NdFeB permanent magnet material basic knowledge

- Oct 30, 2017 -

NdFeB permanent magnet material basic knowledge

First, rare earth elements

1, 17 kinds of rare earth elements, respectively, as follows:

Scandium (Sc) yttrium (Y) lanthanum (Ca) cerium (Ce) praseodymium (Pr)

Neodymium (Nd) 钷 (Pm) samarium (Sm) europium (Eu) gadolinium (Gd)

Terbium (Tb) dysprosium (Dy) holmium (Ho) erbium (Er) thulium (Tm)

Ytterbium (Yb) lutetium (Lu) rare earth metals commonly used in NdFeB products are neodymium, praseodymium, dysprosium, terbium, gadolinium, holmium

2, rare earth metals are active metals

The chemical activity of rare earth metals is between alkali metals (lithium, sodium) and alkaline earth metals (magnesium, calcium). Under certain conditions (sodium is very active only in kerosene) produces the following reaction and produces large amounts of Heat, the provision of heat to further promote the progress of the reaction, such as:


     2Nd + 3O2 2Nd2U3 + Q

    2Nd + 6H2O 2Nd (OH) 3 + 3H2 + Q

    Nd2O3 + 3H2O 2Nd (OH) 3 + Q


From the above equation can be seen in the production of NdFeB when the anti-oxidation, anti-damp, which is very critical to damp, in the wet days and rainy days the workshop should pay full attention to anti-tide.

3, the distribution of rare earth metals

     According to statistics, China's Inner Mongolia, Jiangxi, Zhejiang, Guangdong, Fujian, Guangxi, Hunan and other places have found rare earth. Because of the existence of different states, Inner Mongolia Baotou rare earth is the form of fluoranthene lanthanum ore and is based on light rare earth (neodymium in front of rare earth), and Jiangxi is the existence of ion-type ore in the presence of heavy rare earth. Most of the world's rare earth in China, China accounted for about 80% of the world's rare earth, while 80% of China's Inner Mongolia Baotou. The world, the United States, Russia, Australia, Vietnam and other countries have found rare earth.

Second, magnetic materials

The main use of magnetic materials are ferrite, aluminum nickel cobalt, samarium cobalt and NdFeB.

SmCo and NdFeB are known as rare earth permanent magnetic materials.

At present, the world's most widely used or ferrite, the product is cheap, followed by NdFeB; aluminum nickel cobalt and samarium cobalt temperature stability than NdFeB, so in some pointer instruments, military supplies and high-end consumer goods also Can not be separated from aluminum nickel cobalt and samarium cobalt material.

Ferrite Curie temperature of 465 ℃, neodymium iron boron Curie temperature of 310 ℃, aluminum nickel cobalt Curie temperature of 800 ℃, SmCo Curie temperature between 700 - 800 ℃, so neodymium Iron boron temperature stability of the worst, but the highest performance, known as the "magnetic king", the current production of magnetic materials are sintered and bonded two processes, bonding due to the addition of adhesive magnetic properties will not be high, but the product High accuracy.

Third, the application of NdFeB

1, the application of microwave communication technology: radar technology, satellite communications, remote telemetry technology, electronic tracking, electronic warfare technology need to use, magnetron tube, magnetron wave tube, cathode ray tube, circulator and so on Use neodymium iron boron.

2, the application of electrical engineering: rare earth permanent magnet material production more than one-third of the used to create a variety of permanent magnet motor, permanent magnet motor is the advantage of provincial copper, power, light weight, small size, high power The Electric bicycle motor, computer-driven motor, lathe and other line speed and speed measurement of the motor, the elevator traction motor, mahjong motor, refrigerator air conditioning motor, wind motor, motor-driven motor, and so very widely used.

3, in the application of electro-acoustic devices: such as speakers (speakers), microphones, hearing aids, stereo headphones (MP3, MP4), telephone receivers and electro-acoustic sensors and so on.

Magnetic machinery, magnetic seals , Permanent magnet handling machine.

5, in the application of transport tools: the use of homosexual repression of the principle of manufacturing trains called maglev train; modern luxury cars need to use 15-70 permanent magnet devices, such as: windshield wiper motor, pump motor, window Motor, door lock motor, to fog motor, automatic control, starting motor.

6, in the application of magnetic separation technology: the use of magnetic methods to ferromagnetic materials and non-ferromagnetic material separation technology known as magnetic separation technology. Magnetic separation technology has been widely used in mineral processing, coal preparation, raw material handling, water treatment, waste disposal and in the medical, chemical and food industries.

7, the application of magnetization technology: the use of magnetic field on the magnetization of the material to change the bonded material by the bonding state and nature; or change the atomic, electronic state, promote the chemical reaction of the material and fuel combustion; or change the crystallization of matter Form or freezing point, this technique is called magnetization technology. Magnetizer, fuel economizer in the car, oil anti-wax in oil extraction and so on.

8, in the application of magnetic therapy and fitness equipment: such as magnetic therapy cup, magnetic ball, magnetic therapy machine, magnetic shoes, magnetic therapy caps, magnetic bracelets, necklaces, as well as the rapid development of medical equipment in recent years, nuclear Resonance imager (MRI) each used in the 3 - 4 tons, imagine each hospital in China if equipped with a MRI NdFeB should be the amount of how much!

In short since the invention of NdFeB since 1983, every year there are new applications in the field, the annual increase of more than 30%, the application prospects are very broad.

Fourth, the development of NdFeB

1, product development. NdFeB since the invention in 1983 since the development of the first decade of unhappy, nearly 10 years of rapid development, China's 360 tons in 2006, Japan's production of 2,000 tons, the US production of 1,000 tons, but in 2006 China's output of 60,000 tons, , Almost no other countries, the world's NdFeB production sintering and bonding together about 100,000 tons (of which bonding 20,000 tons).

2, the enterprise: before the Western world in 1998 than China's rapid development, China's development slow But so far, only four companies in Japan, the United States only one, Europe is also only one, and China has more than 100, so China is the world's production of NdFeB, but not a strong country. China's NdFeB production in 60% in Zhejiang, the other in Shanxi and Beijing and Tianjin region, NdFeB sales base in Shenzhen, Ningbo and Beijing.

3, the development of performance: NdFeB performance is dependent on the development of the perfect process and the use of advanced equipment to develop quickly. 96 years ago, China's best performance for the N38, the world's best for the N48, and in 2006 China's best for the N52 world is best for the N52 (large-scale production), performance improved quickly, China's NdFeB performance improved Faster, China has gradually transformed from producing countries into productive countries.

4, the development of technology: the first NdFeB process is wet production, with toluene or gasoline as a protective agent, ball mill production, low performance, and later developed to dry production (air grinding) performance can be greatly improved, but the best performance Can only be N45, but since the invention of the rejection (SC) process performance has been greatly improved, the current batch can do to achieve N52.

5, the development of equipment: ball mill to the air mill, ingot to the cast to the broken, single sintering furnace to continuous multi-sintering furnace, a simple press to the automatic press, equipment development process breakthrough is the cost of NdFeB performance Improve the key.

6, the development of post-processing technology: the early processing of NdFeB relatively monotonous and waste is also large, the main processing technology slices, line cutting, drilling, unintentional grinding, grinding, etc., with the rapid development of NdFeB The use of areas of continuous expansion, processing technology and equipment has also undergone great changes, sets of holes (to improve the comprehensive utilization of materials), sets of tiles, grinds, such as double-sided grinding process is widely used for the NdFeB Reduce costs, improve accuracy to create the conditions.

Fifth, the basic characteristics of NdFeB material and its microstructure

(A) metal properties

Sintered NdFeB is solid, density 7.2-7.7g / cm3, melting point of about 1150 degrees Celsius (different elements of different melting points are different), is the metal conductor can be plated.

(B) strong permanent magnet

The theoretical magnetic energy product of sintered NdFeB is 64MGOe and the saturation magnetization is 1.6T. At present, the largest magnetic energy product is 52MGOe in mass production at home and abroad.

(C) according to the different performance can be used for different temperatures

1, sintered NdFeB according to the intrinsic coercivity Hcj can be divided into N material, M material, H material, SH material, UH material, EH material, AH material, according to a certain aspect ratio (L / D> 0.5) and environmental conditions.

ü N material Hcj ≥ 12KOe maximum operating temperature of 80 ℃

ü M material Hcj ≥ 14KOe maximum operating temperature of 100 ℃

u H material Hcj ≥ 17KOe maximum use temperature of 120 ℃

ü SH material Hcj ≥ 20KOe maximum use temperature of 150 ℃

ü UH material Hcj ≥ 25KOe maximum operating temperature of 180 ℃

ü EH material Hcj ≥ 30KOe maximum use temperature of 200 ℃

ü AH material Hcj ≥ 33KOe maximum use temperature of 230 ℃

2, according to the remanence Br and the maximum magnetic energy product (BH) max can be divided into different grades such as:

       N35 N38 N42 N45 N50 N52 N52 N

       35M 38M 40M 42M 45M 48M 50M 52M and so on

(D) the concept of physical quantities and parameters

     1, Curie temperature (Tc)

     Curie temperature concept: strong ferromagnet from the ferromagnetic or ferrimagnetic transition to paramagnetic critical temperature is called Curie temperature or Curie point Tc.

NdFeB Curie temperature is 312 degrees Celsius, Tc is an important parameter of magnetic materials, Tc high material working temperature can be improved, but also improve the temperature stability of magnetic materials. Plus cobalt, terbium, dysprosium, etc. can improve the Curie temperature of magnetic materials, so in the high-necked neck products (H, SH, ...) are added dysprosium and other materials to improve Tc.

2, the magnetic flux Ф unit is Weber (Wb), to block the magnet as the measurement object, measuring instrument for the flux meter.

3, the surface of the Gaussian unit is Tesla (T) or Gaussian (GS), is a magnet on the surface of a point for the measurement of objects, measuring instruments are Gauss meter, measuring the center of the center Gaussian, the highest table magnetism. So there are Gaussian requirements of the product to the customer to ask is the center of the Gauss or the highest table magnetic.

4, the temperature coefficient: NdFeB material is characterized by the temperature rise, remanence, intrinsic coercivity and maximum magnetic energy product will decline.

ü residual magnetic temperature coefficient α Br is generally -0.09 ~ 0.128% / ℃

ü intrinsic coercive force causes αHcj to be generally between -0.45 and -0.8% / ° C

ü such as a NdFeB material αBr = -0.10% / ℃ αHcj = -0.5% / ℃

The coercive force at 20 ° C is 12 kGS coercivity of 20 kOe

         Ask Br and Hcj at 80 ° C

         Br80 ° C = Br 20 ° C + αBr. (T80-T20). Br20 ° C = Br20 ° - (80-20) * 0.10% / ° C. Br20 ° C = 12 (1-0.06) = 11.28 KGS

Hcj80 ° C = Hcj 20 ° - (80-20). 0.005 * Hcj 20 ° C = 20 (1-0.3)

                = 20 * 0.7 = 14KOe

5, the main physical parameters and units

(BH) max, the residual magnetization expression is Br, the intrinsic coercivity expression is Hcj, and the coercivity expression is Hcd, as follows: (BH) max = Bd * Hd

ü units (divided into international units and centimeters, grams, seconds)




International unit system

Centimeters, grams, seconds, system

Conversion relationship



Tesla (T)

Gaussian (GS)

1T = 104GS

Intrinsic coercivity


Ampere / m (A / M)

Oster (Oe)

1A / M ≈ 0.0125Oe

Maximum magnetic energy product

(BH) max

Joule / m 3 (J / M3)

North Gaoao (MGOe)

1KJ / m ≈ 0.125MGOe

(5) The microstructure of NdFeB

1, the matrix Nd2Fe14B

   Nd2Fe14B is the main phase, like water composed of H2O, NdFeB mainly composed of Nd2Fe14B, it is a ferromagnetic phase, the volume fraction of Nd-Fe-B permanent magnet alloy Br and (BH) max.

2, boron-rich phase

   It is B compound Nd1 + ΣFe4B4, in the Nd-Fe-B permanent magnet alloy, boron-rich phase is harmful, hope that its smaller the better the volume fraction.

3, rich neodymium phase

  The neodymium plays an important role in the magnetic hardening of Nd-Fe-B alloy, and the proper neodymium-rich phase is beneficial to promote the coercivity of sintered NdFeB.

  4, impurities

There are also a certain volume of oxides such as Nd2O3, α-Fe, chloride and voids in the sintered Nd-Fe-B.

(6) other physical properties of NdFeB

1. Hardness (HV) 620

2. Young's modulus 1.6 * 1011 N / m2

3, the compression rate of 9.8 * 10-12 m / N

4, resistivity 1.8 ~ 2.0 * 10-4 Ώ.cm

5, bending strength 295 ~ 345MPa

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