Dong Yoon Chung

Bio: Dong Yoon Chung is an academic researcher. The author has contributed to research in topics: Ceramic & Stress field. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

X-ray Diffraction Analysis of Residual Stress in Laminated Ceramic

Abstract: The strength of ceramic was improved by lamination by suppressing the propagation of cracks with compressive residual stress in the face layer of the laminate. Hot pressed SiAlON+SiC/SiC/SiAlON+SiC laminate discs were fabricated for tailored residual stress. The residual stress in this laminate was studied by X-ray diffraction (XRD). There was considerable compressive residual stress in the face layer. A Finite Element Analysis (FEA) was performed to support the measured XRD results and to determine the stress field in the laminate. The residual stress measured by XRD had satisfactory agreement with the analytically calculated and FEA values. The measured value by XRD was ?385±20 MPa over most of the face layer. The calculated and FEA values were ?386MPa and ?371MPa, respectively. FEA also showed significantly modified stresses and the maximum tensile stress near the edge region which are possible crack generators in the presence of flaws or contact damage.

Effect of substrate bias on microstructure and properties of Ni–TiN nanocomposite thin films deposited by reactive magnetron co-sputtering

Abstract: The effect of substrate bias variation on structure and properties of the Ni–TiN nanocomposite thin films deposited on Si (100) substrates by magnetron sputtering has been investigated. Deposition has been carried out by reactive co-sputtering of high purity Ti and Ni targets as RF and DC sources, respectively in an atmosphere with Ar:N2 = 1:2. The microstructures of the as-deposited films have been examined using grazing incidence X-ray diffraction and transmission electron microscopy. It has been observed that with an increase in negative substrate bias from 0 to − 80 V, the TiN volume fraction increases from 36 to 50%, whereas the average grain sizes of both Ni (≈ 10–17 nm) and TiN (≈ 6–9 nm) decrease. Moreover, the biaxial compressive residual stress as estimated by sin2ψ technique scales with negative substrate bias. The surface roughness determined using atomic force microscopy appears to be the least in the nanocomposite film deposited with substrate bias of − 60 V. Furthermore, X-ray photoelectron spectroscopy studies have confirmed the formation of oxygen-free stoichiometric TiN in this film. Hardness (≈ 12.6–16.9 GPa), elastic modulus (≈ 208–233 GPa) and scratch-resistance determined by nanoindenter, as well as electrical resistivity (≈ 26–47 μΩ·cm) measured using dc four-probe method, are found to scale with TiN content. An increase in hardness and electrical resistivity with an increase in negative substrate bias is also attributed to a decrease in Ni grain size and an increase in point defect density.

Synthesis and Characterization of CoFe 2 O 4 /SiO 2 using Cobalt Precursors from Recycling Waste Cemented Carbide

Abstract: We report the preparation of nanocrystalline cobalt ferrite, CoFe 2 O 4 , particles using recycled Co 3 O 4 and their surface coating with silica using micro emulsion method. Firstly, the Co 3 O 4 powders were separated from waste cemented carbide with acid-base chemical treatment. The cobalt ferrite nanoparticles with the size 10 nm are prepared by thermal decomposition method using recycled Co 3 O 4 . SiO 2 was coated onto the CoFe 2 O 4 particles by the micro-emulsion method. The SiO 2 -coated CoFe 2 O 4 particles were studied their physical properties and characterized by X-ray diffraction (XRD), high resolution-transmission electron microscopy (TEM) analysis and CIE Lab value.

Laser treatment of SiAlON and surface characteristics

Abstract: Laser treatment of SiAlON surface is considered and characteristics of the resulting surfaces are studied incorporating the scanning electron and atomic force miscroscopes, X-ray diffraction and Fourier transform infrared spectroscopy The wetting state of the laser treated surface is assessed using the droplet contact angle method while the friction coefficient of the treated surface is obtained by using the micro-tribometer Microhardness and fracture toughness of the treated surface are also measured Thermal and thermal stress analyses are carried out and temperature and von Mises stress fields are predicted in the laser treated region It is found that in micro/nano size pillars are formed on the laser treated surfaces, which alters the wetting state from hydrophilic to hydrophobic with contact angle 120° and contact angle hysteresis in the order of 182° In general, laser treated surface is free from large size cracks and voids; however, few locally scattered micro-cracks are observed on the surface Microhardness increases slightly for the laser treated surface because of the dense layer formed on the surface under the high cooling rates The fracture toughness of the surface reduces slightly and the friction coefficient of the surface improves after the laser treatment process The laser scanning tracks, which are closely spaced, result in self-annealing effects in the laser treated region; in which case, von Mises attains low values particularly along the recently formed laser scanning tracks

Investigation on the Properties of a Microcellular Light-Weighted Humidity Controlling Tile

Abstract: The humidity controlling ceramic materials was developed by applying the phenomena of dew condensation in the capillary. It issaid that the humidity range which human feels comfortable is from 40 to 70% in relative humidity. In this study, the ceramic tile usingnatural soils such as diatomite for interior wall was investigated. In particular, we had introduced novel processing routes forfabricating microcellular ceramics tile using hollow microsphere as a pore former. The microcellular pores in the humidity controllingceramic materials showed the superior properties such as light-weight, heat insulation. The cell density was ~1.0 × 10 9 cells/cm 3 anddensity of sample was 0.65 g/cm 3 in the case of 1.71 wt% hollow microsphere content. Also, it is observed that the BET surface areaand the pore volume of the sintered diatomite tile have the values of 40.92 m 2 /g and 0.173 cm 3 /g.Key words : Porous materials, Humidity, Diatomite, Adsorption 1. 서론최근 들어 에너지의 효율적인 이용을 목적으로 하여 건물의 밀폐성이 증가함으로써 생활환경에서의 건강문제, 특히습도의 문제가 주목을 받고 있다. 주거환경에서의 적당한환경습도는 40~70% 범위로, 이것보다 습도가 높으면 곰팡이나 진드기의 왕성한 번식에 따라 이들의 배설물이나유해한 미분말에 의해 천식이나 아토피성 피부염과 같은 알레르기 질환이 증가하게 되며, 이것보다 습도가 낮으면 감기 등 바이러스의 증식, 정전기의 축적으로 인한 정밀기기의오작동, 발화 및 미술품의 열화 등의 원인이 된다. 이와 같이 습도 문제로 인하여 생활환경이 곰팡이나 병원균에 의해오염되는 것을 방지하고 청결을 유지하기 위해서는 조습 건축타일의 개발이 필수적이며 사회적으로도 중요한 의의를 갖는다. 자율적으로 습기를 조절할 수 있는 조습 건축타일은 재료의 표면에 존재하는 모세관에 의해 환경 습도가높아지면 수증기(기체)를 응축 액화하고, 환경 습도가 낮아지면 응축수를 증발하는 기능을 갖는 것으로, 건물 내부나밀폐된 공간에서 외부 환경 변화에 대응하여 일정 범위의습도를 유지시키게 되며, 이러한 기능을 갖기 위해서는 기공크기가 3~7 nm 범위에 분포되어야 한다. 그리고 건축용조습 타일 소재로서는 화학적으로 나노 기공을 가지는 소재를 합성하기도 하지만 가격이 비싸기 때문에 경제성 등을고려하여 나노 기공을 활용한 천연재료를 주로 사용하고있다.

Preparation of CdS-AC/TiO 2 Composites Designed for a High Photonic Effect and their Photocatalytic Activity Under Visible Light

Abstract: In this study, CdS combined activated carbon/TiO 2 (CdS-AC/TiO 2 ) composites were prepared by a sol-gel method to improve the photocatalytic performance of TiO 2 . These composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and UV-vis analysis. The photocatalytic activities were examined by the degradation of methylene blue (MB) under visible light irradiation. The photodegradation rate of MB under visible light irradiation reached 90.1% in 120 min. The kinetics of MB degradation was plotted alongside the values calculated from the Langmuir-Hinshelwood equation. The 0.2 CAT sample showed the best photocatalytic activity, which might be due to an increase in the photo-absorption effect by activated carbon and the cooperative effect of CdS.