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Kinetics of Athermal Martensitic Transformation in Yttria Doped Zirconia
Pee, Jae-Hwan,Choi, Eui-Seok,Hayakawa, Motozo The Korean Ceramic Society 2005 한국세라믹학회지 Vol.42 No.11
The high temperature tetragonal phase of zirconia containing $1.40{\~}1.60\;mol\%$ of yttria can be fully retained at room temperature by rapid cooling. The metastable tetragonal phase transforms into the monoclinic phase athermally upon subzero cooling. The transformation exhibited an athermal burst transformation. The effects of yttria content and grain size on the athermal martensitic transformation were studied in detail. The burst temperature linearly decreased with increasing yttria content or decreasing grain size. To consider the distribution of martensite nuclei, the Weibull modulus of the athermal martensitic transformation was evaluated from the distribution of the burst transformation temperature. From the Weibull analysis, the distribution of embryos appears to be more homogeneous than that of the defects responsible for the fracture of similar material.
Silica coating of synthesized Ta<sub>3</sub>N<sub>5</sub> powders by the micro-emulsion method
Pee, Jae-Hwan,Park, Jong-Chul,Kim, YooJin,Cho, Woo-Seok,Park, Hyung-Ho Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139
<P>We synthesized yellow TaON and red Ta3N5 by ammonolysis of amorphous Ta(OH)(5) between 800 and 1000 degrees C. Ta(OH)(5) was prepared by titration, using TaCl5 as the starting material. Yellow TaON was synthesized at 900 degrees C for 2 h, and red Ta3N5 was synthesized at 1000 degrees C for 5 h. In general, red Ta3N5 powders were easily oxidized at 500 degrees C, with the color changing from red to white. To minimize the oxidation problem of Ta3N5 powders, we proposed a silica coating system using tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxy-silane (APTES) as surfactants. The tonality of silica-coated Ta3N5 changes very little, indicating that the silica coating minimizes the oxidation of Ta3N5 nanoparticles.</P>
Effect of Pyrophyllite on the Mullite Generation in Ternary Porcelain System
Pee, J.H.,Kwak, A.N.,Kim, Jong Young,Kim, Yoo Jin,Kim, Kyung Ja Trans Tech Publications, Ltd. 2012 Key Engineering Materials Vol.512 No.-
<P>Promoting of mullite generation has been studied by replacing kaolinite with pyrophyllite because of mullite has excellent strength and thermal shock resistance. Effects of promoting of mullite generation and vitrification by replacing kaolinite with pyrophyllite on the mechanical and thermal properties were investigated. Addition of 45-55% pyrophyllite as a replacement of kaolinite (pyrophyllite (45-55%)-feldspar (30%)-clay (20%)) could vitrify samples (water absorption: 0.05%, bulk density: 2.66g/cm3) and improve the strength (122MPa) of samples fired at 1280°C. In ternary porcelain system, pyrophyllite-feldspar-clay, mullite generation of samples with 50% pyrophyllite reaches about 78.7% and thermal expansion coefficient is 5.4×10-6/K. Beyond 50% pyrophyllite addition, quartz and cristobalite phases increased. And thermal expansion coefficient of samples decreased with increasing of mullite amount.</P>
Hydrothermal Synthesis of Rod-like Copper Oxide Crystals
Pee Jae-Hwan,Lee Dong-Wook,Kim Ung-Soo,Choi Eui-Seok 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
A hyrdrothermal synthesis has been developd to prepare rod-like crystals of copper oxide using copper nitrate trihydrate as a function of synthesis temperature, stirring speed and solution pH value. The properties of the fabricated crystals were studied using scanning electron microscopy, X-ray diffraction and particle size analysis. The morphology of the synthesized CuO was dependent on both the pH value of the solution and the morphology of the seed materials. Synthesized particles have regular morphologies and a uniform size distribution.
Low-Temperature Synthesis of Cordierite Using Magnesite
Pee, Jae Hwan,Kim, Geun Hee,Lee, Na Ri,Kim, Hyung Tea,Punsukumtana, Lada Trans Tech Publications, Ltd. 2014 Key Engineering Materials Vol.608 No.-
<P>Cordierite (2MgO·2Al2O3·5SiO2) has a low density of 2.2 g/cm<SUP>3</SUP> due to its high magnesium content. Because of its low thermal expansion coefficient of 1~2 x10<SUP>-6 </SUP>/<SUP>°</SUP>C, many studies are being conducted on the synthesis of cordierite with the expensive petalite as a replacement for lithium alumina silicate-based heat-resistant materials. The cordierite can be synthesized over a wide range: SiO2 at 50~70%, Al2O3 at 20~40%, and MgO at 10~30%. In this study, the range of chemical composition and temperature of cordierite synthesis is thoroughly investigated. In particular, we use natural materials (magnesite, kaolin and clay) to examine how thermal properties are affected by changes in crystal phase arising from the varying composition of MgO, SiO2 and Al2O3. We focused on factors leading to an increase in the rate of cordierite synthesis at temperatures below 1280 <SUP>°</SUP>C. From observing the synthetic rate over 1250~1280 <SUP>°</SUP>C, the sintered body at 1280 <SUP>°</SUP>C had a high synthetic rate greater than 80%. Magnesite was ball milled at constant intervals, and mean particle size was controlled to improve the synthetic rate of cordierite. As a result, the cordierite synthetic rate increased by more than 15% with decreasing the mean particle size of magnesite.</P>
Effect of Flux Materials on the Melting Characteristics of Ash Glaze
Pee, Jae Hwan,Kim, Geun Hee,Choi, You Dam,Jung, Doo Sub,Kang, Gyung In Trans Tech Publications, Ltd. 2014 Key Engineering Materials Vol.608 No.-
<P>Our objective was to make transparent glaze using oak ash which has a high content of CaO and contains P2O5. However, the melting point of oak ash is above 1340<SUP>°</SUP>C, making it difficult to make transparent glaze using only oak ash. In order to lower the melting point of oak ash, flux materials were mixed to oak ash and melting characterization was carried out. Feldspar, which is largely composed of Na2O and K2O andlimestone largely composed of CaO were used as the flux materials. The materials were added 10, 20 and 30wt%, respectively, in order to produce the glaze. Depending on the type and amount of flux materials added, the samples were fired at temperatures between 1280~1320<SUP>°</SUP>C in the reducing atmosphere. As the amount of feldspar added was increased, the melting point decreased substantially. Samples with limestone added did not melt completely even at temperatures 1300<SUP>°</SUP>C and wollastonite phase was observed in the glaze layer.</P>
Pee, L.G.,Lee, Jung The Korea Society of Management Information System 2016 Asia Pacific Journal of Information Systems Vol.26 No.1
Social media is increasingly being used as a source of information during crises, such as natural disasters and civil unrests. However, the quality and truthfulness of user-generated information on social media have been a cause of concern. Many users find distinguishing between true and false information on social media difficult. Basing on the elaboration likelihood model and the motivation, opportunity, and ability framework, this study proposes and empirically tests a model that identifies the information processing routes through which users develop trust, as well as the factors that influence the use of these routes. The findings from a survey of Twitter users seeking information about the Fukushima Daiichi nuclear crisis indicate that individuals evaluate information quality more when the crisis information has strong personal relevance or when individuals have low anxiety about the crisis. By contrast, they rely on majority influence more when the crisis information has less personal relevance or when these individuals have high anxiety about the crisis. Prior knowledge does not have significant moderating effects on the use of information quality and majority influence in forming trust. This study extends the theorization of trust in user-generated information by focusing on the process through which users form trust. The findings also highlight the need to alleviate anxiety and manage non-victims in controlling the spread of false information on social media during crises.