• 한국자기학회지
• /
• 제16권2호
• /
• pp.111-114
• /
• 2006

Zinc-blonde 구조를 가지는 CrAs와 MnAs에서 (110)면 원자층으로 이루어진 초격자의 자성을 제일원리 방법을 이용하여 연구하였다. 이를 위해 CrAs와 MnAs의 (110)층이 각기 세 층씩 교대로 반복되는 $(CrAs)_3(MnAs)_3(110)$ 초격자계의 전자구조를 총 퍼텐셜 선형보강평면파동(FLAPW) 에너지띠 방법을 이용하여 계산하였다. Cr-As로 이루어진 층과 Mn-As로 이루어진 층이 접합되는 계면에 있는 Cr과 Mn원자의 자기모멘트를 계산한 결과 각기 $3.07\;\mu_B$와 $3.74\;\mu_B$로 가운데 층의 Cr과 Mn의 자기모멘트 값인 $3.06\;\mu_B$와 $3.76\;\mu_B$보다 약간 크거나 작았다. 계산된 상태밀도로부터 이 계의 전자구조와 반쪽금속성을 고찰하였다.

• Architectural research
• /
• 제7권1호
• /
• pp.49-54
• /
• 2005

Conventional studies have focused on the reduction in the water-cement ratio, the use of various admixtures, etc., to ensure the durability of reinforced concrete structures against such deterioration factors as carbonation and chloride attack. However, improvement in the concrete quality alone is not considered sufficient or realistic for meeting the recent demand for a service life of over 100 years. This study intends to improve the durability of reinforced concrete structures by improvement in the reinforcing steel, which has remained untouched due to cost problems, through subtle adjustment of the steel components to keep the cost low. As a fundamental study on the performance of Cr-bearing rebars in steel reinforced concrete structures exposed to corrosive environments, The test specimens were made by installing 8 types of rebars in concretes with a chloride ion content of 0.3, 0.6, 1.2, 2.4 and $24kg/m^3$. Corrosion accelerated curing were then conducted with them. The corrosion resistance of Cr-bearing rebars was examined by measuring crack widths, half-cell potential, corrosion area and weight loss after 155 cycles of corrosion-accelerating curing. The results of the study showed that the corrosion resistance increased as the Cr content increased regardless of the content of chloride ions, and that the Cr-bearing rebars with a Cr content of 5% and 9% showed high corrosion resistance in concretes with a chloride ion content of 1.2 and $2.4kg/m^3$, respectively.

• 한국자기학회지
• /
• 제5권5호
• /
• pp.442-446
• /
• 1995

Electronic structures of Fe overlayers on Cr(Fe/Cr) films, with an Fe coverage of $1-20{\AA}$, have been investigated by using photoemission spectroscopy. Experimental results are compared with supercell band structure calculations for a system with monolayer (ML) Fe on each side of five layer Cr, Fe(1ML)/Cr(5ML)/Fe(1ML). The extracted Fe 3d partial spectral weight in Fe/Cr exhibits very interesting features for very thin Fe overlayers. First, a sharp emissionnear the Fermi energy is observed, which is expected to originate primarily from hybridization between Fe and Cr 3d electrons at the Fe/Cr interface, and partially from the Fe 3d surface states in the Fe overlayer. Second, other structures are observed at higher binding energies which resemble the Cr 3d valence bands, also suggesting large hybridization between Fe and Cr 3d states at the Fe/Cr interface. These conjectures are confirmed by band structure calculations for Fe(1ML)/Cr(5ML)/Fe(1ML).

• Current Applied Physics
• /
• 제18권11호
• /
• pp.1320-1326
• /
• 2018

High crystalline quality CrN thin films have been grown on $La_{0.67}Sr_{0.33}MnO_3$ (LSMO) templates by molecular beam epitaxy. The structure and magnetic properties of CrN/LSMO heterojunctions are investigated combining with the experiments and the first-principles simulation. The N?el temperature of the CrN/LSMO samples is found to be 281 K and the saturation magnetization of CrN/LSMO increases compared to that of LSMO templates. The magnetic property of CrN/LSMO heterostructures mainly comes from Cr atoms of (001) CrN and Mn atoms of (001) LSMO. The (001) LSMO induces and couples the spin of the CrN sublattice at CrN/LSMO interface.

• 한국자기학회지
• /
• 제23권5호
• /
• pp.149-153
• /
• 2013

이 연구에서는 방사광 연 X선 광흡수 분광법(soft x-ray absorption spectroscopy: XAS)을 이용하여 $TCr_2O_4$(T = Fe, Co, Ni) 스피넬 산화물들의 전자 구조를 연구하였다. 전이금속 이온들의 2p 준위의 흡수에 의한 XAS 측정으로부터 T(T = Fe, Co, Ni) 이온들의 원자가는 공통적으로 2가($T^{2+}$)이며, Cr 이온의 원자가는 3가 ($Cr^{3+}$) 임을 발견하였다. 그리고 T 이온들은 정사면체 대칭성을 가진 A 사이트에 주로 위치하고, Cr 이온은 정팔면체 대칭성을 가진 B 사이트에 주로 위치함을 알 수 있었는데, 이러한 발견을 통하여 $TCr_2O_4$는 정상 스피넬에 가까운 구조를 가지고 있다고 결론지을 수 있다. 또한 $FeCr_2O_4$와 $NiCr_2O_4$에서는 얀-텔러 변형이 중요한 역할을 하지만, $CoCr_2O_4$는 얀-텔러 변형이 없는 입방체 구조를 유지하는 원인을 알 수 있었다. 그러므로 $TCr_2O_4$에서 $Cr^{3+}$ 상태의 이온들과 $T^{2+}$ 상태의 이온들 간의 반강자성 결합이 이 산화물들의 자성 특성을 결정하는데 중요한 역할을 한다고 생각된다.

• 한국재료학회지
• /
• 제7권4호
• /
• pp.310-316
• /
• 1997

The effects of carbide and matrix structures on the abrasion wear resistance of multi-component white cast irons with 3.0 mass%C have been studied in this paper. Four different heats were poured in order to obtain the specimens with different combinations of the carbide structures: a basic iron(3.0 mass%C-5.0 mass%Cr-5.0 mass%V-5.0 mass% Mo-12.5mass%W)for M$_{6}$C and M$_{7}$C$_{3}$ carbides, and a Cr free iron(3.0 mass%C-5.0 mass%V-2.5mass%Mo-12.5 mass%W) for MC and M6C carbides. A conventional high Cr free free iron(3.0 mass%C-5.0 mass%V-2.5 mass%Mo-12.5 mass%W) for MC and M6C carbides. A conventional high Cr white cast iron was also poured to compare its wear resistance with those of the multi-component white cast irons. In the as-cast condition, the range of abrasive wear rate(Rw=mg/min) was from 4.15 to 5.98 . The lowest Rw, which means the highest wear resistance, was obtained in the basic iron with nodular MC, lamellar M$_{2}$C and cellular M$_{7}$C$_{3}$ carbides. On the other hand, the Rw of the high Cr white cast iron ranked between the basic iron and the Mo and W free iron. In each alloy, the Rw of air hardened or tempered specimen was lower than that of the as-cast one because of the change of matrix structures by the heat treatments. The Rw of the hear treated speci-mens increased in the order Mo and W free iron, basic iron, Cr free iron, high Cr iron, and V free iron.n.n.n.

• 대한수학회지
• /
• 제37권2호
• /
• pp.193-223
• /
• 2000

In the late 1970's, M. Kuranishi proposed to control the moduli of the germ of a normal Stein space by deformations of the CR structure on the boundary. I this paper, we will see that it is naturally accomplished by considering stably embeddable deformations of CR structures.

• 대한수학회지
• /
• 제37권2호
• /
• pp.177-191
• /
• 2000

All scalar CR invariants of weight $\leq$ 6 are explicitly given for 3-dimensional strictly pseudoconvex CR structures, as an application of Fefferman's ambient metric construction and its generalization by he author.

• 대한수학회지
• /
• 제37권2호
• /
• pp.225-243
• /
• 2000

We explain the notion of complete system and how it naturally arises from the equivalence problem of G-structures. Then we construct a complete system of 3rd order for the infinitesimal CR automorphisms of CR manifold of nondegenerate Levi form.

• Journal of Welding and Joining
• /
• 제26권3호
• /
• pp.37-44
• /
• 2008

Charpy V-Notch test is commonly used to evaluate fracture toughness. However, since the region to be evaluated is limited to bulk material due to the specimen size required, individual evaluation of micro-structures on weldment is very difficult. In this study, ASP(Advanced Small Punch) test was carried out to evaluate material degradation and fracture toughness on the B.M, W.M and each micro-structures of HAZ for X20CrMoV121 and 2.25Cr1Mo steels with artificial aging time. In addition, to evaluate fracture toughness and material degradation of B.M and W.M of X20CrMoV121 steels with aging times, CVN (Charpy V-notch) test was performed. And then the correlation between ASP and CVN test on X20CrMoV121 steels was obtained. Furthermore, through this correlation, material degradation property of each micro-region of the HAZ in weldment, which was impossible to be evaluated by the CVN test, can be estimated and determined.