Surface Spectroscopic Examination of Diesel Particulates—A Preliminary Study

Preliminary studies on the use of combined surface analytical techniques such as X-ray Photoelectron Spectroscopy (XPS or ESCA), Auger Electron Spectroscopy (AES), Secondary Ion Mass Spectrometry (SIMS) and Ion Scattering Spectrometry (ISS) to probe the surfaces of diesel particulates are presented. Studies of two different particulate systems are reported. Results of the first study show common chemical forms associated with the surface of particulate emission. Oxygen, sulfur and nitrogen in various chemical states are seen on the surface of a carbonaceous-graphitic (pyrolytic) center. These elements are postulated as organically bound surface segregated species. Observation of particles extracted for routine adsorbed organic analysis by gas chromatography show that nitrogen and sulfur compounds are left behind, along with residual organics. Trace metals were not seen on any sample. The second study involves samples collected under different running speed conditions of a diesel engine. Typical analytical procedures for surface examination by the above techniques were used to monitor the forms and amounts of elements present. Data are shown to support the applicability of these techniques to a study of source particulate emission, and the unique results obtainable.