How are neodymium magnets made?

Neodymium, a powerful permanent magnet and... difficult to manufacture.

INTRODUCTION TO NEODYMIUM:

Neodymium magnets, qualified as rare earths in the same way as Somarium-Cobalt, are the result of a long and complex manufacturing process. It starts with extraction in mines, and then moves towards high-tech metallurgical methods.

All this manufacturing complexity is however not an obstacle for this grade of permanent magnets which dominate the market. If the quantities manufactured were relatively confidential at the beginning of the 90s, its extraordinary magnetic characteristics and the steady growth of its performance have contributed to its worldwide expansion.

Neodymium is found in all trades : Automotive, industrial electronics, computers and smartphones, generators and wind turbines, magnetic separators... the list of uses contains thousands of references. You'd be surprised to know that even the food industry uses it!

Although it is the king of permanent magnets thanks to its induction which can reach 15,000 Gauss (1.5 Tesla) to date, its manufacturing process is little known. Here is a summary of the ten steps necessary for the production of neodymiums.

CHEMISTRY...OR COOKING RECIPE?

Let's start with a bit of chemistry: Neodymiums are also called neodymium-iron-boron whose symbol is NdFeB. By playing on these 3 components and on other additives, you can create nuances. You still need to know how to "mix" these ingredients in the pot, control the cooking times, use the right mould, etc. Let’s see together the main steps of this recipe:

NEODYMIUM MANUFACTURING STEPS:

1) RARE EARTH EXTRACTION.

The rare earth ore comes from open pit deposits mainly located in China , by machines with disproportionate dimensions. It is not the only country that has natural resources, but it is the one that has the most and above all that exploits them at prices that are impossible to meet with the Australian, American, Burmese or Indian competitors. Out of an annual world production of 200,000 tons, China produces 130,000 tons. Australia, the world's second largest producer, produces less than... 18,000 tons.

There would be the possibility of extracting rare earth ore located on French soil, this was done more than 30 years ago. We stopped because profitability was not at the Rendez-vous. Maybe we will be happy to exploit this resource in a few decades…

2) CRUSHING, GRINDING, REFINING.

The rare earth ore is extracted , crushed and conveyed to crushers which will reduce its particle size. This facilitates its subsequent treatment, in particular the flotation during which it is dumped in water containing agents. The reaction makes it possible to relieve the rare earths of the impurities .

We then enter the field of chemistry, with electrochemical refining and ion exchange. There are other refining methods that depend on the quality of the land, such as electrolytic refining.

The refined ore, called "concentrate", is heated to a very high temperature by an electrode and is thus melted. In the liquid state at 1700°C, the coveted metals separate from the amorphous and useless materials .

The metals are however mixed together, very difficult to separate one from the other. We find in particular precious metals, copper, nickel, etc. Their properties and their densities are sometimes very similar. Separation processes, whether mechanical, densimetric or chemical, are time-consuming and expensive.

It is still impossible to dissociate neodymium from praseodymium to this day, so that a quarter to a third of the volume of a magnet is made up of it. The properties are so close that there is no incidence.

As standard , grades N35 to N55 are resistant to around 60°C Max . Beyond that, they permanently lose their magnetic induction. A range of grades with suffix U, H, SH offer increased resistance to demagnetization, bringing the temperature of use to almost 200°C. In addition to the "rare earths" must be added to the usual mixture of very expensive "heavy rare earths". These include dysprosium and terbium which increase coercivity. To minimize their use, manufacturers inject them homogeneously when compressing the powders. (Step 5)

3) MELT AND FLOW

The Neodymium-iron-boron are therefore melted , a few other metals are added whose magnetic and mechanical properties have a positive effect on the NFB alloy. The molten mixture is continuously pressure cast , in a vacuum atmosphere. On leaving the casting, the metal takes shape and in order to give it specific properties, it is cooled very strongly.

4) FRAGILIZE THEN CRUSH

Usually, metallurgists avoid the introduction of hydrogen into metals because it greatly embrittles them. In the particular case of NFBs, the aim is precisely to weaken this strip at the casting outlet so that it breaks into the smallest possible pieces. Mechanical grinders further reduce the particle size without reaching the usable powder stage. We must therefore go further in the refinement process.

5) TRANSFORMATION INTO NEODYMIUM POWDER

Although the size of the NFB has been considerably reduced, the pieces will then be sent through a pressurized cyclone , which propels the product at very high speed in an atmosphere of inert gas. This process makes it possible to break down the NFBs into an increasingly fine powder , we can now speak of neodymium particles. The coveted neodymium powder is finally obtained!

6) PRESS AND SHAPE A NEODYMIUM BLOCK

Still in an inert atmosphere, the powder is pressed under high pressure in moulds. The particularity of this molding operation lies in the presence of a powerful magnetic field which orients the grains. In most cases, the anisotropy is obtained perpendicularly. Note that the block has not yet become magnetic.

The block is pressed a second time by a very high pressure press, to compact it a little more and avoid air inclusions. But this block still needs a few steps to become a little magnet!

7) SINTERING AND ANNEALING OF THE BLOCK

Our neodymium mass is again introduced into a furnace to bring its temperature to just below its melting point. During the sintering operation , shape and density are controlled because there is no change of state. The atoms keep the same magnetic orientation.

Sintering makes it possible to obtain a very hard assembly , which is not very deformable, but brittle. Kind of like glass. At the end of this operation, the size of the block is final, but it is not yet ready to be cut into small magnets!

To release the mechanical stresses of the preceding steps, in particular the sintering, an annealing is carried out starting from a temperature of several hundred degrees, to go down again in successive steps. We find a classic technique of metallurgy, to remove the tensions in the steels and to avoid the zones of embrittlement .

8) CUTTING THEN MACHINING OF THE NEODYMIUM BLOCK.

It is now necessary to cut this magnificent block in electro-erosion with a wire of small section in order to avoid losses. As you have understood, it is very long and difficult to obtain these blocks, so avoid losing any at this stage. Likewise, when surfaces and angles are ground .

The material is so precious that the manufacturers recover the shavings and dust from these operations. They return to the process to form part of a new block of neodymium.

We finally have small magnets whose shape and dimensions are final !

9) APPLICATION OF A SURFACE TREATMENT

To avoid corrosion in the medium term, our small neodymium magnets will undergo a nickel-based electrolytic deposit. It is even Nickel-Copper-Nickel . You can also buy the magnets raw or with different deposits, including sprayed aluminum zinc . In special cases, such as aggressive saline atmospheres causing rapid corrosion, an epoxy coating is offered by some manufacturers for effective protection.

10) MAGNETIZATION OF NEODYMIUM MAGNETS.

This is the magic step, which is however not the most difficult. The magnet is placed in the center of a solenoid which is electrically powered in such a way as to create a very high number of Ampere-turns. The very strong and very sudden induction passes through the neodymium briefly. This small block of sintered neodymium powder becomes a magnet, offering its remanence for decades, without adding energy. This is the magic of permanent magnets that are said to be " magnetized for life ". A North Pole and a South Pole, a strong power of attraction, and incredible possibilities in many industrial and specific fields.

11) QUALITY AND SAVINGS

You now know that obtaining a neodymium permanent magnet requires many steps, often long and expensive. This is why process control is important, both to guarantee manufacturing quality that satisfies customers, but also to guarantee process quality and efficiency to limit losses and waste.

The initial investment is very heavy , all the machines are very specific and made to measure for the industrialist who requests them. Profitability requires a very large and continuous volume. Demand has been steadily increasing for 15 years, and will continue to do so as applications multiply and develop.

APPLICATIONS OF NEODYMIUM PERMANENT MAGNETS

Impossible to count the number of uses as they are numerous . Neodymium provided a much stronger induction than the ferrites or other permanent magnets that were used. Beyond its strong induction , sometimes 15 times higher than other permanent ones, the neodymium material also made it possible to have an equivalent power in a much smaller space. Neodymium magnets are at the origin of many miniaturizations or at least the reduction of the volume of certain devices.

Here are some uses:

• the growth market for electric cars, Tesla in the lead! Hybrids also have neodymium engines.
• wind turbines on land or at sea, with their enormous generators.
• brushless electric motors, widely used in all industries on robots and machine tools.
• industrial or private air conditioners.
• portable and stationary power tools.
• the loudspeakers of the speakers, video or audio players
• computers and other electronic components
• smartphones that we change regularly
• magnetic traps for the food industry, chemicals, plastics and finally all the powder and pulverulent industries.
• magnetic separators used in recycling centers, mines and quarries, etc.

CONCLUSION:

Not far from criticizing the other materials used for permanent magnets, neodymium is nevertheless the best in induction .

The other materials also have advantages : significant depth of the magnetic field, resistance to high temperatures, and very low prices for some.

Regarding manufacturing and supply, it is clear that both wholesalers and consumers are dependent on China :

Fixed price, and which has already undergone strong variations in the past.
Significant delay, sometimes 3 months for transport by boat and customs clearance.
Short time if you don't go through European resellers with stocks, but who nevertheless take a legitimate commission.
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