Three-Dimensional Chemical Analysis with Synchrotron Tomography at Multiple X-ray Energies: Brominated Aromatic Flame Retardant and Antimony Oxide in Polystyrene

Synchrotron X-ray tomography is used to image, at 3.34 (mu)m resolution, a mixture containing high-impact polystyrene (HIPS) and a two-component flame retardant, a brominated phthalimide dimer (Saytex BT93), and a synergist, antimony oxide (Sb2O3). Complete tomography data sets were acquired at seven X-ray energies in the range of 12-40 keV, closely spanning Br and Sb 1s electron binding energies at 13.474 and 30.491 keV, respectively. Data acquisition required 8 h. Quantification is done for a representative subvolume of 0.582 mm3 containing 2503 cubic volume elements (voxels) which is fitted to a model for X-ray voxel linear attenuation coefficient, yielding the three-dimensional concentration distribution of the flame retardant and the synergist. With successive thresholding, a particle size distribution algorithm yields regions of low flame retardant concentration-a potential safety concern-and regions of excessively high flame retardant concentration-a waste of an expensive product