WO2021143086A1 - 一种可同时提高NdFeB粉末和磁体的抗氧化腐蚀性的方法 - Google Patents

一种可同时提高NdFeB粉末和磁体的抗氧化腐蚀性的方法 Download PDF

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WO2021143086A1
WO2021143086A1 PCT/CN2020/103273 CN2020103273W WO2021143086A1 WO 2021143086 A1 WO2021143086 A1 WO 2021143086A1 CN 2020103273 W CN2020103273 W CN 2020103273W WO 2021143086 A1 WO2021143086 A1 WO 2021143086A1
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magnet
powder
ndfeb
ndfeb powder
oxidation
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PCT/CN2020/103273
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French (fr)
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岳明
王占嘉
刘卫强
奚望
高京园
吴迪
张东涛
路清梅
张红国
吴琼
李玉卿
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北京工业大学
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/026Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets protecting methods against environmental influences, e.g. oxygen, by surface treatment
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047Alloys characterised by their composition
    • H01F1/053Alloys characterised by their composition containing rare earth metals
    • H01F1/055Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0572Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes with a protective layer
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00Magnets
    • H01F7/02Permanent magnets [PM]
    • H01F7/0205Magnetic circuits with PM in general
    • H01F7/021Construction of PM

Definitions

  • the invention relates to a method for forming Al, Zn, Ni, Cu or their alloy coatings on the surface of NdFeB powder or magnets to enhance their oxidation resistance and corrosion resistance, and belongs to the technical field of magnetic materials.
  • NdFeB magnetic material is a kind of rare earth permanent magnetic material. It has the characteristics of high coercivity and high magnetic energy product. It is called a hard magnetic material because it can maintain a constant magnetism once it is magnetized. NdFeB permanent magnet is currently the most cost-effective commercial magnetic material. It has the advantages of high magnetic energy product, small size and light weight. NdFeB magnets are now indispensable and important materials in high-tech fields such as aerospace, information engineering, new energy vehicles, and high-speed train units. Therefore, the preparation and forming of NdFeB materials have become a hot spot in research and development.
  • the neodymium iron boron powder is easy to oxidize because it contains rare earths, causing performance degradation. Therefore, vacuum or inert atmosphere protection is required during the whole preparation process. Therefore, the present invention protects the NdFeB powder by forming a coating layer of Al, Zn, Ni, Cu or their alloy on the surface of the powder, so that it is not easily oxidized in the subsequent processing process, and its use performance is ensured.
  • Invention 201410135609.X proposes an electroless Ni plating method to protect NdFeB powder from oxidation and then prepare an oxidation-resistant sintered NdFeB magnet.
  • the powder is ultrasonically cleaned in distilled water and then placed in a degreasing liquid for degreasing, followed by pickling and activation with an activation liquid. Finally, the treated powder is placed in a mixed solution of NiSO 4 , Na 3 C 6 H 5 O 7 , (NH4) 2 SO 4 , Nd 2 (SO4) 3 and KI, and Ni is electrolessly plated under stirring.
  • the obtained powder is Has antioxidant properties.
  • the method in the invention 201410135609.X has many shortcomings. First, the powder pretreatment process is complicated, which requires not only degreasing but also activation. Second, the composition of the electroless plating solution is complex, and the price is high, and the cost of raw material preparation is high.
  • the amount of powder that can be processed by electroless Ni plating is relatively small, which is not suitable for mass production.
  • the subsequent treatment process of the used solution is likely to cause pollution.
  • the invention only needs to mix the powder uniformly with the metal or alloy of any shape and perform heat treatment at a certain rotating speed to obtain a plating layer with firm bonding and uniform thickness. Not only the raw materials are simple, the cost is low, and no special pre-treatment process is required.
  • the used metals or alloys, such as Al, Ni, etc. can be reused, and the recycling treatment produces almost no pollution, which is very environmentally friendly.
  • NdFeB permanent magnets are easily corroded by oxygen and water vapor in the air during use, which affects their performance. Therefore, NdFeB permanent magnets require a simple process to prevent corrosion.
  • Sintered NdFeB magnets are mainly composed of Nd 2 Fe 14 B main phase, Nd-rich grain boundary phase and B-rich phase, of which Nd element accounts for the largest proportion.
  • the NdFeB magnet is easily corroded in humid, high temperature and acid-base environments, which affects its performance.
  • an invention has proposed a method of adding a coating to the surface of the sintered NdFeB magnet to resist oxidation in various environments.
  • Invention 201910487072.6 proposes to mix organic binders, organic lubricants, and micron-sized AlN powders into anticorrosive materials in a certain mass ratio, and then uniformly coat them on the surface of the preheated NdFeB magnet to obtain a crude product.
  • the crude product is placed in an inert gas atmosphere at 1000-1100 Sintering at a temperature of °C for 30-45min.
  • the micron-sized Al powder is deposited on the surface of the magnet by physical vapor deposition method, and after cooling to room temperature, the corrosion-resistant magnet covered with AlN film and Al film is obtained.
  • the present invention has the following advantages: 1.
  • the anti-corrosion powder in the invention 201910487072.6, a variety of organic solvents are needed to make the anti-corrosion powder can be tightly combined on the magnet.
  • the surface volatilization of the metal or alloy at a certain temperature and the short-term contact with the NdFeB powder or the magnet at high temperature can form a strong anti-corrosion coating; 2.
  • the AlN and Al powders in the invention 201910487072.6 are both micron-sized powders and processed The cost is high and the process is complicated.
  • the metal or alloy required by the present invention only needs to be crushed into blocks or sheets with a length of about 1-10mm and a thickness of 0.5-5mm.
  • the processing method of the metal or alloy is simple; 3.
  • the heating temperature in the invention 201910487072.6 is higher. , The energy consumption is large.
  • the invention can realize the anti-corrosion effect through lower temperature, and the energy consumption is small.
  • the invention 201611157661.0 proposes a method of adding a multi-layer coating on the surface of the magnet to resist corrosion.
  • the magnet needs to be cleaned in a mixed pickling solution of diluted nitric acid and thiourea. After ultrasonic cleaning with alcohol, use a mixed solution of sulfosalicylic acid and ammonium bifluoride for activation, and then perform three-step coating.
  • the nickel sulfate hexahydrate solution, sodium hypophosphite solution, borax solution, sodium citrate solution, ammonium fluoride solution, and succinic acid solution are prepared into an electroless plating solution, and the pretreated neodymium iron boron permanent magnet is placed in the electroless plating solution.
  • electroless nickel plating is performed at a preset electroless plating temperature and a preset electroless plating time.
  • the ultra-high vacuum magnetron sputtering and ion beam combined sputtering system is used for coating.
  • the sputtering target is dysprosium aluminum alloy
  • the working vacuum is 1.0Pa
  • the DC power supply is used for coating
  • the sputtering current is 0.67A
  • the power is 300W
  • the atmosphere is For high-purity argon gas, magnetron sputtering coating is performed within a preset time, and after coating is completed, vacuum thermal diffusion treatment is used at a preset temperature to prepare the dysprosium-plated aluminum alloy thin film layer;
  • Ammonium chloride and boric acid are added to water and heated to dissolve, add sodium lauryl sulfate to the above solution, magnetically stir for 30 minutes, add nano chromium powder to the above solution, raise the temperature to 65 °C, ultrasonic vibration for 30 minutes, mix uniformly
  • the electroplating solution adjusts the acidity and alkalinity of the electroplating solution and saves it at a preset temperature for later use.
  • the nickel plate is used as the anode and the neodymium iron boron is used as the cathode.
  • the operation process of the invention 201611157661.0 is too complicated. There are many kinds of organic solvents used, and the process flow is very complicated.
  • the method in invention 201611157661.0 is not suitable for mass production.
  • the invention uses a simple heat treatment furnace with a rotating function, can realize multi-layer coating through multiple heat treatment coatings with different metals or alloys, the raw materials are simple and easy to obtain, and the operation process is simple and easy to implement. At the same time, the expansion of the heat treatment furnace can realize the coating of large quantities of magnets.
  • a method that can simultaneously improve the oxidation and corrosion resistance of NdFeB powder and magnets which is characterized in that the NdFeB powder or magnets and any shape of metal Al, Zn, Ni, Cu or their alloys are used as raw materials, uniformly mixed according to a certain proportion, and placed Heat treatment in a resistance furnace. At the same time, the furnace body is stirred at a certain speed.
  • the surface volatilization of Al, Zn, Ni, Cu metals or alloys at a certain temperature and short-term contact with NdFeB powder or magnets at high temperatures are used to make NdFeB
  • the powder or magnet surface area forms a continuous and dense single metal and multi-metal compound or multilayer metal or alloy coating, thereby improving the oxidation resistance of the NdFeB powder or the corrosion resistance of the NdFeB magnet, while hardly affecting its performance.
  • step 2) The sample processed in step 1) is sealed and heat-treated in a resistance furnace under the protection of inert gas while stirring;
  • step 2) Take out the powder after heat treatment in step 2), and obtain metal-coated NdFeB powder through sieving, which can improve oxidation resistance.
  • the processed NdFeB powder can be directly subjected to subsequent metal injection molding or 3D printing.
  • the magnet after the heat treatment in step 2) is taken out, and the second heat treatment in step 2) can be performed as needed.
  • the treated NdFeB magnet can be used instead of the magnet after electroplating.
  • the ratio of NdFeB powder or magnet to coated metal in step 2) is 1:2-1:5, and the unidirectional size of any shape of Al, Zn, Ni, Cu metal or alloy is 0.5-10mm , Such as materials with a length and width of 1-10mm and a thickness of 0.5-5mm.
  • the heat treatment temperature used in step 2) is 200-700° C.
  • the time is 1-6 h
  • the pressure of the argon gas is 60-80 kPa
  • the rotation speed is 4-7 r/min.
  • the NdFeB powder or magnet and any shape of metal Al, Zn, Ni, Cu or their alloys are placed in the same container for heat treatment, while stirring at a certain speed, the relative position of the metal and NdFeB powder is changed at any time , The coating of the coating is more uniform;
  • the metal used in the present invention is rich in nature and has low cost.
  • the metal or alloy used in the present invention has a low melting point, which can reduce the heat preservation temperature during heat treatment and reduce energy loss during heat treatment.
  • the metal used in the present invention can be in any shape within a certain length range, does not require complicated and expensive preparation processes, and has low cost.
  • the present invention adopts the volatilization of the surface layer of Al, Zn, Ni, Cu metal or alloy at a certain temperature and short-term contact with NdFeB powder or magnet at high temperature to form a continuous and dense monolith on the surface area of NdFeB powder or magnet.
  • Metal and multi-metal compounds or multi-layer metal or alloy coatings the coating has a strong bonding force with the powder or the surface of the magnet, and it has a good protective effect on the NdFeB powder or the magnet.
  • alloy coating and multi-layer coating can be formed to meet the requirements of various use environments.
  • the thickness of the plating layer formed by the present invention can be accurately controlled, which can be achieved only by adjusting process parameters such as heat treatment temperature and heat treatment time.
  • the traditional sputtering, deposition and other processes are not suitable for magnetic powder, and the present invention is particularly suitable for powder processing.
  • the invention has simple equipment, few steps and low cost.
  • the present invention does not use acid-base solutions, does not cause environmental pollution, and can replace electroplating applications.
  • the coercivity of the coated powder is reduced from 10125Oe to 9843Oe, which is only 282 Oe, and the remanence is reduced from 93.54emu ⁇ g -1 to 93.05emu ⁇ g -1 , which is only 0.49emu ⁇ g -1 . Therefore, the Zn coating has little effect on the performance of the powder.
  • the coercivity is reduced from 13.65kOe to 13.45kOe, which is only 0.20kOe, and the remanence is reduced from 13.74kG to 13.55kG, which is only 0.19kG. Therefore, it has little effect on the performance of the magnet before and after coating the AlZn alloy.
  • the original magnets with the same surface area, the magnets coated with AlZn alloy coatings and the electroplated Zn magnets are all ultrasonically cleaned with alcohol to remove oil, and dried for later use. Weigh using an electronic balance with an accuracy of 0.1 mg.
  • the three types of magnets were placed in a high-pressure accelerated life box for high-pressure accelerated corrosion experiments.
  • the experimental conditions were 121°C, 0.2MPa, and the experimental medium was distilled water.
  • the weight loss method is used to calculate the corrosion rate. Take out the samples at regular intervals, remove the corrosion products with a brush, wash and dry them with alcohol, and weigh their mass until 270h.

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  • Power Engineering (AREA)
  • Environmental & Geological Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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Abstract

一种可同时提高NdFeB粉末和磁体的抗氧化腐蚀性的方法,该方法通过在NdFeB粉末或磁体与包覆层金属共同加热在表面形成Al、Zn、Ni、Cu或其合金包覆层来保护NdFeB粉末及磁体,使磁粉具有较好的抗氧化性,后续处理过程可在空气中实现,磁体无需电镀即可应用在器件中。

Description

一种可同时提高NdFeB粉末和磁体的抗氧化腐蚀性的方法 技术领域
本发明发明涉及在NdFeB粉末或磁体表面形成Al、Zn、Ni、Cu或它们的合金镀层使得其抗氧化性和抗腐蚀性增强的方法,属于磁性材料技术领域。
背景技术
NdFeB磁性材料是一种稀土永磁材料,它具有高矫顽力、高磁能积的特点,由于其一经磁化即能保持恒定的磁性被称为硬磁材料。NdFeB永磁体是目前性价比最高的商品化磁性材料,它具有磁能积高、体积小及质量轻等优点。NdFeB磁体现在航空航天、信息工程、新能源汽车、高铁动车组等高新技术领域都是不可或缺的重要材料。因此NdFeB材料的制备与成形成为研发的热点。
钕铁硼粉末由于含有稀土而易氧化,造成性能降低。因此在制备的全过程中均需要真空或惰性气氛保护。因此本发明通过在粉末表面形成Al、Zn、Ni、Cu或它们的合金镀层来保护NdFeB粉末,使其在后续处理过程中不易氧化,保证其使用性能。发明201410135609.X中提出一种化学镀Ni法来保护NdFeB粉末不被氧化随后制备抗氧化烧结NdFeB磁体的方法。该方法是将粉末在蒸馏水中超声清洗后放入除油液中除油,随后酸洗并使用活化液活化。最后将处理后的粉末置于NiSO 4、Na 3C 6H 5O 7、(NH4) 2SO 4、Nd 2(SO4) 3和KI混合溶液中在搅拌作用下化学镀Ni,得到的粉末即具有抗氧化性。发明201410135609.X中的方法存在许多不足,一是粉末的预处理过程复杂,不仅需要除油,还需要活化。二是化学镀液的成分复杂,且价格昂贵,原料准备成本高。三是化学镀Ni可处理的粉末量偏少,不适合大批量生产。四是使用后的溶液的后续处理过程易造成污染。本发明仅需粉末与任意形状的金属或合金均匀混合后在一定转速下进行热处理即可获得结合牢固、厚度均匀的镀层。不仅原料简单,成本低廉,而且不需要特殊的前期预处理过程。使用后的金属或合金,如Al、Ni等均可重复利用,回收处理几乎不产生污染,对环境十分友好。
NdFeB永磁体在使用过程中易被空气中的氧气和水蒸气作用从而被腐蚀,影响其使用性能,因此NdFeB永磁体需要一种简单的工艺进行防腐蚀。烧结NdFeB磁体主要由Nd 2Fe 14B主相、富Nd晶界相及富B相组成,其中Nd元素占比最大。但由于Nd元素的化学活性最强,使得NdFeB磁体极易在潮湿、高 温及酸碱环境中被腐蚀,影响其使用性能。对此,有发明提出了给烧结NdFeB磁体表面加入镀层来抵抗各种环境的氧化作用的方法。发明201910487072.6提出将有机粘接剂、有机润滑剂、微米级AlN粉末按一定质量比混合为防腐料后均匀涂于预热后的NdFeB磁体表面得到粗品,将粗品在惰性气体气氛中在1000-1100℃温度下烧结30-45min。待烧结料温度降至700-750℃时,使用物理气相沉积法将微米级Al粉沉积在磁体表面,冷却至室温后即得到表面覆有AlN膜和Al膜的抗腐蚀磁体。与发明201910487072.6相比,本发明有以下优点:1.发明201910487072.6中需要多种有机溶剂来使得抗腐蚀粉末能紧密结合在磁体上,本发明方法不需要除包覆原料以外的其它物质,通过磁体与金属或合金在一定温度下的表层挥发以及与NdFeB粉末或磁体在高温下的短暂接触就可以形成结合牢固的抗腐蚀镀层;2.发明201910487072.6中的AlN和Al粉均为微米级粉末,加工成本高,流程复杂。本发明所需的金属或合金仅需将其破碎为长宽约为1-10mm,厚度0.5-5mm的块或薄片即可,金属或合金的加工方法简单;3.发明201910487072.6中加热温度较高,能源消耗较大。本发明通过较低温度就可以实现抗腐蚀效果,能源消耗较小。除上述发明提出的在NdFeB磁体表面加入镀层的方法外,发明201611157661.0提出在磁体表面加入多层镀层抗腐蚀的方法。首先需要将磁体在配好的稀硝酸和硫脲的混合酸洗液中清洗,酒精超声清洗后使用磺基水杨酸和氟化氢铵混合液进行活化,然后进行三步镀膜。首先将六水合硫酸镍溶液、次磷酸钠溶液、硼砂溶液、柠檬酸钠溶液、氟化铵溶液、丁二酸溶液配制成化学镀液,将预处理过的钕铁硼永磁体置于化学镀液中,在预设化学镀温度、预设化学镀时间下进行化学镀镍。接下来采用超高真空磁控溅射与离子束联合溅射系统进行镀膜,溅射靶材为镝铝合金,工作真空度为1.0Pa,直流电源镀膜,溅射电流0.67A,功率300W,气氛为高纯氩气,在预设时间内进行磁控溅射镀膜,镀膜结束后,在预设温度下采用真空热扩渗处理,制得所述镀镝铝合金薄膜层;将六水合硫酸镍、氯化铵、硼酸加入水中并加热溶解,加入十二烷基硫酸钠于上述溶液中,磁力搅拌30min,加入纳米铬粉于上述溶液中,升高温度至65℃,超声波震动30min混合均匀配制电镀液,调节电镀液酸碱度并在预设温度中保存备用,以镍板为阳极,以钕铁硼为阴极,使用数控双脉冲电镀电源进行表面电镀,制得所述耐腐蚀多镀层NdFeB磁体。虽然磁体表面镀层较多,但发明 201611157661.0操作流程过于复杂,使用的有机溶剂种类繁多,工艺流程更是十分繁琐。除此之外,发明201611157661.0中的方法不适用于大批量生产。本发明使用简单的带有旋转功能的热处理炉,通过多次与不同金属或合金的热处理包覆即可实现多层镀膜,原料简单易得,操作流程简单易行。同时,将热处理炉扩大化即可实现大批量磁体的镀层包覆。
发明内容
一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,将NdFeB粉末或磁体与任意形状的金属Al、Zn、Ni、Cu或它们的合金为原料,按照一定比例均匀混合,放置于电阻炉内热处理,与此同时炉体按一定转速进行搅拌,利用Al、Zn、Ni、Cu金属或合金在一定温度下的表层挥发以及与NdFeB粉末或磁体在高温下的短暂接触,在NdFeB粉末或磁体表面区域形成连续而致密的单金属及多金属化合物或多层金属或合金镀层,从而提高NdFeB粉末的抗氧化性或NdFeB磁体的抗腐蚀性,同时几乎不影响其使用性能。包括如下步骤:
1)将NdFeB粉末或磁体与任意形状的包覆金属Al、Zn、Ni、Cu或它们的任意几种成分的合金取适量,按照一定的质量比例混合均匀后置入电阻炉内;
2)将步骤1)中处理好的样品在惰性气体保护下的电阻炉中进行密封热处理,同时加以搅拌;
3)将步骤2)热处理后的粉末取出,通过筛分得到金属包覆处理后的NdFeB粉末,可提高抗氧化性,处理后的NdFeB粉末可直接进行后续金属注射成形或3D打印。
进一步,将步骤2)热处理后的磁体取出,根据需要可进行步骤2)的二次热处理,处理后的NdFeB磁体可取代电镀后磁体直接应用。
进一步,步骤2)中的NdFeB粉末或磁体与包覆金属的比例为1:2-1:5,所采用的任意形状的Al、Zn、Ni、Cu金属或合金的单向尺寸为0.5-10mm,如长宽为1-10mm,厚度为0.5-5mm的材料。
进一步,步骤2)中采用的热处理温度为200-700℃,时间为1-6h,充入氩气气压为60-80kPa,转速为4-7r/min。
本发明的有益效果是:
1)采用本发明将NdFeB粉末或磁体与任意形状的金属Al、Zn、Ni、Cu或它们的 合金置于同一容器中进行热处理,同时加以一定转速进行搅拌,金属与NdFeB粉末的相对位置随时变换,镀层的包覆更加均匀;
2)本发明采用的金属在自然界含量丰富,成本低廉。
3)本发明采用的金属或合金熔点较低,在热处理时可以降低保温温度,减少热处理时能源的损耗。
4)本发明所使用的金属在一定长度范围内任意形状均可,不需要复杂昂贵的制备工艺,成本低廉。
5)本发明采用的是Al、Zn、Ni、Cu金属或合金在一定温度下的表层挥发以及与NdFeB粉末或磁体在高温下的短暂接触,在NdFeB粉末或磁体表面区域形成连续而致密的单金属及多金属化合物或多层金属或合金镀层,镀层与粉末或磁体表面的结合力强,对NdFeB粉末或磁体的保护效果好。
6)通过调整金属成分及多级热处理工艺,可形成合金镀层以及多层镀层,满足各类使用环境的要求。
7)本发明所形成的镀层的厚度可以精确控制,仅需通过调整热处理温度和热处理时间等工艺参数即可实现。
8)传统的溅射、沉积等工艺不适用于磁性粉末,本发明特别适合对粉末进行处理。本发明使用设备简单,步骤少,成本低。
9)与电镀相比,本发明不用酸碱溶液,不产生环境污染,可取代电镀应用。
10)本发明使用的元素和工艺对NdFeB结构没有任何伤害,对NdFeB粉末和磁体性能几乎没有影响。
附图说明
图1.包覆Zn前后NdFeB粉末部分磁滞回线;
图2.包覆Zn后NdFeB磁粉的电子探针测试图。
(a)600倍背散图(b)600倍Nd面分布(c)600倍Zn面分布(d)2000倍背散图
(e)2000倍Nd面分布(f)2000倍Zn面分布。
具体实施方式
以下结合实例对本发明的原理和特征进行描述,所举实例只用于解释本发明,并非用于限定本发明的范围。
实施例1:
1)取大约50g NdFeB磁粉,与质量为100g,直径约3mm的Zn粒均匀混合置入热处理炉内;
2)将热处理炉转速设置为4r/min,炉内真空度大于10 -3Pa时充入Ar至气压为60kPa;
3)将热处理炉开启加热,加热温度为350℃,保温时间6h;
4)热处理结束后取出粉末,使用筛子将NdFeB粉末与Zn粒进行分离,收集得到的粉末;
5)将包覆前后的粉末使用VSM测试其性能:
表1 包覆Zn前后粉末磁性能表
粉末种类 矫顽力/Oe 剩磁/emu·g -1
包覆前粉末 10125 93.54
包覆后粉末 9843 93.05
经过包覆后的粉末,矫顽力从10125Oe降低至9843Oe,仅降低了282Oe,而剩磁从93.54emu·g -1降低至93.05emu·g -1,仅降低0.49emu·g -1。因此在包覆Zn后对粉末性能影响不大。
6)将包覆前后的粉末取大约同质量,使用精度为0.1mg的天平称取其质量,随后放入洁净的坩埚内。将坩埚置入马弗炉内在空气条件下加热老化,加热温度至200℃,保持12h。冷却后取出粉末称重,观察其质量变化。
表2 包覆Zn前后粉末质量变化表
粉末种类 老化前粉末质量 老化后粉末质量 增重
包覆前粉末 2.0008g 2.0024g 0.0016g
包覆后粉末 2.0003g 2.0004g 0.0001g
可以从表中发现,经过Zn包覆的NdFeB粉末在老化后增重明显小于未包覆Zn的粉末。因此,经过Zn包覆的NdFeB粉末的抗氧化性能更好。
7)将包覆后的粉末进行电子探针测试,观察Zn的包覆均匀性并观测Zn层有效厚度。通过宏观观察大量粉末的Zn面分布发现粉末四周Zn壳层厚度较为一致,将其中一部分晶粒放大,通过比例尺测得其厚度大约为3μm,可以给粉末以良好的抗氧化保护。
实施例2:
1)取大约10块NdFeB磁体,其总质量约为30g,与质量约为60g直径约3mm的Cu颗粒均匀混合置入热处理炉内;
2)将热处理炉转速设置为4r/min,炉内真空度大于10 -3Pa时充入Ar至气压为70kPa;
3)将热处理炉开启加热,加热温度为600℃,保温时间3h;
4)热处理结束后取出磁体,并将磁体与60g长宽为10mm,厚度约0.5mm的Al速凝片进行均匀混合,混合均匀后重新置入热处理炉内;
5)热处理炉转速不变,炉内真空度大于10 -3Pa时充入Ar至气压为65kPa;
6)将热处理炉开启加热,加热温度为400℃,保温时间3h;
7)将二级包覆前后的磁体使用BH永磁测量系统测试性能;
表3 二级包覆前后磁体磁性能表
磁体种类 矫顽力/kOe 剩磁/kG
二级包覆前磁体 13.60 13.80
二级包覆后磁体 13.02 13.65
经过二级包覆后的磁体,矫顽力从13.60kOe降低至13.02kOe,仅降低了0.58kOe,而剩磁从13.80kG降低至13.65kG,仅降低0.15kG。因此在包覆Cu后二次包覆Al对磁体的磁性能影响很小。
8)将表面积相同的原始磁体、二级包覆磁体与电镀Zn磁体均使用酒精超声清洗去油,烘干待用。使用精度为0.1mg的电子天平称重。将三种磁体放置于高压加速寿命箱中进行高压加速腐蚀实验,实验条件为121℃,0.2MPa,实验介质为蒸馏水。采取失重法计算腐蚀速率。每隔10h取出试样,用毛刷去除腐蚀产物,用酒精清洗烘干后称量其质量,直至100h为止。
表4 原始磁体、二级包覆磁体及电镀Al磁体腐蚀速率表
磁体种类 原始磁体 二级包覆磁体 电镀Zn磁体
腐蚀速率10 -3/mg·cm -2·h -1 10.05 1.56 1.65
从表4中可明显看出,经过100h腐蚀后的磁体,二级包覆Cu和Al的磁体的腐蚀速率远小于原始磁体的腐蚀速率,甚至略小于电镀Zn磁体的腐蚀速率。说明二级包覆Cu和Al后磁体的抗腐蚀性能有明显提升,可直接取代电镀Zn磁体应用。
实施例3:
1)取10块烧结NdFeB磁体,磁体总重约30g。
2)取质量为90g,长度约6mm,厚度约0.5mm的AlZn合金速凝片,将磁体与速凝片混合均匀装入热处理炉内;
3)将热处理炉转速设置为5r/min,炉内真空度大于10 -3Pa时充入Ar至气压为80kPa;
4)将热处理炉开启加热,加热温度为200℃,保温时间5h;
5)热处理结束后取出磁体,将磁体与速凝片进行分离。
6)将处理后的磁体使用BH永磁测量系统测试其磁性能;
表5 包覆AlZn合金前后磁体能表
磁体种类 矫顽力/kOe 剩磁/kG
包覆前磁体 13.65 13.74
包覆后磁体 13.45 13.55
经过包覆后的磁体,矫顽力从13.65kOe降低至13.45kOe,仅降低了0.20kOe,而剩磁从13.74kG降低至13.55kG,仅降低0.19kG。因此在包覆AlZn合金前后对磁体性能影响不大。
7)将表面积相同的原始磁体、包覆AlZn合金镀层的磁体和电镀Zn磁体均使用酒精超声清洗去油,烘干待用。使用精度为0.1mg的电子天平称重。将三种磁体放置于高压加速寿命箱中进行高压加速腐蚀实验,实验条件为121℃,0.2MPa,实验介质为蒸馏水。采取失重法计算腐蚀速率。每隔一段时间取出试样,用毛刷去除腐蚀产物,用酒精清洗烘干后称量其质量,直至270h为止。
表6 原始磁体、包覆AlZn磁体及电镀Zn磁体腐蚀速率表
磁体种类 原始磁体 包覆AlZn磁体 电镀Zn磁体
腐蚀速率10 -3/mg·cm -2·h -1 40.74 1.86 1.65
从表6中可明显看出,经过270h腐蚀后的磁体,原始磁体的腐蚀速率远大于包覆AlZn合金的磁体,而包覆AlZn镀层的磁体腐蚀速率仅略大于电镀Zn磁体的腐蚀速率。说明包覆AlZn合金后磁体的抗腐蚀性能有明显提升,可取代电镀磁体直接应用。

Claims (9)

  1. 一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,包括以下步骤:
    1)将NdFeB粉末或磁体与任意形状的包覆金属Al、Zn、Ni、Cu或它们的任意几种成分的合金取适量,按照一定的质量比例混合均匀后置入电阻炉内;
    2)将步骤1)中处理好的样品在惰性气体保护下的电阻炉中进行密封热处理,同时加以搅拌;
    3)将步骤2)热处理后的粉末取出,通过筛分得到金属包覆处理后的NdFeB粉末或磁体。
  2. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,将步骤2)热处理后的粉末或磁体取出,根据需要可进行步骤2)的二次热处理。二次热处理所采用的不同种类金属或合金可形成多层金属镀膜。
  3. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,步骤2)中的NdFeB粉末或磁体与包覆金属的比例为1:2-1:5。
  4. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,所采用的任意形状的Al、Zn、Ni、Cu金属或合金的单向尺寸为0.5-10mm。
  5. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,步骤2)中采用的热处理温度为200-700℃,时间为1-6h。
  6. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,充入氩气气压为60-80kPa,转速为4-7r/min。
  7. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,金属或合金包覆层厚度在0.1-5μm之间,可由热处理时间和温度精确控制。
  8. 按照权利要求1所述的一种可同时提高NdFeB粉末和磁体抗氧化腐蚀的方法,其特征在于,通过在磁体表面形成不同金属或合金镀层,可满足不同环境的要求。处理后的NdFeB粉末可在空气中进行后续处理;或取代电镀后磁体直接应用。
  9. 按照权利要求1-7任一项所述的方格制备得到的NdFeB粉末和磁体。
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