patented nanotechnology. The additive functions in a unique manner, and not only reduces friction and prevents wear, but also reduces the propensity to form WEC. The key is that it inhibits hydrogen diffusion into metal surfaces, and has the proven capability to prevent formation of cracks in the microstructure of steel bearings. This marks a new approach in the production of high performance wind turbine gear oils.
Lubricant Solution
The new additive is based on organometallic salt compositions that have been known and used in the lubricant industry for many years. The key innovative step is using a unique activated complex. It comprises of a bimetallic system combined with other solvents, dispersants, and surfactants, which facilitates the formation of dispersed nanoparticles in-situ. The particles are truly oil soluble and show no tendency to agglomerate and drop out of solution. The particles are dispersed in reverse micelles within a stable colloid. The particles have been found to have a typical size in the range 25 to 50 nm.
Lubricant treated with the additive can be depicted as nanoparticles contained in non-polar reverse micelles dispersed in a stable colloid in the lubricant. The process of tribofilm formation involves a three-phase model in which micelles are disrupted by the interaction with metal-metal asperities on the metal surfaces, under the high contact pressures in boundary lubrication conditions. This releases the nanoparticles from the micelles, which are deposited and adsorbed onto the metal surfaces. The nanoparticle deposits organise themselves into a coherent tribofilm, and can also integrate into the near-surface volume of the metal. This modifies the tribochemical composition and micro-structure of the near surface. As the tribofilm is worn away, due to lateral frictional forces, new layers of tribofilm are formed on the metal surface, to give sustained protection and robust performance. This is part of the self-healing process to reinforce and sustain the tribofilm, and deliver long term protection.
Figure 2: Tribofilm
When the additive is added to lubricant, the nanoparticles deposit on metal surfaces to form a tribofilm. The metal ions in the organometallic salt also undergo tribochemical reactions at the metal surface to reinforce and sustain the tribofilm. A rapid reduction of the coefficient of friction occurs, along with a significant decrease in the rate of wear. The tribofilm is able to separate the friction bodies, and withstands mechanical attacks of the asperities at the metal surface. The additive does not interfere with the action of other additives. The additive and tribofilm is found up to a depth of about 10 nm in the near-surface. This is too deep to be caused by simple intermixing. It indicates that the additive tribofilm is also able to integrate into the sub-surface, and modify the metal structure, to improve wear protection, and also prevent the formation of WEC.
Figure 3: Tribofilm formation
Experimental Details Tribometer Tests – The tribological effects of the lubricant additive were demonstrated in tribology tests. This was done in an Anton Paar rotational rheometer with a ball-on-three-plates system. The additive was added to a commercial lubricant and the friction behaviour was measured. Wear was also measured by analysing the wear scars on the plates.
Continued on page 18 LUBE MAGAZINE NO.161 FEBRUARY 2021 17
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