A blue rare earth permanent magnet and its preparation method and application

Abstract

The present invention discloses a blue rare earth permanent magnet and a preparation method and application thereof, wherein the blue rare earth permanent magnet comprises a rare earth permanent magnet substrate and an iron oxide film coated on the surface of the rare earth permanent magnet substrate; wherein the mass ratio of oxygen element to iron element in the iron oxide film is (0.33-0.40): 1. The present invention controls the thickness of the oxide layer on the surface of the rare earth permanent magnet substrate by controlling the process parameters, that is, controls the oxygen / iron content ratio on the surface of the product, so as to control the surface of the product to be uniformly blue.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth permanent magnets and preparation methods thereof, and relates to a blue rare earth permanent magnet and a preparation method and application thereof. Background Art

[0002] Rare earth permanent magnets have high chemical activity and are easily corroded, thus affecting the magnetic properties of the product. Therefore, it is necessary to perform anti-corrosion treatment on the surface of rare earth permanent magnets. Short-term anti-corrosion is to ensure that rare earth permanent magnets do not rust during transportation and storage before use. Currently, the main short-term anti-corrosion method is phosphating, but phosphating treatment has problems such as high energy consumption, high wastewater treatment cost, and easy product appearance to fade. Therefore, it is necessary to develop a new surface treatment technology that can replace phosphating.

[0003] Patent CN113667970A discloses a surface passivation treatment method for NdFeB magnets, which forms a protective layer on the surface of the magnets by subjecting the magnets to surface pretreatment, surface activation treatment and surface passivation heat treatment. However, the process is relatively complicated, and the use of flammable and explosive alcohol poses certain safety hazards. In addition, phosphorus-containing passivation liquid is used during the treatment process, which is not environmentally friendly.

[0004] Patent CN104342614A discloses a surface treatment method for a chemical protective layer of a sintered NdFeB permanent magnet material, in which a protective layer of ferroferric oxide is obtained by subjecting the magnet to a water vapor heat treatment. However, this process requires the control of the water vapor pressure, and instead of preferentially generating a uniform ferric oxide film on the surface of the product and then generating a dense ferroferric oxide film, an iron oxide film mainly composed of ferroferric oxide is directly generated at a high temperature, and it is not easy to generate a protective film with a uniform appearance.

[0005] Patent CN101029389A discloses a new method for protecting the surface of NdFeB permanent magnet materials, which forms a blue-black or dark blue protective film on the surface of NdFeB permanent magnet materials by placing the activated permanent magnet materials in a blackening liquid or a bluing liquid for chemical plating. However, the blackening liquid or the bluing liquid used contains fluoride and nitrite, which are not friendly to human health and the environment. Summary of the invention

[0006] In order to improve the above problems, the present invention provides a blue rare earth permanent magnet, which comprises a rare earth permanent magnet matrix and an iron oxide film coated on the surface of the rare earth permanent magnet matrix;

[0007] In the iron oxide film, the mass ratio of oxygen element to iron element is (0.33-0.40):1.

[0008] The study found that when the mass ratio of oxygen and iron elements is controlled within the said range, there is mutual interference between the iron oxide film of a certain thickness on the surface of the rare earth permanent magnet matrix and the light reflected from the surface of the rare earth permanent magnet matrix, and the light appears blue under natural light.

[0009] According to an embodiment of the present invention, the iron oxide thin film includes ferrosoferric oxide.

[0010] According to an embodiment of the present invention, the thickness of the iron oxide film is H, and H is 80-150 nm, preferably 100-140 nm, for example, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm or 150 nm.

[0011] According to an embodiment of the present invention, in the iron oxide thin film, the mass ratio of oxygen element to iron element is 0.33:1, 0.34:1, 0.35:1, 0.36:1, 0.38:1 or 0.40:1.

[0012] According to the embodiment of the present invention, there is no particular limitation on the components of the elements in the rare earth permanent magnet matrix, and a rare earth permanent magnet matrix without surface treatment after processing known in the art can be used.

[0013] Exemplarily, the composition of the rare earth permanent magnet matrix, calculated as 100% by mass, includes:

[0014] R, 26wt% to 35wt%; R is a rare earth element, and R is selected from at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y;

[0015] B, 0.7wt%~1.1wt%;

[0016] Co, 0wt%~3.0wt%;

[0017] M, 0.05wt% to 4.0wt%; M is selected from at least one of Ga, Cu, Al, Zr and Ti;

[0018] The balance is iron and unavoidable impurities.

[0019] According to an embodiment of the present invention, the composition of the rare earth permanent magnet matrix, based on 100% by mass, includes R, 29wt% to 34wt%; for example, 29wt%, 30wt%, 31wt%, 32wt%, 33wt% or 34wt%.

[0020] According to an embodiment of the present invention, the composition of the rare earth permanent magnet matrix, based on 100% by mass, includes B, 0.8wt% to 1.0wt%, for example, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt% or 1.0wt%.

[0021] According to an embodiment of the present invention, the composition of the rare earth permanent magnet matrix, calculated as 100% by mass, includes Co, 0.1wt% to 1.0wt%; for example, 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt% or 1.0wt%.

[0022] According to an embodiment of the present invention, the composition of the rare earth permanent magnet matrix, calculated as 100% by mass, includes M, 0.3wt% to 3.0wt%, for example, 0.3wt%, 0.4wt%, 0.5wt%, 1wt%, 2wt% or 3wt%.

[0023] According to an embodiment of the present invention, the blue rare earth permanent magnet appears blue under natural light.

[0024] The present invention also provides a cleaning liquid, which is used to clean the rare earth permanent magnet matrix to prepare a blue rare earth permanent magnet;

[0025] The cleaning solution, based on 100% by weight, includes 30-40% corrosion inhibitor, 0.5-2.5% film-forming aid, 0.5-3% pH adjuster, 5-8% surfactant, 0.05-0.5% defoamer, and the rest is water.

[0026] According to an embodiment of the present invention, the corrosion inhibitor is one or more of tungstate, silicate, borate and molybdate; for example, one or more of sodium tungstate, sodium silicate, sodium borate and sodium molybdate.

[0027] According to an embodiment of the present invention, the cleaning solution comprises 30-40% of the corrosion inhibitor, specifically 32-36%, for example, 32%, 33%, 34%, 35% or 36%, based on 100% by weight. When the concentration of the corrosion inhibitor is too high or too low, its corrosion inhibition effect will be deteriorated, affecting the uniform film formation of the product, resulting in poor corrosion resistance and poor appearance consistency of the final product.

[0028] According to an embodiment of the present invention, the film-forming aid is one or more of polyethylene glycol, isopropyl alcohol, and acetylene glycol.

[0029] According to an embodiment of the present invention, the cleaning solution comprises 1-2.2% of the film-forming aid based on 100% by weight, for example, 1%, 1.3%, 1.6%, 1.9% or 2.2%.

[0030] According to an embodiment of the present invention, the pH adjuster is potassium hydroxide.

[0031] According to an embodiment of the present invention, the cleaning solution comprises 1-2.5% of a pH adjuster, for example, 1%, 1.4%, 1.8%, 2.2% or 2.5%, based on 100% by weight.

[0032] According to an embodiment of the present invention, the surfactant is dodecyl diethanolamide.

[0033] According to an embodiment of the present invention, the cleaning solution comprises 5-7% of a surfactant, for example, 5%, 5.5%, 6%, 6.5% or 7%, based on 100% by weight.

[0034] According to an embodiment of the present invention, the defoaming agent is THIX-278 silicone defoaming agent (for example, produced by Hengxin Chemical Technology Co., Ltd.).

[0035] According to an embodiment of the present invention, the cleaning solution comprises 0.1-0.3% of the defoaming agent, for example, 0.1%, 0.14%, 0.18%, 0.22%, 0.26% or 0.3%, based on 100% by weight.

[0036] According to an embodiment of the present invention, the preparation method of the cleaning solution is:

[0037] The cleaning solution is obtained by mixing a corrosion inhibitor, a film-forming aid, a pH regulator, a surfactant, a defoamer and water.

[0038] According to the embodiment of the present invention, the mixing temperature and time are not particularly limited, as long as the raw materials are mixed uniformly.

[0039] The present invention also provides a method for preparing a blue rare earth permanent magnet, the method comprising the following steps:

[0040] (2) Rough cleaning: Mix the above cleaning liquid with water as a cleaning agent to perform rough cleaning on the rare earth permanent magnet matrix;

[0041] (3) Fine washing: the above-mentioned cleaning liquid is mixed with water as a cleaning agent, and the product in step (2) is finely washed;

[0042] (4) Washing with water: Wash the product of step (3) with water;

[0043] (5) Drying: thermally pretreating the product of step (4);

[0044] (6) Bluing: heat treating the product of step (5) to obtain the blue rare earth permanent magnet.

[0045] According to an embodiment of the present invention, the rare earth permanent magnet matrix may be polished before rough washing, specifically: (1) Polishing: the cleaning liquid is mixed with water to grind the rare earth permanent magnet matrix.

[0046] According to an embodiment of the present invention, in step (1), the concentration of the polishing cleaning liquid in water is 0.1-2 wt %, preferably 0.5-1.5 wt %.

[0047] According to an embodiment of the present invention, in step (1), the rare earth permanent magnet substrate can be ground by mechanical vibration for 0.5-5 hours, preferably 1-4 hours.

[0048] According to an embodiment of the present invention, in step (2), the concentration of the cleaning liquid for rough washing in water is 8-15wt%, preferably 10-12wt%, the temperature of the rough washing is 23-60°C, preferably 40-50°C, and the time of the rough washing is 2-6min, preferably 3-5min.

[0049] According to an embodiment of the present invention, in step (3), the concentration of the cleaning liquid for fine washing in water is 2-8wt%, preferably 3-5wt%, the temperature of the fine washing is 23-60°C, preferably 23-45°C, and the time of the fine washing is 0.5-3min, preferably 1-2min.

[0050] In step (3) of the present invention, the cleaning liquid is diluted in a certain proportion, and the corrosion inhibitor in the cleaning liquid can be adsorbed on the active points on the surface of the rare earth permanent magnet matrix, thereby reducing the reaction activity of the rare earth permanent magnet matrix surface, or forming a deposited film on the surface, thereby playing a corrosion inhibition role.

[0051] According to an embodiment of the present invention, in step (4), pure water is used for cleaning at room temperature, and the cleaning time is 1-2 minutes.

[0052] According to an embodiment of the present invention, in step (5), the temperature of the heat pretreatment is below 200°C, preferably 60-200°C, and more preferably 100-150°C, and the drying time is 10-60min, preferably 20-50min. When the heat pretreatment is performed below 200°C, a base oxide film h mainly composed of ferric oxide is uniformly formed on the surface of the rare earth permanent magnet matrix, and the film thickness h is 30-100nm, preferably 40-70nm.

[0053] According to an embodiment of the present invention, in step (6), the heat treatment temperature is 350-450°C, preferably 380-420°C, and the heat treatment time is 30-120 minutes, preferably 40-90 minutes. Through the heat treatment, the oxide film mainly composed of ferric oxide is uniformly converted into an iron oxide film mainly composed of ferroferric oxide, and the film thickness is 80-150nm.

[0054] The present invention also provides application of the blue rare earth permanent magnet in a motor.

[0055] Beneficial Effects of the Invention

[0056] 1. The present invention controls the thickness of the oxide layer on the surface of the rare earth permanent magnet substrate by controlling the process parameters, that is, controlling the oxygen / iron content ratio on the surface of the product, so as to control the surface of the product to be uniformly blue.

[0057] 2. The cleaning liquid used in the polishing, rough cleaning and fine cleaning processes of the present invention is the same cleaning liquid, which can effectively ensure uniform adsorption on the product surface during the entire polishing and cleaning process, and provide a basis for the subsequent formation of a uniform oxide layer film. The cleaning liquid is an environmentally friendly material, and the entire treatment process is friendly to the environment and people.

[0058] 3. The present invention performs heat pretreatment before high-temperature heat treatment, so that an oxide film mainly composed of ferric oxide is uniformly formed on the surface of the rare earth permanent magnet matrix, which is conducive to the formation of an iron oxide film mainly composed of ferric oxide, and improves the appearance consistency and corrosion resistance. The dense iron oxide film that satisfies the mass ratio of oxygen element to iron element of (0.33-0.40):1 has good corrosion resistance. DETAILED DESCRIPTION

[0059] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0060] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0061] In the following embodiments and comparative examples, a square NdFeB product with a specification of 20 mm×10 mm×4 mm is selected as the magnet matrix, and there is no requirement for the raw material composition of the matrix.

[0062] The sintered NdFeB workpieces used in the following examples and comparative examples are all of grade 48HT and have a size of 40*20*5 mm.

[0063] Example 1

[0064] A blue rare earth permanent magnet, the processing steps are as follows:

[0065] (1) Polishing: The cleaning liquid concentration is 1wt%, and 10kg of rare earth permanent magnet substrate is polished in a vibration polishing machine for 3h;

[0066] (2) Rough washing: Roughly wash the product in step (1) with a cleaning solution; the cleaning solution concentration is 10 wt%, the temperature is 40 °C, and the time is 3 min;

[0067] (3) Fine washing: the product in step (2) is fine washed with a cleaning solution; the concentration of the cleaning solution is 3 wt %, the temperature is 25 ° C, and the time is 1 min;

[0068] (4) Water washing: The product of step (3) is washed with pure water at a temperature of 25°C for 1 min;

[0069] (5) Drying: The product of step (4) is subjected to thermal pretreatment at a temperature of 120°C for 30 min.

[0070] (6) Blueing: heat treating the product of step (5) to obtain the blue rare earth permanent magnet; the heat treatment temperature is 400° C. and the time is 60 min;

[0071] The cleaning liquid is composed of the following components in weight proportion: 30% sodium tungstate, 3% sodium silicate, 0.5% polyethylene glycol, 1.5% isopropyl alcohol, 2% potassium hydroxide, 5.5% dodecyl diethanolamide, 0.1% THIX-278 organosilicon defoamer, and the rest is water.

[0072] Example 2

[0073] A blue rare earth permanent magnet, the processing steps are as follows:

[0074] (1) Rough washing: The rare earth permanent magnet substrate is roughly washed with a cleaning liquid; the cleaning liquid concentration is 12wt%, the temperature is 30℃, and the time is 5min;

[0075] (2) Fine washing: the product in step (1) is fine washed with a cleaning solution; the concentration of the cleaning solution is 3 wt %, the temperature is 25 ° C, and the time is 1 min;

[0076] (3) Water washing: Wash the product of step (2) with water at a temperature of 25°C for 1 min;

[0077] (4) Drying: The product of step (3) is subjected to thermal pretreatment at a temperature of 100°C and a time of 50 min;

[0078] (5) Blueing: heat treating the product of step (4) to obtain the blue rare earth permanent magnet; the heat treatment temperature is 380° C. and the time is 90 min;

[0079] The cleaning liquid is composed of the following components in weight proportion: 30% sodium tungstate, 3% sodium silicate, 0.5% polyethylene glycol, 1.5% isopropyl alcohol, 2% potassium hydroxide, 5.5% dodecyl diethanolamide, 0.1% THIX-278 organosilicon defoamer, and the rest is water.

[0080] Example 3

[0081] A blue rare earth permanent magnet, the processing steps are as follows:

[0082] (1) Polishing: The cleaning liquid concentration is 2wt%, and 10kg of rare earth permanent magnet substrate is polished in a vibration polishing machine for 2h;

[0083] (2) Rough washing: Roughly wash the product in step (1) with a cleaning solution; the cleaning solution concentration is 10 wt%, the temperature is 40 °C, and the time is 3 min;

[0084] (3) Fine washing: the product in step (2) is finely washed with a cleaning solution; the concentration of the cleaning solution is 5 wt %, the temperature is 40 ° C, and the time is 0.5 min;

[0085] (4) Water washing: Wash the product of step (3) with water at a temperature of 20°C for 2 min;

[0086] (5) Drying: The product of step (4) is subjected to thermal pretreatment at a temperature of 150°C and a time of 20 min;

[0087] (6) Blueing: heat treating the product of step (5) to obtain the blue rare earth permanent magnet; the heat treatment temperature is 420° C. and the time is 50 min;

[0088] The cleaning liquid is composed of the following components in weight ratio: 34% sodium tungstate, 2% sodium molybdate, 0.2% polyethylene glycol, 1.5% isopropanol, 0.2% acetylene glycol, 1.8% potassium hydroxide, 5.5% dodecyl diethanolamide, 0.15% THIX-278 organosilicon defoamer, and the rest is water.

[0089] Comparative Example 1

[0090] Same as Example 1, except that step (6) of blueing is omitted.

[0091] Comparative Example 2

[0092] Same as Example 1, except that:

[0093] Step (6) blueing: heat treatment temperature is 400°C, time is 20 min;

[0094] Comparative Example 3

[0095] Same as Example 1, except that:

[0096] Step (6) blueing: heat treatment temperature is 320°C, time is 60 min;

[0097] Comparative Example 4

[0098] The same as Example 1, except that step (5) drying is omitted.

[0099] Comparative Example 5

[0100] The same as Example 1, except that: (2) the rough washing and (3) the fine washing process do not use cleaning liquid for washing, but use pure water for washing.

[0101] Test Case

[0102] The rare earth permanent magnets prepared in the above Examples 1-3 and Comparative Examples 1-5 were subjected to surface oxygen content and iron content tests, thickness tests, appearance comparisons, and damp heat tests. The specific test methods are as follows:

[0103] 1) Surface oxygen content and iron content test: Use a scanning electron microscope and an energy spectrometer to analyze the surface of the product and measure the element content.

[0104] 2) Thickness test method: Use a scanning electron microscope and an energy spectrometer to analyze the composition of the product section, and obtain the thickness of the oxide layer by testing the trend of oxygen content changes at different positions. Randomly test the oxygen content at 50 different positions and take the average value.

[0105] 3) Appearance: Observe the appearance of the product under natural light.

[0106] 4) Humidity and heat: Place the product in a high and low temperature humidity and heat chamber at 85°C, 85%RH, and observe it every half an hour until the product shows any abnormality.

[0107] The test results are shown in Table 1 below.

[0108] Table 1

[0109]

[0110] In Table 1, "OK" means that the product has no abnormality.

[0111] From the results in Table 1, we can see that:

[0112] The comparison results of Example 1 and Comparative Example 1 show that by adding bluing heat treatment after drying, the O / Fe mass ratio of the product surface can be significantly improved, and a certain thickness of ferroferric oxide film can be formed at high temperature, the appearance is blue, and the wet heat performance is significantly improved.

[0113] The comparison results of Example 1 and Comparative Example 2 show that: when the bluing time is short, the O / Fe quality of the product surface is relatively low, the formed film is thinner, the appearance is purple, and the wet heat performance is slightly lower.

[0114] The comparison results of Example 1 and Comparative Example 3 show that: when the bluing temperature is low, the O / Fe quality of the product surface is relatively low, the formed film is thinner, the appearance is purple, and the wet heat performance is slightly lower.

[0115] The comparison results of Example 1 and Comparative Example 4 show that when bluing is performed directly without low-temperature drying, the moisture on the surface of the product is not completely removed before bluing, so that a uniform ferric oxide film cannot be preferentially generated on the surface of the magnet and then a dense ferric oxide film cannot be generated. Instead, the iron element on the surface of the magnet directly generates an iron oxide film with undried moisture and oxygen in the air, resulting in uneven film formation, which in turn causes the product to have a flowery appearance and slightly low wet-heat performance.

[0116] The comparison results of Example 1 and Comparative Example 5 show that when no cleaning liquid is used for cleaning during the fine washing and rough washing processes, a loose and thick ferric oxide film with uneven thickness will be generated during the cleaning and blow-drying processes, resulting in a flowery appearance of the product after bluing and low wet heat performance.

[0117] The comparison results of Example 1 and Example 2 show that when the product is polished or not polished, the cleaning and bluing process can be used to control a similar surface O / Fe mass ratio, a bluish appearance, and equivalent wet heat performance.

[0118] The comparison results of Example 1 and Example 3 show that when the product is treated with cleaning solutions of different formulations within a certain range, similar surface O / Fe mass ratios, bluish appearance and comparable wet heat performance can be obtained.

[0119] The above is an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A blue rare earth permanent magnet, characterized in that: The invention comprises a rare earth permanent magnet matrix and an iron oxide film coated on the surface of the rare earth permanent magnet matrix; In the iron oxide film, the mass ratio of oxygen element to iron element is (0.33-0.40):1, and the thickness of the iron oxide film is 80-150nm.

2. The blue rare earth permanent magnet according to claim 1, characterized in that: The blue rare earth permanent magnet appears blue under natural light.

3. A cleaning liquid, which is used to clean a rare earth permanent magnet matrix to prepare the blue rare earth permanent magnet according to claim 1 or 2; in, The cleaning solution, calculated as 100% by weight, includes 30-40% corrosion inhibitor, 0.5-2.5% film-forming aid, 0.5-3% pH regulator, 5-8% surfactant, 0.05-0.5% defoamer, and the rest is water.

4. The cleaning liquid according to claim 3, characterized in that The corrosion inhibitor is one or more of tungstate, silicate, borate and molybdate; The film-forming aid is one or more of polyethylene glycol, isopropanol, and acetylene glycol; The pH regulator is potassium hydroxide; The surfactant is dodecyl diethanolamide; The defoamer is THIX-278 silicone defoamer.

5. The method for preparing the blue rare earth permanent magnet according to claim 1 or 2, characterized in that: The method comprises the following steps: (2) Rough washing: the cleaning liquid described in claim 3 or 4 is mixed with water as a cleaning agent to perform rough washing on the rare earth permanent magnet substrate; (3) Fine washing: the cleaning solution described in claim 3 or 4 is mixed with water as a cleaning agent, and the product in step (2) is finely washed. (4) Washing with water: Wash the product of step (3) with water; (5) Drying: thermally pretreating the product of step (4); (6) Bluing: heat treating the product of step (5) to obtain the blue rare earth permanent magnet.

6. The method according to claim 5, characterized in that Before rough washing, the rare earth permanent magnet matrix is ​​first polished, specifically: (1) Polishing: mixing the cleaning liquid described in claim 3 or 4 with water to grind the rare earth permanent magnet matrix; In step (1), the concentration of the polishing cleaning solution in water is 0.1-2 wt %.

7. The method according to claim 5, characterized in that In step (2), the concentration of the cleaning liquid for rough washing in water is 8-15wt%, the temperature of the rough washing is 23-60°C, and the time of the rough washing is 2-6min; In step (3), the concentration of the cleaning liquid for fine washing in water is 2-8 wt %, the temperature of the fine washing is 23-60° C., and the time of the fine washing is 0.5-3 min.

8. The method according to claim 5, characterized in that In step (5), the temperature of the heat pretreatment is below 200°C and the drying time is 10-60 minutes; In step (5), the thickness of the iron oxide film obtained after thermal pretreatment is 30-100 nm.

9. The method according to claim 5, characterized in that In step (6), the heat treatment temperature is 350-450°C, and the heat treatment time is 30-120 minutes.

10. Use of the blue rare earth permanent magnet according to claim 1 or 2 in a motor.

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