Coatings for magnets: protection and functionality

Magnets, especially those made of neodymium-iron-boron (NdFeB), often require a special coating to protect them from external influences such as corrosion, wear or mechanical damage. At the same time, coatings can improve the optical and functional properties of a magnet and customise it for specific applications.

Why do magnets need coatings?

1. Corrosion protection:
   Many magnetic materials, such as neodymium, are susceptible to rust as they can absorb moisture and oxygen. Without protection, they lose their magnetic properties and decay in the long term.

2. Mechanical protection:
   A coating protects the magnet from scratches, wear and other mechanical effects that could impair its performance.

4. Optics and design:
   A coating can improve the aesthetics of a magnet, e.g. with a shiny or coloured surface.

6. Chemical resistance:
   In aggressive environments, such as in the chemical industry, special coatings protect the magnet from chemicals.

Typical coating materials and their properties

1. Nickel plating (Ni-Cu-Ni):
   Properties:

   • Three-layer system of nickel, copper and nickel.
   • Glossy, metallic surface.
   • Provides good protection against corrosion and mechanical damage.
     Application:
   • Universally applicable, especially for indoor areas.
     Weaknesses:
   • Can become permeable in the long term in very damp or salty conditions.

2. Galvanising (zinc):
   Properties:

   • Favourable coating with a slightly matt appearance.
   • Good protection against moisture and moderate corrosion.
     Application:
   • Suitable for industrial applications.
     Weaknesses:
   • Lower resistance to abrasion and moisture compared to nickel plating.

3. Gold plating (gold):
   Properties:

   • Thin layer of gold over a base coating (usually nickel).
   • Corrosion-resistant and highly decorative.
   • Biocompatible, making them ideal for medical applications.
     Application:
   • Jewellery, sensor technology and electronics.
     Weaknesses:
   • Expensive and sensitive to mechanical wear.

4. Epoxy resin (epoxy):
   Properties:

   • Thick, robust plastic coating.
   • Excellent protection against chemicals and moisture.
   • Available in different colours (e.g. black or white).
     Application:
   • Outdoor applications or harsh environments.
     Weaknesses:
   • Can splinter under heavy mechanical stress.

5. Plastic coating (e.g. PTFE, PVC):


Properties:

• Thick protective film made of plastic, often non-slip.
• High corrosion resistance and chemical stability.
  Application:
• Medical devices, household applications.
  Weaknesses:
• Less abrasion resistant than metallic coatings.

6. Phosphating:
   Properties:

   • Dark, matt protective layer.
   • Favourable and functional, but low corrosion protection.
     Application:
   • Pre-treatment or as temporary protection.

7. Silver coating:
   Properties:

   • High-quality, shiny surface.
   • Offers excellent electrical conductivity.
     Application:
   • Electronic components and jewellery.
     Weaknesses:
   • Prone to mechanical abrasion.

8. Powder coating:
   Properties:

   • Robust, coloured surface that is suitable for a wide range of applications.
     Application:
   • Decorative and functional magnetic applications.

How coatings are applied

The choice of coating and the application process depends on the type of magnetic material, the desired protective effect and the intended application.

1. Galvanisation:
   Processes such as nickel plating, gold plating or galvanising.
   The magnetic workpieces are treated in electrolyte baths to apply the metal coating.

3. Spray or dip coating:
   Process for plastic or epoxy coatings.
   The magnet is dipped or sprayed in liquid epoxy resin and then cured.

4. Powder coating:
   Powdered material is applied electrostatically and melted in an oven.

5. Chemical processes:
   Processes such as phosphating, in which the surface is chemically modified.

Applications of coated magnets

1. Home and office:
   Nickel-plated magnets are popular for whiteboards, fridge magnets or decorations.

3. Medical devices:
   Gold-plated or epoxy-coated magnets are ideal for biocompatibility and sterile environments.

5. Industry:
   Galvanised or epoxy-coated magnets are used in harsh environments, e.g. in the automotive or construction industries.

6. Electronics:
   Magnets with a silver or gold coating are used in sensors and electronic components.

Advantages and disadvantages of coatings

Did you know?

• Without coating, a neodymium magnet will completely disintegrate in a humid environment within a few months.
• The typical nickel layer of a magnet is only a few micrometres thick - thin enough not to impair the magnetic properties, but thick enough to provide protection.
• Gold coatings do not make magnets stronger, but they do protect the surface and provide a luxurious appearance.

Conclusion

Coatings are essential to protect magnets from corrosion, wear and other external influences. Whether for industrial, medical or decorative applications - the right coating significantly extends the service life of a magnet and optimally adapts it to the respective environment. The choice of coating depends on the specific requirements such as durability, appearance and function.