• Advances in environmental research
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• 제4권2호
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• pp.119-133
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• 2015

Water pollution means that the physical, chemical and biological properties of water are changing. In this study, adsorption was chosen as the treatment method because it is an eco-friendly and low cost approach. Magnetite is a magnetic material that can synthesize chemical precipitation. Magnetite was used for the removal of copper in artificial water samples. For this purpose, metal removal from water dependent on the pH, initial concentration of metal, amount of adsorbent and effect of sorption time were investigated. Magnetite was characterized using XRD, SEM and particle size distribution. The copper ions were determined by atomic absorption spectrometry. The adsorption of copper on the magnetite was studied in a batch process, with different aqueous solutions of Cu (II) at concentrations ranging from 10 to $50mg\;l^{-1}$. Optimum conditions for using magnetite were found to be concentration of $10mg\;L^{-1}$, pH: 4.5, contact time: 40 min. Optimum adsorbent was found to be 0.3 gr. Furthermore, adsorption isotherm data were analyzed using the Langmuir and Freundlich equations. The adsorption data fitted well with the Freundlich ($r^2=0.9701$) and Langmuir isotherm ($r^2=0.9711$) equations. Kinetic and equilibrium aspects of the adsorption process were studied. The time-dependent Cu (II) adsorption data were described well by a pseudo-second-order kinetic model.

• 한국환경과학회지
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• 제17권3호
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• pp.351-357
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• 2008

In order to develope an efficient way for the synthesis of highly pure 1,4-sorbitan solution from sorbitol, some experimental studies were performed. The reaction showed first order reaction with activation energy of 118.3 KJ/mol. Color of the product solutions changed to brown with reaction temperature and reaction time. The equilibrium contents of 1,4-sorbitan increased with decrease in reaction pressure, but the content of major impurity, sorbide, showed maximum about 550 torr vacuum with $H_3PO_4$ catalyst. The reasonable catalyst configuration was 0.26 wt% PTSA and 1 wt% $H_3PO_2$ and optimum reaction temperature and pressure range was $110\sim120^{\circ}C$ and $700\sim720$ torr vacuum, respectively. At optimum reaction conditions, we could obtain white product solutions of highly pure 1,4-sorbitan with sorbide less than 10 wt%. This white product solution is advantageous for preparation of high quality span, anti-fogging agent.

• Korean Chemical Engineering Research
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• 제58권2호
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• pp.301-306
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• 2020

We investigated the individual biosorption removal of lead, copper, and nickel ions from aqueous solutions using Chara sp. algae powder in a batch mode. The impact of several parameters, such as initial concentration of the metal ions, contacting time, sorbent dose, and pH on the removal efficiency, was investigated. The maximum removal efficiency at optimum conditions was found to be 98% for Pb(II) at pH = 4, 90% for Cu(II) at pH = 5, and 80% for Ni(II) at pH = 5. The isotherm study was done under the optimum conditions for each metal by applying the experimental results onto the well-known Freundlich and Langmuir models. The results show that the Langmuir is better in describing the isotherm adsorption of Pb(II) and Ni(II), while the Freundlich is a better fit in the case of Cu(II). Similarly, a kinetic study was performed by using the pseudo-first and second-order equations. Our results show that the pseudo-second-order is better in representing the kinetic adsorption of the three metal ions.

• 한국세라믹학회지
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• 제36권9호
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• pp.893-900
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• 1999

Silica films were prepared on Si single crystal substrates by sol-gel process using TEOS as starting materials. Films were fabricated by a spin coating technique. Sol solutions were prepared by varying the compositions of CH3OH, H2O and DMF with fixed molar ratio of TEOS=1, HCl=0.05(mol). Wetting behavior viscosity of solutions gelation time thickness of films and cracking behavior were investigated with the various solution compositions. Wetting behaviors of solutions depended on the solution compositions mixing method and mixing rate. The optimum composition of sol was TEOS : DMF ; CH3OH: H2O :HCl=1:2:4:4:0.05(mol) and the mixing rate of solution was optimized at 1 ml/min. Viscosity of solutions were controlled by choosing a reaction time(elapsed time after mixing) at a room temperature so that we could get up to 800nm thick film The surface roughness was getting poor when thickness of films was thicker than 500nm. Thickness of coated films were increased with decreasing amount of CH3OH. The best surface roughness was obtained at the content of CH3OH 4 mol. The shortest gelation time was obtained with the content of CH3OH 8 mol. Crack-free filkms were fabricated when sintered at 500$^{\circ}C$ for 1 hr with heating rate of 0.6$^{\circ}C$/min.

• 한국해안해양공학회지
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• 제18권3호
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• pp.225-240
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• 2006

판에 작용하는 등분포하중과 등변분포하중에 의한 휨 모멘트를 계산하기 위해 무차원 방정식에 대한 유한 차분법으로 제시하고 변장비와 격자수에 따른 수치해의 수렴을 분석하였다. 유한 차분법의 수치해는 격자점을 최대 11,520개까지 사용하여 해를 구하였고 변장비에 따른 최적 격자수를 제시하였다. 본 수치해는 Levy형 해석 해와 달리 자유단의 모멘트 경계조건을 만족하며 자유단과 고정단의 교점부근에서는 특이한 모멘트 분포를 보인다. 등분포하중과 등변분포하중에 의한 Levy형 해석해의 무차원 휨 모멘트 값과 본 결과를 비교하였으며 특이한 분포를 보이는 자유단과 그 부근을 제외하면 두 값은 동일한 것으로 나타났다.

• 대한전자공학회논문지SD
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• 제41권3호
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• pp.9-14
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• 2004

본 논문에서는 압저항 압력센서 응용을 위한 최적의 멤브레인 구조를 만들기 위하여 tetramethylammonium hydroxide (TMAH)/ammonium persulfate (AP)/isopropyl alcoho 1(IPA) 용액의 Si 이방성 식각 특성을 연구하였다. 독성이 적고 CMOS 공정과의 높은 호환성 때문에 TMAH를 Si 이방성 식각용액으로 사용하였다. 식각온도, TMAH농도 및 식각시간에 따른 Si 식각률의 변화를 측정하였다. 식각온도를 증가 시키고 TMAH농도를 감소시킴에 따라 Si 식각률은 증가한 반면에 (100)면에 hillock 이 생겨 식각표면의 평탄도가 감소하였다. TMAH 에 IPA 용액을 첨가하면 식각표면의 평탄도를 증가 시키나 Si의 식각률을 감소 시켰다. 그러나, TMAH 에 AP 용액을 첨가하면 Si의 식각률과 식각표면의 평탄도 모두를 증가시켰다. 또한 시간당의 AP 첨가 횟수를 증가시킴으로서 Si 식각률을 최대화시킬 수 있었다. TMAH/AP 용액의 최적의 Si 식각조건을 적용하여 한변의 길이가 100∼400㎛이고 두께가 20㎛인 정사각형 모양의 Si 멤브레인을 성공적으로 제작하였다.

• 한국해양공학회지
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• 제27권5호
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• pp.10-15
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• 2013

The crack-healing behavior and corrosion resistance of SiC ceramics were investigated. Heat treatments were carried out from $900^{\circ}C$ to $1300^{\circ}C$. A corrosion test of SiC was carried out in acid and alkaline solutions under KSL1607. The results showed that heat treatment in air could significantly increase the strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature was $1100^{\circ}C$ for one hour at an atmospheric level. In the two kinds of solutions, the cracks in a specimen were reduced with increasing time, and the surface of the crack healed specimen had a greater number of black and white spots. The strength of the corroded cracked specimen was similar to that of the cracked specimen. The strength of the corroded crack healed specimen decreased 47% and 75% compared to that of the crack healed specimen in the acid and alkaline solutions, respectively. Therefore, the corrosion of SiC ceramics is faster in an alkaline solution than in an acid solution.

• Water Engineering Research
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• 제3권1호
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• pp.57-62
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• 2002

This research is intended to integrate long-term operation rules and real time operation policy for conservation & flood control in a reservoir. The familiar Yield model has been modified and used to provide long-term rule curves. The model employs linear programming technique under given physical conditions, i.e., total capacity, dead storage, spillways, outlet capacity and their respective elevations to find required and desired minimum storage fur different demands. To investigate the system behavior resulting from the above-mentioned operating policy, i.e., the rule curves, the simulation model was used. Results of the simulation model show that the results of the optimization model are indeed valid. After confirmation of the above mentioned rule curves by the simulation models, gate operation procedure was merged with the long term operation rules to determine the optimum reservoir operating policy. In the gate operation procedure, operating policy in downstream flood plain, i.e., determination of damaging and non-damaging discharges in flood plain, peak floods, which could be routed by reservoir, are determined. Also outflow hydrograph and variations of water surface levels for two known hydrographs are determined. To examine efficiency of the above-mentioned models and their ability in determining the optimum operation policy, Esteghlal reservoir in Iran was analyzed as a case study. A numerical model fur the solution of two-dimensional dam break problems using fractional step method is developed on unstructured grid. The model is based on second-order Weighted Averaged Flux(WAF) scheme with HLLC approximate Riemann solver. To control the nonphysical oscillations associated with second-order accuracy, TVD scheme with SUPERBEE limiter is used. The developed model is verified by comparing the computational solutions with analytic solutions in idealized test cases. Very good agreements have been achieved in the verifications.

• 한국해양공학회지
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• 제27권2호
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• pp.33-38
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• 2013

In the past, a very popular method for reducing the corrosion on zinc involved the use of chemical conversion layer coatings based on $Cr^{+6}$. However, there is an important problem with using chromium salts as a result of restrictive environmental protection legislation. This study investigated the optimum condition for galvanized steel using an organic/inorganic solution with a Ti composition. In the case of a fixed heat treatment time, the corrosion resistance values of LR-0727(1) and LR-0727(2) were improved as the heat treatment temperature increased, and the optimum minimum temperature decreased with the heat treatment time. At the optimum heat treatment condition of two coating solutions, the heat treatment time of the LR-0727(1) solution was shorter than LR-0727(2) for the same heat treatment temperature. LR-0727(1) coated specimens did not show desquamation, and all of the specimens showed a good adhesive property. In contrast, in the case of the LR-0727(2) coated specimens, desquamation arose. Therefore, the adhesive property of LR-0727(1) was superior to that of LR-0727(2). The pencil hardness had a 3H average for all of the coating solutions and heat treatment conditions. In the case of a corrosion resistance test with boiling water, the coated specimens of LR-0727(1) were discolored, but LR-0727(2) was not. Finally, LR-0727(1) was more moisture proof than LR-0727(2).

• 전기학회논문지
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• 제63권3호
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• pp.349-357
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• 2014

The performance of a Synchronous Reluctance Motor (SynRM) in terms of torque and power factor depends on the two-axis inductances $L_d$ and $L_q$ of the machine. The Axially Laminated Anisotropic (ALA) rotor should be proposed in an effort to increase the $L_d/L_q$ ratio and the $L_d-L_q$ difference to secure high torque density and high power factor. So, ALA rotor is suitable for high speed instruments. This paper deals with optimum design of Axially Laminated Anisotropic Synchronous Reluctance Motor (ALA-SynRM) and comparison of characteristics with induction motor. Coupled Finite Element Methodology (FEM) & Response Surface Methodology (RSM) have been used to evaluate optimum design solutions. Comparisons are given with characteristics of a same rated wattage induction motor and those of ALA-SynRM respectively.