• 한국구조물진단유지관리공학회 논문집
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• 제21권3호
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• pp.138-144
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• 2017

전 세계 적으로 이산화탄소 배출 저감을 위한 노력으로 시멘트 산업에서는 비소성 결합재인 석회석을 시멘트에 첨가하여 콘크리트를 제조하고 있다. 특히, 유럽에서는 석회석을 시멘트의 35%까지 치환하여 사용하기도 한다. 국내에서는 2013년에 KS L 5201을 개정하여 석회석을 보통 포틀랜드 시멘트에 5%까지 혼합하여 사용할 수 있도록 하였으며, 아직 석회석 혼합 시멘트에 대한 규격은 전무한 상태이다. 본 연구에서는 비소성 결합재인 석회석을 활용하여, 석회석 혼입량에 따른 콘크리트의 역학적 특성 및 내구특성에 대한 영향을 살펴보았다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.336-337
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• 2005

ZnO varistor ceramics were fabricated as a function of the amount of $Y_2O_3$ addition and sintered at $1250^{\circ}C$ for 2 hour. The average grain size was decreased from 14.2 ${\mu}m$ to 8.3 ${\mu}m$ with the amount of $Y_2O_3$ addition, and varistor voltage was increased from 433 V to 563 V with $Y_2O_3$ addition. Nonlinear coefficient a of all specimens were increased with the amount of $Y_2O_3$ more than 67, in case of $Y_2O_3$ 0.01wt% addition showed the excellent results of 87. And leakage current was less than $1{\mu}A$ at 82% of varistor voltage. The clamping voltage ratio of the specimens added 0.01wt% $Y_2O_3$ was 1.41 at 25A [8/20${\mu}s$]. At the specimen 0.01wt% $Y_2O_3$ addition. endurance of surge current and deviation of varistor voltage were 5700A/$cm^2$ and $\Delta$-2.86%, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.265-265
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• 2007

In the present work, we have studied low temperature sintering and microwave dielectric properties of $ZnAl_2O_4$-zinc borosilicate (ZBS, 65ZnO-$25B_2O_3-10SiO_2$) glass composites. The focus of this paper was on the improvement of sinterability, low dielectric constant, and on the theoretical proof regarding of microwave dielectric properties in $ZnAl_2O_4$-ZBS glass composites, respectively. The $ZnAl_2O_4$ with 60 vo1% ZBS glass ensured successful sintering below $900^{\circ}C$. It is considered that the non-reactive liquid phase sintering (NPLS) occurred. In addition, $ZnAl_2O_4$ was observed in the $ZnAl_2O_4$-(x)ZBS composites, indicating that there were no reactions between $ZnAl_2O_4$ and ZBS glass. $ZnB_2O_4\;and\;Zn_2SiO_4$ with the willemite structure as the secondary phase was observed in the all $ZnAl_2O_4$-(x)ZBScomposites. In terms of dielectric properties, the application of the $ZnAl_2O_4$-(x)ZBS composites sintered at $900^{\circ}C$ to LTCC substrate were shown to be appropriate; $ZnAl_2O_4$-60ZBS (${\varepsilon}_r$= 6.7, $Q{\times}f$ value= 13,000 GHz, ${\tau}_f$= -30 ppm/$^{\circ}C$). Also, in this work was possible theoretical proof regarding of microwave dielectric properties in $ZnAl_2O_4$-(x)ZBS composites.

• 대한금속재료학회지
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• 제48권4호
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• pp.369-375
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• 2010

Ti-6Al-4V ELI alloy, which is commonly used as a biomaterial, is associated with a high elastic modulus and poor biocompatibility. This alloy presents a variety of problems on several areas. Therefore, the development of good non-toxic biocompatible biomaterials with a low elastic modulus is necessary. Particularly, hydroxyapatite (HA) is an attractive material for human tissue implantation. This material is widely used as artificial bone due to its good biocompatibility and similar composition to human bone. Many scientists have studied the fabrication of HA as a biomaterial. However, applications of bulk HA compact are hindered by the low strength of HA when it is sintered. Therefore, HA has been coated on Ti or Ti alloy to facilitate good bonding between tissue and the HA surface. However, there are many problems when doing this, such as the low bonding strength between HA and Ti due to the different thermal expansion coefficients and mechanical properties. In this study, a Ti-HA composite with a porous surface was successfully fabricated by pulse current activated sintering (PCAS) and a subsequent leaching process.

• 대한금속재료학회지
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• 제47권8호
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• pp.508-515
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• 2009

Ti-6Al-4V biomaterial is widely used as a bone alternative. However, Ti-6Al-4V ELI alloy suffers from numerous problems such as a high elastic modulus and high toxicity. Therefore, non-toxic biomaterials with low elastic moduli need to be developed. Ti-HA(hydroxyapatite) composites were fabricated in the present work by pulsed current activated sintering (PCAS) at $1000^{\circ}C$ under 60 MPa using mixed Ti and HA powders. The effects of HA content on the physical and mechanical properties of the sintered Ti-HA composites have been investigated. X-ray diffraction(XRD) analysis of the Ti-HA composites, including Ti-40 wt%HA in particular, revealed new phases, $Ti_{2}O$, CaO, $CaTiO_3$, and TixPy, formed by chemical reactions between Ti and HA during sintering. The hardness of the Ti-HA composites decreased with an increase in HA content. The corrosion resistance of these composites was observed to be an excellent candidate as a commercial Ti-6Al-4 V ELI alloy. A Ti-5 wt%HA composite fabricated by PCAS is recommended as a new biomaterial, because it offers good corrosion resistance, compressive strength, wear resistance, and biocompatibility, and a low Young's modulus.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.47-51
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• 2022

With the innovative development of bio, pharmaceutical, and semiconductor technologies, it is essential to demand a next-generation transfer system that minimizes dust and vibrations generated during the manufacturing process. In order to develop dust-free and non-contact transfer systems, the high temperature superconductor (HTS) bulks have been applied as a magnet for levitation. However, sintered HTS bulk magnets are limited in their applications due to their relatively low critical current density (J_c) of several kA/cm² and low mechanical properties as a ceramic material. In addition, during cooling to cryogenic temperatures repeatedly, cracks and damage may occur by thermal shock. On the other hand, the bulk magnets made by stacked HTS tapes have various advantages, such as relatively high mechanical properties by alternate stacking of the metal and ceramic layer, high magnetic levitation performance by using coated conductors with high J_c of several MA/cm², consistent superconducting properties, miniaturization, light-weight, etc. In this study, we tried to fabricate HTS tapes stacked bulk magnets with 60 mm × 60 mm area and various numbers of HTS tape stacked layers for magnetic levitation. In order to examine the levitation forces of bulk magnets stacked with HTS tapes from 1 to 16 layers, specialized force measurement apparatus was made and adapted to measure the levitation force. By increasing the number of HTS tapes stacked layers, the levitation force of bulk magnet become larger. 16 HTS tapes stacked bulk magnets show promising levitation force of about 23.5 N, 6.538 kPa at 10 mm of levitated distance from NdFeB permanent magnet.

• 한국결정성장학회지
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• 제31권6호
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• pp.258-263
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• 2021

ZnO 바리스터는 다결정구조를 가지는 반도체 소자로 결정립과 입계의 미세구조 제어를 통해 비선형적인 전류/전압 특성을 가지기 때문에 서지(surge)전압으로부터 회로를 보호하는 역할을 한다. 이러한 ZnO 바리스터에서 원하는 전기적 물성을 얻기 위해서는 소결 공정에서 미세구조의 제어가 중요하다. 따라서 소결 공정에서 중요한 변수들과 소결체의 전기적 물성인 유전율로 구성된 데이터셋을 정의한 후 실험계획법 기반으로 데이터를 수집했다. 수집된 실험데이터셋을 기계학습 알고리즘에 학습하여 메타모델을 개발했고, 개발된 메타모델에 수치기반 최적화 알고리즘인 HMA(Hybrid Metaheuristic Algorithm)를 적용하여 최대 유전율을 가질 수 있는 공정조건을 도출했다. 이러한 메타모델 기반의 최적화를 다변수 시스템인 세라믹공정에 적용한다면 최소한의 실험만으로 최적 공정조건 탐색이 가능할 것으로 판단된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.533-537
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• 2003

Compared to sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills. Because of high performance in high speed machining non-ferrous difficult-to-cut materials in the field of automobiles industry, aeronautics and astronautics industry, diamond-coated drills find large potentialities in commercial applications. However, the poor adhesion of the diamond film on the substrate and high surface roughness of the drill flute adversely affect the tool lift and machining quality and they become the main technical barriers for the successful development and commercialization of diamond-coated drills. In this paper, diamond thin films were deposited on the commercial WC-Co based drills by the electron aided hot filament chemical vapor deposition (EACVD). A new multiple coating technology based on changing gas pressure in different process stages was developed. The large triangular faceted diamond grains may have great contribution to the adhesive strength between the film and the substrate, and the overlapping ball like blocks consisted of nanometer sized diamond crystals may contribute much to the very low roughness of diamond film. Adhesive strength and quality of diamond film were evaluated by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectrum and drilling experiments. The ring-block tribological experiments were also conducted and the results revealed that the friction coefficient increased with the surface roughness of the diamond film. From a practical viewpoint, the cutting performances of diamond-coated drills were studied by drilling the SiC particles reinforced aluminum-matrix composite. The good adhesive strength and low surface roughness of flute were proved to be beneficial to the good chip evacuation and the decrease of thrust and consequently led to a prolonged tool lift and an improved machining quality. The wear mechanism of diamond-coated drills is the abrasive mechanical attrition.

• 자원환경지질
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• 제54권2호
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• pp.285-297
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• 2021

전세계적으로 해체 대상 원자력 시설이 증가하고 있으며, 이러한 원자력 시설을 해체하게 되면 수십만 톤의 콘크리트, 토양, 금속 등의 폐기물이 발생한다. 따라서 고상 방사성 폐기물 감용 및 재활용 기술에 대한 기존 연구를 면밀히 검토할 필요가 있다. 폐콘크리트 미분말은 소성 및 분쇄와 같은 추가적인 공정을 통하여 재수화 반응이 일어나며, 시멘트 수화 반응 및 고화체 압축강도에 영향을 미치는 주요 화합물인 aluminate (C3A), C4AF, C3S, ��-C2S가 생성된다. 기존 연구를 통하여 폐콘크리트 미분말을 재생 시멘트로 재활용할 수 있음을 확인하였으나, 골재의 혼입으로 인한 고화체의 강도 저하와 같은 문제점에 대한 해결방안은 현재까지 연구되지 않았다. 이러한 문제점을 보완하기 위하여 산업부산물인 고로슬래그, 비산회를 성분 조정재로 혼합하여 재생 시멘트의 성능을 증진시키는 연구가 수행되었으며, 고화체의 압축강도가 증진되는 것을 확인하였다. 그러나, 폐토양을 재활용한 비소성 시멘트의 제조에 대한 연구는 많이 수행되지 않았다. 폐토양 내 함유된 일라이트와 제올라이트는 방사성 핵종에 대한 흡착능이 우수하며, 이를 고화재로 재활용하면 원전 해체 폐기물의 부피를 저감함과 동시에 방사성 폐기물을 안전하게 담지할 수 있는 효과를 도출할 수 있다. 이러한 이유에서 폐토양 내 점토 광물을 이용한 비소성 시멘트의 제조에 대한 연구가 필요하다. 본 연구에서는 기존에 수행된 국내외 연구를 통하여 원전 해체 폐기물인 콘크리트의 재생 시멘트로서 재활용 가능성 및 개선 방안과 더불어 폐토양 내 점토 광물을 이용한 비소성 시멘트 제조에 대한 연구 필요성에 대하여 고찰하였다.

• 한국전기전자재료학회논문지
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• 제27권12호
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• pp.803-808
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• 2014

$Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3$ ceramics with an excess $Bi^{3+}$ and a deficiency of $Na^+$ and $K^+$ were synthesized by a conventional solid state reaction method. The structure and morphology of $Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3$ ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. The electric polarization and mechanical strain induced by external electric field, and the temperature dependence of dielectric constant were investigated. These results demonstrated that an ergodic relaxor phase can be induced by controls of the mole ratio of $Bi^{3+}$, $Na^+$ and $K^+$. A phase boundary between non-ergodic and ergodic relaxor phases can be observed at ambient temperature. The ergodic relaxor phase can be transferred to the ferroelectric phase by application of the electric field. The stability of the induced ferroelectric phases strongly depends on the mole ratio of $Bi^{3+}$, $Na^+$ and $K^+$. The maximum strain of 0.31% was observed in $Bi_{0.51}(Na_{0.78}K_{0.22})_{0.47}TiO_3$ ceramics sintered at $1,150^{\circ}C$ for 2 h.