Lubrication mechanism of sodium metasilicate at elevated temperatures through tribo-interface observation

Lubrication is crucial for the improvement of tool durability and energy efficiency. Some inorganic polymers can potentially provide an effective lubrication in high-temperature processes. Herein, the tribological response of environmentally friendly sodium metasilicate to steel-steel contact was evaluated at temperatures ranging from 550 to 960 °C by ball-on-disk testing. The results demonstrated that the presence of sodium metasilicate at 920 °C can reduce up to 50% friction and one magnitude of wear rate from 0.3 to 2.1 x 10−3 mm3/N m for unlubricated condition to 0.15 and 2.5 x 10−4 mm3/N m, respectively. This improved tribological capability is attributed to the temperature/shear-stress induced tribo-layer on the rubbing counterpart. This tribo-layer contains the easily sheared low viscous melt and amorphous Na rich layer on the disc, as well as the bilayer structure of Mn and Na rich layer on the ball.