Effect of nanoparticle additives on the tribological behavior of oil under boundary lubrication

Jazaa, Yosef
Major Professor
Sriram Sundararajan
Committee Member
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Mechanical Engineering
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Mechanical Engineering

In this study, three different nanoparticles (CuO, WC, WS2) of comparable nominal diameter, were added to a Polyalphaolefin (PAO) base oil to evaluate tribological response in the boundary lubrication regime. The concentration of particles was fixed at 1% by weight for this study and different surfactants (Oleic acid, polyisobutylene succinimide) and dispersion methods were employed to determine the impact on agglomeration and the observed tribological response. The results showed that of the methods studied, adding 10 % Oleic acid (OA) while sonicating the particles for 30 minutes reduced the agglomeration the most and adding 1% Oleic acid while sonicating the particles for 120 minutes produced a more uniform dispersion. Furthermore, this study investigates the effect of the surface treatment of MoS2 and WS2 on their tribological behavior in boundary lubricant regime The nanoparticles were dispersed in Polyalphaolefin (PAO) using the following techniques: 1) 60 minutes sonication without using a stabilizing agent, 2) 60 minutes sonication with 1% of weight Oleic acid (OA), and 3) functionalizing the nanoparticles using polyvinylpyrrolidone. The size distribution of the dispersed nanoparticles in PAO was measured by dynamic light scattering. The nanoparticles functionalized using Polyvinylpyrrolidone resulted in the most stable particles size and homogeneous mixture dispersion. Friction studies show that the introduction of nanoparticles additives does not appreciably impact the friction of the interface for most cases in comparison to the base oil. Reciprocating wear experiments showed that the addition of nanoparticles without surfactants did not significantly increase the wear resistance compared to the base oil. Finally, this study investigates the dispersion techniques for CuO and WC nanoadditives on their effect on the rolling contact fatigue, using the best oil formulation that provided a stable suspension and agglomeration reduction for both materials. Tungsten carbide nanofluids showed the best micropitting resistantance behavior followed by copper oxide nanofluids under the boundary lubrication regime. Agglomeration reduction and homogeneous particles dispersion contribute to the wear reduction. The results of the friction and wear studies contributes to a better understanding of the tribological mechanism of the nanoadditives in base oil and clarify the difference between reducing agglomeration and improving dispersion. In this study, it is hypothesized that the additives might deposit on the surface and forming a physical tribofilm. In addition, if the nanoparticles fill the gaps between the surface roughness asperities which increase the true contact area, the particles can assist in movement like a nanoscale ball bearing. Depending upon the nanoparticles used, of evidence both mechanisms were found.