Preparation And Tribological Properties Of Oil-soluble Nano-LaF₃ And Its Application In Heavy Duty Industrial Gear Oil

Although gear oil containing extreme-pressure and anti-wear additives can avoid the friction and wear of gears under harsh working conditions,the extreme-pressure and anti-wear additives not only has corrosiveness to the tooth surface metal,but also will cause harm to human health and natural environment.Nanoparticles as additives can not only significantly improve the anti-friction,anti-wear and load-bearing performance of lubricating oil,but also have outstanding effects in environmental protection and human health,providing a new solution to the above problems.As a common high-temperature solid lubricant,LaF₃ nanoparticles have a layered structure,relatively low hardness,high thermal stability and chemical stability,and have potential application prospects in heavy duty industrial gear oil.However,the dispersion stability and sensitivity of nano-LaF₃ in base oil and its compatibility with gear oil composite make it difficult to put it into practical application.Based on this,LaF₃ nanoparticles modified with di（2-ethylhexyl）phosphate（D2EHPA）were synthesized and their tribological behavior in three different types of base oils was studied.To explore the compatibility between LaF₃ nanoparticles and the core additives of gear oil composite additives,reveal the mechanism of their interaction,further add nano-LaF₃to the full formula gear oil on the market,and investigate its impact on the tribological properties of the finished gear oil on the market.Finally,In order to realize the commercial application of nano-additives,based on the above test results,a heavy duty industrial gear oil composite additives containing oil soluble nano-LaF₃ was finally designed and developed.The main research content and conclusions are as follows:（1）Preparation of oil soluble nano-LaF₃ and its tribological behavior in different base oilsLaF₃ nanoparticles with oil solubility were prepared with sodium fluoride（NaF）,lanthanum chloride heptahydrate（LaCl₃·7H₂O）as reaction raw materials and D2EHPA as surface modifier,which showed good dispersion stability in mineral oil（150N）,polyalpha-olefin（PAO6）,diisooctyl sebacate（DIOS）and other base oils.other base oils.Four-ball tester results show that LaF₃ nanoparticles have a good effect on the tribological properties of the three base oils.When the additive concentration was 0.2 wt%,the friction coefficients of PAO6,150N and DIOS were reduced by 28%,33%and 49%,respectively,while the wear scar diameter was reduced by 38%,53%and 46%.And in the 100 N to 400 N load range,all have certain anti-wear ability.Combined with the analysis results of the worn surface,it was found that the LaF₃nanoparticles modified by D2EHPA surface formed a complex boundary lubrication film composed of phosphate,ferric oxide,lanthanum fluoride and lanthanum oxide on the worn surface during the friction process,which not only significantly reduced the wear and friction coefficient of the contact surface,but also filled and repaired the surface defects.（2）Compatibility of oil-soluble nano-LaF₃ with typical additives of gear oil and its applicationThe compatibility of nano-LaF₃ with typical additives of gear oil,such as sulfurized olefin（T321）,thiophosphate ester amine salt（T307）and butyl isooctyl phosphate dodecylamine salt（T308B）,was investigated.The interaction mechanism between nano-LaF₃ and typical additives of gear oil was analyzed based on the adsorption behavior of additives and the characterization results of wear surface.Finally,the effect of nano-LaF₃ on the tribological properties of commercially available finished gear oil was further explored.The test results show that the combination of nano-LaF₃ and gear oil additives（T321 and T307）not only has an obvious synergistic effect in improving the anti-friction and anti-wear properties of the base oil,but also greatly improves the last nonseizure load（P_B）of the base oil.Through the analysis of the adsorption behavior of additives on metal surfaces and the characterization results of worn surfaces,it was found that the increase in anti-friction and anti-wear performance and the last nonseizure load（P_B）value after compounding is due to the combination of LaF₃ nanoparticles and gear oil additives（T321 and T307）mutually promoted adsorption on the metal surface,which enabled faster adsorption on the contact surface of the friction pair at the initial stage of friction,and formed a thicker tribofilms together with nano-LaF₃.In addition,the test found that the oil soluble nano-LaF₃ and the composite additives of L-CKD 320 heavy duty industrial gear oil showed high compatibility,which could effectively improve the lubrication effect of the commercial heavy duty industrial gear oil.（3）Formulation design and properties study of heavy duty industrial gear oil nanocompositeBased on the tribological behavior of LaF₃ nanoparticles in base oil and the compatibility rule with typical additives of gear oil,combined with the performance characteristics and application conditions of heavy duty industrial gear oil,a heavy duty industrial gear oil composite additives containing oil-soluble LaF₃ nanoparticles was designed and developed.Alkyl naphthalene 30（AN30）was selected as the base oil,and the tribological properties,oxidation resistance and corrosion properties of copper sheet between nanocomposite additives and commercially available composite additives were compared and analyzed using a four-ball tester,a pressurized differential scanning calorimetry and a copper sheet corrosion tester.The results showed that the base oil containing nanocomposite additives had lower friction coefficient,smaller the wear scar diameter and higher last nonseizure load（P_B）,weld load（P_D）and combined wear number（ZMZ）than the commercially available composite additives.In addition,the corrosion and oxidation resistance of the copper sheet of the base oil containing nanocomposite additives are basically equivalent to that of the commercial composite additives.