Chapter 6 - Functional transformation of biodiesel soot

Abstract

To improve the tribological behavior of biodiesel soot (BDS) in liquid paraffin (LP), the order of the BDS was increased through thermally oxidized treatment at 500°C, and the oil solubility was then improved through a modification using oleylamine (OLA). The BDS and thermally oxidized oleylamine-modified BDS (T-BDS-OLA) were characterized through various methods, including the use of TG, FETEM, Raman spectroscopy, FTIR, and a zeta potentiometer. The tribological properties and mechanisms of the BDS before and after the thermally oxidized treatment modification were investigated using a ball-on-disc reciprocating tribometer, FESEM, 3D laser-scanning microscopy, and Raman spectroscopy. The results showed that T-BDS-OLA has a higher degree of order than the BDS, with an onion-like microstructure. BDS and T-BDS-OLA can both improve the antifriction and antiwear properties of LP at a soot content 0.1–0.4 wt%, and T-BDS-OLA in LP shows better antifriction and antiwear properties than BDS. The tribological mechanisms can be attributed to both types of soot acting as spacing and roll bearing between the friction surfaces. In addition, the exfoliated graphitic sheets from T-BDS-OLA can form a carbon lubrication layer providing easy sliding. Additionally, we prepared nitric acid-treated BDS (NA-BDS) as additives in H2O and NA-BDS modified with oleylamine (NA-BDS-OLA) as additives in LP. The results showed that NA-BDS and NA-BDS-OLA are carbon onion-like, with a size of 35–40 nm, and when used as additives can effectively strengthen the antiwear and friction-reduction properties of H2O and LP, respectively. The tribo-mechanisms were attributed to the fact that these soot particles can serve as spacers and ball bearings between the rubbing surfaces. Moreover, exfoliation under high load is a result of the formation of a graphitic layer allowing easy shearing. Furthermore, the lubricity and lubrication mechanisms of the modified biodiesel soot in water are discussed in detail. The antifriction and antiwear properties are significantly improved after adding mass fraction of 0.2% thermally oxidized biodiesel soot (TO-BDS) in water. The main reason for this is that TO-BDS can act as a bearing during the friction process and water containing TO-BDS is more facile than water in forming a lubricating film, since the friction pairs are more wettable for water containing TO-BDS in comparison with water. In addition, friction and wear can be reduced due to friction induced by the exfoliating graphitic sheets of TO-BDS.