Preparation of High-Temperature Lubricants by Blending Castor Oil with Lithium Bis(trifluoromethylsulfonyl)imide

The public awareness in environmental issues has been constantly growing. Lubricants are applied in many diverse areas; therefore, their environmental acceptability has become increasingly important. In this paper, a kind of eco-friendly high-temperature lubricant was prepared by mixing castor oil with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in molar ratios of 1:0.5, 1:1, and 1:1.5. Thermal and rheological analysis indicates that the in situ formed ILs, [Li(castor oil)]TFSI, with various molar ratios, are more resistant to high temperatures and substantially stronger than the pure castor oil. Tribological test results shown that the ILs have excellent friction reduction and antiwear properties for lubrication of steel/steel contacts at 200 °C. Moreover, the tribological performances of these lubricants were also better than those of epoxidized soybean oil fluid, which is an environment-friendly lubricant and has high oxidative stability. XPS analytical results indicated that a boundary lubrication film composed of Fe₂O₃, Fe₃O₄, FeOOH, FeSO₄ or Fe₂(SO₄)₃, FeF₂, FeF₃, and C–O bonding was formed on the worn steel surface, and the film is believed to be responsible for the excellent tribological properties of [Li(castor oil)]TFSI using at elevated temperature.