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Thermal Instability and Proton Conductivity of Ceramic Hydroxyapatite at High Temperatures
Author(s) -
Yamashita Kimihiro,
Kitagaki Kazuhisa,
Umegaki Takao
Publication year - 1995
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1995.tb08468.x
Subject(s) - ceramic , ionic conductivity , conductivity , materials science , sintering , dehydration , oxide , hydroxide , hydrogen , ion , dissociation (chemistry) , thermal conduction , mineralogy , chemical engineering , chemistry , inorganic chemistry , composite material , electrolyte , metallurgy , biochemistry , organic chemistry , electrode , engineering
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 10 3 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 H 2 O vapor to the ambient during sintering, for the lattice hydroxide ions of ceramic HAp were considerably dehydrated in sintering in air at high temperatures.