Preparation of Spherical and Balloonlike Calcium Phosphate Particles from Forced Hydrolysis of Ca(OH)2-Triphosphate Solution and Their Adsorption Selectivity of Water

摘要

The effects of addition of HCl on the formation of monodispersed spherical calcium hydroxyapatite (Hap) particles from the forced hydrolysis reaction of Ca(OH)2-triphosphate (tripolyphosphate, tpp: P3O_(10)~(5-)) mixed solution were investigated. The fairly uniform spherical particles were formed at concentration of HCl (abbreviated as [HCl]) of 8-12 mM, but the particles with various shapes such as very small rodlike and/or large thin platelike were produced at high [HO] region. These fairly uniform spherical particles produced only at [HCl] = 8-12 mM where the solution exhibited almost neutral pH of 6.89-7.24 after aging. The XRD patterns of the spherical particles as prepared were amorphous but they crystallized to β-Ca2P2O7 after the calcining the samples above 600 °C in air. The large amounts of H2O molecules were adsorbed on all the particles after evacuating the samples at 25 °C though they decreased drastically after evacuating the samples above 100 °C, except for the particles precipitated with a high concentration of HCl ([HCl] > 16 mM). The high selective adsorption of H2O was achieved for those amorphous spherical particles and was explained by rehydration of the particles by adsorbed H2O. The cavities formed near the cations by evacuation serve for H2O adsorption but not for N2. The time-resolved TEM experiment revealed that polydispersed spherical particles ranging from 100-300 nm in diameter are formed after aging the solutions for 3-5 h by aggregation of the primary nanometer-sized particles, produced at the first step of the reaction within 2 h, with incorporating calcium and pyrophosphate ions. The calcium and pyrophosphate ions were further deposited on these polydispersed spherical particles and grew to fairly uniform spherical particles with ca. 600-700 nm in diameter. The transparent balloonlike hollow spheres were also formed at 120-140 °C together with solid spheres. This temperature region for producing balloonlike hollow spheres is much wider than those for the system without HCl. This fact was explained by the high acidity of the present system with HCl to dissolve the inside of the solid spheres. Since the inner substances of hollow spheres to penetrate H2O molecules were dissolved, the balloonlike hollow spheres exhibited low adsorption selectivity of H2O.