Bone-like crystals were acceleratingly grown in a simulated body fluid on the negatively charged surface of electrically poled hydroxyapatite ceramics, while the crystal growth was completely inhibited on the opposite surface. The poling effect was generalized by the enhanced crystal growth on the poled ferroelectric ceramics of BaTiO3 and CaTiO3.

In the study of the high‐temperature behavior of ceramic hydroxyapatite (HAp), it was found in relation to its ionic conduction properties that HAp underwent partial dehydration of its lattice hydroxide ions. Considering that HAp ceramics are sintered above 1200°C without destruction of the apatitic structure, the dehydration was interpreted as an unstable phenomenon of aging. The evolution of instability of dehydration was reflected in the time‐dependent characteristics of conductivity, which exhibited up‐and‐down change of 103 S·cm−1 above 700°C. The conduction was proved purely protonic by measurements of a hydrogen concentration cell, and it was noted that the protonic conductivity was increased to a high value of 10−3 S·cm−1 at the initial stage of the aging. The aging phenomenon was demonstrated to be reversible in the deuteration of fully aged HAp; the uptake of OD− inside the specimen was confirmed by infrared spectroscopic analysis after exposure to deuterium oxide vapor. Based on those results, a conduction model was proposed consistent with the aging phenomenon. The present study also showed the importance of the supply of H2O vapor to the ambient during sintering, for the lattice hydroxide ions of ceramic HAp were considerably dehydrated in sintering in air at high temperatures.

No abstract

No abstract