Synthesis And Tribological Properties Of Sodium-Ion-Exchanged Layered Zirconium Phosphates

With the development of modern industry,friction causes a lot of energy consumption and damage of equipments.Lubrication technology is an effective method to reduce friction and wear.Greases are widely used in lubricant products,which calcium-based greases have been used with a long history due to its cheap and practical properties,lithium-based greases with excellent performance dominate the current grease market.In order to satisfy the requirements of different working conditions,a variety of additives are added to the grease formulations.The shortcomings of organic additives under harsh conditions can be avoid through the combination of organic additives and solid lubricants,so the equipment can operate normally.Previous research found that layered zirconium phosphates and their modified materials as solid lubricant additives exhibited good tribological properties.In order to enrich and extend the applicability of layered zirconium phosphates,sodium-ion-exchange layered zirconium phosphate(Na-?-ZrP)as a solid lubricant was studied in this paper.The preparation method of Na-?-ZrP was studied,and the tribological property of Na-?-ZrP as an additive in calcium-based greases and lithium-based greases was studied by using a four-ball tester and a SRV tester.In addition,the synergetic effects of Na-?-ZrP and commonly extreme pressure antiwear agents(SIB,ZDDP,Mo DDP)were also investigated.The main conclusions are as follows:1.Using?-ZrP as a precursor and Na₂HPO₄ as a sodium source,Na-?-ZrP with a hexagonal shape was synthesized at room temperature.Compared with traditional ion exchange methods,this synthesis had the advantages of easier operation,mild reaction conditions and high ion exchange efficiency.2.The tribological properties of Na-?-ZrP as an additive in calcium-based greases was evaluated by a four-ball tester,and traditional solid lubricant graphite was also studied under the same test conditions.The results showed that the maximum operating load of 5.0 wt.%Na-?-ZrP grease was 686 N.Under the applied load of 490 N,the wear scar diameter of Na-?-ZrP grease was reduced by42.65%and 30.36%compared to graphite grease and base grease,respectively.Moreover,the anti-friction and anti-wear performance of Na-?-ZrP were better than graphite grease under the harsh operation of high rotate speed of 1800 rpm or a long running time of 360 min.The extreme pressure performance for Na-?-ZrP and graphite,the P_B and P_D values of Na-?-ZrP grease were 980 N and 2450N,and the P_B and P_D values of graphite grease were 882 N and 1568 N,the extreme pressure performance of Na-?-ZrP was also better than that of graphite.The worn surface analysis showed that there were fewer and shallow furrows on the worn surfaces of Na-?-ZrP grease compared with graphite grease.The reason may be attributed to the fact that Na-?-ZrP can adhere to the surface of the steel ball and form a physical protective film.3.The synergetic effect of Na-?-ZrP and Mo DDP on tribological properties was studied by using a four-ball tester.The result showed that the suitable mass ratio of Na-?-ZrP and Mo DDP was 3.0:2.0.The maximum operating load of Na-?-ZrP/Mo DDP grease reached 1078 N,which was 2.20 times of Na-?-ZrP grease,and 1.57 times of Mo DDP grease,respectively.After a long time test of 10 h,the wear scar diameter of Na-?-ZrP/Mo DDP grease was 0.56 mm,which was reduced by 31.71%and 51.30%compared to Na-?-ZrP grease and Mo DDP grease,respectively.The friction coefficient of Na-?-ZrP/Mo DDP grease was 0.041,which was reduced by 43.84%and 40.58%compared to Na-?-ZrP grease and Mo DDP grease,respectively.As for extreme pressure performance,the P_B and P_Dvalues of Na-?-ZrP/Mo DDP grease were 1373 N and 2452 N,respectively,which were higher than that of Na-?-ZrP grease and Mo DDP grease alone.Obviously,Na-?-ZrP/Mo DDP grease has been significantly improved in extreme pressure performance,friction reduction and anti-wear properties.Analysis of the worn surfaces showed that the physical film of Na-?-ZrP and the chemical reaction film of Mo DDP coexisted on the wear surface of the steel ball,and played a synergistic role together.4.The synergetic effect of Na-?-ZrP and SIB on the tribological properties was studied by using a SRV tester.The result showed that the suitable mass ratio of Na-?-ZrP and SIB was 3.0:2.0.The maximum operating load of base grease,SIB grease and Na-?-ZrP/SIB grease was 300 N,300 N and 500 N,respectively.Under the applied load of 300 N,compared to base grease and SIB grease,the wear volume of Na-?-ZrP/SIB grease was reduced by 70.28%and 84.40%,respectively.The wear volume value and friction coefficient for Na-?-ZrP/SIB grease was similar to Na-?-ZrP grease.As for extreme pressure performance,the P_B value and P_D value of Na-?-ZrP/SIB grease reached 931 N and 3087 N,the P_Dvalue was 1.58 times of Na-?-ZrP grease,1.26 times of SIB grease,there has an obvious synergetic effect in extreme pressure properties.Analysis of the worn surfaces showed that the worn surface of the Na-?-ZrP grease was only slight scratch.During the friction process,the physical adsorption film of Na-?-ZrP coexisted with the chemical reaction film of SIB,and played a synergistic role together.5.The synergetic effect of Na-?-ZrP and ZDDP on the tribological properties was studied by using a SRV tester.The result showed that the suitable mass ratio of Na-?-ZrP and ZDDP was 3.0:2.0.The maximum operating load of base grease,ZDDP grease,Na-?-ZrP grease and Na-?-ZrP/ZDDP grease was 300 N,300 N,500 N and 900 N,respectively.Under the applied load of 300 N,compared to base grease,ZDDP grease and Na-?-ZrP grease,the wear volume of Na-?-ZrP/ZDDP grease was reduced by 84.46%,84.41%and 46.00%,respectively.Compared with base grease,Na-?-ZrP/ZDDP grease and Na-?-ZrP grease had a greater improvement in friction coefficient.As for extreme pressure performance,the P_Bvalue and P_D value of Na-?-ZrP/ZDDP grease reached 1117 N and 1960 N,the P_B value of Na-?-ZrP/ZDDP grease was 1.14 times of Na-?-ZrP grease,1.42 times of ZDDP grease.Analysis of the worn surface showed that there existed the physical film of Na-?-ZrP and the chemical reaction film of ZDDP on the wear surface,the synergetic effect played a synergistic role in lubrication performance6.After mixing Na-?-ZrP with the three organic extreme pressure agents(Mo DDP,SIB,ZDDP),the lubricating performance has been improved to a certain extent,showing obvious compound synergy.The three extreme pressure agents reflect their respective characteristics.When Na-?-ZrP and Mo DDP are compounded,the bearing capacity is significantly improved.When come to SIB,the P_D value is significantly improved.Finally,the antiwear performance is significantly improved when compound with ZDDP.