Synthesis And Tribological Properties Of Boron Based Lubricant Additives

Recently,boron-containing compounds,such as organic borate esters,inorganic borates,and hexagonal boron nitride(h-BN),as environment-friendly lubricant additives have attracted much attention in the field of tribology due to their excellent friction reducing performance,wear resistance,antioxidation,and biodegradability.Firstly,the aim is to improve the hydrolysis stability of borate esters,from the molecular design point of view,we introduced nitrogen-containing compounds and benzene rings into the structure of borate esters and synthesized eight ashless low-phosphorus or non-phosphorus nitrogen-containing phenylboronic acid ester additives and six ashless phosphorus-free nitrogen-containing borate ester additives.As a promising application,their antifriction and antiwear properties in liquid paraffin were investigated.Secondly,in order to improve the dispersion stability and compatibility of boron nitride in the base oil,a series of surface-functionalized boron nitride nanomaterials were prepared,and their tribological performances in liquid paraffin and 150 N base oil were evaluated.Thirdly,a series of carboxyl carbon spheres/sodium bis(oxalate)-borate composites were synthesized,and their antifriction and antiwear performances in liquid paraffin were tested.In addition,the tribological behaviors of inorganic borate modified carbon spheres composites were discussed.The main research contents of this paper are as follows:1.Eight ash-free low-phosphorus or non-phosphorus nitrogen-containing phenylboronic acid ester additives were designed and synthesized.The tribological properties of eight additives were tested by four-ball friction wear tester,and the oil solubility and hydrolytic stability in liquid paraffin were investigated.The experimental results show that eight nitrogen-containing phenylboronic acid esters have good oil solubility and hydrolytic stability in liquid paraffin.Eight phenylboronic acid esters as additives lead to a substantial improvement on antifriction and antiwear properties of liquid paraffin.Moreover,the tribological properties of the phenylboronic acid esters containing phosphorous and nitrogen are better than that of the phosphorus-free nitrogen-containing borate ester additives.In comparison to commercial zinc dialkylthiophosphate(T202),three phenylboronic acid esters containing phosphorous and nitrogen exhibit better friction reducing and wear resistance effects.The worn surfaces of the steel ball were analyzed by SEM and EDS.The results demonstrate that three phenylboronic acid esters containing phosphorous and nitrogen can form a protective film containing boron,nitrogen,and phosphorus elements on the rubbing surfaces.2.Six sulfur-free and phosphorus-free nitrogen-containing borate ester additives were synthesized by using intramolecular coordination bonds of N?B,and applied as additives in liquid paraffin.The oil solubility,hydrolysis stability and tribological properties were examined.In addition,the relationship between their molecular structure and the antifriction and antiwear properties were investigated.The results show that six borate esters have excellent thermal stability,oil solubility,and hydrolysis stability in liquid paraffin.Six nitrogen-containing borate esters as additives to liquid paraffin can significantly reduce the wear scar diameter.With the increase the alkyl chain in the additive molecules,the borate esters possess better the anti-wear effect.None of the six nitrogen-containing borate esters show antifriction performance in liquid paraffin.3.A series of sodium bis(oxalate)-borate functionalized carboxy carbon spheres(HTC/NaBOB)composites were prepared by solid-state reaction from oxalic acid,boric acid,sodium hydroxide,and carboxy carbon spheres.The tribological properties of as-synthesized HTC/NaBOB composites as additives for liquid paraffin were studied.The results show that the HTC/NaBOB composites possess friction reducing and antiwear properties.Compared with HTC-COOH and NaBOB,the HTC/NaBOB composites perform better tribological performances,indicating that there is a certain synergistic lubrication effect in each component of HTC/NaBOB composites.Besides,the ionic conductivity of the HTC/NaBOB composites was studied and discussed.The test results show the HTC/NaBOB composites have moderate solubility in common organic solvents and carbonate solvents of the ion-batteries.These composites excellent high temperature stability and room temperature ionic conductivity which make HTC/NaBOB composites as a very promising electrolyte candidate for Na-ion batteries,and they can be used in high-temperature applications.4.The commercial bulk h-BN was exfoliated by molten alkali metal hydroxide heat treatment,and ultrasonic-assisted stripping to obtain boron nitride nanosheets(h-BNNSs).The surface of h-BNNSs was functionalized with silane coupling agent 3-(trimethoxymethylsilyl)propyl methacrylate(KH570)as modifier.The surface-modified h-BNNSs(m-BNNSs)were prepared and their structure and morphology were determined by a series of characterizations.Additionally,the tribological properties of h-BNNSs and m-BNNSs as additives in liquid paraffin were tested on ball-on-ball configuration.The results show that KH570 is covalently bonded to the h-BNNSs surfaces to form surface-modified m-BNNSs.Compared with commercial bulk h-BN,h-BNNSs and m-BNNSs possess better dispersion stability in liquid paraffin.Both h-BNNSs and m-BNNSs can improve the antifriction and antiwear properties of liquid paraffin,and m-BNNSs excellent the best tribological behaviors.5.Hexagonal boron nitride nanosheets(h-BNNSs)are obtained by a chemical exfoliation method from commercial bulk h-BN powders.The surface of h-BNNSs is functionalized with 3-aminopropyltriethoxysilane(APTS).Further,the amino functional groups on the surface of APTS-modified h-BNNSs(APTS-BNNSs)are reacted with 4-carboxyphenylboronic acid(CPBA)to obtain the covalently linked CPBA-BNNSs.The morphology and structure of h-BNNSs,APTS-BNNSs,and CPBA-BNNSs are comprehensively discussed,and used as additives in 150 N base oil.The tribological tests indicate that h-BNNSs,APTS-BNNSs,and CPBA-BNNSs significantly reduce both the friction and the wear of steel balls.Of all the above additives,the CPBA-BNNSs can most outstandingly improve friction-reducing and antiwear capacities of 150 N base oil.Only 0.075 wt% CPBA-BNNSs is added into the base oil,the coefficient of friction is decreased by 32.3%,and the wear scar diameter and mean wear volume of the rubbing surface are reduced by 42.9% and 88.4%.SEM,EDS and Microsoft XAM-3D were used to analyze the morphology and element distribution of wear scars of the bottom steel ball.The analysis of the worn scar surface demonstrates that CPBA-BNNSs can form a protective film containing boron and nitrogen elements on the rubbing surface,thereby reducing friction and protecting the surface from wear.Thus,the CPBA-BNNSs may be recommended as a potential lubricant additive in practical applications.