An experimental investigation into the elemental composition of several different automobile tire brands was undertaken to determine whether a distinctive chemical signature exists for each brand or type. Two different X-ray spectroscopic methods were employed in the analysis: Total Reflection X-Ray Fluorescence (TXRF) and Electron Dispersive Spectroscopy (EDS). Coupled with a Scanning Electron Microscope (SEM), EDS is an effective method for identifying elements on the surface of tire samples and generating relative elemental ratios. Our current project represents the first application of TXRF to the quantitative elemental analysis of tires. Use of TXRF allows precise quantification of the concentrations for Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, Br, and Pb in a homogeneous sample since the rubber is digested in nitric acid and a Ga internal standard is added. This constitutes a significant improvement over EDS, which supplies only relative concentrations of the elements in the top 1-2 µm of the sample. The results of the tests showed that each of the analyzed tire brands does indeed have a unique elemental composition, and that sulfur and silicon may prove most useful for differentiation between brands. An important application of these results is that the potential exists for analyzing skid marks left by a vehicle at a crime scene to help identify the make of tire.

Quantitative elemental analysis of tires with x-Ray spectroscopy

251st National Meeting (2016)

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