The effect of silicon doping on the transformation of amorphous calcium phosphate to silicon-substituted α-tricalcium phosphate by heat treatment

In the present study, the effects of silicon dopant contents on the phase composition of silicon-substituted hydroxyapatite (Si-HA) powders were investigated. Si-HA as-prepared samples, with varying silicon (Si) dopant contents, were prepared by an aqueous precipitation method. The phase transformation of the as-prepared samples during sintering was also discussed. The analyses of the as-prepared powders confirmed the formation of well-crystallized Si-HA at low Si dopant concentrations ( <= 1.5 wt% Si). Contrarily, silicon-substituted amorphous calcium phosphate (Si-ACE) and amorphous silica formed at high Si dopant concentrations ( > 1.5 wt% Si). Upon sintering at 1000 degrees C, Si-HA (<= 1.5 wt% Si) underwent no phase transformations, whereas Si-ACP ( > 1.5 wt% Si) transformed to biphasic silicon-substituted a-tricalcium phosphate (Si-alpha-TCP) and HA (no additional phases such as beta-TCP, silicocarnotite or CaO were detected). Rietveld refinement on X-ray diffraction patterns was conducted to determine the percentage contents of ACE and differences of lattice parameters between pure alpha-TCP and Si-alpha-TCP. X-ray photoelectron spectroscopy measurements suggested the formation of amorphous silica and decomposition of the Si-ACE to Si-alpha-TCP were correlated. The results confirmed that Si doping led to formation of Si-ACE, which primarily transformed to Si-alpha-TCP upon sintering. The current study highlights a possible account of recrystallization of Si-ACE directly to Si-alpha-TCP at low sintering temperatures. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.