Method for removing calcium and calcium oxide in rare earth permanent magnetic material

Abstract

The invention discloses a method for removing calcium and calcium oxide in a rare earth permanent magnetic material, and relates to a method for removing calcium and calcium oxide. The invention aims to solve the problems that calcium and calcium oxide residues are difficult to remove in the process of preparing the rare earth permanent magnetic material by the existing reduction diffusion method and mechanical chemical synthesis method, and the magnetic performance of the magnetic material is reduced by the conventional removal mode. The method comprises the following steps: 1, mixing the rare earth permanent magnetic material with water for reaction; 2, adding dry ice into a mixed solution containing calcium hydroxide and the rare earth permanent magnetic material, and mixing; and 3, standing and precipitating, and separating calcium carbonate from the rare earth permanent magnetic material under the action of a magnetic field. The method is used for removing calcium and calcium oxide in the rare earth permanent magnetic material.

Description

Technical Field

[0001] The present invention relates to a method for removing calcium and calcium oxide. Background Art

[0002] High-performance rare earth permanent magnet materials have the advantages of high coercivity, high magnetic energy product, high uniformity, high temperature stability and time stability. They are widely used in various fields such as wind power generation, automotive electric drive, medical equipment and aerospace.

[0003] The synthesis method of rare earth anisotropic nanocomposites has been a research hotspot in recent years. The magnetic properties of rare earth permanent magnet materials are closely related to their preparation process technology and methods. Improvements in preparation process technology and methods can greatly improve the magnetic properties of materials. The current mainstream preparation methods for rare earth permanent magnet materials include: sol-gel method, rapid quenching method, reduction diffusion method, microwave combustion method, thermal decomposition method, mechanochemical synthesis method, etc. Among these synthesis methods, reduction diffusion method and mechanochemical synthesis method both require the strong reducing property of calcium or calcium hydride to undergo redox reaction with metal oxides, and some reactions also require the addition of calcium oxide as a dispersant to accelerate the reaction to form alloys. However, in the above process, calcium and calcium oxide residues will be formed after the reaction. These residual impurities are mixed in the alloy, which greatly reduces the remanence of the material and causes the magnetic properties of rare earth permanent magnet materials to decrease.

[0004] To remove calcium and calcium oxide residues from rare earth permanent magnet alloys, water and glycerol washing are usually used. However, this method will leave a large amount of calcium and calcium oxide residues, and after reacting with water or glycerol, some additional hydride phases will be formed, which greatly reduces the coercivity and remanence of the magnetic alloy. In view of the current problems, it is particularly important to study and develop an efficient and convenient method to remove calcium and calcium oxide residues from rare earth permanent magnet materials. Summary of the invention

[0005] The present invention aims to solve the problem that calcium and calcium oxide residues are difficult to remove in the existing reduction diffusion method and mechanochemical synthesis method of rare earth permanent magnet materials, and conventional removal methods will reduce the magnetic properties of magnetic materials, and further provide a method for removing calcium and calcium oxide in rare earth permanent magnet materials.

[0006] A method for removing calcium and calcium oxide from rare earth permanent magnetic materials is carried out according to the following steps:

[0007] 1. Mixing the rare earth permanent magnetic material with water to obtain a mixed solution containing calcium hydroxide and the rare earth permanent magnetic material;

[0008] The rare earth permanent magnet material contains one or a combination of calcium and calcium oxide;

[0009] 2. Adding dry ice to the mixed solution containing calcium hydroxide and rare earth permanent magnetic material and mixing, to obtain a mixed solution containing calcium carbonate and rare earth permanent magnetic material;

[0010] 3. The mixed solution containing calcium carbonate and rare earth permanent magnetic material is allowed to settle, and then the water on the upper surface is removed and dried to obtain a solid containing calcium carbonate and rare earth permanent magnetic material. Under the action of a magnetic field, the calcium carbonate and the rare earth permanent magnetic material are separated, thus completing the method of removing calcium and calcium oxide from the rare earth permanent magnetic material.

[0011] The beneficial effects of the present invention are:

[0012] (1) The present invention can efficiently remove calcium and calcium oxide from rare earth permanent magnet materials. The magnetic properties of the rare earth permanent magnet materials are not affected after the calcium and calcium oxide are removed by this method.

[0013] (2) The method of the present invention has the advantages of simple operation, low cost, and good repeatability.

[0014] (3) In the method of the present invention, the product of the reaction between dry ice and calcium hydroxide, calcium carbonate, is non-magnetic and can be easily separated from the rare earth permanent magnet material by an external magnetic field, thereby reducing the content of impurities in the rare earth permanent magnet material, which is beneficial to significantly improve the purity of the rare earth permanent magnet alloy and the remanence of the alloy, thereby improving the magnetic properties of the rare earth permanent magnet material.

[0015] (4) The method of removing calcium oxide and calcium of the present invention is not only applicable to rare earth permanent magnetic materials, but also to other magnetic materials.

[0016] Attached Notes

[0017] Figure 1 The X-ray diffraction diagram of the NdFeB alloy powder before and after the removal of calcium oxide in Example 1, (a) before the removal of calcium oxide, (b) after the removal of calcium oxide;

[0018] Figure 2 The VSM (vibrating sample magnetometer) test results of NdFeB alloy powder before and after the removal of calcium oxide in Example 1;

[0019] Figure 3 for Figure 2 A partial enlarged view of

[0020] Figure 4 These are SEM images of NdFeB alloy powder before and after the removal of calcium oxide in Example 1, (a) before the removal of calcium oxide, (b) after the removal of calcium oxide. DETAILED DESCRIPTION

[0021] Specific implementation method 1: This implementation method is a method for removing calcium and calcium oxide from rare earth permanent magnet materials, which is carried out according to the following steps:

[0022] 1. Mixing the rare earth permanent magnetic material with water to obtain a mixed solution containing calcium hydroxide and the rare earth permanent magnetic material;

[0023] The rare earth permanent magnet material contains one or a combination of calcium and calcium oxide;

[0024] 2. Adding dry ice to the mixed solution containing calcium hydroxide and rare earth permanent magnetic material and mixing, to obtain a mixed solution containing calcium carbonate and rare earth permanent magnetic material;

[0025] 3. The mixed solution containing calcium carbonate and rare earth permanent magnetic material is allowed to settle, and then the water on the upper surface is removed and dried to obtain a solid containing calcium carbonate and rare earth permanent magnetic material. Under the action of a magnetic field, the calcium carbonate and the rare earth permanent magnetic material are separated, thus completing the method of removing calcium and calcium oxide from the rare earth permanent magnetic material.

[0026] The calcium or calcium oxide contained in the rare earth permanent magnet material described in step 1 of this embodiment reacts with water to generate calcium hydroxide, thereby obtaining a rare earth permanent magnet alloy mixed solution containing calcium hydroxide.

[0027] In step 2 of this embodiment, dry ice is added to the rare earth permanent magnet alloy mixed solution containing calcium hydroxide. The carbon dioxide gas released by the dry ice in contact with water reacts with the calcium hydroxide in the mixed solution to form a solid precipitate of calcium carbonate. When the calcium hydroxide in the solution reacts completely, excess carbon dioxide gas is released into the air during the reaction. When the dry ice reacts completely, the mixed solution is left to stand.

[0028] In step three of this embodiment, after the water in the standing mixture is removed, the mixture is placed in a drying oven to dry and remove the water, leaving a mixture of rare earth permanent magnet material and calcium carbonate.

[0029] In step three of this embodiment, calcium carbonate is not magnetic, while the rare earth permanent magnet material is magnetic. According to the magnetic difference of the materials, the calcium carbonate in the rare earth permanent magnet material is separated by an external magnetic field, thereby achieving the removal of calcium and calcium oxide.

[0030] The reaction equation involved in this embodiment is as follows:

[0031] CaO+H2O→Ca(OH)2;

[0032] CaO+2H2O→Ca(OH)2+H2;

[0033] Ca(OH)2+CO2=CaCO3↓+H2O.

[0034] The beneficial effects of this embodiment are:

[0035] (1) This embodiment can efficiently remove calcium and calcium oxide from the rare earth permanent magnet material. The magnetic properties of the rare earth permanent magnet material are not affected after the calcium and calcium oxide are removed by this method.

[0036] (2) The method of this embodiment has the advantages of simple operation, low cost, and good repeatability.

[0037] (3) In the method of this embodiment, the product of the reaction between dry ice and calcium hydroxide, calcium carbonate, is non-magnetic and can be easily separated from the rare earth permanent magnet material by an external magnetic field, thereby reducing the content of impurities in the rare earth permanent magnet material, which is beneficial to significantly improve the purity of the rare earth permanent magnet alloy and the remanence of the alloy, thereby improving the magnetic properties of the rare earth permanent magnet material.

[0038] (4) The method of removing calcium oxide and calcium in this embodiment is not only applicable to rare earth permanent magnet materials, but also to other magnetic materials.

[0039] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that the rare earth permanent magnet material described in step 1 is in powder or granular form, and the particle size is less than 5 mm. The rest is the same as the specific implementation method 1.

[0040] In this embodiment, the particle size of the rare earth permanent magnet powder or particles is less than 5 mm. When the particle size of the rare earth material is greater than 5 mm, the reaction of calcium or calcium oxide inside with water is limited, and the efficiency of removing calcium or calcium oxide is greatly reduced. The reduction in the particle size of the rare earth permanent magnet material is conducive to further improving the removal efficiency of calcium and calcium oxide in the rare earth permanent magnet material.

[0041] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the rare earth permanent magnet material described in step 1 is one or a combination of neodymium iron alloy, neodymium iron boron alloy, praseodymium iron alloy, praseodymium iron boron alloy, samarium iron alloy and samarium praseodymium iron alloy. Other aspects are the same as specific implementation method 1 or 2.

[0042] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that the water in step 1 is deionized water. The rest is the same as specific implementation methods 1 to 3.

[0043] Specific implementation mode 5: This implementation mode is different from the specific implementation modes 1 to 4 in that: in step 1, 15 mL or more of water is added for every 1 g of rare earth permanent magnet material. The rest is the same as the specific implementation modes 1 to 4.

[0044] Specific implementation method 6: This implementation method is different from specific implementation methods 1 to 5 in that: in step 1, the rare earth permanent magnet material and water are mixed and reacted for 5 minutes to 15 minutes at a stirring speed of 200 to 800 rpm and room temperature. The rest is the same as specific implementation methods 1 to 5.

[0045] In the present embodiment, too low or too high rotation speed during the mixing process will reduce the reaction efficiency. A reasonable rotation speed is conducive to better reaction, improves the sufficiency of the reaction, and is conducive to further improving the removal effect of calcium and calcium oxide in the rare earth permanent magnet material.

[0046] Specific implementation method 7: This implementation method is different from specific implementation methods 1 to 6 in that the purity of the dry ice in step 2 is greater than 99.999%. The rest is the same as specific implementation methods 1 to 6.

[0047] Specific embodiment 8: This embodiment differs from one of specific embodiments 1 to 7 in that the mass ratio of the dry ice in step 2 to the rare earth permanent magnet material in step 1 is (5-15):1. The rest is the same as specific embodiments 1 to 7.

[0048] In this embodiment, the amount of dry ice used needs to be greater than the rare earth permanent magnet material to be separated. When the amount of dry ice placed is too low, the reaction between calcium hydroxide and dry ice is insufficient, and calcium hydroxide residue is easily formed. Too much dry ice does not affect the removal of calcium or calcium oxide, but it will increase the reaction time, and excess carbon dioxide will evaporate into the air.

[0049] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that in step 2, dry ice is added to the mixed solution containing calcium hydroxide and rare earth permanent magnet material, and then mixed for 10 to 25 minutes at a stirring speed of 200 to 500 rpm and room temperature. The rest is the same as specific embodiments 1 to 8.

[0050] In the present embodiment, too low or too high rotation speed during the mixing process will reduce the reaction efficiency. A reasonable rotation speed is conducive to better reaction, improves the sufficiency of the reaction, and is conducive to further improving the removal effect of calcium and calcium oxide in the rare earth permanent magnet material.

[0051] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the drying described in step 3 is carried out at a temperature of 50°C to 85°C and a vacuum degree of ≤1×10 -4 The magnetic field strength in step 3 is 0.1A / m to 0.4A / m. The rest is the same as in the first to ninth embodiments.

[0052] The following examples are used to verify the beneficial effects of the present invention:

[0053] Embodiment 1:

[0054] A method for removing calcium oxide from a rare earth permanent magnet material is carried out according to the following steps:

[0055] 1. Mixing the rare earth permanent magnet material with water at room temperature at a stirring speed of 200 rpm for 5 minutes to obtain a mixed solution containing calcium hydroxide and the rare earth permanent magnet material;

[0056] The rare earth permanent magnet material contains calcium oxide; the mass ratio of the rare earth permanent magnet material to the volume of water is 1g:15mL;

[0057] The rare earth permanent magnet material is a neodymium iron boron alloy powder prepared by a mechanochemical synthesis method, and the average particle size is 250 microns;

[0058] The water is deionized water;

[0059] 2. Adding dry ice to the mixed solution containing calcium hydroxide and rare earth permanent magnet material, and then mixing for 10 minutes at a stirring speed of 200 rpm and room temperature to obtain a mixed solution containing calcium carbonate and rare earth permanent magnet material;

[0060] The mass ratio of the dry ice in step 2 to the rare earth permanent magnet material in step 1 is 5:1; the purity of the dry ice is greater than 99.999%;

[0061] 3. The mixed solution containing calcium carbonate and rare earth permanent magnet material was allowed to settle for 2 hours, and then the water on the upper surface was removed and then heated to 50 °C and vacuum degree of 1×10 -4 Pa for 10 hours to obtain a solid containing calcium carbonate and rare earth permanent magnetic material. Under the condition of a magnetic field strength of 0.1 A / m, the calcium carbonate and the rare earth permanent magnetic material are separated to obtain the rare earth permanent magnetic material with calcium oxide removed.

[0062] Figure 1 The X-ray diffraction diagrams of the NdFeB alloy powder before and after the removal of calcium oxide in Example 1 are shown in (a) before the removal of calcium oxide and (b) after the removal of calcium oxide. As can be seen from the diagram, most of the CaO is removed, with a removal rate of more than 87%.

[0063] Figure 2 The VSM (vibrating sample magnetometer) test results of NdFeB alloy powder before and after the removal of calcium oxide in Example 1; Figure 3 for Figure 2 A partial enlarged view. As can be seen from the figure, the coercivity of the magnetic material has no obvious change, and the remanence of the magnetic material is increased from 3.3emu / g to 5.6emu / g, and the remanence is increased by 75%, which doubles the magnetic energy product of the material.

[0064] Figure 4 The SEM images of the NdFeB alloy powder before and after the removal of calcium oxide in Example 1 are as follows: (a) before the removal of calcium oxide, (b) after the removal of calcium oxide. It can be seen from the figure that the calcium oxide wrapped on the surface of the magnetic powder is effectively removed.

Claims

1. A method for removing calcium and calcium oxide from rare earth permanent magnet materials, characterized in that It is carried out in the following steps:

1. Mixing the rare earth permanent magnetic material with water to obtain a mixed solution containing calcium hydroxide and the rare earth permanent magnetic material; The rare earth permanent magnet material contains one or a combination of calcium and calcium oxide; 2. Adding dry ice to the mixed solution containing calcium hydroxide and rare earth permanent magnetic material and mixing, to obtain a mixed solution containing calcium carbonate and rare earth permanent magnetic material; 3. The mixed solution containing calcium carbonate and rare earth permanent magnetic material is allowed to settle, and then the water on the upper surface is removed and dried to obtain a solid containing calcium carbonate and rare earth permanent magnetic material. Under the action of a magnetic field, the calcium carbonate and the rare earth permanent magnetic material are separated, thus completing the method of removing calcium and calcium oxide from the rare earth permanent magnetic material.

2. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 1, characterized in that The rare earth permanent magnet material described in step 1 is in powder or granular form, and the particle size is less than 5 mm.

3. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 1, characterized in that The rare earth permanent magnet material described in step 1 is one of neodymium iron alloy, neodymium iron boron alloy, praseodymium iron alloy, praseodymium iron boron alloy, samarium iron alloy and samarium praseodymium iron alloy, or a combination of several of them.

4. The method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 1, characterized in that The water described in step 1 is deionized water.

5. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 4, characterized in that In step 1, add greater than or equal to 15 mL of water for every 1 g of rare earth permanent magnet material.

6. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 5, characterized in that In step 1, the rare earth permanent magnet material is mixed with water at a stirring speed of 200 rpm to 800 rpm and room temperature for 5 min to 15 min.

7. The method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 1, characterized in that The purity of the dry ice described in step 2 is greater than 99.999%.

8. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 7, characterized in that The mass ratio of the dry ice described in step 2 to the rare earth permanent magnet material described in step 1 is (5-15):

1.

9. A method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 8, characterized in that In step 2, dry ice is added to the mixed solution containing calcium hydroxide and rare earth permanent magnetic material, and then mixed for 10 min to 25 min at a stirring speed of 200 rpm to 500 rpm and room temperature.

10. The method for removing calcium and calcium oxide from rare earth permanent magnet materials according to claim 1, characterized in that The drying described in step 3 is specifically carried out at a temperature of 50°C to 85°C and a vacuum degree of ≤1×10 -4 The magnetic field strength in step 3 is 0.1A / m to 0.4A / m.

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