PNNL

Abstract

Titanium dioxide (TiO2) particulates are known to exhibit different visible and infrared optical properties compared to the bulk material, showing strong dependence on particle size and morphology. In this study, the optical properties, sizes, and morphologies of TiO2 particles from two different sources (nano and fine) having a) nominally different particle sizes and b) various crystal polymorph mixture fractions are compared using a combination of single particle mass spectrometry, optical spectroscopies, and aerosol characterization methods. There are two commercial products, “nano” and “fine”: The nano sample was found to be largely particles of anatase (88% by mass), while the fine sample was found to consist largely of rutile particles (95% by mass). Two distinct particle morphologies were found in each powder sample and could be separated using an aerodynamic classifier. We find that, for size-selected TiO2, the amount of attenuation of near-infrared (NIR), visible and UV light increases with the fractal dimension of the particle. However, for particles of polydisperse sizes and shape ensembles the optical behaviors are less straightforward to directly correlate to (a combination of) physical parameters.