CN115852273B - Preparation method of nanocrystalline magnesium-based hydrogen storage alloy - Google Patents

Abstract

The invention discloses a preparation method of a nanocrystalline magnesium-based hydrogen storage alloy, which is Mg-RE-TM alloy prepared by induction smelting, rapid solidification, primary crystallization and secondary crystallization in sequence. The invention carries out step-by-step annealing in the hydrogen atmosphere by differential pressure, so that the amorphous alloy is crystallized, and the second phase pinning effect is utilized, thereby finally obtaining the superfine nanocrystalline, the alloy structure is stable, the hydrogen absorption and desorption performance is excellent, the method is simple and easy to operate, the production stability is good, and the method is suitable for large-scale production.

Description

A kind of preparation method of nanocrystalline magnesium-based hydrogen storage alloy

technical field

The invention belongs to the technical field of preparation of rare earth hydrogen storage materials, and relates to a preparation method of a nanocrystalline magnesium-based hydrogen storage alloy.

Background technique

Hydrogen energy is a highly energy-dense and truly clean energy source. In the hydrogen energy utilization link, the storage of hydrogen is very important. The use of metal hydrides for solid-state hydrogen storage is one of the feasible hydrogen storage methods, and the hydrogen storage metal material that has attracted much attention is magnesium-based hydrogen storage alloys because of their high energy storage density and rich content . However, the poor hydrogen absorption and desorption kinetics of magnesium-based hydrogen storage alloys greatly restricts its application and development.

Preparation of magnesium-based alloys into nanocrystals is an effective way to improve their hydrogen absorption and desorption kinetics. At present, many methods for preparing nanocrystalline magnesium-based alloys include mechanical alloying, chemical synthesis, and thin-film methods. Although these methods can effectively obtain ultrafine structures with a size less than 100 nanometers, the process is relatively complicated. More sophisticated instruments and equipment are required, and the suitable process window is very narrow. At the same time, these methods are not suitable for large-scale industrial production. In addition, since magnesium-based hydrogen storage alloys need to absorb and desorb hydrogen at relatively high temperatures (usually exceeding 250 degrees Celsius), a hydride formation-decomposition phase transition reaction will occur during the hydrogen absorption and desorption process. Under the double action of the nanocrystals, the nanocrystals will grow up, which will cause the rapid decline of the nanocrystal structure during the hydrogen absorption and desorption cycle, and the advantages of the nanocrystal properties will be lost.

Traditional physical metallurgy is an important method for large-scale metal material processing in industry. However, due to the high interfacial energy of the nanocrystalline structure, conventional physical metallurgical methods such as smelting, pressure processing, and heat treatment cannot obtain nanocrystalline magnesium-based hydrogen storage alloys. Therefore, there is an urgent need to develop a method for preparing high-performance nanocrystalline magnesium-based hydrogen storage alloys based on the crystallization of amorphous alloys.

Contents of the invention

The present invention aims to provide a method for preparing a nanocrystalline magnesium-based hydrogen storage alloy, the alloy is a Mg-RE-TM alloy, the alloy composition is Mg ₈₀ (La, Y) ₆ Ni ₁₂ Al ₂ , and the alloy is successively subjected to induction melting , rapid solidification, primary crystallization and secondary crystallization, the amorphous alloy is crystallized by differential pressure annealing in a hydrogen atmosphere, and the pinning effect of the second phase is used to finally obtain a super Fine nanocrystals, stable alloy structure and excellent hydrogen absorption and desorption performance, the method is simple and easy to operate, has good production stability, and is suitable for large-scale production.

Technical scheme of the present invention is as follows:

The present invention also provides a preparation method of nanocrystalline magnesium-based hydrogen storage alloy, which is carried out sequentially according to the following steps:

S1. Prepare a Mg-RE-TM alloy by induction melting a high-purity metal with a purity higher than 99.9% in an inert atmosphere. The alloy composition is Mg ₈₀ (La,Y) ₆ Ni ₁₂ Al ₂ , and A is obtained after melting. Considering Mg and RE burning loss during the smelting process, it is necessary to add 5-10wt.% Mg and 1-5wt.% RE as burning supplement;

S2. Spray the melt of A on a rapidly rotating water-cooled copper roller by a rapid solidification method to obtain an amorphous alloy, and obtain B;

S3. Mechanically crush B to less than 200 mesh, put it into a heated airtight container and mechanically evacuate it for more than 0.5h, then introduce high-purity hydrogen under normal pressure, and repeat the gas washing for more than 3 times to remove the surface of the alloy and the inside of the heating container impurity gas; after scrubbing, put 0.05-0.15 MPa high-purity hydrogen into the heating container, heat to 120-160°C, keep warm for 0.1-3h, and the preliminary crystallization is completed to obtain C;

S4. Under the premise of maintaining the temperature of the S3 process, increase the hydrogen pressure to keep the hydrogen pressure at 0.5-1 MPa, then heat to 250-350°C, keep it warm for 0.1-0.5h, and the crystallization is completed to obtain a nanocrystalline magnesium-based hydrogen storage alloy.

The present invention adopts an amorphous-crystallization process, wherein the two crystallization processes are different from activation under a certain hydrogen gas, and the preliminary crystallization of the present invention is carried out under a certain hydrogen pressure, in order to obtain a certain amount of, Fine and dispersed REH _x phase, while retaining most of the amorphous matrix (if there is no hydrogen induction, the intermetallic compound phase will be preferentially formed during the crystallization process); hydrogen pressure should not be too high at this stage, too high will promote the REH _x phase The formation and growth of other phases, while promoting the crystallization of other phases, can not form a dispersion effect. The relationship between hydrogen pressure, container volume and amorphous alloy can be controlled in the range of H/M0.05-H/M0.15 according to the hydrogen absorption experiment. In addition, the initial crystallization temperature is set low to avoid significant crystallization of other phases. The diffusion ability of elements at low temperature is limited. In order to form a sufficient amount of REH _x phase, a slower heating rate and a longer holding time are required; another effect of a certain hydrogen pressure and a longer holding time in the initial crystallization is that in the The short-range ordered enrichment of different element enrichment is formed before the final crystallization of the second step, which provides compositional and structural conditions for a large number of nucleation in the final crystallization of the second step.

The purpose of the secondary crystallization is to quickly complete the crystallization of the remaining amorphous matrix. Maintaining a certain hydrogen pressure is conducive to ensuring the stability of the REH _x phase precipitated by the primary crystallization, and is also conducive to the improvement of the thermodynamic stability of the amorphous alloy, thereby delaying the crystallization. The subsequent crystallization at a higher temperature leads to more crystallization nucleation and shortens the growth time, which is beneficial to the refinement of nanocrystals. However, at this stage, the hydrogen pressure should be controlled not to be too high, so as to avoid all conversion into hydrides and excessive growth of hydrides.

As a limitation of the above-mentioned method of the present invention, in step S2, the rotation speed of the copper roller is 20-30 m/s.

As a second limitation of the above-mentioned method of the present invention, in step S3, the heating rate is 0.5-5° C./min.

As a third limitation of the above method of the present invention, in step S4, the heating rate is greater than or equal to 10° C./min.

Since the crystallization temperature of the final crystallization is significantly higher than that of the initial crystallization, the main reason is to avoid uneven growth during the crystallization process. The heating rate at this stage is not lower than 10°C/min. The crystallization temperature and the short-term heat preservation are used to compress the crystallization to the final stage, which is conducive to a large number of nucleation and inhibition of growth, so as to obtain finer grains; at this stage, the temperature should not be higher (beyond the present invention) heating temperature, in order to avoid the decomposition of REH _x phase and lose the pinning effect. At the same time, although the heating temperature is too high to accelerate the crystallization, due to the accelerated diffusion at high temperature, it will cause serious grain growth. The shorter holding time is also to avoid the growth of grains, and to form as much as possible before hydrogen absorption and desorption. Fine, uniform primary tissue.

The above method of the present invention also has a limitation that the nanocrystalline magnesium-based hydrogen storage alloy can absorb hydrogen at a temperature lower than 100°C, and the hydrogen absorption amount is greater than or equal to 3 wt.%.

The magnesium-based hydrogen storage alloy Mg-RE-TM prepared by the above-mentioned amorphous-crystallization process of the present invention has a uniform ultrafine structure smaller than 50nm, and the phase structure therein includes: Mg ₂ TM, Mg, REH _x and other small amounts The second phase, in which the REH _x phase is evenly distributed around the main phase Mg ₂ TM and Mg, is very fine and dispersed because the REH _x phase is formed at low temperature, and this phase can exist stably at the hydrogen absorption and desorption temperature (below 500 ° does not decompose), thus playing a strong second-phase pinning role. In addition, the REH _{x phase} has more crystallographic interface matching relationship with the Mg ₂ TM phase, so in the second crystallization process, it can be used as the attached particle for the nucleation and growth of the Mg ₂ TM phase, thereby further improving the crystallization structure. The fineness and dispersion of the phase finally achieves the use of the pinning effect of this phase to effectively prevent the growth of the crystal grains during the hydrogen absorption and desorption process and maintain the stability of the nanocrystals.

The Mg content in the hydrogen storage alloy of the present invention cannot be too high, and contains other two types of metal elements to ensure sufficient amorphous formation ability to obtain a complete amorphous structure after rapid solidification; a certain content of rare earth elements to ensure Sufficient REH _x phases are obtained during hydrogen atmosphere crystallization; a certain content of transition group metal elements ensures that the Mg ₂ TM phase is crystallized immediately after the first step of crystallization (before heating to 160°C) (this process needs to be avoided The initial crystallization phase is Mg-RE-TM ternary phase), thus forming an effective interlaced phase structure distribution, and there are more crystallographically good interface matching relationships between the two structures, which is conducive to interface stability and thus is beneficial to Maximize the pinning effect of the second phase.

The preparation method of the present invention is taken as a whole, and each step is closely related and indispensable, and the nanocrystalline magnesium-based hydrogen storage alloy is formed together as a whole. After adopting the technical scheme of the present invention, the obtained technical effects are as follows:

1. The preparation method is simple, the process is easy to control, the cost is low, the cycle is short, and it is convenient for industrialized production.

2. The prepared nanocrystalline hydrogen storage alloy has excellent hydrogen absorption and desorption kinetics and good cycle stability, and can absorb hydrogen below 100°C, and start to release hydrogen below 200°C; structure, and the catalysis of the REH _x phase, the hydrogen absorption and desorption performance of the alloy has been _greatly improved. In addition, unlike the REH _x phase that also exists after the hydrogen absorption and desorption of the alloy under the similar composition, the REH _x phase in the alloy of the present invention is stable and dispersed before the hydrogen absorption and desorption, and will not be subsequently absorbed and desorbed. Participate in the reaction during the process, so the pinning effect always exists in the process of hydrogen absorption and desorption, and the hydrogen storage performance of the alloy is highly stable.

The invention is suitable for preparing magnesium-based hydrogen storage alloy.

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is the XRD pattern of alloy after the rapid solidification of embodiment 1;

Fig. 2 is the TEM image of the alloy after preliminary crystallization of Example 1, wherein: (a)-dark field image, (b)-high resolution electron image, (c)-selected area electron diffraction;

Fig. 3 is the morphology and energy spectrum distribution figure of the alloy after the preliminary crystallization of embodiment 1;

Figure 4 is a TEM image of the alloy structure after the final crystallization of Example 1, wherein: (a)-bright field image, (b)-dark field image, (c)-selected area electron diffraction;

Fig. 5 is the hydrogen absorption curve of the alloy tested by the high pressure differential calorimeter of the nanocrystalline magnesium-based hydrogen storage alloy prepared in Example 1;

Fig. 6 is the graph of the hydrogen absorption test at 70°C of the nanocrystalline magnesium-based hydrogen storage alloy prepared in Example 1;

Fig. 7 is the structure TEM test picture of the nanocrystalline magnesium-based hydrogen storage alloy prepared in Example 1 after absorbing hydrogen, in which: (a)-bright field image (the inset is the dark field image of the corresponding area), (b)-high Resolved electron image, (c)-selected area electron diffraction.

Detailed ways

In the following examples, unless otherwise specified, commercially available reagents are used for the reagents, and the following experimental methods and detection methods, unless otherwise specified, are all used existing experimental methods and detection methods.

Example 1

The composition of the alloy prepared in this embodiment is Mg ₈₀ (La,Y) ₆ Ni ₁₂ Al ₂ . The preparation process of the alloy is carried out in sequence according to the following steps:

S1. According to the design composition, and considering 6wt.% Mg and 2wt.% RE as burning loss, the high-purity metal raw materials (Mg, La, Y, Ni, Al) with a purity higher than 99.9% are melted by induction The alloy is smelted and remelted 3 times to ensure uniformity, and high-purity argon is introduced as a protective gas during the process;

S2, utilizing the rapid solidification method to spray the re-melted alloy melt on a water-cooled copper roll with a rotation speed of 30m/s to obtain an amorphous alloy, the XRD test of Figure 1 shows that the rapid solidification alloy is a complete amorphous alloy;

S3. Mechanically crush the amorphous alloy obtained above to below 200 mesh, put it into a heated airtight container and first mechanically evacuate it for 0.5h, feed high-purity hydrogen under normal pressure, and repeatedly wash the gas more than 3 times to remove the alloy surface and Heating the impurity gas in the container; after scrubbing, inject 0.1 MPa high-purity hydrogen into the heating container, heat it to 150°C at a heating rate of 1°C/min, and keep it for 0.5h to complete the preliminary crystallization process;

After the initial crystallization, the alloy forms a large number of dispersed REH _x phase particles, as shown in (a) and (b) in Figure 2, the size of which does not exceed 20nm, and the distribution is very diffuse. Selected area electron diffraction (c) The diffraction ring also proves the nanocrystalline structure; at the same time, transmission electron microscopy and energy spectrum distribution show that the crystallization phase shows the aggregation of La element distribution, which also proves that the initially formed compound is a nanoscale REH _x phase, as shown in Figure 3 shown;

S4. Then, under the premise of maintaining the above temperature, increase the hydrogen pressure and keep the hydrogen pressure at 0.5 MPa, then heat to 300°C at a heating rate of 10°C/min, and keep it for 0.25h to complete the final crystallization. After the final crystallization The grain size distribution of the alloy is uniform, basically distributed in the 10-20nm scale, as shown in (a), (b) and (c) in Figure 4.

The hydrogen storage alloy prepared above was tested for its hydrogen absorption and desorption performance. After three cycles of hydrogen absorption and desorption at 300°C, the hydrogen absorption temperature of the alloy can be as low as only 70°C, as shown in Figure 5 (the test hydrogen pressure is 3MPa, The heating rate is 10°C/min).

Compared with previously reported magnesium-based alloys, this alloy exhibits excellent hydrogen absorption capacity due to its ultrafine nanocrystalline structure. The hydrogen absorption test of the alloy at 70 °C shows that the alloy can absorb about 3.2 wt.% of hydrogen, as shown in Figure 6.

After hydrogen absorption, the hydrogen storage alloy was tested by TEM, and the results showed that the hydrogen storage alloy still exhibited a good nanocrystalline structure, as shown in (a), (b) and (c) in Figure 7, which shows that through the above The nanocrystalline magnesium-based alloy prepared by the method has good structural stability, which can further ensure its excellent hydrogen absorption and desorption stability after repeated hydrogen absorption and desorption. The kinetic performance of the alloy in this embodiment was measured after 20 cycles of hydrogen absorption and desorption. At 70° C., the alloy can absorb about 3.16 wt.% of hydrogen.

Example 2-4

The preparation of alloys in Example 2-4 of this embodiment is the same as that of Example 1, and the preparation process is similar to that of Example 1, except that the relevant parameters in the preparation process are different. As shown in the table below:

comparative example

In this example, a series of studies on the preparation process of different hydrogen storage alloys were carried out. The compositions of the prepared alloys were all the same as in Example 1, and the alloy composition was Mg ₈₀ (La,Y) ₆ Ni ₁₂ Al ₂ . The difference was only In that: the method steps of the preparation process are different.

Group A: Induction melting was carried out according to the step S1 of Example 1, and then the alloy was cast to form an alloy ingot, and then the hydrogen storage kinetic performance test was performed on it.

Group B: Induction melting is carried out according to the S1 step of Example 1, and then the alloy is cast to form an alloy ingot, which is then placed in a tube furnace for heat treatment and annealing under an inert atmosphere. , the final hydrogen storage alloy was obtained, and its hydrogen storage kinetic performance was tested.

Group C: Steps S1, S2, and S3 were performed according to Example 1. After one-step crystallization was completed, the kinetic performance test was performed on the hydrogen storage alloy.

Group D: Steps S1, S2, and S4 were performed according to Example 1, and after one-step crystallization was completed, the kinetic performance test was performed on the hydrogen storage alloy.

Group E: After performing steps S1 and S2 according to Example 1, the alloy was physically crushed, and the kinetic performance test was performed on the hydrogen storage alloy. Before the test, two cycles of hydrogen charging and discharging were performed. The hydrogen pressure is 0.1 MPa, the holding time is 0.5h, and then the hydrogen is degassed at 300°C for 1h. After activation, the hydrogen storage kinetics performance test was carried out.

Group F: After performing steps S1 and S2 according to Example 1, the alloy was physically crushed, and the kinetic performance test was performed on the hydrogen storage alloy. Before the test, two cycles of hydrogen charging and discharging were performed. The hydrogen pressure is 0.1 MPa, the holding time is 0.5h, and then the hydrogen is degassed at 300°C for 1h. After activation, the hydrogen storage kinetics performance test was carried out.

The test results of the above groups A-G are as follows:

Finally, it should be noted that: the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still The technical solutions recorded in the foregoing embodiments may be modified, or some technical features thereof may be equivalently replaced. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (4)

1. The preparation method of the nanocrystalline magnesium-based hydrogen storage alloy is characterized by sequentially carrying out the following steps:

s1, preparing Mg-RE-TM alloy by an induction smelting method under inert atmosphere by using high-purity metal with purity higher than 99.9%, wherein the alloy comprises the following components of Mg ₈₀ (La,Y) ₆ Ni ₁₂ Al ₂ Obtaining A after smelting, and considering the burning loss of Mg and RE in the smelting process, respectively adding 5-10wt.% of Mg and 1-5wt.% of RE as burning loss supplement;

s2, spraying the melt of the A on a rapidly rotating water-cooled copper roller by using a rapid solidification method to obtain amorphous alloy, so as to obtain B;

s3, mechanically crushing the B to below 200 meshes, putting the crushed B into a heating closed container, mechanically vacuumizing for more than 0.5h, then introducing high-purity hydrogen under normal pressure, and repeatedly washing the gas for more than 3 times to remove impurity gases on the surface of the alloy and in the heating container; after gas washing, introducing 0.05-0.15 MPa high-purity hydrogen into a heating container, heating to 120-160 ℃, preserving heat for 0.1-3h, and obtaining C after preliminary crystallization;

and S4, on the premise of keeping the temperature of the S3 process, raising the hydrogen pressure to keep the hydrogen pressure at 0.5-1 MPa, then heating to 250-350 ℃, keeping the temperature for 0.1-0.5h at a heating rate of more than or equal to 10 ℃/min, and obtaining the nanocrystalline magnesium-based hydrogen storage alloy after crystallization.

2. The method for producing a nanocrystalline magnesium-based hydrogen storage alloy according to claim 1, wherein in step S2, the rotation speed of the copper roller is 20 to 30m/S.

3. The method of claim 1, wherein in step S3, the heating rate is 0.5-5 ℃/min.

4. A method of preparing a nanocrystalline magnesium-based hydrogen storage alloy according to any one of claims 1 to 3, wherein the nanocrystalline magnesium-based hydrogen storage alloy is capable of absorbing hydrogen at a temperature below 100 ℃ in an amount of 3% or more wt%.

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