Optical Properties of Energetic Materials from Infrared Spectroscopy

Abstract

A method of determining infrared (2.5‐ 18 m) optical properties of dielectric, crystalline, particulate solids such as energetic materials was developed based on KBr ‐ FTIR (infrared) spectroscopy. Two techniques (spectral subtraction and baseline shifting ) were used to account for light scattering by the KBr matrix. An independent CO 2 laser‐ spatial e ltering measurement was also developed to check the spectral subtraction approach. The method is demonstrated here for the oxidizer ammonium perchlorate (AP). The Rayleigh ‐ Gans limit of light scattering theory was exploited to establish a relationship between the apparent KBr-pellet absorption coefe cient and the intrinsic AP absorption coefe cient. Dispersion theory was used to determine refractive index from the absorption index for AP. Conventional (nonscattering ) FTIR spectroscopy was also used to determine the absorption coefe cient for the common solid propellant binder hydroxyl-terminated polybutadiene. Nomenclature A = absorbance d = particle diameter fv = particle volume fraction It,0 = intensity, transmitted and incident, respectively n = real part of complex refractive index Ka = absorption coefe cient k = imaginary part of complex refractive index or absorption index