Tribological Performance And Mechanism Of New P-N And B-N Type Lubricant Additives In Biodegradeable Base Fluids

Antiwear (AW) and extreme-pressure (EP) additives are widely used in lubricating oilespecially gear oil and hydraulic oil to decrease wear and prevent seizure. A wide variety oftraditional commercially available additives contain chlorine, zinc, lead, and so on. However,the concern for environmental contaminant has resulted in finding ashless andlow-phosphorus or low-phosphorus replacements for industrial applications. In thisdissertation, series of ashless, sulphur-free phosphorous-nitrogen (P-N) type phosphoramidateand ashless, sulphur-free and phosphorus-free boron-nitrogen (B-N) type borate estersadditives were prepared. The tribological properties and the relationship between molecularstructure and tribological behaviors of these derivatives as additives in biodegradable basestock were evaluated by a four-ball tester. The topographies of the worn surface wereanalyzed by atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM)and Scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) andX-ray absorption near-edge structure (XANES) spectra were employed to investigate thetribofilms generated from the synthesized additives. Possible lubricating mechanism of theadditives was discussed. The main content and conclusions are drawn as below:1. Two novel phosphorous-nitrogen (P-N) type phosphoramidate derivatives, dibutyloctadecylphosphoramidate (coded DBOP) and dimethyl4-dodecylphenylphosphoramidate(coded DMDP) were synthesized and applied as antiwear and extreme pressure (EP) additivesin rapeseed oil. The tribological behavior of these additives in rapeseed oil were compared with commercial additives dodecan-1-aminium butyl7-methyloctyl phosphate (coded T308B)and dibutyl phosphonate (coded T304) using a four-ball machine. The results show that thephosphoramidate derivatives possess excellent friction-reducing properties and high thermalstabilities, moderate extreme pressure capacities. The tribological mechanism wasinvestigated by the analysis of P K-edge XANES. It is proposed that the prepared compoundsas additives in rapeseed oil form a protective film containing phosphate and/or polyphosphatewhich were found on the rubbed surface.2. Two phosphoramidate derivatives, dimethyl octadecylphosphoramidate (coded DMOP) anddibutyl dodecylphosphoramidate (coded DBDP) were synthesized. Together with polysorbate80, the oil-in-water emulsions were applied as antiwear additives in water. The tribologicalbehaviors of these additives in emulsions were compared with commercial additives T308Band DBOP using a four-ball machine. The topography of the worn surface was investigated bySEM. The tribological mechanism was investigated by K-edge and L-edge XANESspectroscopy. Experimental results indicate that the phosphoramidate derivatives possessgood antiwear and friction-reducing properties. XANES analysis shows that the preparedcompounds can form a protective film contain phosphate and/or polyphosphate which affectthe tribological behavior. 3. Four novel borate esters, tris (4-dodecylphenyl) borate (coded TDB),2-(2-(4-dodecylphenoxy)-1,3,6,2-dioxazaborocan-6-yl) ethanol (coded DDB),2-(4-dodecylphenoxy)-6-heptadecyl-1,3,6,2-dioxazaborocane (coded DOB) and(Z)-2-(2-(4-dodecylphenoxy)-1,3,6,2-dioxazaborocan-6-yl)ethyl octadec-9-enoate (codedDNB) were synthesized and applied as anti-wear and extreme pressure additives in rapeseedoil. The tribological properties were examined by using a four-ball machine and the hydrolyticstability was also tested. The borate esters possess high anti-wear and extreme pressureproperties. The worn surface was investigated by SEM and CLSM. XANES and XPS wereused to analyze the composition and structure of boundary films at the worn surfaces for TDBand DDB. It is shown that the additives form a protective film at the rubbed surfaces based onB2O3and/or BN. B-N synergetic effect was found in the results which suggests that tribofilmscomposed of BN are to be preferred over tribofilms that consists of B2O3. This may be due tothe reason that BN has a layered structure similar to that of graphite, which can provide asolid interfacial film of low shear strength, leading to the good lubricating performance. 4. Two novel borate ester additives,(2-(2-(bis(2-hydroxyethyl)amino)ethoxy)-1,3,2-dioxaborolan-4-yl)methyl oleate (code OBN) and tris(2-hydroxyethyl) amine salt of(2-hydroxy-1,3,2-dioxaborolan-4-yl) methyl oleate (code OBS) were prepared and used asanti-wear and extreme pressure agents in rapeseed oil. The tribological performance wasevaluated using a four-ball machine. The results show that the additives possess highanti-wear and extreme pressure properties. SEM and AFM were used to analyze the structureof the worn surface. XANES and XPS were used to analyze the composition of boundaryfilms at the worn surfaces. The results for the compound and salt of borate esters arecompared, and it is shown that the boundary films formed by compound or salt are similarand mainly composed of B2O3. This may be due to the lower shear strength of B2O3.