• 전기화학회지
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• 제1권1호
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• pp.45-51
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• 1998

Ni-MH 전지의 음극으로 쓰이는 수소저장합금(MH)의 한 종류인 $AB_2$계 합금은 수소저장량이 큰 장점이 있으나 초기활성화나 싸이클 수명 및 자기방전 특성이 나쁜 단점이 있다. 본 연구에서는 Zr-Ti-V-Mn-Ni계 합금에 비화학양론적으로 Cr을 소량 첨가했을 때와 La을 첨가하여 불화처리 했을 때의 초기활성화, 싸이클 수명 및 자기방전에 미치는 영향을 조사하였다 EPMA 및 SEM을 이용하여 합금의 표면을 분석하였으며 XRD 분석으로 결정구조를 관찰하였다. 또한 합금으로 전극을 제조하여 정전류 시험법, 임피던스법과 전위주사법 등에 의해 전극특성을 조사하였다. Cr이 첨가될수록 전극표면에 안정한 산화막이 형성되어 V등의 전해질로의 용해를 막아주어 충, 방전에 따른 수명특성 및 자기방전 특성을 향상시키지만 초기 전하이동 반응이 저해되어 초기활성화 특성이 악화되었다. La을 첨가 후 불화처리하면 표면에 반응성이 좋은 입자를 형성하여 전극의 초기 활성화가 크게 향상되었다.

• 한국주조공학회지
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• 제23권3호
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• pp.137-146
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• 2003

The main purpose of this study is to investigate the effects of process parameter on alpha-case formation of Ti and TiAl castings. The previous studies showed that the molten titanium is excessively reactive to the refractory oxide mold, resulting in alpha-caes of the titanium castings regardless of composition of titanium alloys. However, the behavior of the alpha-case formation of TiAl alloy is not consistent with conventional titanium alloy. In order to investigate the alpha-case formation of Ti and TiAl castings with process parameter, especially the associated factors of investment mold such as mold material, binder and mold preheating temperature. An attempt has been made to characterize the alpha-case of titanium casting by using optical microscope, EDS, XRD, EMPA and hardness profiles. The formation of the alpha-case on the surface of pure titanium during investment casting was rather by that of solid solution with metallic element from mold material. The required mold strength was obtained with $CaZrO_3$ because of the possibility of using water soluble binder. However, the separation phenomenon between facing and back-up mold materials should be considered. The interfacial reaction of TiAl alloy showed different behavior from that of pure titanium and $Al_2O_3$ was best mold materials. The effect of binder as well as mold material on the formation of alpha-case was significant.

• 열처리공학회지
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• 제4권3호
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• pp.13-20
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• 1991

The present work was aimed to examine the variation of precipitations and mechanical properties by thermomechanical treatments (TMT) in Al-2.19 wt%Li and Al-2.0 wt%Li-0.11 wt%Zr alloys. This study was performed by TEM, SEM observation, DSC, electrical resistance measurement, hardness and tensile strength measurement. First peak of resistivity aged at $90^{\circ}C$ was caused by precipitation of ${\delta}^{\prime}$-precursor phase, and second peak was caused by precipitation of ${\delta}^{\prime}$ phase. According to this result, the precipitation process of Al-2.19 wt%Li alloy was as follow : $SSSS{\rightarrow}{\delta}^{\prime}$-precursor phase ${\rightarrow}{\delta}^{\prime}$ (Coherent ${\rightarrow}$ Semi-coherent) ${\rightarrow}{\delta}$. In a Al-2.0 wt%Li-0.11 wt%Zr ternary alloy, the first peak of resistivity was appeared at initial aging heat-treatment. It is result from exsistant of ${\delta}^{\prime}$-precursor phase. The effect acceleration in a binary alloy was not appeared and the over-aging ternary alloy was accelerated with increase of the reduction rate. It is caused by combination effect of ${\delta}^{\prime}$ and composite phase.

• Nuclear Engineering and Technology
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• 제40권1호
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• pp.21-36
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• 2008

High bum-up fuel technology has been developed through a national R&D program, which covers key technology areas such as claddings, $UO_2$ pellets, spacer grids, performance code, and fuel assembly tests. New cladding alloys were developed through alloy designs, tube fabrication, out-of-pile test and in-reactor test. The new Zr-Nb tubes are found to be much better in their corrosion resistance and creep strength than the Zircaloy-4 tube, owing to an optimized composition and heat treatment of the new Zr-Nb alloys. A new fabrication technology for large grain $UO_2$ pellets was developed using various uranium oxide seeds and a micro-doping of Al. The uranium oxide seeds, which were added to $UO_2$ powder, were prepared by oxidizing and heat-treating scrap $UO_2$ pellets. A $UO_2$ pellet containing tungsten channels was fabricated for a thermal conductivity enhancement. For the fuel performance analysis, new high burnup models were developed and implemented in a code. This code was verified by an international database and our own database. The developed spacer grid has two features of contoured contact spring and hybrid mixing vanes. Mechanical and hydraulic tests showed that the spacer grid is superior in its rodsupporting, wear resistance and CHF performance. Finally, fuel assembly test technology was also developed. Facilities for mechanical and thermal hydraulic tests were constructed and are now in operation. Several achievements are to be utilized soon by the Korea Nuclear Fuel and thereby contribute to the economy and safety of PWR fuel in Korea

• 한국재료학회지
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• 제11권2호
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• pp.104-114
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• 2001

Zr-Sn-Nb 합금의 재결정에 미치는 Nb과 Sn의 첨가영향을 연구하기 위해 냉간압연한 시편을 $300^{\circ}C$~75$0^{\circ}C$의 온도구간에서 열처리한 후에 미소경도와 TEP (Thermoelectric Power)를 측정하여 재결정 거동을 조사하였으며 광학현미경, 주사전자 현미경 (SEM), 투과전자현미경 (TEM)으로 미세조직을 관찰하였다 미소경도 및 미세조직의 분석 결과에 따르면, Nb과 Sn의 첨가에 의해 재결정 활성화 에너지가 증가하여 재결정이 지연되었으며, 재결정 완료 이후의 결정립 성장도 억제되었음을 관찰하였다. Zr내의 고용도가 매우 낮은 Nb의 첨가는 석출물을 쉽게 형성하는 반면에 고용도가 비교적 큰 Sn은 기지상 내에 대부분 고용되어 석출물의 양이 매우 작았으나, Sn 첨가에 의한 재결정의 지연 효과가 더욱 컸다. Nb보다 Sn의 첨가가 Zr 합금의 재결정 거동을 효과적으로 지연시킨 것은 고용도가 높은 SR에 의한 치환형 고용체 형성과정에서 발생된 응력장이 전위의 이동을 효과적으로 억제했기 때문으로 생각된다. 한편, 회복과 재결정이 진행됨에 따라 전자 산란인자의 감소로 TEP는 증가하였으며, 재결정이 완료되면 TEP의 포화가 발생하였다. 석출물의 형성은 석출물 주변의 용질농도 감소로 인한 전자 산란인자의 감소에 기인하여 TEP의 증가를 가져왔다

• 멤브레인
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• 제34권2호
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• pp.146-153
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• 2024

본 실험에서는 Ti를 기반으로 한 평판 수소 분리막을 설계하여 제조하였다. 새로운 조성의 Ti를 베이스로 한 수소 분리막을 찾기 위하여 여러 합금들의 물리화학적 특성과 수소투과도 사이의 상관관계에 대해 조사하였다. 이를 바탕으로 신조성의 합금막 2종(Ti_14.2Zr_66.4Ni_12.6Cu_6.8 (70 ㎛), Ti_17.3Zr_62.7Ni₂₀ (80 ㎛))을 설계 및 제조하였다. 제조된 평판 수소 분리막은 300~500℃, 1~4 bar의 조건에서 혼합 가스(H₂, N₂), sweep 가스(Ar)를 이용하여 수소 투과 실험을 진행하였다. Ti_14.2Zr_66.4Ni_12.6Cu_6.8 합금막은 500℃, 4bar에서 최대 16.35 mL/cm² min의 flux를 가지며, Ti_17.3Zr_62.7Ni₂₀ 합금막은 450℃, 4 bar에서 최대 10.28 mL/cm² min의 flux를 가진다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.195-195
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• 2016

Titanium and its alloys are widely used as implants in orthopedics, dentistry and cardiology due to their outstanding properties, such as high strength, high level of hemocompatibility and enhanced biocompatibility. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element, such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}-stabilizer$ and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. The aim of this study is to research Si and Mg doped hydroxyapatite film formation by plasma electrolytic oxidation. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. A Si and Mg coating was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• 한국재료학회지
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• 제22권3호
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• pp.150-154
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• 2012

Ti-6Al-4V ELI (Extra Low Interstitial) alloy have been widely used as alternative to bone due to its excellent biocompatibility, although it still has many problems such as high elastic modulus and toxicity. Therefore, biomaterials with low elastic modulus and non toxic characteristics have to be developed. A novel ${\beta}$ Ti-35wt%Nb-7wt%Zr-Calcium pyrophosphate (CPP) composite that is a biocompatible alloy without elemental Al or V was fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70 MPa using high energy mechanical milled (HEMM) powder. The microstructure and phases of the milled powders and the sintered specimens were studied using SEM, TEM, and XRD. Ti-35wt%Nb-7wt%Zr alloy was transformed from ${\alpha}$ phase to ${\beta}$ phase in the 4h-milled powder by sintering. The sintered specimen using the 4h-milled powder showed that all the elements were distributed very homogeneously and had higher density and hardness. ${\beta}$ Ti alloy-CPP composite, which has nanometer particles, was fabricated by SPS using HEMMed powder. During the sintering process, $CaTiO_3$, TixOy, and CaO were formed because of the reaction between Ti and CPP. The Vickers hardness of the composites increases with the increase of the milling time and the addition of CPP. The biocompatibility of the Ti-Nb-Zr alloys was improved by addition of CPP.

• 한국재료학회지
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• 제29권4호
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• pp.271-276
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• 2019

Oxide-dispersion-strengthened (ODS) alloy has been developed to increase the mechanical strength of metallic materials; such an improvement can be realized by distributing fine oxide particles within the material matrix. In this study, the ODS layer was formed in the surface region of Zr-based alloy tubes by laser beam treatment. Two kinds of Zr-based alloys with different alloying elements and microstructures were used: KNF-M (recrystallized) and HANA-6 (partial recrystallized). To form the ODS layer, $Y_2O_3$-coated tubes were scanned by a laser beam, which induced penetration of $Y_2O_3$ particles into the substrates. The thickness of the ODS layer varied from 20 to $55{\mu}m$ depending on the laser beam conditions. A heat affected zone developed below the ODS layer; its thickness was larger in the KNF-M alloy than in the HANA-6 alloy. The ring tensile strengths of the KNF-M and HANA-6 alloy samples increased more than two times and 20-50%, respectively. This procedure was effective to increase the strength while maintaining the ductility in the case of the HANA-6 alloy samples; however, an abrupt brittle facture was observed in the KNF-M alloy samples. It is considered that the initial microstructure of the materials affects the formation of ODS and the mechanical behavior.

• Corrosion Science and Technology
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• 제6권2호
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• pp.37-43
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• 2007

Iodine sulfur (IS) process is one of the promising processes for a hydrogen production by using a high temperature heat generated by a very high temperature gas cooled reactor(VHTR) in the nuclear power industries. Even though the IS process is very efficient for a hydrogen production and it is not accompanied by a carbon dioxide evolution, the highly corrosive environment of the process limits its application in the industry. Corrosion tests of selected materials were performed in sulfuric acid to select appropriate materials compatible with the IS process. The materials used in this work were Fe-Cr alloys, Fe-Ni-Cr alloys, Fe-Si alloys, Ni base alloys, Ta, Ti, Zr, SiC, Fe-Si, etc. The test environments were 50 wt% sulfuric acid at $120^{\circ}C$ and 98 wt% at $320^{\circ}C$. Corrosion rates were measured by using a weight change after an immersion. The surface morphologies and cross sectional areas of the corroded materials were examined by using SEM equipped with EDS. Corrosion behaviors of the materials were discussed in terms of the chemical composition of the materials, a weight loss, the corrosion morphology, the precipitates in the microstructure and the surface layer composition.