Preparation Of CeO₂ Nanoparticles By Continuous Flow Method And Tribological Properties In DLC Liquid-Solid Composite Lubrication System

Facing the increasing demand for diesel engines in the fields of logistics,shipping and mining machinery,and the extremely high requirements for engine fuel economy put forward by the dual-carbon target,the application of Diamond-like carbon（DLC）solid lubrication coating in engine components and the development of high efficiency antifriction lubricating oil are the key of improving engine fuel efficiency.However lubrication failure caused by the mismatch between commercial antifriction agents and DLC make the development of novel antifriction and anti-wear additives,which is an urgent need.Nano additives have attracted much attention in the field of engine lubricant development due to their excellent friction reduction and wear resistance performance and university to different friction pair materials.CeO₂ nano-additives combines the high strength of oxides and the high chemical activity of rare earth elements and have excellent anti-wear properties.In order to promote its application in the new energy-saving diesel engines,this paper discusses the regulatory mechanisms of the molecular structure of raw materials and reaction parameters on the structure of CeO₂ nano-additive.The synergistic adsorption and lubrication mechanism of CeO₂ nano additive and commercial organic friction reducer in DLC.solid-liquid composite lubrication system,and the application performance in DLC piston ring cylinder liner friction system.the main research contents and conclusions are as follows:（1）The study on structural regulation mechanism and dispersion stability of CeO₂ nanoparticles prepared by continuous flow methodThe organic amine-modified CeO₂ nano-additive with excellent dispersibility was prepared by in situ thermal decomposition with the organic amine-containing Inorganic ceric salt dispersing liquid flowing through the spiral tube in the tubular furnace.A systematic study was conducted on the structural parameters such as the thermal decomposition temperature,reaction temperature,feed ratio,particle size distribution of CeO₂ nanoparticles,modifier content,and their effects on dispersion stability in the PAO6 base oil.It is found that the dispersion stability of CeO₂ nano-additive increases with the decrease of particle size and the increase of modifier content.Matching cerium salts with low decomposition temperature and organic amines with high decomposition temperature can effectively suppress the aggregation between inorganic nuclei and the decrease of modifier content.Ammonium cerium nitrate（Ce（NH₄）₂（NO₃）₆）and oleyl amine(C₁₈H₃₇N)were decomposed at 180℃to prepare an average particle size of about 3 nm,with a modifier content greater than 40 wt.%CeO₂ nano-additive modified with oleyl amine exhibit dispersion stability comparable to commercial high base value detergent T106D,with a maximum stable dispersion concentration of 50 wt.%in PAO6.The ball disc reciprocating friction experiment of GCr15 steel pair shows that CeO₂ nano-additive has excellent friction reduction and wear resistance performance in PAO6 base oil.,Compared with PAO6,when the optimal addition amount is 0.2 wt.%,the friction coefficient is reduced by 43%and the wear rate is reduced by 73%.（2）Tribological properties of CeO₂ nanoparticles and commercial antifriction agents in DLC/DLC friction accessory system.The prepared CeO₂ nanoparticles with excellent dispersion were compounded with friction improvers such as molybdenum dialkyldithiocarbamate（Mo DTC）,oleic acid monooleate（GMO）,oleic acid ethylene glycol ester（T403B）,and benzotriazole fatty acid amine salt（T406E）to investigate their friction reduction and wear resistance properties on DLC/DLC pairs.The relationship between the adsorption behavior of additives on DLC and their tribological properties was also investigated by using quartz crystal microbalance（QCM-D）.The tribological test results show that CeO₂ nanoparticles have excellent friction reduction and wear resistance properties for DLC/DLC friction pairs,and the optimal addition amount is 0.2 wt.%.Compared to the base oil PAO6,the friction coefficient is reduced by 15%.The wear rate has been reduced by 50%.When CeO₂ nanoparticles were compounded with four commercial additives,they exhibited a prominent synergistic effect with T406E.After compounding,the friction coefficient further decreased by 5%compared to CeO₂ nanoparticles,while the wear resistance remained unchanged.The analysis of the morphology and elemental distribution of the worn surface showed that neither the nano-additive nor the compound additive had a frictional chemical reaction with DLC,and there was no production of CeO₂ deposition film.The adsorption experiment results show that CeO₂ nanoparticles exhibit monolayer adsorption on DLC,and the equilibrium adsorption mass increases with the increase of concentration and agglomeration particle size.Relying on the high load-bearing capacity of the nanoparticles,the friction pair is isolated and the contact area is reduced,resulting in excellent friction reduction and wear resistance effects.Compared with other compound additive CeO₂ nanoparticles and T406E can form a viscoelastic adsorption layer on the DLC surface that has the maximum balance adsorption mass,the adsorption layer density,the low shear strength and the high bearing capacity at the same time,leading to the further significant improvement of friction reduction performance while the compound additive has excellent anti-wear capacity.（3）Tribological properties of CeO₂ nanoparticles and commercial antifriction agents in GCr15/DLC friction accessory systemThe CeO₂ nanoparticles modified with oleamine were compounded with organic friction modifiers Mo DTC,T406E,T403B,and GMO at the optimal concentration to investigate their friction reduction and wear resistance performance in the GCr15/DLC friction pair system.The friction results indicate that,unlike the DLC/DLC matching system,in the GCr15/DLC system,CeO₂ and GMO exhibit a prominent synergistic effect,overcome the disadvantage of high friction of CeO₂ friction film and compensate for the low bearing capacity of organic friction reducing agents or the problem of corrosive wear on DLC.Compared with PAO6,CeO₂,and GMO,the friction coefficient decreased by 10%,30%,and 4%,and the wear rate decreased by 56%,10%,and 52%,respectively.Scanning,Raman spectroscopy,and XPS analysis were conducted on the friction surface of GCr15 steel balls.The results showed that CeO₂+T403B and CeO₂+T406E were the deposition mechanism of CeO₂,causing high friction;CeO₂+Mo DTC is the frictional chemical reaction film mechanism of Mo DTC,causing high wear.CeO₂+GMO neither undergoes frictional chemical reactions nor generates CeO₂ nanoparticle deposition films.The adsorption results show that CeO₂ nanoparticles and GMO have a synergistic adsorption effect on the metal surface,forming a viscoelastic adsorption layer with high equilibrium adsorption mass and high adsorption layer density.At the same time,a relatively dense viscoelastic adsorption layer is also formed on the DLC surface.At the same time,it has low shear strength and high bearing capacity,which makes the compound have excellent friction reduction and anti-wear properties in the GCr15/DLC friction system.（4）Effect of CeO₂ nano-additive on tribological properties of low viscosity lubricating oil/new friction pair composites lubricating system in diesel engine.CeO₂ nanoparticles and GMO were added to the full formula lubricating oil in the optimal ratio,and the friction reduction and wear resistance performance of the compound additive on new friction pairs（nitriding,DLC,cast iron）of diesel engines and the viscosity temperature performance of the full formula lubricating oil were investigated.The tribological test results show that the addition of CeO₂+GMO reduces the wear rate of the cylinder liner by about 50%,which overcomes the problem of Mo DTC increasing the wear of cast iron cylinder liners.The results of the full lubrication range show that the CeO₂ nanocomposite reduces the friction coefficients of the steel ball/steel disc and the steel ball/DL C disc pairs by about 10%and 25%,respectively.The viscosity temperature results show that the addition of CeO₂ compound additive increases the viscosity index of diesel engine oil 5W20FE by about 10%,which overcomes the disadvantage of Mo DTC causing an increase in viscosity and a decrease in viscosity index of diesel engine oil.Therefore,CeO₂ compound additives are expected to become energy-saving additives,further improving the fuel economy of diesel engines.