SiC coating on various nuclear-grade graphite substrates by chemical vapor reaction

Yootaek Kim 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.5

The dependence of high-temperature oxidation and the thermal shock resistance behavior of α-SiC coated nuclear-grade graphite substrates were investigated at elevated temperatures. The surfaces of three kinds of nuclear-grade graphite substrates were coated with α-SiC by chemical vapor reaction (CVR) at a temperature of 1600 o C and a pressure of 1.3 Pa in a pure polysilicon gas atmosphere. Thermal shock and oxidation resistance tests were performed at 1000 o C and 1300 o C respectively, in which the samples were taken out of a box furnace and directly exposed to air at room temperature. It was found that the initial microstructure of the graphite substrates plays an important role in determining the final thermal properties of the α-SiC coatings when using the CVR method.

Silicon carbide crack healing by chemical vapor deposition

Yootaek Kim 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.5

The combined reactor core and reflector of the very high temperature reactor (VHTR) is supported by a graphite support column composed of several types of graphitic material. Graphite in the VHTR reacts readily with O2, thereby forming CO2. Increasing the resistance of graphite to oxidation is therefore essential to its use as a high-temperature structural material. Conventional silicon carbide (SiC) is widely used as a carbon coating material that is resistant to oxidation. SiC was deposited by E-beam evaporation coating as a functionally gradient material. However, SiC was susceptible to the formation of cracks during thermal shock. These cracks acted as a pathway for the transport of O2 to the graphite substrate. Therefore, this study aimed to heal the cracks via chemical vapor deposition (CVD) and thereby prevent oxidation resulting from the abovementioned cracks. Crack healing was investigated at thermodynamically calculated methane ratios of 0.35-0.55. Micrographs obtained at a methane ratio of 0.55 revealed homogeneously faceted surface structures. A dense SiC coating layer appeared necessary for effective crack healing. Therefore, crack healing was performed at a methane ratio of 0.55 by CVD. In that case, cracks were completely healed by the ~ 0.1-mm-thick chemical-vapor-deposited coating. In contrast, cracks persisted on the surface after crack healing by chemical vapor reaction (CVR). The SiC coating produced via CVD constitutes a promising method for crack healing stemming from thermal shock; this coating is well-suited for use in the VHTR and various semiconductor industries.

Effects of manufacturing conditions on physical properties of integrated gasification combined cycle (IGCC) slag geopolymer

Yootaek Kim 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.3

In this study, we used integrated gasification combined cycle (IGCC) fused slag, a by-product of IGCC, to analyze itsapplicability as a high-strength geopolymer in terms of particle size, alkaline activator concentration, and solid-liquid ratio. We also examined its stability. A planetary ball mill was employed to pulverize the slag for 4, 6, and 8 h so as to adjust theparticle size to a desired value. The results showed that the compressive strength of the geopolymer made of the 6 h pulverizedmaterial and 12 M alkaline activator was the highest (29.8 MPa). In the case of the 8h pulverized material, the compressivestrength of the geopolymer got weaker. Therefore, it was found that an optimal particle size was necessary for strengthdevelopment. When the IGCC fused slag was finely pulverized (average particle size = 128 µm, the strength increased with anincrease in the molar concentration. At 18 M, the maximum strength was 59.908 MPa. A heavy metal dissolution test wasperformed. The specimen’s heavy metal dissolution was detected to be lower than the reference value. Hence, the specimenwas found to be safe. Therefore, if IGCC fused slag with an optimum particle size is used the resulting geopolymer can beapplied as a construction material.

Effect of electric arc furnace (EAF) dust on the formation of artificial lightweight aggregate (ALA)

Yootaek Kim,장창섭,Yunjae Choi 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.1

This study was conducted to evaluate the feasibility of using bottom ash and dredged soil from a coal power plant and EAF dust from the steel industry as primary materials for the production of ALA. The effect of different raw material compositions and sintering temperatures on the lightweight aggregate properties were evaluated. The results indicate that the higher the SiO2 content, the more bloating below 1100 oC. In contrast, ferrous materials were mainly effective for the bloating of ALA above 1100 oC. The optimum EAF dust contents in coal ash mixtures were 10~15 wt.% and artificial lightweight aggregates having an apparent density under 1.0 g/cm3 were produced at 1150 oC~1200 oC in 10 minutes.

A study of the plasticity of lightweight aggregate green bodies including bottom ash

Yootaek Kim,이기강,강승구,Yugwang Ryu,Hyejin Jeon,Junghwan Kim,장창섭,Sung-Gi Lee 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.2

The plasticity of clay-based green bodies including bottom ash(BA) from power plants were investigated. The plasticity indices of clay-base green bodies using Atterberg limits were measured. The usefulness of plasticity indices was confirmed by mapping the applicable forming region and through the actual extrusion process. Possible forming compositions were examined using various contents of water, bottom ash, stone dust, and sewage sludge. The relationship between the properties of aggregates and plasticity of green bodies was also investigated. Suitable compositions for forming aggregates by the extrusion method can be found by measuring the plasticity indices of green bodies and a map of the plasticity indices was matched with the results of actual extrusion process. The properties of aggregates were greatly influenced not only by the raw materials but also by the plasticity of green bodies.

Comparison of thermal shock behavior of SiC coating deposited on graphite substrates by chemical vapor reaction and physical vapor transport

Yootaek Kim 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.5

The thermal shock behavior of α-SiC coatings deposited using the chemical vapor reaction (CVR) and the physical vapor transport (PVT) methods on graphite substrates was investigated. The correlation between the physical properties such as crystallinity, surface roughness, etc. and the thermal shock behavior of the coated specimens was evaluated. Analyses of the SiC-coating layers deposited by CVR and PVT were carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). A better quality of crystal growth was observed on the surfaces prepared by PVT. The surface morphology of the α-SiC-coated substrate obtained by the PVT method was denser than that obtained by CVR. More crystal facets were observed on the surface coated by PVT, which indicates that the crystallinity of the surface coated by PVT is much higher than that by CVR. Judging from confocal laser scanning microscope (CLSM) observation, the surface roughness of the layer coated by CVR looks much smoother than that by PVT. In terms of the thermal shock behavior, the PVT specimen looked more stable as compared to the CVR specimen. The crystallinity and microstructure of the α-SiC-coated surface play an important role in the thermal shock properties of the SiC coatings; the greater the degree of crystallinity and the greater the surface roughness, the more resistant the coating is to thermal shock.

Enhancement of compressive strength of lightweight geopolymers

Yootaek Kim,Minjeong Kim 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.5

For recycling purposes, integrated gasification combined cycle (IGCC) slag and Si sludge were used as the basis for preparing lightweight panels with high compressive strength. The properties of the specimens were examined with the variation in the alkaline activator, addition of frames, addition of aluminum dihydrogen phosphate, particle-size separation of the IGCC slag, and variation in the specimen size by preparing large specimens with different W/S ratios and cutting the specimens at different positions. An optimum specimen with a low density and high compressive strength (8.1 MPa and 0.74 g cm−3, respectively) was acquired from larger specimens (300 × 300 × 100 m3) having various densities and compressive strengths by controlling the W/S ratio and particle size of the IGCC slag. Therefore, it is expected that specimens with both, a low density and high compressive strength, can be obtained by developing and controlling the process factors during the production of lightweight geopolymers.

Porosity-dependent absorption capacity of red tide algae by ceramic absorbers

Yootaek Kim 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.5

Cochlodinium red tides occur over a wide area in South Korea, from the south coast to the east coast, and last from Augustuntil October. The damage to fisheries caused by these red tides amounts to tens of billions per year. Chemical spray,sedimentation, and red clay spray methods can prevent red tides, but the most practical method, the red clay spray method,also has a negative effect on marine ecosystems. Therefore, to protect marine life from a Cochlodinium red tide withoutaffecting the marine ecosystem, six ceramic absorbers were applied to a pontoon system, a type of cage fish farm, to comparetheir absorbing capacity for red tide algae that is dependent on the porosity of the ceramic absorber. This experiment wasperformed to determine which ceramic absorber can effectively prevent red tide penetration. Previous studies have shown thatmost fish die when exposed to 8.0 × 103 cells/mL of Cochlodinium polykrikoides for 8 hrs. From the results of this experiment,the concentration of red tide algae that passed through ceramic absorber D (average porosity 60.3%), was 0.14 × 103 cells/mL. For ceramic absorber L (average porosity of 57.3%) it was 0.18 × 103 cells/mL. These two values were the highest red tideabsorption rates recorded in this study. Even when the average porosity was as low as 34.6%, such as in ceramic absorberK that had a small particle size, a high absorption efficiency of 0.18 × 103 cells/mL was observed.

THERMAL PROPERTIES OF SIC/C FUNCTIONALLY GRADIENT MATERIALS BY CVD

Yootaek Kim,Keun Ho Auh 한국표면공학회 1996 한국표면공학회지 Vol.29 No.5

CO2 Reduction Rate of Photosynthetic Bacteria with Ceramics

Yootaek Kim,Kyongwoo Lee 보안공학연구지원센터 2016 International Journal of Bio-Science and Bio-Techn Vol.8 No.2

To address global warming caused by increased CO2 emissions, many studies on CO2 reduction have been conducted worldwide. In carbon capture and storage (CCS) technology, the mineral carbonation process causes CO2 to react with particular metals or compounds to stably fix CO2. Many relevant studies have been performed on this capture process. Based on research describing photosynthetic bacteria that fix CO2 in the process of producing H2 under light irritation, this study combines ceramics with photosynthetic bacteria to develop a material capable of reducing environmental CO2. To investigate the possible combinations this study conducted experiments on ceramic materials of hardened cement pastes and lightweight aggregates made using waste from the Korean Y power plant. The photosynthetic bacteria Rhodopseudomonas pentothenatexigens AE8-5 was used and cultivated in a standard culturing medium. To examine the CO2 reduction rate, a 165 mL sealable glass bottle was used and CO2 was injected through the rubber lid using a syringe. Ceramic specimens were placed in the medium with the photosynthetic bacteria, and then were cultured in a shaking incubator at 25-30°C, a pH of 7, 6000 lux irradiation, and a shaking rate of 120 RPM. After the injection of the bacteria, gas chromatography-thermal conductivity detection analysis was performed on the gases in the bottles, and the presence of CO2 was confirmed. When 30 g of the ceramic aggregate with a low reaction rate with CO2 was used and the photosynthetic bacteria were irradiated, the CO2 concentration was reduced by ~40%. It is necessary to address the amount of ceramic material used and the shaking friction generated in order for uniform light irradiation when the ceramic is combined with photosynthetic bacteria. The results demonstrated that materials combining photosynthetic bacteria and ceramic are applicable for future studies.