Research On Preparation And Current-carrying Friction Mechanism Of Conductive Lubricant

Electrical contact exists extensively in power electronics,aviation,aerospace,transportation and so forth.The performance of electrical contact directly determines the reliability and service life of the entire system.Due to fretting or sliding etc.,electrical contact needs to transfer electrical energy or signal when relative displacement occurs between the electrical contact interfaces.Therefore,electrical contact is required to have better tribological properties and electrical conductivity.However,along with the current flow and the relative displacement of the contact interface,electrical contact areas tend to undergo complex physical and chemical phenomena,such as thermal effect,mechanical effect,electrical effect,chemical effect and so forth.These phenomena can cause severe wear,large contact resistance,serious corrosion,etc.,resulting a sharp drop in the quality of electrical contact.Conductive lubricant is a kind of special lubricant with excellent electrical conductivity and tribological properties,which can effectively improve the friction-reducing,anti-wear and electrical performances of electrical contact.Meanwhile,it also can play a role in corrosion protection and sealing.Therefore,in order to improve the performances of electrical contact,this thesis focuses on the studies of conductive lubricant,and the main research contents are listed as follows:(1)Two kinds of ionic liquids(ILs)including 1-butyl-3-methylimidazolium tetrafluoroborate(LB 104)and 1-butyl-3-methylimidazolium hexafluorophosphate(LP104)were employed as conductive lubricants,and their chemicophysical nature,tribological and conductive performances were investigated in detail.The results show that two kinds of ILs have good thermal stability.Compared with polyalkylcyclopentane(MACs),ILs exhibited much lower coefficient of friction,wear volume and contact resistance.The analysis indicates that the good tribological and electrical performances are mainly related to the characteristics of the ionic bond and the lubricating protective film formed on the friction surface.(2)A series of conductive lubricants were prepared by using graphene,carbon nanotubes and silver powder as conductive additives and polyalkylcyclopentane(MACs)as the base oil.The chemicophysical test indicates that all the conductive lubricants have good thermal stability and corrosion resistacne,and graphene and carbon nanotubes could reduce the volume resistivity of MACs by two orders of magnitude.Tribological tests show that both graphene and carbon nanotubes conductive lubricants exhibit better tribological proeprties and lower contact resistance than Ag.The analysis show the good tribological properties and electrical performance of conductive lubricants are mainly dependent on the unique structures of graphene,carbon nanotubes and the lubricating protective film formed on the friction surface.(3)Conductive polyaniline was used as additive and lithium-based complex grease and ionic liquid greases of "in situ" formation were used as base greases to prepare conductive lubricants.The results show that conductive polyaniline significantly improves the corrosion resistance,tribological properties and electrical conductivity of the lubricating greases.The analysis shows that the improvement of corrosion resistance is mainly related to the "passivation mechanism",and the good tribological properties and electrical conductivity are mainly dependent on the lubricating protective film.(4)Based on the interfacial polymerization method,two kinds of ionic liquid functionalized nano-polyanilines were prepared,and they were employed as conductive additives to afford lubricants.The results show that two kinds of nano-polyanilines could reduce the volume resistivity by two orders of magnitude,and polyurea grease containing polyaniline exhibit an excellent corrosion resistance during the salt spray test of 720 h.Tribological test and analysis indicate that the ionic liquids and polyaniline synergistically improve the tribological and electrical performances.(5)The effects of montmorillonite on the conductivity and tribological properties of lubricating greases were investigated in details.The results show that montmorillonite can increase the number of "electron trap" and reduce the conductivity of prepared grease.Montmorillonite has a special layered structure,which can form a good protective film on the friction surface to improve the tribological properties.This provides the theoretical and technical support for the preparation of insulating grease.(6)A synergistic strategy based on conductive grease and surface texture is proposed to improve the tribological properties and electrical performances of Ag coating.The results show that the textured Ag coating under the lubrication of graphene conductive grease exhibits lower coefficient of friction,wear loss and contact resistance.The analysis shows that the good tribological and electrical performances of the textured Ag coating are attributed to the synergistic effects of conductive grease and surface texture.