• Korean Journal of Materials Research
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• v.23 no.10
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• pp.574-579
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• 2013

The milling and particulate characteristics of Al alloy-$Al_2O_3$ powder mixtures for a reaction-bonded $Al_2O_3$ (RBAO) process were studied. A commercially available prealloyed Al powder with Zn, Mg, Cu and Cr alloying elements (7475 series) was mixed with a calcined sinter-active $Al_2O_3$ powder and then milled in centrifugal milling equipment for ~48 hrs. The Al alloy-$Al_2O_3$ powder mixtures after milling were characterized and evaluated in various ways to reveal their particulate characteristics during milling. The milling efficiency of the Al alloy increased with a longer milling time. Comminution of the Al alloy particles started with its elongation, showing a high aspect ratio. With a longer milling time, the elongated Al alloy particle changed in terms of its shape and size, becoming equiaxially fine particles. Regardless of the milling efficiency of the Al alloy particles, all of the Al alloy particles repeatedly experienced strong plastic deformation during milling, giving rise to higher density of surface defects, such as microcracks, and leading to higher residual microstress within the Al alloy particles. The chemical reactions, oxidation behavior and hydration behavior of the Al alloy particles and the hydrolysis characteristics of their reaction with the environment were also observed during the milling process and during the subsequent powder handling steps.

• Bulletin of the Korean Chemical Society
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• v.7 no.1
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• pp.29-35
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• 1986

An empirical formula for semiconductive metal oxides is proposed relating nonstoichiometric value x to a temperature or an oxygen partial pressure such that experimental data can be represented more accurately by the formula than by the well-known Arrhenius-type equation. The proposed empirical formula is log x = A + $B{\cdot}1000/T\;+\;C{\cdot}$exp$(-D{\cdot}1000/T)$ for a temperature dependence and $log\;{\times}\;=a\;+b{\cdot}log\;Po_2\;+\;c{\cdot}$exp$(-d{\cdot}log\;Po_2)$ for an oxygen partial pressure dependence. The A, B, C, D and a, b, c, d are parameters which are evaluated by means of a best-fitting method to experimental data. Subsequently, this empirical formula has been applied to the n-type metal oxides of $Zn_{1+x}O,\; Cd_{1+x}O,\;and\;PrO_{1.8003-x}$, and the p-type metal oxides of $CoO_{1+x},\; FeO_{1+x},\;and\;Cu_2O_{1+x}$. It gives a very good agreement with the experimental data through the best-fitted parameters within 6% of relative error. It is also possible to explain approximately qualitative characters of the parameters A, B, C, D and a, b, c, d from theoretical bases.

• Solar Energy
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• v.20 no.2
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• pp.43-54
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• 2000

We prepared and characterized $Cu(In_{1-x}Ga_x)Se_2$(CIGS) films using a elemental co-evaporation method for absorbing layer of high efficiency thin film solar cells. The CIGS films deposited on a soda-lime glass exhibited low resistivity because of higher carrier concentration. Na was accumulated at the CIGS surface and the 0 and Se were also accumulated at the surface, suggesting that oxidation is a driving force of Na accumulation. The structure of CIGS film was modified or a secondary phase was formed in the Cu-poor CIGS bulk films probably due to the incorporation of Na into Cu vacancy sites. As the Ga/(In+Ga) ratio increased, the diffraction peaks of $Cu(In_{1-x}Ga_x)Se_2$ films were shifted to larger angle and splitted, and the grain size of $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films became smaller. All $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films showed the p-type conductivity regardless of the Ga/(In+Ga) ratio. Ag/n-ZnO/i-ZnO/CdS/$Cu_{0.91}(In_{0.7}Ga_{0.3})Se_2$/Mo solar cells were fabricated. The currently best efficiency in this study was 14.48% for $0.18cm^2$ area ($V_{oc}=581.5mV,\;J_{sc}=34.88mA$, F.F=0.714).

• Journal of the Korean Institute of Gas
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• v.5 no.2 s.14
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• pp.14-21
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• 2001

In order to investigate the damage mechanism of the coupler transferring LPG, microstructural observation and chemical analysis of the couplers operated for the long time in the LPG stations and virgin 6/4 forged-brass corrosion-tested were conducted. Their microstructure was consisted of two phases that bright $\beta$ precipitates were irregularly dispersed in $\alpha$ matrix. The chemical compositions of oxide layer on the surface of the used coupler were composed of S, C, O, Al, Si, etc. as well as Cu and Zn. In environmental corrosion tests of both $10\%$ HCl and Mattsson solutions, no apparent deviations in mechanical impact strength of forged-brass was observed. While, in U-bend stress corrosion cracking specimen, some microcracks were observed.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.551-554
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• 2002

As a general rule, the brazing process between cemented carbides and steel used by Silver (Ag) type brazing filler. The composition of Ag type filler were used Ag-Cu-Zn-Cd type filler mainly. But, the demand of Cadmium (Cd)-free in Ag type filler was raised recently. The reason why Cd-free in Ag brazing filler were occupied to vaporize as a CdO$_2$ when brazing process, because of Cd element was almost low boiling point of all Ag type filler elements. And, CdO$_2$ was a very harmful element for the human body. This experiment was developed Cd-freeing on Ag type filler that was used Indium (In) instead of Cd element. In this experiment, there were changed from 0 to 5% In addition in Ag brazing filler and investigated to most effective percentage of Indium. As a result, the change of In addition instead of Cd, there was a very useful element and obtained same property only 3% In added specimens compared to Cd 19% added specimens. These specimens were obtained same or more deflective strength. In this case, there were obtained 70 MPa over strength and wide brazing temperature range 650-800 C. A factor of deflective strength were influenced by composition and the shape of $\beta$ phase and between $\beta$ phase and cemented carbides interface. Indium element presented as $\alpha$ phase and non-effective factor directly, but it's occupied to solid solution hardening as a phase. $\beta$ phase were composed 84-94% Cu-Ni-Zn elements mainly. Especially, the presence of Ni element in interface was a very important factor. Influence of condensed Ni element in interface layer was increased the ductility and strength of brazing layer. Therefore, these 3% In added Ag type filler were caused to obtain a high brazing strength.

• Advances in Energy Research
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• v.2 no.1
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• pp.33-45
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• 2014

Photocatalytic hydrogen generation by water splitting ($H_2O_{(1)}{\rightarrow}H_2_{(g)}+1/2O_2_{(g)}$) has been studied on photocatalysts based on Zn, Cd, Fe and Cu, synthesized by coprecipitation. Iron and copper nanoparticles were incorporated as cocatalysts to enhance the photocatalytic activity of the ZnCd solid solution. The effect of the different synthesis parameters (temperature, elemental atomic ratios, amount of Cu and Fe incorporated in the catalyst and calcination temperature) on the photocatalytic production of hydrogen has been studied in order to determine the best experimental synthesis conditions. The catalysts have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and BET. The experiments of photocatalytic water splitting were performed in aqueous solution of the photocatalysts previously dispersed in a soft ultrasound bath. The photocatalysts were irradiated under different lights ranging from 220 to 700 nm. The photocatalytic activity was found to be clearly dependent on the specific area of the photocatalyst.

• Korean Journal of Microbiology
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• v.23 no.3
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• pp.177-183
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• 1985

Some properties of an extracellular cytosine deaminase produced from Arthrobacter sp.JH-13 were examined after 20-80% of ammonium sulfate fractionation. Among some substrates, this enzyme utilized cytosine and 5-fluorocytosine as a substrate. The optimum pH and temperature for the activity of this enzyme were found to be near 8.0 and $40^{\circ}C$, respectively. The ensyme was more stable in 0.2M of Tris-HCl buffer than 0.2M of potassium phosphate buffer. The enzyme was generally stable below $50^{\circ}C$, but inactivated completely at $70^{\circ}C$. 1mM of $Fe^{3+},\;K^+\;and\;Na^+$ increased the enzyme activity, but 0.01mM of $Co^{2+},\;Cu^{2+},\;Ni^{2+},\;Hg^{2+},\;Ag^{2+},\;Zn^{2+},\;Ba^{2+},\;and\;Mg^{2+}$ markedly inactivated the enzyme activity. 0.1mM of p-chloromercuribenzoate, trichloroacetic acid, and N-ethylmaleimide compleyely inhibited the enzyme activity, but 0.1mM of 2-mercaptoethanol slightly increased the enzyme activity.

• Journal of Periodontal and Implant Science
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• v.36 no.1
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• pp.97-112
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• 2006

유리 라디칼과 활성 산소종, 산화방지제 간의 불균형이 염증성 구강내 질환의 발생과 진행에 있어 중요한 역할을 한다는 주장이 제기되었고 최근에는 만성 염증성 치주질환에서도 산화에 의한 소실이 관찰되었다. 다양한 내적인 항산화 방어 기전 중 superoxide dismutase 가 $O_2$를 $H_2O_2$로 효과적으로 전환시킴으로써 활성산소종에 대한 일차적인 방어를 맡고 있다. 현재까지 인간에서 발견된 superoxide dismutase 는 cytoplasmic copper-zinc SOD와 mitochondrial manganase SOD, extracellular SOD의 3가지 아형이다. 이번 연구는 만성 치주질환을 가전 환자의 치주조직에서 효소 항산화제인 SOD의 발현정도를 알아봄으로써 질환조직 내의 산화자극 정도를 평가해 보고자하였다. 전남대학교 치주과에 내원한 33명의 만성 치주질환자와 20명 의 임상적으로 건강한 대상으로부터 조직을 얻어 Cu/Zn-SOD와 Mn-SOD, EC-SOD를 이용한 면역조직화학 염색을 시행하였다. 임상적 소견과 조직학적 소견이 일치하지 않아 조직학적 소견을 기준으로 건강한 조직, 경도, 중등도, 중도 치주질환 조직으로 그룹을 나누고 완전한 상피와 결합조직을 가진 27개의 표본에 대한 분석을 시행하였다. 치주질환 조직에서 건강한 조직에 비해 Cu/Zn-SOD가 상피의 기저층과 상피에 근접한 결합조직에서 발현되고 Mn-SOD는 염증이 증가함에 따라 크게 상피의 과립증과 각화층, 그리고 상피에 근접한 결합조직에서 발현됨으로써 활성산소종이 치주조직 파괴에 관여한다는 것을 알 수 있었다. 세 아형 모두 혈관주위에서 발현되었고 특히 EC-SOD는 작은 모세혈관주위에서만 발현되었으나 염증에 의해 혈관벽이 두꺼워지고 혈관 수가 증가한 곳에서 뚜렷하게 염색되었다. 이번 연구는 염증성 치주조직내 증가된 SOD의 활성이 치주질환자의 산화자극 정도와 관련되어 있음을 시사하였다.

• Journal of the Korean institute of surface engineering
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• v.41 no.3
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• pp.121-128
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• 2008

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% $H_2O_2$ and 0.6M $Na_2SO_4$ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% $H_2O_2$ + 0.6M $Na_2SO_4$ solution. When the strain rate was below $2{\times}10^{-6}$, the stress corrosion cracking induced fracture start to be observed.

• Proceedings of the KSEEG Conference
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• 2000.04a
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• pp.110-110
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• 2000

Temporal and spatial distribution patterns of the magmatic rocks and associated ore deposits in the Mesozoic magmatic - metallogenic belt along the Yangtz River, Anhui Province are used to determine and discuss the crust - mantle interaction processes. The magmatic rocks are Cu - Au mineralized high - K calc - alkalic intermediate ¬acidic (CAK) and Fe - Cu mineralized high - Na alkalic - calc intermediate - basic intrusive rocks (FCN) in the central part of the belt and grade to Cu - Mo - Pb - Zn - Ag mineralized calc - alkalic granitoids (CMG) and A - type granites (AG) in the southern and northern parts of the belt. Samples from the CAK and CMG yield Rb - Sr isochron ages of 137 - 140Ma with $(^{87}Sr/^{86}Sr)_{o}$ = 0.7060 - 0.7101, while those from the FCN and AG yield the ages of 120 - 129Ma with $(^{87}Sr/^{86}Sr)_{o}$ = 0.7047 - 0.7077. The Sr isotope ratios, CriTh ratios 0.4 - 3.1), Eu/Eu* ratios < 0.79 - 1.05) and initial epsilon (Nd) values (-16.6 - -6.3) for the CAK and CMG are consistent with magma derivation from old metamorphic basement rocks rich in metallogenic elements through a two - stage process of mantle - derived magma underplating caused by primary lithosphere extension and subsequent partial melting. On the basis of Sr isotope data, CriTh ratios (3.4 - 13.8), Eu/Eu* ratios (0.86 - 1.13) and initial epsilon (Nd) values (-7.7 - +1.4), the FCN and AG are considered to be formed through syntexis with material input from the mantle that resulted from further lithosphere extension followed by mantle - derived magma underplating on a large scale.