Synthesis and tribological property study of oleic acid-modified copper sulfide nanoparticles

Oleic acid-modified copper sulfide nanoparticles were prepared by means of a surface modification technique in absolute alcohol–distilled water mixed solution. Through varying the mole ratio of surface modifier to copper sulfide, a series of nanoparticles were prepared with the mole ratio of 0.5:1, 1:1, 2:1, 3:1. The friction–reduction and antiwear behaviors of the prepared nanoparticles as an oil additive in liquid paraffin were evaluated with FALEX-6 model four-ball wear tester, and the morphologies of the rubbed surfaces were evaluated with scanning electron microscope (SEM). The results showed that at the concentration of about 0.4 wt.% when the mole ratio of oleic acid to copper sulfide was up to 2:1, the wear scar diameter (WSD) became the smallest, and the antiwear performance was best; when the mole ratio of oleic acid to copper sulfide was up to 1:1, the friction coefficient became the smallest, and the friction reducing performance was best.