Formation of nanocrystalline MoSi₂compound subjected to mechanical alloying

Chung-Hyo Lee 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.3

Molybdenum disilicide has been recognized as an attractive candidate material for high temperature structural applications. In this study, we have used mechanical alloying by a high-energy ball milling process to produce alloy powders of α-MoSi2 starting from mixtures of elemental molybdenum and silicon powders at room temperature. The α-MoSi2 plus Mo phases have been obtained by ball milling of a Mo33Si67 mixture of the pure elements for 100 hours, which was transformed to a single α-MoSi2 phase by subsequent heat treatment up to 725 oC. The grain size of the α-MoSi2 powders thus obtained was 19 nm, being approximately four times smaller than that of commercial alloy powders. It was also seen that the α-MoSi2 phase once formed begins to transform to the high-temperature β-MoSi2 phase when the total milling time exceeds 160 hours. Molybdenum disilicide has been recognized as an attractive candidate material for high temperature structural applications. In this study, we have used mechanical alloying by a high-energy ball milling process to produce alloy powders of α-MoSi2 starting from mixtures of elemental molybdenum and silicon powders at room temperature. The α-MoSi2 plus Mo phases have been obtained by ball milling of a Mo33Si67 mixture of the pure elements for 100 hours, which was transformed to a single α-MoSi2 phase by subsequent heat treatment up to 725 oC. The grain size of the α-MoSi2 powders thus obtained was 19 nm, being approximately four times smaller than that of commercial alloy powders. It was also seen that the α-MoSi2 phase once formed begins to transform to the high-temperature β-MoSi2 phase when the total milling time exceeds 160 hours.

건축용 내화강재(FR 490) 적용 H형강 보부재의 고온내력 연구

권인규 한국화재소방학회 2014 한국화재소방학회논문지 Vol.28 No.5

When structural elements of steel framed structures are exposed to fire situations, the structural stability begins todecrease due to dislocation of substantial. The increase of the beam length causes an additional stress and deflection. These can be serious factors to cause a severe failure of structures. To improve the fire resistance of beams, prevention ofthe heat from a fire by coating with fire protection material is essential for beams. The FR 490 was developed to enhancefire resistance compared with SM 490 steel. However, the fire resistance of FR 490 H-beams has not been evaluated byanalysis method since it was developed. In this paper, materials properties in high temperature and a heat transfer andthermal stress theory were used in the evaluation of the fire resistance of FR490 H-beams. The fire resistance of FR490steel beams was compared with that of SM490 beams. The comparison verified that the structural stability of FR490beams at high temperature was superior to that of SM490 beams. 구조용 강재는 고온 시 물질 내부의 구성 물질의 결합력 약화로 인하여 내력과 변형이 추가적으로 발생됨으로써, 구조적 성능이 저하되고, 국부 및 연속적 붕괴로 이어질 수 있다. 따라서 강재로 구성된 구조부재는 화재 시 열영향부를 최소화하기 위한 수단이 강구되는 내화설계가 요구된다. 건축용 내화강재(FR 490)는 용접 구조용 강재(SM 490)와 상온시 특성은 동일하나, 고온 시의 내력유지 성능이 우수한 강종으로써 이로 구성된 보부재의 고온 시 내력 평가 자료는거의 없다. 따라서 본 연구에서는 FR 490강재로 구성된 보부재의 고온 시 거동을 고온 시 재료 특성과 이론적 방법을통하여 해석적으로 평가하고, 이를 SM 490강재보와 비교함으로써 내화성능을 확인하고자 하였으며, 그 결과 FR 490강재보의 경우 SM 490강재보에 비해서 고온 시 내력유지 성능이 우수하였다.

TFT Structure Simulation with Various High K Dielectric Materials for Non-volatile Memory Device

Keka Mukhopadhyaya,P. Srividya 한국전기전자재료학회 2024 Transactions on Electrical and Electronic Material Vol.25 No.3

In this rapidly growing and changing world of electronics industry it is very critical to have precise model and simulation for device. This paper presents the work on simulating the performance of thin fi lm transistors (TFT) structure with diff erent high K dielectric materials and source drain materials. TFT structure plays an important role in the TFT performance and this paper compares the I D –V D and I D –V G , threshold voltage (V T ), subthreshold swing and on and off current (Ion/Ioff ) of the TFT. Further, for a bottom gate staggered confi guration, the eff ect of diff erent materials as Source and Drain as well as the eff ect of dielectric strength on the tunneling layer of the TFT is studied to evaluate its suitability for applications like non-volatile memory. The eff ect of temperature on diff erent performance characteristics of the bottom gate TFT structure like threshold voltage, sub-threshold swing, on–off current ratio are also analysed.

해양구조물용 강재의 온도에 따른 동적 물성치

정세환(Sehwan Jeong),허훈(Hoon Huh),이재익(Jae-Yik Lee) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5

This paper is concerned with the material properties of API steel plates for off-shore structures. Strain rate and temperature dependency on the material properties are investigated. Tensile tests have been performed with the variation of strain rate from 0.001/sec to 200/sec and the variation of the environmental temperature from -40℃ to 200℃. Differences in material properties through thickness direction of the steel plates are also investigated. Tensile specimens are obtained from two layers which are obtained from two different locations in a steel plate. One layer is collected in the middle and the other layer is collected near outer surface of the steel plate. Thermo-mechanical responses of the specimens of two layers are quantitatively compared and micro-structures are observed.

Corrosion Behavior of Ni-Base Alloys in a Hot Lithium Molten Salt under an Oxidizing Atmosphere

( Soo Haeng Cho ),( Il Je Cho ),( Gil Sung You ),( Ji Sup Yoon ),( Seong Won Park ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 METALS AND MATERIALS International Vol.13 No.4

The electrolytic reduction of a spent oxide fuel involves the liberation of the oxygen in molten LiCl electrolyte, which is a chemically aggressive environment that is excessively corrosive for typical structural materials. Accordingly, it is essential to choose the optimum material for the processing equipment that handles the molten salt. In this study, the corrosion behaviors of Haynes 263, Haynes 75, Inconel 718 and Inconel X-750 in a molten LiCl-Li2O salt under an oxidizing atmosphere were investigated at 650 ℃ for 72 to 216 hrs. The Haynes 263 alloy showed the best corrosion resistance among the examined alloys. The corrosion products of Haynes 263 were Li(Ni,Co)O2 and LiTiO2; those of Haynes 75 were Cr2O3, NiFe2O4, LiNiO2 and Li2NiFe2O4; while Cr2O3, NiFe2O4 and CrNbO4 were identified as the corrosion products of Inconel 718. Inconel X-750 produced Cr2O3, NiFe2O4 and (Cr,Nb,Ti)O2 as its corrosion products. Haynes 263 showed a localized corrosion behavior while Haynes 75, Inconel 718 and Inconel X-750 showed a uniform corrosion behavior.

Site-Selective Excitation and Luminescence Properties of Eu^3 + Ions Doped in SrZn₂ ( PO₄ ) ₂

Ding, Haiyan,Huang, Yanlin,Shi, Liang,Seo, Hyo Jin The Electrochemical Society 2010 Journal of the Electrochemical Society Vol.157 No.3

<P>SrZn2(PO4)(2) doped with Eu3+ ions was prepared by high temperature solid-state reaction. The site-selective excitation and emission spectroscopy and luminescence decay (lifetime) have been investigated in the D-5(0)-> F-7(0) region by using a pulsed, tunable, and narrowband dye laser. We observed two crystallographic sites for Eu3+ in SrZn2(PO4)(2) below 250 K and energy transfer from Eu3+ at one site to Eu3+ at the other site. The Stark energy levels of Eu3+ at two different sites were assigned from the site-selective emission spectra. The luminescence from Eu3+ at one of the two sites was quenched at room temperature. The lifetime of Eu3+ ions at the two sites is compared. The defect structures and charge compensation mechanisms are discussed.</P>

고온 용융염계에서 Ni-Base 초합금의 부식거동

조수행 ( Soo Haeng Cho ),강대승 ( Dae Seong Kang ),홍순석 ( Sun Seok Hong ),허진목 ( Jin Mok Hur ),이한수 ( Han Soo Lee ) 대한금속·재료학회 2008 대한금속·재료학회지 Vol.46 No.9

용접구조용 강재 적용 부정정 보부재의 해석적 내화성능 연구

권인규 대한건축학회지회연합회 2015 대한건축학회연합논문집 Vol.17 No.5

용접 구조용 강재(SM 490)로 제작된 보부재가 양단 고정단인 부정정 구조물이라 하더라도 화재와 같은 고온에서의 내력 유지성능 평가는 한단 자유, 타단 힌지단인 단순보의 조건으로 이루어지고 있는 것이 현재의 실정이다. 따라서 본 논문에서는 실제 강구조 건축물의 양단 고정단 조건인 부정정 보부재의 내화시험에 적용되고 있는 단순보 조건과의 내화성능 차이를 해석적으로 평가함으로써 화재 안전성을 확인하고, 향후 해석적인 내화설계의 기본 자료 제공을 목적으로 한다. Structural beams plays a role to carry the applied load on the floor into columns and the typical boundary conditions of the beams would be designed as a fixed. This is regarded as an indeterminate structure, for it cannot be solved by condition of equilibrium forces. A fixed boundary condition has a better performance than that of simple beam in aspects of sustaining of applied loads or it is possible to design with a smaller section. However when the fire resistance performance of a beam made of a submarined structural steels and with a fixed boundary is required, the fire test of it is done as a simple beam by a Korean standard. In this paper, an analytic method is used to know the fire resistance performance of statistically indeterminate beams made of a submarine structural steels(SM 490) and to clarify that it is resonable to test by simple beam condition instead of a fixed boundary condition.