What is a high-energy magnet?
This is a very exciting question and relatively easy to answer.
High Energy Magnets
Are permanent magnets. They come from the rare earth group. These magnets have a very high energy product of over 385 kJ/m³ or 48 MGOe and enable completely new technical solutions. These include reductions/minimisations of existing or completely new magnet systems or considerably higher magnetic energies with the same size compared to conventional magnet materials such as BaFe or AlNiCo.
Let's look at a simple comparison:
For the same energy content, a BaFe magnet must have a volume 6 x larger than/strong>. In order to generate a field of 100 mT (1000 Gauss) at a distance of 1 mm from the pole face, a barium ferrite magnet must have a volume >strong>. 25 x larger than a samarium-cobalt magnet. This example alone shows a positive development of the new magnet generation.
Also the energy product of the new neodymium-iron-boron magnets, which are already widely used today, is about 70% higher than the samarium-cobalt magnets mentioned in the example. The disadvantage is rather corrosion and oxidation. You have to pay attention to the application possibilities under humid conditions.
Below is a comparison of the energy products (W x H) max. of some magnetic materials:
Hard ferrite, sintered, anisotropic (SrFe) = 32 kJ/m3
AlNiCo = 40 kJ/m3
Samarium-Cobalt (SmCo) = 225 kJ/m3
Neodymium iron boron (NdFeB) = 360 kJ/m3
What are "rare earths"?
In the current periodic table the rare earths belong to the lanthanide group. They are the 15 elements with the atomic number 57 to 71 in the periodic table of elements. In total, they represent one seventh of all elements found in nature. Rare is therefore actually the wrong expression for it. They occur far more often.
Rare earths are not only needed for the production of magnets. They are also needed for the production of modern mobile phones/smart phones and laptops, as well as for the latest generation of flat screens. Samarium and cobalt are used for the production of magnetic materials with the highest energy product, as mentioned above. However, samarium is contained in the rare earths with a very small proportion. Samarium is also more expensive than neodymium, because the preparation with a high degree of purity is very complex compared to neodymium.
Neodymium on the other hand is more abundant than samarium. Easier to process and therefore cheaper to purchase.
How are the high-energy magnets manufactured?
The manufacturing process is quite simple. As with other metals, it is melted down and further processed. First the alloy of samarium-cobalt or neodymium magnets is melted down. Then the resulting cooled materials are crushed, finely ground - to a powder - and then pressed in a magnetic field and then sintered (joining or compacting materials by heating).
Magnetisation is carried out after the shaping of the future magnet. This is achieved by high magnetic field strengths. These can be generated differently, but the principle is similar. It is important that the future magnet is magnetized by a pulse discharge, by the strong, induced magnetic field (possible up to saturation). The field strengths of the magnetic field can be generated by different capacitors and air coils.
Properties of the SmCo and NdFeB magnet types
These are very hard and brittle. Oxidise very little in a humid atmosphere and are very resistant to water.
These are hard, but less brittle. Oxidize relatively strongly in a humid atmosphere. Also in water these magnets oxidize very strongly and even dissolve after some time. Therefore, their use in humid areas and under water is not recommended.
However, attempts are made to protect them from corrosion by applying a protective layer/alloy by electroplating them with tin or nickel. However, this can quickly flake off.
Neither magnet type should necessarily be exposed to radioactive radiation. This would result in structural losses, and the magnetic properties would also be negatively influenced and changed.
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