Research On Lubricating Oil Condition Monitoring Based On Inorganic Nano-Luminescent Materials

As an important means of predicting and diagnosing mechanical equipment failures,oil monitoring has been widely used in aviation,railway,petrochemical and defense industries.Nanomaterials have unique physicochemical and biological properties,and have aroused strong research interest in the fields of energy,catalysis,materials,and biomedicine.More importantly,nanomaterials exhibit special stimulus(chemical,optical,electrical,magnetic,thermal,etc.)response properties due to the small size effect caused by the change in particle morphology,which means that as a functional lubricant additive,it will give lubricants specific sensing and monitoring functions help to develop new intelligent lubrication products.This thesis focuses on the problem of lubricant performance monitoring.The two prepared nano luminescent materials are compounded with lubricants,combined with fluorescence spectroscopy,and a sensor method based on fluorescence signals to monitor lubricant performance is developed.The specific research results are summarized as follows:1.The monodisperse,oil-soluble CaF₂ nano-luminescent material was prepared by hydrothermal method,and the particle size distribution?crystallinity?morphology and surface structure of the nanoparticles were characterized by X-ray diffraction(XRD),Transmission electron microscopy(TEM)and Fourier transform infrared spectroscopy(FTIR).The effect of CaF₂ nanoparticles on the tribological properties of lubricating oil was evaluated by the friction and wear test.The experimental results show that the prepared CaF₂ nanoparticles(?10 nm)can be stably dispersed in PAO base oil for a long time,and have no adverse effect on the lubricating performance of the base oil.Due to the small particle size and surface modification,the CaF₂ nanoparticles exhibit a higher level of surface defects,which leads to a special dual fluorescence emission phenomenon which is temperature-dependent.As a functional lubricant additive,CaF₂nano luminescent material can be used as a temperature sensing medium for lubricants.2.The monodisperse,oil-soluble up-conversion Na YF₄:Yb³⁺/Er³⁺nano luminescent material was prepared by thermal decomposition method,and its structure and surface chemistry were characterized in detail,and its anti-wear performance as a lubricant additive was evaluated.The results show that the prepared Na YF₄:Yb³⁺/Er³⁺nanoparticles are a very excellent lubricant anti-wear additive,and 0.5 wt.%addition can reduce wear by more than 70%.As a functional additive,when mixed with lubricating oils with different degradation levels,due to the difference in the chemical structure of the oil sample and the internal filtration effect.Under the excitation of 980nm,the characteristic fluorescence emission(409 nm and 656 nm)of the nanoparticles showed obvious response characteristics to the state change of lubricant.State changes show obvious response characteristics.By calculating the corresponding emission intensity ratio(I₆₅₆/I₄₀₉),it is possible to track and monitor the degree of lubricant degradation or predict the service life.In addition,with the help of the temperature dependence of energy levels ²H_11/2 and ⁴S_3/2 of NaYF₄:Yb³⁺/Er³⁺,the lubricating oil temperature can be monitored by calculating the intensity ratio of the characteristic emission(I₅₄₂/I₅₂₄)when the lubricating oil temperature changes.