Controllable synthesis of 0D, 1D, and 2D nano lanthanum borates and their dispersion stabilities and tribological properties in rapeseed oil

Abstract

0D, 1 D and 2 D nano lanthanum borates were prepared by changing the reaction conditions of the hydrothermal method. The effect of reaction time, pH value, temperature, and reactant molar ratio on the shapes and sizes were investigated. The as-obtained nano lanthanum borates were demonstrated by scanning electron microscope (SEM), FT-IR and water contact angle test. The dispersion stability was then evaluated by a spectrophotometry. Moreover, the tribological properties of the prepared 0 D, 1 D and 2 D nano lanthanum borates as lubricating additives in rapeseed oil were investigated on a four-ball tribo-tester. Furthermore, the contact model and underlying lubricating mechanisms were proposed based on the results of surface analysis. The results indicated that nano lanthanum borates with different shapes and sizes could be obtained by regulating the reaction conditions of a hydrothermal method. Ethanol rapid evaporation ultrasonic dispersion method and stearic acid surface modification could improve the dispersion stability of nano lanthanum borates in rapeseed oil. In addition, the as-obtained 0 D, 1 D and 2 D nano lanthanum borates could significantly facilitate the anti-wear and friction-reducing properties of rapeseed oil, especially for 2 D nanoflakes. The enhanced lubricating performance of 2 D lanthanum borate nanoflakes might be attributed to the combined action of relatively lower loads under planar contact forms, thicker and stronger adsorption film generated by plate-like additives, and the enhanced activity of boron atoms and the increased boron-permeation amount on the friction surface to form tribochemical films containing Fe2O3, B2O3 and La2O3.