How To Prevent Magnets Against Corrosion

Magnets play a crucial role in millions of today's applications, from consumer devices to equipment. They are vulnerable to the environment, however, which may compromise their operation. Corrosion is one example. Magnets become weakened, flake, or even fail completely if not protected.

Why Would Magnets Rust?

Corrosion is simply a chemical reaction between the magnet material and the environment. In the case of most magnets, such a reaction involves water, oxygen, or chemicals, which can engage with the surface of the magnet and compromise its composition. Rare-earth magnets like neodymium contain iron and boron, extremely reactive materials with water and oxygen. When left in damp air or salt water, such magnets can rust, pit, or oxidise on their surface.

Some contributing factors include:

• Water contact or high humidity, which accelerates oxidation.

• Marine-type atmospheres with high salt or acid content, which increase the chemical reactivity of the magnet surface.

• Thermal variations, which cause micro-cracking of coatings or material, allowing penetration by water.

Even slight corrosion can compromise magnetic strength, induce fit interference in mechanical assemblies, or annihilate sensitive electronics components. Understanding the causes of corrosion will enhance prevention.

Preventing Corrosion in Magnets

A variety of techniques are available to prevent magnets from corroding. The techniques range from coatings to environment controls and maintenance practices.

1. Use Protective Coatings

The most common and efficient way to shield magnets from corrosive agents is coatings. Some of the well-known coatings applied are:

• Nickel-Copper-Nickel (Ni-Cu-Ni) Plating: The most common coating for neodymium magnets, a hard metallic coating that is oxidation, moisture, and light chemical resistant. It can be applied in humid and industrial settings.

• Epoxy Coating: A polymer coating with excellent protection against moisture and chemical contact. Epoxy is widely used in electronics, motors, and where water contact will occur.

• Zinc or Gold Plating: These coatings provide less protection in milder environments. Zinc is sacrificial, i.e., corrodes preferentially to protect the underlying magnet, whereas gold resists corrosion almost entirely but is expensive and used primarily in electronics.

2. Control Exposure to the Environment

Limiting exposure of a magnet to corrosive elements is crucial. Principal practices include:

• Control of humidity and moisture: Store magnets in a dry, climate-conditioned area.

• Sealing or encapsulation: Encapsulate magnets in protective casings, plastic enclosures, or resin coverings, especially in marine, weather, or high-humidity conditions.

3. Use Cathodic Protection

For particularly sensitive magnets, sacrificial coatings may be employed. These are an external layer of a metal that corrodes before the integrity of the magnet is impaired. Less common in household products, this method is used in niche industrial or marine environments.

4. Regular Inspection and Maintenance

Regular inspection allows corrosion and coating damage to be identified early on. Maintenance guidelines include:

• Cleaning surfaces for dust, salt, or chemical residue removal.

• Repainting coatings or replacing magnets with visible rust or wear.

• Checking environmental conditions during storage or use to avoid damage.

Which Magnet Materials Do We Have?

The material of the magnet has a very significant impact on corrosion susceptibility. Material properties knowledge enables informed selection based on environmental conditions and application needs.

• Neodymium-Iron-Boron (NdFeB): The strongest commercially produced magnets but extremely susceptible to corrosion from iron content. Protective coatings are critical.

• Samarium-Cobalt (SmCo): Naturally more resistant to oxidation and corrosion. Best suited for aerospace, marine, or high-temperature applications.

• Ferrite Magnets: Composed of iron oxides, ferrite magnets are corrosion-resistant by nature. Suitable for outdoor or wet conditions, but weaker than rare-earth magnets.

• Plastic or Polymer-Bonded Magnets: Enclosed in plastic, these magnets do not come into direct contact with chemicals and moisture, offering a balance between protection and acceptable strength.

Summary Table: Successful Corrosion Prevention for Magnets

For more information, please check Stanford Advanced Materials (SAM).

Conclusion

Corrosion poses a serious problem for magnets, especially for high-performance magnets. Through the incorporation of protective coatings, material selection, environmental control, and regular maintenance, it is possible to significantly extend magnet life and ensure performance.

Frequently Asked Questions

Why do magnets corrode?

Corrosion results from magnet materials reacting with oxygen, moisture, or chemicals and causing surface damage and loss of performance.

Are all magnets equally susceptible?

No. Neodymium magnets are highly susceptible, but ferrite and samarium-cobalt magnets have greater natural resistance.

Which coating is best for protection?

Nickel plating provides better durability in harsh environments, while epoxy resin is appropriate for average moisture and chemical protection.

Is damage by corrosion reversible?

Corrosion cannot be fully reversed. Preventive measures and initial treatments must be taken to protect magnets.

How do environmental controls minimise corrosion?

Humidity, temperature, and exposure to chemicals are regulated to limit decay reactions that spoil magnet surfaces.