• 한국결정성장학회지
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• 제31권6호
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• pp.240-246
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• 2021

도자 생산현장에서 아연결정유약을 제조하여 사용할 때 조성원료에 따라 유약의 결정생성이 불안정하고, 특히 결정이 잘 생성되는 유약도 습식제조 후 시간이 경과하면 결정생성이 급격히 저하되는 문제점이 있다. 도예가들이 주로 사용하는 산화아연(ZnO)과 하소아연(calcined ZnO), 프리트 3110, 그리고 규석을 출발 물질로 3성분계 실험을 통하여 아연결정 조성을 선택하고 선 연구된 소성 조건을 사용하였다. 유약을 제조하고 1일~24주까지 습식으로 보관하면서 침수 과정에서 아연이 아연결정유의 결정생성에 미치는 영향을 규명하고자 하였다. 원료 입도 및 침수 영향을 측정하기 위해 입도분석, XRD, Raman Spectroscopy 그리고 SEM 분석 등을 하였다. 연구결과, 산화아연은 습식으로 유약 사용 시 willemite 결정 생성 및 성장이 우수하지만 유약을 보관하는 동안 ZnO가 물과 반응하여 Zn(OH)2를 생성하고 응집되면서 유약내 ZnO량이 감소되어 willemite 생성을 저해하여 결정이 감소됨을 확인하였다.

• 한국지반환경공학회 논문집
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• 제12권10호
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• pp.51-56
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• 2011

본 연구에서는 스케일형성 제어와 막 파울링 저감을 위한 펄스 전기장 처리의 적용성을 실험적으로 검토하였다. 수용액 중의 칼슘이온 78%가 감소되었으며, $CaCO_3$입자의 크기는 커지는 것으로 확인되었다. 또한, $CaCO_3$의 결정형태는 비교적 제거가 힘든 Aragonite 구조에서 비교적 제거가 쉬운 Calcite 구조로 변화됨을 알 수 있었다. 막투과 유량과 막투과 유속은 펄스 전기장처리전에 비하여 더 높게 나타났으며, 스케일형성 가능성지수인 LI값 역시 감소하는 경향을 나타내었다. 결과로부터 펄스 전기장처리가 막 여과의 전처리로써 $CaCO_3$파울링을 경감시키기 위한 효과적인 방법으로 판단된다.

• 한국분말재료학회지
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• 제28권2호
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• pp.134-142
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• 2021

In this study, AlSi10Mg powders with average diameters of 44 ㎛ are additively manufactured into bulk samples using a selective laser melting (SLM) process. Post-heat treatment to reduce residual stress in the as-synthesized sample is performed at different temperatures. From the results of a tensile test, as the heat-treatment temperature increases from 270 to 320℃, strength decreases while elongation significantly increases up to 13% at 320℃. The microstructures and tensile properties of the two heat-treated samples at 290 and 320℃, respectively, are characterized and compared to those of the as-synthesized samples. Interestingly, the Si-rich phases that network in the as-synthesized state are discontinuously separated, and the size of the particle-shaped Si phases becomes large and spherical as the heat-treatment temperature increases. Due to these morphological changes of Si-rich phases, the reduction in tensile strengths and increase in elongations, respectively, can be obtained by the post-heat treatment process. These results provide fundamental information for the practical applications of AlSi10Mg parts fabricated by SLM.

• 자원리싸이클링
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• 제30권2호
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• pp.61-67
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• 2021

밀링 및 터닝 가공 중 발생되는 칩 형태 타이타늄 스크랩을 세라믹스 원료로 활용하기 위한 연구를 수행하였다. 우선, 칩 형태 타이타늄 스크랩에 포함되어 있는 다량의 절삭유와 철 성분 제거를 위해 유기세정 및 산 세정 과정을 거쳐 스크랩 표면 세척을 진행하였다. 아세톤과 질산을 사용한 세정 과정을 통해 스크랩 내 유기물과 철 함량은 5 wt.% 수준에서 0.07 wt.% 이하로 감소하는 것을 확인하였고 세정에 이어진 산화 과정을 통해 타이타늄 스크랩은 이산화타이타늄화 되었다. 타이타늄 스크랩의 이산화타이타늄화 과정은 800 ℃ 이상의 온도에서 이루어졌으며 이산화타이타늄은 고에너지 밀링 과정을 통해 나노 결정립으로 미세화되어 탄소에 의한 환원 및 탄화 반응은 기존 이산화타이타늄 탄화환원 온도인 1500 ℃보다 낮은 1200 ℃에서 가능하게 되었다. 이산화타이타늄 탄화환원을 통해 얻어지는 타이타늄 탄화물은 질소 및 타이타늄 이외 전이금속 원소의 첨가 및 고용을 통해 물성이 개선될 수 있었다. 타이타늄 탄화물 내 질소 첨가 및 고용상 형성 가능성은 열역학 계산을 통해 예측되었고 질소 첨가 및 전이금속 고용에 의해 타이타늄 탄화물의 특성 중 경도 및 파괴인성 제어가 가능하였다.

• Journal of Microbiology and Biotechnology
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• 제33권7호
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• pp.895-908
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• 2023

Disposal of waste containing heavy metals into the environment is a major threat to human health and can result in toxic or chronic poisoning in aquatic life. In the current study, metal-resistant Raoultella ornithinolytica was isolated from metal-contaminated samples collected from the Tanjaro River, located southwest of Sulaymaniyah, Iraq. R. ornithinolytica was identified by partial amplification of 16S rRNA. The uptake potency of heavy metals was assessed using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and indicated that R. ornithinolytica removed 67, 89, 63.4, 55.6, 56.5, 65, and 61.9% of Cd, Pb, Cr, Ni, Zn, Co, and Fe, respectively. These removal rates were influenced by temperature, pH, and contact time; at 35℃ and pH 5 with a change in the incubation time, the reduction rate improved from 89 to 95% for Pb, from 36.4 to 45% for Cu, and from 55.6 to 64% for Ni. Gene analysis indicated that R. ornithinolytica contained pbrT, chrB, nccA, iroN, and czcA genes, but the pcoD gene was absent. Energy-dispersive X-ray spectroscopy (EDS) images showed evidence of metal ion binding on the cell wall surface with different rates of binding. Transmission electron microscopy (TEM) detected different mechanisms for metal particle localization; cell surface adsorption was the main mechanism for Pb, Zn, and Co uptake, while Cd, Ni, and Fe were accumulated inside the cell. The current study describes, for the first time, the isolation of R. ornithinolytica from metal-contaminated water, which can be used as an eco-friendly biological expedient for the remediation and detoxification of metals from contaminated environments.

• 한국재료학회지
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• 제32권12호
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• pp.545-552
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• 2022

Tin-antimony sulfide nanocomposites were prepared via hydrothermal synthesis and a N₂ reduction process for use as a negative electrode in a sodium ion battery. The electrochemical energy storage performance of the battery was analyzed according to the tin-antimony composition. The optimized sulfides exhibited superior charge/discharge capacity (770 mAh g^-1 at a current density of 100 mA g^-1) and stable lifespan characteristics (71.2 % after 200 cycles at a current density of 500 mA g^-1). It exhibited a reversible characteristic, continuously participating in the charge-discharge process. The improved electrochemical energy storage performance and cycle stability was attributed to the small particle size, by controlling the composition of the tin-antimony sulfide. By optimizing the tin-antimony ratio during the synthesis process, it did not deviate from the solubility limit. Graphene oxide also acts to suppress volume expansion during reversible electrochemical reaction. Based on these results, tin-antimony sulfide is considered a promising anode material for a sodium ion battery used as a medium-to-large energy storage source.

• 한국환경농학회지
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• 제42권2호
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• pp.83-92
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• 2023

Excess N and P from the livestock manure applied to farmlands, have entered the water systems and poses a serious threat to the natural environment. Consequently, there has been recent awareness towards the management of livestock manure and its related fields. In this study, piggery wastewater was collected from a piggery in Pohang city, Korea. At 800℃, thermal decomposition of a natural stone, magnesite (MgCO₃), yielded powered MgO with particle sizes ranging between 10 to 100 ㎛. Furthermore, NH₄⁺-N and PO₄^3--P were recovered as struvite precipitates from the piggery wastewater, by adjusting the pH with MgO and H₃PO₄. At pH 10, the recovery efficiencies of NH₄⁺-N and PO₄^3--P were found to be 86.1% and 94.1%, respectively. Using an X-ray Diffractometer (XRD), the struvite in the precipitate was confirmed to be consistent with standard pure struvite. Further, the purity of the struvite precipitate was analyzed using an energy dispersive X-ray (EDX) and thermal gravimetry-differential thermal analysis (TG-DTA), and found to be between 79.2% and 93.0%. Additionally, struvite-containing piggery wastewater and sawdust were mixed in a weight ratio of 2.5:1 and processed into a mature compost. The newly manufactured compost passed all quality standards required for first-class graded livestock composts. Moreover, this compost was sprayed directly onto the soil at the test site, and various parameters of the soil's effluent, such as total organic carbon (TOC), total nitrogen (T-N), total phosphorus (T-P), and dissolved oxygen (DO), were analyzed and measured. Based on these results, it is determined that the newly manufactured compost can more significantly reduce water pollution than commercial compost.

• Geomechanics and Engineering
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• 제36권4호
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• 한국ITS학회 논문지
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• 제22권6호
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• pp.182-195
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• 2023

최근 인공지능 알고리즘을 활용한 교통 신호 제어에 관한 관심 증대와 함께, 관련 모델구축 연구가 활발히 진행되고 있다. 그러나 대부분의 연구는 독립 교차로를 대상으로, 교통량 변화에 연동되는 신호 주기 산정을 위한 이론 전개가 주를 이루고 있다. 본 연구에서는 신호제어 알고리즘 구축을 위한 실증 분석을 통해, 신호운영과 회전교차 방식의 실제 교차로를 대상으로 분석을 진행하였다. 기존 연구에서 많이 활용되는 GA와 PSO 알고리즘을 개선한 PSO-BFO 알고리즘을 제시하여 두 교차로의 운영 효과 증진을 위한 신호제어 방안을 강구 하였다. 그 결과, 158초의 신호 주기하에 신호 교차로의 경우, 용량 증대 3.4%, 지체도 및 정지횟수 감소는 각각 8.2%, 8.3%의 효과가 발생하고, 회전교차로에서는 용량증대 9.2%, 지체도 및 정지횟수 감소가 각각 7.1%, 27.2%에 이르는 효과가 발생하는 것으로 나타났다.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1803-1812
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• 2024

The attractive properties of gadolinium-based nanoparticles as a positive contrast agent for magnetic resonance imaging (MRI) have piqued the interest of both researchers and clinicians. Nonetheless, due to the biotoxicity of gadolinium (III) ions' free radicals, there is a need to address this issue. Therefore, this research aimed to develop a biocompatible, dispersible, stable, hydrophilic, and less toxic cellulose nanocrystals/gadolinium oxide nanocomposite as contrast agent properties for MRI purposes. This study aimed to synthesize gadolinium oxide nanoparticles coated with cellulose nanocrystals with polyethylene glycol and sodium hydroxide (CNCs-PEG/NaOH)/Gd₂O₃ using the gamma irradiation method to reduce the particle size. The results showed that using a gamma irradiation dose of 10 kGy, quasi-spherical morphology with a size of approximately 5.5 ± 0.65 nm could be produced. Furthermore, the cytocompatibility of (CNCs-PEG/NaOH)/Gd₂O₃ nanocomposite synthesized was assessed through MTT assay tests on Hep G2 cells, which demonstrated good cytocompatibility without any cytotoxic effects within a concentration range of (10 ㎍/mL - 150 ㎍/mL) and had sufficient cellular uptake. Moreover, the T₁-weighted MRI of (CNCs-PEG/NaOH)/Gd₂O₃ nanocomposite revealed promising results as a positive contrast agent. It is envisaged that the gamma irradiation method is promising in synthesizing (CNCs-PEG/NaOH)/Gd₂O₃ nanocomposite with nanoscale for different applications, especially in the radiotherapy field.