• 대한치과보철학회지
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• 제59권2호
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• pp.248-260
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• 2021

코발트-크롬 합금은 다양한 치과보철물 제작에 이용되고 있고, 다른 합금에 비해 저렴한 가격과 우수한 기계적 특성이 장점이다. 최근, 기존 제작 방식의 단점을 극복하기 위해 적층제조 방식인 선택적 레이저 용융 방법이 보철물 제작에 이용되고 있다. 선택적 레이저 용융 방법의 공정 중 급속 가열과 냉각 과정은 제작된 합금의 미세구조와 결정립을 미세화하고, 기포를 감소시켜 기존 제작 방식에 의한 합금에 비해 기계적 특성을 향상시킨다. 반면, 적층과 급속 가열 및 냉각은 다량의 잔류응력 축적을 초래하는데, 추후 기계적 특성에 악영향을 미칠 수 있다. 따라서, 잔류응력을 제거하기 위해 주로 열처리를 시행하고, 회복과 재결정화에 의한 잔류응력의 감소뿐만 아니라 상변태, 석출물 및 미세구조의 균질화가 동반되어 기계적 특성의 복잡한 변화가 나타난다. 본 문헌고찰에서 코발트-크롬 합금의 제작 방식 비교 및 선택적 레이저 용융 방법으로 제작된 합금의 특징에 대해 알아보고자 한다.

• 대한환경공학회지
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• 제34권9호
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• pp.613-622
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• 2012

본 연구에서는 MTMD의 합성을 통해 빠른 자성회수 및 재사용이 용이한 크롬 흡착제를 개발하였다. 합성을 위해 공침법 및 교대성장을 통한 발산법을 사용하였으며, methyl propionate 및 glutaric acid를 통해 덴드리머를 멀티터미널화 하였다. 합성된 시료의 특성분석은 XRD, FT-IR, TEM, EDS, TGA, Zeta potential analyzer를 통해 이루어졌다. MTMD의 자성코어는 마그네타이트 결정구조를 가졌으며, 4세대 덴드리머의 크기는 15 nm에서 20 nm로 확인되었다. TGA 분석결과 1세대 덴드리머의 유기전도성 가지의 비율은 약 7%였으며 1세대 증가시 3%의 중량 감소가 나타났고 멀티터미널화시 덴드리머의 포텐셜은 -25.26 mV에서 -6.53 mV까지 변화하였다. MTMD 흡착실험 결과 5분 이내에서 80% 이상의 크롬을 흡착하였으며 6.308 mg/g의 흡착능을 나타냈다. 자성 회수시 COOH D와 비교하여 회수시간이 2배 이상 단축되었으며 30분 이내에 100% 회수가 가능하였다. 크롬을 이용한 재생실험의 경우 4회 흡착에도 동일한 흡착능을 유지하였다.

• 한국환경과학회지
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• 제24권10호
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• pp.1253-1264
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• 2015

This study assessed the fertilizing value of struvite deposit recovered from swine wastewater in cultivating Chinese cabbage. Struvite deposit was compared with commercial fertilizers: complex, organic and compost to evaluate the fertilizing effect of struvite deposit. Laboratory pot test obviously presented that the struvite deposit more facilitated the growth of Chinese cabbage than organic and compost fertilizers even though complex fertilizer was the most effective in growing Chinese cabbage. It was revealed that the growth rate of Chinese cabbage was simultaneously controlled by phosphorus (P) and potassium (K). Also, the nutrients such as nitrogen (N), P, K, calcium (Ca) and magnesium (Mg) were abundantly observed in the vegetable tissue of struvite pot. Specifically, P was the most abundant component in the vegetable tissue of struvite pot. Meanwhile, the utilization of struvite as a fertilizer led to the lower accumulation of chromium ($Cr^{6+}$) than other pots, except for compost fertilizer pots, and no detection of cadmium (Cd), arsenic (As) and nickel (Ni) in the Chinese cabbage. The experimental results proved that the optimum struvite dosage for the cultivation of Chinese cabbage was 2.0 g struvite/kg soil. On the basis of these findings, it was concluded that the struvite deposits recovered from swine wastewater were effective as a multi-nutrient fertilizer for Chinese cabbage cultivation.

• Bulletin of the Korean Chemical Society
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• 제27권5호
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• pp.694-698
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• 2006

A method has been described for the chemical speciation, preconcentration and determination of Cr(III) and Cr(VI) species in filtered tannery waste waters by flame atomic absorption spectrometry using ion-exchange resins. Amberlite IR-120($H^+$) strongly acidic cation exchanger and Amberlite IRA-410($CI ^-$) strongly basic anion exchanger resins were used for the separation and preconcentration of Cr(III) and Cr(VI) species, respectively. Optimum condition for preconcentration and speciation was obtained by testing pH of sample and eluent, flow rates of sample and eluent, amount of resins, volume of sample and eluents, and effect of foreign ions. The recommended method has been successfully applied for the preconcentration and determination of chromium species in the dissolved phase of waste water samples collected from a tannery waste water treatment plant in Kayseri, Turkey. The detection limits achieved were 0.73 $\mu$g/L for Cr(III) and 0.81 $\mu$g/L for Cr(VI). Recovery studies showed 99% for Cr(III) and 98% for Cr(VI), for samples spiked with single species.

• Environmental Engineering Research
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• 제21권1호
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• pp.29-35
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• 2016

This study evaluated the fertilizing value of struvite deposit recovered from swine wastewater in cultivating lettuce. Struvite deposit was compared to complex fertilizer, organic fertilizer and compost to evaluate the fertilizing effect of struvite deposit. Laboratory pot test showed that the struvite deposit better enhanced lettuce growth in comparison to commercial fertilizers. It was revealed that the growth rate of lettuce was simultaneously controlled by phosphorus (P) and magnesium (Mg). Moreover, nutrients such as nitrogen (N), P, K, calcium (Ca) and magnesium (Mg) were abundantly observed in the vegetable tissue of struvite pot. Meanwhile, struvite application led to the lower accumulation of mercury (Hg), lead (Pb), chromium ($Cr^{6+}$) and nickel (Ni). In addition, no detection of cadmium (Cd), arsenic (As) and nickel (Ni) in the lettuce tissue was observed in struvite application pots. The experimental results proved that the optimum struvite dosage for lettuce cultivation was 0.5 g struvite/kg soil. The column experiments clearly showed that ammonia nitrogen was more slowly released from struvite deposit than from complex fertilizer. Consequently, it was concluded that the struvite deposits recovered from swine wastewater were effective as a multi-nutrient fertilizer for lettuce cultivation.

• 분석과학
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• 제20권6호
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• pp.496-501
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• 2007

ICP-AES를 이용하여 금을 분석할 때 감도가 가장 우수한 242.795 nm 파장은 분광학적 간섭을 일으키는 망간, 크롬, 코발트, 철 등의 원소들 때문에 광물에서 금의 분석은 불가능하다. 여기에서는 이들 원소들을 정량적으로 분리하는 분리방법을 연구하였다. 광물에서 금을 분리하기 위하여 광물을 용해한 산 용액에 MIBK 용매를 사용하여 정량적으로 추출하였다. 이때 질산과 염산의 혼산과 MIBK/n-hexane의 혼합용매는 효율적으로 금을 추출할 수 있었으며, 회수율은 97.5% 이상이었다.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1293-1296
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• 2006

In this study, a solid phase extraction method has been developed for the preconcentration and separation of the elements Cr(III), Fe(III), Co(II) and Pb(II) at trace levels by using a column packed with Amberlite XAD-1180 resin loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. After preconcentrating, the metals retained on the column were eluted with 20 mL of 3 mol/L $HNO_3$ and then determined by flame atomic absorption spectrometry (FAAS). The factors affecting the recovery of the elements, such as pH, type and concentration of eluent, volume of sample and elution solution, and matrix components, were also ascertained. The recoveries of Cr(III), Fe(III), Co(II) and Pb(II) were found to be $99\;{\pm}\;4,\;97\;{\pm}\;3,\;95\;{\pm}\;3$ and $98\;{\pm}\;4$%, respectively, under the optimum conditions at 95% confidence level and the relative standard deviations found by analyzing of nine replicates were $\leq4.4$%. The preconcentration factors for Cr(III), Fe(III), Co(II) and Pb(II) were found as 75, 125, 50 and 75 respectively. The detection limits (DL, 3s/b) were 3.0 $\mu g/L$ for Cr(III), 1.25 $\mu g/L$ for Fe(III), 3.3 $\mu g/L$ for Co(II), and 7.2 $\mu g/L$ for Pb(II). The recoveries achieved by adding of metals at known concentrations to samples and the analysis results of Buffalo river sediment (RM 8704) show that the described method has a good accuracy. The proposed method was applied to tap water, stream water, salt and street dust samples.

• 자원리싸이클링
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• 제7권1호
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• pp.27-33
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• 1998

유리질산 및 불산이 제거된 산세폐액으로부터 Ni을 회수하기 위하여 컬럼식 연속추출장치에 의한 연속실험을 수행하였다. 먼저 Ni 회수 실험에 앞서 폐액중 다량 함유되어 있는 Fe나 Cr을 효과적으로 침전 제거하기 위해서는 중화제로 $CaCO_3$가 적절하며 이대 Ni은 전혀 침전되지 않는다. 한편 컬럼식 연속추출장치에 의한 No의 추출특성을 살펴보면 pulse velosity(Amplitude$\times$Frequency)가 증가함에 따라 수상과 유기상의 혼합효과가 증대되어 Ni의 추출율이 높아지고 이에 딸 HETS도 감소하고 있으나, pulse velosity가 임계치 이상으로 증가하게 되면 수상과 유기상의 강력한 혼합에 의해 원판과 원판사이에 분리층이 형성되지 못하고 컬럼 전체가 완전한 혼합 형태로 되어 추출율이 낮아지고 HETS도 길어지게 된다. 유기상에 추출된 Ni은 탈거시 탈거액으로 2M ${H}_{2}{SO}_{4}$액을 사용하면 효과적으로 농축 회수할 수 있다. 그리고 ${H}_{2}{SO}_{4}$용액중 $NiSO_4$의 용해도는 ${H}_{2}{SO}_{4}$ 농도가 증가함에 따라 감소하여 2M ${H}_{2}{SO}_{4}$ 용액에서는 55 gr/$\ell$ 정도로 나타나고 있으며, 이같은 $NiSO_4$의 과포화특성을 이용하면 탈거액의 증발과정을 거치지 않고 $NiSO_4$결정을 얻을 수 있다.

• Asian-Australasian Journal of Animal Sciences
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• 제13권8호
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• pp.1178-1187
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• 2000

Many immunostimulating substances have been developed to improve immunity of domestic animals, although their exact mode of action and effects are not clearly defined, and they are now widely used in feed industry. Bacterial lipopolysaccharides, called endotoxin, in particular may have a profound effect not only on the immune system but also on macrophages of the reticuloendothelial system. Glucans from a variety of yeast cell wall have been shown to stimulate both specific and non-specific immune responses and to increase growth performance in pigs. Recently, there has been great interest in the role of complex carbohydrates in disease prevention and treatment. Mannanoligosaccharide is a glucomannoprotein complex derived from the cell wall of yeast. Generally, it was also known that the deficiencies of some major vitamins (vitamin A, E and C) and minerals (chromium and selenium) lead to impaired immune system and, as a result, immune function is depressed and recovery delayed. On the other hand, many researchers suggested that one possible reason for the superior performance observed in pigs fed plasma protein may be because of the presence of biologically active plasma proteins (e.g., immunoglobulins) which are known to contribute to the health of the starter pig. And, immunoglobulins present in plasma protein have been implicated as contributing to the overall immunocompetence of the newborn pig. Other immunostimulants, lactoferrin and lysozyme, mainly found in milk and egg white, have been known as having bacteriocidal and bacteriolytic effect. When considering practical use of immunostimulants, the concept of using immunostimulants is new to many people and, in most cases, it is poorly understood how and why such compounds act, and how they should be used in practice. Therefore, in order to clarify the reason for discrepancies in results, special attention should be paid to the dose/response relationship of immunostimulants and the duration of the effect.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.16-25
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• 2016

In severe loss of coolant accidents (LOCA), similar to those experienced at Fukushima Daiichi and Three Mile Island Unit 1, the zirconiumalloy fuel claddingmaterials are rapidlyheateddue to nuclear decay heating and rapid exothermic oxidation of zirconium with steam. This heating causes the cladding to rapidly react with steam, lose strength, burst or collapse, and generate large quantities of hydrogen gas. Although maintaining core cooling remains the highest priority in accident management, an accident tolerant fuel (ATF) design may extend coping and recovery time for operators to restore emergency power, and cooling, and achieve safe shutdown. An ATF is required to possess high resistance to steam oxidation to reduce hydrogen generation and sufficient mechanical strength to maintain fuel rod integrity and core coolability. The initiative undertaken by Electric Power Research Institute (EPRI) is to demonstrate the feasibility of developing an ATF cladding with capability to maintain its integrity in $1,200-1,500^{\circ}C$ steam for at least 24 hours. This ATF cladding utilizes thin-walled Mo-alloys coated with oxidation-resistant surface layers. The basic design consists of a thin-walled Mo alloy structural tube with a metallurgically bonded, oxidation-resistant outer layer. Two options are being investigated: a commercially available iron, chromium, and aluminum alloy with excellent high temperature oxidation resistance, and a Zr alloy with demonstratedcorrosionresistance.Asthese composite claddings will incorporate either no Zr, or thin Zr outer layers, hydrogen generation under severe LOCA conditions will be greatly reduced. Key technical challenges and uncertainties specific to Moalloy fuel cladding include: economic core design, industrial scale fabricability, radiation embrittlement, and corrosion and oxidation resistance during normal operation, transients, and severe accidents. Progress in each aspect has been made and key results are discussed in this document. In addition to assisting plants in meeting Light Water Reactor (LWR) challenges, accident-tolerant Mo-based cladding technologies are expected to be applicable for use in high-temperature helium and molten salt reactor designs, as well as nonnuclear high temperature applications.