Infrared extinction properties of nanostructured and conventional particles

Brass flakes and carbon-based particulates are effective obscurants in the infrared (IR) region of the electromagnetic spectrum; however, they are toxic and can cause respiratory problems and environmental concerns. There is a need to develop or identify nontoxic IR obscurants. This research was conducted to determine the potential of nanostructured particles as IR obscurants. Three commercial nanostructured particles were compared with two conventional particles and common obscurants. Experiments involved dispersing a known mass of particles into a particle chamber and measuring the IR transmission through the chamber with a Fourier transform infrared analyzer and the mass concentration with filter samplers. The size distribution of the aerosolized particles was also measured with an aerodynamic particle sizer spectrometer. From the measured data, the mean values of the mass extinction coefficient, σ _m , and volume extinction coefficient, σ _v , for the spectral bands of interest (i.e., 3-5m and 8-12m) were calculated. Results showed that ISO fine test dust, NaHCO ₃ and NanoActive TiO ₂ (for 3-5m) appeared to be the most promising alternatives to brass or graphite flakes. By manipulating the size and/or morphology of these particles, it might be possible to enhance their IR extinction performance.