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A model was proposed for describing the observed in vitro release behavior of drugs from porous HAPs. The model consists of three successive stages; during the first stage, the dissolution medium penetrating into the porous HAP, the amount of the drug released is proportional to the square root of release time. During the second stage, after the pores in the HAP are filled out by the dissolution medium, the drug release being proceeded by dissolution into the dissolution medium outside of the HAP, the amount of the drug released is proportional to release time. During the third stage, after the drug concentration is decreased and below the solubility limit of the drug in the dissolution medium, the drug diffusing to the stirred dissolution medium outside of the HAP, the release rate is markedly slowed and the release amount approaches a plateau value.

Dielectric studies in epoxy and epoxy composites, containing different volume fractions of three different dielectric fillers, have been performed using the impedance bridge method for the high frequency region, 102 to 105 Hz, and the d.c. transient current method for the low frequency region, 10−4 to 10−1 Hz. It has been observed that, in the high frequency region, the dielectric constants of the epoxy composites increased with the addition of the dielectric filler and with the increase of the dielectric constant of the filler. The intensity of the β‐relaxation was reduced for the composites compared to an equal volume of epoxy, owing to the decrease in the concentration of the diester segments in the composites. From the low frequency data, the epoxy and epoxy composites behaved more debye‐like with increasing temperature. Also, the dielectric loss factor increased, but the thermal activation energy value to relaxation decreased two to four times in going from the unfilled to filled materials, which was thought to be attributed to Maxwell‐Wagner buildup of interfacial charges at the epoxy/fillers interfaces.

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