• Electrical & Electronic Materials
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• v.4 no.3
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• pp.201-210
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• 1991

본 논문에서는 (B $i_{1-x}$ P $b_{x}$)$_{2}$S $r_{2}$C $a_{2}$C $u_{3.6}$ $O_{y}$ (x=0~0.5)로 조성된 분말의 최적 하소온도를 결정하고 시편의 최적 소결온도를 규명하기 위하여 열분석을 하였다. 또 단일상의 고온 초전도체를 제작하기 위하여 열처리 온도, 시간 및 Pb 함량 변화에 따라 제작된 시편의 미세구조, 조성, 전기저항 및 전류밀도를 측정하여 상호 연관성을 종합적으로 분석, 검토하여 상변이에 관한 원인을 규명하고자 하였다. 또한 실용화 전 단계로서 임계특성 해석을 위하여 성형조건을 변화시켜 시편을 제작, 전류밀도값을 측정하였다.였다.다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.217-217
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• 2008

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC (Multi Layer Ceramic Capacitor), PTC thermistor 등에 널리 사용되어지고 있으며, 그 특성을 향상시키기 위하여 많은 연구가 진행되고 있다. 현제 $BaTiO_3$ 분말 제조의 대표적인 합성법으로는 하소와 분쇄공정이 없는 수열합성법이 대표적이나, 나노 사이즈로 제작시 $BaTiO_3$는 마이크로 크기와 달리 입방정상으로 우세한 상태로 존재한다. 이는 제조과정 중의 hydroxyl defect의 영향과 나노 분말의 표면에너지 증가 때문이라고 보고된다. 따라서 본 연구는 이러한 문제점을 해결하기 위해 일반적인 세라믹 제조 방법인 고상반응법을 이용한 나노 사이즈의 $BaTiO_3$ 제조를 위한 최적의 공정 조건을 확립하기 위하여 본 연구를 진행하였다. 조성은 $BaTiO_3$와 반응온도를 낮추기 위한 anatase의 $TiO_2$를 사용하였고, $BaCO_3/TiO_2$ 의 조성비 (1. 1.01, 1.02, 1.03)를 제어하여 혼합한 후, 24h ball-mill 하여 하소 온도 ($860^{\circ}C{\sim}1000^{\circ}C$) 변화에 따른 입자 사이즈와 입도 분포를 측정하였다. 제조된 $BaTiO_3$분말의 결정 구조 분석을 위하여 XRD (X-ray diffraction) 분석을 수행 하였는데, 분석 결과로부터 제조된 분말들이 정방정 (tetragonal)의 perovskite구조를 갖고 있음을 확인하였다. 또한 분말의 미세구조 확인을 위하여 SEM (scanning electron microscope) 관찰을 수행하였는데, 나노 사이즈의 구형 분말을 얻을 수 있음을 확인할 수 있었다.

• Resources Recycling
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• v.5 no.3
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• pp.50-55
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• 1996

The synthesis of Ca,,(PO,),(OH), by adding (NFIa)J),HPO, to lhe solution of Ca(NO,), dlssolvad CaO in HNO, and contmlled pH with NH,OH was carried out for certain time at room temperahire and atmosphere. Ca,,(PO,),(OH), was rorrned at the range from pN 10 to pH 13. The particle s~zeof Ca,,(PO,),(OH)i was 0.1-0.5 &In. Thc optimum reaction lime was 30 min, and the temperature was 40-70$^{\circ}$C. the shape also was not changed in spite of heating to iDVC hr 1 hour the c~ystalliratian temperature was 90$^{\circ}$C Ca,,(PO,),(OH), was calcinatcd and the shape also was not changzd, in spile of hcaling to 500$^{\circ}$C for 1 hour. But Ca,,(PO,),(OH), calcinated for lhour al 800$^{\circ}$C was changed to the spheric particle of Ca,,,(PO,),(OH),, CaO and Ca,(PO,),.

• Journal of Sensor Science and Technology
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• v.5 no.3
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• pp.93-100
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• 1996

Polycrystalline $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ and $La_{2}Ti_{2}O_{7}$ ceramics having very high Curie temperatures were synthesized by the conventional oxide mixing method (CON) and the molten salt synthesis method (MSS). Physical characteristics and phase relationship of calcined powders, as well as the sintering behavior, the grain-orientation and dielectric properties of sintered ceramics were investigated as a function of composition and firing temperature. The single $A_{2}B_{2}O_{7}$ phase was synthesized by using the MSS method at 100 - $150^{\circ}C$ lower temperature compared to the CON method. As Nb content increased in $Sr_{2}(Ta_{1-x}Nbx)_{2}O_{7}$ ceramics, the Curie temperature and the dielectric constant at Curie temperature were raised, and the sintering behavior and the degree of grain-orientation were also improved at the same time. The use of MSS-derived powders made it possible to lower the sintering temperature and to improve the dielectric properties of the sintering samples. However, the piezoelectric properties as well as the grain-orientation were not improved any further by the MSS route.

• Journal of the Korean Ceramic Society
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• v.29 no.10
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• pp.773-778
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• 1992

The effect of temperature on the structural changes of petroleum raw coke during calcination was studied and then the properties of carbon solids prepared from those calcined coke using binder were examined. The notable structural change of raw coke was observed in the range from 800$^{\circ}C$ to 900$^{\circ}C$ from the results of volatile matter, porosity, X-ray diffraction and scanning electron microscopy. The bending strength, density of the carbon solid carbonized at 1400$^{\circ}C$ was 400 kg/$\textrm{cm}^2$ and 1.40g/㎤, respectively.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.664-668
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• 2011

Spherical alumina precursors represented by $AlO_xCl_y(OH)_z$, 30~200 nm in particle diameter, were prepared by partial hydrolysis of $AlCl_3$ vapor in a 500 ml reactor. Investigated on the particle morphology and size were the effects of the reaction time, the stirring speed and the reaction temperature. The particle morphology and size was insensitive to the reaction time in the range 20 to 300 s. The variation of the stirring speed from 0 to 300 and 800 rpm showed that the particle size was the largest at 0 rpm. As the temperature was varied from 180 to 190, 200, $140^{\circ}C$, the particle size showed a maximum at $190^{\circ}C$. By calcination of the as-produced particles at $1,200^{\circ}C$ for 6h with a heating rate of $10^{\circ}C$/min, ${\alpha}$-alumina particles 45 nm in surface area equivalent diameter were obtained. The particle shape after calcination turned wormlike due to sintering between neighboring particles. A rapid calcination at $1400^{\circ}C$ for 0.5 h with a higher heating rate of $50^{\circ}C$/min reduced the sintering considerably. An addition of $SiCl_4$ or TMCTS(2,4,6,8-tetramethylcyclosiloxane) to the $AlCl_3$ reduced the sintering effectively in the calcination step; however, peaks of ${\gamma}$ or mullite phase appeared. An addition of $AlF_3$ to the particles obtained from the hydrolysis resulted in a hexagonal disc shaped alumina particles.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.1
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• pp.27-32
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• 2001

The 0.9PMN-0.1PT powders was prepared by the sol-gel process, and the effect amounts of ${Mg(OC_{2}H_{5})}_2$ and ${Pb(CH_{3}COO)}_2.3H_{2}O$ as starting materials was studied. As a result the percent of perovskite phase of the calcined powders increased with increased calcination temperatures. Maximum of perovskite phase was at $850^{\circ}C$ for 4 hrs. 0.9PMN-0.1PT powder by addition of 5 wt% excess ${Mg(OC_{2}H_{5})}_2$ crystallized to perovskite phase with a ${\fallingdotseq}100%$ yield.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.166-171
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• 2015

In this study, using solid-state and flux, $Y_3Al_5O_{12}:Er^{3+}\;(YAG:Er^{3+})$ powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at $1400^{\circ}C$ and pure YAG phase could be obtained. But when $BaF_2$ was added to YAG, YAG was synthesized at lower temperature (1000^{\circ}C$). It was thus found that the synthesis temperature could be lowered by about $400^{\circ}C$. Also, when BaF2 with an optimal concentration was added to $YAG:Er^{3+}$, the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.393-401
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• 2012

Inorganic pigment is excellent at stability to human body and compatibility with different materials and has been used in a variety of field such as cosmetics, printing inks, paints, and construction materials for improving the aesthetic features. In this paper, hydrothermal synthesis method was used to prepare the manganese and iron dopped with titania pigment. As process parameters, the amount of manganese precursor and iron precursor, and calcined temperature was changed. Optimum amounts of manganese and iron dopped with titania precursor to give excellent color index was manganese 1.0wt% and iron 1.5wt% for dopped titania, and Optimum calcination temperature was $550^{\circ}C$. The synthesized pigments were analyzed by XRD, SEM, EDS, Spectrophotometer and UV-Vis Spectrometer.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.36-41
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• 1995

Dielectric properties were investigated at Mn doped $(Pb_{1-x}Ca_{x})ZrO_{3}$ with x=0.38 in microwavefrequencies. Both the density and Q values of sintered ceramics increased with increasing calciningtemperature. In the sample sintered at $1300^{\circ}C$ for 2 hrs, the deped Mn ions completely solubled in $(Pb,Ca)ZrO_{3}$ phase until 0.5wt% and the grain size was independent of doping amount. It was observed thathigh dielectric constant of 90 - 100 and high quality factor of 1300 at 4 GHz for O.l5wt% Mn doped$(Pb_{0.62}Ca_{0.38})ZrO_{3}$. The Mn" and Mn" worked as acceptors in $(Pb,Ca)ZrO_{3}$ which created the oxygen vacancies and affected the increment of the Q values. However, the excess Mn doping more than 0.5wt% resulted in decreasing Q values.decreasing Q values.