Calculation of the Effective Absorption Coefficient in Multi‐Phase Powders

A calculation of the effective absorption coefficientμ e f fin multi-phase powders is presented. Characteristic inthe calculation is, that the distribution function of the grainsis similar to the correlation function for fluids. It is shown,that for average grain diameters comparable to the inverse of theabsorption coefficients, the commonly used formulae forμ 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 forμ e f fare compared with numerical simulations, which show that, within certain limits, the former give reasonable estimates ofμ e f f. The simulations also show, however, that shape effects can have influence onμ e f fwhich 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.