Application of an Effective Medium Theory to Composite Materials with tandomly Dispersed Particles of Specific Shapes

摘要

The Effective Medium Theory used to describe the magnetic properties of randomized heterogeneous materials includes as parameters the intrinsic permeabilities uj of the magnetic particles and an effective shape factor N. This paper compares the experimental variations of N to the theoretical variations predicted by an EMT. It is shown that the effective shape /actor N cannot be seen as the mean shape factor of the composite components. The values of N belong to the range ]0,l/3[, and are strongly correlated to the permeabilities u. j. In the low concentration range, random distributions of needle-like and flake-like particles both lead to low values for N. The result N=l/3 is obtained in the whole concentration range only in the case of randomly diper-sed spheres. The values of the uj might be kept constant up to a volumic fraction c in magnetic matter equal to 50%, according to previous results we got. The experimental results presented here are well described by this theory up to c=50%.