α-tricalcium phosphate synthesis from amorphous calcium phosphate: structural characterization and hydraulic reactivity

Abstract

In the present study, amorphous tricalcium phosphate (TCP) has been synthetized by a wet route to obtain low temperature -TCP at 650 °C (LT-TCP) and compare its structural, physical-chemical and thermal properties with those of -TCP obtained by the conventional solid-state reaction method at 1400°C (HT-TCP). Even if no significant differences were observed concerning the values of lattice parameters measured by Rietveld refinement, LT-TCP presented lower crystallinity and higher crystal strains than HT-αTCP. The reactivity in water of the -TCP obtained by the two different routes was assessed. Both raw samples appeared relatively inert in solution and did not favour the nucleation of calcium deficient apatite (CDA); the LT-TCP and HT-TCP were converted into apatite only after milling. The mechanical process leads to a decrease in crystallinity and the formation of an amorphous phase, which is supported in this work by Raman spectroscopy.The faster rate of conversion of milled LT-TCP compared to HT-TCP can be assigned to its higher specific surface area, lower crystallinity and higher residual crystal strain; these favour the dissolution of the -TCP phase. Finally, the setting properties of -TCP based bone cements were compared regarding their synthesis route. Although the synthesis route does not significantly affect the setting times, the kinetic of conversion into CDA was faster for LT-TCP than for HT-TCP. Thus, the modulation of the dissolution rate of -TCP based cement determined by the preparation route and the grinding process allows control of the overall setting reaction.

The influence of silane coupling agents on the properties of α-TCP-based ceramic bone substitutes for orthopaedic applications

“…Generally, the specic surface area of a-TCP ranged from 2.0 to 11.0 g m −2 and depends on many factors, such as synthesis, processing routes and presence of modiers. 35,36 The decreasing value of the specic surface area of silane coupling agent-modied powders is due to the connement of micropores in the powder grains with the silane coupling agents. The silane coupling agents form a thin layer on the surface of the grains, which reduce the overall surface area of calcium phosphate powders.…”

Strontium-Substituted α-TCP: Structure, Stability, and Reactivity in Solution

“…The structure consists of calcium and phosphate (PO 4 ) ions arranged in columns along the [001] direction: C–C columns containing just Ca cations and C–A columns containing both Ca cations and PO 4 anions . The most common methods of synthesis of α-TCP are by the solid-state reaction of solid precursors at high temperatures and by the heat treatment of a precursor with a Ca/P molar ratio of 1.5. ,, Thermal treatment of β-TCP at temperatures higher than 1130 °C is the most direct route to get α-TCP . The transformation from β to α-TCP involves a significant reorganization of the crystal structure, which justifies the great amount of energy required for the transformation.…”