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박형일,신석주,이헌창,장서일,김태옥 한국산업안전학회 2002 한국안전학회지 Vol.17 No.3
The runaway reaction was analyzed experimently and theoretically at the batch styrene suspension polymerization process. In the experiments, the reaction temperature with time was measured at various experimental conditions. According to the experimental results, the risk of the runaway reaction was increased with increasing the ratio of the monomer(styrene, M) to the dispersion medium(water, W), the concentration of the initiator(BPO), and the monomer mass, respectively. And simulation results showed that the runaway reaction was significantly affected by the reaction rate constant of the propagation and that the phenomena of the runaway reaction occurred at about 70% conversion. Also, we found that the runaway reaction did not occur under the operation condition of below 0.5 for M/W, approximate 3 wt% BPO, and below 75℃ for the cooling temperature.
The Effects of the Humidity and Thickness on YBCO Film Prepared Using the TFA-MOD Method
Seok Hern Jang,Jun Hyung Lim,Kyung Min Yoon,Seung Yi Lee,Kyu Tae Kim,Eui Cheol Park,Jinho Joo,Seung-Boo Jung,Hyoungsub Kim Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>This study examined the epitaxial growth of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (YBCO) films on (00l) LaAlO<SUB>3</SUB> substrates prepared by metal organic deposition (MOD) using a trifluoroacetate (TFA) solution. The effects of humidity (0-20% of P<SUB>H2O</SUB>) and film thickness (0.4-2.1 mum) on the phase formation, texture, and microstructures of the YBCO films were examined by X-ray diffraction, pole-figure, and scanning electron microscopy (SEM). The microstructure and resultant critical properties varied remarkably with humidity. With increasing humidity, the amount of the second phase (BaF<SUB>2</SUB>) decreased, the degree of texture was enhanced, and consequently the critical current (I<SUB>C</SUB>) and temperature (T<SUB>C</SUB> ) were improved. In the case of multi-coated films, the I<SUB>C</SUB> value increased from 35 to 152 A/cm-width with an increasing number of coatings from one to three, while the corresponding critical current density (J<SUB>C</SUB>) was in the range of 0.9-1.5 MA/cm<SUP>2</SUP> . Both the I<SUB>C</SUB> and J<SUB>C</SUB> decreased when an additional coating was applied due to microstructural degradation.</P>
Fabrication of Bi-2212/ Composite Superconductors by Melting Powder Mixtures
Kim Kyu-Tae,Jang Seok-Hern,Lim Jun-Hyung,Park Eui-Cheol,Joo Jin-Ho,Lee Hoo-Jeong,Hong Gye-Won,Kim Chan-Joong,Kim Hye-Rim,Hyun Ok-Bae 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
We fabricated Bi-2212/ composite superconductors and evaluated the effects of the powder mixing method and melting temperature on their microstructure and superconducting properties. The Bi-2212 powders were mixed with by hand-mixing (HM) and planetary ball milling (PBM) and then the powder mixtures were melted at , solidified, and annealed. We found that the powder mixture prepared by PBM was finer and more homogeneously mixed than that prepared by HM, resulting in more homogeneous microstructure and smaller and second phases after annealing.
Fabrication of TFA-MOD YBCO Films Using the and Powders
Lim Jun-Hyung,Jang Seok-Hern,Yoon Kyung-Min,Lee Seung-Yi,Joo Jin-Ho,Lee Hoo-Jeong,Kim Chan-Joong 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
We fabricated YBCO film using a TFA-MOD method. In order to enhance the reaction kinetics and to control the formation of the second phases, and powders were used as precursors (the so called "211 process"). The films were calcined at and then fired at in a 12.1% humidified atmosphere. We found that the microstructure varied significantly with the firing temperature. The textures of all of the films were similar and mainly biaxial. For the film fired at , the critical current was obtained to be 39 A/cm-width (corresponding critical current density is 2.0 MA/).
Fabrication of Bi-2212/SrSO<sub>4</sub> Composite Superconductors by Melting Powder Mixtures
Kim, Kyu Tae,Jang, Seok Hern,Lim, Jun Hyung,Park, Eui Cheol,Joo, Jin Ho,Lee, Hoo Jeong,Hong, Gye Won,Kim, Chan Joong,Kim, Hye Rim,Hyun, Ok Bae Trans Tech Publications, Ltd. 2007 Materials science forum Vol.534 No.-
<P>We fabricated Bi-2212/SrSO4 composite superconductors by the melt casting process and evaluated the effects of the powder mixing method and melting temperature on their microstructure and superconducting properties. In the melt casting process, the Bi-2212 powders were mixed with SrSO4 by hand-mixing (HM) and planetary ball milling (PBM) and then the powder mixtures were melted at 1100°C~1200°C, solidified, and annealed. We found that the powder mixture prepared by PBM was finer and more homogeneously mixed than that prepared by HM, resulting in more homogeneous microstructure and smaller SrSO4 and second phases after annealing. The critical current (Ic) also varied significantly with the powder mixing method and the melting temperature. The Ic of the annealed rod prepared by PBM was 193 A at 77 K when melted at 1100°C, which is higher than that of the annealed rod prepared by HM (132 A). This enhancement in the Ic value for the former is considered to be due to its more uniform microstructure.</P>
Fabrication of YBCO film approached by the ‘211 process’ in the TFA-MOD method
Lim, Jun Hyung,Jang, Seok Hern,Joo, Jinho,Kim, Hyoungsub,Lee, Hee-Gyoun,Hong, Gye-Won,Kim, Chan-Joong IOP Publishing Ltd 2006 Superconductor science & technology Vol.19 No.4
<P>We fabricated YBCO film using a new approach to the TFA-MOD method. In the fabrication process, Y<SUB>2</SUB>Ba<SUB>1</SUB>Cu<SUB>1</SUB>O<SUB><I>x</I></SUB> and Ba<SUB>3</SUB>Cu<SUB>5</SUB>O<SUB>8</SUB> powders were used as precursors (the so called ‘211 process’), instead of Y-, Ba-, and Cu-based acetates, and dissolved in trifluoroacetic acid followed by calcining and firing heat treatment. Consequently, we successfully synthesized YBCO film and evaluated the phase formation, texture evolution, and critical properties as a function of the calcining and firing temperature and humidity, in order to explore its possible application in coated conductor fabrication.</P><P> The films were calcined at 430–460 ?C and then fired at 750–800 ?C in a 0–20% humidified Ar–O<SUB>2</SUB> atmosphere. We observed that the amount of BaF<SUB>2</SUB> phase was effectively reduced and that a sharp and strong biaxial texture formed under a humidified atmosphere, leading to increased critical properties. In addition, we found that the microstructure varied significantly with the firing temperature; the grains grew further, the film became denser, and the degree of texture and phase purity varied as the firing temperature increased. For the film fired at 775 ?C after calcining at 460 ?C, the critical current was found to be 39?A?cm<SUP>−1</SUP>?width (the corresponding critical current density is 2.0?MA?cm<SUP>−2</SUP>), which was probably attributable to such factors as the enhanced phase purity and out-of-plane texture, the moderate film density and grain size, and the crack-free surface. </P>
A Study on the Processing Variables of the BSCCO-2212 Bulk Superconductors
Kyu Tae Kim,Jun Hyung Lim,Seok Hern Jang,Jinho Joo,Hoo-Jeong Lee,Gye-Won Hong,Chan-Joong Kim,Hye-Rim Kim,Ok-Bae Hyun Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>Bi-2212/SrSO<SUB>4</SUB> bulk superconductors were fabricated using a casting process, and the effects of the powder mixing method, annealing temperature, and SrSO<SUB>4</SUB> content on the texture, microstructure, and critical properties were evaluated. The Bi-2212 powders were mixed with SrSO<SUB>4</SUB> either by hand-mixing (HM) or planetary ball milling (PBM), followed by melting at 1100degC-1200degC, solidification, and annealing. The rod produced by PBM had a more homogeneous microstructure and smaller grain size of SrSO<SUB>4</SUB> and minor phases, resulting in increased I<SUB>c</SUB>, than the rod made by HM. The I<SUB>c</SUB> of the rod was also dependent on the annealing temperature with the highest I<SUB>c</SUB> of 200 A being obtained at an annealing temperature of 810degC. This was attributed to the moderate density and 2212 texture as well as the smaller and less minor phase than that observed at higher temperature. In addition, the optimum SrSO<SUB>4</SUB> content was found to be 6 wt.% for an increased I<SUB>c</SUB>. SEM, EPMA, and DTA analyses indicated that the differences in microstructural evolution caused the variations of the I<SUB>c</SUB> with the powder mixing method, annealing temperature, and SrSO<SUB>4</SUB> addition.</P>