ESR Study on Sintering Process of Hydroxyapatite Using Manganese Ion for Marker

Part I. Effect of Firing Temperature

Abstract

This study examined the sintering process of hydroxyapataite (HAp) by measuring the electron spin resonance (ESR) signal intensity of Mn²⁺ naturally present as an impurity in synthesized HAp. For HAp, the ESR signal of Mn²⁺ appeared above 950℃, whereas for Li₃PO₄^- added apatite (Li-HAp) the signal appeared at 750℃. The intensity of ESR signal of HAp and Li-HAp increased linearly with increases in the firing temperature. This finding suggests that Mn²⁺ of HAp could diffuse to sites responsible for the spherical symmetry field shown in an ESR signal, indicating that other lattice ion species could diffuse as well. This sintering behaviour shown by ESR was the same as that measured by thermo mechanical analysis (TMA).
Thus far, the sintering process of HAp was measured only indirectly by thermo mechanical analysis (TMA), but ESR measurement can trace the behavior of the ion directly, and can elucidate the mechanism of sintering.