팽창 흑연의 전압 변환법을 이용한 전기화학 박리 그래핀 제조

임성묵(Sungmook Lim),이원오(Wonoh Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

그래핀은 뛰어난 물성으로 인해 다양한 분야에서 주목을 받고 있으며, 많은 연구가 이루어지고 있고, 그에 따라 생산 방법도 다양해지고 있다. 다양한 그래핀의 생산 방법 중 전기화학 박리법은 다른 제조방법에 비해 순도 높은 그래핀을 저렴하게 대량생산할 수 있다는 장점을 가지고 있으며 박리 공정에서 전기화학적 활성화를 이용하기 때문에 친환경적으로 그래핀의 생산이 가능하다. 그러나 기존의 전기화학 박리법은 고정된 정전압을 이용하기 때문에 인터칼레이션 도중 흑연 층의 선단에서 전해질 이온이 적체되는 현상을 해결할 수 없고 이로 인해 얻어지는 그래핀의 수율 및 품질이 저하되는 문제가 발생할 수 있다. 본 연구에서는 이러한 층간 삽입 이온의 병목현상을 해결하고자 양전압과 음전압을 반복적으로 변환하여 인가하는 전압 변환법을 개발하였고, 이를 층간 간격을 팽창시킨 흑연에 적용하여 기존의 정전압 및 벌크 흑연을 이용한 방식으로 생산한 그래핀과 비교하였다. 그 결과 전압 변환법 및 팽창 흑연을 이용한 그래핀이 기존의 방식에 비해 최대 600% 넓고(17.1 ㎛), 50% 얇으며(2.3 nm), 10 배 이상 향상된 전기전도도(812 S cm^–1)를 10 배의 수득률(3.21 mg min^–1)으로 생산할 수 있음을 확인하였다. 이러한 연구 결과는 전압 변환법을 적용한 전기화학 박리법이 높은 품질의 그래핀을 효율적으로 생산할 수 있을 것이라고 기대될 수 있다. Graphene has been hailed as a miracle material due to its extraordinary properties according to honeycomb lattice carbon atom structure, and its production process varies depending on its quality and production cost. Compare to chemical vapor deposition (CVD) method, mechanical exfoliation, and chemical oxidation, the electrochemical exfoliation can produce high quality graphene sheets with lower price. In addition, electrochemical exfoliation is an environmentally friendly method that use chemical activation, so it does not need any harsh chemicals, which occur additional purification step. In this study, to make higher quality graphene sheets than those from the conventional electrochemical exfoliation method by constant DC (cDC) (1), a diverted DC (dDC) with microwave-assisted expanded graphite (EG) is proposed, which enables more efficient intercalation between graphite layers. The results show that the graphene sheets by the dDC exfoliation have 600% larger area, 50% thinner thickness, 10 times higher electrical conductivity than those by the cDC method. Consequently, dDC method can lead more effective intercalation in exfoliation process and produce higher quality graphene sheets than the conventional method. Therefore, the dDC method with EG has great potential for mass production of high-quality graphene sheets.

Electrochemical Study on Localized Corrosion of Laser Surface Melted Alloy 600

Lim, Yun Soo,Hur, Do Haeng,Kim, Hong Pyo,Kim, Joung Soo,Kwon, Hyuk Sang 한국부식방식학회 2002 Corrosion Science and Technology Vol.31 No.6

The effects of laser surface melting (LSM) on the resistance to localized corrosion such as intergranular stress corrosion cracking (IGSCC) and pitting of Ni-base Alloy 600 were investigated by electrochemical methods. The degree of sensitization ofthe laser heated Alloy 600 measured using the double loop electrochemical potentiokinetic reactivation method in a 0.1 M Na₂S₄O_6 + 20 ppm KSCN solution was considerably low, which demonstrates that the resistance to IGSCC of Alloy 600 in sulfur bearing environments was improved by LSM. The pitting potentials of Alloy 600 in 1 M NaCl at pH 4 and 9 were also markedly increased by the LSM process, compared with that of the non-laser treated Alloy 600. From the microscopic examination, it was found that pitting was initiated around sulfides associated TiN in the matrix of Alloy 600. Homogeneous microstructure associated with the reduction of inclusion size during LSM could be attributed to the increase of resistance to pitting corrosion in the LSM Alloy 600. On the other hand, complete dissolution of pre-existing intergranular Cr-rich carbides and the resultant Cr healing around grain boundaries was responsible for the improvement of IGSCC properties. The resistance to localized corrosion of the laser treated Alloy 600 was discussed from the results of the electrochemical test and microscopic examination.

수중 경화형도료의 부식특성에 관한 전기화학적 고찰

오민석(Min-Seok Oh),이명훈(Myung-Hoon Lee),이성렬(Syung-YUl Lee),김윤해(YUn Hae Kim),문경만(Kyung-Man Moon) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

Many protection methods such as surface coating, electric protection or some other methods etc. have been applied to numerous steel structures being widely used in continental and marine areas to control corrosion of those structures in economic point of view. And most of those steel structures are mainly protected by coating methods. However, some steel piles being under seawater are generally protected by electric protection method, that is, either as an impressed current or as a sacrificial anode method. Furthermore, environmental contamination may be resulted in increasing severe corrosive environment, which, in turn, cause to be accelerated corrosion of the steel structures. Subsequrntly, coated steel structures would deteriorate more rapidly than the designed life time due to acid rain caused by air pollution etc. Therefore coating for the marine plant exposed to the seawater, that is, underwater hardening paintg is increasingly required to a fast dryness as well as a high corrosion resistance. In this study five types of underwater hardening paints are prepared with different resin series and additives. And their corrosion and water resistances were investigated with electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements etc.. Even though, it is generally accepted that corrosion resistance of a bare steel tends to increase with shifting the corrosion potential in the noble direction, however, the corrosion resistance of the sample with coating relatively exhibited a better tendency when had lower corrosion potential in this study. Corrosion current density was also decreased with decreasing the diffusion limiting current density, which may mean that there is a somewhat relation between corrosion and water resistance. S sample of a ceramic resin series relatively showed the best corrosion as well as water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of epoxy resin series. Corrosion and water resistance of those samples tended to be deteriorated with increasing immersion days, and their corrosion and water resistances are considered to be apparently improved by the types of resin and additives.

수중 경화형도료의 부식특성에 관한 전기화학적 고찰

문경만(Kyung-Man Moon),오민석(Min-Seok Oh),이명훈(Myung-Hoon Lee),이성렬(Syung-Yul Lee),김윤해(Yun-Hae Kim) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.2

Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of view. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the electric protection method, that is, either using an impressed current or a sacrificial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coating of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corrosion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally accepted that the corrosion resistance of bare steel tends to increase with a shift of the corrosion potential in the noble direction, the corrosion resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistances were considered to be apparently improved by the types of resin and additives.

Cathode Materials LaNi1−xCuxO3 for Low Temperature Solid Oxide Fuel Cells

Juncai Sun,Chengli Wang,Song Li,Shijun Ji 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.12

New cathode materials LaNi1−xCuxO3 (typically LaNi0.8Cu0.2O3) were synthesized using a co-precipitation method. The structure and morphology of the powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composite material [Ce0.8Sm0.2O2-ä(SDC) and carbonate (Na2CO3,Li2CO3)], NiO and LaNi1−xCuxO3 were used as the electrolyte, anode and cathode, respectively. The electrochemical performance of La-Ni-Cu-O perovskite oxide at low temperatures (400~550oC) was studied. The results showed that LaNi0.8Cu0.2O3 precursor powder prepared through a co-precipitation method and calcined at 860oC for 2 h formed uniform grains with diameters in the range of 400~500 nm. The maximum power density and the short circuit current density of the single cell unit at 550oC were found to be 390 mW/cm2 and 968 mA/cm2, respectively. New cathode materials LaNi1−xCuxO3 (typically LaNi0.8Cu0.2O3) were synthesized using a co-precipitation method. The structure and morphology of the powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composite material [Ce0.8Sm0.2O2-ä(SDC) and carbonate (Na2CO3,Li2CO3)], NiO and LaNi1−xCuxO3 were used as the electrolyte, anode and cathode, respectively. The electrochemical performance of La-Ni-Cu-O perovskite oxide at low temperatures (400~550oC) was studied. The results showed that LaNi0.8Cu0.2O3 precursor powder prepared through a co-precipitation method and calcined at 860oC for 2 h formed uniform grains with diameters in the range of 400~500 nm. The maximum power density and the short circuit current density of the single cell unit at 550oC were found to be 390 mW/cm2 and 968 mA/cm2, respectively.

혈당 측정에 있어서 반사광 비색법과 전기 화학 전극법의 비교

황유성,이도훈,우재근 충북대학교 의과대학 충북대학교 의학연구소 1995 忠北醫大學術誌 Vol.5 No.1

당뇨병환자에서 적절한 혈당을 유지하기 위한 목적으로 시험지봉 검사 방법이 1970년대 초 처음으로 개발된 이후 많은 자가 혈당기들이 고안되어 사용되고 있으며, 대부분이 반사광 비색법을 이용한 자가 혈당 측정기로 현재 국내에는 Glucometer(Ames), Glucoscan(Eiken), One TouchTRM Ⅱ(Lifescan), Accu-check Ⅲ(BM)등이 사용되고 있다. 저자들은 본원에서 이미 사용하고 있었던 반사광 비색법을 이용한 시험지봉으로 LIFESCAN사의 One TouchTM Ⅱ와 전기 화학 전극법을 이용한 Medisense사의 CompanionTM 2에 대하여 정밀도, 직선성, 비교방법과의 상관관계 및 혈액량과 헤마토크리트에 의한 영향, 관찰자간의 변이, 항응고제가 미치는 영향 등 측정에 영향을 미치는 여러 인자들에 대하여 평가를 시행하였다. 검사일내 정밀성(within day precision)은 두 기기 모두 5% 정도이었고, 검사일간 정밀성(day-to-day precision)은 CompanionTM 2가 3.14%∼6.53%, One touchTM Ⅱ가 4.69%∼8.13%의 변이계수를 보였다. 두 기기 모두 직선성이나 비교방법과의 상관관계가 우수하였다. CompanionTM 2와 One touchTM Ⅱ사이의 상관관계는 y=1.040x+21.679, r=0.9716이었다. 두 기기 모두 혈액량, 관찰자, 항응고제에 의해서는 영향을 받지 않았으며, 헤마토크리트에 의해서는 헤마토크리트가 낮을 때는 높은 혈당치를, 헤마토크리트가 높을 때는 낮은 혈당치를 나타냈다. The purpose of this study is to assess two monitors of blood glucose : One touch?? Ⅱ(Lifescan Inc.), which is using reagent strips by reflectance photometry and CompanionTM 2(Medisense Inc.), which is using electrochemical electrode method. Glucose was determined on capillary and venous blood samples from 70 adult diabetics by three different methodologies : One touchTM Ⅱ, CompanionTM 2 portable glucose meters (capillary) and the Hitachi 7150 analyzer(venous), which is using hexokinase method. In within-run precision studies for One touchTM Ⅱ and CompanionTM 2, coefficient variations (CVs, %) were 1.92∼5.09, 2.95∼4.79 at three different levels, respectively. In between-day percision studies for One touchTM Ⅱ and CompanionTM 2, CVs(%) were 4.69∼8.13, 3.14∼6.53 at three different levels, respectively. The linearity studies revealed r=0.9996 in One touch?? Ⅱ, r=0.9977 in CompanionTM 2, which were satisfactory. Correlation equation and coefficient for results by One touchTM Ⅱ and CompanionTM 2 vs those by hexokinase method(x) were : y=0.8087x-8.9566(r=0.9824) for One touchTM Ⅱ, y=0.8885x+4.4992(r=0.9807) for CompanionTM 2, which were satisfactory. The glucose levels were falsely high at low hematocrit concentration and falsely low at high hematocrit concentration in both monitors. The volume of blood applied to the test strips is not critical. We concluded that "One touchTM Ⅱ" using reagent strip by reflectance photometry and "Companion?? 2" using electrochemical electrode method is suitable for self monitoring of blood glucose.

Electrochemical properties of LiNiO2 and LiNiO2 substituted with Ga, Al and/or Ti

박혜령 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.5

The LiNi1yMyO2 specimens with compositions LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995-Ti0.005O2, and LiNi0.990Al0.005Ti0.005O2 were synthesized by wet milling and solid-state reaction method. All the synthesized samples possessed the a-NaFeO2 structure of the rhombohedral system (space group; R3m) with no evidence of any impurities. Among all the specimens, LiNi0.990Al0.005Ti0.005O2 has the largest first discharge capacity, 196.3 mAh/g, at a rate of 0.1 C. At n = 50 LiNiO2 has the largest discharge capacity, 126.7 mAh/g. LiNiO2 has the best cycling performance, its degradation rate of discharge capacity being 0.73 mAh/g/cycle. 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

졸-겔법에 의해 제조된 LiMPO₄(M = Fe, Mn) 양극 활물질의 전기화학적 특성

김재광,백동호,신용조,안주현,서양곤,김지수,윤석준,조명훈,Kim, Jae-Kwang,Baek, Dong-Ho,Shin, Yong-Jo,Ahn, Jou-Hyeon,Seo, Yang-Gon,Kim, Chi-Su,Yoon, Seok-Jun,Cho, Myung-Hun 한국전기화학회 2008 한국전기화학회지 Vol.11 No.2

리튬이차전지의 양극 활물질로 카본 코팅된 $LiFePO_4$와 $LiMn_{0.4}Fe_{0.6}PO_4$를 졸-겔방법으로 합성하였다. 제조된 양극 활물질을 X-선 회절분석과 주사전자현미경을 통하여 불순물이 존재하지 않으며 기공이 잘 발달되어 있다는 것을 확인하였다. 액체전해질을 사용하여 0.1 C-rate의 전류밀도에서 충방전하였을 경우 $LiFePO_4$는 132 mAH/g, $LiMn_{0.4}Fe_{0.6}PO_4$는 145 mAh/g의 방전용량을 각각 나타내었다. 전기방사에 의해 만들어진 겔 고분자 전해질을 사용하였을 경우에 $LiFePO_4$와 $LiMn_{0.4}Fe_{0.6}PO_4$는 각각 114, 130 mAh/g의 우수한 방전용량을 나타내었다. Carbon-coated $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ cathode materials for lithium batteries were synthesized by a sol-gel method. X-ray diffraction and scanning electron microscopy data showed that the cathode materials are pure crystalline and are surrounded by porous carbon. The initial discharge capacities of $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ with the liquid electrolyte of 1M $LiPF_6$ in EC/DMC are 132 mAh/g and 145 mAh/g, respectively, at current density of 0.1 C-rate. $LiFePO_4$ and $LiMn_{0.4}Fe_{0.6}PO_4$ with an electrospun polymer-based electrolyte exhibit initial discharge capacities of 114 and 130 mAh/g at 0.1 C-rate at room temperature, respectively.

Electrochemical Characteristics of Nanotubular Ti-25Nb-xZr Ternary Alloys for Dental Implant Materials

Byeon, In-Seop,Park, Seon-Young,Choe, Han-Cheol Korean Academy of Dental Science 2017 Journal of korean dental science Vol.10 No.1

Purpose: The purpose of this study was to investigate the electrochemical characteristics of nanotubular Ti-25Nb-xZr ternary alloys for dental implant materials. Materials and Methods: Ti-25Nb-xZr alloys with different Zr contents (0, 3, 7, and 15 wt.%) were manufactured using commercially pure titanium (CP-Ti), niobium (Nb), and zirconium (Zr) (99.95 wt.% purity). The alloys were prepared by arc melting in argon (Ar) atmosphere. The Ti-25Nb-xZr alloys were homogenized in Ar atmosphere at $1,000^{\circ}C$ for 12 hours followed by quenching into ice water. The microstructure of the Ti-25Nb-xZr alloys was examined by a field emission scanning electron microscope. The phases in the alloys were identified by an X-ray diffractometer. The chemical composition of the nanotube-formed surfaces was determined by energy-dispersive X-ray spectroscopy. Self-organized $TiO_2$ was prepared by electrochemical oxidation of the samples in a $1.0M\;H_3PO_4+0.8wt.%$ NaF electrolyte. The anodization potential was 30 V and time was 1 hour by DC supplier. Surface wettability was evaluated for both the metallographically polished and nanotube-formed surfaces using a contact-angle goniometer. The corrosion properties of the specimens were investigated using a 0.9 wt.% aqueous solution of NaCl at $36^{\circ}C{\pm}5^{\circ}C$ using a potentiodynamic polarization test. Result: Needle-like structure of Ti-25Nb-xZr alloys was transform to equiaxed structure as Zr content increased. Nanotube formed on Ti-25Nb-xZr alloys show two sizes of nanotube structure. The diameters of the large tubes decreased and small tubes increased as Zr content increased. The lower contact angles for nanotube formed Ti-25NbxZr alloys surfaces showed compare to non-nanotube formed surface. The corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface showed longer the passive regions compared to non-treatment surface. Conclusion: It is confirmed that corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface has longer passive region compared to without treatment surface.

Potentiodynamic formation of diaminobenzene films on an electrochemically reduced graphene oxide surface: Determination of nitrite in water samples

Kesavan, Srinivasan,Kumar, Deivasigamani Ranjith,Baynosa, Marjorie Lara,Shim, Jae-Jin Elsevier 2018 Materials science & engineering. C, Materials for Vol.85 No.-

<P><B>Abstract</B></P> <P>An electrode comprised of a polydiaminobenzene (p-DAB) film formed on electrochemically reduced graphene oxide (ERGO) on a glassy carbon (GC) (p-DAB@ERGO/GC) was fabricated using a potentiodynamic method for the sensitive and selective determination of nitrite in the presence of a common interference. The p-DAB@ERGO/GC film-modified electrode surfaces were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The film fabrication was initiated via the NH<SUB>2</SUB> groups of DAB, which was confirmed by XPS from the peaks corresponding to NH (396.7eV), NH (399.4eV), NN (400.2eV), and N<SUP>+</SUP>H (402.2eV). The Raman spectra revealed the characteristic D and G bands at 1348 and 1595cm<SUP>−1</SUP>, respectively, which confirmed the fabrication of GO on the GC electrode, and the ratio of the D and G bands was increased after the electrochemical reduction of GO. The surface coverage of the modified electrode was 8.16×10<SUP>−11</SUP> molcm<SUP>−2</SUP>. The p-DAB@ERGO/GC film-modified electrode was used successfully for the determination of nitrite ions. The p-DAB@ERGO/GC film-modified electrode exhibited superior activity for the determination of nitrite compared to the bare GC and p-DAB@GC electrodes. The amperometric current increased linearly with increasing nitrite concentration from 7.0×10<SUP>−6</SUP> to 2.0×10<SUP>−2</SUP> M. The detection limit was 30nM (S/N=3). In addition, the modified electrode was used successfully to determine the nitrite ion concentration in the presence of a 100-fold excess of common interferents. The practical application of the modified electrode was demonstrated by determining the nitrite ion concentration in water samples.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel diaminobenzene film on ERGO was fabricated by potentiodynamic method. </LI> <LI> p-DAB@ERGO/GC shows excellent activity towards nitrite. </LI> <LI> The proposed sensor exhibits lowest detection limit and wide linear range. </LI> <LI> Modified electrode was successfully applied to the analysis in water samples. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>