Fabrication of Hydroxyapatite Sheet by a Sol-gel Method and Its Ion-exchange Characterictics

Abstract

Fabrication of hydroxyapatite (HAp) sheets was attempted by the sol-gel method. The sol, the starting material, was prepared with 5% sodium alginate solution and sodium diphosphate. The sol sheet was dragged out 0.5-2.0mm thick on a glass plate with a chromatographic sheet maker and subjected to an ion-exchange process in the solution consisting of Ca(CH₃COO)₂ and CaCl₂. The gel sheet, after calcium substitution, was fired at 900-1200°C for 1h. The gel sheet ion-exchanged simultaneously from both sides maintained its shape after firing but became uneven. Therefore, it was tried to produce a flat sheet on an alumina plate by a dip-coating method. The thickness of the sheet was proportional to the number of repeated runs consisting of dip-coating, ion-substituting and firing. The fired HAp can remove Pb²⁺ ions in a strong acidic solution of pH 3 and pH 2 containing Pb²⁺ ions.