Effect of Micro Nano-Structured Copper Additives with Different Morphology on Tribological Properties and Conductivity of Lithium Grease

In order to explore the effect of micro nano-structured copper additives with different morphology on tribological properties and conductivity of lithium base grease, nano-sized copper sheets (denoted as Cu NSs), micro-sized copper wires (denoted as Cu MWs), and copper particles (denoted as Cu Ps) between micrometer and nanometer scale were prepared by liquid-phase chemical methods. The effects of synthetic variables such as reaction temperature, reaction time, and pH value of reactant solution on the morphology of the final products were investigated. The as-prepared Cu NSs, Cu MWs, and Cu Ps were characterized by field emission scanning electron microscopy and X-ray diffraction. Their effects on the tribological properties and conductivity of lithium grease were investigated via ball-on-disk sliding tests and contact resistance measurements, as well as morphology and element composition analyses of worn block surface. The experimental results show that the morphology of the product is significantly affected by the experimental conditions. This makes it feasible to fabricate copper additives with the desired morphology by properly tuning the reaction conditions. Also, the as-prepared copper additives can improve the tribological properties and conductivity of lithium-base grease because they can be adhered to and deposited on rubbed steel surfaces to form boundary lubricating films consisting of cuprous oxide, cupric oxide, ferric oxide, and other oxides.