Investigation of the Tribological Properties of Two Different Layered Sodium Silicates Utilized as Solid Lubrication Additives in Lithium Grease

Layered sodium silicates β-Na2Si2O5 and kanemite were synthesized via facile methods under mild conditions. The tribological properties of β-Na2Si2O5 and kanemite utilized as additives in lithium grease were evaluated with a four-ball tester under different experimental conditions. The maximum nonseizure load value of 5.0 wt % β-Na2Si2O5 grease jumped from 353 N (the base grease) to 1568 N. However, 5.0 wt % MoS2 grease could only reach 617 N under the same conditions. The SEM and EDS results confirm that a protective film mainly composed of sodium silicates was formed on the worn surface during the friction process. The structural stability of β-Na2Si2O5 and kanemite after the wear test was studied by XRD. It was found that a loss of interlamellar water causes the layer structure of kanemite to collapse during a long-duration wear test. The layered structure of β-Na2Si2O5 is stable, and its tribological properties are better than those of kanemite.