Influence of Si substitution on the reactivity of α-tricalcium phosphate

•The influence of Silicon on α-TCP hydrolysis was investigated in this article•Silicon reduced α-TCP reactivity by reducing its solubility•Silicon has increased cement's mechanical resistance due to the smaller size of precipitated apatite crystals•The reduction on setting reaction velocity may be due to the formation of a silica-rich layer on the surface of Si-α-TCP

Silicon substituted calcium phosphates have been widely studied over the last ten years due to their enhanced osteogenic properties. Notwithstanding, the role of silicon on α-TCP reactivity is not clear yet. Therefore, the aim of this work was to evaluate the reactivity and the properties of Si-α-TCP in comparison to α-TCP. Precursor powders have similar properties regarding purity, particle size distribution and specific surface area, which allowed a better comparison of the Si effects on their reactivity and cements properties. Both Si-α-TCP and α-TCP hydrolyzed to a calcium-deficient hydroxyapatite when mixed with water but their conversion rates were different. Si-α-TCP exhibited a slower setting rate than α-TCP, i.e. kSSA for Si-TCP (0.021 g·m− 2·h− 1) was almost four times lower than for α-TCP (0.072 g·m− 2·h− 1). On the other hand, the compressive strength of the CPC resulting from fully reacted Si-α-TCP was significantly higher (12.80 ± 0.38 MPa) than that of α-TCP (11.44 ± 0.54 MPa), due to the smaller size of the entangled precipitated apatite crystals.