Investigation of tribological mechanisms of a boron additive in lubricants and fuel enhancer

Sammanfattning: The effect of using a boric acid based additive in lubricants and fuel enhancers was investigated in this study. Experiments were performed in a reciprocating and a continuous sliding ball-on-disk test equipment. Different oil types and temperatures were used. The aim of the experiments was to provide information about how these boron containing lubricants work in terms of chemistry and tribology. The surfaces after tribological contact were analyzed with Light Optical Microscopy (LOM), Vertical Scanning Interferometry (VSI), Scanning Electron Spectroscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). The boric acid based additive and the temperature used affected both the friction and wear. A higher oil temperature resulted in wider wear tracks. Oil with boron additive seemed to lower the friction coefficient at temperatures above 50 °C, compared to the same oil without boric acid; the reference oil. The tests also indicated that friction coefficients as low as 0.05 can be achieved by using a boron additive layer on the disk surface together with PAO-oil. Tribofilms containing Zn, P, S, Mg and O were formed in the wear tracks at high temperatures for both the reference oil and oil with boron additive. Oxidized regions were found in the tracks created from tests at 25 °C. Tests with oil containing boron additive resulted in lower Zn concentrations in the tracks, which is an indication that the boric acid based additive hinders the formation of these Zn rich tribofilms. To summarize, both oils and fuel enhancers with boric acid can obtain lower friction coefficients compared to those without this additive. The role of boric acid in the tests performed, both regarding the tribology and chemistry, is not yet fully understood and more chemical investigations are needed.