Mechanochemical Synthesis of Hydroxyapatite with SiO4 Substitutions
M. V. CHAIKINA1, N. V. BULINA1, I. YU. PROSANOV1, A. V. ISHCHENKO2, O. V. MEDVEDKO3 and A. M. ARONOV3
1 Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the Russian Academy of Sciences, Ul. Kutateladze 18, Novosibirsk 630128 (Russia)
2 Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Pr. Akademika Lavrentyeva 5, Novosibirsk 630090 (Russia)
3 NEVZ-SOYUZ JSC, Krasny Pr., 220, Novosibirsk 630049 (Russia)
chaikinam@solid.nsc.ru
Keywords: mechanochemical synthesis, silicate-substituted hydroxyapatite
Pages: 431–443
Abstract
Using the mechanochemical method during 30 min in the planetary mill, we synthesized the samples of hydroxyapatite (HAP) modified with silicate ions in the amount of 0.1, 0.2, 0.4 and 0.8 molar fractions of the ion in HAP at the given molar ratio Са/(Р + Si) = 1.67. As a result of activation in the air medium, hydroxyapatite with the average crystallite size of ~20 nm was formed. The mechanochemically sy6nthesized samples contain carbonate ion substituting the phosphate ion, with the formation of carbonatehydroxyapatite of B type; its amount decreases with an increase in the amount of silicate introduced. Modification of hydroxyapatite with silicate ions is a competing reaction for phosphate substitution with carbonate. Depending on the ratio of silicate to carbonate amounts in hydroxyapatite structure, the mechanism of substitution changes. In the case of predominance of the carbonate ion in apatite, the composition corresponds to the general formula Сa10 - (x - y)/2(PO4)6 - (y + x)(SiO4)y(CO3)x(OH)2 (х > у). In the case of the equal number of substituents (х = у) silicate-substituted hydroxyapatite has the stoichiometric composition with the general formula Ca10(PO4)6 - (y + x)(SiO4)у(CO3)х(OH)2. In the case of predominance of silicate ion (х < у), charge compensation occurs due to the formation of vacancies in the positions of (ОН)- groups: Ca10(PO4)6 - (y + x)(SiO4)у(CO3)х(OH)2 - у. After annealing the samples, the silicate group occupies the positions of phosphate ion in hydroxyapatite structure with the formation of vacancies in the positions of (ОН)- group; the composition is described by the general formula Са10(PO4)6 - x(SiO4)x(OH)2 - x х.
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