EFFECTS OF YTTRIUM AND SODIUM ADDITION ON PREPARATION AND HUMIDITY SENSITIVITY OF POROUS APATITE CERAMICS

Abstract

Sodium yttrium calcium-oxyhydroxyapatites powders with compositions of {[Ca_9.98-0.9xY_0.9xNa_0.02](PO₄)₆[(OH)_1.98-0.9xO_0.9x_??__0.02], x=0-1.0 (here _??_ denotes vacancies at OH lattice sites} were synthesized by the wet process. Porous (Ca, Y, Na)-Ap (here Ap denotes apatite) ceramics having apparent porosities of around 33% were prepared at high temperature under steam flow. On the basis of the results of X-ray diffraction, all the obtained ceramics exhibited almost single-phase (Ca, Y, Na)-Ap with hexagonal structure. The impedance for all samples linearly changed from 10⁶ to 10⁴Ω at 50°C in the humidity range of 40-95%RH. Apatites produced by substituting Y³⁺ and Na⁺ for Ca²⁺ in apatite structure showed an excellent conductivity. This is attributed to both ordinary protonic conduction caused by the self-dissociation of physically adsorbed water and another conduction caused by OH vacancies introduced by substituting Y³⁺ and Na⁺ for Ca-sites.