Analysis and comparison of tribological performance of fatty acid-based lubricant additives with phosphorus and sulfur

Two environmentally friendly, water-based lubricant additives (phosphorus-containing ricinoleic acid (PRA) and sulfur-containing ricinoleic acid (SRA)) were prepared. The lubrication performance of the additives in a water-based lubricant was tested using a four-ball tribotester. The stainless steel surface was analyzed by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The additives reduced the coefficient of friction (COF) value, wear scar diameter (WSD) and improved the extreme pressure (PB) value. Water-based fluids containing the PRA exhibited lower COF, WSD, and PB values than the SRA. The good tribological performances of the PRA and SRA were attributed to the synergistic action of long aliphatic chains and highly active phosphorus and sulfur elements.