage alloy PCT tester to test its activation temperature and hydrogen storage capacity. Take the block sample and cut it into 1cm×1cm×1cm blocks by wire cutting, grind and polish the surface, and place it in a Vickers hardness tester for Vickers hardness testing.

[0061] Example 3 The heat treatment method for vanadium-based hydrogen storage alloys, which integrates activation, powder preparation, and microstructure homogenization, provided in this embodiment, has the following components and their weight percentages: Table 3 below. Table 3. Composition table of sample 3 of the hydrogen storage alloy in this embodiment.

[0062] The heat treatment process in this embodiment includes the following steps: Step 1: Place the vanadium-based hydrogen storage alloy block into the quartz tube, evacuate for 10 minutes until the vacuum gauge reads below 0.1 Pa, then fill with inert protective gas argon until the vacuum pressure gauge reads -0.05 MPa. Evacuate again for 10 minutes until the vacuum gauge reads below 0.1 Pa. Repeat this process three times, purging completely to ensure thorough air replacement within the quartz tube.

[0063] Step 2: Fill the quartz tube with a mixture of hydrogen and argon until the pressure gauge reaches -0.03 MPa. The hydrogen volume in the mixture should be 12% of the total volume. Seal the quartz tube. Place the sealed quartz tube into a heat treatment furnace and heat it to 800°C at a rate of 10°C / min. After reaching 800°C, continue heating to 1050°C at a rate of 3°C / min. Hold the temperature for 12 hours, then cool to room temperature.

[0064] Step 3: Take samples before and after heat treatment, crush them separately, and take 1g of each sample into a hydrogen storage alloy PCT tester to test its activation temperature and hydrogen storage capacity. Take a block sample and cut it into 1cm×1cm×1cm blocks by wire cutting, grind and polish the surface, and then place it in a Vickers hardness tester for Vickers hardness testing.

[0065] Example 4 The heat treatment method for vanadium-based hydrogen storage alloys, which integrates activation, powder preparation, and microstructure homogenization, provided in this embodiment, has the following components and their weight percentages: Table 4 below. Table 4. Composition table of sample 4 of the hydrogen storage alloy in this embodiment.

[0066] The heat treatment process in this embodiment includes the following steps: Step 1: Place the vanadium-based hydrogen storage alloy block into the quartz tube, evacuate for 10 minutes until the vacuum gauge reads below 0.1 Pa, then fill with inert protective gas argon until the vacuum pressure gauge reads -0.05 MPa. Then evacuate again for 10 minutes until the vacuum gauge reads below 0.1 Pa. Fill with inert gas three times and then purge completely to ensure that the air inside the quartz tube is completely replaced.

[0067] Step 2: Fill the quartz tube with a mixture of hydrogen and argon gas until the pressure gauge reaches -0.03 MPa. The hydrogen volume in the mixture should account for 15% of the total volume. Seal the quartz tube. Place the sealed quartz tube into a heat treatment furnace and heat it to 800°C at a rate of 10°C / min. After reaching 800°C, continue heating to 950°C at a rate of 3°C / min. Hold the temperature for 12 hours and finally cool it to room temperature.

[0068] Step 3: Take samples before and after heat treatment, crush them separately, and take 1g of each sample into a hydrogen storage alloy PCT tester to test its activation temperature and hydrogen storage capacity. Take the block sample and cut it into 1cm×1cm×1cm blocks by wire cutting, grind and polish the surface, and then place it in a Vickers hardness tester for Vickers hardness testing.

[0069] Table 5 Test data of samples before and after heat treatment in the examples

[0070] The results of Example 1 are analyzed as follows: Example 1 shows the alloy composition and weight percentage as follows: V: 80%, Ti: 8%, Cr: 12%. Before heat treatment, the alloy had a high activation temperature (400℃), a high hardness (285 HV), and a hydrogen storage capacity of 3.45 wt%. Under heat treatment conditions of 12% hydrogen volume in a mixed gas, 1050℃, and a holding time of 12 hours, the alloy activation temperature was reduced to 40℃, the Vickers hardness was reduced to 213 HV, and the hydrogen storage capacity of the hydrogen storage alloy was increased by 0.1 wt%. Therefore, the heat treatment process of this invention can effectively reduce the activation temperature and hardness of the alloy, improve its performance, and play a positive role in its applications in powder preparation and hydrogen storage.

[0071] The results of Example 2 are analyzed as follows: The composition and weight range of the alloy in Example 2 are: V: 75%, Ti: 8%, Cr: 14%, Fe: 3%. In this example, the addition of Fe increased the Vickers hardness of the alloy, making activation more difficult. Therefore, in the heat treatment process, increasing the volume ratio of hydrogen and extending the activation time allowed for a more complete reaction between the alloy and hydrogen, resulting in a more uniform microstructure. Under heat treatment conditions of 17% hydrogen volume in the mixed gas, 1050℃, and a holding time of 16 hours, the alloy activation temperature was reduced to 80℃, the Vickers hardness decreased to 218 HV, and the hydrogen storage capacity of the hydrogen storage alloy increased from 3.38 wt% to 3.51 wt%. This heat treatment process effectively reduces the alloy's hardness, significantly reduces the difficulty of crushing and pulverizing the alloy, and also significantly improves the alloy's activation performance and hydrogen storage capacity.

[0072] The results of Example 3 are analyzed as follows: The alloy composition and weight content of Example 3 were: V: 70%, Ti: 7%, Cr: 17%, Fe: 3%. Compared with Examples 1 and 2, the V content was reduced, and the Vickers hardness of the alloy decreased to 275 HV. However, due to the presence of Fe, the alloy was still difficult to activate. Therefore, under the heat treatment conditions of 12% hydrogen volume in the mixed gas, 1050℃, and 12 hours of holding, the alloy activation temperature was reduced to 80℃, the Vickers hardness was reduced to 210 HV, and the hydrogen storage capacity of the hydrogen storage alloy increased from 3.49 wt% to 3.61 wt%. The effect of improving the activation temperature, alloy hardness, and hydrogen storage capacity of the alloy was very significant.

[0073] Regarding Example 4: The alloy composition and weight percentage of Example 4 are as follows: V: 75%, Ti: 8%, Cr: 12%, Mn: 5%. The addition of Mn reduced the hydrogen storage capacity of the alloy, but also decreased its Vickers hardness. Under heat treatment conditions of 17% hydrogen volume in the mixed gas, 950°C, and 12 hours of holding, the activation temperature of the alloy decreased from 400°C to 40°C, and the Vickers hardness decreased to 213 HV. Simultaneously, the hydrogen storage capacity of the alloy increased from 3.21 wt% to 3.37 wt%, an increase of 0.16 wt%. This demonstrates that when the hydrogen volume fraction is higher than 10%, and with appropriate heat treatment temperature and time, the activation temperature and hydrogen storage capacity of vanadium-based hydrogen storage alloys can be significantly improved, optimizing the alloy's high strength, high hardness, and fracture-resistant physical properties.

[0074] In summary, the heat treatment method for vanadium-based hydrogen storage alloys that integrates activation, powder preparation, and microstructure homogenization provided by this invention offers an effective approach and measure for the practical application of vanadium-based hydrogen storage alloys, and promotes the development of the solid-state hydrogen storage industry.

[0075] In summary, this is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this invention should be included within the scope of protection of this invention.

Claims

1. A vanadium-based hydrogen storage alloy, characterized in that, Its chemical composition by weight percentage includes: V: 68%~80%, Ti: 7%~12%, Cr: 10%~20%, (Fe+Zr+Mn): 2%~8%; It is prepared by a heat treatment method for vanadium-based hydrogen storage alloys, the heat treatment method comprising the following steps: Step 1: Atmosphere alteration and preparation; The vanadium-based hydrogen storage alloy sample was placed inside a quartz tube and subjected to inert atmosphere replacement. Step 2: Filling and sealing the mixed gas; After the atmosphere replacement is completed, a mixture of hydrogen and argon in a specific ratio is introduced into the quartz tube so that the vacuum pressure gauge shows -0.02 to -0.04 MPa. In the mixture of hydrogen and argon, the volume fraction of hydrogen is 10% to 20%. After the gas filling is completed, the quartz tube is sealed. Step 3: Staged high-temperature heat treatment; The sealed quartz tube is placed in a heat treatment furnace for two stages of heating and heat preservation. First stage of heating: rapidly raise the furnace temperature to 800℃ at a rate of 10~20℃ / min; The second stage of heating and holding: After the furnace temperature reaches 800℃, continue to heat up to the specified temperature of 900℃~1200℃ at a rate of 3~5℃ / min, and hold at this temperature for 10~20 hours. Step 4: Cooling; After the heat treatment is completed, the quartz tube is removed from the heat treatment furnace and cooled to room temperature.

2. The vanadium-based hydrogen storage alloy according to claim 1, characterized in that, Its chemical composition by weight percentage includes: V: 70%~80%, Ti: 9%~12%, Cr: 14%~20%, (Fe+Zr+Mn): 4%~8%.

3. The vanadium-based hydrogen storage alloy according to claim 1, characterized in that, Its chemical composition by weight percentage includes: V: 72%~80%, Ti: 10%~12%, Cr: 16%~20%, (Fe+Zr+Mn): 4%~6%.

4. A heat treatment method for a vanadium-based hydrogen storage alloy, characterized in that, A method for heat-treating the vanadium-based hydrogen storage alloy according to any one of claims 1 to 3; the heat treatment method includes the following steps: Step 1: Atmosphere alteration and preparation; The vanadium-based hydrogen storage alloy sample was placed inside a quartz tube and subjected to inert atmosphere replacement. Step 2: Filling and sealing the mixed gas; After the atmosphere replacement is completed, a mixture of hydrogen and argon in a specific ratio is introduced into the quartz tube so that the vacuum pressure gauge shows -0.02 to -0.04 MPa. Step 3: Staged high-temperature heat treatment; The sealed quartz tube is placed in a heat treatment furnace for two stages of heating and heat preservation. Step 4: Cooling; After the heat treatment is completed, the quartz tube is removed from the heat treatment furnace and cooled to room temperature.

5. The heat treatment method for the vanadium-based hydrogen storage alloy according to claim 4, characterized in that, In step 1, the vacuum is evacuated for 9-11 minutes to ensure the vacuum level is between 0.01 and 0.1 Pa; then, inert protective gas is introduced until the vacuum pressure gauge shows -0.05 MPa.

6. The heat treatment method for the vanadium-based hydrogen storage alloy according to claim 5, characterized in that, In step 1, the vacuum is evacuated again for 9-11 minutes to ensure that the vacuum degree is 0.01~0.1 Pa; the inflation-vacuuming process is repeated three times to ensure that the air in the quartz tube is completely expelled.

7. The heat treatment method for the vanadium-based hydrogen storage alloy according to claim 6, characterized in that, In step 2, the volume fraction of hydrogen in the hydrogen and argon mixture is 14% to 20%.

8. The heat treatment method for the vanadium-based hydrogen storage alloy according to any one of claims 4 to 7, characterized in that, In step 4, after heat treatment and cooling, the alloy is vacuumed for 3000s at an activation temperature ≤80℃, and then hydrogen is absorbed once under hydrogen conditions at 40℃ and 8MPa. The vanadium-based hydrogen storage alloy can then be fully activated.

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