By Coating

Introduction to Coatings of Magnets

Coatings are mostly applied to magnets to provide protection against corrosion. Not all types of magnets require coating as some magnetic materials do not easily corrode.

Coatings are not just applied for their ability to fight corrosion too. In some cases, they’re applied to offer more kinetic durability, reflectivity and conductivity of the magnet. Some are even applied for their ability to fight bacteria.

In any case, if you need a magnet that is prone to corroding, choosing the coating is an important but straight forward step to having a magnet that works perfectly for your intended use.

Which Magnets Need Coating? (✔️)

✔️ Neodymium Magnets
The rare earth material neodymium (NdFeB) is very prone to corrosion when in contact with humid or wet environments so in most cases, coating the magnet is an absolute must. The only case where this doesn’t apply is where the magnet is used in a vacuum or environment that does not have any moisture.

The most commonly used coating for Neodymium magnets is Ni-Cu-Ni, which is a triple layer of nickel, copper and nickel. This creates an excellent barrier and helps protect the magnet from corrosion. It’s important noting that piercing, drilling and cutting the magnet will expose the neodymium and corrosion is likely to occur.

✔️/❌ Samarium Cobalt (Sm2Co17) Magnets
It’s important to note that Sm2Co17 magnets mostly do not need to be coated, however, they contain samarium (Sm) , cobalt (Co), iron (Fe) and zirconium (Zr). The iron content of this grade of samarium cobalt make it slightly prone to corrosion.

If you expect these magnets to be exposed to humidity or an acidic environment, it may be worth considering Sm1Co5 grades or coating the magnet. The most common coating for Sm2Co17 to prevent corrosion from humidity is nickel. The melting point of nickel is very high which means it works well in hot environments.

Which Magnets Do Not Need Coating? (❌)

❌ Samarium Cobalt Magnets
If you’ve read our guide on Samarium cobalt magnets, you’ll know there are two different types of the magnet – Sm1Co5 and Sm2Co17.

Sm1Co5 magnets are the original samarium cobalt magnets which were first produced in the 1960s and contain no iron. This means there is no possibility of Sm1Co5 magnets corroding in wet or humid environments. This is why a coating for this magnet is not usually necessary.

❌ Alnico Magnets
Alnico magnets are made from an alloy of aluminium, nickel and cobalt – none of these elements corrode in humid environments which means a coating is not usually required.

This may come as a surprise to some people because they’re often painted red, but this is simply because, when they haven’t been machined, their raw unadulterated appearance is a grainy dark grey texture. This is often considered unsightly by some, hence the paint.

❌ Ferrite / Ceramic Magnets
Ferrite magnet have excellent resistance to corrosion and rust which means a protective coating is not usually applied.

This characteristic of ferrite magnets make them ideal for use in wet, humid and outdoor environments. If the magnet is in harsh or acidic environments, a coating may be required but these conditions would be rare.

Neodymium Magnets (NdFeB) By Coating

Neodymium magnets are also known as Neodymium-Iron-Boron or Nd-Fe-B or NIB super magnets since they are composed of these elements. The chemical composition is Nd2Fe14B. These magnets are extremely strong for their small size and are metallic in appearance.
Attributes Of Neodymium Magnets
-There are several attributes of Neodymium magnets that differentiate them from other magnets.
-Neodymium magnets are very strong permanent magnets. In fact they are the strongest of all rare earth magnets and also the strongest permanent magnets that exist today.
-Neodymium magnets have a very high resistance to demagnetization. This makes them very useful in many different kinds of industrial applications.
-Even small sized Neodymium magnets have a very high energy. This makes them easily portable from one place to another.
-They are good in ambient temperature.
-Another major attribute of Neodymium magnets that has added to their popularity is the affordability factor. Neodymium magnets, unlike previous high strength magnets like tiny cobalt-samarium magnets, are priced very low and can be afforded by educators and experimenters on their limited budgets.
-Neodymium magnets are very corrosive and hence have to be handled carefully. It is best to coat them for long-term maximum energy output and usage.
-Neodymium magnets have a low working temperature for heat applications and can catch fire at high temperatures.

Neodymium Magnet Coatings:
Titanium (Ti)
Tin (Sn)
Silver (Ag)
Gold (Au)
Zinc (Zn)
Epoxy
Nickel (Ni)
Nickel-Copper-Nickel (Ni-Cu-Ni)
Titanium Nitride (TiN)
Parylene C
Everlube
Chrome
PTFE (also known as “Teflon”; white, black, gray, silvery)
Ni-Cu-Ni plus Epoxy
Ni-Cu-Ni plus Rubber
Zn plus Rubber
Ni-Cu-Ni plus Parylene C
Ni-Cu-Ni plus PTFE
Tin (Sn) plus Parylene C
Zinc Chromate
Phosphate Passivation

Sintered Neodymium Magnet By General Coating / Palting

Nickel-Copper-Nickel (Ni-Cu-Ni) Most common coating on magnets Actually 3 layers, nickel-copper-nickel Protection of the magnet from corrosion in ambient air Not a protective coating from humidity, water, or salt water Light protection of the magnet from chipping A decorative finish Shiny metallic gray finish Thickness: 12-25 microns Cost: Low Max working Temp: Approximately 200o C Gluing nickel coated magnets onto steel or plastic should be done with glue or epoxies specifically designed for magnets. Main Industries: motors, medical devices (outside of body), sensors, automotive, holding, generators, pumps, thin film deposition.  Used in almost all industries	Zinc (Zn) Good adhesion when glued onto steel with a glue or epoxy specifically rated for magnets Protection of the magnet from corrosion in ambient air Slight protection from humidity, water, or salt water, but not consider a good choice if magnet is in moisture or fluids Thickness of coating is thin, so less air gap between magnet and steel Dull gray finish Thickness: 4-8 micron Cost: Low Max working Temp: Approximately 120o C Main Industries: any application where low temp, low coating cost and little protective barrier is required.	Black Epoxy (EP) Gray Epoxy (EP) Epoxy coating is excellent as a barrier for salt air and salt water Can scratch easily, must be handled carefully during assembly Very good adhesion to steel with magnet rated glue Mainly colored in black, however, can be colored in white Thickness: 15-30 microns Cost: Medium Max working Temp: Approximately 200o C Gluing nickel coated magnets onto steel or plastic should be done with glue or epoxies specifically designed for magnets. Main Industries: Marine, motor, sensors, consumer products, automotive	Color Zinc (Cr+Zn) Good adhesion when glued onto steel with a glue or epoxy specifically rated for magnets Protection of the magnet from corrosion in ambient air Slight protection from humidity, water, or salt water, but not consider a good choice if magnet is in moisture or fluids Thickness of coating is thin, so less air gap between magnet and steel Dull gray finish Thickness: 4-8 micron Cost: Low Max working Temp: Approximately 120o C Main Industries: any application where low temp, low coating cost and little protective barrier is required.

Gold (Au) FDA approved medical coating for in-body use Has an undercoating of Ni-Cu-Ni Protection of the magnet from corrosion in ambient air Slight protection from humidity, water, or salt water. The thickness of the gold is very thin, so performance in salt spray tests will ultimately show failure of the coating.  Making the coating thicker will help, but gold is intended to be thin. Gold finish Thickness of gold layer: 0.3-0.6 micron Cost: High Max working Temp: Approximately 200o C Main Industries: medical (in and out of body applications), jewelry, decorative uses.	Copper (Cu) Mostly used as a decorative coating Protection of the magnet from corrosion in ambient air, but is less then nickel Can rub off over time Not a protective coating from humidity, water, or salt water Copper finish Thickness: 8-10 microns Cost: Medium Max working Temp: Approximately 200o C Main Industries: Decorative	Chrome (Cr) Mostly used as a decorative coating Protection of the magnet from corrosion in ambient air, but is less then nickel Not a protective coating from humidity, water, or salt water Chrome finish, dull metallic gray color Thickness: 12-15 microns Cost: Low – Medium Max working Temp: Approximately 200o C Main Industries: Jewelry, decorative, cosmetic, consumer products	PTFE (Teflon) Requires molds and tooling Excellent protection to magnet against breakage, impact, and corrosion Available on magnets that are medium to larger in size. Small magnets cannot be molded, but can be sprayed (see Spray PTFE – Teflon) Provides a protective coating from humidity, fluids and AutoClave Color of PTFE is white Thickness: 0.5-1 mm Cost: molds & tooling are required, and cost is dependent upon complexity of each.  Cost / pc will decrease quickly with large quantities Max working Temp: Approximately 250o C Gluing PTFE magnets onto steel or plastic has very poor adhesion. A mechanical hold is recommended Main Industries: Predominantly medical and food industries.

Phosphate Passivation Approved as a Food-grade coating Requires tooling Excellent protection to magnet against corrosion Unlike molded PTFE, smaller magnets can be sprayed as well as larger magnets Provides a protective coating from humidity and fluids Can scratch, so proper handling is required Color can be white or black Thickness: 0.1 – 0.5 mm Cost: Medium Max working Temp: Approximately 200o C Gluing PTFE magnets onto steel or plastic has very poor adhesion. A mechanical hold is recommended Main Industries: Predominantly medical and food industries.	Parylene FDA approved medical coating for in-body use Protection of the magnet from corrosion in ambient air Slight protection from humidity, water, or salt water. Parylene will slowly fail in salt water, so an undercoating may be required. Transparent finish Thickness: 3-7 micron Cost: Quantity Dependent.  Done in batches, so the higher the quantity, the lower the cost / pc. Max working Temp: Approximately 150o C Main Industries: medical (in body applications), and any product that needs a thin coating	Titanium (Ti-Tin) FDA approved medical coating for in-body use Hard coating that has a very strong bond to the magnet Resilient to most chemicals and environmentally friendly Protection from humidity and fluids Finished color is a metallic gold with a smooth surface Thickness of: 2-3 microns Cost: Medium Max working Temp: Approximately 500o C Main Industries: Medical	Silver (Ag) Mostly used as a decorative coating Protection of the magnet from corrosion in ambient air, but is less then nickel Soft metal, so can scratch easily Silver finish Thickness: 12-15 microns Cost: Low – Medium Max working Temp: Approximately 200o C Main Industries: Jewelry, decorative, cosmetic, consumer products

Features, Pros and Cons of Magnet Coatings

Nickel-Copper-Nickel (Ni-Cu-Ni) Coated Magnets
Ni-Cu-Ni is by far the most common and popular coating for neodymium magnets. This is because it’s cost effective and excellent at preventing corrosion from ambient air. They have a reflective silver appearance which gives them an elegant and high-quality appearance. Although Ni-Cu-Ni offers excellent resistance to corrosion, they are not recommended for outdoor use because prolonged exposure can penetrate the pores and corrode the magnet.

Thickness: 10-25um
Cost: Low
Max Operating Temperature: Est 200°C
Industries: Ni-Cu-Ni coated neodymium magnets are used in all industries, such as manufacturing, engineering, domestic, commercial, generators, automotive, oil and gas, air conditioning, education & research, construction, transport, mining, agriculture and green energy.
✔️ Pros: Excellent corrosion against ambient air (general atmosphere)

❌ Cons: Not ideal for use in outdoor, wet, salty or acidic environments.

Epoxy Coated Magnets
Epoxy coated magnets offer one of the most superior coating methods. The epoxy coating can withstand an impressive 72 hours in salt spray tests which means they are perfect for harsh, wet and salty conditions. They also have a lot of advantages over other metal coatings as they provide excellent electrical insulation. Epoxy magnets cost slightly more than traditional Ni-Cu-Ni magnets but offer a superior level of protection.

Thickness: 15-25um
Cost: Medium
Max Operating Temperature: Est 200°C
Industries: Epoxy coated neodymium magnets are used in many industries, such as marine, manufacturing, engineering, consumer products, commercial, sensors and jewellery.
✔️ Pros: Excellent protection against humid, wet and salty environments

❌ Cons: Can crack under significant impacts

Teflon (PTFE) Coated Magnets
Teflon is a very durable synthetic resin that provides a smooth finish. PTFE has excellent resistance to many acids, chemicals and solvents which makes it an ideal option if the magnets may come into contact with them. Additionally, Teflon coatings help reduce friction and wear on surfaces, making them last longer in abrasive conditions. Lastly, the durability of this coating mustn’t be understated – they are the supreme coating option for harsh conditions.

Thickness: 1.5-3um
Cost: High
Max Operating Temperature: Est 250°C
Industries: Teflon (PTFE) coated neodymium magnets are used in many industries, such as marine, medical, manufacturing, engineering, oil and gas.
✔️ Pros: Offers the best protection against all elements; humidity, wet, salty and acidic environments / Superior protection against breakage

❌ Cons: Can slip due to smooth surface, mechanical hold may be required.

Zinc (Zn) Coated Magnets
When zinc is exposed to ambient air, it oxidises which provides a stronger protective barrier. Although it isn’t the best coating against corrosive environments, it is one of the most cost effective coatings available

Thickness: 8-15um
Cost: Low
Max Operating Temperature: Est 120°C
Industries: Zinc coated neodymium magnets are used in projects that require low cost solutions such as DIY, consumer goods and education.
✔️ Pros: Low Cost

❌ Cons: Corrodes if exposed to wet and humid environments over a prolonged period

Black Nickel (Ni) Coated Magnets
Black nickel is very similar to Ni-Cu-Ni as it offers great resistance to ambient air and light resistance to chipping/breaking on impact. Black nickel maintains electrical conductivity with low reflectivity making it perfect for use in discreet and hidden applications. Additionally, black nickel coatings can provide a barrier against friction and heat, helping surfaces to last longer.

Thickness: 12-30um
Cost: Medium
Max Operating Temperature: Est 200°C
Industries: Black nickel coated neodymium magnets are used in industries such as manufacturing, automotive, pumps, hydraulics and jewellery.
✔️ Pros: Aesthetic / Low Reflectivity / Same protection properties as the most common coating Ni-Cu-Ni

❌ Cons: Increase cost / Increased lead times

Titanium Nitrate (TiN) Coated Magnets
Titanium Nitrate (TiN) is a very durable coating that protects the magnet from harsh environments, chemicals and acids. This is a non-toxic material that is safe for the environment and holds a gold / yellow colour.

Thickness: 2-6um
Cost: Medium
Max Operating Temperature: Est 500°C
Industries: Medical, research, engineering
✔️ Pros: Extremely durable / Environmentally friendly / Offers protection against most hazardous environments

❌ Cons: Can increase lead times of custom-ordered magnets.

Gold (Au) Coated Magnets
Gold coating has an under coating of Ni-Cu-Ni and provides slight resistance from humidity and moisture. Gold plated magnets have a thin layer of gold which offers excellent oxidation resistance. This coating does not provide sufficient protection for wet, harsh or abrasive environments.

Thickness: 20-25um
Cost: High
Max Operating Temperature: Est 1,000°C
Industries: Medical, jewellery, research, decorative.
✔️ Pros: Premium aesthetic / The element (Au) has been approved for in-body and outer-body medical use
❌ Cons: Expensive coating method / Does not offer adequate protection in abrasive environments

Copper (Cu) Coated Magnets
Copper coated magnets have an undercoating of nickel (Ni) are primarily used for decorative purposes rather than performance. This is because the material can rub off over time which means it is not ideal for harsh conditions.

Thickness: 10-20um
Cost: Low
Max Operating Temperature: Est 200°C
Industries: Jewellery and decorative.
✔️ Pros: A unique aesthetic that’s primarily used for decoration and jewellery
❌ Cons: Not suitable for harsh, wet environments or toxic.