Antioxidant coating liquid and application

Abstract

The application provides an anti-oxidation coating solution and application. The anti-oxidation coating solution comprises 1-60 g / L H3PO4, 10-60 g / L Zr3(PO4)4, 10-30 g / L Zn3(PO4)2, 1-10 g / L Na2SiO3, 10-20 g / L SmPO4 and 60-150 g / L FePO4. The anti-oxidation coating solution is used to treat the surface of a samarium-iron-nitrogen magnetic material, so that the surface of the samarium-iron-nitrogen magnetic material is corroded by phosphoric acid and phosphate is formed; the solid particles of the phosphate with specific composition are attached to the surface of the samarium-iron-nitrogen magnetic material, so that a protective film with specific composition and thickness is formed. The addition of sodium silicate with specific amount can make the coating layer more compact, and can enhance the binding force between the coating layer and the magnetic material particles, so as to improve the stability and anti-oxidation property of the modified magnetic material. The anti-oxidation coating solution is especially suitable for Sm2Fe 17 N x magnetic powder with a particle size of 1-3 microns.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic materials, in particular to an anti-oxidation coating liquid and application. BACKGROUND

[0002] In the 1990s, Coey et al. synthesized a rare earth iron-based permanent magnetic material represented by samarium iron nitride (Sm2Fe 17 N x ) using a gas-solid phase reaction, which attracted widespread attention. Sm2Fe 17 N x Permanent magnetic material has very excellent intrinsic magnetic properties, with a saturation magnetization of 1.54T, which is comparable to that of neodymium-iron-boron (Nd2Fe 14 B) permanent magnetic material, 1.6T, a Curie temperature of 470℃, and an anisotropy field of 14T, which are higher than those of Nd2Fe 14 B permanent magnetic material. Due to the excellent magnetic properties of Sm2Fe 17 N x permanent magnetic material, it is considered to have the potential to become a new generation of rare earth permanent magnetic material.

[0003] In recent years, due to the large use of neodymium-iron-boron rare earth permanent magnetic materials in the fields of automobiles, household appliances, industrial equipment, etc., the prices of Nd and Pr have rapidly increased, which has led to an increase in material costs; on the other hand, Sm ore resources are relatively surplus, and a large amount of Sm-containing tailings are accumulated, and their prices have been relatively low. Therefore, the effective use of domestic surplus Sm resources to prepare Sm2Fe 17 N x magnetic material has gradually become a focus in the field of iron-based rare earth permanent magnetic materials.

[0004] Sm2Fe 17 N x compound will irreversibly decompose at a temperature exceeding 550℃, making it difficult to prepare a dense magnet by sintering like NdFeB material, so researchers generally mix Sm2Fe 17 N x magnetic powder with a binder and then form a bonded magnet through a specific process, of which the most widely used is injection molding. The above molding method can be used to prepare plastic magnets of various shapes. The Sm2Fe 17 N x granular material (magnetic mixture) used for injection molding is generally prepared at 200-300℃ by a double-screw granulation method. In this process, fine Sm2Fe 17 N x magnetic powder (about 1-3μm) has a high specific surface area and is extremely susceptible to air oxidation, which leads to a significant decrease in the magnetic properties of the magnetic material, with the most severe decrease being in the coercivity.

[0005] In order to solve this problem, the commonly used method is to first carry out surface coating treatment on the Sm2Fe 17 N x compound, so as to form a dense anti-oxidation film on the surface of the magnetic powder, and then carry out granulation (i.e. glue-magnetic mixing). At present, Japanese companies (such as Sumitomo Mining) master the most advanced technology of anti-oxidation treatment of Sm2Fe 17 N x magnetic powder, and there is still a big gap between the existing anti-oxidation treatment technology in China and Japan.

[0006] On this basis, it is of great significance to research and develop a kind of Sm-Fe-N magnetic material with excellent anti-oxidation, corrosion resistance and high temperature resistance, which can improve its magnetic properties (including residual magnetism, coercive force, maximum magnetic energy product and other magnetic parameters). SUMMARY

[0007] The main purpose of the present application is to provide an anti-oxidation coating liquid and application, so as to solve the problem of poor anti-oxidation ability, corrosion resistance and high temperature resistance of Sm-Fe-N magnetic material in the prior art, which leads to poor subsequent processing performance and poor magnetic properties.

[0008] In order to achieve the above purpose, the present application provides an anti-oxidation coating liquid, which comprises: 1-60 g / L H3PO4, 10-60 g / L Zr3(PO4)4, 10-30 g / L Zn3(PO4)2, 1-10 g / L Na2SiO3, 10-20 g / L SmPO4 and 60-150 g / L FePO4.

[0009] Further, the anti-oxidation coating liquid further comprises one or more of the group consisting of NdPO4, PrPO4, Cu3(PO4)2 and CePO4; preferably, the anti-oxidation coating liquid further comprises: 1-5 g / L NdPO4, 1-5 g / L PrPO4, 1-5 g / L Cu3(PO4)2 and 1-5 g / L CePO4.

[0010] Further, the anti-oxidation coating liquid further comprises a water-soluble binder; preferably, the water-soluble binder is selected from one or more of the group consisting of sodium silicate, polyethylene glycol and polyacrylic acid; more preferably, the anti-oxidation coating liquid further comprises: 5-10 g / L sodium silicate and / or 5-10 g / L polyethylene glycol and / or 5-10 g / L polyacrylic acid.

[0011] Further, the viscosity average molecular weight of the polyethylene glycol is 200-2000, and the viscosity average molecular weight of the polyacrylic acid is 200-2000.

[0012] Further, the anti-oxidation coating solution further comprises a diluent, and the diluent comprises an organic solvent and water, and the weight ratio of the organic solvent to the water is (7-9):1; preferably, the organic solvent is selected from one or more of ethanol, isopropanol, and acetone.

[0013] Further, the pH of the anti-oxidation coating solution is 3-6; preferably, the pH of the anti-oxidation coating solution is 3-4.

[0014] In order to achieve the above-mentioned purpose, another aspect of the present application further provides a preparation method of a modified samarium-iron-nitrogen magnetic material, which comprises: coating a samarium-iron-nitrogen magnetic material with the anti-oxidation coating solution provided by the present application to obtain a modified samarium-iron-nitrogen magnetic material.

[0015] Further, the temperature of the coating process is 120-200°C, and the time is 2-5h.

[0016] Another aspect of the present application provides a modified samarium-iron-nitrogen magnetic material, which is prepared by the preparation method of the modified samarium-iron-nitrogen magnetic material provided by the present application.

[0017] Another aspect of the present application provides a bonded magnet, which is obtained by sequentially mixing the modified samarium-iron-nitrogen magnetic material provided by the present application with a binder and an optional lubricant, extruding and granulating, and injection molding; preferably, the bonded magnet has a remanence of 6500-7500Gs, a coercivity of 7000-11000Oe, and a maximum magnetic energy product of 10-15MGOe.

[0018] By using the anti-oxidation coating solution with the above-mentioned ratio to treat the surface of the samarium-iron-nitrogen magnetic material, a specific amount of phosphoric acid can corrode the surface of the samarium-iron-nitrogen magnetic material and form phosphate, which is slightly soluble in water or insoluble in water and forms tiny solid particles attached to the surface of the samarium-iron-nitrogen magnetic material, thereby forming a protective film with a specific composition and thickness composed of samarium phosphate and iron phosphate. During the treatment of the samarium-iron-nitrogen magnetic material, as the reaction proceeds, the specific content of the slightly soluble phosphate in the anti-oxidation coating solution will gradually deposit on the surface of the protective film, so that the protective film gradually thickens and finally forms a phosphate coating layer with a specific composition. Meanwhile, the addition of a specific amount of sodium silicate can fill the pores on the surface of the inorganic phosphate coating layer, so that the coating layer is more dense, and the adhesion between the coating layer and the magnetic material particles is enhanced, so that the coating layer is difficult to fall off, and the structural stability and long-term oxidation resistance of the modified magnetic material are improved.

[0019] In addition, the phosphate coating layer formed by the above-mentioned anti-oxidation coating solution has good magnetic shielding performance and does not cause magnetic interference to the magnetic material inside. The above-mentioned anti-oxidation coating solution is particularly suitable for Sm2Fe 17 N x magnetic powder. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0021] As described in the background, the existing Sm-Fe-N magnetic material has poor oxidation resistance, corrosion resistance and high temperature resistance, which leads to poor subsequent processing performance and poor magnetic performance. In order to solve the above technical problems, the present application provides an anti-oxidation coating solution, which comprises: 1-60 g / L H3PO4, 10-60 g / L Zr3(PO4)4, 10-30 g / L Zn3(PO4)2, 1-10 g / L Na2SiO3, 10-20 g / L SmPO4 and 60-150 g / L FePO4.

[0022] The surface of the Sm-Fe-N magnetic material is treated by the anti-oxidation coating solution with the above-mentioned ratio, which can cause the specific amount of phosphoric acid to corrode the surface of the Sm-Fe-N magnetic material and form a phosphate. The phosphate with the above-mentioned specific composition is difficult to dissolve in water or insoluble in water, and forms a small amount of solid particles attached to the surface of the Sm-Fe-N magnetic material, forming a protective film with a specific composition and thickness composed of Sm phosphate and Fe phosphate. During the treatment of the Sm-Fe-N magnetic material, with the progress of the reaction, the specific content of the insoluble phosphate in the anti-oxidation coating solution will gradually deposit on the surface of the protective film, so that the protective film gradually thickens and finally forms a phosphate coating layer with a specific composition. At the same time, the addition of a specific amount of water-soluble binder (such as sodium silicate, polyethylene glycol, polyacrylic acid) can fill the pores on the surface of the inorganic phosphate coating layer, making the coating layer more dense, and can enhance the bonding force between the coating layer and the magnetic material particles, so that the coating layer is difficult to fall off, and the structural stability and long-term oxidation resistance of the modified magnetic material are improved.

[0023] In addition, the phosphate coating layer formed by the above-mentioned anti-oxidation coating solution has good magnetic shielding performance and does not cause magnetic interference to the magnetic material inside. The above-mentioned anti-oxidation coating solution is particularly suitable for Sm2Fe 17 N x magnetic powder.

[0024] In a preferred embodiment, the anti-oxidation coating solution further comprises one or more of the group consisting of NdPO4, PrPO4, Cu3(PO4)2and CePO4. The addition of the above-mentioned kinds of phosphate can also participate in the formation of the phosphate coating layer, so that the modified samarium-iron-nitrogen magnetic material has better anti-oxidation and corrosion resistance. In order to further improve the anti-oxidation and corrosion resistance of the samarium-iron-nitrogen magnetic material, preferably, the anti-oxidation coating solution further comprises 1-5 g / L of NdPO4, 1-5 g / L of PrPO4, 1-5 g / L of Cu3(PO4)2and 1-5 g / L of CePO4.

[0025] In a preferred embodiment, the anti-oxidation coating solution further comprises a water-soluble binder. The addition of the water-soluble binder can fill the pores on the surface of the inorganic phosphate coating layer, make the coating layer more dense, and enhance the binding force between the phosphate particles and the crystal nucleus formed on the surface of the samarium-iron-nitrogen magnetic material, so that the coating layer is difficult to fall off, and the structural stability and long-term anti-oxidation of the modified magnetic material are improved. Preferably, the water-soluble binder includes but is not limited to one or more of the group consisting of sodium silicate, polyethylene glycol and polyacrylic acid. Compared with other kinds of water-soluble binders, the above-mentioned water-soluble binders have better binding force with the phosphate attached to the surface of the samarium-iron-nitrogen magnetic material, so that the use of the above-mentioned kinds of water-soluble binders to fill the pores in the phosphate coating layer is conducive to improving the density of the coating layer, thereby improving the anti-oxidation performance of the samarium-iron-nitrogen magnetic material. In order to further improve the density of the coating layer and the anti-oxidation performance of the samarium-iron-nitrogen magnetic material, more preferably, the anti-oxidation coating solution further comprises 5-10 g / L of sodium silicate and / or 5-10 g / L of polyethylene glycol and / or 5-10 g / L of polyacrylic acid.

[0026] In a preferred embodiment, the viscosity average molecular weight of the polyethylene glycol is 200-2000, and the viscosity average molecular weight of the polyacrylic acid is 200-2000. Compared with other ranges, the limitation of the viscosity average molecular weight of the water-soluble binder within the above-mentioned range is not only conducive to improving its dispersibility in water, but also conducive to further enhancing the binding force between the coating layer and the modified samarium-iron-nitrogen magnetic material, improving the density and stability of the coating layer and long-term anti-oxidation.

[0027] In a preferred embodiment, the anti-oxidation coating solution further comprises a diluent, and the diluent comprises an organic solvent and water, and the weight ratio of the organic solvent to water is (7-9): 1. The weight ratio of the organic solvent to water includes but is not limited to the above-mentioned range, and the limitation of the weight ratio of the organic solvent to water within the above-mentioned range is conducive to controlling the hydrolysis degree of H3PO4 in the anti-oxidation coating solution, and conducive to achieving good coating effect. In a preferred embodiment, the organic solvent includes but is not limited to one or more of the group consisting of ethanol, polyethylene glycol and acetone.

[0028] In a preferred embodiment, the pH of the anti-oxidation coating solution is 3-6. The pH of the anti-oxidation coating solution includes but is not limited to the above range, and limiting it in the above range is conducive to keeping the degree of etching reaction between phosphoric acid and the samarium-iron-nitrogen magnetic material in a suitable range, while providing a suitable chemical reaction environment for subsequent deposition of phosphate, and is conducive to improving the compactness and stability of the phosphate coating layer. In order to further improve the compactness and stability of the phosphate coating layer, and thus improve the anti-oxidation property of the samarium-iron-nitrogen magnetic material, preferably, the pH of the coating solution composition is 3-4.

[0029] The second aspect of the present application provides a preparation method of a modified samarium-iron-nitrogen magnetic material, which comprises: coating a samarium-iron-nitrogen magnetic material with the above anti-oxidation coating solution provided by the present application to obtain a modified samarium-iron-nitrogen magnetic material.

[0030] Coating a samarium-iron-nitrogen magnetic material with the above anti-oxidation coating solution in the above ratio can finally form a phosphate coating layer with a specific composition on the surface of the samarium-iron-nitrogen magnetic material, thereby obtaining a modified samarium-iron-nitrogen magnetic material. This is conducive to improving the structural stability and long-term anti-oxidation property of the modified magnetic material. At the same time, the above coating process is low in cost and easy to operate. In addition, the phosphate coating layer finally formed by the above coating process also has good magnetic shielding performance and does not interfere with the magnetic material inside. The above coating process is particularly suitable for Sm2Fe 17 N x Surface coating of magnetic powder.

[0031] In order to improve the effect of the coating process, improve the compactness and thickness uniformity of the coating layer, and thus improve the anti-oxidation property and corrosion resistance of the modified samarium-iron-nitrogen magnetic material, in a preferred embodiment, the temperature of the coating process is 120-200°C, and the time is 2-5h.

[0032] The third aspect of the present application provides a modified samarium-iron-nitrogen magnetic material, which is prepared by the above preparation method of a modified samarium-iron-nitrogen magnetic material provided by the present application.

[0033] The above modified samarium-iron-nitrogen magnetic material has a phosphate coating layer with a specific composition, which is firm and not easy to fall off, and has a compact structure, so that the modified samarium-iron-nitrogen magnetic material has excellent anti-oxidation property and corrosion resistance. In addition, the above phosphate coating layer also has good magnetic shielding performance and does not interfere with the samarium-iron-nitrogen magnetic material inside.

[0034] The fourth aspect of the present application provides a bonded magnet, which is obtained by mixing the modified Sm-Fe-N magnetic material provided by the present application with a binder and optionally a lubricant, extruding and granulating, and injection molding. The bonded magnet prepared by using the modified Sm-Fe-N magnetic material provided by the present application has excellent oxidation resistance, corrosion resistance and high temperature resistance, and also has a large residual magnetism, a large coercivity and a maximum magnetic energy product.

[0035] In a preferred embodiment, the residual magnetism of the bonded magnet is 6500-7500 Gs, the coercivity is 7000-11000 Oe, and the maximum magnetic energy product is 10-15 MGOe. The bonded magnet prepared by using the modified Sm-Fe-N magnetic material provided by the present application has a large residual magnetism, a large coercivity and a maximum magnetic energy product.

[0036] The present application will be further described in detail below in combination with specific examples, which should not be construed as limiting the scope of the present application.

[0037] It should be noted that the Sm-Fe-N magnetic powder used in the embodiments of the present application is prepared by the following method, which specifically includes the following steps:

[0038] The metal samarium powder and the metal iron powder are mixed in a molar ratio of 2.2:17, and the mixed powder is subjected to a solid-phase diffusion reaction at 1000-1200°C for 12 hours to form a Sm-Fe alloy. The Sm-Fe alloy is coarsely broken into particles of 0.1-1 mm, and the Sm-Fe alloy particles are placed in a tube furnace and heated to 500°C under ammonia gas for 6h to obtain a Sm-Fe-N magnetic material. The Sm-Fe-N magnetic material is broken into Sm-Fe-N magnetic powder with an average particle size of 1-3 μm.

[0039] Example 1

[0040] A preparation method of a modified Sm-Fe-N magnetic material, which specifically includes the following steps:

[0041] (1) An anti-oxidation coating solution is prepared, and the composition and concentration of each component in the anti-oxidation coating solution are as follows: 60 g / L H3PO4, 60 g / L Zr3(PO4)4, 30 g / L Zn3(PO4)2, 10 g / L Na2SiO3, 20 g / L SmPO4, 150 g / L FePO4, 10 g / L polyethylene glycol, 10 g / L polyacrylic acid, and diluents including isopropyl alcohol and water, and the weight ratio of isopropyl alcohol to water is 9:1; the pH value of the anti-oxidation coating solution is adjusted to 3 by using ammonia water. The viscosity average molecular weight of the polyethylene glycol is 2000, and the viscosity average molecular weight of the polyacrylic acid is 2000.

[0042] (2) 1 kg of the SmFeN magnetic powder prepared by the above method is mixed with 100 g of the anti-oxidation coating liquid prepared above, and the mixture is subjected to coating treatment in a stirring machine, and the mixture becomes a slurry state.

[0043] (3) The slurry mixture is transferred to a vacuum drying oven, and vacuum drying treatment is performed at 120°C for 2 h to obtain the modified SmFeN magnetic material.

[0044] A method for preparing a bonded magnet is as follows:

[0045] (1) 0.5 wt% of a silane coupling agent based on the total weight of the modified SmFeN magnetic material is added, and diluted with 5 times the volume of ethanol relative to the coupling agent, and then added to the modified SmFeN magnetic powder, and high-speed mixing and vacuum drying are performed. 0.5 wt% of zinc stearate based on the total weight of the modified SmFeN magnetic powder is added, and the two are dispersed.

[0046] (2) The above modified Sm2Fe 17 N x Nylon 12 (polydodecanolactam) is added to the SmFeN magnetic powder, and the weight ratio of the nylon 12 to the modified SmFeN magnetic powder is 9:1, and the magnetic mixture is subjected to granulation in a twin-screw extruder, and the processing temperature is 200°C; then the particles are transferred to an injection machine, and injection molding is performed at 245°C to obtain a cylindrical bonded magnet.

[0047] The cylindrical bonded magnet prepared above is subjected to magnetic property testing at an ambient temperature of 23°C using a permanent magnet material testing system (Changsha Tianheng Measurement and Control TD8310), and the testing results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0048] Example 2

[0049] The difference from Example 1 is that the components and concentrations of the anti-oxidation coating liquid are as follows: 10 g / L H3PO4, 10 g / L Zr3(PO4)4, 10 g / L Zn3(PO4)2, 1 g / L Na2SiO3, 10 g / L SmPO4, 10 g / L FePO4, 10 g / L polyethylene glycol, and 10 g / L polyacrylic acid, and the pH value of the anti-oxidation coating liquid is adjusted to 6 using ammonia water.

[0050] The method for preparing a bonded magnet is the same as in Example 1. The cylindrical bonded magnet prepared is subjected to magnetic property testing using the same testing method as in Example 1, and the testing results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0051] Example 3

[0052] The difference from Example 1 is that the composition of the anti-oxidation coating solution and the concentration of each component are as follows: 20 g / L H3PO4, 10 g / L SmPO4, 100 g / L FePO4, 30 g / L Zr3(PO4)4, 30 g / L Zn3(PO4)2, 5 g / L Na2SiO3, 10 g / L polyethylene glycol, 10 g / L polyacrylic acid, and the pH value of the anti-oxidation coating solution is adjusted to 4 by using ammonia water.

[0053] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by using the same testing method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0054] Example 4

[0055] The difference from Example 1 is that in the preparation method of the modified samarium iron-nitrogen magnetic material, the drying treatment in step (3) is performed at a temperature of 200°C.

[0056] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by using the same testing method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0057] Example 5

[0058] The difference from Example 1 is that the anti-oxidation coating solution further comprises 1 g / L NdPO4, 1 g / L PrPO4, 1 g / L Cu3(PO4)2, and 1 g / L CePO4.

[0059] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by using the same testing method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0060] Example 6

[0061] The difference from Example 1 is that the anti-oxidation coating solution further comprises 5 g / L NdPO4, 5 g / L PrPO4, 5 g / L Cu3(PO4)2, and 5 g / L CePO4.

[0062] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by using the same testing method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0063] Example 7

[0064] The difference from Example 6 is that the concentration of each of the following components is different, including 8 g / L NdPO4, 8 g / L PrPO4, 8 g / L Cu3(PO4)2, and 8 g / L CePO4.

[0065] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by the same method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0066] Example 8

[0067] The difference from Example 1 is that the pH of the anti-oxidation coating solution is 4.

[0068] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by the same method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0069] Example 9

[0070] The difference from Example 1 is that the pH of the anti-oxidation coating solution is 6.

[0071] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by the same method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0072] Example 10

[0073] The difference from Example 1 is that the pH of the anti-oxidation coating solution is 7.

[0074] The bonded magnet is prepared by the same method as in Example 1. The cylindrical bonded magnet prepared is tested for magnetic properties by the same method as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that no phosphoric acid is added to the anti-oxidation coating solution.

[0077] The bonded magnet was prepared in the same manner as in Example 1. The cylindrical bonded magnet prepared was subjected to magnetic property tests in the same manner as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that sodium silicate was not added to the anti-oxidation coating solution.

[0080] The bonded magnet was prepared in the same manner as in Example 1. The cylindrical bonded magnet prepared was subjected to magnetic property tests in the same manner as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0081] Comparative Example 3

[0082] The uncoated Sm2Fe 17 N x The uncoated Sm2Fe 17 N x The magnetic powder and nylon 12 were mixed and granulated in a twin-screw extruder at a weight ratio of 10:1 and a processing temperature of 200°C, and then the granules were transferred to an injection machine to be injection-molded at 245°C to obtain a cylindrical magnet.

[0083] The bonded magnet was prepared in the same manner as in Example 1. The cylindrical bonded magnet prepared was subjected to magnetic property tests in the same manner as in Example 1, and the test results of the residual magnetization (Br), the coercive force (Hcj), and the maximum magnetic energy product (BHmax) are shown in Table 1.

[0084] Table 1

[0085] Br (Gs) Hci (Oe) BHmax (MGOe) Example 1 6930 9610 11.2 Example 2 7150 8500 12.3 Example 3 7070 8730 11.7 Example 4 6810 8330 10.1 Example 5 6890 9850 10.6 Example 6 6750 10750 10.3 Example 7 6520 10680 10.1 Example 8 7120 9620 11.8 Example 9 7130 8170 11.5 Example 10 6940 7230 9.5 Comparative Example 1 6540 6430 7.5 Comparative Example 2 6730 6770 8.8 Comparative Example 3 6110 5330 6.7

[0086] From the above description, it can be seen that the above-described embodiments of the present application achieve the following technical effects:

[0087] According to the magnetic property test results in Table 1, the coercivity and maximum magnetic energy product of the cylindrical bonded magnet prepared in Comparative Example 1 are obviously smaller than those of Example 1. This shows that, since the anti-oxidation coating solution does not contain phosphoric acid, even if the coating treatment is performed on the samarium iron-nitrogen magnetic material using the anti-oxidation coating solution, no etching reaction occurs on the surface of the samarium iron-nitrogen magnetic material, and no phosphate crystal nucleus is generated, which inhibits the deposition of the subsequent phosphate on the surface, resulting in the failure to form a coating layer. However, the anti-oxidation coating solution provided by the present application can etch the surface of the samarium iron-nitrogen magnetic material and form phosphate, and the phosphate coating layer formed finally has good magnetic shielding performance and does not cause magnetic interference to the magnetic material inside.

[0088] According to the magnetic property test results in Table 1, the coercivity and maximum magnetic energy product of the cylindrical bonded magnet prepared in Comparative Example 2 are obviously smaller than those of Example 1. This shows that the addition of a specific amount of sodium silicate in the present application can fill the holes on the surface of the inorganic phosphate coating layer, making the coating layer more dense, and can enhance the bonding force between the coating layer and the magnetic material particles, making the coating layer difficult to fall off and improving the structural stability of the modified magnetic material.

[0089] As can be seen by comparing Example 1 and Comparative Example 3, the modified samarium iron-nitrogen magnetic material prepared by using the preparation method of the modified samarium iron-nitrogen magnetic material provided by the present application has excellent anti-oxidation and corrosion resistance. In addition, the phosphate coating layer has good magnetic shielding performance and does not cause magnetic interference to the samarium iron-nitrogen magnetic material inside.

[0090] The magnetic property test results of Example 4 in Table 1 are slightly worse than those of Example 1, which shows that a too high drying temperature can reduce the magnetic properties of the modified samarium iron-nitrogen magnetic material. As can be seen by comparing Example 1 and 4, different drying temperatures can affect the structure and density of the coating layer, thereby affecting the magnetic properties of the modified samarium iron-nitrogen magnetic material.

[0091] According to the magnetic property test results of Examples 1, 5 and 6 in Table 1, the remanence, coercivity and maximum magnetic energy product of the cylindrical bonded magnet prepared thereby are maintained at a high level, which shows that the preferred NdPO4, PrPO4, Cu3(PO4)2 and CePO4 added in the present application can also participate in the formation of the phosphate coating layer, so that the samarium iron-nitrogen magnetic material after coating modification has better anti-oxidation and corrosion resistance, thereby having higher coercivity. The coercivity of the cylindrical bonded magnet prepared in Example 7 is higher than that of Examples 1, 5 and 6, which shows that excessive addition can lead to an increase in the non-magnetic phase in the magnetic material, resulting in a decrease in the remanence. Therefore, compared with other ranges, limiting the amount of NdPO4, PrPO4, Cu3(PO4)2 and CePO4 within the preferred range of the present application is beneficial to further improving the anti-oxidation and corrosion resistance of the modified samarium iron-nitrogen magnetic material.

[0092] It can be seen from comparative examples 1, 8 to 10 that the pH of the anti-oxidation coating solution in examples 1, 8 to 10 gradually increases, and the pH thereof is 3, 4, 6 and 7 respectively. The coercivity and maximum magnetic energy product of example 10 are both significantly lower than that of example 1. The pH of the anti-oxidation coating solution includes but is not limited to the preferred range of the present application, and it is beneficial to limit the pH within the preferred range of the present application to make the etching reaction between phosphoric acid and samarium-iron-nitrogen magnetic material within an appropriate range, and at the same time to provide a suitable chemical reaction environment for the subsequent deposition of phosphate, and to improve the compactness and stability of the phosphate coating.

[0093] It should be noted that the terms "first", "second" and the like in the description and claims of the application are used for distinguishing between similar objects and do not necessarily have a specific chronological or chronological order. It should be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of accomplishing the same objectives stated herein using either sequence or arrangement.

[0094] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a modified samarium iron nitrogen magnetic material, characterized in that, The preparation method of the modified samarium iron nitrogen magnetic material includes: The modified samarium iron nitrogen magnetic material is obtained by coating the samarium iron nitrogen magnetic material with an anti-oxidation coating solution used in samarium iron nitrogen magnetic materials; the coating process is carried out at a temperature of 120-200℃ for 2-5 hours; the anti-oxidation coating solution comprises: 1~60g / L H3PO4, 10~60g / L Zr3(PO4)4, 10~30g / L Zn3(PO4)2, 1~10g / L Na2SiO3, 10~20g / L SmPO4 and 60~150g / L FePO4; The antioxidant coating solution also includes: 5-10 g / L sodium silicate, 5-10 g / L polyethylene glycol and 5-10 g / L polyacrylic acid.

2. The preparation method according to claim 1, characterized in that, The antioxidant coating solution also includes one or more of the following: NdPO4, PrPO4, Cu3(PO4)2 and CePO4.

3. The preparation method according to claim 1, characterized in that, The antioxidant coating solution also includes: 1-5 g / L NdPO4, 1-5 g / L PrPO4, 1-5 g / L Cu3(PO4)2 and 1-5 g / L CePO4.

4. The preparation method according to claim 1, characterized in that, The viscosity-average molecular weight of the polyethylene glycol is 200-2000, and the viscosity-average molecular weight of the polyacrylic acid is 200-2000.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The antioxidant coating solution further includes a diluent, which comprises an organic solvent and water, and the weight ratio of the organic solvent to the water is (7-9):1; the organic solvent is selected from one or more of the group consisting of ethanol, isopropanol and acetone.

6. The preparation method according to claim 5, characterized in that, The pH of the antioxidant coating solution is 3-6.

7. The preparation method according to claim 5, characterized in that, The pH of the antioxidant coating solution is 3-4.

8. A modified samarium iron nitrogen magnetic material, characterized in that, The modified samarium iron nitrogen magnetic material is prepared by the method described in any one of claims 1 to 7.

9. A bonded magnet, characterized in that, The bonded magnet is obtained by mixing the modified samarium iron nitrogen magnetic material of claim 8 with a binder and an optional lubricant in sequence, followed by extrusion granulation and injection molding; the remanence of the bonded magnet is 6500-7500 Gs, the coercivity is 7000-11000 Oe, and the maximum energy product is 10-15 MGOe.