Electronic-Control Friction Behavior of Porous Metal-Organic Framework@Ag Nanocrystals as Self-Repairing Lubricant Additive

The low conductivity and poor antifriction performanceof lubricantsare the main causes of wear failure in mechanical equipment underelectronic-control friction. Metal-organic framework (MOF)nanocomposites can be used to fabricate a new kind of lubricant additive.Herein, porous Cu-BTC@Ag MOF nanocrystals were successfully synthesizedvia an in situ generation method. Transmission electron microscopyresults showed that the nano-Ag element was evenly dispersed throughoutthe Cu-BTC matrix. Cu-BTC@Ag nanocrystals can significantly improvethe electrical conductivity of the EMI-BF4 ionic liquid, which increasedby 38.8%. The average coefficients of friction (COF) and wear volumeof EMI-BF4 ionic liquid with 0.5 wt % Cu-BTC@Ag decreased by 8.3 and16% without applied voltage, respectively. This finding was due tothe continuous extrusion of the EMI-BF4 stored in the Cu-BTC@Ag poresunder external load. It entered the contact zone, thereby maintainingthe continuous supply of lubricant. At 20 V applied voltage in thefriction process, the COF of the EMI-BF4/2.0wt %Cu-BTC@Ag lubricantdecreased by 18.8%, and its wear volume decreased by 32.7%. The Cu-BTC@Ag nanocrystals adsorbed onto the metal surface to form a frictionreaction film by the action of electric fields, which can repair thewear defects on the friction interface. Therefore, Cu-BTC@Ag nanocrystalsacting as an additive in lubricant have remarkable prospects in thearea of electronic-control friction.