Tribological Investigation Of Layered α-zirconium Phosphates As An Additive In Anhydrous Calcium Grease

In order to overcome a large amount of energy loss caused by mechanical friction and wear and prolong the service life of equipment to meet complex working conditions,it is always primary topics for tribologists to explore the lubricant products with high performance,long service life and reasonable price.Grease is a kind of widely used lubricant products.At present,lithium grease has the largest production quantity.While lithium element is a relatively rare element on the earth,the scarcity of lithium element will become increasingly with the rapid development of lithium battery industry.Therefore,it is urgent to find a wealthy,safe and economic element to replace lithium for the lubricating grease industry.Calcium element is abundant on the earth.Calcium grease is a type of versatile grease at the reasonable price.In order to meet the application requirement,the grease formulations need to add various additives to improve the properties of the original grease.The solid lubricants can effectively enhance the friction-reducing,anti-wear and extreme pressure of grease to make up for the defects of lubricating grease in harsh conditions.Previous studies have found that layered zirconium phosphates as lithium-based grease additives have excellent lubricating properties.In order to more fully understand the performances of layered zirconium phosphate as a solid lubricant additive,and to further expand its scope of application.In this paper,naphthenic mineral oil,synthetic oil polydecene olefin,castor oil and coconut oil were used as base oil for anhydrous calcium greases.The SRV tester was used to study the tribological properties of layeredα-zirconium phosphate as a solid additive in anhydrous calcium grease with different base oil.Meanwhile,a comparative study with molybdenum disulfide and graphite was studied in the same experimental conditions,the main contents and conclusions are as follows:1.Whenα-ZrP was an additive in naphthenic oil anhydrous calcium-based grease,the maximum operating load and the maximum operating frequency of3.0 wt%α-ZrP grease was 900 N,70 Hz,respectively.The maximum operating load for 3.0 wt%MoS₂ and 3.0 wt%graphite was 700 N,40 Hz,respectively.Under 700 N-40 Hz-360 min test condition,the wear volumes forα-ZrP grease,Mo S₂ grease and graphite grease(×10^-4 mm³)were 44.45±3.37,44.59±4.30 and 62.49±6.19,respectively.The corresponding widths and depths of the wear scar were 1.15 mm×12.39μm,1.22 mm×13.69μm and 1.17 mm×15.13μm,respectively.Compared with MoS₂ and graphite,the tribological properties ofα-ZrP grease was less affected by applied load,frequency and temperature,which had excellent anti-friction and anti-wear performance under long running conditions.2.Whenα-ZrP was an additive in PAO8 oil anhydrous calcium-based grease,the maximum operating load and the maximum operating frequency of3.0 wt%α-ZrP grease was 900 N,70 Hz,respectively.The maximum operating load and the maximum operating frequency for 3.0 wt%MoS₂ and 3.0 wt%graphite grease,was 600 N,40 Hz,respectively.Under 600 N-40 Hz-360 min test condition,the wear volumes(×10^-4 mm³)of disk lubricated byα-ZrP grease,MoS₂ grease and graphite grease were 18.86±1.89,77.40±7.74 and 41.26±4.13,respectively.The Corresponding widths and depths of the wear scar were0.75 mm×10.95μm,1.23 mm×18.51μm and 0.98 mm×11.24μm,respectively.The wear volume and friction coefficient ofα-ZrP grease under each load were the lowest among the three kinds of greases,and were not affected by the temperature.While the wear volumes of MoS₂ grease and graphite grease increased as the temperature went up,especially MoS₂ grease.3.Whenα-ZrP was an additive in castor oil anhydrous calcium grease,the maximum operating load for 3.0 wt%α-ZrP grease,3.0 wt%Mo S₂ grease and3.0 wt%graphite grease was 1000 N,600 N and 600 N,respectively.The wear volume and friction coefficient ofα-ZrP grease were the smallest under each applied load.Under the applied load of 300 N,the wear volume of Mo S₂ and graphite grease increased as the frequency increased from 30 Hz to 60 Hz.The wear volume ofα-ZrP grease kept the smallest value among the three greases.Under the 300 N-30 Hz-360 min test condition,the wear volumes forα-ZrP grease,MoS₂ grease and graphite grease(×10^-4 mm³)were 3.62±0.36,71.03±0.71 and 205.15±15.12,respectively.The corresponding widths and depths of the wear scar were 0.64 mm×1.00μm,1.03 mm×14.23μm and 1.26 mm×25.69μm,respectively.Compared with MoS₂ and graphite,α-ZrP grease kept the lowest wear among the three greases,and had stable and excellent anti-wear performance.4.Whenα-ZrP was an additive in coconut oil anhydrous calcium grease,the maximum operating load of 3.0 wt%α-ZrP grease,3.0 wt%Mo S₂ grease and 3.0 wt%graphite grease can reach 1000 N,600 N and 600 N.Under the operating load of 300 N,α-ZrP grease has the smallest wear volume among the three greases as the frequency increased from 30 Hz to 60 Hz.Under the 300 N-30 Hz-360 min test condition,the wear volumes(×10^-4 mm³)of the steel disk forα-ZrP grease,MoS₂ grease and graphite grease were 3.29±0.33,56.40±5.64 and 288.95±28.90,respectively.The corresponding widths and depths of the wear scar were 0.72 mm×0.59μm,1.08 mm×10.42μm and 1.41 mm×42.67μm,respectively.Compared with MoS₂ and graphite,α-ZrP grease kept the lowest wear among the three greases,and had stable and excellent anti-wear performance.The corresponding worn surface was examined by using SEM,EDS and 3D non-contact surface mapping profiler.The results showed that the worn surface lubricated byα-ZrP grease had less grooves and gougings than that of MoS₂ and graphite grease,which can form a stable and dense solid protective film on the surface of friction pairs.