Research progresses of nanomaterials as lubricant additives

Friction and wear are unavoidable in mechanical movement. The use of lubricants with nano-additives can effectively reduce friction and wear, which is of great significance to saving energy and protecting the environment. At present, great progress has been made in the scientific research and industrial application of nano-additives for lubricants. This paper mainly introduces the types of nano-additives for lubricants (such as carbon nanomaterials, nano-metals, nano-oxides, sulfides, complexes, polymers, etc.), the tribological properties of lubricants with different components of nano-additives, and the lubrication mechanisms of the nano-additives (including tribofilm formation, rolling ball bearing effect, repairing effect, polishing effect, and synergistic effect). It also deals with the dispersion of nano-additives in lubricants and the influences of their particle size and microstructure on the tribological properties of lubricants. This review outlines the performance requirements of nano-additives in different lubrication states, discusses the use of nano-additives in challenging working conditions, and identifies various industrial oil nano-additives with reference to the appropriate options in diverse working environments. Furthermore, the existing problems of nano-additives and their application prospects are summarized. This review, hopefully, would help to shed light on the design and synthesis of novel high-performance nano-additives and promote their application in engineering.