The Tribology Characters Of Several Silicate Powder As Lubricant Additives

In this paper,the tribological properties of five kinds of natural silicate powder were studied,the experimental results showed that: (1) Anti-wear and friction-reduction properties were related to the composition and crystal structure of silicates. Anti-wear properties of silicates of the same mineral family had no obvious difference. (2) As lubricating additives, silicates showed better tribological properties after calcination at a certain temperature. (3) Liquid paraffin showed excellent tribological properties when mixed with silicate powder with a suitable concentration. (4) There had no shutdown phenomenon in the wear test due to high friction coefficient when palygorskite and sepiolite were used as additives. After palygorskite was calcined at a certain temperature,XRD test showed obvious broad peaks, but sepiolite, chlorite, serpentinite and pyrofillite had no such phenomenon. That means, the palygorskite powder with amorphous structure showed the better tribological properties.More experiment results of Tribo-test showed that palygorskite and sepiolite as the lubricating additive had a significant effect on anti-wear and friction-reduction properties of 150SN base oil. Raman analysis results showed that the enrichment of C element made sample surface have better mechanical and tribological properties due to the present of nano-crystalline graphite or DLC structure. TEM was used to analyze the particles in oil. It was found that palygorskite and sepiolite were broken,and the fiber bundles was untied in the wear process. Palygorskite powder participated in the friction chemical reaction during wear test, and the silicate structure and composition were changed. While the sepiolite fibers had no such phenomenon. Ion-exchange was the main process of friction chemical reaction for palyforskite. Tribo-test, Raman and XPS analyses proved that the oxide film formed on the surface of disc specimen for sepiolite experiments, contained more concentration of FeOOH, which had better anti-wear and friction-reduction properties.The mechanism of palygorskite and sepiolite used as lubricanting additives are as follows: (1) Silicate powder entering into friction pair, the friction force makes silicate fiber bundles broken and untied forming a fiber net. The net can isolate the contact of friction pair, reduce the friction coefficient and wear loss. (2) In lubrication system, silicate powder make friction chemical reaction more complicated. Oxide film plays an important role for improving anti-wear and friction-reducing properties. The enrichment of element C has a limited effect on anti-wear and friction-reduction properties.