Transmission Electron Microscopic Study on the Migration of Ca Ions in Ca-Deficient Hydroxyapatite during Thermal Decomposition

摘要

The migration of Ca ions during thermal decomposition of Ca-deficient hydroxyapatite (Ca-def HAp) involving the formation of beta-TCP was discussed in the present paper. The migration of Ca ions at high temperature was examined by studying the thermal behavior of Sr ions in Sr-substituted Ca-def HAp using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (TEM-EDX). Substitutions of Ca ions in Ca-def HAp by Sr ion were carried out by hydrothermal treatment in Sr(NO_3)_2 solution. The composition of samples obtained by hydrothermal treatment was identified as Ca_(9.27)Sr_(0.27)(HPO_4)_(0.46)(PO_4)_(5.54)(OH)_(1.54). In addition, it was considered that Sr ions would be in Ca(II) site in Sr-substituted Ca-def HAp lattice. Since the thermal behavior of Sr-substituted Ca-def HAp was almost the same as that of Ca-def HAp, the migration of Sr ions in Sr-substituted Ca-def HAp during thermal decomposition could be regarded as the same as that of Ca (II) ions in Ca-def HAp. By TEM and TEM-EDS analysis, it was revealed that Sr ions were detected only in beta-TCP phase after thermal decomposition. Therefore, these results suggested that beta-TCP phase would be formed by the priority migration of Ca(II) ions in Ca-def HAp.