• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.67-72
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• 2006

Precipitated calcium carbonate (PCC) was prepared in a cylindrical reactor by the nozzle spouting method. The reactor was filled with $CO_2$ and $Ca(OH)_2$ suspensions were circulated through a nozzle to prepare PCC. This method has several advantages such as provision of large contact area between suspension and $CO_2$ and production of large number of nuclei in short time. By changing suspension concentrations, suspension temperature, flow rates of $CO_2$ and nozzle sizes, PCC from homogeneously dispersed $0.1{\mu}m$ to heterogeneous $0.3{\mu}m$ can be obtained. According to XRD analyses, most PCC formed was calcite with small amount of aragonite depending on the reaction conditions. Usually, the reaction proceeded at high pH and electric conductivities initially. Then, pH and electric conductivities decreased rapidly to the saturation condition. Results indicated that the specific conditions (temperature: $25^{\circ}C$, suspension concentration: 0.5 wt%, $CO_2$ flow rate: 1 L/min, nozzle size: 0.4 mm) were required to prepare uniform particle size (particle diameter: $0.1{\mu}m$) of PCC.

• Clean Technology
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• v.26 no.2
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• pp.131-136
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• 2020

Biomass bamboo charcoal is utilized as anode for lithium-ion battery in an effort to find an alternative to conventional resources such as cokes and petroleum pitches. The amorphous phase of the bamboo charcoal is partially converted to graphite through a low temperature graphitization process with iron oxide nanoparticle catalyst impregnated into the bamboo charcoal. An optimum catalysis amount for the graphitization is determined based on the characterization results of TEM, Raman spectroscopy, and XRD. It is found that the graphitization occurs surrounding the surface of the catalysis, and large pores are formed after the removal of the catalysis. The formation of the large pores increases the pore volume and, as a result, reduces the surface area of the graphitized bamboo charcoal. The partial graphitization of the pristine bamboo charcoal improves the discharge capacity and coulombic efficiency compared to the pristine counterpart. However, the discharge capacity of the graphitized charcoal at elevated current density is decreased due to the reduced surface area. These results indicate that the size of the catalysis formed in in-situ graphitization is a critical parameter to determine the battery performance and thus should be tuned as small as one of the pristine charcoal to retain the surface area and eventually improve the discharge capacity at high current density.

• Journal of the Mineralogical Society of Korea
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• v.32 no.3
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• pp.213-222
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• 2019

Birnessite (birnessite, $7{\AA}$ manganate, ${\delta}-MnO_2$) is a major mineral comprising manganese nodule. Various synthetic methods have been studied and evaluated because it can be used as an ion exchange agent and a battery recharging material. However, it is difficult to obtain a single birnessite phase because it does not have a stoichiometric chemical composition. Feitknechtite (${\beta}-MnOOH$) is formed as an intermediate product during birnessite synthesis and in this study, the transition of this phase to birnessite was compared by using XRD and SEM. Two different methods, Feng et al. (2004) and Luo et al. (1998), based on redox reaction were used. It was possible to obtain the impurity-free birnessite for the sample aged 60 days at $27^{\circ}C$ by Feng et al. (2004) method and 3 days at $60^{\circ}C$ by Luo et al. (1998) method. The phase transition rate of the feitknechtite phase was slower in the case of $Mg^{2+}$ doped birnessite which was synthesized by Luo et al. (1998) method, and almost single phase almost single phase birnessite was identified at high temperature. Crystal surface and morphology also confirmed the difference between the samples synthesized by two methods.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.163.2-163.2
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• 2010

In this work, nano-flake shaped nickel oxide (NiO) films were synthesized by chemical bath deposition technique for electrochemical capacitors. The deposition was carried out for 1 and 2 h at room temperature using nickel foam as the substrate and the current collector. The structure and morphology of prepared NiO film were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). And, electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge-discharge, and AC impedence measurement. It was found that the NiO film was constructed by many interconnected NiO nano-flakes which arranged vertically to the substrate, forming a net-like structure with large pores. The open macropores may facilitate the electrolyte penetration and ion migration, resulted in the utilization of nickel oxide due to the increased surface area for electrochemical reactions. Furthermore, it was found that the deposition onto nickel foam as substrate and curent collector led to decrease of the ion transfer resistance so that its specific capacitance of a NiO film had high value than NiO nano flake powder.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.49.2-49.2
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• 2010

Polycrystalline CdTe thin films for solar cell continues to be a promising material for the development of cost effective and reliable photovoltaic processes. The two key advantages of this material are its high optical absorption coefficient and its near ideal band gap for photovoltaic conversion efficiency of 1.4-1.5 eV. In this study we made the CdTe thin films for solar cell application which was deposited on the glass substrates using a modified chemical spray method at low temperature. This process does not require the sophisticated and expensive vacuum systems. The prepared CdTe films were characterized with the aid of scanning electron microscope (SEM), UV-visible spectrophotometer, and X-ray diffraction spectrometer (XRD). Following are results of a study on the "Human Resource Development Center for Economic Region Leading Industry" Project, supported by the Ministry of Education, Science & Tehnology(MEST) and the National Research Foundation of Korea(NRF).

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1465-1468
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• 2014

In this study, an intermediate temperature ionic conductor, $Ce_{0.95}Eu_{0.05}P_2O_7$, was prepared by solid state reaction. The variation of conductivities with the pressure $pH_2O$ or time were studied. The highest conductivity of $Ce_{0.95}Eu_{0.05}P_2O_7$ sample was observed in dry air atmosphere at $300^{\circ}C$ to be $1.1{\times}10^{-4}S{\cdot}cm^{-1}$ and in wet air atmosphere ($pH_2O=7.4{\times}10^3Pa$) at $100^{\circ}C$ to be $1.4{\times}10^{-3}S{\cdot}cm^{-1}$, respectively. The log ${\sigma}$ ~ log ($pO_2$) plot result indicated that $Ce_{0.95}Eu_{0.05}P_2O_7$ was almost a pure ionic conductor under high oxygen partial pressure and a mixed conductor of ion and electron under low oxygen partial pressure.

• Korean Journal of Materials Research
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• v.27 no.8
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• pp.416-421
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• 2017

V-substituted $SrTiO_3$ thermoelectric oxide materials were fabricated by the conventional solid state reaction method. From X-ray diffraction pattern analysis, it can be clearly seen that almost every vanadium atom incorporated into the $SrTiO_3$ provided charge carriers. The electrical conductivity ${\sigma}$, Seebeck coefficient S, and thermal conductivity k were investigated in a high temperature regime above 1000 K. The addition of vanadium significantly reduced the thermal conductivity and enhanced the Seebeck coefficient, as well as the electrical conductivity, thus enhancing the ZT value. A maximum ZT value of 0.084 at 673 K was observed for the sample with 1.0 mole% of vanadium substitution. In this study, the reason for the enhanced thermoelectric properties via vanadium addition was also investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.134-134
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• 2016

CMC(Ceramic Matrix Composites)는 $1500^{\circ}C$ 이상의 고온에서 내열성, 내산화성, 내식성이 우수하여, 초음속 비행체, 가스터빈 엔진 및 원자로용 초고온 부품 등에 수요가 증가하고 있다. 하지만 이러한 특성은 비산소 환경에 국한되는 것으로 약 $400^{\circ}C$ 이상의 산화 분위기에는 탄소섬유가 산화되는 문제로 인하여 적용의 한계를 가지고 있다. 따라서 CMC의 적용범위 확대를 위하여 내산화 코팅으로 CMC의 초고온 산화특성을 개선하는 것이 필수적이며, 장시간 초고온 산화환경 분위기에서 사용되기 위하여 안정적인 코팅기술이 최근 기술개발의 핵심현안으로 부각되고 있다. 본 연구에서는 pack cementation 공정을 이용하여 내산화성이 우수한 SiC 코팅층을 제조하였다. Pack cementation 공정에 사용된 코팅 분말은 57wt.% SiC, 30wt.% Si, 3wt.% B, 10wt.% Al2O3의 비율로 혼합된 것이다. 실험은 3D 직조된 CMC 모재를 혼합분말 내에 침적한 후, Ar 분위기에서 $1600^{\circ}C$, 4~12시간 반응시켜 수 마이크론 두께의 SiC 코팅층을 형성하였다. 더 우수한 산화 특성을 부여하기 위하여 pack 처리된 CMC 표면에 초고온 세라믹인 TaC 소재를 진공플라즈마 코팅 공정으로 적층시켰다. 제조된 코팅층을 SEM, XRD를 이용하여 미세구조 및 결정구조를 분석하였으며, pack cementation에 따른 내산화 특성을 비교 분석하고자 $2000^{\circ}C$에서 산화 실험을 진행하였다. 산화 실험 이후 미세구조 및 결정구조 분석으로 산화거동을 규명하고자 하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.307.1-307.1
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• 2016

Amorphous zinc tin oxide (ZTO) thin films are being widely studied for a variety electronic applications such as the transparent conducting oxide (TCO) in the field of photoelectric elements and thin film transistors (TFTs). Thin film transistors (TFTs) with transparent amorphous oxide semiconductors (TAOS) represent a major advance in the field of thin film electronics. Examples of TAOS materials include zinc tin oxide (ZTO), indium gallium zinc oxide (IGZO), indium zinc oxide, and indium zinc tin oxide. Among them, ZTO has good optical and electrical properties (high transmittance and larger than 3eV band gap energy). Furthermore ZTO does not contain indium or gallium and is relatively inexpensive and non-toxic. In this study, ZTO thin films were formed by UHV RF magnetron co-sputter deposition on silicon substrates and sapphires. The films were deposited from ZnO and SnO2 target in an RF argon and oxygen plasma. The deposition condition of ZTO thin films were controlled by RF power and post anneal temperature using rapid thermal annealing (RTA). The deposited and annealed films were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), ultraviolet and visible light (UV-VIS) spectrophotometer.

• Transactions on Electrical and Electronic Materials
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• v.10 no.4
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• pp.135-139
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• 2009

$H_2S$ micro-gas sensors have been developed employing $SnO_2$:CuO composite thin films. The films were prepared by e-beam evaporation of Sn and Cu metals on silicon substrates, followed by oxidation at high temperatures. Results of various studies, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that $SnO_2$ and CuO are mutually non-reactive. The CuO grains, which in turn reside in the inter-granular regions of $SnO_2$, inhibit grain growth of $SnO_2$ as well as forming a network of p-n junctions. The film showed more than a 90% relative resistance change when exposed to $H_2S$ gas at 1 ppm in air at an operating temperature of $350^{\circ}C$ and had a short response time of 8 sec.