Oxidative stability and thermal performance of ester based lube oil with lithium salt additives

Abstract

In the present study, the performance of bis(trifluoromethylsulfonyl)amine lithium (LiTFSI) and lithium tetrafluoroborate (LiBF4) salts as a novel lubricant additive was assessed. The oxidative stability of ester based lube oil (L2) when mixed with LiTFSI and LiBF4 (1.0 and 5.0 mass%) was estimated by calorimetric techniques combined with the thermokinetic model. A significant improvement in the viscosity index by 8.0% was observed when 5.0 mass% LiTFSI was used. Thermogravimetric analysis revealed two major mass loss steps between 98.0 and 336.0 °C and 292.0 to 454.0 °C at different heating rates. The chemical composition of treated samples revealed the formation of octatriacontyl pentafluoropropionate complex, which could be responsible for the increase in thermal stability of L2. The estimated average value of apparent activation energy (Ea) of L2 was 82.5 kJ·mol−1. The 5.0 mass% LiTFSI sample had the highest oxidative stability, and the kinetic models revealed that the Ea was 121.1 kJ·mol−1. The thermal performance of lubricant oil could be improved by increasing the concentration of Li salt additives up to 5.0 mass%.