Modeling Particle Size and Clumping Effects in the IR Absorbance Spectra of Dilute Powders

Abstract

The calculation of the IR absorbance of a powdered crystalline, ionic material, diluted in an appropriate IR-transparent matrix in a known proportion, is in principle possible, provided that the size and shape distributions of the particles, as well as the optical parameters of the bulk material, and those of the matrix, are known, and, in the case of the FT-IR technique, whether absolute calibration is possible, particularly at high absorbance values. In practice, a close match between observed and calculated absorbance is hindered by several factors intrinsic to the sample that are difficult to quantify, such as the degree of crystallinity of the particles and the very common clumping and aggregation of these particles, which produce a serious problem in the determination of the real filling factor of the composite sample. Some remedies to these problems are proposed in this paper and are applied to several well-known materials.