Carbon-based quantum dots for green-lubrication technologyNadeem, Irfan (Avtor) Cavaleiro, Albano (Mentor) Kalin, Mitjan (Mentor) graphene quantum dotssuperlubricitygreen tribologyboundary lubricationaqueous glyceroldiamond-like carbonamorphous-carbon coatingsFriction and wear contribute significantly to energy loss and component failure in mechanical systems. As such, reducing friction and achieving superlubricity in engineering materials is a promising strategy to decrease material losses and energy consumption in industrial systems. Recently, the use of aqueous green lubricants to achieve superlubricity has gained interest due to their potential to reduce energy consumption and carbon footprint. However, it is still a challenge to achieve superlubricity with high load-bearing capacity in aqueous-lubricated systems. In particular, for self-mated steel contacts, the contact pressure rarely exceeds 50 MPa during super-low friction, due to excessive wear during the long running-in period. Additionally, maintaining superlubricity under different sliding conditions over extended durations is a major obstacle for real-scale applications. This thesis addresses these challenges by investigating the tribological performance of graphene quantum dots (GQDs) as nano-additives in aqueous glycerol between various friction pairs. The results show that GQDs in aqueous glycerol achieve super-low friction and even superlubricity in self-mated steel contacts at a contact pressure as high as 316.5 MPa. Carboxyl-functionalized GQDs (CGQDs) have been shown to provide robust and durable superlubricity in self-mated steel contacts that is maintained over a prolonged time and adapts to different sliding conditions without an additional supply of CGQDs-based nanolubricants. Furthermore, nitrogen-doped GQDs (NGQDs) as an additive in aqueous glycerol provide superlubricity with friction coefficients ranging between 0.005 and 0.009 in friction pairs of steel and silicon-doped hydrogenated amorphous carbon (a-C:H:Si). This comprehensive investigation of the lubrication mechanisms and the effects of various tribological parameters on the performance of GQDs and their functionalized forms aims to improve the energy efficiency and longevity of lubricated engineering contacts. By providing new insights into the role of GQDs in reducing friction, this thesis work represents a significant step toward implementing energy-efficient and green lubrication technologies for industrial applications.[I. Nadeem]20242024-12-24 09:39:27Doktorsko delo/naloga166191sl