ELECTRON-MICROSCOPIC OBSERVATION OF SOOTS IN USED DIESEL-ENGINE OILS

Actual states of soots in used diesel engine oils were investigated with a transmission electron microscope (TEM) by means of the freeze fracture replica (FFR) method. Most soots disperse in oil as small aggregates of a few particles 20-30 nm in diameter and do not form a chain structure. Sulfur and calcium were observed on the surfaces of the soots, but neither phosphorus nor zinc was detected. In some cases, large aggregates with more than 30 particles were observed. On the large aggregates, phosphorus and zinc as well as calcium and sulfur were detected. Soots sampled from an exhaust gas have a microcrystalline structure of graphite with a lattice distance of 0. 34 nm. However, with soots in oil, the microcrystalline structure was not observed clearly. A mechanism of deterioration of the antiwear property of used diesel engine oils is discussed.