Rare earth-silane composite film on the surface of sintered NdFeB and preparation method thereof

Abstract

The present invention discloses a rare earth-silane composite film on the surface of sintered NdFeB. A three-dimensional network structure connected by Si-O-Si bonds is formed on the surface of sintered NdFeB through a chemical reaction. Rare earth oxides and hydroxides are formed within the three-dimensional network structure, and the rare earth oxides and the hydroxides are distributed in the film layer, making the rare earth-silane composite film uniformly dense as a whole, having superhydrophobicity and corrosion resistance, and having little influence on magnetic properties. It has a strong bonding force with the sintered NdFeB substrate, can be used for the surface protection of magnetic materials such as NdFeB, is easy to operate, and is suitable for mass production.

Description

Technical Field

[0001] The present invention relates to the technical field of silane composite film materials, and particularly relates to a rare earth-silane composite film on the surface of sintered NdFeB and a preparation method thereof. Background Art

[0002] Sintered neodymium iron boron (NdFeB) permanent magnets have excellent magnetic properties and are widely used in application fields such as electronics, acoustics, communication, automation, magnetic resonance imaging, and biomedicine. However, NdFeB has a multiphase composed of ferromagnetic tetragonal compounds Nd2Fe 14 B, Nd4Fe-rich Nd phase, and Nd1 +ε Fe4B4, resulting in poor corrosion resistance and thermal stability, which greatly limits its further application. In order to improve its corrosion resistance, many studies on alloying and surface treatment have been carried out. Organosilane films are economical, effective, environmentally friendly, and easy to operate, and are commonly used for the anti-corrosion of metals and alloys. However, the characteristics of the silane film layer such as non-dense structure and poor binding force with the substrate will cause molecules or ions such as H2O, O2, and Cl - to cause corrosion of the protected material through the film layer defects.

[0003] CN202110348129.1 discloses a preparation method of a superhydrophobic silane film based on hydrophobic nanoparticles. The specific preparation method is as follows: First, the nanoparticles are modified with stearic acid to obtain hydrophobic nanoparticles; then the obtained hydrophobic nanoparticles are added to the silane film solution to obtain a hydrophobic nanoparticle silane film solution; the hydrophobic nanoparticle silane film is prepared on the pretreated metal substrate by dip coating, spraying, electrochemically assisted deposition, and vapor deposition methods. Stearic acid plays a good role in hydrophobicity, but the stearic acid silane film has the disadvantages of weak binding force and easy abrasion.

[0004] Through literature research, the traditional preparation methods of silane composite film layers mainly include dip coating method, spin coating method, sol-gel method, etc. The film layers prepared by these methods have weak binding with the substrate, are easy to crack and fall off, and the obtained film layers have the disadvantages of insufficient density (there are pinholes and cracks), poor self-healing property, and poor corrosion resistance, and the film formation thickness is uncontrollable, the operation is difficult to unify in actual production applications, and the stability of products in different batches is not good. Summary of the Invention

[0005] In order to solve certain or some technical problems existing in the prior art, one of the purposes of the present application is to provide a rare earth-silane composite film on the surface of sintered NdFeB. The film layer is overall uniform and dense, has no obvious defects, has a strong binding force with the substrate, has good superhydrophobicity and corrosion resistance, has little influence on the magnetic properties, can be used for the surface protection of magnetic materials such as NdFeB, is easy to operate, and is suitable for batch production.

[0006] The second object of the present application is to provide a method for preparing a rare earth-silane composite film on the surface of sintered NdFeB. The preparation method is simple, has a short cycle, and strong practicability. It can form a firm whole after the film layer is joined with the substrate, and there will be no phenomenon of cracking and peeling. The obtained film layer has good compactness, self-healing property and corrosion resistance, and the film-forming thickness is uniform and stable, and the product stability is high.

[0007] To solve the above existing technical problems, the first object of the present application is achieved by adopting the following technical solution:

[0008] A rare earth-silane composite film on the surface of sintered NdFeB, in which a three-dimensional network structure connected by Si-O-Si bonds is formed on the surface of sintered NdFeB through a chemical reaction. Rare earth oxides and hydroxides are generated within the three-dimensional network structure, and the rare earth oxides and the hydroxides are distributed in the film layer, making the rare earth-silane composite film as a whole uniformly dense, having superhydrophobicity and corrosion resistance, and having little influence on magnetic properties.

[0009] The second object of the present application is achieved by adopting the following technical solution:

[0010] A method for preparing a rare earth-silane composite film on the surface of sintered NdFeB, characterized in that the steps of the preparation method include:

[0011] S1. Perform anhydrous pretreatment on the surface with sintered NdFeB as the substrate to obtain sample M1;

[0012] S2. Immerse M1 in an organosilane solution to obtain a pre-impregnated silane film and obtain sample M2;

[0013] S3. Prepare an electrolyte with deionized water, ethanol, stearic acid, a silane coupling agent, and a rare earth salt;

[0014] S4. Immerse M2 in the electrolyte and use an electrochemical assisted deposition method to prepare sample M3;

[0015] S5. Perform post-treatment on the sample M3 to obtain the rare earth-silane composite film on the surface of sintered NdFeB described in claim 1.

[0016] Preferably, the anhydrous pretreatment in step S1 includes:

[0017] A1. Remove the surface oxide layer and stains by sandblasting;

[0018] A2. Ultrasonically clean with acetone to remove oil stains, dry and then put it into a laser ablation chamber;

[0019] A3. Perform vacuum pumping on the chamber, and then introduce an inert gas for 5-8 minutes;

[0020] A4. Further remove the surface oxide layer of the sintered NdFeB substrate through laser ablation of the box body to activate the substrate surface, thereby improving the bonding strength between the substrate and the subsequent rare-earth-silane composite film.

[0021] Preferably, the organosilane solution in step S2 comprises 10-30 parts of a functional silane with a hydrophobic functional group and 30-50 parts of ethanol.

[0022] Preferably, the method of immersing the organosilane solution in step S2 is to immerse M1 in the organosilane solution at room temperature of 25-30 °C for 5-10 minutes to obtain sample M2.

[0023] The purpose of this step is to form a pre-immersed silane film on the surface of sample M1, allowing the organosilane to seal the pores in sample M1 to avoid the penetration and erosion of the subsequent electrolyte.

[0024] Preferably, the silane coupling agent in step S3 is composed of a functional silane with a hydrophobic functional group and a silane without an organic functional group, and the electrolyte components include: 30-50 parts of deionized water, 120-200 parts of ethanol, 3-5 parts of sodium nitrate, 4-6 parts of a functional silane with a hydrophobic functional group, 4-6 parts of a silane without an organic functional group, 4-6 parts of stearic acid, and 1-3 parts of a rare-earth salt.

[0025] Preferably, the specific preparation steps of the electrolyte include:

[0026] B1. Using deionized water and ethanol as solvents, adding sodium nitrate, and adjusting the pH to 3-4 with 1 mol / L acetic acid to obtain solution Y1;

[0027] B2. Adding a functional silane with a hydrophobic functional group and a silane without an organic functional group to Y1, and hydrolyzing at 30-35 °C for 24-48 h to obtain solution Y2;

[0028] B3. Adding stearic acid and a rare-earth salt to Y3, and stirring at 40-60 °C for 20-35 min to prepare the electrolyte.

[0029] The sodium nitrate in step S3 acts as a conductive salt, and during the subsequent electrodeposition process, nitrate ions can accelerate local alkalization and reduce the generation of hydrogen evolution reactions, making the finally obtained silane film layer denser and having fewer defects. The reason for using acetic acid instead of hydrochloric acid to adjust the pH is to reduce the erosion of the film layer and the substrate by chloride ions in the solution. Selecting a slightly acidic environment is beneficial to the hydrolysis of silane.

[0030] Preferably, the rare earth salts in the step S3 include: cerium salts, lanthanum salts, yttrium salts, praseodymium salts or samarium salts, and the functional silanes with hydrophobic functional groups include: dodecyltrimethoxysilane, cetyltrimethoxysilane, vinyltrimethoxysilane; the silanes without organic functional groups include: tetraethoxysilane and tetramethoxysilane.

[0031] The silanes without organic functional groups are a silane system of inorganic SiO2 source. During the film formation process, an inorganic SiO2 skeleton is formed; the functional silanes with hydrophobic functional groups can in-situ modify and modify the inorganic SiO2 skeleton, making the prepared silane film denser and having superhydrophobic properties. Rare earth salts such as cerium salts, lanthanum salts, yttrium salts, praseodymium salts, neodymium salts and samarium salts are used as an environmentally friendly corrosion inhibitor and have properties such as self-healing. Doping rare earth salts into the silane film can improve the protective performance of the film layer.

[0032] Preferably, the electrochemical assisted deposition method in the step S4 includes: adding the electrolyte in the S3 into an electrolytic cell, applying a voltage of -1.2V to -1.6V using a three-electrode system, with a deposition time of 300 to 500s and a working temperature of 30 to 35°C to obtain sample M3.

[0033] This process can cause local alkalization on the surface of the sample, which not only promotes the formation of a network film of silane, but also oxidizes rare earth salts into oxides and hydroxides.

[0034] Preferably, the three-electrode system includes a working electrode, a reference electrode and an auxiliary electrode. The working electrode is sample M2, the reference electrode is a saturated calomel electrode, and the auxiliary electrode is a platinum sheet.

[0035] Through the cathodic reaction, abundant OH can be generated in the solution near the surface of the substrate - , forming a local alkaline environment, which provides power for the condensation of silanol molecules obtained by hydrolysis. Compared with other film-forming processes, it has the advantages of strong film-forming power, thick film-forming, few defects, more uniform and dense film layer, and larger surface roughness.

[0036] Preferably, the post-treatment of the sample M3 in the step S5 is to wash the sample M3 with 30 to 50 parts of ethanol and 30 to 50 parts of deionized water respectively, and then dry it at a temperature of 30 to 55°C for 5 to 24h.

[0037] The relevant mechanism of the experiment of the present invention is as follows:

[0038] H3C(H2C) 10 H2C-Si(OCH3)3+H2O→H3C(H2C) 10 H2C-Si-OH+CH3OH……(1)

[0039] Si-OH + Si-OH → Si-O-Si + H2O………………………………………………(2)

[0040] H3C(H2C) 10 H2C-Si(OCH3)3 + 3Si-OH → H3C(H2C) 10 H2C-Si-O-Si + 3CH3OH....(3)

[0041] Si-OC2H5 + Si-OH → Si-O-Si + C2H5OH………………………………………(4)

[0042] O2 + 2H2O + 4e - → 4OH - …………………………………………………………(5)

[0043] NO3 - + H2O + 2e - → NO2 - + 2OH - ………………………………………………(6)

[0044] 2H2O + 2e - → 2OH - + H2↑……………………………………………………(7)

[0045] Ce 3+ + 3OH - → Ce(OH)3↓………………………………………………………(8)

[0046] 2Ce(OH)3 → Ce2O3 + 3H2O……………………………………………………(9)

[0047] 4Ce 3+ + 12OH - + O2 + 2H2O → 4Ce(OH)4……………………………………(10)

[0048] 2Ce2O3 + O2 → 4CeO2…………………………………………………………(11)

[0049] La 3+ + 3OH - → La(OH)3↓…………………………………………(12)

[0050] 2La(OH)3 → La2O3 + 3H2O……………………………………………………(13)

[0051] Among them, formulas (1)-(4) are the silane film formation mechanism, formulas (5)-(7) are the electrochemically assisted local alkalization mechanism of the cathode, and formulas (8)-(13) are the corrosion inhibition mechanism of rare earth salts.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] (1) The rare earth-silane film prepared by the present invention is uniform, dense, has no obvious defects, has a strong bonding force with the substrate, has significant superhydrophobicity and corrosion resistance, and has little influence on magnetic properties;

[0054] (2) The anhydrous pretreatment is adopted to avoid the corrosion of the substrate by the conventional acid and alkali pretreatment aqueous solutions;

[0055] (3) The organic silane solution pre-impregnation process is adopted, so that the pores on the surface of the NdFeB substrate are sealed by the organic silane, avoiding the penetration and erosion of the acidic electrolyte on the NdFeB substrate during the electrochemically assisted deposition process. In addition, the organic silane on the surface of the substrate after pre-impregnation will also participate in the film formation reaction during the electrodeposition process, promoting the formation of the composite film;

[0056] (4) The electrochemically assisted deposition preparation process adopted, the local alkaline environment caused by the cathode reaction process provides power for the condensation of silanol molecules obtained by hydrolysis, promoting the silane film layer to be more uniform, less defective and thicker;

[0057] (5) The present invention uses rare earth salts doped with corrosion inhibition effects to improve the corrosion resistance of the film layer. Rare earth metal ions can inhibit the cathode reaction on the metal surface in the corrosive medium, and the generated rare earth oxides or hydroxides have certain corrosion resistance. Moreover, when the film layer is damaged, the rare earth ions in the surface film layer will migrate to the scratch to form a new oxide and protective film layer, reducing the pores and defects of the film layer and effectively inhibiting the penetration of the corrosive medium;

[0058] (6) The method for preparing the rare earth-silane film of the present invention has the characteristics of simple process, short cycle, strong practicability, etc. Description of the Drawings

[0059] Figure 1 is the surface morphology of the rare earth-silane composite film of the product prepared in Example 1;

[0060] Figure 2 is the surface morphology of the rare earth-silane composite film of the product prepared in Example 2;

[0061] Figure 3 is the surface morphology of the rare earth-silane composite film of the product prepared in Comparative Example 1;

[0062] Figure 4 Secondary ion mass spectrometry analysis diagram of the rare earth-silane composite film of the product prepared in Example 1;

[0063] Figure 5 Electrochemical impedance diagrams of the rare earth-silane composite films and substrates of the products prepared in Examples 1 and 2 and Comparative Example 1;

[0064] Figure 6 Hydrophobic property comparison diagrams of the rare earth-silane composite films and substrates of the products prepared in Examples 1 and 2 and Comparative Example 1;

[0065] Figure 7 Adhesion force comparison diagrams of the composite films and substrates prepared in Examples 1 and 2 and Comparative Examples 1 and 2;

[0066] Figure 8 Hysteresis loops of the substrates and the rare earth-silane composite films of the products prepared in Examples 1 and 2. Detailed implementation manners

[0067] Next, in combination with the accompanying drawings and specific implementation manners, the present application will be further described. It should be noted that, on the premise of non-conflict, the following-described embodiments or technical features can be arbitrarily combined with each other to form new embodiments.

[0068] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present application.

[0069] The terms "first", "second", etc. in the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are usually of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally represents an "or" relationship between the associated objects before and after.

[0070] Example 1:

[0071] (1) Surface anhydrous pretreatment of sintered NdFeB

[0072] Remove the surface oxide layer, oil stains, etc. by sandblasting, ultrasonically clean with acetone to further remove oil stains, dry it, and then place it in the laser ablation chamber. First, evacuate the chamber, and then introduce inert gas for 6 minutes. Laser ablation further removes the surface oxide layer of the substrate, activates the surface of the substrate, and obtains sample M1.

[0073] (2) Immersion in organosilane film

[0074] Put sample M1 into the ethanol organic solvent of dodecyltrimethoxysilane (composed of 15 parts of dodecyltrimethoxysilane and 30 parts of ethanol), and immerse it at room temperature (25 °C) for 9 minutes to obtain a pre-impregnated silane film and get sample M2.

[0075] (3) Preparation of electrolyte

[0076] Use 40 parts of deionized water and 160 parts of ethanol as solvents, add 4 parts of sodium nitrate, adjust the pH to 3 with 1 mol / L acetic acid, then add 5 parts of dodecyltrimethoxysilane and 5 parts of tetraethyl orthosilicate, and hydrolyze at 35 °C for 24 h; finally, add 5 parts of stearic acid and 1 part of lanthanum nitrate and stir at 60 °C for 25 min to prepare the electrolyte;

[0077] (4) Electrochemical-assisted deposition

[0078] Add the electrolyte to the electrolytic cell, apply a voltage of -1.4 V using a three-electrode system (the working electrode is sample M2, the reference electrode is a saturated calomel electrode, and the auxiliary electrode is a platinum sheet), the deposition time is 350 s, and the working temperature is 35 °C to prepare a rare earth-silane composite film on the surface of the pre-impregnated silane film and get sample M3.

[0079] (5) Post-treatment of composite film

[0080] Rinse sample M3 with 40 parts of ethanol and 30 parts of deionized water, and dry it at 40 °C for 8 h to obtain the product rare earth-silane composite film.

[0081] Example 2:

[0082] (1) Pretreatment of the surface of sintered NdFeB without water

[0083] Remove the surface oxide layer, oil stains, etc. by sandblasting, ultrasonically clean with acetone to further remove oil stains, dry it, and then place it in the laser ablation chamber. First, evacuate the chamber, and then introduce inert gas for 7 minutes. Laser ablation further removes the surface oxide layer of the substrate, activates the surface of the substrate, and obtains sample M1.

[0084] (2) Immersion in organosilane film

[0085] Put sample M1 into the ethanol organic solvent of dodecyltrimethoxysilane (composed of 20 parts of dodecyltrimethoxysilane and 35 parts of ethanol), and immerse it at room temperature (25 °C) for 9 minutes to obtain a pre-impregnated silane film and get sample M2.

[0086] (3) Preparation of electrolyte

[0087] Using 45 parts of deionized water and 135 parts of ethanol as solvents, adding 5 parts of sodium nitrate, adjusting the pH to 3 with 1 mol / L acetic acid, then adding 6 parts of dodecyltrimethoxysilane and 4 parts of tetraethyl orthosilicate, hydrolyzing at 35 °C for 36 h; finally adding 4 parts of stearic acid and 2 parts of cerium nitrate and stirring at 50 °C for 30 min to prepare the electrolyte;

[0088] (4) Electrochemical-assisted deposition

[0089] Adding the electrolyte into the electrolytic cell, applying a voltage of -1.5 V using a three-electrode system (the working electrode is sample M2, the reference electrode is a saturated calomel electrode, and the auxiliary electrode is a platinum sheet), with a deposition time of 400 s and a working temperature of 30 °C, to obtain a rare earth-silane composite film on the surface of the pre-impregnated silane film, getting sample M3.

[0090] (5) Post-treatment of the composite film

[0091] Rinsing sample M3 with 50 parts of ethanol and 40 parts of deionized water, and drying at 35 °C for 12 h to obtain the product rare earth-silane composite film.

[0092] Comparative Example 1

[0093] Same as Example 1, the only difference is that no rare earth salt is added to the electrolyte, obtaining the product rare earth-silane composite film.

[0094] Comparative Example 2

[0095] (1) Surface pretreatment of sintered NdFeB

[0096] Grinding the sintered NdFeB successively with a grinding wheel, 300-mesh, 800-mesh, and 1000-mesh metallographic sandpapers to remove the surface oxide layer, and then performing alkali washing, water washing, acetone washing, and alcohol washing on the neodymium iron boron. This includes placing the galvanized neodymium iron boron in a 1 mol / L NaOH solution for 10 min, taking it out and placing it in deionized water and standing for 5 min to remove the residual NaOH solution on the surface. Then wiping the treated galvanized neodymium iron boron with acetone and ethanol solution to remove the residual sodium hydroxide and some hanging ash from the previous process, obtaining sample M1.

[0097] (2) Preparation of electrolyte; (3) Electrochemical-assisted deposition; (4) The post-treatment steps are the same as the relevant steps in Example 1, obtaining the product rare earth-silane composite film.

[0098] Performance analysis

[0099] The surface morphology of the product was analyzed using a FEI Quanta 650 scanning electron microscope. The surface morphologies of the rare earth-silane composite films of the products prepared in Examples 1 and 2 are shown in Figure 1 , 2 . Compared with the rare earth-silane composite film of the product prepared in Comparative Example 1 ( Figure 3 ), it can be seen that the defects such as holes and cracks in the rare earth-silane composite films of the products prepared in Examples 1 and 2 are significantly reduced, and the film structure is dense. Figure 4 is the secondary ion mass spectrometry analysis diagram (SIMS, the detection equipment is IMS1280 secondary ion mass spectrometer) of the rare earth-silane composite film of the product prepared in Example 1. The presence of SiO indicates the presence of a Si-O-Si three-dimensional network structure in the film layer, and the presence of LaO proves the presence of lanthanum oxide. The electrochemical impedance diagrams (EIS, the detection equipment is CHI660e electrochemical workstation) of the substrates (sintered NdFeB), the rare earth-silane composite films of the products prepared in Examples 1 and 2, and Comparative Example 1 in 3.5 wt% sodium chloride solution are as shown in Figure 5 . Table 1 shows the EIS analysis data (R s : electrolyte resistance, R ct : charge transfer resistance, CPE f : film capacitance, R f : film resistance, CPE dl : double-layer capacitance). Compared with the rare earth-silane composite film of the product prepared in Comparative Example 1 and the substrate, the resistance values of the rare earth-silane composite films of the products prepared in Examples 1 and 2 are significantly increased. Among them, the resistance value of the rare earth-silane composite film of the product prepared in Example 2 is nearly 10 times that of the substrate and nearly 2 times that of the rare earth-silane composite film of the product prepared in Comparative Example 1; while the resistance value of the rare earth-silane composite film of the product prepared in Example 1 is more than 3 times that of the rare earth-silane composite film of the product prepared in Example 2. The addition of rare earth salts significantly improves the corrosion resistance of the silane film.

[0100] Table 1 Fitting data

[0101]

[0102] Figure 6 is the hydrophobicity comparison diagram of the rare earth-silane composite films of the products prepared in Examples 1 and 2 and Comparative Example 1 and the substrate. The test equipment is a JC2000D3B series contact angle measuring instrument. It can be seen from the figure that the contact angles of the rare earth-silane composite films of the products prepared in Comparative Example 1 and Examples 1 and 2 are much larger than those of the substrate, indicating good hydrophobicity. Among them, the contact angles of the rare earth-silane composite films of the products prepared in Examples 1 and 2 are both greater than 150°, showing obvious superhydrophobicity.

[0103] Figure 7For Examples 1 and 2, and Comparative Examples 1 and 2, the adhesion contrast diagram of the rare earth-silane composite film of the prepared products was obtained by the cross cut test method. The surface of the film layer was cut to form 100 1 mm 2 grids. Tape was placed on the grids to ensure good contact with the film layer surface. Within 90 ± 30 seconds, grasp the free end of the tape and quickly fold it at 180° to remove the tape. The sample was observed with a polarized light microscope. The coating adhesion is divided into four grades, namely (1) the edges of the cuts are complete and smooth, and there is no peeling at the edges of the grids; (2) there is a small amount of coating peeling at the intersections of the cuts, and the peeling area ≤ 5%; (3) there is coating peeling at the intersections of the cuts or along the edges of the cuts, and the peeling area > 5% and cannot be significantly greater than 15%; (4) the coating layer falls off in large pieces partially or completely along the cutting edges, and the peeling area > 15% and cannot be significantly greater than 35%. As Figure 7 can be seen, compared with Comparative Example 2 (the peeling area accounts for about 25%), the peeled area of the rare earth-silane composite films of the products obtained in Comparative Example 1 and Examples 1 and 2 is reduced (accounting for about 15%), indicating that the anhydrous pretreatment and silane solution immersion on the surface of sintered NdFeB improve the adhesion.

[0104] Figure 8 The hysteresis loops of the substrates and the rare earth-silane composite films of the products prepared in Examples 1 and 2 were measured using a LakeShore 7404 vibrating sample magnetometer. The magnetic property analysis is shown in Table 2. Through the comparison of the saturation magnetization intensity (M s ), the remanent magnetization intensity (M r ), and the coercivity (H c ), it can be seen that the saturation magnetization intensity and remanence of sintered NdFeB after cerium nitrate-silanization treatment only decreased by 0.74% and 0.63% respectively, and the saturation magnetization intensity and remanence of sintered NdFeB after lanthanum nitrate-silanization treatment only decreased by 1.56% and 1.63% respectively. The presence of the rare earth-silane composite film has a very small impact on the magnetic properties of the NdFeB magnet itself.

[0105] Table 2 Magnetic property data

[0106] substrate Example 1 Example 2 <![CDATA[M s (emu / g)]]> 149.82 148.71 147.47 <![CDATA[M r (emu / g)]]> 143.89 142.99 141.54 <![CDATA[H c (Oe)]]> 24.98 25.38 25.28

[0107] The above embodiments are only the preferred embodiments of the present application and cannot be used to limit the scope of protection of the present application. Any non-substantial changes and substitutions made by those skilled in the art based on the present application fall within the scope of protection required by the present application.

Claims

1. A rare earth-silane composite film on the surface of sintered NdFeB, characterized in that: A three-dimensional network structure connected by Si-O-Si bonds is formed on the surface of sintered NdFeB through a chemical reaction. Rare earth oxides and hydroxides are formed within the three-dimensional network structure, and the rare earth oxides and the hydroxides are distributed in the film layer, making the rare earth-silane composite film as a whole uniform and dense, having superhydrophobicity and corrosion resistance, and having little influence on magnetic properties.

2. A preparation method of a rare earth-silane composite film on the surface of sintered NdFeB, characterized in that: The steps of the preparation method include: S1. Perform anhydrous pretreatment on the surface with sintered NdFeB as the substrate to obtain sample M1; S2. Immerse M1 in an organosilane solution to obtain a pre-impregnated silane film and obtain sample M2; S3. Prepare an electrolyte with deionized water, ethanol, sodium nitrate, stearic acid, a silane coupling agent, and a rare earth salt; S4. Immerse M2 in the electrolyte and use an electrochemical assisted deposition method to prepare sample M3; S5. Perform post-treatment on the sample M3 to obtain the rare earth-silane composite film on the surface of a sintered NdFeB as described in claim 1.

3. The preparation method of the rare earth-silane composite film on the surface of sintered NdFeB according to claim 2, characterized in that: The anhydrous pretreatment in the step S1 includes: A1. Sandblast to remove the surface oxide layer and stains; A2. Ultrasonically clean with acetone to remove oil stains, dry and then put it into a laser ablation chamber; A3. Perform vacuum pumping on the chamber, and then introduce an inert gas for 5 to 8 minutes; A4. Further remove the surface oxide layer of the sintered NdFeB substrate through laser ablation in the chamber to activate the surface of the substrate, thereby improving the bonding force between the substrate and the subsequent prepared rare earth-silane composite film.

4. The preparation method of the rare earth-silane composite film on the surface of sintered NdFeB according to claim 2, characterized in that: The organosilane solution in the step S2 includes 10 to 30 parts of a functional silane with a hydrophobic functional group and 30 to 50 parts of ethanol.

5. The preparation method of the rare earth-silane composite film on the surface of sintered NdFeB according to claim 4, characterized in that: The method of immersing the organosilane solution in the step S2 is to immerse M1 in the organosilane solution at room temperature of 25 to 30 °C for 5 to 10 minutes to obtain sample M2.

6. A method for preparing a rare earth-silane composite film on the surface of sintered NdFeB according to claim 2, characterized in that: The silane coupling agent in the step S3 is composed of a functional silane with a hydrophobic functional group and a silane without an organic functional group. The components of the electrolyte include: 30 to 50 parts of deionized water, 120 to 200 parts of ethanol, 3 to 5 parts of sodium nitrate, 4 to 6 parts of a functional silane with a hydrophobic functional group, 4 to 6 parts of a silane without an organic functional group, 4 to 6 parts of stearic acid, and 1 to 3 parts of a rare earth salt.

7. A method for preparing a rare earth-silane composite film on the surface of sintered NdFeB, characterized in that: The specific preparation steps of the electrolyte include: B1. Use deionized water and ethanol as solvents, add sodium nitrate, and adjust the pH to 3 to 4 with 1 mol / L acetic acid to obtain solution Y1; B2. Add a functional silane with a hydrophobic functional group and a silane without an organic functional group to Y1, and hydrolyze at 30 to 35 °C for 24 to 48 h to obtain solution Y2; B3. Add stearic acid and a rare earth salt to Y3, and stir at 40 to 60 °C for 20 to 35 min to prepare the electrolyte.

8. A method for preparing a rare earth-silane composite film on the surface of sintered NdFeB, characterized in that: The rare earth salts in the step S3 include: cerium salts, lanthanum salts, yttrium salts, praseodymium salts, or samarium salts. The functional silanes with hydrophobic functional groups include: dodecyltrimethoxysilane, hexadecyltrimethoxysilane, vinyltrimethoxysilane. The silanes without organic functional groups include: tetraethoxysilane and tetramethoxysilane.

9. The preparation method of the rare earth-silane composite film on the surface of sintered NdFeB according to claim 2, characterized in that: The electrochemical assisted deposition method in the step S4 includes: adding the electrolyte in the S3 into an electrolytic cell, applying a voltage of -1.2V to -1.6V using a three-electrode system, with a deposition time of 300 to 500s and a working temperature of 30 to 35°C, to obtain the sample M3.

10. A method for preparing a rare earth-silane composite film on the surface of sintered NdFeB according to claim 2, characterized in that: The post-treatment of the sample M3 in the step S5 is to wash the sample M3 with 30 to 50 parts of ethanol and 30 to 50 parts of deionized water respectively, and then dry it at a temperature of 30 to 55°C for 5 to 24h.

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