Yootaek Kim

Effect of source gas composition on the synthesis of SiCC functionally gradient materials by CVD

Abstract SiC C composite layers with various compositions were deposited on graphite substrates by chemical vapor deposition. The effects of the C [C + Si] and H 2 [C + Si] ratios in the source gas on the composition, growth rate, preferred orientation and morphology of the deposited layers were studied. It was revealed that the C [C + Si] as well as H 2 [C + Si] ratios in the input gas affected the carbon content of the deposited film. SiC C functionally gradient materials (FGMs) were prepared on the basis of conditions established by the deposition of the SiC C mixed phase. It turned out that the CH4SiCl4H2, C3H8SiCl4Ar and C3H8SiCl4ArH2 systems were suitable for the deposition of SiC-rich layers, C-rich layers and layers in between, respectively.

Carbonation of coal fly ash for construction materials

Carbon dioxide (CO2) could be stored in the form of Ca and Mg compounds including alkaline earth metal by carbonation. The possibility of CO2 storage was tested by using desulfurized ash from fluidized bed type boiler as raw material. Autoclave was used for maintaining the reaction pressure and temperature for the carbonation. The analysis of weight change rate, XRD, and TG/DTA proved that more than 15 % of carbonation rate was obtained under 10 kgf/cm 2 and 120 o C-10 min.

Dielectric properties of (Pb0.4Ca0.6)((Fe0.5Nb0.5)1−xTix)O3 ceramics at microwave frequencies

Abstract Microwave dielectric properties of (Pb0.4Ca0.6)((Fe0.5Nb0.5)1−xTix)O3 system have been investigated as a function of the amount of Ti+4 substitution (0.01 ≤ X ≤ 0.15). The dielectric constant was increased with increase of Ti content and the Qf showed a maximum value 8200 GHz at x = 0.1, then decreased with Ti content. The temperature coefficient of resonant frequency (TCF) can be adjusted from negative value of-14 ppm/°C to positive value of +21 ppm/°C with Ti content. This change could be explained by the change of tolerance factor with increasing Ti content. Typical value of K = 91, Qf=8100GHz and TCF = +7ppm/°C were obtained for X = 0.1.

Property enhancement of lightweight aggregate by carbonation processing

The mechanical property enhancement was studied using fly ash produced from fluidized bed type boiler in power plant, which contains a lot of Ca component being used to carbonate for fixation in the lightweight aggregates made of cement and some portion of fly ash as a cement substitution under the supercritical condition. Specimens having various fly ash substitution rates and curing periods were carbonated under the supercritical condition at . The weight change rate, carbonation rate by TG/DTA analysis, 1% Phenolphthalein test, specific gravity and mechanical compression strength test were performed to observe the mechanical property enhancement of the cemented materials after carbonation under the supercritical condition and to make sure those could be classified as lightweight aggregates having specific gravity under 2.0.

Dependence of microwave dielectric properties on bond valence in (Pb1-xCax)(Fe0.5Nb0.5)O3 ceramics

Abstract Dielectric properties of (Pb1-xCax)(Fe0.5Nb0.5)O3 (0.55≤×≤0.64) have been investigated at microwave frequencies. The dielectric constant was decreased with the increase of Ca content and the Qf showed a maximum value of 9000(GHz) at x=0.62, and then decreased. The decrease of bond valence with the substitution of Ca caused the deviation of observed dielectric polarizability from the calculated one. The temperature coefficient of resonant frequency (TCF) can be adjusted from a negative value of-12.0 ppm/°C to a positive value of +3.4 ppm/°C with the increase of Ca content. This result was due to the increase of tolerance factor with Ca content. Typically, K of 77, Qf of 9000 (GHz) and TCF of-9 ppm/°C were obtained in the (Pb1-xCax)(Fe0.5Nb0.5)O3.

Properties of non-cement mortars with small addition of alkali activator using fly ash and fused waste slag

Recently the world wide efforts reduce occurrence of CO ; global warming main reason. The aim of this study is to improve recycling rate of the fly ash (FA) and fused waste slag (FWS) from the power plant and to carbonate under supercritical condition (40 C, 80 kgf/cm pressure, 60 min) for CO fixation. Specimens of mortar with various mixing ratios of FA, FWS (from 100:0 to 20:80 in 5 steps of 20 % reduction each time), distilled water and 3 M NaOH alkali activators were prepared. As a result, the proportion of weight change ratio increases with CaO content, to 12 % after carbonation under the supercritical condition. There is difference of compressive strength between the carbonated and the alkali activator mortar specimens. The stabilization of CO fixation through carbonation which could confirm the applicability of the eco-friendly materials without loss of compressive strength.