ABSTRACT
Abstract .................................................................................................................. 152 7.1 Introduction .................................................................................................. 152
7.1.1 Inuence of Wear Debris on Tribological Properties ....................... 153 7.1.2 Suspending Metal Nanoparticles and Wear Debris in Lubricants ...... 156
7.2 Experimental ................................................................................................ 157 7.2.1 Materials ........................................................................................... 157 7.2.2 Methods ............................................................................................ 158
7.3 Results and Discussion ................................................................................. 158 7.3.1 Surfactant Effects on Stability of Nanoparticle Suspensions ........... 158
7.3.1.1 Nanoparticle Suspension Stability without Surfactants ...... 160 7.3.1.2 Screening of Surfactants to Improve Stability of
Nanoparticle Suspensions .................................................. 161 7.3.1.3 Rate of Separation of Nanoparticle Suspensions ............... 164
7.3.2 Nanoparticle Effects on Lubricity .................................................... 165 7.3.2.1 Inuence of Selected Surfactants on Wear Resistance
of Oils without Lubricity Additives or Nanoparticles ....... 169 7.3.2.2 Effect of Nanoparticles on Tribological Properties
of Oils without AW Additives and Surfactants .................. 170 7.3.2.3 Surfactant Effects on Wear Resistance of
Nanoparticle Suspensions .................................................. 173 7.3.2.4 Nanoparticle Effect on AW Additive Performance ........... 175
7.3.3 Nanoparticle Effects on Oil Oxidation ............................................. 177
Typically, only large particles from wear debris can be ltered out from lubricating oils. Ultra-ne particles (usually nano-sized) stay suspended and participate in the lubrication processes as an oil component. Surfactants are important in affecting the behavior of such nanoparticles. This study focuses on suspending pre-fabricated Cu, Fe and Zn nanoparticles in mineral and vegetable oils and observing the inuence of surfactants on a number of lubricant properties. Appearance and suspension stability depend on base oil, mechanisms of surfactant action and the nature of the nanoparticles. Oxidation stability is usually jeopardized by metal nanoparticles. Lubricity can be improved by the presence of nanoparticles in case no other additives are used, but nanoparticles may negatively affect the performance of antiwear additives. Nevertheless, some benets of nanoparticle presence to tribolm formation can be observed.
