Purification method of lanthanum-cerium alloy
阅读说明：本技术 一种镧铈合金的提纯方法 (Purification method of lanthanum-cerium alloy ) 是由 王飞 陆从理 陈钰臻 徐宝强 杨斌 刘大春 邓勇 曲涛 田阳 熊恒 郁青春 陈 于 2021-08-18 设计创作，主要内容包括：本发明公开一种镧铈合金的提纯方法,在高真空条件下将镧铈合金熔炼2～4h,使得合金中的高蒸气压杂质镁、铝等挥发并冷凝在冷凝盘中,将熔炼冷却后得到的物料与钙进行混合热处理,打磨去除表面杂质得到高纯镧铈合金；本发明有效解决了目前真空熔炼对氧杂质脱除效果较差的问题,通过外吸气剂法有效地脱除了氧杂质,真空熔炼之后部分金属杂质的去除促进了外吸气剂实验的效果。(The invention discloses a method for purifying lanthanum-cerium alloy, which comprises the steps of smelting the lanthanum-cerium alloy for 2-4 hours under the condition of high vacuum, volatilizing and condensing high-vapor-pressure impurities such as magnesium and aluminum in the alloy in a condensation disc, carrying out mixed heat treatment on materials obtained after smelting and cooling and calcium, and polishing to remove surface impurities to obtain high-purity lanthanum-cerium alloy; the method effectively solves the problem of poor oxygen impurity removal effect of the existing vacuum melting, effectively removes the oxygen impurities by an external getter method, and promotes the effect of an external getter experiment by removing part of metal impurities after the vacuum melting.)
1. A purification method of lanthanum-cerium alloy is characterized by smelting the lanthanum-cerium alloy for 2-4 hours under a high vacuum condition, carrying out mixed heat treatment on the material obtained after smelting and cooling and calcium, and polishing after cooling to remove surface impurities to obtain the high-purity lanthanum-cerium alloy.
2. The purification method of lanthanum-cerium alloy as claimed in claim 1, wherein the degree of vacuum of the high vacuum condition is 10- 2Pa～10-3Pa。
3. The method for purifying lanthanum-cerium alloy as claimed in claim 1, wherein the melting temperature is 930 ℃ to 1130 ℃ and the heating rate is 10 ℃/min.
4. The purification method of lanthanum-cerium alloy as claimed in claim 1, wherein the mass ratio of the material obtained after melting and cooling to calcium is 1: 1-2, and the calcium is calcium particles with a purity of 99%.
5. The lanthanum cerium alloy purification method as claimed in claim 1, wherein the specific method of the mixed heat treatment of the material obtained after melting and cooling and calcium is as follows: processing the material obtained after smelting and cooling into a cylindrical bar, polishing the cylindrical bar until the surface is smooth, cleaning the cylindrical bar with distilled water and ethanol in sequence, drying the cylindrical bar by blowing, putting the cylindrical bar into a high-purity graphite crucible, burying and wrapping the surface of the bar with calcium, carrying out heat treatment for 2-5 h under a high vacuum condition, and cooling a sample to room temperature under a vacuum environment and then taking out the sample.
6. The method of claim 5, wherein the degree of vacuum is 10 under high vacuum condition-3Pa, heat treatment temperature of 500-700 ℃, and heating rate of 10 ℃/min.
Technical Field
The invention relates to the field of rare earth metal refining, in particular to a method for purifying lanthanum-cerium alloy.
Background
Rare earth metals are widely used in high-precision industries as important strategic resources. With the rapid development of science and technology, the requirement on the purity of rare earth metals is higher and higher, and the preparation and purification of rare earth metals become more and more important. Lanthanum-cerium alloy is widely applied to the field of hydrogen storage materials and metallurgy as a main rare earth alloy, but because of the active chemical property and strong affinity with oxygen, the removal of interstitial impurities, particularly oxygen, in the purification process is very difficult, the existing purification method has the problems of low efficiency, long period, high energy consumption and the like, and the development of a novel and efficient purification technology is particularly important.
At present, the main rare earth purification methods at home and abroad include a vacuum melting method, a vacuum distillation method, a zone melting method, an electrolytic refining method, solid-state electromigration and the like, and the combination of the methods. The removal effect of the vacuum melting and zone melting method on the interstitial impurities O is not obvious and the latter is complicated to operate; the vacuum distillation method can be used for removing interstitial impurities in rare earth metals, but is only suitable for purifying metals with higher vapor pressure near the melting point and has higher requirements on vacuum degree and temperature; the electrolytic refining cannot effectively remove O in the rare earth metal, and new impurities may be introduced in the refining process; solid-state electromigration can effectively remove O in rare earth metals, but the method has long time consumption, low yield and high cost.
In addition, the external getter method can also be used for purifying the metal, and the method can remove oxygen in the metal under the conditions of lower temperature and vacuum degree, save energy and reduce cost. However, the method is mainly suitable for purifying VIB and VIIB elements with higher melting points, and has less application on rare earth metals. Kamihira et al (Materials transformations, JIM, VOL.34, No.3,1993) tried to deoxidize rare earth metals lanthanum, praseodymium, neodymium, gadolinium, terbium and dysprosium by using metallic calcium as a getter, mixed calcium and rare earth metals were subjected to argon atmosphere, the heat treatment temperature was 850 ℃, and the rare earth metals were wrapped by calcium melt and steam in the whole process, but the experimental results showed that the purification effect was not significant at the temperature of 850 ℃, and even for the rare earth metals terbium and dysprosium, the oxygen content in the metal matrix after heat treatment tended to increase.
Most of the existing purification methods can only purify single rare earth metal, and the research on the purification of rare earth alloy is less. Therefore, there is a need to improve the prior art and provide a purification method capable of efficiently removing oxygen impurities in lanthanum-cerium alloy.
Disclosure of Invention
Aiming at the problem of poor effect of vacuum melting on removing interstitial impurity oxygen in the lanthanum-cerium alloy, the method comprises the steps of firstly removing part of high vapor pressure impurities by vacuum melting by utilizing the vapor pressure difference of main components and impurities in the lanthanum-cerium alloy, then adding a getter after the vacuum melting to further remove the oxygen impurities by utilizing the strong bonding energy of the getter calcium and the interstitial impurities, and combining the two methods to obtain the high-purity lanthanum-cerium alloy.
The purpose of the invention is realized by the following technical scheme:
a method for purifying lanthanum-cerium alloy comprises the following specific steps: and smelting the lanthanum-cerium alloy for 2-4 h under a high vacuum condition, volatilizing and condensing high-vapor-pressure impurities such as magnesium, aluminum and the like in the alloy in a condensation disc, carrying out mixed heat treatment on the material obtained after smelting and cooling and calcium, and polishing to remove surface impurities to obtain the high-purity lanthanum-cerium alloy.
The degree of vacuum of the high vacuum condition is 10-2Pa～10-3Pa。
The melting temperature is 930-1130 ℃, and the heating rate is 10 ℃/min.
The mass ratio of the material obtained after smelting and cooling to calcium is 1: 1-2, and the calcium is calcium particles with the purity of 99%.
The specific method for carrying out mixed heat treatment on the materials obtained after smelting and cooling and calcium comprises the following steps: processing the material obtained after smelting and cooling into a cylindrical bar, polishing the cylindrical bar until the surface is smooth, cleaning the cylindrical bar with distilled water and ethanol in sequence, then drying the cylindrical bar, putting the cylindrical bar into a high-purity graphite crucible, burying and wrapping the surface of the bar with calcium, and performing secondary sintering at 10 DEG C-3And (3) carrying out heat treatment for 2-5 h at 500-700 ℃ under the Pa high vacuum condition, wherein the heating rate is 10 ℃/min, and taking out the sample after the sample is cooled to room temperature under the vacuum environment.
The principle of the invention is as follows:
(1) the vacuum melting purification principle is as follows: under high vacuum, heating the rare earth metal to be near the melting point to melt the metal, according to the difference of the vapor pressures of the matrix metal and the impurities, the vapor pressures of all the components can visually reflect the difficulty degree of purification, and the vapor pressures of the main component and 8 impurity elements in the lanthanum-cerium alloy are calculated by using a derivation formula of a Clausius-Claipron equation and are shown in figure 1, wherein the impurities with higher vapor pressures are preferentially volatilized and condensed to be removed in the melting process.
(2) The purification principle by an external getter method is as follows: the external getter method is to place the getter and the metal sample together in a closed environment and carry out heat treatment on the getter and the metal sample to achieve the purpose of purification. The change of Gibbs free energy of the reaction of the main component in the calcium and lanthanum cerium alloy with oxygen as a function of temperature is shown in FIG. 2, La2O3、Ce2O3The oxygen potential of (2) is extremely low and the stability is high, but the reaction of Ca with oxygen proceeds more easily than the reaction of La and Ce with oxygen, and the chemical activity of Ca is higher than that of La and Ce. Lower deoxygenation limits can be achieved when metallic calcium is present in the reaction vessel, which acts as a reducing agent in the deoxygenation process, which is shown in fig. 3。
The invention has the beneficial effects that:
(1) the method effectively solves the problem of poor clearance impurity removal effect of the existing vacuum melting, effectively removes oxygen impurities by an external getter method, and promotes the effect of getters by removing part of metal impurities after vacuum melting so that the oxygen impurities are easier to remove.
(2) The method further removes interstitial impurities, particularly oxygen impurities, by adopting an external getter method, adopts calcium with the purity of 99% as a getter, and under the high vacuum state, oxygen on the surface of the metal reacts with the calcium, so that the oxygen content on the surface of the metal is reduced to form a concentration gradient with the interior of the matrix, and further diffusion of the internal oxygen to the outside is promoted.
Drawings
FIG. 1 shows the vapor pressure of the main component and 8 impurity elements in lanthanum-cerium alloy;
FIG. 2 is a graph showing Gibbs free energy of reaction of a main component in calcium and lanthanum cerium alloys with oxygen at different temperatures;
FIG. 3 is a model of deoxidation of lanthanum cerium alloy by calcium metal;
FIG. 4 is a scanning electron micrograph (calcium element in dark) of a cross section of a sample obtained in step (4) of example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below with reference to examples, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limitations of the present invention.
Example 1
A method for purifying lanthanum-cerium alloy comprises the following specific steps:
(1) polishing the lanthanum-cerium alloy by using abrasive paper to remove a surface oxide layer, and then sequentially cleaning by using distilled water and ethanol and drying;
(2) placing lanthanum-cerium alloy into a high-purity graphite crucible, placing the crucible into a distillation furnace, and vacuumizing to 10 DEG-3Pa, heating to 930 ℃ at a speed of 10 ℃/min, preserving the heat for 4h, cooling under a vacuum condition, and taking out the material;
(3) machining the smelted and cooled material into a cylindrical bar with the diameter of 10mm and the length of 35mm, polishing the cylindrical bar until the surface is smooth, cleaning the cylindrical bar with distilled water and ethanol in sequence, and then blowing the cylindrical bar for later use;
(4) adding the processed sample and calcium metal particles with the purity of 99% into a graphite crucible according to the mass ratio of 1:1.5 to ensure that the calcium metal completely wraps the sample, and vacuumizing to 10%-3Pa, heating to 600 ℃ at a speed of 10 ℃/min, preserving heat for 3.5 hours, and taking out the sample after the sample is cooled to room temperature in a vacuum environment;
(5) and (3) polishing the sample in a vacuum glove box, removing the calcium film on the surface, and sequentially cleaning with distilled water and ethanol to obtain the high-purity lanthanum-cerium alloy.
The impurities volatilized by vacuum melting are mainly magnesium, aluminum and the like, the removal of the impurities is beneficial to the removal of the gap impurities in the next step, and a layer of calcium film is uniformly attached to the surface of the material after the getter experiment in the step (4) through a scanning electron microscope (as shown in figure 4), and is the key for removing the gap impurities.
The magnesium in the lanthanum-cerium alloy is reduced from 100ppm to 13ppm, the aluminum is reduced from 110ppm to 42ppm, and the oxygen content in the lanthanum-cerium alloy is reduced from 510ppm to 60ppm, which is measured by an inert pulse infrared method.
Example 2
A method for purifying lanthanum-cerium alloy comprises the following specific steps:
(1) polishing the lanthanum-cerium alloy by using abrasive paper to remove a surface oxide layer, and then sequentially cleaning by using distilled water and ethanol and drying;
(2) placing lanthanum-cerium alloy into a high-purity graphite crucible, placing the crucible into a distillation furnace, and vacuumizing to 10 DEG-2Pa, heating to 1030 ℃ at the speed of 10 ℃/min, preserving the heat for 2h, cooling under the vacuum condition, and taking out the material;
(3) machining the smelted materials into cylindrical bars with the diameter of 10mm and the length of 35mm, polishing the cylindrical bars until the surfaces are smooth, cleaning the cylindrical bars with distilled water and ethanol in sequence, and then blowing the cylindrical bars for later use;
(4) adding the processed sample and metal calcium particles with the purity of 99% into a graphite crucible according to the mass ratio of 1:1 to ensure that the metal calcium completely wraps the sample, and vacuumizing to 10%-3Pa, heating to 500 ℃ at the speed of 10 ℃/min, preserving the heat for 5h, and taking out the sample after the sample is cooled to room temperature in a vacuum environment;
(5) and (3) polishing the sample in a vacuum glove box, removing the calcium film on the surface, and sequentially cleaning with distilled water and ethanol to obtain the high-purity lanthanum-cerium alloy.
The magnesium in the lanthanum cerium alloy is reduced from 100ppm to 16ppm, the aluminum is reduced from 110ppm to 40ppm, and the oxygen content in the lanthanum cerium alloy is reduced from 510ppm to 38ppm, which is measured by an inert pulse infrared method.
Example 3
A method for purifying lanthanum-cerium alloy comprises the following specific steps:
(1) polishing the lanthanum-cerium alloy by using abrasive paper to remove a surface oxide layer, and then sequentially cleaning by using distilled water and ethanol and drying;
(2) placing lanthanum-cerium alloy into a high-purity graphite crucible, placing the crucible into a distillation furnace, and vacuumizing to 10 DEG-3Pa, heating to 1130 ℃ at a speed of 10 ℃/min, preserving the heat for 3h, cooling under a vacuum condition, and taking out the material;
(3) machining the smelted materials into cylindrical bars with the diameter of 10mm and the length of 35mm, polishing the cylindrical bars until the surfaces are smooth, cleaning the cylindrical bars with distilled water and ethanol in sequence, and then blowing the cylindrical bars for later use;
(4) adding the processed sample and calcium metal particles with the purity of 99% into a graphite crucible according to the mass ratio of 1:2 to ensure that the calcium metal completely wraps the sample, and vacuumizing to 10%-3Pa, heating to 700 ℃ at the speed of 10 ℃/min, preserving heat for 2h, and taking out the sample after the sample is cooled to room temperature in a vacuum environment;
(5) and (3) polishing the sample in a vacuum glove box, removing the calcium film on the surface, and sequentially cleaning with distilled water and ethanol to obtain the high-purity lanthanum-cerium alloy.
The magnesium in the lanthanum-cerium alloy is reduced from 100ppm to 15ppm, the aluminum is reduced from 110ppm to 39ppm, and the oxygen content in the lanthanum-cerium alloy is reduced from 510ppm to 55ppm, which is measured by an inert pulse infrared method.
Comparative example 1
The lanthanum-cerium alloy is purified by simply adopting vacuum melting, and the method comprises the following specific steps:
(1) polishing the lanthanum-cerium alloy by using abrasive paper to remove a surface oxide layer, and then sequentially cleaning by using distilled water and ethanol and drying;
(2) placing lanthanum-cerium alloy into a high-purity graphite crucible, placing the crucible into a distillation furnace, and vacuumizing to 10 DEG-3Pa, heating to 930 ℃ at a speed of 10 ℃/min, preserving the heat for 4h, cooling under a vacuum condition, and taking out the material.
The magnesium in the lanthanum-cerium alloy is reduced from 100ppm to 15ppm, the aluminum is reduced from 110ppm to 44ppm, the oxygen melting content is reduced from 510ppm to 400ppm, and the oxygen content in the lanthanum-cerium alloy is not obviously removed by simply adopting vacuum melting.
Comparative example 2
The method adopts metal calcium as a getter to directly carry out an external getter experiment, and comprises the following specific steps:
(1) machining a lanthanum-cerium alloy into a cylindrical bar with the diameter of 10mm and the length of 35mm, polishing the bar until the surface is smooth, cleaning the bar with distilled water and ethanol in sequence, and then blowing the bar for later use;
(2) adding the processed sample and calcium metal particles with the purity of 99% into a graphite crucible according to the mass ratio of 1:1.5 to ensure that the calcium metal completely wraps the sample, and vacuumizing to 10%-3Pa, heating to 600 ℃ at a speed of 10 ℃/min, preserving heat for 3h, and taking out the sample after the sample is cooled to room temperature in a vacuum environment;
(3) and (3) polishing the sample in a vacuum glove box, removing the calcium film on the surface, and sequentially cleaning with distilled water and ethanol to obtain the sample.
The magnesium content in the lanthanum-cerium alloy is 105ppm and the aluminum content in the lanthanum-cerium alloy is 112ppm measured by Glow Discharge Mass Spectrometry (GDMS), the magnesium content is basically the same as that in the original material, the oxygen content is reduced from 510ppm to 290ppm measured by an inert pulse infrared method, the oxygen removal effect is certain but not obvious, and probably because the metal impurities of the lanthanum-cerium alloy can fix the oxygen in the lanthanum-cerium alloy, so that the oxygen removal is hindered.
In summary, the oxygen content in the lanthanum-cerium alloy obtained in the embodiments 1-3 of the present invention is much lower than that in the comparative examples 1-2, the single purification method has no significant effect on removing the oxygen content in the lanthanum-cerium alloy, the vacuum melting removes impurities such as magnesium and aluminum while removing part of oxygen, and the removal of the impurities promotes the effect of the external getter experiment.
While the present invention has been described in detail with reference to the specific embodiments thereof, it will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and various changes may be made without departing from the spirit and scope of the invention.