화학적 활성화를 이용한 석유계 피치 음극소재의 전기화학적 특성

황진웅 충북대학교 2018 국내석사

In this study, the electrochemical performance of surface modified carbon using the PFO(pyrolyzed fuel oil) was investigated by chemical activation with KOH and K2CO3. PFO was heat treated at 390~420 ℃ for 1~3h to prepared the pitch. Three carbon precursors(pitch) prepared by the thermal reaction were 3903(at 390 ℃ for 3h), 4001(at 400 ℃ for 1h) and 4002(at 400 ℃ for 2h), 4203(at 420 ℃ for 3h). Also, the effect of chemical activation catalysts and mixing time on the development of porosity during carbonization was investigated. The prepared carbon was analyzed by BET and FE-SEM. It was shown that chemical activation with KOH could be successfully used to develop carbon with specific surface area (100 m2/g) and mean pore size (25 nm). The electrochemical characteristics of modified carbon as the anode were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests. The coin cell using pitch(4203) modified by KOH has better initial capacity (420 mAh/g) than that of other pitch coin cells. Also, this prepared carbon anode appeared a high initial efficiency of 81% and the retention rate capability of 2C/0.1 C was 90%. It is found that modified carbon anode showed improved cycling and rate capacity performance.

항공서비스 불만족 요인과 불평행동에 관한 연구

황진웅 영산대학교 경영대학원 2007 국내석사

Despite the fact that there have been many studies on airline customer satisfaction; it is also true that there has been scanty of investigation into the dissatisfaction and complaints of airline services. Considering the issue rose afore, the study, therefore, is to investigate into the types of dissatisfaction and complaint of airline services based on the theoretical observation and factual analysis, and thereby to suggest measures to tackle this matter by airline market. To this end, existing studies on complaint behavior and dissatisfaction factors was reviewed to set study area, and decisive factors of complaint behavior were looked into, and then questionnaireresearch was carried out. And the data was processed through the SPSS12.0 for the reliability analysis to see the internal consistency and then a factor analysis was carried out for feasibility assessment. And for the understanding of the relationship of the decisive factors of complaint behavior and the type of complaint behaviors, regression analysis was carried out, and to look into the difference of types of dissatisfaction factors and complaint behaviors by characteristics of airline customers, and them T-test and Anova were carried out. And the findings are as follows: First, dissatisfaction factor was known to affect the complaint factor, especially, of them, the factors that appeared to affect personal principle were only responsiveness, tangibles, security, and reliability. Second, Complaint behavior decisive factors appeared to affect the types of complaint-causing behaviors, especially personalprinciple, social damage or benefit, complaint cost, controllability over high status men, and success factor appeared to influence the stoppage of the type of service purchasing, while only personal principle, the important of product, and complaint cost factor appeared to influence the category of negative transmission. Third, there appeared categorical difference regarding complaint behaviors. The analysisresulted in that there appeared to be difference in the category of complaint behaviorby sex, age, occupation and monthly income, educational background, nationality of airline, annual frequency of use and the purpose of the use. In conclusion, even though there can be various factors that can cause dissatisfaction to airline customers, it is important to analyze a factor which can critically affect complaint-causing factor, so thereby airline companies should do their best to remove complaintfactors making use of their marketing efforts. And it is necessary to set up various marketing strategy by subdivision of the markets. It is also necessary for the managers to minimizedissatisfaction and to review the process of complaint handling by providing continued service education to remove cause for dissatisfaction and by promoting service orientation through employee incentive system. And understanding the types of customer complaint behaviors from the analysis of previous cases and resolving them can turn around dissatisfaction customers to satisfied customers.

Electrochemical Characteristics of Artificial Graphite Anode Materials based on Petroleum Pitch for Lithium Ion Battery

황진웅 충북대학교 2023 국내박사

Graphite materials have high chemical/physical stability and low resistance due to the structure in which graphene is stacked. These layered structures exchange electrons from the graphite surface through reactions with lithium ions in the organic electrolyte to provide a path by which lithium ions are stored. Lithium ions entering inside via the path accumulate between the graphite layers to form a lithium layer. Due to such lithium storage and transfer mechanisms, graphite has low fast charge-discharge performance. Also, it is difficult to manufacture good quality artificial graphite(or synthetic graphite) because high processing temperature(over 3000 ℃) is required. In order to understand the disadvantage of graphite, carbon anode materials were produced according to the different temperatures, and the lithium intercalation-deintercalation mechanism was considered according to the structure of carbon. Based on this, we designed an artificial graphite anode material that composites small particles into secondary particles. An artificial graphite anode material (10-15 ㎛) is produced using coke at two sizes (10-15 ㎛, 2-5 ㎛) and the electrochemical properties are compared and discussed. We produce and measure an artificial graphite anode material using coke with a particle size of 10-15 ㎛, limited lithium ion insertion-desorption pathways, increased migration pathways, and low-speed charge-discharge characteristics. When a block is manufactured using coke at a particle size of 2-5 ㎛ and an anode material is created with a particle size of 10 to 15 ㎛, voids capable of storing lithium ions between the coke particles form inside the anode material. These spaces are utilized and the capacity was measured. In addition, the lithium ion insertion-deintercalation path and lithium ion diffusion distance are controlled and the high-speed discharge properties were measured (78.3%) at low temperatures (5C / 0.1C, -10 ℃). At the same time, the high specific surface area due to the small size of the coke was controlled by the binder pitch used in the block, leading to excellent initial efficiency performance. Elements used as additive to lower temperature the graphitic process include boron, phosphorus, and nitrogen. Boron is known as a graphitization additive, because it accelerates the homogeneous continuous graphitization process of the entire carbon without any formation of specific carbon components such as graphite. In this study, various amount of boron and PFO (pyrolysis fuel oil, carbon precursor) were used in an attempt to reveal the boron additive effect. Pitch was produced using a boric acid and pyrolysis fuel oil (PFO), and high-temperature carbonization was carried out at 2,600 ℃. As a result, synthetic graphite exhibiting high crystallinity at a relatively low temperature was produced. The electrochemical performance of several boron-doped and non-doped carbon materials with different structures as anodes in lithium ion batteries was investigated by a structure analysis.

탄화규소 기판 위에 성장한 그래핀의 전자구조 특성 연구

황진웅 부산대학교 대학원 2016 국내석사

Single-layer graphene exhibits intriguing electronic properties stemming from its geometric structure. For example, charge neutral graphene shows strong electronic correlations that are not explained by the theory that describes typical metallic systems. In addition, when the sublattice symmetry is broken, energy gap, whose absence has been the main reason preventing graphene from industrial applications, is predicted and observed. Among them, the electron-plasmon interaction, so-called plasmaron, and energy gap are observed at the Dirac energy where the conduction and valence bands of graphene touch at a single point. Although the physical origin of the two phenomena is apparently different, they become non-trivial to differentiate when graphene is placed on an SiC(0001) substrate. More specifically, when the dielectric screening from the substrate is strong compared to that for free-standing graphene, additional band structure induced by the formation of plasmaron is not separated from the quasiparticle band, but leaves its signature at Dirac energy as increased intensity in conjunction with an elongated band structure along energy direction. Meanwhile, the presence of the buffer layer, a carbidic layer with the same geometric structure as graphene but in which the conical dispersion is absent due to the formation of covalent bonds with the substrate, on an SiC substrate can break the sublattice symmetry of single-layer graphene to induce an energy gap at Dirac energy. For this case, the gap region can be filled with spectral intensity originating from the coupling between the localized π states of the buffer layer and the π bands of single-layer graphene. This controversial issue can be investigated by analyzing electron band structure of buffer layer, single-layer, and double-layer graphene samples using angle-resolved photoemission spectroscopy. Within the plasmaron picture, single- and double-layer graphene grown on the same dielectric substrate may show the similar spectral features at Dirac energy, because both systems are predicted to exhibit the plasmaron. On the other hand, within the in-gap states picture, the spectral intensity at Dirac energy is expected to decrease as the surface is transformed from single-layer to double-layer graphene as their Dirac energy is different in energy with respect to the Fermi energy. In this study, I have investigated this controversial issue to better understand electronic properties of graphene on an SiC substrate. I found that double-layer graphene does not show the characteristic features of the plasmaron introduced in the single-layer graphene. More specifically, the electronic states from the buffer layer is found to gradually decrease in spectral intensity with the evolution of overlying graphene layers, suggesting that the buffer layer states increasingly couple to the graphene π bands as predicted in the in-gap states picture. In double-layer graphene, the Dirac energy shows relatively weak spectral intensity at Dirac energy compared to that of the valence band maximum and the conduction band minimum, and the extended lines along its valence bands perfectly overlap with the conduction bands. These are in contrast to the maximum spectral intensity at Dirac energy and the mismatching bands of single-layer graphene, and hence not explained by the plasmaron picture. Consequently, these results suggest that the in-gap states picture induced by the buffer layer has a main contribution to the high spectral intensity at Dirac energy of single-layer graphene epitaxially grown on an SiC(0001) substrate.

Electronic correlations in graphene studied using angle-resolved photoemission spectroscopy

황진웅 부산대학교 대학원 2019 국내박사

Strong electronic correlations have been a fascinating theme in condensed matter physics over the past decades. Indeed, tons of research have been performed to create and manipulate such correlations by introducing localized orbitals to investigate the Kondo effect or heavy fermions, and to examine the Mott insulators or charge/spin-density waves with triggering the structural instabilities. Another beautiful and simple way to implement the strong electronic correlations is to lower the dimension of a system. As the dimension decreases, the interactions of charge, spin, and lattice vibrations become very sensitive to thermal and quantum fluctuations. Hence, a two-dimension (2D) system is possible to host novel phenomena that its three-dimensional counterpart cannot exhibit. However, plausible routes to realize such phenomena and their experimental evidences still remain unveiled. Thus, the essential question is how to realize strong electronic correlations in the 2D system and how to manipulate the fundamental physical properties. In this dissertation, the electronic correlations in graphene, a prototypical two-dimensional system, were investigated by using angle-resolved photoemission spectroscopy (ARPES). First, electron-electron interactions in charge neutral graphene were investigated by using an SrTiO3 substrate. The observed electron band structure of graphene shows strong deviation from the characteristic linearity at low temperatures, suggesting a possible realization of strong correlations among Dirac fermions at low temperatures. Second, the Kondo effect has been explored for the Ce-intercalated graphene on an SiC(0001) substrate. The ARPES results show that the Ce-induced localized states near Fermi energy are hybridized with the graphene π band and exhibit gradual increase in spectral weight upon decreasing temperature. The observed temperature-dependence reveals a direct evidence of the Kondo resonance induced by graphene π electrons that antiferromagnetically screen the localized spin of the 4f electron of a cerium atom at low temperature. These findings provide a novel insight for the role of substrates and adatoms on the electronic properties of graphene.