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

The low conductivity and poor antifriction performance of lubricants are the main causes of wear failure in mechanical equipment under electronic-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 synthesized via an in situ generation method. Transmission electron microscopy results showed that the nano-Ag element was evenly dispersed throughout the Cu-BTC matrix. Cu-BTC@Ag nanocrystals can significantly improve the electrical conductivity of the EMI-BF4 ionic liquid, which increased by 38.8%. The average coefficients of friction (COF) and wear volume of EMI-BF4 ionic liquid with 0.5 wt % Cu-BTC@Ag decreased by 8.3 and 16% without applied voltage, respectively. This finding was due to the continuous extrusion of the EMI-BF4 stored in the Cu-BTC@Ag pores under external load. It entered the contact zone, thereby maintaining the continuous supply of lubricant. At 20 V applied voltage in the friction process, the COF of the EMI-BF4/2.0wt %Cu-BTC@Ag lubricant decreased by 18.8%, and its wear volume decreased by 32.7%. The Cu-BTC@ Ag nanocrystals adsorbed onto the metal surface to form a friction reaction film by the action of electric fields, which can repair the wear defects on the friction interface. Therefore, Cu-BTC@Ag nanocrystals acting as an additive in lubricant have remarkable prospects in the area of electronic-control friction.