• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.12
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• pp.955-961
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• 2011

We investigated the physical properties of stoichiometric and non-stoichiometric oxide doped complex perovskite, $Ba(Zn_{1/3}Ta_{2/3})O_3$ ceramics and their impacts on the microwave dielectric performances using various characterization techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and network analyzer. According to the measurement of lattice constant changes, anomalous lattice volume contraction of $ZrO_2$ doped $Ba(Zn_{1/3}Ta_{2/3})O_3$ sample only showed the dielectric quality factor enhancements, which was due to the lattice volume contraction as well as the 1:2 B-site cation ordering. In addition, NiO doping was useful to the stabilization of temperature coefficient of resonance frequency.

• Korean Journal of Materials Research
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• v.29 no.3
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• pp.150-154
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• 2019

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$, which has a rhombohedral-tetragonal phase boundary composition. $MnO_2$ and CuO-added $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$ ceramics sintered at a relatively low temperature of $1020^{\circ}C$ show a pure perovskite phase with no secondary phase. As the addition of $MnO_2$ and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of $MnO_2$.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.546-552
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• 1993

본 연구에서는 입계의 성질을 이용한 PTCR 재료에 입계 modifier로서 $Bi_{2}$$O_{3}$와 BN을 첨가하고 입계의 미세구조와 결함농도를 변화시켜 이에 따른 소결 및 전기적 특성변화를 TMA, XRD, 복합 임피던스방법 등을 이용하여 해석하였다. 실험 결과 Y이 도우핑된 BaT$iO_{3}$ PTCR 재료에 $Bi_{2}$$O_{3}$를 첨가하였을때 약 0.1mol%까지 고용이 되는 것으로 밝혀졌다. $Bi_{2}$$O_{3}$를 고용한계 이하로 첨가시에는 생성되는 vacancy등의 결함으로 말미암아 Y-BaT$iO_{3}$의 치밀화가 촉진되었으나, 그 이상 첨가하면 치밀화 뿐만 아니라 결정립 성장도 억제되었다.$Bi_{2}$$O_{3}$ 결정립 내부에 Ba와 Ti vacancy가 동시에 생길 수 있어 고온저항이 높아짐을 알 수 있었다. BN은 BaT$iO_{3}$에 고용이 되지 않는 것으로 밝혀졌으며 $B_{2}$O/wub/3를 주성분으로한 액상형성으로 인하여 저온에서의 급격한 치밀화가 관찰되었다. 또 Ba-Y-Ti-B-O의 비정질 상이 tripie junction에 존재함으로서 상온저항이 크게 변화하였으며, PTCR jump도 높아졌다.

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1547-1554
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• 2017

VESTA (Verification of Ex-vessel corium STAbilization) and VESTA-S (-small) test facilities were constructed at the Korea Atomic Energy Research Institute in 2010 to perform various corium melt experiments. Since then, several tests have been performed for the verification of an ex-vessel core catcher design for the EU-APR1400. Ablation tests of an impinging $ZrO_2$ melt jet on a sacrificial material were performed to investigate the ablation characteristics. $ZrO_2$ melt in an amount of 65-70 kg was discharged onto a sacrificial material through a well-designed nozzle, after which the ablation depths were measured. Interaction tests between the metallic melt and sacrificial material were performed to investigate the interaction kinetics of the sacrificial material. Two types of melt were used: one is a metallic corium melt with Fe 46%, U 31%, Zr 16%, and Cr 7% (maximum possible content of U and Zr for C-40), and the other is a stainless steel (SUS304) melt. Metallic melt in an amount of 1.5-2.0 kg was delivered onto the sacrificial material, and the ablation depths were measured. Penetration tube failure tests were performed for an APR1400 equipped with 61 in-core instrumentation penetration nozzles and extended tubes at the reactor lower vessel. $ZrO_2$ melt was generated in a melting crucible and delivered down into an interaction crucible where the test specimen is installed. To evaluate the tube ejection mechanism, temperature distributions of the reactor bottom head and in-core instrumentation penetration were measured by a series of thermocouples embedded along the specimen. In addition, lower vessel failure tests for the Fukushima Daiichi nuclear power plant are being performed. As a first step, the configuration of the molten core in the plant was investigated by a melting and solidification experiment. Approximately 5 kg of a mixture, whose composition in terms of weight is $UO_2$ 60%, Zr 10%, $ZrO_2$ 15%, SUS304 14%, and $B_4C$ 1%, was melted in a cold crucible using an induction heating technique.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.24-27
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• 2000

Ferroelectric P $b_{0.99}$〔(Z $r_{0.6}$S $n_{0.4}$)$_{0.9}$ $Ti_{0.1}$〕$_{0.98}$N $b_{0.02}$ $O_3$(PNZST) thin films were deposited by a RF magnetron sputtering on (L $a_{0.5}$S $r_{0.5}$)Co $O_3$(LSCO)/Pt/Ti/ $SiO_2$/Si substrate using a PNZST target with excess PbO of 10 mole％. The thin films deposited at the substrate temperature of 500 $^{\circ}C$ were crystallized to a perovskite phase after rapid thermal annealing(RTA) The thin films annealed at 650 $^{\circ}C$ for 10 seconds in air exhibited the good crystal structures and ferroelectric properties. The remanent polarization and coercive field of the PNZST capacitor were about 20 $\mu$C/$\textrm{cm}^2$ and 50 kV/cm, respectively. The reduction of the polarization after 2.2$\times$10$^{9}$ switching cycles was less than 10 ％.0 ％.％.0 ％.0 ％.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.57-62
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• 2001

Korea Atomic Energy Research Institute (KAERI) launched an intermediate scale steam explosion experiment named Test for Real cOrium Interaction with water (TROI) using reactor material to investigate whether the corium would lead to energetic steam explosion when interacted with cold water at low pressure. The melt-water interaction is confined in a pressure vessel with the multi-dimensional fuel and water pool geometry. The cold crucible technology, where the mixture of powder in a water-cooled cage is heated by high frequency induction, is employed. In this paper, results of the first series of tests ($TROI-1{\sim}5$) were discussed. The ZrO2 jets with 5kg mass and 5cm diameter were poured into the 67cm deep water pool at $30{\sim}95^{\circ}C$. Either spontaneous steam explosions or quenching was observed. The morphology of debris and pressure wave profiles clearly indicates the each case.

• Journal of Powder Materials
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• v.18 no.2
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• pp.149-158
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• 2011

Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.

• Korean Journal of Materials Research
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• v.7 no.7
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• pp.592-596
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• 1997

LI$_{2}$형 결정구조를 갖는 Ni-20at.%AI-10at%Fe 금속간화합물에 boron, zirconium 과 hafnium을 최고 0.5at.% 까지 첨가하여 항복강도, 연성, 파괴 등 기계적 성질의 변화를 인장시험과 X선분석 및 XPS분석 등을 통하여 관찰하였다. Ni-20at.% AI-10at.% Fe금속간화합물에 boron을 첨가하였을 때는 연신율의 현저한 증가가 나타났으나 zirconium이나 hafnium첨가의 경우에는 별다른 효과가 나타나지 않았다. Ni-20at.%AI-10at%Fe 금속간화합물의 경우, boron의 양이 증가할수록 인장연신율이 증가하였으며 0.1at.%의 boron을 첨가한 경우 최고 48.5%의 상온인장연신율을 나타내었다. 첨가물을 넣지 않은 경우와 zirconium과 hafnium을 첨가한 경우, 파괴모드는 입계파괴의 형태를 나타내었으나 boron을 첨가한 경우에는 파괴모드가 입계파괴에서 입내파괴로 변화되었다. XPS분석을 통하여 boron이 입계에 편석된 것을 관찰할 수 있었으며 이는 이미 제시된 여러가지 해석들과 일치하는 결과이다. 이로부터 boron의 첨가에 따른 인장연신율의 증가는 boron의 입계편석거동과 관련이 있음을 알 수 있다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1887-1897
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• 2001

Korea Atomic Energy Research Institute (KAERI) launched an intermediate scale steam explosion experiment named "Test for Real Corium Interaction with water (TROI)" using reactor material to investigate whether the molten reactor material would lead to energetic steam explosion when interacted wish cold water at low pressure. The melt-water interaction experiment is performed in a pressure vessel with the multi-dimensional fuel and water pool geometry. The novel concept of cold crucible technology, where powder of the reactor material in a water-cooled cafe is heated by high frequency induction, is firstly implemented for the generation of molten fuel. In this paper, the lest facility and cold crucible technology are introduced and the results or the first series of tests were discussed. The 5 kg of molten ZrO$_2$jet was poured into the 67cm deep water pool at 30 ∼ 95 $\^{C}$. Either spontaneous steam explosions or quenching was observed. The morphology of debris and pressure wave profiles clearly indicate the differences between the two cases.

• Progress in Superconductivity and Cryogenics
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• v.5 no.3
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• pp.11-14
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• 2003

The detailed conditions of dc-sputtering for depositions of yttria-stabilized ZrO$_2$ (YSZ) films were investigated, while the films were grown on the CeO$_2$ template layers on biaxially textured Ni-tapes. The window of oxygen pressures for proper growth of YSZ films, which was dependent on sputtering powers, was determined by sufficient oxidations of the YSZ films and the de-oxidation of the target surface, which was required for rapid sputtering. The window turned out to be fairly wide under certain values of argon pressure. When the sputtering power was raised, the deposition rate increased without narrowing the window. The fabricated YSZ films showed good texture qualities and surface morphologies.