Mechanism of Action of Colloidal Solid Dispersions

Abstract

In the past there has been considerable interest in the possibility of using liquid lubricants containing dispersed, solid particles in the 1–50 micron size range to reduce friction and wear. These particles are used in greases and some industrial oils. Researchers are now directing their attention to the behavior of much smaller colloidal particles in the range of 5 nm to 200 nm diameter. Such systems are formally known as “colloidal sols” and have been claimed to influence friction and wear. Further reasons for studying such colloidal particles is that they are present in soot-contaminated engine lubricating oils, as wear debris and as partially-soluble additives. Thus, the objective of the work derived in this paper was to investigate the mechanism of action of colloidal solid particles in the range of 5 to 200 nm diameter in lubricating oils. Of particular interest was the effect of slide-roll ratio on particle entrainment and the influence of the ratio of particle diameter to elastohydrodynamic lubricant film thickness on particles’ behavior. This study has shown that in thin film contacts, colloid nanoparticles penetrate EHD contacts mainly by a mechanism of mechanical entrapment. It is found also that in rolling contacts at slow speeds, colloids formed a boundary film of at least 1 or 2 times the particle size. This film influence friction and wear. However, this film is lost at high speed and the film thickness reverts to the colloid-free fluid. The results of this study have enabled a mechanism of lubricating action by colloid sols to be derived.

Colloidal Stability of Metal Nanoparticles in Engine Oil under Thermal and Mechanical Load

“…The obtained results have shown that dispersed gold nanoparticles in full-synthetic engine oil have great potential as nanolubricants since besides known good tribological properties [3] they possess a high stability at room temperature and under harsh conditions, i.e., 150°C, 6 bar, 2 h, representing real engine conditions [36]. This high colloidal stability can originate from different physicochemical aspects as discussed in the following.…”

“…Therefore, permanent lubrication of combustion engines is required. Among different approaches to improve lubricants for tribological applications, metallic, e.g., Au, Bi, and Ni [1][2][3][4], and ceramic, e.g., CaCO 3 , CuO, and MOS x [5][6][7][8], nanoparticles were examined [9]. It was found that the magnitude of improvement significantly depends on nanoparticle material, size, shape, and mass concentration [6,7].…”

“…Furthermore, the colloidal stability of particles in engine oil is compared to particles in additive-free polyalphaolefin under ambient conditions, to elucidate the influence of additives in the liquid. Gold is chosen as nanomaterial since it is known to improve tribological properties [3], is easy to characterize, is one of the best investigated materials on nanoscale, and is colloidally stable in different liquids.…”

Tribological Properties of the Lubricant Containing Titanium Dioxide Nanoparticles as an Additive

“…The utilization of oil additives as nanolubricants presents many advantages, as they are relatively insensitive to temperature, and tribochemical reactions are limited, compared to traditional additives. Different anti-friction and anti-wear mechanisms using the nanoparticulate additives have been explained in previous papers [10,[12][13][14]23,24].…”

Researches on Tie Rod Ends Lubricated by Grease with TiO2 and ZrO2 Nanoparticles

“…Studies described in ref. [3][4][5] show that nanoparticle additives play the role of ball bearings between friction surfaces, resulting in decreased friction and wear. Further studies, described in [6][7][8], show that nanoparticle additives can also form a protective film over friction surfaces.…”