• Korean Journal of Materials Research
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• v.17 no.3
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• pp.179-183
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• 2007

A plate heat exchanger (PHE) normally uses vacuum brazing technology for connecting plates and fins. However, the reliability of high temperature brazing, especially with nickel-based filler metals containing boron the formation of brittle intermetallic compounds (IMCs) in brazed joints is of major concern. since they considerably degrade the mechanical properties. This research was examined the vacuum brazing of commercially SUS304 stainless steel with BNi-2 (Ni-Cr-B-Si) filler metal, and discussed to determine the influence of brazing temperatures on the microstructure and mechanical strength of brazed joints. In the metallographic analysis it is observed that considerable large area of Cr-B intermetallic compound phases at the brazing layer and the brazing tensile strength is related to removal of this brittle phase greatly. The mechanical properties of brazing layer could be stabilized through increasing the brazing temperature over $100^{\circ}C$ more than melting temperature of filler metals, and diffusing enough the brittle intermetallic compound formed in the brazing layer to the base metal.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.615-620
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• 1996

Chromium-Molybdenum steel was plasma-nitrided at 823 K for 10.8 ks in an atmosphere of 30% $N_2$-70% $H_2$ gas under 665 Pa without and with a subsidiary cathode of $MoS_2$ to compare ion-nitriding and plasma-sulfnitriding using subsidiary cathode. When the steel was ion-nitrided without $MoS_2$, iron nitride layer of 4$\mu\textrm{m}$ and nitrogen diffusion layer of 400mm were formed on the steel. A compound layer of 15$\mu\textrm{m}$ and nitrogen diffusion layer of 400$\mu\textrm{m}$ were formed on the surface of the steel plasma-sulfnitrided with subsidiary cathode of $MoS_2$. The compound layer consisted of FeS containing Mo and iron nitrides. The nitrides of $\varepsilon$-$Fe_2$, $_3N$ and $\gamma$-$Fe_4N$ formed under the FeS. The thicker compound layer was formed by plasma-sulfnitriding than ion-nitriding. In plasma-sulfnitriding, the surface hardness was about 730 Hv. The surface hardness of the steel plasma-sulfnitrided with $MoS_2$ was lower than that of ion-nitrided without $MoS_2$. This may be due to the soft FeS layer formed on the surface of the plasma-sulfnitrided steel.

• Journal of Magnetics
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• v.9 no.4
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• pp.105-108
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• 2004

The attempt for the addition of double-phase nanocomposite $Nd_2Fe_{14}BFe_3B$ powders, respectively, into several $RE_2Fe_{14}B$(RE=Pr, Nd) powders with high magnetic properties was carried out. The powders were compounded and compressed to take shape bonded magnets. By means of investigating the variation of compound magnet $B_r$, the interaction between magnetic powders was revealed. The result shows that not chemical just but physical interaction exists between elements. The compound effect of $Nd_2Fe_{14}BFe_3B$-ferrite bonded magnets was detailed studied. The functional relation was revealed between magnetic properties and ferrite content. That is $Y = 5.42 x^2 -11.34x + 6.62$. The variation of $_iH_c$ temperature coefficient ${\beta}_{iHc}$ with ferrite content was investigated. Following the ferrite content increased, ${\beta}_{iHc}$ and $h_{irr}$ were obviously decreased, compression-resistant strength was enhanced.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.95-99
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• 2012

Two novel copper(II) complexes, [Cu(dmamhp)$(H_2O)_2(SO_4)]_n$ (1) and [Cu(dmamhp)$(NO_3)_2(H_2O)]{\cdot}H_2O$ (2) [dmamhp = 2-dimethylaminomethyl-3-hydroxypyridine] have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 displays a double one-dimensional chains structure, in which each chain is constituted with the distorted octahedral copper(II) complex bridged through bidentate sulfate ligands resulting in a coordination polymer. The bifurcated hydrogen bonds and $\pi-\pi$ interactions play important roles in the formation of the double chains structure. On the other hand, compound 2 adopts a distorted square pyramidal geometry around copper(II) ion and exists as a discrete monomer. There are intermolecular bifurcated hydrogen bonds and $\pi-\pi$ stacking interactions between the monomeric units. The magnetic properties revealed that the paramagnetic behaviors are dominantly manifested and there are no intermolecular magnetic interactions in both compound 1 and 2.

• Journal of the Korean Chemical Society
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• v.19 no.1
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• pp.43-49
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• 1975

Small amounts of iodine compound in mineral oils are usually effective in reducing friction of metallic surfaces. Such improvement in frictional behaviour of wear characteristics was explained by the formation of a diiodide layer lattice structure at the metallic contact surfaces. The lubrication mechanism, however, by which organoiodine compounds functions is not based on the formation of such lattice structure iodide. It was tested and shown, by a static surface chemical reactivity test, wear and EP tests, and a hot wire method, that compound such as N-iodopyridinium dichlorodate, a double charge transfer complex, reacted with metals as an interhalogen compound and that the resultant thin film product reduced appreciable the friction of metallic surfaces, more than compounds such as methyl iodide, diiodomethane, and iodoform. These results suggest that the action of iodine, included in organoiodine compounds, is not that of a classical layer structure iodide, and an entirely new mechanism may be derived from a further studies on charge transfer complex compounds of organoiodine compounds.

• Electronics and Telecommunications Trends
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• v.32 no.6
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• pp.8-16
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• 2017

In this paper, we review studies attempting to triumph over the limitation of Si-based semiconductor technologies through a heterogeneous integration of high mobility compound semiconductors on a Si substrate, and the co-integration of electronic and/or optical devices. Many studies have been conducted on the heterogeneous integration of various materials to overcome the Si semiconductor performance and obtain multi-purpose functional devices. On the other hand, many research groups have invented device fusion technologies of electrical and optical devices on a Si substrate. They have co-integrated Si-based CMOS and InGaAs-based optical devices, and Ge-based electrical and optical devices. In addition, chip and wafer bonding techniques through TSV and TOV have been introduced for the co-integration of electrical and optical devices. Such intensive studies will continue to overcome the device-scaling limitation and short-channel effects of a MOS transistor that Si devices have faced using a heterogeneous integration of Si and a high mobility compound semiconductor on the same chip and/or wafer.

• Journal of the Korean Society of Safety
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• v.11 no.1
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• pp.53-59
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• 1996

To protect the damages or the disasters caused by overheating of industrial electric equipments or electric home appliances, a temperature sensitive thermal fuse is generally used in those equipments. Thermal fuses cutoff the current flow when the temperature of the electric equipments are abnormally overheated and over the certain temperature. Therefore thermal fuse is one of the most important elements in the sense of safety. Thermal fuses are classified into two types according to thermally sensitive materials, a low temperature melting alloy and an organic chemical compound. Domestic products of thermal fuses are now only with an organic chemical compound. Domestic products tested by using cutoff test and aging test etc. are satisfied UL specification. It's shown that the accuracy and the precision of the domestic products are as good as those of the overseas products obtained UL mark. However, some of domestic products show the reclosing problem which is mainly related the safety. This problem should be solved to make the reliable thermal fuses. In this paper, our Interest is to find out the causes of reclosing. In the comparison between thermally sensitive materials occurred reclosing and those occurred no reclosing, the test effects show that the characteristics of emitting heat and absorbing heat are different.

• Composite Materials and Engineering
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• v.3 no.3
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• pp.221-239
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• 2021

This paper presents a multiscale modeling method for sheet molding compound (SMC) composites through a novel bundle packing reconstruction algorithm based on a micro-CT (Computed Tomography) image processing. Due to the complex flow pattern during the compression molding process, the SMC composites show a spatially varying orientation and overlapping of fiber bundles. Therefore, significant inhomogeneity and anisotropy are commonly observed and pose a tremendous challenge to predicting SMC composites' properties. For high-fidelity modeling of the SMC composites, the statistical distributions for the fiber orientation and local volume fraction are characterized from micro-CT images of real SMC composites. After that, a novel bundle packing reconstruction algorithm for a high-fidelity SMC model is proposed by considering the statistical distributions. A method for evaluating specimen level's strength and stiffness is also proposed from a set of high-fidelity SMC models. Finally, the proposed multiscale modeling methodology is experimentally validated through a tensile test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.06a
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• pp.63-73
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• 1996

CAFE(기업평균연비) 규제의 적극적 대응책의 하나로 차체 경량화가 주목받고 있다. 이를 위해 사용되는 고분자 복합소재 중 특히 Exterior Body Panel에 많이 채택되고 있는 SMC(Sheet Molding Compound)에 대해 제조방법, 성형공정, 기술적 과제, 재활용, 적용 예 등을 살펴보았다. 1973년 GM의 Corvette로부터 본격적으로 사용되기 시작한 SMC는 미국, 유럽을 중심으로 사용량이 계속 증가되고 있으며, 자동화가 용이하고 성형Cycle이 짧아 타 열경화성 고분자복합재료 성형방법에 비해 대량생산에 유리하며, 도장 특성이 우수하며 자 동차 부품용으로 가장 보편적인 방식이다.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.43-52
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• 2014

Recent developing tendency of thermal spray for green automotive industry are studied by searching of NDSL, KIPRIS, ScienceDirect and so on. Spraying techniques such as plasma spray, microwave treatment, dry-ice blasting, HVOF thermal spray, cold spraying, aerosol deposition are introduced, further more spraying materials such as nano particles, intermetallic compound, TiAlN, TiC, Si-Al alloys are investigated.