• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.141-152
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• 2018

The heating process such as line heating, triangular heating and so on is widely used in plate forming of shell plates found in bow and stern area of outer shell in a ship. Local shrinkage during heating process is main physical phenomenon used in plate forming process. As it is well appreciated, the heated plate undergoes the change in material and mechanical properties around heated area due to the harsh thermal process. It is, therefore, important to investigate the changes of physical and mechanical properties due to heating process in order to use them plate the design stage of shell plates. This study is concerned with the development of formula of plastic hardening constitutive equation for steel plate on which line heating is applied. In this study the stress correction formula for the heated plate has been developed based on the numerical simulation of tension test with varying plate thickness and heating speed through the regression analysis of multiple variable case. It has been seen the developed formula shows very good agreement with results of numerical simulation. This paper ends with usefulness of the present formula in examining the structural characteristic of ship's hull.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3824-3832
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• 2022

Prompt capture gammas are an important part of the fission reactor gamma field. Because some of the structural materials after neutron capture can emit photons with high energies forming the dominant component of the gamma spectrum in the high energy region, the following study of the high energy capture gamma was carried out. High energy gamma radiation may play a major role in areas of the radiation sciences as reactor dosimetry. The HPGe measurements and calculations of the high-energy aluminum capture gamma were performed at two moderator levels in the VR-1 pool-type reactor. The result comparison for nominal levels was within two sigma uncertainties for the major 7.724 MeV peak. A larger discrepancy of 60% was found for the 7.693 MeV peak. The spectra were also measured using a stilbene detector, and a good agreement between HPGe and stilbene was observed. This confirms the validity of stilbene measurements of gamma flux. Additionally, agreement of the wide peak measurement in 7-9.2 MeV by stilbene detector shows the possibility of using the organic scintillators as an independent power monitor. This fact is valid in these reactor types because power is proportional to the thermal neutron flux, which is also proportional to the production of capture gammas forming the wide peak.

• Journal of Powder Materials
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• v.30 no.6
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• pp.478-483
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• 2023

High-entropy alloys (HEAs) are characterized by having five or more main elements and forming simple solids without forming intermetallic compounds, owing to the high entropy effect. HEAs with these characteristics are being researched as structural materials for extreme environments. Conventional refractory alloys have excellent high-temperature strength and stability; however, problems occur when they are used extensively in a high-temperature environment, leading to reduced fatigue properties due to oxidation or a limited service life. In contrast, refractory entropy alloys, which provide refractory properties to entropy alloys, can address these issues and improve the high-temperature stability of the alloy through phase control when designed based on existing refractory alloy elements. Refractory high-entropy alloys require sufficient milling time while in the process of mechanical alloying because of the brittleness of the added elements. Consequently, the high-energy milling process must be optimized because of the possibility of contamination of the alloyed powder during prolonged milling. In this study, we investigated the high-temperature oxidation behavior of refractory high-entropy alloys while optimizing the milling time.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.9-10
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• 2010

Since the discovery of graphene by mechanical exfoliation from graphite[1], various fabrication methods are available today such as chemical exfoliation, epitaxial graphene on SiC substrates, etc. In view of industrialization, the mechanical exfoliation method may not be an option. Epitaxial graphene on SiC substrates, in this respect, is by far more practical because the method consists of conventional thermal treatments familiar to semiconductor industry. Still, the use of the SiC substrate itself, and hence the incompatibility with the Si technology, lessens the importance of this technology in its future industrialization. In this context, we have tackled the problem of forming graphene on Si substrates (GOS). Our strategy is to form an ultrathin (~80 nm) SiC layer on top of a Si substrate, and to graphitize the top SiC layers by a vacuum annealing. We have actually succeeded in forming the GOS structure [2,3,4]. Raman-scattering microscopy indicates presence of few-layer graphene (FLG) formed on our annealed SiC/Si heterostructure, with the G ($1580\;cm^{-1}$) and the G'($2700\;cm^{-1}$) bands, both related to ideal graphene, clearly observed. Presence of the D ($1350\;cm^{-1}$) band indicates presence of defects in our GOS films, whose elimination remains as a challenge in the future. To obtain qualified graphene films on Si substrate, formation of qualified SiC films is crucial in the first place, and is achieved by tuning the growth parameters into a process window[5]. With a potential for forming graphene films on large-scale Si wafers, GOS is a powerful candidate as a key technology in bringing graphene into silicon technology.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.214.2-214.2
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• 2013

Device performance for the 45 and 32 nm node CMOS technology requires the integration of ultralow-k materials. To lower the dielectric constant for PECVD and spin-on materials, partial replacement of the solid network with air (k=1.01) appears to be more intuitive and direct option. This can be achieved introducting of second "labile" phase during depositoin that is removed during a subsequent UV curing and annealing step. Besides, with shrinking line dimensions the resistivity of barrier films cannot meet the International Technology Roadmap for Semiconductors (ITRS) requirements. To solve this issue self-forming diffusion barriers have drawn attention for great potential technique in meeting all ITRS requirments. In this present work, we report a Cu-V alloy as a materials for the self-forming barrier process. And we investigated diffusion barrier properties of self-formed layer on low-k dielectrics with or without UV curing treatment. Cu alloy films were directly deposited onto low-k dielectrics by co-sputtering, followed by annealing at various temperatures. X-ray diffraction revealed Cu (111), Cu (200) and Cu (220) peaks for both of Cu alloys. The self-formed layers were investigated by transmission electron microscopy. In order to compare barrier properties between V-based interlayer on low-k dielectric with UV curing and interlayer on low-k dielectric without UV curing, thermal stability was measured with various heat treatment temperature. X-ray photoelectron spectroscopy analysis showed that chemical compositions of self-formed layer. The compositions of the V based self-formed barriers after annealing were strongly dominated by the O concentration in the dielectric layers.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.37.2-37.2
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• 2021

Turbulence produces the density and velocity fluctuations in molecular clouds, and dense regions within the density fluctuation are the birthplace of stars. Also, turbulence can produce non-thermal pressure against gravity. Thus, turbulence plays a crucial roles in controlling star formation. However, despite many years of study, the detailed relation between turbulence and star formation remain poorly understood. As part of the Taeduk Radio Astronomy Observatory (TRAO) Key Science Program (KSP), "mapping Turbulent properties In star-forming MolEcular clouds down to the Sonic scale (TIMES; PI: Jeong-Eun Lee)", we mapped two star-forming molecular clouds, the Orion A and the ρ Ophiuchus molecular clouds, in six molecular lines (¹³CO 1-0/C¹⁸O 1-0, HCN 1-0/HCO⁺ 1-0, and CS 2-1/N₂H⁺ 1-0) using the TRAO 14-m telescope. We applied the Principal Component Analysis (PCA) to the observed data in two different ways. The first method is analyzing the variation of line intensities in velocity space to evaluate the velocity power spectrum of underlying turbulence. We investigated the relation between the star formation activities and properties of turbulence. The other method is analyzing the variation of the integrated intensities between the molecular lines to find the characteristic correlation between them. We found that the HCN, HCO⁺, and CS lines well correlate with each other in the integral shaped filament in the Orion A cloud, while the HCO⁺ line is anti-correlate with the HCN and CS lines in L1688 of the Ophiuchus cloud.

• Journal of the Korean Ceramic Society
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• v.50 no.1
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• pp.75-81
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• 2013

We fabricated translucent opal glass to replace the polycarbonate diffuser in LED lighting systems in order to solve the durability problem. Batch materials of opal glass with a composition of calcium phosphate were created and melted at $1550^{\circ}C$, and the effect of opaqueness was identified by an addition of 1~7% calcium phosphate as an opacifier raw material. As a result, translucent opal glass was obtained by the melting of the mixed batch materials with a composition of more than 5% calcium phosphate glass at $1550^{\circ}C$ for 2 hrs, which had excellent optical properties for the diffuser of a LED lighting system with no dazzling from direct light by a high haze value exceeding 90% and a low parallel transmittance value of about 5%. For the thermal properties, the thermal expansion coefficient was found to be $5.6{\sim}5.9{\times}10^{-6}/^{\circ}C$ and the softening point was $874{\sim}884^{\circ}C$. In addition, good thermal properties such as good thermal shock resistance and feasibility for use with a general manufacturing process during the forming of glass tubes and bulbs were noted. Therefore, it is concluded that this translucent opal glass can be used as a glass diffuser material for LED lighting due to its high heat resistance and high durability as a replacement for a polycarbonate diffuser.

• Carbon letters
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• v.12 no.3
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• pp.131-137
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• 2011

Kenaf fibers, cellulose-based natural fibers, were used as precursor for preparing kenafbased carbon fibers. The effects of carbonization temperature ($700^{\circ}C$ to $1100^{\circ}C$) and chemical pre-treatment (NaOH and $NH_4Cl$) at various concentrations on the thermal change, chemical composition and fiber morphology of kenaf-based carbon fibers were investigated. Remarkable weight loss and longitudinal shrinkage were found to occur during the thermal conversion from kenaf precursor to kenaf-based carbon fiber, depending on the carbonization temperature. It was noted that the alkali pre-treatment of kenaf with NaOH played a role in reducing the weight loss and the longitudinal shrinkage and also in increasing the carbon content of kenaf-based carbon fibers. The number and size of the cells and the fiber diameter were reduced with increasing carbonization temperature. Morphological observations implied that the micrometer-sized cells were combined or fused and then re-organized with the neighboring cells during the carbonization process. By the pre-treatment of kenaf with 10 and 15 wt% NaOH solutions and the subsequent carbonization process, the inner cells completely disappeared through the transverse direction of the kenaf fiber, resulting in the fiber densification. It was noticeable that the alkali pre-treatment of the kenaf fibers prior to carbonization contributed to the forming of kenaf-based carbon fibers.

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.650-657
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• 2012

For the purpose of improving the durability problem, translucent opal glass was fabricated as a substitute for the polycarbonate diffuser of LED lighting. Calcium phosphate was used as an opacifier of opal glass and melted in an electric furnace. The opaque effect was identified according to the change of the cooling procedure. As results, translucent opal glass was obtained by the melting of a batch with a composition of 3.8% calcium phosphate at $1550^{\circ}C$ for 2 hrs and then the cooling of the material in the furnace. For the cooling condition of the glass sample, HTCG (High Temperature Cooled Glass) was found to have better optical properties than LTAG (Low Temperature Annealed Glass). It had excellent optical properties for a diffuser of LED lighting, with no dazzling from direct light due to its high haze value of over 99% and low parallel transmittance value of under 1%. For the thermal properties, it had an expressed thermal expansion coefficient of $5.7{\times}10^{-6}/^{\circ}C$ and a softening point of $876^{\circ}C$; it also had good thermal properties such as good thermal shock resistance and was easy to apply to the general manufacturing process in the forming of glass tubes and bulbs. Therefore, it is concluded that this translucent opal glass can be used as a glass diffuser material for LED lighting with high heat resistance and high durability; this material is suitable as a substitute for polycarbonate diffusers.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.41.2-41.2
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• 2011

Recently, scaling down of ULSI (Ultra Large Scale Integration) circuit of CMOS (Complementary Metal Oxide Semiconductor) based electronic devices become much faster speed and smaller size than ever before. However, very narrow interconnect line width causes some drawbacks. For example, deposition of conformal and thin barrier is not easy moreover metallization process needs deposition of diffusion barrier and glue layer. Therefore, there is not enough space for copper filling process. In order to overcome these negative effects, simple process of copper metallization is required. In this research, Cu-V thin alloy film was formed by using RF magnetron sputter deposition system. Cu-V alloy film was deposited on the plane $SiO_2$/Si bi-layer substrate with smooth and uniform surface. Cu-V film thickness was about 50 nm. Cu-V layer was deposited at RT, 100, 150, 200, and $250^{\circ}C$. XRD, AFM, Hall measurement system, and XPS were used to analyze Cu-V thin film. For the barrier formation, Cu-V film was annealed at 200, 300, 400, 500, and $600^{\circ}C$ (1 hour). As a result, V-based thin interlayer between Cu-V film and $SiO_2$ dielectric layer was formed by itself with annealing. Thin interlayer was confirmed by TEM (Transmission Electron Microscope) analysis. Barrier thermal stability was tested with I-V (for measuring leakage current) and XRD analysis after 300, 400, 500, 600, and $700^{\circ}C$ (12 hour) annealing. With this research, over $500^{\circ}C$ annealed barrier has large leakage current. However V-based diffusion barrier annealed at $400^{\circ}C$ has good thermal stability. Thus, thermal stability of vanadium-based thin interlayer as diffusion barrier is good for copper interconnection.