Increase in graphitization and electrical conductivity of glassy carbon nanowires by rapid thermal annealing

Lim, Yeongjin,Chu, Jae Hwan,Lee, Do Hee,Kwon, Soon-Yong,Shin, Heungjoo ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.702 No.-

<P><B>Abstract</B></P> <P>Glassy carbon (GC) exhibits numerous desirable properties such as high thermal and chemical stabilities, good hardness, and good thermal and electrical conductivities. Moreover, GC can be manufactured into micro-/nanostructures through the versatile microfabrication technology, or carbon-micro electromechanical systems, which includes polymer patterning and pyrolysis. However, despite these advantages, there are growing demands for enhancing the electrical conductivity of GC, so that it can compensate or be substituted for other carbon allotropes such as graphite, carbon nanotubes, and graphene. In this study, we demonstrated that simple rapid thermal annealing (RTA) can dramatically enhance the electrical conductivity of pyrolyzed GC nanostructures by ∼ 300%. In this research, two different architectures of 1D carbon nanostructures such as a suspended nanowire that was separated from the substrate with a fixed distance and a substrate-bound nanowire were fabricated using conventional UV-lithography and pyrolysis processes, and their conductivity enhancement behaviors via RTA were studied. After the RTA process, the carbon/oxygen content and G-/D-band intensity ratios, which are correlated to the electrical conductivity, were enhanced, depending on the pyrolysis temperature. GC structures pyrolyzed at relatively low temperatures became more electrically conductive after the RTA process owing to their relatively higher oxygen content. This is because carbon atoms interconnected to oxygen atoms tend to align more readily than those corresponding to other carbon compositions because of the graphene healing mechanism. In addition, the architecture of the carbon nanostructures (<I>i.e</I>., whether they were suspended or substrate-bound nanowires) influenced the RTA-induced increase in electrical conductivity; the former showed a greater increase in electrical conductivity owing to its larger portion of well-aligned carbon atoms at the surface compared to the latter carbon structure. This is because graphitization is initiated on the surface and then proceeds to the carbon core in the heat treatment. In addition, tensile stress generated only at the suspended carbon nanowires during the pyrolysis process is assumed to enhance further the electrical conductivity via RTA. For instance, the electrical conductivity of the suspended carbon nanowires formed by pyrolysis at 600 °C was enhanced to ∼59,000 S/m after the RTA process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suspended/substrate-bound glassy carbon nanowires were fabricated using carbon-MEMS. </LI> <LI> The electrical conductivity of carbon nanowires was enhanced by ∼3 times using RTA. </LI> <LI> Long-range graphitic order was induced via RTA. </LI> <LI> Suspended nanowires exhibited twice higher increase in electrical conductivity. </LI> </UL> </P>

Correlation between Hydraulic Conductivity and Electrical Conductivity for Porous Media

Tae Min Oh,Kyu Won Kim,Gye Chun Cho 한국지반공학회 2013 international journal of geo-engineering Vol.5 No.2

Hydraulic conductivity (permeability) is a very important physical property in geotechnical engineering. Monitoring of the hydraulic conductivity is useful for evaluating the ground condition by nondestructive methods. An electrical conductivity measurement technique can be applied to infer hydraulic conductivity. The goal of this study is theoretically to correlate the hydraulic conductivity and electrical conductivity for porous materials and to verify the developed correlation. The verification process is carried out through experimental tests involving glass beads and Joomunjin standard sand. The test variables are the electrical conductivity of the pore fluid, the porosity, and the particle size. The test results show that the estimated hydraulic conductivity realized by the developed correlation is in good agreement with the measured hydraulic conductivity results. Therefore, this preliminary study provides evidence of the strong possibility of the electrical conductivity being feasible for use to monitor the hydraulic conductivity of porous materials.

흙-벤토나이트월에 대한 전기전도도 모니터링 기법의 적용성 평가

오명학,유동주,김용성,박준범 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.7

In this study, applicability of electrical conductivity monitoring technique for containment barrier such as soil-bentonite wall was evaluated. Laboratory tests including permeability tests and column tests were performed to understand variations in electrical conductivity at different bentonite contents, hydraulic conductivities, and heavy metal concentrations. The electrical conductivity of compacted soil-bentonite mixtures was found to increase proportionally with bentonite content. Accordingly, the hydraulic conductivity of compacted soil-bentonite mixtures which decreases linearly with increasing bentonite content was found to have an inversely proportional relationship with the electrical conductivity. In column tests, electrical conductivity breakthrough curves and concentration breakthrough curves were simultaneously obtained. These results indicated that electrical conductivity measurement can be an effective means of detecting heavy metal transport at the desired locations within barriers and verifying possible contaminant leakage. Experimental results obtained from this study showed that the electrical conductivity measurement can be a promising tool for monitoring of containment barrier.

그래핀 나노플레이트 및 카본블랙을 첨가한 아스팔트 혼합물의 공용성 평가

고동영,가현길,이시원,문성호 한국도로학회 2021 한국도로학회논문집 Vol.23 No.5

PURPOSES : Graphene nanoplates, which have recently been in the spotlight in various fields, are a layer of graphite used in pencil leads, with carbon arranged in hexagonal honeycomb shapes. The graphene is 0.2 nanometers thick, and it possesses high physical and chemical stability, high strength, and conductivity. These graphene nanoplates have been studied for application in various devices such as semiconductors and batteries, and in the construction sector, where they are used as additives to improve the durability of cement concrete. The purpose of this study was to investigate the physical, and functional properties of graphene-modified asphalt mixtures. METHODS : In this study, the graphene input content of asphalt mixture samples was determined using an asphalt performance grade (PG) test. Based on the results of the test, their strength, stiffness, thermal properties, and electrical conductivity were evaluated. Indirect tensile strength test and dynamic modulus (DM) test were conducted to evaluate the strength and stiffness, and thermal conductivity tests and electrical conductivity evaluations were conducted for determining the functionality of the graphene-modified asphalt mixtures. The thermal conduction test was used to measure the external temperature change over time by placing a general heated asphalt mixture and graphene-modified asphalt with the same raw material-specific mixing ratio inside the temperature chamber in order to measure the heat conductivity. The electrical conductivity was evaluated using a digital multimeter to measure the resistance of DC voltage and DC current via a 4-probe method. RESULTS : The performance grade (PG) test results showed that, for a dynamic shear rheometer (DSR), both tests met the baseline and that physical changes in the binder did not appear evident with graphene addition. Furthermore, each content met the baseline for the bending beam rheometer (BBR). The increasing ratio of flexural creep stiffness approached the maximum when 7.5% graphene was used. In indirect tensile strength test, an average of thrice the indirect tensile strength for graphene-modified asphalt was 0.92 N/mm2, which was approximately 0.04 N/mm2 higher than the average measured three times that of hot mix asphalt mixture, with the same raw material mixing ratio. In the thermal conduction tests, the temperature and the rate of change of temperature of the graphene-modified asphalt mixture were higher than those of the hot-mix asphalt mixture. Lastly, the results of the electric conductivity test using the 4-probe method showed that the electrical conductivity increased slightly as the graphene content increased, but overall, it showed very low electrical conductivity. CONCLUSIONS : In this study, the potential for enhancing the physical and functional performance of graphene nanoplates applied to asphalt mixtures was demonstrated. However, it is practically difficult to arrange graphene particles continuously within an asphalt mixture, which is believed to have very low electrical conductivity.

Age Hardening Characteristics of Cu-Ag-Zr Alloy

S. G. Jia,X. M. Ning,M. S. Zheng,G. S. Zhou,P. Liu 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4

Cu-Ag-Zr alloy is a newly developed copper alloy material which has an excellent combination of high mechanical strength and high electrical conductivity. By means of vacuum induction melting, Cu-Ag-Zr alloy was produced. The effects of aging processes on the microhardness and electrical conductivity characteristics of Cu-Ag-Zr alloy were studied. After aging at 450 °C for 4h, the alloy showed an excellent combination of microhardness and electrical conductivity: the microhardness and electrical conductivity reach 126 HV and 84%IACS, respectively. The precipitates responsible for the age-hardening effect are the fine and dispersed Cu5Zr, which has a face center cubic structure. Cu5Zr precipitates are fully coherent with the Cu matrix and give the Cu- Ag-Zr alloy higher microhardness and higher electrical conductivity. Cu-Ag-Zr alloy is a newly developed copper alloy material which has an excellent combination of high mechanical strength and high electrical conductivity. By means of vacuum induction melting, Cu-Ag-Zr alloy was produced. The effects of aging processes on the microhardness and electrical conductivity characteristics of Cu-Ag-Zr alloy were studied. After aging at 450 °C for 4h, the alloy showed an excellent combination of microhardness and electrical conductivity: the microhardness and electrical conductivity reach 126 HV and 84%IACS, respectively. The precipitates responsible for the age-hardening effect are the fine and dispersed Cu5Zr, which has a face center cubic structure. Cu5Zr precipitates are fully coherent with the Cu matrix and give the Cu- Ag-Zr alloy higher microhardness and higher electrical conductivity.

Effects of Cesium Salts on the Electrical Conductivity of the Weakly Ionized Gas in a Hypersonic MHD Channel

Hao Li,Peng Lu,Hulin Huang,Yining Zhang,Chenyuan Liu 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.5

To adequately utilize the high enthalpy of the weakly ionized gas and improve the performance of the magnetohydrodynamic generator (MHDG) in a hypersonic channel, cesium salts are homogeneously injected into the gas at the entrance of the MHD channel for elevating the gas electrical conductivity. The finite rate chemical dynamics and multi-species electrical conductivity model for seven-species (N2, O2, N, O, NO, NO+, e−) were adopted to simulate the electrical conductivity of the weakly ionized gas under different magnetic fields. The results demonstrate that the electrical conductivity of the weakly ionized gas with cesium salts is significantly higher than that without cesium salts due to two positive contributions of cesium salts, one is that a portion cesium atom ionize much more electrons, and the second is that cesium salts reduce the activation energy of N + O <-> NO + e− by 3.5 times, which accelerates the production rate of electrons. The electrical conductivity of the gas with cesium salts is decreased monotonically along the flow direction, which is contrary to the trend of that without cesium salts. The variation of the collision frequency plays a crucial role in the electrical conductivity of the gas without cesium salts, nevertheless, this effect is marginal on the gas with cesium salts. The magnetic fields have negative impacts on the electrical conductivity of the gas with/without cesium salts. Additionally, the MHDG power generation efficiency is augmented with B for the gas with cesium salts, whereas the trend is reversed for that without cesium salts.

Electrical conductivity of Zr- and Gd- doped UO₂

노혜란,이동우,최현명,김종윤,이정묵,김태형,임상호 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-

The UO₂ fuel irradiated in the reactor contains various elements from cladding materials and fission products generated during irradiation, and reacts with them to form a solid solution. UO₂ should have Mott insulator characteristics. Even with a small amount of dopants, the electrical conductivity can vary significantly. We used ZrO₂ and Gd₂O₃ as dopants which can form the solid solution with UO₂ to investigate the effect of the dopant level on the electrical conductivity. Various compositions of U_1-x-yZr_xGd_yO_2+δ were prepared, and the electrical conductivity was measured at room temperatures. Electrical conductivities of (x=0, y=0), (x=0.05, y=0.005), (x=0.05, y=0.01), (x=0.1, y=0.005) were 0.10, 1.11, 1.51, and 0.35 S/m, respectively. As the dopant level of Zr increased, electrical conductivity showed the maximum value of 1.11 S/m. Whereas the electrical conductivity increased up to 1.51 S/m as the dopant level of Gd increased.

Investigation of electromagnetic interference shielding effectiveness and electrical percolation of carbon nanotube polymer composites with various aspect ratios

Lee Dong-Kwan,Yoo Jongchan,Kim Hyunwoo,Park Sung-Hoon 한국탄소학회 2024 Carbon Letters Vol.34 No.1

Metals are recognized as electromagnetic interference (EMI) shielding materials owing to their high electrical conductivity. However, the need for light and flexible EMI shielding materials has emerged, owing to the heavyweight and inflexible nature of metals. Carbon nanotube (CNT)/polymer composites have been studied as promising flexible EMI shielding materials because of their lightweight nature due to the low density of CNTs and their high electrical conductivity. CNTs evenly dispersed in the polymer form an electrically conductive network, and the aspect ratio of the CNTs, which are one-dimensional nanofillers, is an important factor affecting electrical conductivity. In this study, we prepared three types of multi-walled carbon nanotubes (MWNTs) with different aspect ratios and fabricated polydimethylsiloxane (PDMS)/MWNT composites. Subsequently, the electrical conductivities and electrical percolation thresholds of the three PDMS/MWNT composites with different MWNT aspect ratios were measured to analyze the behavior of electrically conducting network formation according to the aspect ratio. Furthermore, the total EMI shielding effectiveness of each composite was determined to evaluate the effect of the MWNT aspect ratio on the EMI shielding. Reflection and absorption of electromagnetic wave were measured for the PDMS/MWNT composite with the largest aspect ratio to analyze the EMI shielding mechanism of the composite. Additionally, the effects of the MWNT content on the conductivity and EMI shielding performance were examined. The results provide valuable guidance for designing polymer MWNT composites with good electrical conductivity and EMI shielding performance under different aspect ratios of MWNTs.

도전성 분말에 의한 아크전류의 파형 및 실효값 특성

김두현 ( Doo Hyun Kim ),강양현 ( Yang Hyun Kang ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.3

This paper is aimed to make an analysis of characteristics of the parallel arc waveform and RMS of current at the electrical tracking state by conductive powder. In order to achieve the goal in this paper, field state investigation at metal processing companies in Chung-Nam province area was conducted. With the field state investigation, conductive powder were collected from metal processing companies. By experiment on electrical connector (breaker, connector) over which the conductive powder were scattered, are waveform and RMS of current were measured. The measured waveform and RMS (root-mean-square) of current were analyzed to describe characteristics and patterns of electrical arc by the conductive powder. It was proved that conductive powder on electrical connector can flow electrical current enough to make electrical fire with high thermal energy. Also the change of sine waveform and RMS of current can be used to find out relationship between electrical fire and fault signal by conductive powder. The results obtained in this paper will be very helpful for the prevention of electrical fires occurred at the metal processing companies.

Electrically conductive composites prepared from 3-methyl thiophene by the FeCl3 oxidation method

Eun-Kyoung Lee,Sei-Young Choi 한국화학공학회 2006 Korean Journal of Chemical Engineering Vol.23 No.6

thiophene and butyltin dilaurate can be successfully prepared by the diffusion-oxidative polymerization method. Variouseffects of the doping conditions, such as the reaction time, the FeCl3 concentration, the weight ratio of the 3-methylthiophene to PU and the temperature on the electrical conductivity and thickness of the conductive layer of the 3-methylthiophene/PU composite were investigated. Decomposition temperature rises gradually from pure undoped PU to dopedcomposite that indicates blending took place in FeCl3/ethyl acetate solution. As oxidative reaction time increases, theelectrical conductivity of the 3-methyl thiophene doped PU film increases together with the thickness of the coatinglayer. With increasing FeCl3 concentration and weight ratio of the 3-methyl thiophene to PU, the thickness of the coatinglayer decreases, while the electrical conductivity increases. The increase of the thickness of the PU film leads to therise of the electrical conductivity. The thickness of the coating layer decreases, while the electrical conductivity of the 3-MT doped PU film increases with increasing reaction temperature. As the reaction time and temperature increase, thepolar components of the PU film increase resulting into the increase of moisture regain value.