• 열처리공학회지
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• 제18권1호
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• pp.18-23
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• 2005

Effect of cold rolling on microstructural changes has been investigated for a Zn-15%Al alloy to elucidate the reason for its work softening behavior. Fully annealed microstructure of the Zn-15%Al alloy is characterized by ${\eta}$ grains and (${\eta}+{\alpha}$) lamellar colonies, where ${\eta}$ and ${\alpha}$ are Zn-rich HCP and Al-rich FCC phases, respectively. The hardness decreases continuously with increasing cold rolling degree, exhibiting work softening behavior. It is revealed that during the cold rolling, (${\eta}+{\alpha}$) lamellar colonies gradually change into equiaxed ${\eta}$ and ${\alpha}$ grains due to dynamic recrystallization at room temperature, while pre-existing ${\eta}$ grains are only deformed without recrystallization. Furthermore, cold rolling causes the precipitation of dissolved Al solutes in ${\eta}$ grains. In view of these results, change of (${\eta}+{\alpha}$) phases from lamellar to equiaxed morphology, which results in structural softness and increase in equiaxed ${\eta}/{\alpha}$ grain boundaries with higher mobility, and deterioration of solution hardening by precipitation of Al solutes from ${\eta}$ grains, are thought to contribute to the work softening of Zn-15%Al alloy.

• 소성∙가공
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• 제31권3호
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• pp.160-166
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• 2022

The purpose of this study is to investigate the effects of combined addition of Ca and Y on the precipitation and age-hardening behavior of an extruded AZ91 alloy by conducting the aging treatment at 200 ℃ for hot-extruded AZ91 and AZ91-0.3Ca-0.2Y alloys. In the AZ91 alloy, many Mg₁₇Al₁₂ discontinuous precipitate (DP) bands formed during air cooling immediately after extrusion are present, whereas in the AZ91-0.3Ca-0.2Y alloy, a few DP bands and numerous Al₂Y, Al₈Mn₄Y, and Al₂Ca phase particles are distributed along the extrusion direction. The peak-aging time of the AZ91-0.3Ca-0.2Y alloy is 16 hours, twice that of the AZ91 alloy. Although both alloys have similar hardness before aging treatment, the hardness after peak-aging treatment (i.e., peak hardness) of the AZ91-0.3Ca-0.2Y alloy is higher than that of the AZ91 alloy, as 93.1 and 88.7 Hv, respectively. The microstructures of both peak-aged alloys comprise DPs and continuous precipitates (CPs). However, the peak-aged AZ91-0.3Ca-0.2Y alloy has a smaller amount of DPs and a larger amount of CPs than the peak-aged AZ91 alloy. Additionally, the inter-particle spacings of DPs and CPs in the former are significantly narrower than those in the latter. These results demonstrate that the addition of small amounts of Ca and Y to a commercial AZ91 alloy considerably affects the formation rate, size, and amount of CPs and DPs during aging and resultant age-hardening behavior.

• 한국생산제조학회지
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• 제23권2호
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• pp.152-156
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• 2014

Lightweight materials such as aluminum and magnesium have recently received much attention in the automotive industries because of environmental and fuel-efficiency concerns. Using the powder metallurgy (PM) process for these materials creates significant opportunities for the cost-effective manufacture of lightweight automotive parts. In the present study, an Al-Cu-Mg alloy was fabricated using conventional PM processes. Primarily, the effects of the alloying elements on the sintering characteristics and mechanical behavior after heat treatment were investigated. A microstructural analysis was performed using an optical microscope and a scanning electron microscope to investigate the behavior of liquid phase sintering, including the formation of precipitates. The dependence of the mechanical behavior on the alloying elements was evaluated based on the transverse rupture strength.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.901-905
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• 2008

This study was conducted to clarify the heat load characteristics and heat and moisture behavior of underground structures. The authors achieved this by carrying out a numerical analysis using simple heat diffusion and simultaneous heat and moisture transfer equations based on measurement data. This paper presents the results of a numerical analysis on the heat load characteristics and heat and moisture behavior of an underground basement and its surrounding ground under a condition of internal heat generation. The authors found it difficult to predict the heat behavior and heat load of the underground basement by simple heat diffusion alone. Accurate prediction of the thermal environment and heat load requires careful consideration of the influences of moisture and precipitation

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.831-835
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• 2015

본 연구에서는 바이오매스 유래 생리활성물질인 (+)-dihydromyricetin을 정제하기 위한 분별침전공정에서 분별침전용액의 제타전위가 분별침전 양상(순도, 수율, 침전물 형태와 크기)에 미치는 영향을 조사하였다. 제타전위 조절을 위한 실리카-알루미나의 첨가량(반응액 부피당 표면적) $100mm^{-1}$에서 가장 높은 수율을 얻을 수 있었다. 실리카-알루미나의 제타전위가 양(+)의 값으로 증가할수록 (+)-dihydromyricetin 수율과 침전물의 크기는 증가하였다. 가장 큰 제타전위 값(+4.99 mV)을 가진 실리카를 이용한 분별침전의 경우에는 가장 작은 제타전위 값(-19.00 mV)을 가진 알루미나를 이용한 분별침전의 경우보다 2배 이상 높은 수율을 얻을 수 있었다. 또한 분별침전 과정에서 제타전위 절대값이 증가할수록 (+)-dihydromyricetin 수율과 침전물의 크기는 감소하여 제타전위 절대값에 반비례함을 알 수 있었다. 반면 표면적증가물질 실리카-알루미나의 제타전위 변화에도 (+)-dihydromyricetin 순도는 거의 변화가 없었다.

• 한국물환경학회지
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• 제31권3호
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• pp.241-252
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• 2015

Runoff behaviors by five bias correction methods were analyzed, which were Change Factor methods using past observed and estimated data by the estimation scenario with average annual calibration factor (CF_Y) or with average monthly calibration factor (CF_M), Quantile Mapping methods using past observed and estimated data considering cumulative distribution function for entire estimated data period (QM_E) or for dry and rainy season (QM_P), and Integrated method of CF_M+QM_E(CQ). The peak flow by CF_M and QM_P were twice as large as the measured peak flow, it was concluded that QM_P method has large uncertainty in monthly runoff estimation since the maximum precipitation by QM_P provided much difference to the other methods. The CQ method provided the precipitation amount, distribution, and frequency of the smallest differences to the observed data, compared to the other four methods. And the CQ method provided the rainfall-runoff behavior corresponding to the carbon dioxide emission scenario of SRES A1B. Climate change scenario with bias correction still contained uncertainty in accurate climate data generation. Therefore it is required to consider the trend of observed precipitation and the characteristics of bias correction methods so that the generated precipitation can be used properly in water resource management plan establishment.

• 열처리공학회지
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• 제21권1호
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• pp.20-25
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• 2008

Structural studies have been performed on precipitation hardening and microstructural variations found in Ti-Al-Cr ternary $L1_0$- and $L1_2$-phase alloys using transmission electron microscopy. Both the $L1_0$ and $L1_2$ phase alloys harden by aging at 973 K after solution annealing at higher temperatures. The amount of age hardening of the $L1_2$ phase alloy is larger than that of the $L1_0$ phase alloy. The phase separation between $L1_0$ and $L1_2$ phase have not been observed by aging at 973 K. But $Al_2Ti$ was formed in each matrix alloy during aging. The crystal structure of the $Al_2Ti$ phase is a $Ga_2Zr$ type in the $L1_0$ and a $Ga_2Hf$ type in the $L1_2$ phase, respectively. At the beginning of aging the fine coherent cuboidal $Al_2Ti$-phase are formed in the $L1_0$ phase. By further aging, two variants of $Al_2Ti$ precipitates grow along the two {110} habit planes. On the other hand, in the $L1_2$ phase, the $Al_2Ti$ phase forms on the {100} planes of the $L1_2$ matrix lattice. After prolonged aging the precipitates are rearranged along a preferential direction of the matrix lattice and form a domain consisting of only one variant. It is suggested that the precipitation of $Al_2Ti$ in each matrix alloy occurs to form a morphology which efficiently relaxes the elastic strain between precipitate and matrix lattices.

• 한국분말재료학회지
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• 제13권3호
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• pp.178-186
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• 2006

The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.

• 한국광물학회지
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• 제31권3호
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• pp.173-182
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• 2018

산성광산배수에서 철광물의 침전 및 상전이 과정은 배수 내의 미량원소의 거동에 많은 영향을 미친다. 그러나 자연에서 일어나는 이러한 과정을 정확하게 추적하기는 쉽지 않아 많은 연구들이 산성광산배수에서 일어나는 광물의 침전 및 상전이에 대하여 실내 실험에 의존하는 경우가 많았다. 본 연구에서는 달성광산에서 채취한 배수를 대상으로 실제 산성광산배수에서 서로 다른 pH 값을 갖는 조건에서 시간이 지남에 따라 일어나는 광물의 침전과 이에 따른 배수 내의 미량 원소 변화를 살펴보았다. 침전된 광물의 양이 많지 않아 동정이 어려운 경우도 있었지만 침전된 광물들의 정보를 종합해 보면 대체적으로 비정질의 광물 먼저 형성된 후 아마도 슈베르트마나이트를 거쳐서 추후에 침철석이 침전된 것으로 사료된다. 그러나 시료 중 pH가 높은 경우(10)에는 계속적으로 비정질 상태로 남아있었다. 시간이 지남에 따라 광물의 침전 및 전이에 의하여 배수의 pH는 계속적으로 낮아지는 경향을 보였다. 모든 원소들이 높은 pH (8, 10)에서 낮은 농도를 보였는데 이는 높은 pH에서의 광물의 침전과 표면전하의 영향으로 판단되며 각 원소의 농도는 시간이 지남에 따라 조금씩 증가하였다. 황의 농도는 슈베르트마나이트에서 침철석으로의 전이의 영향으로 배수 내에서 역시 증가하였다.

• 자원리싸이클링
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• 제26권5호
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• pp.39-47
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• 2017

본 연구에서는 희토류 황산수용액으로부터 희토류 원소를 철로부터 분리/회수하고자, 황산나트륨을 이용한 희토류 황산복염 침전반응에 관하여 고찰하였다. 네오디뮴(Nd)은 황산나트륨과 결합하여 복염으로 침전이 용이하게 일어나는 반면에 디스프로슘(Dy)은 황산복염으로 침전되기 위해서 과량의 황산나트륨이 필요하였다. 또한 황산수용액에서 네오디뮴의 존재는 디스프로슘 황산복염 침전을 촉진시켜서 디스프로슘 황산복염 침전률을 증가시켰다. 본 연구에서 사용된 네오디뮴 함량 23.39 mg/ml, 디스프로슘 함량 8.67 mg/ml인 황산수용액으로부터 반응온도 $60^{\circ}C$, 반응 3시간에서 황산나트륨을 7 당량 첨가하였을 때, 네오디뮴 복염 침전률은 99.7%, 디스프로슘 복염 침전률은 94.3%이었다. 또한 네오디뮴과 디스프로슘의 황산복염 침전특성을 이용한 두 원소의 분리 가능성을 고찰한 결과, 염화나트륨 첨가에 의한 염석효과가 디스프로슘 품위 증가에 중요한 역할을 하며 본 연구조건에서 최대 98.7% 품위의 디스프로슘을 얻을 수 있었다.