Kyu-Seog Hwang

Sol–gel derived hydroxyapatite films on alumina substrates

Abstract The crystallinity and structural changes of hydroxyapatite films prepared on alumina substrates using a sol–gel process were analyzed by X-ray diffraction (XRD) θ−2θ scans and Fourier transform infrared (FTIR) spectroscopy. Hydroxyapatite films, confirmed by XRD θ−2θ scanning, were obtained by heat treatment at 500 and 700°C from the pre-fired films. A film heat treated at 700°C showed the strongest peak intensities. For a film heat-treated at 500°C, the FTIR and XRD results indicated that carbonate was substituted into the hydroxyapatite lattice.

Effect of poling conditions on growth of calcium phosphate crystal in ferroelectric BaTiO3 ceramics

Recently, ceramic materials have been given a lot of attention as candidates for implant materials, since they possess biologically favorable characteristics for osseointegration. Among them, BaTiO3 (BTO) ceramics are ferroelectric and piezoelectric after poling treatments. However, little or no information is available on the poling condition of BTO and their effect on calcium phosphate (CaP) formation. In this study, the effect of poling conditions on the formation of CaP layer was investigated. It was observed from this study that CaP was formed on negatively charged BTO surfaces. An increase in Ca/P ratio to 1.67 was observed when the poling temperature was increased above the Curie temperature. On positively charged BTO, no CaP layer was observed.

Preparation of Epitaxial Pb(Zr, Ti)O3 Thin Films on Nb-Doped SrTiO3 (100) Substrates by Dipping-Pyrolysis Process

Epitaxially grown Pb(Zr, Ti)O3 (PZT, Pb:Zr:Ti=1:0.52:0.48) thin films were prepared on Nb-doped SrTiO3 (100) substrates by dipping-pyrolysis process with metal naphthenates used as starting materials. The alignments of the films were investigated based on X-ray diffraction (XRD) θ–2θ scans, β scans (pole figures), and asymmetric ω–2θ scans (reciprocal-space maps). Epitaxial films with smooth surfaces were obtained by heat treatment of prefired films at 600°–750° C; a film heat-treated at 750° C showed the strongest peak intensities in the XRD θ–2θ scans. These PZT films were found by reciprocal-space map analysis to consist of the c-axis-oriented tetragonal phase.

Functionally graded Ti/HAP coatings on Ti–6Al–4V obtained by chemical solution deposition

Graded Ti100−x/HAPx (x=0 – 100%) films were prepared on Ti–6Al–4V implants by chemical solution deposition using a titanium-isopropoxide chelated by acetylacetone, calcium nitrate and phosphoric acid as starting materials. Ti/HAP solutions with variable HAP contents from 0 to 100% at 10% intervals were spin coated on the substrates and prefired at 500 °C. X-ray diffraction and field emission-scanning electron microscope analysis showed that Ti/HAP coatings were obtained with a dense interface between coating and substrate by final annealing at 500 °C and higher. The effectiveness of the functionally graded HAP/Ti coatings was discussed based on the analysis of the variation of Ca and P contents in simulated body fluid as a function of annealing temperature.

Waste fluorescent glass and shell derived glass-ceramics

We prepared glass-ceramics by using fluorescent glass and waste shell as starting materials to recycle waste fluorescent glass containing harmful Hg to human body and waste shell, and to resolve environmental problems. Pressed specimens after quenching and grinding were heat treated at 800°C, 900°C and 1000°C for 1 h, respectively. β-wollastonite, gehlenite and sodium calcium silicate were observed by X-ray diffraction studies. Surface morphology and chemical composition were evaluated by field emission-scanning electron microscopy and energy dispersive X-ray spectrometer.

Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Abstract Epitaxial and polycrystalline Bi 4 Ti 3 O 12 thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi 4 Ti 3 O 12 may be suppressed by the formation of a titanium-rich phase such as Bi 2 Ti 2 O 7 owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.

Glass-ceramics prepared by waste fluorescent glass

To prepare glass-ceramics reinforced by β-wollastonite, fluorescent glass and calcium carbonate were used as starting materials. β-Wollastonite, gehlenite and sodium calcium silicate were observed by X-ray diffraction analysis, and surface morphology and chemical composition were evaluated by field emission-scanning electron microscopy and energy dispersive X-ray spectrometer.

Formation of highly-oriented and polycrystalline lanthanum nickelate films by a spin coating-pyrolysis process

Abstract LaNiO 3 films were prepared by a spin coating-pyrolysis technique on various substrates using metal naphthenates as starting materials. By X-ray diffraction θ–2θ scan, highly oriented LaNiO 3 films with smooth surface were prepared on SrTiO 3 (100) and LaAlO 3 (012) substrates, while the films on sapphire (0001) and polycrystalline Y 2 O 3 -doped ZrO 2 exhibited random orientation. The highly-oriented LaNiO 3 films on SrTiO 3 (100) and LaAlO 3 (012) showed a good metallic character. In this study, we conclude that lattice-mismatches between films and substrates used affect film properties such as crystallization, surface morphology and resistivity.

Sol-gel derived functionally graded TiO2/HAP films on Ti-6Al-4V implants

Functionally graded TiO2/HAP coatings were prepared on Ti6Al4V implants by sol-gel process using calcium nitrate and phosphoric acid dissolved in ethylene glycol monomethyl ether, and titanium isopropoxide chelated by acethylacetone, isopropanol and water as starting materials. TiO2/HAP coating sols with variable HAP concentrations from 0% to 100% at 10% intervals were orderly spin coated on the substrates and pyrolyzed at 500°C in air. Well-crystallized HAP coatings between coating and substrate confirmed by X-ray diffraction and field emission-scanning electron microscopy were obtained by final annealing at 500°C in argon. In this work, bioactivities of the coating were studied by examining the variation of ion concentration of Ca and P in simulated body fluid after soaking using an inductively coupled plasma-atomic emission spectrometer. Coating surfaces after soaking in simulated body fluid indicated significant morphological changes by field emission-scanning electron microscopy.

Nanocrystalline TiO2 thin films on soda-lime-silica glass by using a titanium naphthenate precursor

Abstract TiO 2 thin films were prepared on soda-lime–silica slide glasses by spin coating-pyrolysis process using titanium naphthenate as a starting material. Precursor films were prefired at 500 °C for 10 min in air and finally annealed at 500, 550 and 600 °C for 30 min in air, followed by rapid cooling. Crystallinity of the TiO 2 films was investigated by X-ray diffraction (XRD) analysis. A field emission-scanning electron microscope and an atomic force microscope were adopted for characterizing the surface morphology and the surface roughness of the TiO 2 films. After final annealing at 550 and 600 °C, the XRD patterns consist of only anatase peak of TiO 2 film. Films annealed at 500 and 550 °C exhibited flat surfaces. On the contrary, with the increase in annealing temperature to 600 °C, the TiO 2 film showed growth of three-dimensional needle-shaped grains. For all samples, high transmittance at visible range was obtained by ultra violet–visible–near infrared spectrophotometer.