Extending Applicability of Amino-Functionalized Silica Nanoparticle as Poly-Alpha-Olefin Additive for Different Metal–Metal Sliding Pairs via Secondary Surface-Capping by Polyisobutylene Succinic Anhydride

The tribological properties of lubricants containing the same additives often vary with varying hardness and composition of the frictional parts. This means that, in terms of the effectiveness of lubricant additives, most of current researches using GCr15 steel to assemble the frictional pair could not be directly cited by the moving parts made of other materials. Aiming at verifying if RNS-1A-PIBSA (referring to amino-functionalized silica nanoparticle [RNS-1A] after secondary surface-capping by polyisobutylene succinic anhydride [PIBSA]) is suitable for multiple frictional parts made of different materials with varying hardness and composition, herein we investigate its applicability an additive in poly-alpha-olefin 6 (PAO6) base oil to three types of sliding pairs constructed from GCr15 steel, #45 steel, and ductile iron with much different hardness and composition by SRV-5. A series of analyses of worn surface morphology and composition demonstrate that, independent of the composition and hardness of the frictional pairs, RNS-1A-PIBSA added in PAO6 base oil can form silica deposition film on the rubbed surfaces of the three kinds of sliding pairs, thereby effectively reducing friction and wear. Besides, we also examine the effect of RNS-1A-PIBSA on the thermal stability of the PAO6 base oil, and found the nano-additive RNS-1A-PIBSA can delay the thermal decomposition of PAO6 base oil to some extent, which is favourable for its application in lubrication engineering.