Superlubricity of nanodiamonds glycerol colloidal solution between steel surfaces

• Superlubricity (COF ≈ 0.006) is achieved between steel surfaces with nanodiamonds glycerol colloid solution.
• The wear volume is significantly reduced due to the rolling effect of nanodiamonds.
• It is the first time that colloid solution is introduced into the field of liquid superlubricity.

In this paper, nanodiamonds glycerol colloidal solution is investigated as a lubricant between steel ball and disk, and it is compared with glycerol solution. Although stable superlubricity (coefficient of friction ≈ 0.006) can be achieved with both solutions after a running-in period, the colloidal solution causes much less wear than the glycerol solution. With the content of the nanodiamonds at only 0.01 wt%, the colloidal solution can lead to a reduction of 32.5% in the diameter of the wear scar on the ball, resulting in an increase of 119.3% in the contact pressure between the rubbing surfaces during the superlubricity period. Therefore, a novel superlubricity system based on nanodiamonds glycerol colloidal solution is discovered. Through theoretic calculations, the novel superlubricity system is determined to be in the mixed lubrication regime, but not far from the hydrodynamic lubrication regime. It is believed that the ultralow COF is attributed to the hydrodynamic effect and the hydrogen bond layer. And the reduced wear derives from the rolling effect of the nanodiamonds. This work enriches the field of water-based superlubricity by firstly introducing nanoparticles into this area and has prosperous potential applications.

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