Papers by Author: H. Ivankovic

Abstract: Scaffold of hydroxyapatite for further tissue-engineering application was produced by hydrothermal treatment of cuttlefish bone originated aragonite at 200°C. Aragonite (CaCO3) monoliths were completely transformed into hydroxyapatite after 48 hours of HT treatment. The substitution of CO3- groups predominantly into the PO4 3- sites of the Ca10(PO4)6(OH)2 structure was suggested by FTIR spectroscopy. SEM micrographs have shown that the interconnected hollow structure with pillars connecting parallel lamellae in cuttlefish bone is maintained after conversion. Specific surface area (SBET) and total pore volume increased and mean pore size decreased by HT treatment.

Abstract: Gels with cordierite stoichiometry, Mg2Al4Si5O18, were prepared by sol-gel technique using three different starting aluminum sources: nano-sized γ-Al2O3, aluminium nitrate nonahydrate and Al-sec-butoxide, as aluminum sources, using tetraetoxysilane (TEOS) and magnesium nitrate hexahydrate in all three gels as sources for silicon and magnesium. The influence of Al-precursors on formation mechanism and sintering behavior of gels was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and dilatometry. Gels calcined at 700°C were characterized by different specific surface area, pore sizes and different crystallization sequences. For gel with nano-sized γ-Al2O3 α-cordierite was formed at 1220°C through intermediate MgAl2O4 phase. If aluminum was introduced as Al-sec-butoxide μ-cordierite crystallized in two steps (760 and 1070°C) and the transformation μ-cordierite→α-cordierite occurred at 1250°C. When Al(NO3)3·9H2O was introduced as intermediate phase crystallized MgAl2O4 at ~870°C and μ- cordierite at ~950°C. Both phases reacted with amorphous silica forming α-cordierite at ~1210°C. Compacts prepared from gels with aluminum-nitrates and Al-sec-butoxide, respectively, sintered between 700 and 1000°C, whereas the gel derived from γ-Al2O3 sintered in two steps; between 700- 1000°C and 1010 and 1250°C.