• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.953-957
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• 2001

To study various relaxation phenomena of $Pb(Mg_{1/3}Nb_{2/3})O_3$ relaxor ferroelectrics, weak electric-field properties as well as strong electric-field properties were investigated in the frequency range from 1 Hz to 100 kHz. The temperature dependence of the dielectric properties were measured under the low electric-field of 1 V/mm in the phase transition temperature range from $-40^{\circ}C$ to $90^{\circ}C$. The dielectric properties obtained from the slope of the dielectric hysteresis loop and the temperature dependence of the pyroelectric properties were also investigated. When fitting all the experimental data with the Vogel-Fulcher relation, experimental data were agreed with the equation closely. Thus, dielectric relaxations could be modeled by the Vogel-Fulcher relation not only for the low electric-field but also for the high electric-field.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.68-68
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• 2003

최근의 전자부품은 고밀도 고집적화 됨에 따라 여러 가지 문제점들이 발생되고 있다. 그 중 부품이 실장되는 부분에 사용되는 솔더나 전기적 회로를 구성하는 패턴간에 금속 이온 마이그레이션(Metallic Ion Migration)이 발생하여 전기적 단락(Short)를 유발함으로써 전자제품의 치명적 고장을 유발한다. 본 연구는 이온 마이그레이션 현상을 물방울시험(Water Drop Test)을 통하여 재현함으로써 발생 메카니즘을 확인하여 발생원인을 직접적으로 관찰하고, 각 종 패턴의 거리 및 전압에 따른 발생속도의 차이를 조사하기 위하여 수행되었다. 이러한 실험을 위하여 콤 패턴(Comb Pattern)의 FR-4 재질 인쇄회로기판(PCB : Printed Circuit Board)을 사용하였으며, 사용된 전극재질로는 Cu, SnPb, Au를 사용하였고, 패턴간 거리는 0.5, 1.0, 2.0mm의 3가지 종류로 구분하였다. 또한 패턴간에 인간 된 전압은 6.5V, 15V를 인가한 후 마이그레이션이 발생되는 시간을 측정하였다. 이러한 실험으로부터 다음과 같은 결론을 얻었다. (1) 6.5V의 인가전압에서는 Cu 패턴이 대체적으로 가장 빠르게 마이그레이션이 발생하였으며, 다음으로 Au가 발생하였고, Cu와 SnPb의 발생시간은 대체적으로 근사한 값을 나타내었다. 이것은 비슷한 평형전위를 갖는 재료는 마이그레이션 발생시간이 유사하게 나타나며, 높은 (+)전위를 갖을수록 발생시간이 지연됨을 알 수 있다. (2) 15V를 인가하였을 때 패턴간격이 0.5mm인 경우 Cu, Au, SnPb의 순으로 나타났으며, 1.0mm는 SnPb, Cu, Au, 2.0mm인 경우는 SnPb, Au, Cu의 순으로 마이그레이션이 발생하였다. 인가전압이 높은 경우 초기 발생에는 큰 차이가 없지만 수지상이 발생 후 성장하는데 많은 영향을 미치는 것으로 보인다. 이것은 초기 수지상의 형성에 큰 영향을 미치는 것은 재료의 평형전위에 의한 값이 좌우하지만, 수지상이 일정길이 이상 형성된 이후에는 성장속도가 평형전위에 따른 값과는 다소 다르게 나타남을 알 수 있다.

• Korean Journal of Materials Research
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• v.12 no.2
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• pp.160-165
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• 2002

High-frequency dielectric and microwave absorbing properties have been investigated in ferroelectric materials (BaTiO$_3$(BT), (1-x)Pb$Mg_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O$_3$-xPbTiO$_3$(PMN-PT), (1-x)Pb$Mg_{\frac{1}{3}}Nb_{\frac{2}{3}}$O$_3$-xPb(Zn_{\frac{1}{3}}Nb_{\frac{2}{3}}$)O$_3$(PMN-PZN) for the aim of thin microwave absorbers in the frequency range of mobile telecommunication. The specimenns are prepared by conventional ceramic processing and complex permittivity has been measured by transmission/reflection method. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave range and their domiant loss mechanism is considered to be domain wall relaxation. The microwave absorbance of BT 0.9PMN-0.1PT, and 0.8PMN-0.2PZN specimen (determined at 2) are found to be 99.5% (at a thickness of 4.5 mm), 50% (2.5 mm), and 30% (2.5 mm), respectively. It is suggested that PMN-PT or PMN-PZN ferroelectrics are good candidate materials for the spacer of λ/4 absorber. The use of ferroelectric materials is effective in reducing the thickness of absorber with their advantage of high dielectric constant.

• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.571-580
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• 2018

In this study, hybrid adsorbents (SS) were prepared by mixing spent coffee grounds (SCG) and sericite, a kind of clay minerals, to adsorb Pb(II) from an aqueous solution. In FT-IR analyses, the main functional groups of SS adsorbents were O-H, C=O and C-N groups. The specific surface area, cation exchange capacity and the pore diameter of SS were larger than those of using SCG and sericite. Formation conditions of the SS adsorbent were the optimum pyrolysis temperature of $300^{\circ}C$, SCG : sericite ratio of 8 : 2, and particle size of 0.3 mm. Langmuir adsorption isotherm was more suitable than Freundlich one, and the maximum adsorption capacity was reached 44.42 mg/g. As a result of the adsorption thermodynamic analysis, the adsorption of Pb(II) onto SS was the physical adsorption and exothermic process in nature. The regeneration of SS adsorbent using distilled water showed 88~92% recovery and the active site of SS adsorbent decreased with increasing the reuse cycle time. As a result, SS adsorbent showed that it can be used to remove Pb(II) easily, inexpensively and efficiently without any pre-treatment from aqueous solutions.

• Journal of the Korean Society of Radiology
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• v.8 no.7
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• pp.449-454
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• 2014

The purpose of this study is(was) to investigate the shielding ratio of 1 mmPb and the off axis ratio outside the field edge at depth of 1 cm from a phantom surface for 6 MV photon beam. A dose of 180 cGy was delivered to a depth of 10 cm for a $10{\times}10cm^2$ and $15{\times}15cm^2$ field in the SAD technique. The off axis ratio was calculated by measuring the dose of optically stimulated luminescent nanoDot dosimeters(OSLnDs) positioned at 2, 4 and 6 cm from the field edge, and the center axis of field. And the shielding ratio of 1 mmPb was calculated by measuring the dose of OSLnDs positioned at 2, 4 and 6 cm from the field edge.. As a result, for a $10{\times}10cm^2$ and $15{\times}15cm^2$ field, the off axis ratios were acquired 0.008-0.023 and 0.011-0.028, respectively. Also the shielding ratios of 1 mmPb were acquired 0.868-0.888 and 0.807-0.842, respectively. These results provide data to protect organs at risk outside the radiation treatment field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.2
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• pp.191-196
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• 2023

In this paper, for the application of ultrasonic cleaners for cleaning dentures and transparent braces, Pb(Mn_1/3Nb_2/3)O₃-Pb(Ni_1/3 Nb_2/3)O₃-Pb(Zr,Ti)O₃ [PMN-PNN-PZT] system ceramics were manufactured and their dielectric and piezoelectric properties were investigated. Overall the best properties suitable for the device applications such as ultrasonic cleaner were obtained from the ceramics sintered at 920℃: bulk density of 7.8 g/cm³, the dielectric constant (ε_r) of 1,689, piezoelectric charge constant (d₃₃) of 433 pC/N, planar electromechanical coupling factor (k_p) of 0.64, mechanical quality factor (Qm) of 835, S₁₁^E of 13.37 (10^-12 N/m²), and Curie temperature of 315℃ By using the physical properties of this composition, the ultrasonic cleaner was designed and simulated using the commercial ATILA software. For the three-layered ceramics with the dimension of 25 mm × 25 mm × 2.5mm, an excellent displacement of 8.998 10^-3 m) and the sound pressure of 147.68 dB were recorded.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.259-265
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• 2003

For the aim of thin microwave absorbers used in mobile telecommunication frequency band, this study proposed a high permittivity dielectrics(λ/4 spacer) coated with ITO thin films of 377 $\Omega$/sq(impedance transformer). High frequency dielectric properties of ferroelectric ceramics, electrical properties of ITO thin films and microwave absorbing properties of ITO/dielectrics were investigated. Ferroelectric materials including $BaTiO_3$(BT), 0.9Pb($Mg_{1}$3/Nb$_{2}$3/)$O_3$-0.1 $PbTiO_3$(PMN-PT), 0.8 Pb (Mg$_{1}$3/$Nb_{2}$3/)$O_3$-0.2 Pb($Zn_{1}$3$_Nb{2}$3/)$O_3$(PMN-PZN) were prepared by ceramic processing for high permittivity dielectrics,. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave frequency range. The microwave absorbance (at 2 ㎓) of BT, 0.9PMN-0.1PT, and 0.8PMN-0.2PZN were found to be 60%(at a thickness of 3.5 mm), 20% (2.5 mm), and 30% (2.5 mm), respectively. By coating the ITO thin films on the ferroelectric substrates with λ/4 thickness, the microwave absorbance is greatly improved. Particularly, when the surface resistance of ITO films is closed of 377 $\Omega$/sq, the reflection loss is reduced to -20 ㏈(99% absorbance). This is attributed to the wave impedance matching controlled by ITO thin films at a given thickness of high permittivity dielectrics of λ/4 (3.5 mm for BT, 2.5 mm for PMN-PT and PMN-PZN at 2 ㎓). It is, therefore, successfully proposed that the ITO/ferroelectric materials with controlled surface resistance and high dielectric constant can be useful as a thin microwave absorbers in mobile telecommunication frequency band.

• Journal of the Korean Society of Radiology
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• v.10 no.8
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• pp.559-563
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• 2016

Recently, a barium(Ba) and an iodine(I) being studied as a conventional lead(Pb) alternatives of shielding material has excellent shieding rate, but the characteristic x-ray photons in the energy range near 30 keV line is released. In this study, with bismuth oxide(BiO) coupled barium sulfate($BaSO_4$) double layer, transmitted spectra, shieding rates and relative weighting rates were evaluated to validate the applicability of eco-friendly double layer shieding structure using monte carlo simulations as a prior study. From the evaluation results, in 0.4mm and 0.5mm thickness of BiO layers coupled with top 0.1mm-$BaSO_4$ layer, the shieding rate showed 1.9% and 3.9% higher than 0.6mm thickness of Pb single layer, respectively. In addition, the relative weight also 28% and 34.5% lower than 0.6mm-Pb in 0.4mm and 0.5mm thickness of BiO layers coupled with top 0.1mm-$BaSO_4$ layer.

• Journal of Korea Foundry Society
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• v.17 no.3
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• pp.252-257
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• 1997

The 8 mm dia: Sn-38%Pb eutectic alloy rods were produced by use of the horizontal continuous casting process with the heated mold and chill cast process. The cast rods were rolled into 2.0${\sim}$0.5 mm thick plates and structural and mechanical properties were examined. The results revealed that the plates produced by the continuous casting process with the heated mold show much higher superplasticity at ambient temperature (1550% elongation at 0.5mm thick plate and 0.5mm/min strain rate) than the plates procuced by chill cast process (630% elongation). Such a high superplasticity of the continuous cast plates is due to the high-quality plates free from any inside and surface defects with fine and uniform distribution of eutectic phases.

• The Journal of Korean Society for Radiation Therapy
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• v.27 no.1
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• pp.87-95
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• 2015

Purpose : This study presents the usefulness assessment of secondary shield for the lens exposure dose reduction during radiation treatment of peripheral orbit. Materials and Methods : We accomplished IMRT treatment plan similar with a real one through the computed treatment planning system after CT simulation using human phantom. For the secondary shield, we used Pb plate (thickness 3mm, diameter 25mm) and 3 mm tungsten eye-shield block. And we compared lens dose using OSLD between on TPS and on simulation. Also, we irradiated 200 MU(6 MV, SPD(Source to Phantom Distance)=100 cm, $F{\cdot}S\;5{\times}5cm$) on a 5cm acrylic phantom using the secondary shielding material of same condition, 3mm Pb and tungsten eye-shield block. And we carried out the same experiment using 8cm Pb block to limit effect of leakage & transmitted radiation out of irradiation field. We attached OSLD with a 1cm away from the field at the side of phantom and applied a 3mm bolus equivalent to the thickness of eyelid. Results : Using human phantom, the Lens dose on IMRT treatment plan is 315.9cGy and the real measurement value is 216.7cGy. And after secondary shield using 3mm Pb plate and tungsten eye-shield block, each lens dose is 234.3, 224.1 cGy. The result of a experiment using acrylic phantom, each value is 5.24, 5.42 and 5.39 cGy in case of no block, 3mm Pb plate and tungsten eye-shield block. Applying O.S.B out of the field, each value is 1.79, 2.00 and 2.02 cGy in case of no block, 3mm Pb plate and tungsten eye-shield block. Conclusion : When secondary shielding material is used to protect critical organ while irradiating photon, high atomic number material (like metal) that is near by critical organ can be cause of dose increase according to treatment region and beam direction because head leakage and collimator & MLC transmitted radiation are exist even if it's out of the field. The attempt of secondary shield for the decrease of exposure dose was meaningful, but untested attempt can have a reverse effect. So, a preliminary inspection through Q.A must be necessary.