Amide-Based Anti-Wear/Extreme-Pressure Additives for Silica-Thickened Greases: Structure and Wear Resistance

The lubricating properties of three secondary amides were evaluated using the four-ball apparatus method. It was found that the studied amides—N-propylpropanamide (AC3C3), N-propyloctanamide (AC3C8), and N-propyldodecanamide (AC3C12)—could be a promising group of new AW/EP (anti-wear/extreme-pressure) additives for lubricants, especially for silica-thickened greases. Of the amides tested, AC3C8 was found to have the best properties. The synthesized amide structures were immobilized on SBA-15 nanosilica and examined as described above. Notably, SBA-15 has not previously been reported as a potential lubricant additive. The results of the tribological tests showed that SBA-15-immobilized amides performed better than non-immobilized amides. Nevertheless, the lack of stability of the amide-grafted SBA-15 when dispersed in oil limits its use in targeted formulations and should be improved through further research. By testing a silica-thickened grease, a synergistic effect was observed between the free-amide AC3C8 and a commercially available additive containing butylated triphenyl phosphate. A 240% increase in the Goz40 parameter (anti-wear properties) and a 150% increase in welding load (extreme-pressure properties) were obtained with the addition of 2%w/w of commercial additive and 3%w/w of AC3C8 to a base oil.