• Nonlinear Functional Analysis and Applications
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• 제27권1호
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• pp.99-110
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• 2022

The main object of this paper is to provide necessary and sufficient conditions for the generalized Struve functions of first kind to be in the classes 𝒮(k, λ) and 𝒞(k, λ). Furthermore, we give conditions for the integral operator 𝓛(m, c, z) = ∫^z₀(2 - u_p(t))dt to be in the class 𝒞^*(k, λ). Several corollaries and consequences of the main results are also considered.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.149-152
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• 2009

Hydrotalcites are anionic clays that are quite prevalent in nature and their importance is growing more and more because of their very wide range of potential applications and uses. Understanding the structural and compositional changes that occur on the molecular scale during the thermal decomposition of hydrotalcite compounds is essential for the basic prediction and comprehensive understanding of the behavior and technical application of these materials. In this study, several hydrotalcite compounds calcined at different temperatures for applications in a chlorine resistant textile were prepared and 27-Aluminm solid-state nuclear magnetic resonance (NMR) spectroscopy was used as a tool to study their local structure and behavior. The changes in the Al coordination of the hydrotalcite compounds were investigated with one dimensional (1D) solid-state magic angle spinning (MAS) NMR spectroscopy. The two broad resonances arising from the structurally different Al coordinations of these compounds were clearly resolved by two dimensional (2D) triple quantum magic angle spinning (3QMAS) NMR spectroscopy.

• 센서학회지
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• 제16권3호
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• pp.240-245
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• 2007

AlN thin film for SAW filter application was deposited on (100) silicon, sapphire, $Si_{3}N_{4}$/Si, and $Al_{2}O_{3}$/Si substrates by reactive magnetron sputtering method, respectively. The structural characteristics were dependent on the structure of substrates. Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Atomic Force Microscope (AFM) have been used to analyze structural properties and preferred orientation of AlN thin films. Preferred orientation and SAW characteristic of AlN were improved by insertion of $Al_{2}O_{3}$ buffer layer. Insertion loss of SAW devices using AlN/Si and AlN/$Al_{2}O_{3}$/Si were about 33.27 dB and 30.20 dB, respectively.

• 대한화학회지
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• 제39권8호
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• pp.627-634
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• 1995

하이드로탈시이트류 음이온성 점토광물로 잘 알려진 증상이중수산화물($Mg-Al-CO_3$ 체계)을 마그네슘과 알루미늄의 비를 달리하면서 공침전법으로 합성하였다. 얻어진 생성물들의 특성을 원소조성분석, 분말 X-선회절분석, 열분석(시차주사열량분석과 열무게분석), FT-IR분광분석 및 $^{27}$/Al-MAS NMR분석등으로 규명하였다. 분말 X-선회절분석으로 생성물들이 층상구조를 이루고 있음을 확인하였다. 시차주사열량분석결과에서는 20-280$^{\circ}C$ 영역에서 표면수 및 층간수의 이탈로 인한 흡열피크가 관찰되며, 280-500$^{\circ}C$ 영역에서격자수 및 이산화탄소의 이탈로 일어나는 화학변화에 의한 강한 흡혈피크가 관찰되었다. 열무게분석결과에서는 두 영역의 질량감소량을 측정할 수 있었다(LDH4의 경우 각각 16.2%와 28.6%). FT-IR 분광분석결과층간의 탄산이온은 층과 평행하게 $D_{3h}$ 대칭구조로 존재하며, $^{27}$/Al-MAS NMR분석결과 층안의 알루미늄은 마그네슘과 마찬가지로 수산화이온에 의해 6배위환경으로 존재하였다. 공기분위기하의 560$^{\circ}C$에서 3시간 소성되어진 시료는 본래의 층상구조가 파괴된 균일한 혼합금속산화물로 변화하며, 이 물질은 크롬산이온 수용액에서 빠르게 재수화반응을 일으켜 본래의 층상구조를 회복하였다.

• 멤브레인
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• 제27권3호
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• pp.226-231
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• 2017

이산화탄소 분리를 위해 이온성 액체/금속 산화물 복합막이 제조되었으며, 이온성 액체로서 1-butyl-3-methylimidazolium tetrafluoroborate ($BMIM^+BF_4{^-}$)와 금속산화물로서 $Al_2O_3$가 사용되었다. 13 nm의 $Al_2O_3$가 이온성 액체 $BMIM^+BF_4{^-}$에 도입되었을 때, 복합체 분리막의 성능은 $CO_2/N_2$ 선택도 30.5과 $CO_2$ 투과도 45.7 GPU로 관찰되었다. neat $BMIM^+BF_4{^-}$ 분리막의 성능($CO_2/N_2$ 선택도 5와 $CO_2$ 투과도 17 GPU)에 비해서 성능이 증가한 이유는 $Al_2O_3$의 옥사이드 층과 이온성 액체 내 자유로운 이온농도의 상승으로 인해 $CO_2$ 용해도가 상승한 것으로 확인되었다. 특히 $Al_2O_3$ 나노입자는 질소 기체에 대해서 장애물로서 작용함으로써 질소기체의 투과도가 감소하여 결과적으로 이산화탄소 분리 성능은 급격히 증가하였다.

• 한국재료학회지
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• 제27권10호
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• pp.563-568
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• 2017

In this study, the coating of an Al-Cr layer on the surface of a Zircaloy-4 alloy was carried out through plasma pretreatment coating and a laser surface melting process. Two different conditions for laser treatment, severe or minimal surface melting of the Zr alloy substrate, were applied to form the final coating. When there was significant surface melting of the Zr alloy, the solidification microstructure of the newly formed coating layer was mainly composed of needle-shaped $Al_3Zr$, Al(Cr) and $Al_7Cr$ phases. On the other hand, the solidification microstructure of the coating layer was mainly composed of Al(Cr) and $Al_7Cr$ phases when there was minimal surface melting of Zr base in the laser process. However, when the coating was maintained at $1100^{\circ}C$ for 2 hours, significant inter-diffusion occurred between the phases in the coating. As a result, the upper part of the coating layer was observed to mainly consist of $Al_3Zr$ and $Al_8Cr_5$ phases, regardless of the laser treatment conditions.

• 한국분말재료학회지
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• 제27권5호
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• pp.406-413
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• 2020

Ti_0.5Al_0.5N/CrN nano-multilayers, which are known to exhibit excellent wear resistances, were prepared using the unbalanced magnetron sputter for various periods of 2-7 nm. Ti_0.5Al_0.5N and CrN comprised a cubic structure in a single layer with different lattice parameters; however, Ti_0.5Al_0.5N/CrN exhibited a cubic structure with the same lattice parameters that formed the superlattice in the nano-multilayers. The Ti_0.5Al_0.5/CrN multilayer with a period of 5.0 nm exceeded the hardness of the Ti_0.5Al_0.5N/CrN single layer, attaining a value of 36 GPa. According to the low-angle X-ray diffraction, the Ti_0.5Al_0.5N/CrN multilayer maintained its as-coated structure up to 700℃ and exhibited a hardness of 32 GPa. The thickness of the oxidation layer of the Ti_0.5Al_0.5N/CrN multilayered coating was less than 25% of that of the single layers. Thus, the Ti_0.5Al_0.5N/CrN multilayered coating was superior in terms of hardness and oxidation resistance as compared to its constituent single layers.

• 한국재료학회지
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• 제27권8호
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• pp.397-402
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• 2017

We used an etching process to control the line-width of screen printed Ag paste patterns. Ag paste was printed on anodized Al substrate to produce a high power LED. In general, Ag paste spreads or diffuses on anodized Al substrate in the process of screen printing; therefore, the line-width of the printed Ag paste pattern increases in contrast with the ideal line-width of the pattern. Smudges of Ag paste on anodized Al substrate were removed by neutral etching process without surface damage of the anodized Al substrate. Accordingly, the line-width of the printed Ag paste pattern was controlled as close as possible to the ideal line-width. When the etched Ag paste pattern was used as a seed layer for electroless Ni plating, the line width of the plated Ni film was similar to the line-width of the etched Ag paste pattern. Finally, in pattern formation by Ag paste screen printing, we found that the accuracy of the line-width of the pattern can be effectively improved by using an etching process before electroless Ni plating.

• 열처리공학회지
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• 제27권2호
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• pp.59-64
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• 2014

Cu-Al-Mn shape memory alloys of a variety of composition were characterized in terms of shape memory properties and cold workability. Cold workability tested by cold rolling indicated that the alloys solution treated in the ${\alpha}+{\beta}$ region have a higher ductility than those solution treated in the ${\beta}$ region. Also it is known that cold workability increased with the decrease in Al content in the ${\beta}$ region. This seems to be resulted from the fact that Mn addition causes to expand ${\beta}$ region toward lower Al content and lower order-disorder transition temperature, consequently, ${\beta}$ of excellent workability being frozen even at room temperature. Experimental results regarding shape memory showed that the properties were better with a higher Al contents at a given Mn content, which is closely related with martensitic transformation. It is also shown that super elasticity limit was enhanced with decrease in the yield strength of alloys because a lower yield strength seems to initiates slip at the lower applied stress.

• 소성∙가공
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• 제27권5호
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• pp.314-322
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• 2018

AlSi12 is a heat-resistant aluminum alloy that is lightweight, corrosion-resistant, machinable and attracting attention as a functional material in aerospace and automotive industries. For that reason, AlSi12 powder has been used for high performance parts through 3D printing technology. The purpose of this study is to observe deposition characteristics of AlSi12 powder in a direct energy deposition (DED) process (one of the metal 3D printing technologies). In this study, deposition characteristics were investigated according to various process parameters such as laser power, powder feed rate, scan speed, and slicing layer thickness. In the single track deposition experiment, an irregular bead shape and balling or humping of molten metal were formed below a laser power of 1,000 W, and the good-shaped bead was obtained at 1.0 g/min powder feed rate. Similar results were observed in multi-layer deposition. Observation of deposited height after multi-layer deposition revealed that over-deposition occurred at all conditions. To prevent over-deposition, slicing layer thickness was experimentally determined at given conditions. From these results, this study presented practical conditions for good surface quality and accurate geometry of deposits.