Lubricating Properties of Sodium Alginate as an Additive for Water in Surface Contact

By using sodium alginate as a water-based lubricating additive, the tribological properties of self-mated quartz tribo-pairs were explored in the condition of surface contact. The molecular structure of sodium alginate was analyzed by fourier transform infrared spectroscopy. The surface topographies of worn quartz surface before and after sliding test were measured by a 3D optical surface profiler. The tribological experiments for tribo-pairs of different surface roughness combination were carried out by using a micro-tribometer. The results indicate that, for lower specimen with Ra of 0.555 nm, no stable sliding occurred unless surface roughness of the upper specimen was higher than 0.555 nm. In addition, the higher surface roughness, the higher friction coefficient. Stable lubricating film at the tribo-interface is responsible for the extremely low friction coefficient, as long as the upper and lower specimen had matched surface roughness. By adding saturated chloride to the solution, the hydration layer of sodium alginate was destroyed, and as a result, the friction coefficient increased suddenly. The lubricating film was composed of a water layer and a hydration layer of sodium alginate, in which the latter was dominant.