FeC₂O₄·2H₂O의 열처리 조건이 Fe₃O_4-_δ 형성에 미치는 영향

오경환,박원식,이상인,서동수,Oh, Kyoung-Hwan,Park, Won-Shik,Rhee, Sang-In,Suhr, Dong-Soo 한국재료학회 2012 한국재료학회지 Vol.22 No.11

A general synthetic method to make $Fe_3O_{4-{\delta}}$ (activated magnetite) is the reduction of $Fe_3O_4$ by $H_2$ atmosphere. However, this process has an explosion risk. Therefore, we studied the process of synthesis of $Fe_3O_{4-{\delta}}$ depending on heat-treatment conditions using $FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. The thermal decomposition characteristics of $FeC_2O_4{\cdot}2H_2O$ and the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ were analyzed with TG/DTA in Ar atmosphere. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method using $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$. The concentration of the solution was 0.1 M and the equivalent ratio was 1.0. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed to $H_2O$ and $FeC_2O$4 from $150^{\circ}C$ to $200^{\circ}C$. $FeC_2O4$ was decomposed to CO, $CO_2$, and $Fe_3O_4$ from $200^{\circ}C$ to $250^{\circ}C$. Single phase $Fe_3O_4$ was formed by the decomposition of ${\beta}-FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. However, $Fe_3C$, Fe and $Fe_4N$ were formed as minor phases when ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed in $N_2$ atmosphere. Then, $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by decomposion of CO. The reduction of $Fe_3O_4$ to $Fe_3O_{4-{\delta}}$ progressed from $320^{\circ}C$ to $400^{\circ}C$; the reaction was exothermic. The degree of exothermal reaction was varied with heat treatment temperature, heating rate, Ar flow rate, and holding time. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was greatly influenced by the heat treatment temperature and the heating rate. However, Ar flow rate and holding time had a minor effect on ${\delta}$-value.

지속 가능한 미래를 위한 교수.학습 프로그램(TLSF Program)과 우리나라 환경 교육과정 비교 분석

오경환(Kyoung-Hwan Oh),민병미(Byeong-Mee Min),손연아(Yeon-A Son),최돈형(Don-Hyung Choi) 한국환경교육학회 2004 環境 敎育 Vol.17 No.1

In this study a comparative analysis is conducted to evaluate TLSF(Teaching and Learning for a Sustainable Future) program, which is a module type environmental education program developed by UNESCO, and the Korean environmental education curriculum.<br/> The Korean environmental curriculum is mainly focused on conceptualization and the matters of fact. As a result, students may not be able to acquire contextualized and synthesized<br/> views on the environmental problems. The Korean environmental curriculum hardly supplies ample variety in the methods of teaching, learning and assessment, or the theories characteristic of the environmental education. Thus it would not make a useful material for teachers to reorganize various materials to be applied in class.<br/> TLSF program would be useful for a teacher to use in the environment education field because it supplies not only many various activities and samples for constructing a proper program but also the theoretical base and examples for education and assessment strategy. Finally, TLSF also offers the theoretical base of the environment education for the assessment, and it makes the best use of feedback from the environment educational field for improving its own quality.<br/> In conclusion, this study can be a meaningful preview for those who are involved in the process of developing of a curriculum, which consists of steps like formulating theories for developing a curriculum, organizing the curriculum contents, activating and evaluating a curriculum.

FPGA를 이용한 무인기용 통신제어기 설계 및 구현

오경환(Kyoung-hwan Oh),심형식(Hyung-sik Shim),박대환(Dae-hwan Park),나성웅(Sung Woong Ra) 한국항공우주학회 2012 韓國航空宇宙學會誌 Vol.40 No.5

무인기의 안정된 통신링크 보장을 위해 오류정정 및 시분할 다중화/역다중화 기능을 갖춘 통신제어기를 FPGA를 이용하여 개발하였다. 아울러 데이터링크의 실시간성을 보장하기 위해 RTOS인 VxWorks를 사용하였다. FPGA를 이용한 통신제어기의 설계는 다양한 입출력 장치의 수정 및 확장이 용이하며, S/W 설계 변경의 유연성을 제공하여 다양한 무인기 시스템에 쉽게 적용이 가능하도록 했다. DTC(Data Terminal Controller) for UAV has been developed using FPGA. It provides the functions of Error Correction and Time-division Mux/Demux for stable data-link. RTOS VxWorks also has been used for real-time control of data-link. FPGA Design of DTC facilitates the modification and extension of various I/O device, and VxWorks ensures real-time availability of data-link control and provides flexibilities of changes of S/W design. The DTC is expected to be deployed easily for various UAV systems.

Fe₃(PO₄)₂ 생성에 미치는 침전제와 첨가량의 영향

안석진,이선영,오경환,서동수,An, Suk-Jin,Lee, Sun-Young,Oh, Kyoung-Hwan,Suhr, Dong-Soo 한국재료학회 2011 한국재료학회지 Vol.21 No.11

The effect of the precipitator (NaOH, $NH_4OH$) and the amount of the precipitator (150, 200, 250, 300 ml) on the formation of $Fe_3(PO_4)_2$, which is the precursor used for cathode material $LiFePO_4$ in Li-ion rechargeable batteries was investigated by the co-precipitation method. A pure precursor of olivine $LiFePO_4$ was successfully prepared with coprecipitation from an aqueous solution containing trivalent iron ions. The acid solution was prepared by mixing 150 ml $FeSO_4$(1M) and 100 ml $H_3PO_4$(1M). The concentration of the NaOH and $NH_4OH$ solution was 1 M. The reaction temperature (25$^{\circ}C$) and reaction time (30 min) were fixed. Nitrogen gas (500 ml/min) was flowed during the reaction to prevent oxidation of $Fe^{2+}$. Single phase $Fe_3(PO_4)_2$ was formed when 150, 200, 250 and 300 ml NaOH solutions were added and 150, 200 ml $NH_4OH$ solutions were added. However, $Fe_3(PO_4)_2$ and $NH_4FePO_4$ were formed when 250 and 300 ml $NH_4OH$ was added. The morphology of the $Fe_3(PO_4)_2$ changed according to the pH. Plate-like lenticular shaped $Fe_3(PO_4)_2$ formed in the acidic solution below pH 5 and plate-like rhombus shaped $Fe_3(PO_4)_2$ formed around pH 9. For the $NH_4OH$, the pH value after 30 min reaction was higher with the same amount of additions of NaOH and $NH_4OH$. It is believed that the formation mechanism of $Fe_3(PO_4)_2$ is quite different between NaOH and $NH_4OH$. Further investigation on this mechanism is needed. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the pH value was measured by pH-Meter.

활성화된(Fe_1-xMn_x)₃O_4-_δ과 (Fe_1-xCo_x)₃O_4-_δ의 이산화탄소 분해 특성

박원식,오경환,이상인,서동수,Park, Won-Shik,Oh, Kyoung-Hwan,Rhee, Sang-In,Suhr, Dong-Soo 한국재료학회 2013 한국재료학회지 Vol.23 No.4

Activated magnetite ($Fe_3O_{4-{\delta}}$) has the capability of decomposing $CO_2$ proportional to the ${\delta}$-value at comparatively low temperature of $300^{\circ}C$. To enhance the $CO_2$ decomposition capability of $Fe_3O_{4-{\delta}}$, $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$ and $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$ were synthesized and then reacted with $CO_2$. $Fe_{1-x}Co_xC_2O_4{\cdot}2H_2O$ powders having Fe to Co mixing ratios of 9:1, 8:2, 7:3, 6:4, and 5:5 were synthesized by co-precipitation of $FeSO_4{\cdot}7H_2O$ and $CoSO_4{\cdot}7H_2O$ solutions with a $(NH_4)_2C_2O_4{\cdot}H_2O$ solution. The same method was used to synthesize $Fe_{1-x}Mn_xC_2O_4{\cdot}2H_2O$ powders having Fe to Mn mixing ratios of 9:1, 8:2, 7:3, 6:4, 5:5 with a $MnSO_4{\cdot}4H_2O$ solution. The thermal decomposition of synthesized $Fe_{1-x}Co_xC_2O_4{\cdot}2H_2O$ and $Fe_{1-x}Mn_xC_2O_4{\cdot}2H_2O$ was analyzed in an Ar atmosphere with TG/DTA. The synthesized powders were heat-treated for 3 hours in an Ar atmosphere at $450^{\circ}C$ to produce activated powders of $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$ and $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$. The activated powders were reacted with a mixed gas (Ar : 85 %, $CO_2$ : 15 %) at $300^{\circ}C$ for 12 hours. The exhaust gas was analyzed for $CO_2$ with a $CO_2$ gas analyzer. The decomposition of $CO_2$ was estimated by measuring $CO_2$ content in the exhaust gas after the reaction with $CO_2$. For $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$, the amount of $Mn^{2+}$ oxidized to $Mn^{3+}$ increased as x increased. The ${\delta}$ value and $CO_2$ decomposition efficiency decreased as x increased. When the ${\delta}$ value was below 0.641, $CO_2$ was not decomposed. For $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$, the ${\delta}$ value and $CO_2$ decomposition efficiency increased as x increased. At a ${\delta}$ value of 0.857, an active state was maintained even after 12 hours of reaction and the amount of decomposed $CO_2$ was $52.844cm^3$ per 1 g of $(Fe_{0.5}Co_{0.5})_3O_{4-{\delta}}$.

N₂분위기에서 FeC₂O₄·2H₂O의 열분해에 의한 Fe₃O_4-_δ합성

박원식,오경환,안석진,서동수,Park, Won-Shik,Oh, Kyoung-Hwan,An, Suk-Jin,Suhr, Dong-Soo 한국재료학회 2012 한국재료학회지 Vol.22 No.5

Activated magnetite ($Fe_3O_{4-{\delta}}$) was applied to reducing $CO_2$ gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a $CO_2$ removal process. One of the typical dry methods is $CO_2$ decomposition using activated magnetite ($Fe_3O_{4-{\delta}}$). Generally, $Fe_3O_{4-{\delta}}$ is manufactured by reduction of $Fe_3O_4$ by $H_2$ gas. This process has an explosion risk. Therefore, a non-explosive process to make $Fe_3O_{4-{\delta}}$ was studied using $FeC_2O_4{\cdot}2H_2O$ and $N_2$. $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$ were used as starting materials. So, ${\alpha}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method. During the calcination process, $FeC_2O_4{\cdot}2H_2O$ was decomposed to $Fe_3O_4$, CO, and $CO_2$. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 $m^2/g$ to 9.32 $m^2/g$. The densities of $FeC_2O_4{\cdot}2H_2O$ and $Fe_3O_4$ were 2.28 g/$cm^3$ and 5.2 g/$cm^3$, respectively. Also, the $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by CO. From the TGA results in air of the specimen that was calcined at $450^{\circ}C$ for three hours in $N_2$ atmosphere, the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was estimated. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was 0.3170 when the sample was heat treated at $400^{\circ}C$ for 3 hours and 0.6583 when the sample was heat treated at $450^{\circ}C$ for 3 hours. $Fe_3O_{4-{\delta}}$ was oxidized to $Fe_3O_4$ when $Fe_3O_{4-{\delta}}$ was reacted with $CO_2$ because $CO_2$ is decomposed to C and $O_2$.

버어리종 잎담배 건조 환경 개선을 위한 건조실 개발 (I. 건조기간중의 미기상 변화)

차광호,장수원,양진철,오경환,신승구,조천준,Cha, Kwang-Ho,Jang, Soo-Won,Yang, Jin-Chul,Oh, Kyoung-Hwan,Shin, Seung-Ku,Jo, Chun-Joon 한국연초학회 2007 한국연초학회지 Vol.29 No.2

This study was carried out to investigate the changes of curing condition on microclimate of temperature, relative humidity during curing process of burley tobacco leaves. The developed facility, ridge opening type was designed to open the central top roof. The air-cured variety, (N. tabacum cv KB111) was normally grown at the Eumseong tobacco experimental station in 2007. Mean daily temperature of $3^{\circ}C$ in ridge opening type curing facility was lower than that of conventional, whereas mean daily relative humidity of 12.6 % RH was lower in conventional curing facility for the entire stage of curing. The frequency distribution of optimal air temperature at daytime was higher 37.5 % in ridge opening type curing facility than that of conventional, while that of optimal relative humidity was lower 8.2 %. In the ridge opening type curing facility, the excessive drying leaves were low, however the price per kilogram was high. These results suggest that the new developed curing facility may be applied to improved microclimate inside the curing facility for curing burley.

Fe₃O₄ 생성에 미치는 황산제일철/황산제이철 몰비의 영향

엄태형,김삼중,안석진,오경환,서동수,Eom, Tae-Hyoung,Tuan, Huynh Thanh,Kim, Sam-Joong,An, Suk-Jin,Oh, Kyoung-Hwan,Suhr, Dong-Soo 한국재료학회 2011 한국재료학회지 Vol.21 No.4

The effect of ferrous/ferric molar ratio on the formation of nano-sized magnetite particles was investigated by a co-precipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide was used as a precipitant. In this experiment, the variables were the ferrous/ferric molar ratio (1.0, 1.25, 2.5 and 5.0) and the equivalent ratio (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0), while the reaction temperature ($25^{\circ}C$) and reaction time (30 min.) were fixed. Argon gas was flowed during the reactions to prevent the $Fe^{2+}$ from oxidizing in the air. Single-phase magnetite was synthesized when the equivalent ratio was above 2.0 with the ferrous/ferric molar ratios. However, goethite and magnetite were synthesized when the equivalent ratio was 1.0. The crystallinity of magnetite increased as the equivalent ratio increased up to 3.0. The crystallite size (5.6 to 11.6 nm), median particle size (15.4 to 19.5 nm), and saturation magnetization (43 to 71 $emu.g^{-1}$) changed depending on the ferrous/ferric molar ratio. The highest saturation magnetization (71 $emu.g^{-1}$) was obtained when the equivalent ratio was 3.0 and the ferrous/ferric molar ratio was 2.5.

일 지역 성인의 대장암에 대한 낙관적 편견과 생활습관

박수호(Park, Su Ho),김성은(Kim, Seong Eun),오경환(Oh, Kyoung Hwan),김희숙(Kim, Hee Sook),김주형(Kim, Joo Hyung),김광숙(Kim, Gwang Suk) 한국보건간호학회 2009 韓國保健看護學會誌 Vol.23 No.2

Purpose: To identify relationship between the life styles and optimistic bias about colorectal cancer(CRC) of adults. Methods: The participants were 338 adults who live in Seoul. The measurements were consisted optimistic bias about CRC and life styles. The life styles were included smoking, alcohol consumption, dietary habits, and CRC screening. Results: 30.5% of the participants regarded their possibility of CRC to be less than others, while 69.5% viewed their likelihood of CRC as at least the same as others. The optimistic bias about CRC was associated with alcohol consumption and dietary habits, but not with smoking and CRC screening. Conclusion: It is difficult to relate optimistic bias about CRC with life style since CRC inspection and alcohol consumption are negatively related with optimistic bias while displaying a positive relation in other aspects. Since the relationship between optimistic bias and life style can change, promotion of a healthy life style as part of a health program could be influential in lessening CRC.

HMM 기반 소용량 가창 음성 합성 시스템 구현

홍두와(Doo Hwa Hong),성준식(June Sig Sung),오경환(Kyoung Hwan Oh),김남수(Nam Soo Kim) 한국통신학회 2010 한국통신학회 학술대회논문집 Vol.2010 No.6