• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.333-339
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• 1983

Semiconducting glaxe of iron system for the recent use as high Voltage porcelain insulators often showed the tendancy of unstable thermal properties. Thus the development of frit including magnetite was studied to cover the defect. In the experimental process melted and quenched frits were ground pelletized and heat-treated at various temperatures in the range of 800-1 $300^{\circ}C$ for various soaking time within 4 hours and then crystallized specimens were obtained. The speciment were studied with optical and electron microscope DTA x-ray diffractometer and electrometer The results obtained were as follows : 1) The optimum condition for the crystal growth of magnetite in the frite was the heat-treatment of $1300^{\circ}C$ for 3hrs and in this case the range of crystal size was $10-11\mu\textrm{m}$ 2) The activation energy for the crystal growth of magnetite was 21.1 kcal/mole. 3) The heat-treament at $1, 250^{\circ}C$ and $1, 300^{\circ}C$ resulted in the good thermal stability and the range of surface resistivity was $3.5{\times}10^4-4.0{\times}10^7$, /TEX> $\Omega$/$cm^2$ which was adguate to semiconducting frit. 4) The conduction mechanism seems to be due to the electron mobility rather than ion mobility and the activa-tion energy for the conduction was 0.07-0.15eV/mole for the heat-treated specimes in the range of 1, 250-1, 300C

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.204-208
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• 2015

Synthesis of hydroxyapatite (HA) was attempted through a room-temperature reaction of calcined eggshell with phosphoric acid. Ball-milled, calcined eggshell powder, which has a specific surface area of $31.6m^2/g$, was mixed with various concentrations of phosphoric acid at room temperature. The mixtures showed high reactivity and a vigorous exothermic reaction ; the reacted samples showed both $Ca(OH)_2$ and $CaHPO_4$ crystal phases. After heating at temperatures above $400^{\circ}C$, an HA crystal phase was observed in all samples. The calcined eggshell showed a pure CaO single phase, while the $Ca(OH)_2$ phase was only observed in the wet, ball-milled calcined powder. The degree of formation of the HA crystal phase increased as the phosphoric acid concentration and the heating temperature were increased. A mixture with 50 wt% phosphoric acid concentration showed a well-developed HA crystal phase after heat treatment at $800^{\circ}C$, while the formation of a more intensive amorphous phase was observed in the products of the room-temperature reaction.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.517-523
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• 2007

For the preparation of tricalciumaluminate $(C_3A)$ clinker, in traditional clinkering method using oxides and carbonates as a raw material, uneconomical repetition of burning have been necessary to avoid the melting of clinker by eutectic reaction in the system $CaO-Al_2O_3$. In this study, special starting raw materials for the clinker burning were prepared from a mixture of oyster shell and aluminium hydroxide by heating to $1100^{\circ}C$ and hydrating at $30^{\circ}C$. The starting raw materials, hardened body with weak hydraulic strength, were mainly composed of $C_3AH_6$ formed by resolution-precipitation mechanism of the system $CaO-Al_2O_3-H_2O$. By heating them, relatively pure $C_3A$ clinker could be obtained by one-time burning at the fairly lower temperature than that of conventional method. The easier formation of $C_3A$ clinker seemed to be caused by higher compositional homogeneity and stoichiometry of the starting materials, high surface area and crystallographic instability of the thermally decomposed products, and the catalytic effect of decomposed moisture on the early-stage crystallization of calciumaluminates. The basic hydration behavior of the clinker was also confirmed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.9
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• pp.711-717
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• 1998

BST(70/30) and BST(50/50) thin films were prepared by Sol-Gel method and studied about the microstructural and dielectric properties with Pt and ITO bottom electrodes. The stock solution was synthesized and spin coated on the Pt/Ti$SiO_2$/Si and Indium Tin Oxide(ITO)/ glass substrate. the coated films were dries at 350$^{\circ}C$ for 10 minutes and annealed at $750^{\circ}C$ for 1 hour for the crystallization. The thin films coated on ITO substrate were crystallized easily and the packing density and roughness of surface were better that those of films coated on Pt substrates. In the BST(50/50) composition the structural properties were similar to the BST(70/30) composition and grain size were decreased with increasing the contents of Sr. The dielectric constant was higher in the BST(50/50) composition compared with the BST(70/30) composition. Using the ITO substrate, the dielectric constant was higher than the Pt substrate while the dielectric loss was showed a reverse trend. The dielectric constant with and increase of temperature was decreased slowly.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.193-200
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• 2007

Micro forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Al5083 superplastic alloy with very small grains has a great advantage in achieving micro deformation under low stress due to its relatively low strength at a specific high temperature range. Micro forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, the micro formability of Al5083 superplastic alloy and bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$, was investigated with the specially designed micro vibration forming system using pyramid-shape, V-shape and U-shape micro die pattern. With these dies, micro vibration forming was conducted by varying the applied load, time. Micro formability was estimated by comparing the hight of formed shape using non-contact surface profiler system. The vibration load effect to metal flow in the micro die and improve the micro formability of Al5083 superplastic alloy and $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG).

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1962-1966
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• 2012

Boehmite sols have been prepared by crystallization of amorphous aluminum hydroxide gel obtained by hydrolysis and peptization of aluminum using acetic acid. The size of the boehmite crystallites could be controlled by Al molar concentration in amorphous gel by means of controlling grain growth at nucleation stage. The size of boehmite increases as a function of Al molar concentration. With increasing boehmite crystallite size, the $d_{(020)}$ spacing and the specific surface area decreases, whereas the pore volume increases along with pore size. Especially, the pore size of the boehmite sol particles is comparable to the crystallite size along the b axis, suggesting that the fibril thickness along the b axis among the crystallite dimensions of the boehmite contributes to the pore size. Therefore, the physical properties of boehmite sols can be determined by the crystallite size controlled as a function of initial Al concentration.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3679-3683
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• 2010

Niobium oxide ($Nb_2O_5$) and phosphated $Nb_2O_5$ were synthesized and used as catalysts for sorbitol dehydration to isosorbide. The characterization results of $N_2$ adsorption, XRD and $NH_3$-TPD revealed that the phosphoric acid modification could well prevent the crystallization of $Nb_2O_5$. And the amorphous phosphated $Nb_2O_5$ catalysts kept the relatively large surface area and stable acidity at high calcination temperature. The catalytic results showed that the selectivity to isosorbide could be dramatically enhanced over phosphated $Nb_2O_5$. The excellent catalytic performance with 100.0% sorbitol conversion and 62.5% isosorbide selectivity were obtained over the 0.8P/NBO-400 catalyst. Comparing with $Nb_2O_5$ catalysts, phosphated $Nb_2O_5$ catalysts regenerated through a simple calcination process showed no significant activity loss after recycling three runs.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.151-151
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• 2010

In this paper, the electrically properties of nonvolatile memory (NVM) using multi-stacks gate insulators of oxide-nitride-oxynitride (ONOn) and active layer of the low temperature polycrystalline silicon (LTPS) were investigated. From hydrogenated amorphous silicon (a-Si:H), the LTPS thin films with high crystalline fraction of 96% and low surface's roughness of 1.28 nm were fabricated by the metal induced crystallization (MIC) with annealing conditions of $650^{\circ}C$ for 5 hours on glass substrates. The LTPS thin film transistor (TFT) or the NVM obtains a field effect mobility of ($\mu_{FE}$) $10\;cm^2/V{\cdot}s$, threshold voltage ($V_{TH}$) of -3.5V. The results demonstrated that the NVM has a memory window of 1.6 V with a programming and erasing (P/E) voltage of -14 V and 14 V in 1 ms. Moreover, retention properties of the memory was determined exceed 80% after 10 years. Therefore, the LTPS fabricated by the MIC became a potential material for NVM application which employed for the system integration of the panel display.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.660-666
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• 2010

30 nm thick Ni layers were deposited on a glass substrate by e-beam evaporation. Subsequently, 30 nm or 60 nm ${\alpha}-Si:H$ layers were grown at low temperatures ($<220^{\circ}C$) on the 30 nm Ni/Glass substrate by catalytic CVD (chemical vapor deposition). The sheet resistance, phase, microstructure, depth profile and surface roughness of the $\alpha-Si:H$ layers were examined using a four-point probe, HRXRD (high resolution Xray diffraction), Raman Spectroscopy, FE-SEM (field emission-scanning electron microscopy), TEM (transmission electron microscope) and AES depth profiler. The Ni layers reacted with Si to form NiSi layers with a low sheet resistance of $10{\Omega}/{\Box}$. The crystallinty of the $\alpha-Si:H$ layers on NiSi was up to 60% according to Raman spectroscopy. These results show that both nano-scale NiSi layers and crystalline Si layers can be formed simultaneously on a Ni deposited glass substrate using the proposed low temperature catalytic CVD process.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.429-434
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• 2012

Ignition delay of micro/nano aluminum particles is caused by aluminum oxide shell. The method of minimizing this ignition delay is proposed in the study. Generating and heating of particles are processed at the same time. As soon as heated particles are produced, they immediately contact with oxygen. Chemical reaction is induced on the contact surface instead of crystallization of oxide shell. Finally particles are ignited. Aluminum particles are generated by laser ablation on an aluminum plate using Nd:YAG pulse laser. Injected particles are confirmed through visualization of particles using scattering method. $CO_2$ continuous laser supplies heat to aluminum plate and generated particles. Trace of burning particles is observed in the experiment.