Investigation On Preparation And Tribological Properties Of Surface Functionalized Nanocarbon-based Lubricant Additives With Low Dimension

High-performance lubricant additive is the quintessence of lube and hence is always the research hotspot of friction and lubrication science.Low demension carbon nanomaterials have attracted lots of attentions because of their unique self-lubricating property.Whereas,the relatively poor compatibility of carbon nanomaterials in base lubricants greatly hinders their practical applications in lubrication field.In this paper,we prepared a series of suface functionalized carbon nanomaterials by chemcial methods.The compatibility of carbon nanomaterials in base lubricants was obviously improved,and their tribological properties were investigated in detail.Moreover,the lubrication mechnisms were also discussed and the specific reasearch results are described as follows:(1)The ionic liquid(IL)functionalized one dimension muti-walled carbon nanotubes(MWCNTs-IL)were prepared based on amidation.The characterization results indicated that the MWCNTs-IL kept the tube-structure after modification treatments.The IL groups were decorated on the surfaces of MWCNTs-IL by amide bonds.The dispersion stability of MWCNTs-IL was much better than the carboxyl modified carbon nanotubes.The tribological property of the MWCNTs-IL as water-based lubricant additives was studied.The MWCNTs-IL exhibited the best friction-reducing and anti-wear properties at the concentration of 0.015 wt%and the load of 40 N.Specifically,the mean friction coefficient and wear volume of base liquid containing 0.015 wt%MWCNTs-IL were 42%and 72%lower than that of base liquid.The worn surface analyses showed that some patched structures composed of iron oxide and filling structures containing MWCNTs-IL formed on the rubbing surfaces when the MWCNTs-IL were used as lubricant additives.The lubrication mechanism illustrated that the nano-lubrication effects of MWCNTs-IL and patched structures worked together to reduce the friction and wear.(2)The IL modified two dimension graphene oxides(GO-IL)were synthesized by the amidation and cation-? stacking.The characterization results demonstrated that the functionaliztion treatments was successful and brought in neglectable demage on the sheet structure of GO.The degree of functionalization of IL on GO-IL was higher than 20 wt%.Meanwhile,the content of oxygen-containing groups on the basal planes of GO-IL was reduced compared with GO.The dispersion stability of GO-IL in base liquid was much better than not only GO but also IL/GO mixture.The tribological property of the GO-IL as water-based lubricant additives was studied.The results reflected that the tribological property of the GO-IL was far superior to the IL,GO and IL/GO mixture.The GO-IL exhibited the best friction-reducing and anti-wear properties at the concentration of 0.02 wt%and the load of 40 N.Under the above optimal conditions,the mean friction coefficient and mean wear volume of base liquid reduced by 57%and 76%,respectively.The worn surface analyses showed that the effective boundary tribofilm composed of GO-IL deposition film and tribochemical film(main constituents:amorphous carbon,iron oxide and boron nitride)was formed on the rubbing surfaces when the GO-IL were used as the lubricant additives.The lubrication mechanism illustrated that the IL groups and GO of GO-IL played an synergistic effect during the friction process.The IL groups improved the embedded stability of GO-IL between the rubbing surfaces by electrostatic interactions and promoted the formation of boundary tribofilm.The boundary tribofilm played an significant role in reducing the friciton and wear.(3)Using citric acid monohydrate as the carbon source and IL as the reaction medium and modification regent,the IL capped zero demension carbon quantum dots(CQDs-IL)were synthesized by one-pot pyrolysis.The characterization results demonstrated that the CQDs-IL with an average particle size of 1.73 nm were mainly composed of amorphous carbon and capped by IL and oxygen-containing groups.The CQDs-IL exhibited a so high dispersion stability in base liquid that they could emitted bright blue fluorescence under UV irradiation.The CQDs-IL as the water-based lubricant additives exhibited the best friction-reducing and anti-wear properties at the concentration of 0.05 wt%and the load of 50 N.Specifically,the mean friction coefficient and mean wear volume of base liquid reduced by 65%and 60%,respectively.The discussion on the lubrication mechanism illustrated that the effective boundary tribofilm were formed on the rubbing surfaces by the absorption and depositon of CQDs-IL,which remarkably reduced the friction and wear.(4)Using citric acid monohydrate as the carbon source and oleylamine(OA)as the reaction medium and modification regent,the OA capped carbon nanoparticles(CPs-OA)were synthesized by one-pot pyrolysis.The characterization results demonstrated that the CPs-OA with an average particle size of 25-35 nm were mainly composed of amorphous carbon and capped by OA and oxygen-containing groups.The CPs-OA exhibited a so high dispersion stability in base oil(PAO)that they emitted the bright blue-green fluorescence under UV irradiation.The CPs-OA as the oil-based lubricant additives exhibited the best friction-reducing and anti-wear properties at the concentration of 1.0 wt%and the load of 392 N.Specifically,the the mean friction coefficient and mean wear volume of base liquid reduced by 47%and 76%.Moreover,the friction-reducing and anti-wear performance of CPs-OA displayed no attenuation when the tested time was prolonged to 8 h,reflecting a long service life.The discussion on the lubrication mechanism illustrated that the effective mixed boundary tribofilm were formed on the rubbing surfaces by the absorption and depositon of PAO molecules and CPs-OA,which remarkably reduced the friction and wear.