Synthesis Of ZIF-8 And ZIF-71 Crystals And Investigation Of Their Tribological Properties

Zeolitic Imidazolate Frameworks(ZIFs) is a new kind of metal organic framework materials, owing to their stability of structure and diversified chemical composition, ZIFs are increasingly attracting the attention of the research community. ZIFs with large surface area and tunable pore sizes suited for a range of application such as gas storage / separation, catalysis and drug delivery. Based on the characteristics of mechanical properties of ZIFs and the characteristics of its lipophilic properties, the research group has found that the ZIF-8 material has good solid lubrication performance. Therefore, this paper has carried out the synthesis of representative ZIFs materials with different sizes and groups. The tribological properties of ZIFs crystals as additives in different oil were evaluated with a four-ball tester.The main research contents and conclusions are as follows :1. Using the solvent thermal method, the different particle sizes of ZIF-8 were synthesized. The average particle sizes were about 2 μm and 100 nm. And by varying temperature on the ZIF-71 synthesis rules, we obtained micrometer- sized ZIF-71, which were about 1 ~ 2 μm. The smaller particles size of ZIF-71 with 450 nm were obtained by adding formic acid.2. The preparation of ZIFs material were added into the base oil liquid paraffin as a solid lubricant additives. First, adding different particle sized ZIF-8, the maximum non-seizure load(PB value) increased from 431 N to 549 N. And adding 2.0- 3.0 wt.% of large particles ZIF-71, PB value increased from 431 N to 598 N; while adding with a mass fraction of small particles ZIF-71, the PB value only increased to 549 N. Of course, adding ZIF-8 or ZIF-71 have showed good carrying capacity. Adding 0.05 wt.% small sized ZIF-71 in liquid paraffin, the wear scar diameter was deceased to 0.54 mm, but there was no effect on the anti-wear property by adding ZIF-8 with different particle sizes.3. The preparation of ZIFs material were added into the base oil polyethylene glycol 200(PEG200) as a solid lubricant additives. Adding 0.25 wt.% larger or small sized ZIF-8, the wear scar diameter was decreased from 0.50 mm to 0.36 or 0.41 mm, respectively. Adding0.5 wt.% larger or small sized ZIF-71, the wear scar diameter was decreased from 0.50 mm to 0.44 or 0.40 mm, respectively.4. SEM images and EDS spectrum were used to investigate the worn steel ball surface lubricated by base oil and oil containing different sized ZIF-8(or ZIF-71). It can be seen that the steel ball surface had scratches, EDS elemental distribution map indicated that the worn surface only had Fe, Cr element, no ZIFs elemental distribution. 3D profiler images showed that the worn scar of different sized ZIF-8(or ZIF-71) in liquid paraffin is larger than their worn scar in PEG200.5. In order to further understand the lubrication properties of ZIFs materials, ZIF-8 with an average size of 2 μm were added in lithium grease as an additive. Adding 15.0 wt.% of ZIF-8 in grease, PB value increased from 314 N to 617 N; the sintering load PD value increased from 1235 N to 1960 N. So, it can be concluded that ZIF-8 crystals have good load-carrying capacity and extreme pressure property. The wear volume reduced from 4.80 × 10-4 mm3 to 2.48 ×10-4 mm3. ZIF-8 as an additive are effective in improving anti-wear ability of base grease.