Calculation of the Effective Absorption Coefficient in Multi‐Phase Powders

Abstract

A calculation of the effective absorption coefficient μ e f f in multi‐phase powders is presented. Characteristic in the calculation is, that the distribution function of the grains is similar to the correlation function for fluids. It is shown, that for average grain diameters comparable to the inverse of the absorption coefficients, the commonly used formulae for μ e f f (either a linear combination of the contituting μ′s or simply μ for a single component) do not hold. The analytical expressions derived for μ e f f are compared with numerical simulations, which show that, within certain limits, the former give reasonable estimates of μ e f f . The simulations also show, however, that shape effects can have influence on μ e f f which are not included (yet) in the formulae. Also shown is that surface roughness can give effects comparable to those of microabsorption, but can be much more sensitive to particle statistics.