Effect of g-C3N4 morphology on its performance as lubricating additive for grease

In this study, three forms of graphite carbon nitrides (g-C3N4), in bulky (CNB), sheet (CNS), and tubular (CNNT) morphology, are prepared and used as additives to improve the tribological properties of grease. A comparison between traditional additives and other two g-C3N4 forms, CNB and CNS, reveals CNNT exhibit the best lubricant improvement. Furthermore, by adding 0.06 wt% of CNNT, the average wear scar diameter and average coefficient of friction of a semi-fluid extreme pressure lithium grease are reduced by 28 % and 10 %, respectively. This attractive lubricity improvement of grease can be ascribed to the stable high dispersion of CNNT in the grease, thereby guaranteeing the effective formation of a lubricating film on the surface of the friction pair. Additionally, it ensures the itself moderate structural strength and a relatively weak adsorption on metal surfaces, thus providing a slide-roll mode prone to relative sliding. This promotes the renewal of CNNT on the surface of the friction pair. The significant improvement of the tribological properties of grease by CNNT widens the practical application of g-C3N4-based materials, and provides a reference for further improvement strategies for lubricating grease.