Passivation

Passivation Coating Magnets / Passivated Magnet

Material: Phosphated or Passivation
Coating thickness: 1-3um.
Advantage: Excellent humidity, heat & salt spray resistance, excellent adhesion
Application: High requirement of adhesion force between the magnet and the glue, such as Industrial motor.

Passivation is the active use of strong oxidants or electrochemical methods to oxidize magnets, forming a dense passivation film on their surface, transforming the chemical properties of the surface into an inactive state, thereby improving their corrosion resistance.

Neodymium Magnet Passivator

A neodymium magnet passivator is a specialized chemical mixture designed to protect the surface of neodymium magnets and prevent rusting. Its main components and their functions are as follows:

1. Metal Passivators:

Function: These components are the core of the passivator, functioning by chemically reacting with the metal surface to form an extremely thin yet dense protective layer. This layer effectively isolates the metal from direct contact with corrosive media such as air and moisture, significantly preventing oxidation and corrosion.

2. Surfactants:

Function: Surfactants possess properties that lower surface tension, enhancing the solution’s wetting ability on the metal surface. They assist in distributing the passivator and other components more evenly across the metal surface, improving the effectiveness of the passivation process. Additionally, they help remove oil and impurities from the metal surface, providing a clean substrate for the formation of the passivation layer.

3. Buffer Agents:

Function: During chemical treatment, buffer agents maintain the pH of the solution within a stable range, preventing drastic fluctuations in acidity or alkalinity that could affect the passivation reaction and the quality of the passivation film. A stable pH environment is crucial for ensuring the effective operation of the passivator and the formation of a high-quality passivation layer.

4. Complexing Agents:

Function: The complexing agent assists in the dissolution of metal ions from the surface of the neodymium magnet and their re-deposition to form a protective film. It can also adjust the dissolution rate of metal ions, thereby controlling the growth speed and thickness of the passivation film, ensuring that the film layer is even and dense. The complexed film layer formed is more stable than a simple metal oxide film layer, able to better resist corrosion factors in the environment, and is less likely to fall off.

Surface Treatment of NdFeB Magnets – Passivation

The passivation of neodymium magnets is to form a protective film on the surface of the neodymium magnets through chemical methods to achieve the purpose of corrosion protection.

The NdFeB magnet passivation process generally includes: degreasing → water washing → ultrasonic water washing → pickling → water washing → ultrasonic water washing → pure water washing → passivation treatment → pure water washing → dehydration → drying.

1. Degreasing
Degreasing can only remove grease, dust, sweat, and attached metal chips on the surface of the NdFeB magnet, but not the rust on the magnet. The oil stain on the surface of the NdFeB magnet is brought from the processing of the material, such as the anti-rust grease used to prevent rust during storage and transportation.

NdFeB magnets must be cleaned of oil on the surface before further surface treatment. Due to the wide range of sources and types of oil pollution, the degree of pollution varies greatly, so the problem of degreasing is very complicated. In order not to cause corrosion and subsequent residues during the degreasing process, try to use a degreasing agent with low free alkalinity and total alkalinity.

2. Pickling
The purpose of pickling is to remove the black ash and rust left on the surface of NdFeB magnets. The pickling liquid generally uses 2%~4% nitric acid, and the time is 0.5~2.0 min. High acid concentration and long pickling time are both detrimental to the magnet.

3. Passivation Treatment
The passivation treatment method is to place the magnet in a container containing passivation liquid and soak it for a period to achieve passivation, that is, to form a passivation film on its surface. As an important surface anti-corrosion treatment, passivation is commonly used in many metals, especially metals such as aluminum, zinc, cadmium, tin, and magnesium, and their alloy materials.

Most of the traditional passivation treatments use chromic acid and chromate as treatment agents, called chromate passivation. The chromate conversion film formed on the metal surface after treatment has a good corrosion protection effect on the base metal.

In recent years, the corrosion resistance requirements for NdFeB conversion films have become higher and higher, and passivation technology alone has made it difficult to meet the requirements. The commonly used process is to use composite conversion film technology, that is, first phosphating and then passivating, by filling the pores of the phosphating film, the corrosion resistance of the composite conversion film is effectively improved.