The Causes of Nano Tungsten Disulfide Agglomeration

Nano tungsten disulfide is usually used as lubricant additive to improve the lubricating performance of original lubricating oil. However, it is prone to agglomeration during the addition, which is closely connected with its small particle size and high surface energy.

The following are the main causes of agglomeration.

1. External force produces electrostatic force. In the stirring process of tungsten disulfide and lubricating oil, because of external forces such as impact, friction and extrusion, a large number of positive or negative charges are produced and accumulated on the surfaces of nano tungsten disulfide particles. Most of these charges are concentrated in the corner of the irregular surfaces, which produces the electrostatic forces to attract particles. The particles connect with each and the agglomeration occurs.

2. Strong van der Waals force is produced between nano tungsten disulfide particles. The particle size increases continuously when the particles come together. And when the particle size reaches a certain value, the particle density in unit space increases. With the distance between particles becoming closer and closer, the van der Waals force is much larger than their gravity, which leads to the agglomeration.

3. Nano tungsten disulfide has high surface energy. The particles are mostly in a very unstable state because of the high surface energy. In order to reach a stable state, they have to close to each other, resulting in the agglomeration.

4. Hydrogen bonds or other chemical bonds are formed on the surface of nano tungsten disulfide particles, which cause the agglomeration.

5. There are liquid films between nano tungsten disulfide particles. The particles close to each other by the negative pressure in the liquid film and the surface tension of the liquid film, which leads to the agglomeration.

The lubrication effect may be influenced by the agglomeration of nano tungsten disulfide. So it is important for us to analyse the causes behind such a phenomenon.

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