Composites have been fabricated by compressing polycrystalline brushite mix
ed with a polymer powder into pellets to study the surface activities and p
roton mobilities of acid CaHPO4 . 2H(2)O phosphates (brushite), The electro
chemical properties of such composites are studied using complex impedance
spectroscopy analyses. Two types of surface proton migrations have been obs
erved by following the water content of the samples. The various proton mig
rations through these granular materials and the percolation threshold of t
hese currents are interpreted using various modeling approaches. Three mode
ls are used and compared: the effective medium approximation (EMA), a model
based on the percolation theory, and a semiempirical microstructural elect
rical model. (C) 1998 Academic Press.