A getter alloy that can be used for the purification of nitrogen and inert gases, its preparation and application

Abstract

A getter alloy that can be used for the purification of nitrogen and inert gases. The alloy is composed of three main elements: zirconium, niobium, and iron, with a nominal composition of (Zr 1‑x Nb x )yFe 1‑y . The alloy composition also contains one or two of the additional elements such as rare earth RE (Ce, La), etc. The alloy is made by induction melting using 99.9% metallic elements of Zr, Fe, Nb and rare earth elements with a purity of 99.5% under the protection of vacuum or inert atmosphere. The alloy has a high H2 absorption capacity and an adjustable N2 adsorption capacity, and can be used in occasions such as the purification of nitrogen and inert gases.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-evaporable getter materials, and particularly relates to a getter alloy that can be used for purifying nitrogen and inert gases and a preparation method thereof, which can be used for applications such as purifying nitrogen or inert gases or recovering hydrogen in nitrogen and inert gases. Background Art

[0002] Getter alloys can effectively absorb active gases such as H2, CO, CH4, H2O, N2, etc., and are widely used in fields such as high vacuum acquisition or maintenance, gas purification, and recovery of hydrogen isotope-containing tail gas. When purifying gas or treating and recovering hydrogen isotope-containing tail gas, the mixed gas passes through a purification column containing a getter material, and the getter alloy in the column selectively absorbs and adsorbs H2, CO, CH4, H2O, etc. to achieve the purpose of purifying gas or recovering hydrogen.

[0003] Zr2Fe alloy has an extremely low hydrogen adsorption equilibrium pressure (Fusion Engineering and Design. 1997, 36(4): 471-478) and a hydrogen adsorption capacity of about 120 ml / g. When the alloy is heated to 200-350 °C, it can undergo chemisorption reactions with gases such as CO, CH4, H2O, CO2, etc., but the adsorption of N2 gas is slow and the adsorption capacity is very low. Therefore, it is often used for nitrogen purification and adsorption and recovery of trace hydrogen isotope gases in nitrogen-containing atmospheres. For example, Zr2Fe alloy adsorbs and recovers 0.1 vol.% and 1 vol.% hydrogen in pure nitrogen at a pressure of 350 °C and 2.5×10 5 Pa, and the recovery efficiencies reach 94% and 98% respectively (Fusion Science and Technology. 2017, 71(3): 321-325).

[0004] Zr2Fe reacts slowly with nitrogen and has a low capacity, and does not undergo any chemical reaction with inert gases. Therefore, it can also be used for the recovery of hydrogen isotope gases in inert gases. To improve the adsorption efficiency of the alloy for hydrogen isotope gases, the alloy generally needs to be heated to 350 °C to promote the reaction process. At this time, in addition to adsorbing hydrogen, the alloy can also undergo irreversible chemical reactions with CO, CH4, H2O, CO2, etc., thereby realizing the purification function of inert gases. However, due to the slow reaction of the Zr2Fe alloy with nitrogen and its very low adsorption capacity, it is relatively easy to reach the nitrogen adsorption stable state. Therefore, it is impossible to effectively remove nitrogen in inert gases and reduce the purification purity of inert gases. Generally, Zr2Fe is used in combination with getter alloys such as ZrVFe or ZrC to achieve chemical desorption of hydrogen and nitrogen in inert gases. However, the mixing ratio and filling state of different types of getter alloys have a great impact on the purification effect. When the mixing is uneven, the inert gas may short-circuit through the reaction bed, resulting in the inert gas containing a high amount of nitrogen or H2. In addition, although almost all getter alloys can adsorb hydrogen, there are significant differences in the hydrogen adsorption capacity and rate, which will all cause potential hazards of inconsistent purification performance of inert gases.

[0005] Therefore, it is necessary to develop a getter alloy that can be easily designed according to the purification requirements of nitrogen or inert gases. By adjusting the alloy composition, it can have a high hydrogen adsorption capacity and rate, as well as a suitable nitrogen adsorption capacity to meet the purification requirements of inert gases; or it has a high hydrogen adsorption capacity and rate and a low nitrogen adsorption capacity to meet the nitrogen purification requirements, realizing multiple applications of one alloy. Summary of the Invention

[0006] In view of the defects existing in the prior art, in the first aspect of the present invention, a getter alloy capable of adsorbing nitrogen and hydrogen by adjusting the alloy composition is proposed. The getter alloy is composed of three main elements: zirconium, niobium, and iron, and the nominal composition is (Zr 1-x Nb x ) 67 Fe 33 , where 0 < x ≤ 0.5.

[0007] In the present invention, the composition of the getter alloy further includes one or two of the rare earth RE (Ce, La) additional elements. The weight of the additional element is 0.5 wt.% - 2.0 wt.%, preferably 1.0 wt.% - 1.5 wt.%, of the total weight of the three raw materials of the (Zr 1-x Nb x ) 67 Fe 33 alloy;

[0008] In the present invention, the particle size of the getter alloy powder of the getter alloy is less than 500 μm, preferably less than 300 μm.

[0009] In the present invention, by adjusting the alloy composition, the adsorption capacity and adsorption rate of nitrogen and hydrogen are adjusted to meet the purification requirements of nitrogen or inert gases.

[0010] In the second aspect of the present invention, a method for preparing the getter alloy described in the first aspect of the present invention is provided. It is prepared by melting pure elements (preferably in the form of lumps or flakes). The raw materials are high-purity Zr, Fe, and Nb metal with a purity greater than 99.9%, and the rare earth element has a purity greater than 99.5%. Melting is carried out under vacuum or inert gas protection to avoid oxidation of the alloy. Methods such as arc melting, vacuum induction melting, and electron beam melting can be used. Then, under argon gas protection, the alloy ingot is ground by mechanical crushing or ball milling, and the desired alloy powder is obtained by screening. Usually, the particle size is less than 500 μm, and a more preferred choice is below 300 μm.

[0011] In the present invention, the hydrogen and nitrogen performance of the getter alloy is evaluated by the isochoric method on a high-vacuum workbench. The stainless-steel sample container and the test system are separated by valves. Weigh 0.5 g of getter alloy powder labeled with different compositions and place them in stainless-steel containers with a volume of 20 ml respectively. After heating the containers containing the getter alloy to 673 K with an electric furnace and evacuating and activating for 60 minutes (the vacuum degree is better than 1.0×10 -4 Pa), then cool down and maintain at a certain temperature. Close the valve between the sample and the system, close the system vacuum, and fill the system with hydrogen and nitrogen at a certain pressure through the charging valve. After the pressure is stable, open the valve between the sample and the system. At this time, the getter is completely exposed to the hydrogen and nitrogen atmosphere with a certain initial pressure for testing. The adsorption of the above gases by the getter alloy will cause a change in the gas pressure in the system. According to the pressure change value, the adsorption isothermal kinetic curves of the getter alloy for hydrogen and nitrogen can be calculated, and the final adsorption capacity of different gases at different pressures can be obtained.

[0012] The advantages of the present invention are as follows:

[0013] The getter alloy of the present invention has a high hydrogen adsorption capacity under high-temperature conditions, and the N2 adsorption capacity can be adjusted within a wide range according to the alloy composition. This getter alloy belongs to the technical field of non-evaporable getter materials and can be used for the purification of nitrogen or inert gases, as well as for the recovery of low-pressure hydrogen in nitrogen or inert gases and other applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the hydrogen adsorption kinetic curve of (Zr 1-x Nb x ) 67 Fe 33 -Ce alloy at 603 K and 3 KPa.

[0015] Figure 2 is (Zr 0.95 Nb 0.05 ) 67 Fe 33 -RE alloy nitrogen adsorption kinetic curve at 623K and 0.5MPa Specific implementation mode

[0016] The technical solutions of the present disclosure will be described in detail below with specific embodiments in combination with the accompanying drawings.

[0017] Example 1

[0018] (Zr 1-x Nb x ) 67 Fe 33 -Ce alloy hydrogen adsorption performance. The alloy compositions of getter alloys A, B, C, D, E, F, and G are shown in Table 1. Specifically, the addition amount of the additional element Ce is kept unchanged at 1.5 wt%, and the Nb content is increased from 0.05 at% to 33 at%. The alloy is induction melted in a water-cooled copper crucible under argon atmosphere protection using Zr, Fe, and Nb metal single-element sheets with a purity greater than 99.9% and rare earth Ce with a purity greater than 99.5%. The alloy powder with a particle size less than 300 μm is obtained by mechanical crushing and screening under argon atmosphere protection. After the alloy powder is vacuum activated, the hydrogen adsorption performance test is carried out at 603K and 3KPa, and the kinetic curve is as Figure 1 shown. As can be seen from the attached Figure 1 figure, the alloy shows rapid hydrogen adsorption and reaches the saturated hydrogen adsorption phenomenon, that is, at the beginning of hydrogen adsorption, the adsorption capacity increases rapidly with time, and then the adsorption capacity slowly rises and finally reaches the saturated state. There are significant differences in the hydrogen adsorption rate and capacity of alloys with different Nb contents. As the Nb content increases, the saturated hydrogen adsorption capacity of the alloy shows a decreasing trend, but the hydrogen adsorption rate increases. For example, the saturated hydrogen adsorption capacity of the alloy with 3.4 at% Nb content is 85 ml / g, and the hydrogen adsorption is relatively fast in the first 10 minutes, but it takes 35 minutes to reach hydrogen saturation. The saturated hydrogen adsorption capacity of the alloy containing 33 at% Nb is 37.6 ml / g, and it reaches hydrogen saturation in 5 minutes. The saturated hydrogen adsorption capacity of all alloys is shown in Table 1.

[0019] Table 1

[0020]

[0021] Example 2:

[0022] Getter alloys A, B, C, D, E, F, and G with the same composition and preparation process as in Example 1 are used for the nitrogen adsorption performance test at 623K, and the nitrogen adsorption pressure is 0.5 MPa. The nitrogen adsorption kinetic curve is as Figure 2 shown. As can be seen from the attached Figure 2 figure, the alloy's adsorption of N2 is the same asFigure 1 The hydrogen absorption kinetic curves are significantly different. The N2 adsorption kinetics shows a parabolic shape, and the adsorption rate increases rapidly with the increase of Nb content. For example, the nitrogen absorption capacity of the alloy containing 33 at% Nb reaches 4 ml / g within 10 minutes, which is higher than the nitrogen absorption capacity of 1.53 ml / g of the 0.05 at% Nb alloy within 120 minutes. The nitrogen absorption capacity of the alloy with 3.4 at% Nb content reaches 3.5 ml / g in 120 minutes, which is more than twice that of the 0.05 at% Nb alloy. Different from the fact that hydrogen absorption can reach saturation relatively quickly, although the nitrogen absorption capacity and rate of the alloy increase with the increase of Nb content, they do not reach the saturation state even at 120 minutes. This shows that the nitrogen adsorption of the alloy is a continuous and slow process. Since the alloy has not reached the saturation capacity after 120 minutes of nitrogen absorption, the statistical results of the N2 adsorption capacity at 120 minutes are shown in Table 2 for comparison.

[0023] Table 2

[0024] Sample N2 absorption capacity at 120 min (ml / g) Alloy A 1.53 Alloy B 2.36 Alloy C 2.76 Alloy D 3.50 Alloy E 4.25 Alloy F 6.95 Alloy G 8.56

[0025] Example 3:

[0026] Relationship between the addition amount of additional element RE and the hydrogen absorption and nitrogen absorption characteristics of the alloy. The compositions of the getter alloys H, I, J, K, L, M, N, O, P, Q, R, S are shown in Table 3. Specifically, the alloy (Zr 0.95 Nb 0.05 ) 67 Fe 33 remains unchanged, and different RE elements are added and the total RE content is adjusted to vary from 0.5 at% to 2.0 at%. The alloy is made by induction melting using Zr, Fe, Nb metal single-element sheets with a purity greater than 99.9% and rare earth La and Ce with a purity greater than 99.5% as raw materials in a water-cooled copper crucible under argon atmosphere protection. The alloy ingot is mechanically crushed under argon atmosphere protection and screened to obtain powders with a particle size less than 300 μm. After vacuum activation, the alloy powders are respectively tested for hydrogen adsorption performance at 603 K and 3 KPa and nitrogen adsorption performance at 623 K and 0.5 MPa. The results are summarized in Table 3. It can be seen that whether La or Ce is added, when the weight of the added rare earth element increases to 1.5 wt%, the hydrogen absorption capacity of the alloy reaches the maximum value, and then begins to decrease with the increase of the rare earth amount; under the same addition weight, the hydrogen absorption capacity of the alloy with the added rare earth element Ce is higher than that with La added, and the hydrogen absorption capacity is in the middle when La and Ce are added in combination. The variation trend of the nitrogen adsorption capacity with the content and type of rare earth elements is similar to the hydrogen absorption performance.

[0027] Table 3

[0028]

[0029] As can be seen from the above embodiments and the results of the attached drawings, increasing the amount of alloy Nb reduces the hydrogen absorption capacity of the alloy, but increases the rate, which is very beneficial for improving the hydrogen adsorption and recovery rate in inert gases. At the same time, the nitrogen adsorption capacity of the alloy increases with the increase of Nb content, and the alloy has the ability to react with nitrogen to remove it. Therefore, the alloy with a high Nb content can be used for the purification of inert gases to remove hydrogen and nitrogen in the inert gases.

[0030] When used for nitrogen purification, the nitrogen absorption capacity and rate of the alloy with an Nb content of less than 3.4 at% are still very small even at 350 °C and a nitrogen pressure of 0.5 MPa (for example, only 3.4 ml / g in 120 min), but it has an adsorption capacity of 88 ml / g for 3 kPa hydrogen and a relatively high hydrogen absorption reaction rate. Therefore, the alloy with a low Nb content can be used for nitrogen purification or the recovery of hydrogen in nitrogen.

[0031] For the above alloys used for nitrogen or inert gas purification, when rare earth elements La or Ce are added, the hydrogen absorption and nitrogen absorption capacities of the alloy increase with the increase of the rare earth content, and reach the maximum value when the addition amount reaches 1.5 wt%. Under the same addition weight, the rare earth element Ce is more beneficial for improving the performance than La.

[0032] After considering the specification and the disclosure herein in practice, those skilled in the art will readily think of other embodiments of the present disclosure. This application is intended to cover any variations, uses, or adaptations of the present disclosure, which follow the general principles of the present disclosure and include the common general knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present disclosure are pointed out by the claims of this application.

Claims

1. A getter alloy that can be used for the purification of nitrogen and inert gases, characterized in that, The alloy is an alloy composed of three elements, zirconium, niobium, and iron. The atomic percentage composition of the getter alloy is (Zr 1-x Nb x ) 67 Fe 33 , where 0 < x ≤ 0.

5. The composition of the getter alloy also includes rare earth additive elements, and the additive element is one or two of Ce or La. The weight of the additive element is 0.5 wt.% - 2.0 wt.% of the total weight of the three raw materials of the (Zr 1-x Nb x ) 67 Fe 33 alloy.

2. The getter alloy according to claim 1, characterized in that, The weight of the additional element is (Zr 1- x Nb x ) 67 Fe 33 1.0 wt.% - 1.5 wt.% of the total weight of the three raw materials of the alloy.

3. The getter alloy according to claim 1 or 2, characterized in that, The getter alloy is powder, and the powder particle size is less than 500 μm.

4. The getter alloy according to claim 3, wherein The powder particle size of the getter alloy is less than 300 μm.

5. A method for preparing a getter alloy according to claim 1, characterized in that: It is prepared by smelting pure elements. The raw materials are high-purity Zr, Fe, and Nb metal elements with a purity greater than 99.9%, and rare earth elements with a purity greater than 99.5%. The smelting is carried out under vacuum or inert atmosphere protection, and then the alloy ingot is ground by mechanical crushing under argon atmosphere protection, and the desired alloy powder is obtained by screening.

6. The preparation method according to claim 5, wherein the alloy powder has a particle size less than 500 μm.

7. The preparation method according to claim 6, wherein the alloy powder has a particle size of less than 300 μm.

8. The getter alloy prepared according to the preparation method according to any one of claims 5 to 7 is used for recovering hydrogen-containing gas from nitrogen and inert gas, or for high-temperature purification of nitrogen and inert gas.

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