Effect of the particle size on tribological properties of nanometer Fe₃O₄ as lubricating oil additives

Surface-modified Fe₃O₄ nanoparticles having an average particle size of 10 nm and 45 nm respectively were prepared by chemical co-deposition method and chemical deposition-oxidation method correspondingly, and tribological properties of the prepared nanoparticles as additives in 32 machine lubricating oils on the improved M-200 tribotester were investigated. Results indicate the Fe₃O₄ nanoparticles both 10 nm in size and 45 nm in size can improve the friction-reducing and anti-wear properties of 32^# machine lubricating oil effectively. But surface-modified Fe₃O₄ nanoparticles used as additives in the lubricating oils show different friction-reducing and anti-wear abilities depending on their particle size. The Fe₃O₄ nanoparticles 10 nm in size have better friction-reducing and anti-wear abilities than those 45 nm in size.