Tribology: The Science of Oil and Lubrication


Cool-X Nanoparticles act like mini ball bearings rolling the surface flat

Cool-X Nanoparticles act like mini ball bearings rolling the surface flat

The surface finish of metals has a direct correlation with friction. Smoother surfaces generate less friction. There are fewer points of contact (asperities) with less magnitude that require less force to overcome. Surface finish is normally measured by expressions like Ra, an integral of the area above or below the mean surface height divided by the surface area. Improvements in tolerances and surface finish are one of the main ways that engine fuel economy  has improved over the past thirty years.

Cool-X nanoparticles burnish metal surfaces. The photo shows two cam carriers that ran for a year for a race team in the SCCA. The cam on the left was burnished by Cool-X, the one on the right showed normal pitting, oxidation, and corrosion. The Cool-X nanoparticles burnished the cams. Burnishing – also called honing – is a process of flattening, where the surface is “pounded flat” without removing material. It is not an abrasive process. The Cool-X nanoparticles act like mini ball bearings, and when under pressure flatten the metal surfaces. Note that this is a gradual process – the Cool-X nanoparticles are dispersed in the oil in very small quantities (by weight) and while they have the surface area of 10 football fields, most of them are not in contact with the metal at any given point. In practice, we have found that burnishing may first be noticeable after 30 or 40 hours of use under load, but will continue for 30K – 40K miles of driving in a diesel engine.

The burnishing process has a second effect. It strain hardens the metal surfaces. Metals deform by fracturing along fault lines in their crystaline structure. When these fault lines are disturbed by burnishing, it prevents cracks from propagating, and makes the crystalline structure more stable. This is the same process used in cold welding fasteners, or by medieval swordsmiths repeatedly pounding their blades flat. The end result is that the surface of the metal becomes much harder, difficult to break, and thus resistant to wear. This is an excellent outcome for gears, pistons, and tappets subject to repeated stresses in a hot engine, as it prevents warping and parts from breaking.

There are several studies showing how nanodiamonds can be used to harden metals. Note that the carbon nanoparticles do not appear to lodge in the metal or create a layer on the surface, which is different from the results you get using carbon vapor deposition techniques. In some ways, this could be described as a poor man’s CVD coating – Cool-X is much less expensive, yet achieves similar results over time as the burnishing process unfolds.


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