• Journal of Electrochemical Science and Technology
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• 제8권2호
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• pp.101-106
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• 2017

$Li_2SiO_3$ was used as a coating material to improve the electrochemical performance of $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$. $Li_2SiO_3$ is not only a stable oxide but also an ionic conductor and can, therefore, facilitate the movement of lithium ions at the cathode/electrolyte interface. The surface of the $Li_2SiO_3$-coated $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ was covered with island-type $Li_2SiO_3$ particles, and the coating process did not affect the structural integrity of the $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ powder. The $Li_2SiO_3$ coating improved the discharge capacity and rate capability; moreover, the $Li_2SiO_3$-coated electrodes showed reduced impedance values. The surface of the lithium-ion battery cathode is typically attacked by the HF-containing electrolyte, which forms an undesired surface layer that hinders the movement of lithium ions and electrons. However, the $Li_2SiO_3$ coating layer can prevent the undesired side reactions between the cathode surface and the electrolyte, thus enhancing the rate capability and discharge capacity. The thermal stability of $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ was also improved by the $Li_2SiO_3$ coating.

• 한국세라믹학회지
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• 제32권12호
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• pp.1323-1330
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• 1995

The effects of various additives on the microstructures of sintered ZnO varistors were examined. Bi2O3, Sb2O3 and Cr2O3 were added to ZnO step by step to identify the effect of each component. The specimens were prepared by sintering at 110$0^{\circ}C$ and 120$0^{\circ}C$ in ambient atmosphere. In ZnO-Bi2O3-Sb2O3 ternary system, decrease of averge grain size due to antimony oxide addition depends on sintering temperature as well as Bi2O3 content. When Sb2O3 was partly or completely replaced by Cr2O3, grain size was further reduced. A significant amount of pyrochlore phase which was not transformed to spinel and Bi2O3-rich liquid phase seemed to remain during sintering at 110$0^{\circ}C$. Unlike ZnO-Bi2O3-Sb2O3 system, the $\alpha$-spinel phase containing significant amount of Cr did not transform to pyrochlore during furnace cooling. Fine spinel particles around 1${\mu}{\textrm}{m}$ size were ovserved within ZnO grains and grain boundaries, which were believed to be responsible for grain-growth inhibition in ZnO-Bi2O3-Sb2O3.

• 한국자기학회지
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• 제24권6호
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• pp.186-190
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• 2014

뫼스바우어 선원 $^{57}Co/Cu$의 제조조건을 도출하기 위하여, 금속 분말 코발트(Co)를 황산에 용해시킨 후 $H_3BO_3$, KOH와 NaCl을 첨가하여 Sulfamate 도금용액을 제조 후 Cu plate 기판에 도금하였다. 도금두께는 $4{\mu}m$로 일정하게 유지하였다. 전류밀도를 $2mA/cm^2$와 $30mA/cm^2$로 유지하면서 pH에 변화를 준 결과 pH가 4 이상으로 증가하면 hcp 결정의 Co 금속 이외의 2차상이 생성되었다. pH가 증가할수록 Co 후막 표면이 거칠어 졌으며 균열된 표면형상을 관찰하였다. pH가 5까지 증가할 경우 평균입도는 54 nmfh 증가함을 확인하였다. 열처리조건을 변화시키면서 Co가 Cu기지 내에 구속되는 온도가 $900^{\circ}C$에서 2 h임을 확인하였다. 열처리는 진공 후 Ar 분위기(1.5 l/min)를 유지하면서 수행하였다.

• 접착 및 계면
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• 제16권2호
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• pp.55-62
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• 2015

자외선 경화를 통한 2-EHA/AA 점착제 제조 시 나노 충전제로 실리카를 도입하는 경우 실리카의 표면 처리 여부와 실리카 함량이 점착제의 점착 물성 및 열 안정성에 미치는 영향을 조사하였다. 또한 서로 다른 반복단위 길이를 가진 경화제에 따른 실리카의 보강 효과 차이도 관찰하였다. 실란으로 표면 처리된 실리카의 경우 실리카 표면과 고분자 매트릭스 간 계면 상호 작용으로 고분자 매트릭스 내 분산 정도를 높여 겔 함량의 저하 없이 0.3 wt%의 농도까지 점착 물성을 증가시키는 것으로 확인되었다. 특히 경화제로 PEGDMA를 사용할 때 분자 내 상대적으로 긴 에틸렌옥사이드 반복단위에 기인하는 분자 유연성으로 EGDMA를 사용한 계에 비해 실리카 보강 역할에 더 긍정적인 것으로 나타났다. 또한 열 분해 후 잔존량을 통해 실리카와 고분자 간 강한 계면 결합으로 인한 열 장벽 효과로 점착제의 열 안정성이 향상되는 것을 알 수 있었다.

• 한국재료학회지
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• 제20권8호
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• pp.429-433
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• 2010

In this study, activated carbon (AC) as a carbon source was modified with different concentrations of cobalt chloride ($CoCl_2$) to prepare a Co-AC composite, and it was used for the preparation of Co-AC/$TiO_2$ composites with titanium oxysulfate (TOS) as the titanium precursor. The physicochemical properties of the prepared Co-AC/$TiO_2$ composites were characterized by $N_2$ adsorption at 77 K, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The photocatalytic treatments of organic dyes were examined under an irradiation of visible light with different irradiation times. $N_2$ adsorption data showed that the composites had decreased surface area compared with the pristine AC, which was $389\;m^2/g$. From the XRD results, the Co-AC/$TiO_2$ composites contained a mixturephase structuresof anatase and rutile, but a cobalt oxide phase was not detected in the XRD pattern. The EDX results of the Co-AC/$TiO_2$ composites confirmed the presence of various elements, namely, C, O, Ti, and Co. Subsequently, the decomposition of methylene orange (MO, $C_{14}H_{14}N_3NaO_3S$) and rhodamine B (Rh.B, $C_{28}H_{31}ClN_2O_3$) in an aqueous solution, respectively, showed the combined effects of an adsorption effect by AC and the photo degradation effect by $TiO_2$. Especially, the Co particles in the Co-AC/$TiO_2$ composites could enhance the photo degradation behaviors of $TiO_2$ under visible light.

• 한국재료학회지
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• 제23권2호
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• pp.104-111
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• 2013

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an $NH_3$ flow with the variation of $B_2O_3$ additives within a temperature range of $300-1050^{\circ}C$. The additive effect of $B_2O_3$ on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of $B_2O_3$ additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time ($t_c$) shortened. The XPS results showed that Boron compounds of $B_2O_3$ and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase $B_2O_3$ due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and $B_2O_3$ mixed powder by an ammonification route through ${\beta}-Ga_2O_3$ intermediate state. During the ammonification process, boron compounds of $B_2O_3$ and BN coated ${\beta}-Ga_2O_3$ and GaN particles limited further nitridation processes.

• 한국결정성장학회지
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• 제26권3호
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• pp.109-114
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• 2016

용매열합성법과 하소 과정으로 이루어진 두 단계 공정을 통해 단분산된 마이크로 크기의 구형 $ZnGa_2O_4$ 입자를 합성하였다. 합성된 3차원 구조의 구형 $ZnGa_2O_4$ 입자는 핵 생성과정에서 발생된 $ZnGa_2O_4$ 핵들이 자기 조립에 의해 형성된다. 이렇게 3차원 구조의 입자를 형성하는 원리인 '핵 성성'과 '자기 조립' 과정은 계면활성제인 PEG(polyethylene glycol)의 영향을 받는다. 그 이유는 계면활성제인 PEG의 농도가 임계응집농도(critical aggregation concentration)를 결정짓기 때문이다. 그리고 $ZnGa_2O_4$ 단상 합성을 위해 원료인 zinc acetate의 양을 조절했으며, 최적의 하소 조건을 결정하고자 TG-DTA를 통해 열적 거동을 확인했다. 또한 열처리 전 모체와 $900^{\circ}C$에서 1시간의 열처리 과정을 거친 산화물을 구성하는 작용기의 변화를 규명하기 위해 FT-IR을 측정하였다.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3761-3766
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• 2012

$Ag_2Se$-Graphene/$TiO_2$ composite was synthesized by a facile sonochemical method. The as-prepared products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectrophotometer. During the reaction, both of the reduction of graphene oxide and loading of $Ag_2Se$ and $TiO_2$ particles were achieved. The as-prepared $Ag_2Se$-Graphene/$TiO_2$ composites possessed great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties simultaneously. Hence, in the photodegradation of rhodamine B (Rh.B), a significant enhancement in the reaction rate was observed with $Ag_2Se$-Graphene/$TiO_2$ composites, compared to the pure $TiO_2$. The high activity can be attributed to the synergetic effects of high charge mobility, and red shift in absorption edge of $Ag_2Se$-Graphene/$TiO_2$ composites.

• Bulletin of the Korean Chemical Society
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• 제30권8호
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• pp.1738-1742
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• 2009

Nanocrystalline Zn$Fe_2O_4$ oxide-semiconductor with spinel structure was synthesized by the polymerized complex (PC) method and investigated for its photocatalytic and photoelectric properties. The observation of a highly pure phase and a lower crystallization temperature in Zn$Fe_2O_4$ made by PC method is in total contrast to that was observed in Zn$Fe_2O_4$ prepared by the conventional solid-state reaction (SSR) method. The band gap of the nanocrystalline Zn$Fe_2O_4$ determined by UV-DRS was 1.90 eV (653 nm). The photocatalytic activity of Zn$Fe_2O_4$ prepared by PC method as investigated by the photo-decomposition of isopropyl alcohol (IPA) under visible light (${\geq}$ 420 nm) was much higher than that of the Zn$Fe_2O_4$ prepared by SSR as well as Ti$O_{2-x}N_x$. High photocatalytic activity of Zn$Fe_2O_4$ prepared by PC method was mainly due to its surface area, crystallinity and the dispersity of platinum metal over Zn$Fe_2O_4$.

• 한국세라믹학회지
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• 제33권9호
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• pp.1057-1063
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• 1996

Y2O3-CeO2-ZrO2 powders were prepared from water-soluble salts using a coprecipitation method. The forming process of oxide and the characteristics of the calcined powders treated in different drying conditions were investigated. The oxidation was occurred at the temperature of around 40$0^{\circ}C$ and the main crystallization of ZrO2 around $600^{\circ}C$. On calcination at $600^{\circ}C$ heating lamp-dried powders consisted of agglomerates of globular morphology with average agglomerate size of 2.27${\mu}{\textrm}{m}$ and specific surface area of 68.3m2/g and spray dried powders contained dense spheric particles with average agglomerate size of 1.35${\mu}{\textrm}{m}$ and specific surface area of 11.0m2/g which exhibited low agglomeration tendency. Removal of the water by a freeze-drying technique produced calcined powders containing flake-like secondary particle structures with wide agglomerate size distri-bution of 0.1-60${\mu}{\textrm}{m}$ and specific surface area of 24.5${\mu}{\textrm}{m}$. The 20 MPa-pressed density (36.8-41.4% T,D) of calcined powders did not nealy depend on drying methods whilst compaction ratio of calcined powders derived from freeze-drying was the highest ( 6.24) among three drying methods. On continuous heating up to 150$0^{\circ}C$ the sinterability of calcined powders derived from heating lamp-drying was superior to those derived from spray-and freeze-drying. The final sintered density of calcined powders was the highest (96% T,D at 150$0^{\circ}C$) in case of heating lamp-drying.