The Anti-Scuffing Ultra Low Friction Performance of Diamond Nano-Particles as an Oil aAdditive  (Independent study as reported in WEAR Tribology Magazine) 

Introduction 

Generally, the tribological regimes for sliding lubricated surfaces are broadly categorized into (i) solid/boundary lubrication, (ii) mixed lubrication, and (iii) fluid film lubrication (hydrodynamic or elastohydrodynamic lubrication). In many cases, most of the applied load is supported by hydrodynamic or elastohydrodynamic lubrication (EHL). However, an additional lubrication mechanism is required to reduce friction and wear in contacts between large asperities from opposing surfaces. Even if the fraction of the load supported by non-hydrodynamic means is small, severe wear and perhaps seizure can occur if this additional component of lubrication is not available. 

This study used diamond nano-particles as an additive in paraffin oil and investigated the tribological properties of the two-phase lubricant of paraffin oil and diamond nano-particles. Their results showed that a lubricant with diamond nano-particles possessed excellent load-carrying capacity, anti-wear, and friction-reduction properties. They found that diamond nano-particles dispersed in oil can penetrate into the rubbing surfaces. The ball bearing effect of diamond particles existed between the two rubbing surfaces. The particles became polished and inlaid into the rubbing surfaces, forming a boundary lubrication film that prevented the rubbing faces from coming into direct contact. Surface hardness increased due to the bearing effect of these diamond nano-particles between the rubbing surfaces. 

Nanoparticle additives or nano-additives have a particle size of less than 100 nanometer (nm) in at least one dimension. In comparison, a human hair is approximately 80,000- 100,000 nm wide.

Nano-additives have demonstrated their ability to reduce friction and wear of lubricants even at concentrations of less than 1 wt%. This has been made possible by several methods:

1. The ball-bearing effect, where nanoparticles effectively act as ball bearings between two surfaces, thus reducing friction and wear;    
2. Protective film effect, where the nanoparticles form an anti-wear film;    
3. Mending effect, where nanoparticles deposit onto a surface and compensate for the loss of mass;    
4. Polishing effect, where nanoparticles act as an abrasive, reducing surface roughness.

Surface polishing and the increase in rubbing surface hardness effects of diamond nano-particles are the main reasons for the reductions in wear and friction. They found that the spherical diamond nano-particles in base oil exhibit a viscosity-increasing effect and form a thicker film than that in the pure base oil. The friction coefficient decreased with sliding distance. 

Conclusions:

1. The addition of the nano-diamond particle resulted in an improvement of anti-scuffing performance in the oil samples. The number of a surface failure, attributed to the scuffing, was reduced after adding the nano-diamond particles in the oil samples. 
2. The nano-diamond additive is most favorable for reducing both friction coefficient and wear loss.  This Ultra-low Friction surface reduces wear, heat and improves the performance of low viscosity oils such as 0W-20 oils.
3. Automobile companies such as Nissan are now using very similar additive packages to prevent wear in their high-performance engines.