• 한국추진공학회지
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• 제12권5호
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• pp.26-34
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• 2008

고농도 과산화수소를 분해시킬 수 있는 다양한 촉매의 성능을 비교하였다. 감마 알루미나에 산화망간, 백금, 이리듐을 각각 코팅하여 펠렛 촉매를 제작하였다. 각기 다른 세 가지 촉매를 이용하여 플라스크 반응기에서 반응성을 비교하였고, 50 Newton 급 추력기를 이용하여 펄스 응답 특성을 비교하였다. 그 결과 이리듐 촉매가 가장 높은 활성, 빠른 응답성을 나타내었으나, 연속모드에서 반응 실패 경향을 보여 과산화수소 분해용 촉매로는 부적절하였다. 백금, 산화망간 촉매 또한 우수한 반응성을 보여 높은 가능성을 보였으며, 고추력 추력기와 같이 촉매양이 많이 요구되는 경우, 비용문제를 고려한다면 산화망간 또한 과산화수소 분해에 적합할 것으로 판단된다.

• 한국재료학회지
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• 제22권10호
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• pp.499-503
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• 2012

The present study is intended to comparatively investigate the changes in microstructure and tensile properties at room and elevated temperatures in commercial AM50(Mg-5%Al-0.3%Mn) and 0.3 wt%CaO added ECO-AM50 alloys produced by permanent mould casting. The typical microstructure of AM50 alloy was distinctively characterized using two intermetallic compounds, ${\beta}(Mg_{17}Al_{12})$ and $Al_8Mn_5$, along with ${\alpha}$-(Mg) matrix in an as-cast state. The addition of a small amount of CaO played a role in reducing dendrite cell size and quantity of the ${\beta}$ phase in the AM50 alloy. It is interesting to note that the added CaO introduced a small amount of $Al_2Ca$ adjacent to the ${\beta}$ compounds, and that inhomogeneous enrichment of elemental Ca was observed within the ${\beta}$ phase. The ECO-AM50 alloy showed higher hardness and better YS and UTS at room temperature than did the AM50 alloy, which characteristics can be mainly ascribed to the finer-grained microstructure that originated from the CaO addition. At $175^{\circ}C$, higher levels of YS and UTS and higher elongation were obtained for the ECO-AM50 alloy, demonstrating that even 0.3 wt%CaO addition can be beneficial in promoting the heat resistance of the AM50 alloy. The combinational contributions of enhanced thermal stability of the Ca-containing ${\beta}$ phase and the introduction of a stable $Al_2Ca$ phase with high melting point are thought to be responsible for the improvement of the high temperature tensile properties in the ECO-AM50 alloy.

• 소성∙가공
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• 제28권1호
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• pp.34-42
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• 2019

In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, $CuAl_2$ phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the $CuAl_2$ phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped $Al_6$ (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral ${\alpha}-Al_{15}Si_2$ $(Fe,Mn,Cr)_3$ was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.

• Journal of Electrochemical Science and Technology
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• 제10권2호
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• pp.196-205
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• 2019

Ni-rich layered oxides $Li(Ni_xCo_yMn_z)O_2$ (x + y + z = 1) have been extensively studied in recent times owing to their high capacity and low cost and can possibly replace $LiCoO_2$ in the near future. However, these layered oxides suffer from problems related to the capacity fading, thermal stability, and safety at high voltages. In this study, we use surface coating as a strategy to improve the thermal stability at higher voltages. The uniform and conformal $Al_2O_3$ coating on prefabricated electrodes using atomic layer deposition significantly prevented surface degradation over prolonged cycling. Initial capacity of 190, 199, 188 and $166mAh\;g^{-1}$ is obtained for pristine, 2, 5 and 10 cycles of ALD coated samples at 0.2C and maintains 145, 158, 151 and $130mAh\;g^{-1}$ for high current rate of 2C in room temperature. The two-cycle $Al_2O_3$ modified cathode retained 75% of its capacity after 500 cycles at 5C with 0.05% capacity decay per cycle, compared with 46.5% retention for a pristine electrode, at an elevated temperature. Despite the insulating nature of the $Al_2O_3$ coating, a thin layer is sufficient to improve the capacity retention at a high temperature. The $Al_2O_3$ coating can prevent the detrimental surface reactions at a high temperature. Thus, the morphology of the active material is well-maintained even after extensive cycling, whereas the bare electrode undergoes severe degradation.

• 생명과학회지
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• 제11권2호
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• pp.153-158
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• 2001

To investigate the effects of soil acidification on growth of Impatiens balsamina L. plants were transplanted to acidified soils with H$_2$SO$_4$ solution. The concentrations of soluble Ca, Mg, K, Al and Mn in the acidified soils increased with increment of H$^{+}$ addition to the soil. In both species, the plant height and root length were inhibited by soil acidification, showing much severer inhibition in Impatiens balsamina L. than in Tagetes patula L., As the soil pH decreases, the growth of underground parts decreased greatly than that of above ground parts in both species. Total dry weight decreased with increased Al concentration as well as lowered soil pH in both plants. There was a strong positive correlation between relative total dry weight and molar (Ca+Mg+K) / Al ratio of the soil. The results suggest that molar(Ca+Mg+K)/ Al ratio of the soil may be useful indicator for assessing the critical load of acid deposition in herb species.s.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.234-237
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• 2004

As an automotive industry's demand for lighter materials gets bigger and bigger, a lot of new strength Al alloys have been developed recently. In the present study, Al 6xxx series alloys were designed to get the strength level of 350MPa with the elongation of $12\%$. For that purpose, three alloy systems were selected based on the thermodynamics calculation. The effect of both $Mg_{2}Si$ precipitate and excess Si amount on the newly designed alloys was investigated. Also, heat treatment procedure was studied to optimize the mechanical properties.

• 한국세라믹학회지
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• 제26권2호
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• pp.201-209
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• 1989

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. $\beta$-Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the $\beta$-Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of $\beta$-Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.

• 대한금속재료학회지
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• 제49권4호
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• pp.281-290
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• 2011

In order to gain better understanding of the selective surface oxidation and its influence on the galvanizability of a transformation-induced plasticity (TRIP) assisted steel containing 1.5 wt.% Si and 1.6 wt.% Mn, a model experiment has been carried out by depositing Si and Mn (each with a nominal thickness of 10 nm) in either monolayers or bilayers on a low-alloy interstitial-free (IF) steel sheet. After intercritical annealing at $800^{\circ}C$ in a $N_2$ ambient with a dew point of $-40^{\circ}C$, the surface scale formed on 590 MPa TRIP steel exhibited a microstructure similar to that of the scale formed on the Mn/Si bilayer-coated IF steel, consisting of $Mn_{2}SiO_{4}$ particles embedded in an amorphous $SiO_{2}$ film. The present study results indicated that, during the intercritical annealing process of 590 MPa TRIP steel, surface segregation of Si occurs first to form an amorphous $SiO_{2}$ film, which in turn accelerates the out-diffusion of Mn to form more stable Mn-Si oxide particles on the steel surface. During hot-dip galvanizing, particulate $Fe_{3}O_{4}$, MnO, and Si-Mn oxides were reduced more readily by Al in a Zn bath than the amorphous $SiO_{2}$ film. Therefore, in order to improve the galvanizability of 590 TRIP steel, it is most desirable to minimize the surface segregation of Si during the intercritical annealing process.

• 자원환경지질
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• 제34권1호
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• pp.89-104
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• 2001

전주시내에는 전주천과 삼천천이 흐르고 있으며 그 주변에는 여러 오염원이 분포하고 있다. 삼천천은 고사평 쓰레기 매립장에서 전주천과 합류하고 전주천은 최종적으로 만경강에 합류된다. 본 연구에서는 중금속과 음이온에 대한 전주천과 삼천천의 오염현황과 오염원 그리고 이들 하천이 만경강 수질에 미치는 영향을 연구하였다. 전주천과 삼천천에 대한 연구를 위한 시료채취지점을 선정하기 위하여 하천 구간을 오염정도가 다를 것으로 예상되는 여러 구간으로 나누고 각 구간에서 난수표를 이용하여 대표적인 시료를 채취하는 층화랜덤추출 방법을 이용하였다. 연구결과 시료 채취 당시 전주천과 삼천천은 중금속이나 음이온에 대해서 전반적으로 음용수 기준치 이상으로 오염되지는 않았다. 그러나 중금속과 음이온은 현재 하천으로 계속 공급되고 있으며 가뭄 동안에는 하천을 오염시킬 가능성이 있다. 본 연구에서 두 쓰레기 매립장은 Fe, Mn, Al, Zn, Cl￣, SO$_4$$^{2-}$ , NO$^2$-N, NH$_3$-N, 그리고 미처리된 하수는 Al, Zn, Mn, Cl￣, SO$_4$$^{2-}$ , NH$_3$-N, PO$_4$$^{3-}$ 의 오염원인 것으로 나타났다. 또한 전주천은 Fe, Mn, $Cl^{-}$, $SO_{4}^{2-}S$ 성분에 대한 만경강 오염에 중요한 영향을 미치고 있다.

• 한국수소및신에너지학회논문집
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• 제13권3호
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• pp.181-189
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• 2002

A series of multicomponent $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{1-x}Fe_{x}$ (x=0.00, 0.08, 0.15, 0.22, and 0.30) alloys are prepared and their oystal structure and P-C-T curves are examined. The electrochemical properties of these allqys such as activation conditions, discharge capacity, cycling performance are also investigated. $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{1-x}Fe_{x}$ (x=0.00, 0.08, 0.15, 0.22 and 0.30) have the C14 Laves phase hexagonal structure. The electrode was activated by the hot-charging treatment. The best activation conditions were the current density 120 mA/g and the hot-charging time 12h at $80^{\circ}C$ in the case of the alloy with x=0.00. The discharge capacity increased rapidly until the fourth cycle and then decreased. The discharge capacity increased again from the 13th cycle, arriving at 234 mAh/g at the 50th cycle. The discharge capacily just after activation decreases with the increase in the amount of the substituted Fe but the cycling performance is improved. The discharge capacity after activation of the alloy with x=0.00 is 157 mAh/g at the current density 120 mA/g. $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}Fe_{0.15}$ is a good composition with a medium quantity of discharge capacities and a good cycling performance. The ICP analysis of the electrolyte for these electrodes after 50 charge-discharge cycles shows that the concentrations of V and Zr are relatively high. Another series of multicomponent $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}M_{0.15}$ (M = Fe, Co, Cu, Mo and Al) alloys are prepared. They also have the C14 Laves phase hexagonal structure. The alloys with M = Co and Fe have relatively larger hydrogen storage capacities. The discharge capacities just after activation are relatively large in the case of the alloys with M = Al and Cu. They are 212 and 170 mAh/g, respectivety, at the current density 120mA/g. The $Zr_{0.8}Ti_{0.2}Mn_{0.4}V_{0.6}Ni_{0.85}Co_{0.15}$ alloy is the best one with a relatively large discharge capacity and a good cycling performance.