Development of precipitation lubrication with palmitic acid and its friction mechanism

• Published in: Tribology international 2024-12, Vol.200, p.110066, Article 110066
• Main Authors: Hashizume, Naoya, Takano, Riki, Umehara, Noritsugu, Tokoroyama, Takayuki, Zhang, Ruixi, Hanyuda, Kiyoshi, Otsuka, Ayano, Ueda, Mao
• Format: Article
• Language: English
• Subjects: Friction modifier; In situ reflectance spectroscopy; Palmitic acid; Precipitation
• ISSN: 0301-679X
• DOI: 10.1016/j.triboint.2024.110066

Conventional friction modifier MoDTC becomes ineffective at lower temperatures. This paper investigates the concept of "precipitation lubrication," where saturated fatty acid precipitation enhances load-bearing capacity and solid lubrication at contact points to overcome this issue. PAO8 with 4.2 % palmitic acid lubricant was prepared, precipitating below 35 °C, reducing friction by approximately 14 % at 30 °C for both boundary and mixed lubrication. In situ reflectance spectroscopy demonstrated palmitic acid forming a solid layer on the disk specimen, preventing direct contact between asperities and significantly reducing friction. These findings underscore the effectiveness of palmitic acid precipitation in enhancing lubrication performance at lower temperatures. •The friction decreased upon precipitation of palmitic acid into the base oil.•In situ reflectance spectroscopy was utilized to analyze the contact point.•The optical properties indicated that the palmitic acid layer existed as solid.•The palmitic acid layer was thicker than the effective roughness of the surfaces.•A direct contact of the surfaces was prevented by the precipitated palmitic acid.