Preparation and Tribological Study of Triazine Borate Ester as Lubricant Additives

Author:Li Jian Chang

Supervisor:ren tian hui


Degree Year:2016





Energy saving,consumption reduction,environmental protection and sustainable development of society are the main aims of the countries in the world.Except for improving the quality of fuel oil,the improvement of the quality of lubricant oil is also fundamental to energy and waste control for automotive industry.Phosphoruscontaining lubricant additives have been used widely in lubricant oil,especially in engine oil,for reducing energy consumption,preventing fritting and the wear of machinery.With the rapid rise of the amount of car,the exhaust gas from cars makes the air pollution more and more serious.The traditional phosphorus-containing lubricant additives can poison the catalyst in the catalytic converter to reduce the efficiency of exhaust system and make the emission of lots of CO,NOx,hydrocarbon and volatile organic compounds(VOCs)to aggravate the air.Besides,the emission of phosphorus-containing lubricant additives is one of main cause for water pollution.Therefore,the research and development of novel environmentally friendly multifunction lubricant additives which is the main development direction of the current oil industry has good practical and strategic significance.Nitrogen-containing heterocyclic compounds and organic borate esters are viewed as the potential environmentally friendly lubricant additives.In this dissertation,firstly based on the molecular design principle,by means of the combination of triazine compounds and borated functional group,three kinds of triazine borate esters were synthesized.Their hydrolytic stability in base oil were evaluate using a method of wet heating treatment that cause accelerated hydrolysis;Their tribological properties in mineral oil and rapeseed oil,and the relationship between molecular structure and tribological properties of the triazine borate esters were evaluated by four-ball tester.XANES spectroscopy was employed to explore the chemistry of the thermal films and tribofilms generated from the prepared additives to reveal the lubrication mechanism of the additives combining with the tribological properties.In the last,two borate esters with different molecular structures were combined with phosphite for studying the interaction of borate ester and phosphorus-containinglubricant additive.Using X-ray absorption near-edge structure(XANES)spectroscopy to reveal the lubrication mechanism after combination.The main content and conclusions are drawn as below:1.Synthesize two triazine phenylboric estersTPBT and TPBTL possess high hydrolytic stability.They hydrolyze in oil after 180 h and 360 h,respectively,with an increase of 840% and 1800% relative to the hydrolytic stability of tributyl borate which hydrolyze in oil after 2 h.It indicates that the introduction of benzene with π-bond can form p-π conjugating system with boron,resulting in improving the hydrolytic stability of borate ester conspicuously.The extreme pressure properties of TPBT and TPBTL in rapeseed oil is not good,but the antiwear performances are excellent,with an increase of 33% and 44%,respectively.TPBT shows better antiwear performance than TPBTL at low concentration,while TPBTL shows better antiwear performances than TPBT at high concentration.From the XANES analysis,boron in additives is trigonal boron.N→B coordination bond in the form of inter-/intra-molecular is also detect by XANES.As for the thermal films,a part of trigonal boron in borate additives took part in thermo-chemistry reaction with oxygen on the steel surface to form tetrahedral boron in the thermal condition.The results from tribofilms analysis show that boron mainly presents as boron oxide and borate,as well as less h-BN in the tribofilms.TPBTL shows better antiwear performance than TPBT due to more h-BN in the tribofilm generated from TPBTL.Lots of exoelectrons produced under sliding process are catched by the electron-deficient p orbit in boron,and react with Fe to form iron borate.Some friction decomposition fragments take part in tribochemical reaction to form boron oxide under the pressure and friction heat effect.These compounds compose the tribofilms with good antiwear performance.2.Synthesize two triazine borate esters with diethanolamine groupThe two borate esters show excellent hydrolytic stability,with an increase of 1800% relative to the hydrolytic stability of tributyl borate.This means that the introduction of diethanolamine can increase the hydrolytic stability of borate esrer.TOBT improven the extreme pressure property of mineral oil with an increase of 23.6% when the addition is 1.0 wt.%.After introduction of sulfur,TSOBT can inprovent the extreme pressure property of mineral oil with an increase of 36.8%.TOBT and TSOBT all show good antiwear performances,with an increase of 24.3% and 51.2% as compare to base oil,respectively.As for XANES analysis of thermal films,boron is oxidized to boron oxide and little inorganic borate,sulfur is oxidized to ferrous sulfate.As for XANES analysis of tribofilms,boron forms boron oxide,h-BN,and inorganic borate.Sulfur forms ferrous sulfate and sulfid3.Synthesize two novel triazine borate estersThe synthesized borate ester TOB and TOBS show excellent hydrolytic stability in mineral oil with an increase of 1800% relative to the hydrolytic stability of tributyl borate.Both TOB and TOBS own good antiwear performaces in mineral oil.At the optium concentration,they can increase the antiwear performace of base oil with an increase of 47.0% and 45.7%,respectively.When the concentrations of TOB and TOBS are higher than the best concentration,the corrosive wear appeares on the wear surface.TOBS with active sulfur displays better antiwear performance.TOB does not own extreme pressure property in mineral oil.After the introduction of sulfur,TOBS can improve the extreme pressure property of base oil with an increase of 80.0%.The B K-edge XANES spectra analysis shows that boron exists as the forms of boron oxide and adsorbed organic boron in the thermal film.As for tribofilm,there are boron oxide and h-BN.Ferrous sulfate and organic sulfide are detected in thermal film generated from TOBS by S k-edge XANES.Ferrous sulfate and ferrous sulfide are detected in tribofilm generated from TOBS by S k-edge XANES,resulting in excellent extreme pressure property of TOBS.4.Study the interaction of phosphite and triazine borate esterThe extreme pressure properties of the combination of P-8 and borate ester are worse than that of P-8 alone.It is because that boron with electron-deficient p orbit tends to adsorb on the iron surface which enrich lots of exoelectrons,resulting in reducing the phosphorus content in the tribofilms at the competitive adsorption process.Addition of ODDB or TSOBT to P-8 has a marked synergistic effect on the antiwear performances.ODDB can improve the friction-reducing property of P-8,but TSOBE does not have a effect on the friction-reducing property of P-8.In the thermal film,the components are changed obviously after the addition of borate ester.The polyreaction of phosphate iron is inhibited.Boron can react with phosphorus to form phosphorus-boron compounds.The tribofilm generated from P-8 mainly consists of phosphate iron and polyphosphate iron.As same as the thermal film,the polyreaction of phosphate iron is inhibited and boron-phosphorus compounds are formed with the addition of borate esters to P-8.Combination with the tribological properties,it is known that the tribofilm own both boron and phosphorus shows better antiwear and fricition-reducing properties.From the XANES analysis for tribofilms,it obtains that the mor active boron is,the synergistic effect with phosphorus is more marked.