• Journal of the Korean Magnetics Society
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• v.4 no.4
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• pp.347-354
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• 1994

The structural change and magnetic properties of mechanically milled Fe-N and Mn-Al alloy powders have been investigated by XRD, TEM, VSM, $M\"{o}ssbauer$ spectroscopy and inelastic neutron scattering measurements. During milling of ${\gamma}'-Fe_{4}N$ powders, and fcc ${\gamma}'-Fe_{4}N$ phase is transformed to a bct ${\alpha}'-Fe(N)$ phase by stress-induced martensitic transformation, being accompanied by an initial increase in saturation magnetization. During annealing the bct ${\alpha}'-Fe(N)$ nanocrystalline phase which is obtained by mechanical grinding for a long time, an ${\alpha}'-Fe_{16}N_{2}$ phase partially appears as an intermediate phase at 673~773 K, causing an increase in saturation magnetization. During milling of Mn-45, 70 and 85 at.% Al mixed powders, Al atoms are partially solubilized into an ${\alpha}-Mn$ phase. The Al supersaturated ${\alpha}-Mn-type$ phases change from paramagnetic to ferromagnetic : the saturation magnetization is 11 emu/g for the as-milled Mn-70 at.% Al powders. Moreover, by removing almost all Al atoms from the as-milled Mn-85 at.% Al powders using chemical leaching, the saturation magnetization increases up to 36 emu/g. The above bct ${\alpha}'-Fe(N)$ and ferromagnetic ${\alpha}-Mn$ type alloys are the magnetic materials found for the first time, by using the present mechanochemical process.

• Journal of Life Science
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• v.19 no.4
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• pp.486-491
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• 2009

This study was conducted to investigate microbial distribution in the processing steps and to estimate quality index and shelf life of packaged Tofu (soybean curd). Sanitation and safety of Tofu were analysed in aspects of total viable counts (TVCs) and coliforms. Organoleptic deterioration was observed from some packaged Tofu when their TVCs were over $10^6\;CFU/g$. The controlled simply packaged Tofu and sterilized Tofu with TVCs of under $10^5\;CFU/g$ were 32.0% and 86.9% of the total samples, respectively. Also, the controlled simply packaged Tofu and sterilized Tofu with negative coliforms were 12.0% and 83.7% of the total samples, respectively. TVCs and coliforms increased in some processing steps, which include washing and soaking of raw soybeans, and formation and 1st cooling of packaged Tofu. Increases of TVCs and coliforms in the washing and soaking step were due to contamination from the soaking tank and airborne bacteria, whereas increases of TVCs and coliforms in the grinding step were due to contaminations from the grinder, line and reserving tank. TVCs and coliforms increased in the formation and 1st cooling step of packaged Tofu due to contaminations from filter wools, trays, employee's hands, cooling water, formed products and filter wools.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.831-836
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• 1998

The B1914 Ni-base superalloy was manufactured according to crystal structures of poly-, directionally solidified- and single crystals. We observe deformation as type of different crystal structure from room to high temperature. Specimens are controled by cooling rate and thermal gradient and then heat treatment in vacuum and then cooling with Ar gas. Different crystal structure has different stress-strain characteristic. At $600^{\circ}C$, yield strength and ultimate strength is increased single-, directionally solidified- and poly crystals in order.

• Clean Technology
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• v.20 no.3
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• pp.306-313
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• 2014

Nanoporous $TiO_2$ films are commonly used as working electrodes in dye-sensitized solar cells (DSSCs). So far, there have been attempts to synthesize films with various $TiO_2$ nanostructures to increase the power-conversion efficiency. In this work, vertically aligned rutile $TiO_2$ nanorods were grown on fluorinated tin oxide (FTO) glass by hydrothermal synthesis, followed by deposition of an anatase $TiO_2$ film. This new method of anatase $TiO_2$ growth avoided the use of a seed layer that is usually required in hydrothermal synthesis of $TiO_2$ electrodes. The dense anatase $TiO_2$ layer was designed to behave as the electron-generating layer, while the less dense rutile nanorods acted as electron-transfer pathwaysto the FTO glass. In order to facilitate the electron transfer, the rutile phase nanorods were treated with a $TiCl_4$ solution so that the nanorods were coated with the anatase $TiO_2$ film after heat treatment. Compared to the electrode consisting of only rutile $TiO_2$, the power-conversion efficiency of the rutile-anatase hybrid $TiO_2$ electrode was found to be much higher. The total thickness of the rutile-anatase hybrid $TiO_2$ structures were around $4.5-5.0{\mu}m$, and the highest power efficiency of the cell assembled with the structured $TiO_2$ electrode was around 3.94%.

• Korean journal of food and cookery science
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• v.30 no.6
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• pp.774-784
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• 2014

The purpose of this study was to present management guidelines for critical control points by analyzing microbiological hazardous elements through screening Potentially Hazardous Foods (PHF) menus in an effort improve the microbiological quality of foods prepared by restaurant operations. Steamed spinach with seasoning left at room temperature presents a range of risk temperatures which microorganisms could flourish, and it exceeded all microbiological safety limits in our study. On the other hand, steamed spinach with seasoning stored in a refrigerator had Aerobic Plate Counts of $2.86{\pm}0.5{\log}\;CFU/g$ and all other microbiological tests showed that their levels were below the limit. The standard plate counts of raw materials of lettuce and tomato were $4.66{\pm}0.4{\log}\;CFU/g$ and $3.08{\pm}0.4{\log}\;CFU/g$, respectively. Upon washing, the standard plate counts were $3.12{\pm}0.6{\log}\;CFU/g$ and $2.10{\pm}0.3{\log}\;CFU/g$, respectively, but upon washing after chlorination, those were $2.23{\pm}0.3{\log}\;CFU/g$ and $0.72{\pm}0.7{\log}\;CFU/g$, respectively. The standard plate counts of baby greens, radicchio and leek were $6.02{\pm}0.5{\log}\;CFU/g$, $5.76{\pm}0.1{\log}\;CFU/g$ and $6.83{\pm}0.5{\log}\;CFU/g$, respectively. After 5 minutes of chlorination, the standard plate counts were $4.10{\pm}0.6{\log}\;CFU/g$, $5.14{\pm}0.1{\log}\;CFU/g$ and $5.30{\pm}0.3{\log}\;CFU/g$, respectively. After 10 minutes of chlorination treatment, the standard plate counts were $2.58{\pm}0.3{\log}\;CFU/g$, $4.27{\pm}0.6{\log}\;CFU/g$, and $4.18{\pm}0.5{\log}\;CFU/g$, respectively. The microbial levels decreased as the time of chlorination increased. This study showed that the microbiological quality of foods was improved with the proper practices of time-temperature control, sanitization control, seasoning control, and personal and surface sanitization control. It also presents management guidelines for the control of potentially hazardous foods at the critical control points in the process of restaurant operations.

• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.27-41
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• 1999

The Ag-Pd-Cu alloys containing a small amount of Au is commonly used for dental purposes, because this alloy cheaper than Au-base alloys for clinical use. However, the most important characteristic of this alloy is age-hardenability, which is not exhibited by other Ag-base dental alloys. The specimens used were Ag-30Pd-10Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electric furnace and centrifugal casting machine in Ar atmosphere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at 350-$550^{\circ}C$ Age-hardening characteristic of the small Au-containing Ag-Pd-Cu dental alloys were investigated by means of hardness testing, X-ray diffraction and electron microscope observations, electrical resistance, differential scanning calorimetric, energy dispersed spectra and electron probe microanalysis. Principal results are as follows ; Maximum hardening occured in two co-phases of ${\alpha}_2$ + PdCu In stage II, decomposition of the $\alpha$ solid solution to a PdCu ordered phase($L1_o$ type) and an Ag-rich ${\alpha}_2$ phase occurred and a discontinuous precipitation occurred at the grain boundary. From the electron microscope study, it was concluded that the cause of age-hardening in this alloy is the precipitation of the PdCu redered phase, which has AuCu I type face-centered tetragonal structure. Precipitation procedure was ${\alpha}{\to}{\alpha}_1+PdCu{\to}{\alpha}_2+PdCu$ at Pd/Cu = 3 Pd element of Ag-Pd-Cu alloy is more effective dental alloy on anti-corrosion and is suitable to isothermal ageing at $450^{\circ}C$.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.219-222
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• 1996

수열법은 밀폐용기중에서 10$0^{\circ}C$이상의 가열, 가압된 수용액이 반응에 관여하는 것으로써, 수정, CaCO3, AlPO4, GaPO4 등과 같은 단결정의 육성 뿐만 아니라 균일분산계로부터 균일한 결정성의 미립자 합성에도 폭넓게 이용되고 있다. 세라믹분말의 합성에 있어서, 이 방법은 특히 형상, 입자크기의 제어가 용이할 뿐만 아니라 고상법, 졸-겔법, 공침법에서와 같은 열처리, 분쇄과정이 필요없기 때문에 고순도의 초미립자를 얻을 수 있는 장점이 있다. 근년 미국, 일본에서는 수열법을 이용한 유전, 압전체 등 세라믹분말의 일부가 공업적인 규모로 대량 생산되고 있다. 그러나 이에 대한 국내 기술은 아직 초기단계에 이르고 있는 실정이다. 따라서 본 연구실에서는 수열법에 의한 단결정 육성 (예; 자수정, CaCO3, AlPO4, GaPO4, KTP, Emerald 등), 박막제조 (예; GaP, PbTiO3, BaTiO3 등), 정제 (고령토, 장석, 도석 등), 원석처리 (진주, 인공 emerald, 비취 등) 그리고 각종 세라믹분말의 합성 등과 같은 다양한 기반기술의 축적과 동시에 공업화에 대응한 수열장치를 위하여 반응용기의 대형화, 엄밀한 밀폐방식, 실용적인 수열조건 등을 개발해 오고 있다. 본 발표에서는 현재까지의 연구개발 내용 중에서 결정성 미립자에 관련한 세라믹분말의 합성에 대한 일부의 결과들을 보고한다. 일반적으로 수열장치는 전기로, 반응용기, 온도 및 압력제어계 등을 기본으로 하고 있으며 시판용의 대부분이 교반기가 부착된 수직형 (vertical type)이다. 이와 같은 방식에 있어서는 엄밀한 밀폐가 곤란, 반응온도의 한계성 (25$0^{\circ}C$ 이하), 증진율의 한계성 (소량생산) 등과 같은 점이 있기 때문에 본 연구실에서는 개폐식 전기로내에 엄밀한 밀폐가 가능한 수평식(horizontal type)의 반응용기를 채택한 뒤 이를 회전 또는 시이소(seesaw)식으로 움직일 수 있도록 하여 연속공정화, 온도구배의 자율조절 그리고 보다 저온에서도 인위적인 이온의 확산을 효율적으로 유도할 수 있도록 하였다. 이와 같은 방식은 기존의 방식과 비교하여 반응용기 내에 응집현상과 미반응물이 존재하지 않으며 또한 단분산으로 결정성 미립자를 대량적으로 얻을 수 있는 장점이 있었다. 다음은 이상과 같이 본 연구실에서 자체 개발한 수열장치를 이용하여 PbTiO3, (Pb,La)TiO3Mn, BaTiO3, ZnSiO4:Mn, CaWO4 등과 같은 세라믹분말에 대한 합성 실험의 결과이다. 압전성, 초전성이 우수한 PbTiO3 및 (Pb,La)TiO3:Mn 분말의 수열합성은 PbO, TiO2, La2O3 등의 분말을 출발원료로 하여 합성도도 25$0^{\circ}C$부근의 알카리성 용액중에서 결정성 PbTiO3 및 (Pb,La)TiO3:Mn 미립자를 단상으로 얻었으며 입자의 형상 및 크기는 합성온도와 수열용매의 종류에 의존하였다. 유전체로서 폭넓게 응용되고 있는 BaTiO3 분말은 Ba(OH)2.8H2O, TiO2와 같은 최적의 출발원료를 선택함으로써 15$0^{\circ}C$ 부근의 저온영역에서도 용이하게 합성할 수 있었다. 특히 본 연구에서는 수용성인 Ba(OH)2.8H2O를 사용함으로써 host-guest적인 반응을 유도시키는데 있어 물의 가장 실용적이고 효과적인 수열용매임도 알았다. ZnSiO4:Mn, CaWO4, MgWO4와 같은 형광체 분말은 공업적으로 고상반응 또는 습식법에 의해 얻어지고 있으나 이들 방법에 있어서는 분쇄공정으로 인한 형광특성의 저하와 같은 문제점이 있다. 따라서 본 연구에서는 수열법을 이용하여 이들 화합물의 합성을 시도하였으며 그 결과 합성온도 30$0^{\circ}C$ 부근의 알칼리성 용액중에서 수열적으로 얻어짐을 알았다. 여기서의 합성분말을 이용하여 실제 조명램프로 제조한 결과 녹색, 청색 발광용 형광체로서 우수한 형광특성을 나타내었다. 천연에서 소량 산출되고 있는 고가의 (Li,Al)MnO2(OH)2:Co 분말은 도자기의 전사지용 청색안료로써 이용되고 있다. 본 연구실에서는 LiOH.H2O, Al(OH)3, MnO2 등의 분말을 출발원료로 하고 24$0^{\circ}C$ 온도 부근 그리고 물을 수열용매로 하여 천연산에 필적하는 (Li,Al)MnO2(OH)2:Co 분말을 인공적으로 합성하였다.

• Journal of the Korea Organic Resources Recycling Association
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• v.11 no.4
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• pp.105-113
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• 2003

Successful operation of a reactor can be accomplished when it is operated at proper D depending on the state of degradation. Operation at high D leads to the washout of biomass in the reactor while operation at low D leads to product inhibition due to the accumulation of excess VFA. These appear to limit the production of hydrogen to reach a higher level. Operation by D control was performed to improve the efficiency of hydrogen fermentation of food waste. Although simple organic matters were rapidly degraded in the early stage (day 1-2), proper VFA concentration and pH values were kept in the reactor at D of $4.5d^{-1}$, which was previously reported to be optimum initial D. High butyrate/acetate (B/A) ratios over 3.2 were obtained. Without D control, the reduction of simple organic matters after day 2 caused the decrease of VFA production and the increase of pH. Hydrogen production also decreased, as microbial proliferation was less than microbial loss by washout. However, the reactor performance was dramatically improved at D control from 4.5 to $2.3d^{-1}$. It showed the highest B/A ratios over 2.0 among the reactors on day 4-7. The second hydrogen peak appeared on day 4, resulting in the highest fermentation efficiency (70.8%) among the reactors. It was caused by the enhanced degradation of slowly degradable matters. The COD removed was converted to hydrogen (19.3%), VFA (36.5%), and ethanol (15.0%). Therefore, the strategy using D control, depending on the state of degradation, was effective in improving the efficiency of hydrogen fermentation.

• Journal of Food Hygiene and Safety
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• v.35 no.4
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• pp.375-381
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• 2020

This study assessed the contamination levels of total aerobic bacteria, fungi, coliforms, Escherichia coli, Bacillus cereus, and Staphylococcus aureus and qualitative analysis of Salmonella spp. and Listeria monocytogens in six raw materials (beef, bean sprout, Chinese cabbage, king oyster mushroom, Korean cabbage, and sweet pumpkin) of home meal replacement (HMR) Shabu-Shabu meal kit distributed in markets. The total aerobic bacteria, fungi, and coliforms were detected as 3.98-6.50, 2.78-3.52, and 2.02-3.28 log CFU/g, respectively. Especially, beef was highly contaminated with total aerobic bacteria (6.50 log CFU/g) and coliforms (3.28 log CFU/g). Over 5 log CFU/g of total aerobic bacteria were also detected in bean sprout, Chinese cabbage, and sweet pumpkin. Less than < 2 log CFU/g of coliforms were detected in all vegetables. E. coli was not detected in any of the six samples (ND: < 1 log CFU/g). S. aureus was detected as 1.33-1.71 log CFU/g in most samples but it was not detected in beef and Korean cabbage. B. cereus was assessed as 1.15-2.01 log CFU/g in most samples but it was not detected in Korean cabbage. L. monocytogenes was qualitatively detected as 25-50% in most samples except for king oyster mushroom. Salmonella spp. were not qualitatively detected in any of the six samples. The microbial contamination levels determined in the current study may be potentially used as the basic data to execute microbial risk assessments of HMR foods such as Shabu-Shabu meal kit.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.11
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• pp.1458-1464
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• 2007

This study was conducted to develope a new type of ready-to-eat smoked Sebastes schlegeli product with high acceptability and extended shelf-life. A Sebastes schlegeli was salted at 4% salt concentration for 6 hr at $4^{\circ}C$. The cold smoking conditions for the salted Sebastes schlegeli consisted of drying for 2 hr at $22{\sim}24^{\circ}C$ followed by smoking for 2 hr at $22{\sim}24^{\circ}C$. The warm smoking conditions for the salted Sebastes schlegeli consisted of drying for 2 hr at $22{\sim}24^{\circ}C$, smoking for 2 hr at $22{\sim}24^{\circ}C$, and smoking again for 30 min at $47{\sim}50^{\circ}C$. The rancidity of the smoked Sebastes schlegeli did not change after 1 year storage at $-20^{\circ}C$ by monitoring the iodine value, peroxide value, and acid value. The number of viable cells in the cold and warm smoked samples were counted as $7.4{\times}10^5$ and $6.2{times}10^5$ CFU/g, respectively. Viable cells were not detected after 1 year of storage at $-20^{\circ}C$. The sensory evaluations of the processed Sebastes schlegeli showed that elastic texture increased with smoking as compared to with salting. There were no significant differences between cold and warm smoking in terms of sweetness, elastic texture, color, and smoke flavor. However, for overall acceptability, preference were in the oder of cold smoked, warm smoked, and salted.