In situ visualization study of tribofilm growth process from magnesium silicate hydroxide nanoparticles

Utilizing environmentally-friendly magnesium silicate hydroxide (MSH) nanoparticles as a lubricant additive is considered a promising concept. However, whether large particle agglomerates would enter the small lubrication contact area is a worthwhile issue to consider. This study aimed to investigate in situ visualization the lubrication behaviour of MSH-containing oil in rolling contact. The results indicate that MSH nano-additives can enter the contact zone in granular, sheared, and unrestricted states as the velocity increases. The MSH tribofilm can spontaneously grow on the lubrication track regardless of whether the lubrication is in the boundary, mixed, or elastohydrodynamic (EHD) regime. A mass fraction of 0.50% MSH produces a tribofilm thickness of approximately 200 nm, significantly improving tribological properties under rolling conditions. With the velocity increasing, the MSH-based tribofilm thickness decreases. The size of aggregates and the sheared effect affect tribofilm growth. In addition, the interferogram presents that the lubricant flow also affects tribofilm growth. The velocity profile of the lubricant flow is obtained by numerical calculation. The results show that the tribofilm decreases because the backflow in the inlet reduces the probability of MSH particles entering the contact.