Tribological capabilities of carbon based nano additives in liquid and semi-liquid lubricants
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The growing population, the environmental challenges and limitations of nonrenewable resources have enforced researchers to improve the energy efficiency and reduce energy wastage in all industrial sectors including manufacturing and automotive. The significant losses in the automotive and manufacturing industries are associated with frictional energy between the mating surfaces. In addition, high frictional forces accumulate material removal rate which directly affects the service life, efficiency, and maintenance cost of the components. This results into loss of functionality and efficiency depletion of the systems. One of the possible solutions includes focusing on the refinement of tribological applications by researchers and industrial sectors. Along with that, rapid growth in nanomanufacturing industries has opened an enormous range of opportunities to enhance tribological capabilities of lubricants. Improved physical and chemical characteristics of the nanomaterials allowed them to be used for many applications including production of new generation of lubricants. In this study, applications of carbon based nanomaterial and hybrid nanoadditives to both liquid and semi-liquid lubricants have been investigated. This thesis is divided into three phases based upon the type of nano additive into the liquid and semi-liquid lubricants. In phase 1, three forms of reduced graphene oxides (rGO) were evaluated for the tribological application using four-ball tester at 0.01% concentration. All three forms of rGO were produced using modified hummers method; however, different filtration method and synthesis time were used to vary the bulk densities and lattice structures of rGO nanoplatelets. In the second phase of this study, the best rGO nanoplatelets were further studied at three different weight concentrations to discover the optimum concentration to modify friction and wear preventive characteristics. In order to obtain precise results about friction and worn surface characterization, ball-ondisk tribometer was used in situ condition. In the last phase of this research, graphene nanoplatelets and titanium dioxide nanoparticles were used individually at three different concentrations. Furthermore, hybrid nanoadditives (graphene and titanium dioxide mixed in three different ratios) were tested in both liquid and semi-liquid lubricants. Apart from tribological evaluation, physical, chemical, and structural properties were evaluated in three phases using viscometer, RPVOT, Fourier-transform infrared spectroscopy, electron microscopy (SEM and TEM) and Raman spectroscopy.