title: Growth kinetics of hexagonal sub-micrometric β-tricalcium phosphate particles in ethylene glycol.
abstract: Recently, uniform, non-agglomerated, hexagonal β-tricalcium phosphate (β-TCP) platelets (diameter≈400-1700nm, h≈100-200nm) were obtained at fairly moderate temperatures (90-170°C) by precipitation in ethylene glycol. Unfortunately, the platelet aspect ratios (diameter/thickness) obtained in the latter study were too small to optimize the strength of polymer-β-TCP composites. Therefore, the aim of the present study was to investigate β-TCP platelet crystallization kinetics, and based on this, to find ways to better control the β-TCP aspect ratio. For that purpose, precipitations were performed at different temperatures (90-170°C) and precursor concentrations (4, 16 and 32mM). Solution aliquots were retrieved at regular intervals (10s-24h), and the size of the particles was measured on scanning electron microscopy images, hence allowing the determination of the particle growth rates. The β-TCP platelets were observed to nucleate and grow very rapidly. For example, the first crystals were observed after 30s at 150°C, and crystallization was complete within 2min. The crystal growth curves could be well-fitted with both diffusion- and reaction-controlled equations, but the high activation energies (∼100kJmol(-1)) pointed towards a reaction-controlled mechanism. The results revealed that the best way to increase the diameter and aspect ratio of the platelets was to increase the precursor concentration. Aspect ratios as high as 14 were obtained, but the synthesis of such particles was always associated with the presence of large fractions of monetite impurities.
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland; Technical University Bergakademie Freiberg, Institute for Ceramic, Glass- and Construction Materials, Agricolastraße 17, 09596 Freiberg, Germany.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Galea
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland. Electronic address: marc.bohner@rms-foundation.ch.
authors.forename: Marc
authors.initials: M
authors.lastname: Bohner
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland; ETH Zürich, Department of Materials, Laboratory of Multifunctional Materials, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
authors.forename: Juerg
authors.initials: J
authors.lastname: Thuering
authors.affiliation: RMS Foundation, Bischmattstrasse 12, CH-2544 Bettlach, Switzerland.
authors.forename: Nicola
authors.initials: N
authors.lastname: Doebelin
authors.affiliation: University of Utah, Chemical Engineering, 50 South Central Campus Drive, Salt Lake City, UT 84112-9203, USA.
authors.forename: Terry A
authors.initials: TA
authors.lastname: Ring
authors.affiliation: Technical University Bergakademie Freiberg, Institute for Ceramic, Glass- and Construction Materials, Agricolastraße 17, 09596 Freiberg, Germany.
authors.forename: Christos G
authors.initials: CG
authors.lastname: Aneziris
authors.affiliation: Technical University Bergakademie Freiberg, Institute for Ceramic, Glass- and Construction Materials, Agricolastraße 17, 09596 Freiberg, Germany; EMPA, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Graule
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D003460:Crystallization; D019855:Ethylene Glycol / Q000737:chemistry*; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; C485817:beta-tricalcium phosphate; D019855:Ethylene Glycol
keywords: Bone substitute; Calcium phosphate; Ethylene glycol; Growth kinetics; Reaction-controlled