Physical-chemical properties and tribological characterization of water-glycerine based metal oxide nanofluids

Nanofluids have been recently used in minimum quantity lubrication (MQL) applications to counteract the disadvantages of conventional cooling lubrication. However, comparative investigations of different types of metal oxide particles, their corresponding nanofluids, and their application in tribological tests to assess their usability as MQL-cutting fluids in machining is still in research. The technical application of those fluids is hindered by the lack of combined knowledge regarding the physical-chemical properties and their corresponding behavior as cutting fluids. Therefore, in this research, Al2O3, ZrO2 and TiO2 nanoparticles are added in different concentrations to base fluids to form water-glycerine-based nanofluids. The fluids were investigated regarding their physical-chemical properties such as particle distribution and viscosity and applied in tribological experiments to elaborate wear and particle deposition on steel workpieces. The influence of physical-chemical properties on the corresponding surfaces after tribological treatment was evaluated by scanning electron microscope imaging of the processed specimen. By varying the water-in-glycerine concentration, the often neglected viscosity increase of base fluid to mixed fluid was considered revealing a stronger influence of particle presence compared to viscosity increase caused by nanoparticle addition.