• 한국재료학회지
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• 제31권12호
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• pp.682-689
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• 2021

NbC, HfC, TaC, and their solid solution ceramics have been identified as the best materials for ultrahigh-temperature ceramics. However, their structural stability and elastic properties are mostly unclear. Thus, we investigated structure and elastic properties of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C solid solutions via ab initio calculations. Our calculated results show that the stability of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C increases with the increase of Hf and Ta content, and (Nb_1-xHf_x)C is more stable than (Nb_1-xTa_x)C at the same content of Hf and Ta. The lattice constants decrease with increasing of Hf and Ta content. (Nb_1-xTa_x)C and (Nb_1-xHf_x)C carbides are mechanically stable and brittle. Bulk modulus of (Nb_1-xTa_x)C increases with increasing Ta content. In contrast, bulk modulus of (Nb_1-xHf_x)C decreases with increasing Hf content. Hardness of solid solutions shows the highest values at the (Nb_0.25Ta_0.75)C and (Nb_0.75Hf_0.25)C. In particular, (Nb_0.75Hf_0.25)C shows the highest hardness for the current system. The results indicate that the overall mechanical properties of (Nb_1-xHf_x)C solid solutions are superior to those of (Nb_1-xTa_x)C solid solutions. Therefore, controlling the Hf and Ta element and content of the (Nb_1-xTa_x)C and (Nb_1-xHf_x)C Solid solution is crucial for optimizing the material properties.

• 공업화학
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• 제31권1호
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• pp.90-96
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• 2020

본 연구는 혼합비료를 유도용액으로 하는 정삼투 기술을 하수에 적용하여 하수를 재이용하기 위한 연구이다. 이를 위하여 본 연구에서는 J 하수처리장의 1차 침전지 유입수와 유출수, 그리고 2차 침전지 유출수를 각각 처리 대상으로 하였다. 평균 수투과선속은 KCl + NH₄Cl > KCl + NH₄H₂PO₄ > KCl + (NH₄)₂HPO₄의 순서로 크게 나타났으며, 역용선속은 KCl + NH₄H₂PO₄ < KCl + NH₄Cl < KCl + (NH₄)₂HPO₄의 순서로 작게 나타났다. 혼합비료의 종류에 관계없이 2차 침전지 유출수의 수투과선속이 가장 높게 나타났다. KCl과 NH₄H₂PO₄의 혼합 유도용액은 비료의 주요 성분인 질소, 인 및 칼륨을 모두 포함하고 있을 뿐 아니라 낮은 비역용질 선속을 갖고 있어서 하수의 재이용에 가장 유용하게 사용될 수 있을 것으로 판단되었다. KCl과 NH₄H₂PO₄의 혼합 유도용액을 사용한 경우, 2차 침전지 유출수에 대한 평균 수투과선속과 역용질선속은 각각 12.14 LMH과 0.012 mol/㎡s이었다.

• 대한조선학회논문집
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• 제61권1호
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• pp.51-60
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• 2024

Hi Air Korea and Hanwha ocean are currently developing an Onboard Carbon dioxide Capture System (OCCS) to absorb CO₂ emitted from ship's engine using a sodium hydroxide(NaOH) solution, and converting the resulting salt into a solid form through a chemical reaction with calcium oxide (CaO). The system process involves the following steps; 1)The reaction of CO₂ gas absorption in water, 2)The reaction between carbonic acid (H₂CO₃) and NaOH solution to produce carbonate or bicarbonate, and 3)The reaction between carbonate or bicarbonate and CaO to form calcium carbonate (CaCO₃). And ultimately, the solid material, CaCO₃, is separated and discharged using a separator. The OCCS has been installed on an ship and the test results have confirmed significant reduction effects of CO₂ in the ship's exhaust gas. A portion of the exhaust gas emitted from the engine was transferred to the OCCS using a blower. The flow rate of the transferred gas ranged from 800 to 1384 m³/hr, and the CO₂ concentration in the exhaust gas was 5.1 vol% for VLSFO, 3.7 vol% for LNG and a 12 wt% NaOH solution was used. The results showed a CO₂ capture efficiency of approximately 42.5 to 64.1 vol% and the CO₂ capture rate approximately 48.4 to 52.2kg/hr. Additionally, to assess the impact of the discharged CaCO₃on the marine ecosystem, we conducted "marine ecotoxicity test" and performed Computational Fluid Dynamics (CFD) analysis to evaluate the dispersion and dilution of the discharged effluent.

• 동력기계공학회지
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• 제21권2호
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• pp.5-13
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• 2017

This study has developed an organic/inorganic hybrid solution according to amount of $SiO_2$ polysilicate, and the amount of melamine is constant. The three types of cold rolled steel were evaluated a corrosion resistance properties by using these solutions. $US_3M_3$ and $US_{11}M_3$ solutions were generate a lot of corrosion. $US_7M_3$ solution was excellent in corrosion resistance, regardless of the steel type. The appearance of coating by $US_3M_3$ and $US_{11}M_3$ solutions were bumpy surface, and were a lot of fine defects. $US_7M_3$ solution was made a sophisticated molecular cross-linking structure inside the coating, it was a slick surface. Other characteristics are exhibited the excellent property for all solutions.

• 한국염색가공학회지
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• 제21권6호
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• pp.39-45
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• 2009

The importance of nano gold particles has been increased in the field of bio physics and medicine, recently. In this regard, the study aims to analyze how the harmless nano gold particles can be transformed by respective variables. In this study, electrospun PU nano-webs were impregnated with aqueous $HAuCl_4$ solution and UV light was irradiated on the webs. Au-ions were reduced to nano particles by photocatalytic reduction and these nano gold particles were characterized by SEM, UV-vis, Zetasizer, Spectrophotometer, EDS. $HAuCl_4$ solution concentration and UV irradiation time have heen examined to change the amount of absorption. Nano gold particles size and UV-Vis absorbances were increased with $HAuCl_4$ solution concentration and UV irradiation time.

• Membrane and Water Treatment
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• 제13권4호
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• pp.191-199
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• 2022

In industrial production, the development of traditional polyamide nanofiltration (NF) membrane was limited due to its poor oxidation resistance, complex preparation process and high cost. In this study, a composite NF membrane with high flux, high separation performance, high oxidation resistance and simple process preparation was prepared by the method of dilute solution dip coating. And the sulfonated polysulfone was used for dip coating. The results indicated that the concentration of glycerin, the pore size of the based membrane, the composition of the coating solution, and the post-treatment process had important effects on the structure and performance of the composite NF membrane. The composite NF membrane prepared without glycerol protecting based membrane had a low flux, when the concentration of glycerin increased from 5% to 15%, the pure water flux of the composite NF membrane increased from 46.4 LMH to 108.2 LMH, and the salt rejection rate did not change much. By optimizing the coating system, the rejection rate of Na₂SO₄ and PEG1000 was higher than 90%, the pure water flux was higher than 40 LMH (60psi), and it can withstand 20,000 ppm.h NaClO solution cleaning. When the post treatment processes was adjusted, the salt rejection rate of NaCl solution (250 ppm) reached 45.5%, and the flux reached 62.2 LMH.

• 센서학회지
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• 제32권3호
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• pp.154-158
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• 2023

This study aimed to improve the moisture resistance of salt cores by investigating the suitability of a two-dimensional kaolinite colloidal solution and a commercially available SiO₂ ink solution as coating agents. X-ray diffraction analysis (XRD) results showed that the intercalation of urea into kaolinite did not significantly change its layer structure. Scanning electron microscopy (SEM) images revealed that the dip-coating only affected the surface of the salt core, and the texture of the surface is differ depending on the coating solution. The humidity absorption test results showed that both coatings reduced the hygroscopicity of the salt core by more than 50%. However, in the water-solubility test, the kaolinite dissolved with the salt core, whereas the SiO₂-coated salt core left a residue. These results strongly suggest that with the coating of the exfoliated kaolinite solution, salt core will remain stable in humid environments.

• 대한수학회보
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• 제59권1호
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• pp.241-263
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• 2022

We consider a nonlinear Schrödinger equation with critical frequency, (P_𝜀) : 𝜀²∆v(x) - V(x)v(x) + |v(x)|^p-1v(x) = 0, x ∈ ℝ^N, and v(x) → 0 as |x| → +∞, for the infinite case as described by Byeon and Wang. Critical means that 0 ≤ V ∈ C(ℝ^N) verifies Ƶ = {V = 0} ≠ ∅. Infinite means that Ƶ = {x₀} and that, grossly speaking, the potential V decays at an exponential rate as x → x₀. For the semiclassical limit, 𝜀 → 0, the infinite case has a characteristic limit problem, (P_inf) : ∆u(x)-P(x)u(x) + |u(x)|^p-1u(x) = 0, x ∈ Ω, with u(x) = 0 as x ∈ Ω, where Ω ⊆ ℝ^N is a smooth bounded strictly star-shaped region related to the potential V. We prove the existence of an infinite number of solutions for both the original and the limit problem via a Ljusternik-Schnirelman scheme for even functionals. Fixed a topological level k we show that v_k,𝜀, a solution of (P_𝜀), subconverges, up to a scaling, to a corresponding solution of (P_inf ), and that v_k,𝜀 exponentially decays out of Ω. Finally, uniform estimates on ∂Ω for scaled solutions of (P_𝜀) are obtained.

• Bulletin of the Korean Chemical Society
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• 제24권7호
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• pp.1002-1004
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• 2003

• 한국지반공학회논문집
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• 제35권11호
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• pp.75-95
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• 2019

본 연구에서는 사질토층을 지나 풍화암에 소켓된 매입 PHC말뚝에 대한 수치해석 결과를 분석하여 정리한 도표 또는 도해로부터 매입 PHC말뚝의 동원지지력을 구하는 방법을 제안하였다. 즉, 수치해석 결과인 하중-침하량 곡선에서 5% 직경에 해당하는 침하량에서 발현된 사질토층의 동원주면마찰력, 풍화암층의 동원주면마찰력과 동원선단지지력을 산정할 수 있는 표해 또는 도해를 제안하였다. 이때 허용압축지지력은 동원 지지력에 안전율 3.0을 적용하여 산정하였다. 사질토층을 지나 풍화암에 소켓된 매입 PHC말뚝의 허용압축지지력은 사질토층의 허용주면마찰력과 풍화암층의 허용주면마찰력 및 허용선단지지력을 합산하여 산정하는 것으로 제안하였고, 각 허용압축지지력 성분을 구할 수 있는 절차도 제시되어 있다. 본 연구에서 제안된 동원지지력 산정용 표해(또는 도해)를 사용할 경우, 적정 설계에서 PHC말뚝의 설계효율(D_E)은 85%로 나타났으며, 따라서 최적 설계에서는 PHC말뚝의 장기허용압축하중(P_all) 까지도 활용할 수 있는 것으로 나타났다. 그리고 PHC말뚝의 우수한 압축하중 지지 성능을 효과적으로 활용하기 위하여 지반의 허용압축지지력(Q_all)이 말뚝의 허용압축하중(P_all) 이상이 될 수 있도록 설계할 것을 권장하였다.