Morphology, structure and chemistry of extracted diesel soot—Part I: Transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and synchrotron X-ray diffraction study Mihir Patel a , Cristy Leonor Azanza Ricardo b , Paolo Scardi b , Pranesh B. Aswath a,n a Materials Science and Engineering Department, University of Texas at Arlington, Arlington, TX 76019, USA b Department of Materials and Industrial Technology, University of Trento, Trento, Italy article info Article history: Received 27 September 2011 Received in revised form 6 March 2012 Accepted 9 March 2012 Available online 29 March 2012 Keywords: Diesel soot Synchrotron X-ray diffraction Lubrication Exhaust gas recirculation soot abstract Inclusion of soot in lubricating oil can result in increased wear and decreased lubricity. In this study we have attempted to gain fundamental insight into the morphology, structure and chemistry of diesel soot. Energy dispersive spectroscopy using TEM suggests interaction between lubrication additives and crankcase soot resulting in the presence of C, Ca, S, P, O and Zn. Synchrotron X-ray diffraction indicates the presence of different sulfates of calcium as well as the presence of amorphous zinc based compounds. Raman spectroscopy and selected area diffraction using TEM indicates that the turbostratic structures of the carbon in both are very similar. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Exhaust Gas Recirculation (EGR) is one of the most effective post combustion protocols that heavy-duty diesel engine manu- facturers have adopted as an effort to reduce emission of NOx and to comply with stringent emission norms API CJ 4 imposed by the Environmental Protection Agency (EPA) [1,2]. One of the undesir- able effects of EGR is the accumulation of soot and transfer of highly reactive acidic materials to crankcase oil resulting in increased wear of power train components, piston cylinder and piston rings [3,4]. This puts increasingly greater stress on the functionality of lubrication oil to handle soot accumulation and adverse effect of corrosive products transferred from EGR. This problem is further aggravated by the EPA regulation known as SAPS (Sulfated Ash, Phosphorous and Sulfur) where chemical limits have been imposed on the amount of phosphorous (0.1 wt%), sulfur (0.12 wt%), sulfated ash (1 wt%) [2]. Since phos- phorous and sulfur are major contributors in formation of anti- wear film in engine, their restriction would aggravate the wear of engine components in the diesel engine equipped with EGR protocols. This requires lubricating additives manufacturers to optimize their products to sustain the stringent and conflicting demands of chemical limits of main anti-wear elements while maintaining longer drain interval at the same time comply with EPA pollution norms. Many studies have contributed significantly to understand this problem and various mechanisms have been proposed to explain the soot induced wear of diesel engine components equipped with EGR [1,3–34]. Although these mechanisms have contrasting explanation of the role played by soot to induce wear they have also established that the presence of soot degrades the lubrication oil properties physically and/or chemically. Diesel engines operate under harsh conditions where presence of higher temperature and reactive decomposition products of lubricating oil increase the possibility of interaction between lubricating oil and soot. These interactions with reactive com- pounds might be responsible for adsorption of decomposition product on the soot structure. In addition, there also exists the possibility of modification in crystalline structure of diesel soot. Studies have suggested that three body wear condition are present when soot particles are trapped between two surfaces in relative motion [27]. Hence, it is possible that during three body wear, trapped diesel soot between two rubbing components experience extremely high local temperature and pressure that might induce modification in crystalline and/or amorphous domains of carbonaceous soot. It has also been shown that the higher hardness of soot particle compared to diesel engine component is another factor responsible for increased wear [27]. This higher surface hardness of the soot particles can possibly be due to changes in the turbostratic structure. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/triboint Tribology International 0301-679X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.triboint.2012.03.004 n Corresponding author. E-mail address: aswath@uta.edu (P.B. Aswath). Tribology International 52 (2012) 29–39