Please use this identifier to cite or link to this item: doi:10.22028/D291-24691
Title: Sol-gel-derived hydroxyapatite powders and coatings
Author(s): Tkalcec, Emilija
Sauer, Markus
Nonninger, Ralph
Schmidt, Helmut K.
Language: English
Year of Publication: 2001
OPUS Source: Journal of materials science. - 36. 2001, 21, S. 5253-5263
SWD key words: Sol-Gel-Verfahren
DDC notations: 620 Engineering and machine engineering
Publikation type: Journal Article
Abstract: Hydroxyapatite (HAP) and tri-calcium phosphate (TCP) powders and coatings with a Ca/P molar ratio from 1.56 to 1.77 were prepared by the sol-gel technique using calcium 2-ethylhexanoate (Ca(O2C8H15)2) and 2-ethyl-hexyl-phosphate as calcium and phosphorus precursors, respectively. The structural evolution and phase formation mechanisms of HAP and tri-calcium phosphate in calcined powders and coatings on Si wafer and Ti-alloy substrates (Ti-30Nb-3Al and Ti-5Al-2.5Fe) were characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The elimination of organics was studied by differential thermal analysis (DTA) and thermogravimetry (TGA). Two different formation mechanisms of crystallization are proposed. In sols with Ca/P ≤ 1.67, β-tricalcium phosphate is formed as the major phase and hydroxyapatite as a minor phase by calcination at 700°C. At 900°C these phases react to form AB-type carbonated hydroxyapatite (Ca10—2x/3[(PO4)6—x (CO3) x ][(OH)2—x/3—2y (CO3) y ]). A release of CO2 substituting PO4 3— occurs between 900°C and 1100°C yielding carbonate apatite, Ca10(PO4)6[(OH)2—2y (CO3) y ], whereas CO2 substituting OH— groups in the apatite structure is released above 1200°C. In sols with Ca/P ≥ 1.70, rather than carbonate apatite, B-carbonated hydroxyapatite Ca10—2x/3[(PO4)6—x (CO3) x ](OH)2 is formed, which subsequently decomposes into HAP and CaO above 1200°C. The optimum sintering conditions for coatings on Ti-alloys are found to be 600°C for 10 minutes, since, at higher temperature, oxidation of titanium and the formation of rutile (TiO2) occur. Dip coating and sintering in two cycles yielded a homogeneous and dense coated film with a thickness of 250 nm.
Link to this record: urn:nbn:de:bsz:291-scidok-30139
Date of registration: 27-Oct-2010
Faculty: SE - Sonstige Einrichtungen
Department: SE - INM Leibniz-Institut für Neue Materialien
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