The effects of Mg2+ ion on morphology and chemical composition of hydroxyapatite (HAp) were investigated by the use of oxidative decomposition of calcium chelate. When Mg2+ ion was free in the reaction system, the precipitate comprised calcium-deficient (Ca/P molar ratio = 1.46) and carbonate-containing apatite and had a Japanese bladder cherry-like form (polyhedron crystal based on hexagon). When Mg2+ ion was added in the reaction system, however, the crystallinity of the HAp obtained fell and the crystal shape changed to spherical form with increasing of Mg2+ ion content. Further, the precipitate was produced Mg-containing whitlockite when Mg2+ ion was added above conditions of z (= Mg/ (Ca + Mg)) = 0.25.
The lattice constants of HAp, a-axis and c-axis decreased linearly till Mg2+ ion content of 11mol% against Ca2+ ion. The adsorption of Mg2+ ion of 8% on the crystal surface was observed on dissolved the Mg-containing HAp in very dilute HNO3 solution. The substituted limit of Mg2+ ion in HAD structure was 10 mol%.
