Kyung Nam Kim

Synthesis and Characterization of Nano-Size CoAl2O4 Spinel Powder Using Sol-Gel Process

Nano-size CoAl 2 O 4 spinel powders were synthesized by the sol-gel process. Co(NO 3 ) 2 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O and C 6 H 8 O 7 ·H 2 O were used as precursor materials. The formation of CoAl 2 O 4 crystals occurred when the precursors were calcined at 400°C in air for 1 h. Homogeneous CoAl 2 O 4 spinel powders with a particle size of∼88.3 nm and with a specific surface area of ∼69.2 m 2 .g -1 were obtained. The gel formation, microstructure and optical properties of the CoAl 2 O 4 spinel powders were characterized by TG-DTA, FT-IR, XRD, SEM, BET and UV-Vis. techniques.

Sol-Gel Derived TiO2 Coating for Chemical Protection of Stainless Steel

Sol-gel coatings of TiO2 have been prepared from TiO2 sol and deposited by a dip-coating technique on 316L stainless steel sheets to study their electrochemical behavior in corrosive solutions. The influence of the coatings on the chemical corrosion of the substrate was evaluated by potentiodynamic polarization curves in different aqueous NaCl solution at 25°C. Comparative tests were performed on uncoated one. The thickness of the TiO2 coatings varied from 0.5~0.8 µm. The values of the electrochemical parameters allow for an explanation of the role of the TiO2 films in the increased resistance of stainless steel against corrosion in moderately aggressive environments.

Effective of SiO2 Addition on the Self-Cleaning and Photocatalytic Properties of TiO2 Films by Sol-Gel Process

Thin films of various composition in the system of TiO2•SiO2 have been fabricated by the sol-gel process using Si(OC2H5) and Ti(OC3H7i)4 as precursors. TiO2•SiO2 films were formed on the glass substrate by spin-coating technique and heated at 500°C for 1 h. The relationship between hydrophilicity, photocatalytic properties and self-cleaning property with SiO2 addition and UV light irradiation were investigated. Photocatalytic activity of TiO2•SiO2 films showed decomposition of ~97% of acetaldehyde in 2 h and a water contact angle of ~10°. TiO2•SiO2 films can have more hydrophilic activity and less photocatalytic activity by increasing of SiO2 addition. XPS measurements revealed that the amount of organic compounds adsorbed on the films decreased with the UV light irradiation and SiO2 addition, because of the increased of both OH group contents in films and decomposed organic contaminants of the films surface.

Properties of Cement Paste Using Mine Tailing and Polymer Materials

In this study, mine tailings obtained in a region near to Youngwol Sangdong(Korea) was used to investigate the contamination of heavy metal ions. Some amount of mine tailings and lignin(AE agent) were added in the general cement pastes, of which the compressive strength and leaching rate were investigated. X-ray fluorescence analysis shows that the major constituents of mine tailings are 56.9wt% of SiO2, 10.8wt% of Fe2O3, 11.2wt% of CaO and 11.4wt% of Al2O3, and the major phases are quartz and calcite. In the content of heavy metal ions, the concentration of As ion is the highest as 257.261mg/ℓ. When mine tailings and lignin were added in cement pastes, the compressive strength was higher in the cement pastes adding only lignin. Lignin addition significantly improved the compressive strength of cement pastes by approximately 15% when being cured in distilled water. The compressive strength was lower in the cement pastes adding mine tailings than in the cement pastes not adding. The leaching rates of Cr, Pb and As ion in distilled water were decreased in the cement pastes adding lignin, compared to in the cement pastes not adding. The leaching rates of all heavy metal ions in the cement pastes curing for 28 days were within the maximum permitted limits in KSLT and EPT method. Therefore, it is thought that mine tailings can be used as an ecological material.

Effects of Eu2+, Dy3+ Contents and Particle Sizes on the Luminescent Properties of SrAl2O4 Phosphor by the Sol-Gel Process

A green emitting SrAl2O4:Eu2+, Dy3+ phosphor with high brightness and long afterglow was synthesized by the sol-gel method. SrAl2O4: Eu2+, Dy3+ phosphor exhibited broad band extending from 450 to 650 nm and maximum emission spectra peaking at 520 nm. Three excited levels existed, two shoulders were observed at 270 and 330 nm in addition to the maximum at 360 nm on the excitation spectrum. After the removal of excitation light, the excellent after-glow characteristic of the phosphorescence was obtained as a result of low decay time, although the after-glow intensities of phosphor varied exponentially with the time.

Improvement of Corrosion Resistance of Stainless Steel by ZrO2-SiO2 Sol-Gel Coatings

ZrO2-SiO2 coatings deposited on 316 L stainless steel were prepared to protect chemically the substrates by sol-gel process using Zr(OC3H7 n)4/Si(OC2H5)4 as precursors. The influence of the ZrO2-SiO2 coatings on the corrosion resistance of the 316 L stainless steel was evaluated with the potentiodynamic polarization curves in deareated 15% H2SO4 solutions at 25, 40 and 50 °C . Comparative test was performed on uncoated one. The values of the electrochemical parameters explain how. ZrO2-SiO2 films increase the resistance of stainless steel against corrosion.

Synthesis and Photocatalytic Properties of Nano TiO2 Coated on Fly Ash

Nano TiO 2 particles coated on fly ash were synthesized by the precipitation dropping method under various hydrolysis conditions in order to develop the low-price photocatalyst. The photocatalytic properties of TiO 2 coated on fly ash have been investigated. About 10 nm anatase TiO 2 particles and homogeneous precipitated layer were produced on the surface of fly ash under the conditions; pH 6 of the solution, 1.0 ml/min of the addition rate of NH 4 HCO 3 and 1000 rpm of the stirring speed. The crystallinity of anatase was increased with raising heating temperature and anatase was changed to rutile by heating at 800°C. The photocatalytic decomposition of acetic acid was affected by both the morphology and the crystallinity of precipitated TiO 2 particles.

Synthesis of Calcium Carbonate from Calcium Chlorine Solution Using Homogeneous Precipitation Method

Calcium carbonate(CaCO3) was synthesized from aqueous CaCl2 solution, using the homogeneous precipitation technique, which uses the hydrolysis of urea. The effects of reaction conditions on the morphology of CaCO3 were examined at 50-90°C. Particle size of CaCO3 decreases, as the concentrations of urea and [Ca2+] are increased. Calcite is produced more, as the concentration of [Ca2+] is increased. Method to stir the reaction solution affects significantly the particle size and morphology of CaCO3. Uniform needle-like aragonite particles were obtained, when left at 90°C for 4hours without stirring.

Synthesis of Calcium Carbonate Particles Modified by Coating with Nickel Precursor

CaCO3 powders were prepared by the homogeneous precipitation method using CaCl2, urea as the starting materials. Uniform CaCO3(calcite, aragonite, vaterite) powders were obtained by various conditions. The surfaces of CaCO3 powders were modified by coating them with a lithium precursor using two different precipitation techniques: homogeneous decomposition of precipitating agents(urea, NaHCO3, NH4HCO3) and forced hydrolysis in pure water. Selecting the Ni(NO3)26H2O and urea(or NaHCO3, NH4HCO3) as Ni-source and precipitating agent respectively, the NiO could be uniformly coated on the CaCO3 powder in the aqueous system. The coating NiO layer dominated the surface properties of the coated lime powders. Calcination of these nickel hydroxide crystals in air at 500°C transformed them into NiO.

Effect of Solvents on Cadmium-Doped Zinc Oxide Nanoparticles Synthesised by Sol-Gel Technique

In this study, a comparative investigation of the effect of two solvents on cadmium-doped zincoxide (Cd-ZnO) nanoparticles synthesized via the sol-gel method is presented and discussed. Zinc acetate was used as the precursor with ethanol and methanol as solvents, and cadmium nitrate tetrahydrate was used as the cadmium dopant source. The properties of the synthesized ZnO nanoparticles were examined by XRD, SEM, TEM,TG-DTA and UV-vis spectroscopy (UV-vis). It was found that the crystallite sizes of the ZnO nanoparticles ranged from 35 to 50nm and had spherical shapes, and that the particle size decreased with Cd doping. Consequently, absorbance spectra showed that the Cd-doped ZnO nanoparticles extended the light absorption properties of the material into the visible region. Furthermore, the ZnO nanoparticles synthesized with ethanol had a relatively smaller sizethan methanol which resulted in higher absorbance of ZnO synthesized with ethanol than methanol.