Effect of metal-oxide addition on the sintering of beta-calcium orthophosphate

The effect of metal-oxide addition (1 approximately 10 mol %) on the sintering of beta-calcium orthophosphate (beta-Ca(3)(PO(4))(2)) was examined by pressureless sintering at 1070 degrees C for 5 h. The metal-oxide additives used were as follows: (i) monovalent metal-oxides, Li(2)O, Na(2)O, and K(2)O; (ii) divalent metal-oxides, MgO, CaO, SrO, and BaO; (iii) trivalent metal-oxides, Al(2)O(3) and Fe(2)O(3); and (iv) tetravalent metal-oxides, SiO(2), TiO(2), and ZrO(2). The relative densities of the sintered beta-Ca(3)(PO(4))(2) compacts were reduced with increasing amounts of monovalent and divalent metal-oxide additions, except for the case of MgO addition when the relative density remained with increasing amount of MgO up to 4 mol %. In the case of trivalent metal-oxide additions, the relative density of sintered beta-Ca(3)(PO(4))(2) compact was reduced with increasing amount of Al(2)O(3) addition, whereas it was enhanced with increasing amount of Fe(2)O(3) addition and reached 98.7% at 10 mol % Fe(2)O(3) addition. In the case of tetravalent metal-oxide additions, relative densities of the sintered beta-Ca(3)(PO(4))(2) compacts were slightly reduced with increasing amounts of SiO(2) and ZrO(2) additions, whereas no appreciable changes in the relative density were observed with increasing amount of TiO(2) addition.