Preparation Of Borate Salt (Ester) And Investigation Of Their Tribological Properties As Lubrication Oil Additive

Due to the rare earth element and its compounds show wide prospects in the field of tribology, and surface-modified rare earth compound nanoparticles can greatly improve the tribological properties of lubricating oil, hence it is very meaningful to research and develop rare earth compounds in the field of lubrication. In this paper, borate lanthanum, lanthanum fluoride and lanthanum fluoborate modified by oleylamine were synthesized as lubricant additive by direct precipitation method with oleylamine as the surface-modifying agent in distilled water-ethanol mixed solvent. Besides, we characterized the tribological properties of as-obtained nanoparticles in different base oils and explored the synergistic or antagonistic of different active elements for reducing friction friction anti-wear properties.As a versatile lubricant additives, borate esters have attracted significant attention, because they are non-toxic and exhibit pleasant odor, good rust resistance and oxidation resistance, outstanding frictionreducing and anti-wear ability and a certain degree of biodegradability. However, boron atom was sp2 hybrid, the deficient of electron makes it was easily attacked by water so organic borate esters are liable to hydrolysis, which severely limits their application in industry. which causes the loss of the B-containing component and reduces the efficiency of borate eaters as lubricant additives. In the present research work, we synthesized two kinds of N-containing borate esters. This article reports the preparation and characterization as well as the evaluation of tribological properties of as-synthesized borate esters as potential green lubricant additives in three kinds of base oils. The main contents and results are as follows:?1? Preparation of borate esters and evaluation of their tribological properties as lubricant additives in different base oilsTwo kinds of N-containing borate esters as green lubricant additives were synthesized. Their tribological properties used as lubrication additive in liquid paraffin?LP?, poly-alpha-olefin?PAO? and dioctyl sebacate?DIOS? were evaluated using a four-ball machine, and the worn surfaces of the steel balls were analyzed with a field emission scanning electron microscope?FESEM? equipped with an energy dispersive spectrometer accessory?EDX?. The worn surfaces of the upper balls with X-ray photoelectron spectroscopy?XPS?, and the action mechanisms in different base oils were also explored. Results shows that as-synthesized borate ester has adverse effect on the friction-reducing ability of three kinds of base oils, that possibly because as-synthesized borate ester tend to be adsorbed on sliding steel surfaces to form adsorption film or reaction film with increased shear strength or surface roughness thereby resulting in increased friction coefficient. However, borate esters have great anti-wear properties in LP an PAO, that possibly because the protective films on the worn surface composed of /B₂O₃,BN, Fe₂O₃, polyoxyethylene ether moiety and other N-containing organic compounds. The inorganic and organic protective films in the metal surface effectively improve the antiwear ability of the base stock LP and PAO. However, assynthesized borate esters as lubricant additives in DIOS have adverse effect on the antiwear ability, that maybe resulted by the polarity of additive and base oil, which affects the adsorption ability and the reaction activity.?2? Preparation of lanthanum fluoborate and evaluation of its tribological propertieBorate lanthanum and lanthanum fluoride modified by oleylamine were synthesized as lubricant additives by direct precipitation method. The morphology, structure and chemical composition of the nanoparticles have been analyzed by means of X-ray power diffraction?XRD?, transmission electron microscopy?TEM?, and Fourier transform spectrometry?FT-IR?, the tribological properties of as-prepared nanoparticles used alone and with a certain proportion in LP and DIOS were evaluated with a four–ball machine. The chemical states of typical elements on the worn surfaces of the steel balls were analyzed by X-ray photoelectron spectroscopy?XPS?, the tribological action mechanism of the additives was discussed. Results show that as-synthesized borate lanthanum and lanthanum fluoride posseses excellent frictionreducing and anti-wear performance in LP and DIOS when they were used alone. When they were used with different proportion in LP, the tribological properties are significantly different from that when they used alone, when the total concentration is 0.6%, and LaBO₃/LaF₃=0.3/0.3, the cof and WSD were minimum, shows most excellent tribological properties. The tribological action mechanism of the additives was form a boundary lubricating film consisting of the tribochemical reaction film of B₂O₃, Fe₂O₃, FeF₃ and La₂O₃ and the deposited film of LaF3 on rubbed steel surface. Besides, the difference of the tribological properties at different composite ratio may due to the differences of the product content generated during friction. However, when they were used with different proportion in DIOS, there was almost no frictionreducing and anti-wear ability.In addition, lanthanum fluoborate modified by oleylamine was synthesized as a potential lubricant additive by direct precipitation method with OAm as the surface-modifying agent in distilled water-ethanol mixed solvent. The reaction conditions which effect the morphology and particle size of particles were investigated. The optimized reaction condition is that: with NaBF4 and La?NO3?3 as the staring materials, OAm as the surface-modifying agent, cetyltrimethyl ammonium bromide?denoted as CTAB? as the surfactant, the proper OAm to La?NO3?3 molar ratio maintained as 1:2, the temperature is 60 ?while the reaction time is 3h. As-synthesized lanthanum fluoborate posseses excellent friction-reducing and anti-wear performance in two kinds of base oils. Moreover, as-synthesized La?BF4?3-OAm nanoflake as an additive in DIOS is able to form a boundary lubricating film consisting of the tribochemical reaction film of B₂O₃, Fe₂O₃, FeF₃ and La₂O₃ and the deposited film of La?BF4?3-OA nanoflakes on rubbed steel surface therefore improve the tribological properties of the base oil.