Tribological Properties Of Metal Azolate Framework(MAF-6) As A Solid Lubricant

Friction and wear are the main factors,which can cause the increasing energy consumption and the failure of mechanical equipments.Therefore,it is a major research topic to explore excellent lubricant additives.Solid lubricants can effectively improve the bearing capacity,friction-reducing andanti-wear performance,and meet the needs of lubricants under severeworking conditions such as high temperature,high speed and heavy load.Metal Azolate Framework,（MAFs）have good thermal stability,chemicalstability and a variety of mechanical properties,so ZIFs may be used as potential solid lubricants.Previous research found that MAF-6 had good tribological properties as an additive in lithium grease.In order to fully understand the tribological performance of MAF-6 as a solid lubricant,MAF-6 as a solid additive were studied in cottonseed oil,anhydrous calcium grease,and polypropylene grease,the tribological properties were evaluated with a SRV high-frequency linear reciprocating tester.The main conclusions are as follows:1.MAF-6 used as an additive in cottonseed oil.The optimum concentration of MAF-6 as an additive in cottonseed oil was 0.50 wt.%.The maximum operating load for MAF-6 oil sample was 500 N.Under the operating conditions of 500 N-50 Hz-30 min,the wear volume(×10^-4 mm³)for cottonseed oil and 0.50 wt.%MAF-6 oil sample were 33.05 and 21.45,respectively,the corresponding the width and depth of wear scar were 0.76 mm×9.82μm and 0.69 mm×6.34μm,respectively.Compared to cottonseed oil,the anti-wear properties of MAF-6 oil sample was less affected by loads,frequencies and temperature,but MAF-6 had a little effect on the friction-reduction performance.2.Using MAF-6 as an additive in anhydrous calcium grease.The optimum concentration of MAF-6 was 5.00 wt.%.The maximum operating load of base grease and 5.00 wt.%MAF-6 grease were 400 N and 500 N,respectively.Under long-time operating condition of 300 N-50 Hz-450 min,the average friction coefficients of the base grease and MAF-6 grease were 0.15 and 0.13,respectively,the wear volume(×10^-4 mm³)of the base grease and MAF-6 grease were 80.43and 54.70,the wear volume of MAF-6 grease reduced 32.00%.The corresponding wear scar width and depth were 0.94 mm×17.78μm and 0.97 mm×11.48μm,respectively.MAF-6 grease kept good anti-wear and friction-reduction properties under different loads,temperatures and frequencies.3.Using MAF-6 as an additive in polypropylene grease.The optimum concentration of MAF-6 was 5.00 wt.%.The maximum operating load of base grease and 5.00 wt.%MAF-6 grease were 300 N and 400 N,respectively.Under the operating condition of 300 N-50 Hz-30 min,the average friction coefficients of the grease and MAF-6 were 0.14 and 0.12,respectively,the wear volume(×10^-4 mm³)of the base grease and the MAF-6grease were 19.00 and 13.37,the wear volume of MAF-6 grease reduced 29.63%.The corresponding wear scar width and depth were 0.63 mm×6.10μm and 0.70 mm×3.19μm,respectively.MAF-6 grease kept good anti-wear and friction-reduction properties under different loads,temperatures and frequencies.The contact surfaces of friction pairs have been characterized by scanning electron microscopy（SEM）,energy-dispersive X-ray spectroscopy（EDS）,three-dimensional（3D）optical profiling,it can be found that the worn surfaces of MAF-6 lubricant samples are relatively flat and smooth.During the friction process,the flexible crystal structure of MAF-6 framework can form a physical film on the contact surface to prevent direct contact,thus reducing the wear between the steel plate and the steel ball.