• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1104-1105
• /
• 2006

Several boride sintered bodies such as $TiB_2$, $ZrB_2$, and $SiB_6$ were previously reported. In the present study, the sinterability and physical properties of chromium boride $(CrB_2)$ containing chromium carbide $(Cr_3C_2)$ sintered bodies were investigated in order to determine its new advanced material. The samples were sintered at desired temperature for 1 hour in vacuum under a pressure by hot pressing. The relative density of sintered bodies was measured by Archimedes' method. The relative densities of $CrB_2$ addition of 0, 5, 10, 15 and 20 mass% $Cr_3C_2$ composites were 92 to 95%. The Vickers hardness of the $CrB_2$ with 10 and 15 mass% $Cr_3C_2$ composites were about 14 and 15 GPa at room temperature, respectively. The Vickers hardness at high temperature of the $CrB_2$ addition of 10 mass% $Cr_3C_2$ composite decreased with increasing measurement temperature. The Vickers hardness at 1273 K of the sample was 6 GPa. The Vickers hardness of $CrB_2$ addition of $Cr_3C_2$ composites was higher than monolithic $CrB_2$ sintered body. The powder X-ray diffraction analysis detected CrB and $B_4C$ phases in $CrB_2$ containing $Cr_3C_2$ composites.

• Nuclear Engineering and Technology
• /
• v.50 no.2
• /
• pp.223-228
• /
• 2018

AREVA NP (Courbevoie, Paris, France) is actively developing several enhanced accident-tolerant fuels cladding concepts ranging from near-term evolutionary (Cr-coated zirconium alloy cladding) to long-term revolutionary (SiC/SiC composite cladding) solutions, relying on its worldwide teams and partnerships, with programs and irradiations planned both in Europe and the United States. The most advanced and mature solution is a dense, adherent chromium coating on zirconium alloy cladding, which was initially developed along with the CEA and EDF in the French joint nuclear R&D program. The evaluation of the out-of-pile behavior of the Cr-coated cladding showed excellent results, suggesting enhanced reliability, enhanced operational flexibility, and improved economics in normal operating conditions. For example, because chromium is harder than zirconium, the Cr coating provides the cladding with a significantly improved wear resistance. Furthermore, Cr-coated samples exhibit extremely low corrosion kinetics in autoclave and prevents accelerated corrosion in harsh environments such as in water with 70 ppm Li leading to improved operational flexibility. Finally, AREVA NP has fabricated a physical vapor deposition prototype machine to coat full-length cladding tubes. This machine will be used for the manufacturing of full-length lead test rods in commercial reactors by 2019.

• Korean Journal of Materials Research
• /
• v.9 no.3
• /
• pp.263-268
• /
• 1999

In this study, a new concept of aluminum-matrix composites and the possibility of in-situ processing are suggested, and preliminary results on AI- Ti system are presented. Fine powders of AI-lO% Ti were prepared by the gas atomization so that fine $Al_3Ti$ formed into flake shape. A 25v/o $Al_3Ti/Al$ composite sample was made by the pow­d er metallurgy process involving hot extrusion. Microstructure and mechanical behavior both at room temperature and high temperatures were analysed by OM, SEM, TEM and tension test. Microstructural characteristics and mechanical properties of the composites exhibited similar behavior to those of $SiC_w/2124$ composites. Merits and drawbacks of the $Al_3Ti/Al$ composites are discussed together with a possibility of further improvement.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.135-135
• /
• 2016

차세대 가스터빈 엔진 및 초음속 항공기 내 고온부의 온도가 증가함에 따라, 기존의 초내열합금 기반 소재를 사용하기 어려워지고 있다. 초고온 세라믹스는 높은 기계적 물성, 화학적 안정성 등 우수한 고온 특성을 가지고 있어 기존의 초고온 소재를 대체 할 수 있는 물질로 부상되고 있다. 하지만 기존의 금속 기반 소재 대비 높은 밀도로 인하여 초고온 세라믹 단일체를 비행체 부품에 적용하기에는 어려움이 있다. 이에 초고온 세라믹스와 탄소섬유를 포함하는 세라믹 복합체(Ceramic Matrix Composite, CMC)를 제작하여 동등한 기계적 물성을 보이면서 무게를 감소시키는 연구들이 진행 중에 있다. 초고온 세라믹스가 함침 된 세라믹 복합체의 경우 우수한 내삭마, 내산화 특성을 보이지만, 장시간 고온에 노출되어 탄소 섬유가 드러나게 되면 급격한 산화로 인해 소재 특성의 열화가 진행되는 단점을 가지고 있다. 따라서, 탄소 섬유가 드러나지 않도록 복합체 표면에 코팅층을 형성하여 세라믹 복합체 모재를 보호하는 방법이 활발히 연구되고 있다. 본 연구에서는 진공 플라즈마 용사 공정을 이용하여 다양한 공정조건 하에서 초고온 세라믹 코팅층을 형성하였다. 수십 마이크론 크기 분포를 갖는 HfC 분말을 Ar 유송 가스를 이용하여 플라즈마 화염 내부로 투입하였다. 플라즈마 화염 가스는 Ar 과 H2를 혼합하여 구성되었으며, 분위기 가스로는 N2를 사용하였다. 코팅에 사용된 모재로는 ZrB2 단일체와 SiC가 미량 포함된 HfC 단일체를 사용하였다. 다양한 공정 조건하에서 형성된 HfC 코팅층의 두께, 미세 조직구조를 SEM을 이용하여 관찰하였으며, XRD를 이용하여 형성된 HfC 코팅층의 결정구조를 분석하였다.

• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.611-616
• /
• 2010

A cobalt oxide - tin oxide nanocomposite based gas sensor on an $SiO_2$ substrate was fabricated. Granular thin film of tin oxide was formed by a rheotaxial growth and thermal oxidation method using dc magnetron sputtering of Sn. Nano particles of cobalt oxide were spin-coated on the tin oxide. The cobalt oxide nanoparticles were synthesized by polymer-assisted deposition method, which is a simple cost-effective versatile synthesis method for various metal oxides. The thickness of the film can be controlled over a wide range of thicknesses. The composite structures thus formed were characterized in terms of morphology and gas sensing properties for reduction gas of $H_2$. The composites showed a highest response of 240% at $250^{\circ}C$ upon exposure to 4% $H_2$. This response is higher than those observed in pure $SnO_2$ (90%) and $Co_3O_4$ (70%) thin films. The improved response with the composite structure may be related to the additional formation of electrically active defects at the interfaces. The composite sensor shows a very fast response and good reproducibility.

• Journal of Powder Materials
• /
• v.26 no.5
• /
• pp.421-431
• /
• 2019

In this study, the formation, microstructure, and wear properties of Colmonoy 88 (Ni-17W-15Cr-3B-4Si wt.%) + Stellite 1 (Co-32Cr-17W wt.%) coating layers fabricated by high-velocity oxygen fuel (HVOF) spraying are investigated. Colmonoy 88 and Stellite 1 powders were mixed at a ratio of 1:0 and 5:5 vol.%. HVOF sprayed self-fluxing composite coating layers were fabricated using the mixed powder feedstocks. The microstructures and wear properties of the composite coating layers are controlled via a high-frequency heat treatment. The two coating layers are composed of ${\gamma}-Ni$, $Ni_3B$, $W_2B$, and $Cr_{23}C_6$ phases. Co peaks are detected after the addition of Stellite 1 powder. Moreover, the WCrB2 hard phase is detected in all coating layers after the high-frequency heat treatment. Porosities were changed from 0.44% (Colmonoy 88) to 3.89% (Colmonoy 88 + ST#1) as the content of Stellite 1 powder increased. And porosity is denoted as 0.3% or less by inducing high-frequency heat treatment. The wear results confirm that the wear property significantly improves after the high-frequency heat treatment, because of the presence of well-controlled defects in the coating layers. The wear surfaces of the coated layers are observed and a wear mechanism for the Ni-based self-fluxing composite coating layers is proposed.

• Journal of Electrochemical Science and Technology
• /
• v.15 no.1
• /
• pp.198-206
• /
• 2024

Given the high theoretical capacity (1,675 mAh g^-1) and the inherent affordability and ubiquity of elemental sulfur, it stands out as a prominent cathode material for advanced lithium metal batteries. Traditionally, sulfur was sequestered within conductive porous carbons, rooted in the understanding that their inherent conductivity could offset sulfur's non-conductive nature. This study, however, pivots toward a transformative approach by utilizing diatom shell (DS, diatomite)-a naturally abundant and economically viable siliceous mineral-as a sulfur host. This approach enabled the development of a sulfurlayered diatomite/S composite (DS/S) for cathodic applications. Even in the face of the insulating nature of both diatomite and sulfur, the DS/S composite displayed vigorous participation in the electrochemical conversion process. Furthermore, this composite substantially curbed the loss of soluble polysulfides and minimized structural wear during cycling. As a testament to its efficacy, our Li-S battery, integrating this composite, exhibited an excellent cycling performance: a specific capacity of 732 mAh g^-1 after 100 cycles and a robust 77% capacity retention. These findings challenge the erstwhile conviction of requiring a conductive host for sulfur. Owing to diatomite's hierarchical porous architecture, eco-friendliness, and accessibility, the DS/S electrode boasts optimal sulfur utilization, elevated specific capacity, enhanced rate capabilities at intensified C rates, and steadfast cycling stability that underscore its vast commercial promise.

• Journal of Electrochemical Science and Technology
• /
• v.3 no.3
• /
• pp.116-122
• /
• 2012

As an effort to address the chronic capacity fading of Si anodes and thus achieve their robust cycling performance, herein, we develop a unique electrode in which silicon nanoparticles are embedded in the carbon nanotubes network. Utilizing robust contacts between silicon nanoparticles and carbon nanotubes, the composite electrodes exhibit excellent electrochemical performance : 95.5% capacity retention after 140 cycles as well as rate capability such that at the C-rate increase from 0.1C to 1C to 10C, the specific capacities of 850, 698, and 312 mAh/g are obtained, respectively. The present investigation suggests a useful design principle for silicon as well as other high capacity alloying electrodes that undergo large volume expansions during battery operations.

• Transactions on Electrical and Electronic Materials
• /
• v.12 no.4
• /
• pp.160-163
• /
• 2011

Polymer nanocomposite has been attracting more attention as a new insulation material because homogeneous dispersion of nano-sized inorganic fillers can improve various properties significantly. In this paper, various kinds of epoxy-based nanocomposites were made, and the AC breakdown strengths of Nano filler and micro-$SiO_2$ filler mixtures of epoxy-based composites were analyzed using sphere-to-sphere electrodes. Moreover, nano- and microfiller combinations were investigated as an approach to practical application of nanocomposite insulation materials. Its composition ratio was 100 (resin):82 (hardener):1.5 (accelerator). AC breakdown tests were performed at room temperature ($25^{\circ}C$), $80^{\circ}C$, and $100^{\circ}C$ in the vicinity of $T_g$ ($90^{\circ}C$). Thermal conductivity was measured using TC-30.

• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.623-627
• /
• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.