• 청정기술
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• 제29권3호
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• pp.178-184
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• 2023

전이금속 칼코젠화물은 소듐 이차전지의 음극재로서 높은 이론 용량을 가지나 충·방전 과정에서 큰 부피 팽창으로 인해 짧은 수명 특성을 보이며, 낮은 전기전도도로 인해 출력 특성을 저하시킨다는 문제가 있다. 이를 해결하기 위해, 본 연구에서는 분무열분해와 후 열처리 공정을 통해 다공성의 CNT ball과 (Ni,Co)Se₂ 나노결정이 복합된 구조체를 합성하였으며, 이를 소듐 이차전지의 음극에 적용시켜 전기화학적 특성을 평가하였다. 합성된 소재는 분무열분해 동안 Polystyrene(PS) 나노비드의 분해로 인해 다공성 구조를 형성하여 충방전 과정에서 발생하는 부피팽창을 효과적으로 수용하였으며, CNT 소재와의 복합화를 통해 전기화학적 성능을 향상시킬 수 있었다. 이로 인해 다공성 구조의 (Ni,Co)Se₂-CNT 복합소재는 0.2 A g^-1의 전류밀도에서 698 mA h g^-1의 높은 초기 방전용량을 보였으며, 100 사이클 후 400 mA h g^-1의 방전용량을 유지함을 보였다.

• Corrosion Science and Technology
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• 제4권2호
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• pp.56-59
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• 2005

In rebar concrete structure, the corrosion of rebar can arise the deterioration of concrete structure and may affect the safety of the whole system. Recently, several methods for corrosion protection have been used and are more important for concrete structure using the sand including chloride ion. Among several protections, electrical cathodic protection has been expected to be one of the most useful methods in corrosion protection for reinforcement of concrete structures. The anode for cathodic protection needs high current density, high corrosion resistance and low overvoltage. To fill up the special qualities, the insoluble anodes were developed and these anodes were coated with metal oxide of $TiO_2$, $ZrO_2$, $RuO_2$, and $IrO_2$. Lifetime of these anodes can be one of the important factors affecting the lifetime of concrete structure in cathodic protection. In this work, several anodes were made by sol-gel method and thermal decomposition method and the lifetime of these anodes was evaluated by NACE international standard test method, TM 0294-94. Also, we did analyze the properties of coated metal oxides.

• 한국세라믹학회지
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• 제53권3호
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• pp.263-272
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• 2016

Electronic structure calculations have become a powerful foundation for computational materials engineering. Four major factors have enabled this unprecedented evolution, namely (i) the development of density functional theory (DFT), (ii) the creation of highly efficient computer programs to solve the Kohn-Sham equations, (iii) the integration of these programs into productivity-oriented computational environments, and (iv) the phenomenal increase of computing power. In this context, we describe recent applications of the Vienna Ab-initio Simulation Package (VASP) within the MedeA$^{(R)}$ computational environment, which provides interoperability with a comprehensive range of modeling and simulation tools. The focus is on technological applications including microelectronic materials, Li-ion batteries, high-performance ceramics, silicon carbide, and Zr alloys for nuclear power generation. A discussion of current trends including high-throughput calculations concludes this article.

• 한국표면공학회지
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• 제46권6호
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• pp.271-276
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• 2013

The demand for stainless steel is continuously increasing with the development in offshore industry due to its excellent corrosion resistance characteristics. However, it suffers cavitation-erosion in application of high rotating fluid and the damage accelerates in combination with electrochemical corrosion because of Cl-ion in sea water. This paper investigated the complex damage behavior for 431 stainless steel, that is one of martensite stainless steels, through the hybrid test in sea water. Various experiments were carried out, including potential measurement, anodic/cathodic polarization experiment and Tafel analysis. Surface morphology was observed and damage depth was analyzed by SEM and 3D microscope after each experiment, respectively. The results revealed that more active potential was observed under cavitation condition than static condition due to breakdown of passive film and activation of charge transfer, and that higher corrosion current density was obtained under cavitation condition due to synergistic effect of corrosion and erosion.

• Corrosion Science and Technology
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• 제12권1호
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• pp.50-55
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• 2013

The purpose of this study was to investigate corrosion characteristics of Ti-xTa alloys with Ta contents. Ti-xTa alloys used as samples (x=30, 40%) were arc-melted under argon atmosphere of 99.9% purity. Ti-xTa alloys were homogenized for 12hr at $1000^{\circ}C$ and then water quenched. The surface characteristics of Ti-xTa alloys were investigated using optical microscopy (OM) and X-ray diffractometer (XRD). The anodic corrosion behaviors of the specimens were examined through potentiodynamic, potentiostatic and galvanostatic test in 0.9 % NaCl solution at $36.5{\pm}1^{\circ}C$. After corrosion test, the surface characteristics of Ti-xTa alloys were investigated using OM. The microstructure of Ti-Ta alloy showed the beta structure with Ta content. The corrosion resistance of Ti alloy was improved by increasing Ta content and the corrosion morphology of Ti-Ta alloy showed that the site attacked by chloride ion decreased from the active to passive region with Ta content. Potential of Ti-40Ta alloy increased as time increased, whereas, current density of Ti-40Ta alloy decreased as time increased compared to Ti-30 alloy.

• 한국분말재료학회지
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• 제16권5호
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• pp.305-309
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• 2009

The effect of light scattering layers (400 nm, TiO$_2$ particle) of 4 $\mu$m thickness on the dye-sensitized solar cell has been investigated with a 12 $\mu$m thickness of photo-anode (20 nm, TiO$_2$ particle). Two different structures of scattering layers (separated and back) were applied to investigate the light transmitting behaviors and solar cell properties. The light transmittance and cell efficiency significantly improved with inserting scattering layers. The back scattering layer structure had more effective transmitting behavior, but separated scattering layer (center: 2 $\mu$m, back: 2 $\mu$m) structure (9.83% of efficiency) showing higher efficiency (0.6%), short circuit current density (0.26 mA/cm$^2$) and fill factor (0.02). The inserting separating two scattering layers improved the light harvesting, and relatively thin back scattering layer (2 $\mu$m of thickness) minimized interruption of ion diffusion in liquid electrolyte.

• 한국환경과학회지
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• 제29권4호
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• pp.383-393
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• 2020

To increase electrolysis performance, the applicability of seawater to the iron-fed electro-Fenton process was considered. Three kinds of graphite electrodes (activated carbon fiber-ACF, carbon felt, graphite) and dimensionally stable anode (DSA) electrode were used to select a cathode having excellent hydrogen peroxide generation and organic decomposition ability. The concentration of hydrogen peroxide produced by ACF was 11.2 mg/L and those of DSA, graphite, and carbon felt cathodes were 12.9 ~ 13.9 mg/L. In consideration of durability, the DSA electrode was selected as the cathode. The optimum current density was found to be 0.11 A/㎠, the optimal Fe²⁺ dose was 10 mg/L, and the optimal ratio of Fe²⁺ dose and hydrogen peroxide was determined to be 1:1. The optimum air supply for hydrogen peroxide production and Rhodamine B (RhB) degradation was determined to be 1 L/min. The electro-Fenton process of adding iron salt to the electrolysis reaction may be shown to be more advantageous for RhB degradation than when using iron electrode to produce hydrogen peroxide and iron ion, or electro-Fenton reaction with DSA electrode after generating iron ions using an iron electrode.

• Transactions on Electrical and Electronic Materials
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• 제14권4호
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• pp.165-171
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• 2013

Nanostructured pure a-C and nitrogen doped a-C: N thin films with small particle size of, ~50 nm were obtained by Aerosol-assisted CVD method from the natural precursor camphor oil. Five samples were prepared for the a-C and a-C: N respectively, with the deposition temperatures ranging from $400^{\circ}C$ to $600^{\circ}C$. At high temperature, the AFM clarifies an even smoother image, due to the increase of the energetic carbon ion bombardment at the surface of the thin film. An ohmic contact was acquired from the current-voltage solar simulator characterization. The higher conductivity of a-C: N, of ${\sim}{\times}10^{-2}Scm^{-1}$ is due to the decrease in defects since the spin density gap decrease with the nitrogen addition. Pure a-C exhibit absorption coefficient, ${\alpha}$ of $10^4cm^{-1}$, whereas for a-C:N, ${\alpha}$ is of $10^5cm^{-1}$. The high ${\sigma}$ value of a-C:N is due to the presence of more graphitic component ($sp^2$ carbon bonding) in the carbon films.

• Membrane and Water Treatment
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• 제5권1호
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• pp.31-40
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• 2014

Papermaking tobacco sheet is an important reclaimed process for cigarette making. Traditionally, the pressure driven membrane was often used to isolate the effective compounds from the tobacco sheet extract. However, this method is difficult to remove small ionic compounds. Besides, membrane fouling is a major problem for effective use of these pressure driven membrane technologies. In this study, the electrodialysis process is used to removal the chloride ions and nitrate ions, thus the smoking quality of papermaking tobacco sheet extract can get improved. Three types of electrolytes ($Na_2SO_4$, NaCl and HCl) are chosen to prevent the generation of precipitation. The results indicate that 0.1mol/L HCl at current density of $30mA/cm^2$ is the optimal condition for the electrodialysis process. The removal rates of the Cland $NO{_3}^-$ in tobacco sheet extract are 97% and 98.4%, respectively. The electrodialysis process cost was estimated to be 0.11$/L. Naturally, electrodialysis is not only technological feasible, environmental-friendly and economical-attractive for tobacco extract treatment.

• Advances in Energy Research
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• 제4권4호
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• pp.285-297
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• 2016

Fundamental understanding of vanadium ion transport and the detrimental effects of cross-contamination on vanadium redox flow battery (VRFB) performance is critical for developing low-cost, robust, and highly selective proton-conducting membranes for VRFBs. The objective of this work is to examine the effect of conductivity and diffusivity, two key membrane parameters, on long-cycle performance of a VRFB at different operating conditions using a transient 2D multi-component model. This single-channel model combines the transport of vanadium ions, chemical reactions between permeated ions, and electrochemical reactions. It has been discovered that membrane selecting criterion for long cycles depends critically on current density and operating voltage range of the cell. The conducted simulation work is also designed to study the synergistic effects of the membrane properties on dynamics of VRFBs as well as to provide general guidelines for future membrane material development.