Moving towards sustainable tribology: waste silica fumes as a novel lubricant base

We conducted ball-on-disk tests to explore the tribological properties of a carbon sodium silicate lubricant (CSS). This lubricant consists of a water-based sodium silicate (SS) suspension and amorphous carbon particles. Its solidification occurs as water gradually evaporates from the mixture. The CSS samples were derived from waste silica fume (SF), which is a mixture of SiO2 and carbon. We analyzed the SF by using X-ray fluorescence and optical microscopy. In order to investigate the impact of lubrication on hot metalworking we used various proportions of SF and NaOH, creating samples S2, S3, and S4 with modulus 1, 1.5, and 2. Additionally, a comparative SS lubricant sample (Sample S5 with modulus 1.5) was made from pure SiO2. We conducted two types of tests: a steady-state test at a constant sliding speed of 50 mm s(-1) and a fretting test involving oscillations at a 75 degrees angle and a frequency of 2 Hz, both at 100 degrees C. Distilled water served as the benchmark tribological fluid (Sample S1) for comparing coefficients of friction (CoF) values. The average CoF (fretting test) values for S1, S2, S3, S4 and S5 are 0.43 +/- 0.026, 0.29 +/- 0.048, 0.22 +/- 0.042, 0.34 +/- 0.041, and 0.25 +/- 0.041, respectively. In steady-state CoF test, average values for S1, S2, S3, S4, and S5 are 0.27 +/- 0.076, 0.28 +/- 0.034, 0.40 +/- 0.027, 0.42 +/- 0.077, and 0.35 +/- 0.051, respectively. Statistical analysis, including one-way ANOVA and post-hoc comparisons, revealed significant differences in friction means between sample types in both test types (p-values < 10(-15)). These results highlight the potential of repurposing SF waste material as a novel lubricant base.