• Title/Summary/Keyword: Arrhenius

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Synthesis and Magnetic Property of Nanocrystalline Fe-Ni-Co Alloys during Hydrogen Reduction of Ni0.5Co0.5Fe2O4 (Ni0.5Co0.5Fe2O4의 수소환원에 의한 나노구조 Fe-Ni-Co 합금의 제조 및 자성특성)

  • Paek, Min Kyu;Do, Kyung Hyo;Bahgat, Mohamed;Pak, Jong Jin
    • Korean Journal of Metals and Materials
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    • v.49 no.2
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    • pp.167-173
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    • 2011
  • Nickel cobalt ferrite($Ni_{0.5}Co_{0.5}Fe_2O_4$) powder was prepared through the ceramic route by the calcination of a stoichiometric mixture of NiO, CoO and $Fe_2O_3$ at $1100^{\circ}C$. The pressed pellets of $Ni_{0.5}Co_{0.5}Fe_2O_4$ were isothermally reduced in pure hydrogen at $800{\sim}1100^{\circ}C$. Based on the thermogravimetric analysis, the reduction behavior and the kinetic reaction mechanisms of the synthesized ferrite were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction, scanning electron microscopy, reflected light microscope and vibrating sample magnetometer to reveal the effect of hydrogen reduction on the composition, microstructure and magnetic properties of the produced Fe-Ni-Co alloy. The arrhenius equation with the approved mathematical formulations for the gas solid reaction was applied to calculate the activation energy($E_a$) and detect the controlling reaction mechanisms. In the initial stage of hydrogen reduction, the reduction rate was controlled by the gas diffusion and the interfacial chemical reaction. However, in later stages, the rate was controlled by the interfacial chemical reaction. The nature of the hydrogen reduction and the magnetic property changes for nickel cobalt ferrite were compared with the previous result for nickel ferrite. The microstructural development of the synthesized Fe-Ni-Co alloy with an increase in the reduction temperature improved its soft magnetic properties by increasing the saturation magnetization($M_s$) and by decreasing the coercivity($H_c$). The Fe-Ni-Co alloy showed higher saturation magnetization compared to Fe-Ni alloy.

Effect of Teaching Program for Model Ignorance on the Perception and Teaching Practice of Pre-service Chemistry Teachers (모델 이그노런스 교수프로그램이 예비화학교사의 인식 및 교수 실행에 미치는 효과)

  • Jeon, Eunsun;Paik, Seoung-Hey
    • Journal of the Korean Chemical Society
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    • v.66 no.3
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    • pp.228-242
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    • 2022
  • In this study, the educational effect was investigated by providing a teaching program so that pre-service chemistry teachers could apply model ignorance education to teacher training practice. The teaching program was constructed in consideration of the sensemaking concept proposed in the study of Odden & Russ and the process of teacher sensemaking proposed by Asli et al. The subjects of this study were 23 pre-service teachers in the 4th year of chemistry education department at a teacher training university in the central region of Korea. In order to form a sensemaking for the model's ignorance education, the teaching program consisted of four stages; the initial idea generation stage, cognition of model's ignorance stage in a inconsistent situation, the lesson strategy construction stage for model ignorance education, and lesson plan & practice stage during teacher training practice. In the first stage of this program, pre-service teachers' initial ideas about the Arrhenius model and Bronsted-Lowry model of acid-base reaction, and the electron transfer model of the oxidation-reduction reaction were investigated. In the second stage, inconsistant situation that cannot be explained by the knowledge of model was presented to recognize the ignorance of the model. The third stage was to develop the teaching ability of model's ignorance through textbook analysis and lesson strategy composition activities. As a final stage, during the teacher training practice, the pre-service teachers were asked to plan and practice the implementation of the model's ignorance education. Through the teaching program to form a sensemaking for ignorance education of the models, pre-service teachers had come to recognize the ignorance of the model, acquired ability to organize and execute lesson strategies reflecting model ignorance, and acquired recognition of the educational value and necessity of teaching the ignorance of models.

Life assessment of monitoring piezoelectric sensor under high temperature at high-level nuclear waste repository (고준위방사성폐기물 처분장 고온 환경 조건에 대한 모니터링용 피에조 센서의 수명 평가)

  • Changhee Park;Hyun-Joong Hwang;Chang-Ho Hong;Jin-Seop Kim;Gye-Chun Cho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.25 no.6
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    • pp.509-523
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    • 2023
  • The high-level nuclear waste (HLW) repository is exposed to complex environmental conditions consisting of high temperature, high humidity, and radiation, resulting in structural deterioration. Therefore, structural health monitoring is essential, and piezo sensors are used to detect cracks and estimate strength. However, since the monitoring sensors installed in the disposal tunnel and disposal container cannot be replaced or removed, the quantitative life of the monitoring sensor and its suitability must be assessed. In this study, the life of a piezo sensor for monitoring was assessed using an accelerated life test (ALT). The failure mode and mechanism of the piezo sensor under high temperature conditions were determined, and temperature stress's influence on the piezo sensor's life was analyzed. ALT was conducted on temperature stress and the relationship between temperature stress and piezo sensor life was suggested. The life of the piezo sensor was assessed using the Weibull probability distribution and the Arrhenius acceleration model. The suggested relationship can be used in multiple stress ALT designs for more precise life assessment.

Effect of Heat Processing on Thermal Stability of Kudzu (Pueraria thumbergiana Bentham) Root Isoflavones (가열처리가 칡 이소플라본의 열 안정성에 미치는 영향)

  • Choi, Sung-Won;Kim, Kyung-Seon;Hur, Nam-Yun;Kim, Kyung-Seon;Ahn, Soon-Cheol;Park, Cheon-Seok;Kim, Byung-Yong;Baik, Moo-Yeol;Kim, Dae-Ok
    • Journal of Life Science
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    • v.18 no.10
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    • pp.1447-1454
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    • 2008
  • Effect of heat processing on thermal stability of kudzu root isoflavone was investigated for future use such as various processed foods and functional foods. Kudzu root extracts were heated at 80, 100, 121, 140, 165, and $180^{\circ}C$ for up to 90 minutes before and after concentration, respectively. Changes in the amount of isoflavones were monitored using HPLC and thermal stability was investigated using Arrhenius equation. The amount of both daidzin and genistin decreased slightly during heating at 80, 100 and $121^{\circ}C$ but decreased significantly above $140^{\circ}C$. This indicated that daidzin and genistin are stable at temperatures near the boiling point of water. The degradation of both daidzin and genistin occurred in two steps and each step showed typical first order kinetic. The degradation rates were faster in the first step than the second step in both daidzin and genistin. Additionally, the degradation was accelerated when they heated after concentration compared to the sample heated before concentration. These results suggested that degradation of kudzu root isoflavone was highly dependent on both their concentration and heating temperature. This study provides the basic information on thermal stability of kudzu root isoflavones, which can be used for future processing of functional foods.

Prediction of Isothermal and Reacting Flows in Widely-Spaced Coaxial Jet, Diffusion-Flame Combustor (큰 지름비를 가지는 동축제트 확산화염 연소기내의 등온 및 연소 유동장의 예측)

  • O, Gun-Seop;An, Guk-Yeong;Kim, Yong-Mo;Lee, Chang-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.7
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    • pp.2386-2396
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    • 1996
  • A numerical simulation has been performed for isothermal and reacting flows in an exisymmetric, bluff-body research combustor. The present formulation is based on the density-weighted averaged Navier-Stokes equations together with a k-epsilon. turbulence model and a modified eddy-breakup combustion model. The PISO algorithm is employed for solution of thel Navier-Stokes system. Comparison between measurements and predictions are made for a centerline axial velocities, location of stagnation points, strength of recirculation zone, and temperature profile. Even though the numerical simulation gives acceptable agreement with experimental data in many respects, the present model is defictient in predicting the recoveryt rate of a central near-wake region, the non-isotropic turbulence effects, and variation of turbulent Schmidt number. Several possible explanations for these discrepancies have been discussed.

Interface Reaction of Molten Converter Slag and Sintered CaO Pellet (용융 전로슬래그와 소결 CaO 펠렛 사이의 계면반응)

  • Kim Yaung-Hwan;Ko In-Yang
    • Resources Recycling
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    • v.13 no.1
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    • pp.47-53
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    • 2004
  • As a basic study of the re-using molten converter slag as an ordinary portland cement by conversion process, molten slag and sintered CaO pellet was reacted each other. The dissolution rate of the sintered CaO pellet into the molten slag was measured and the changes of the reaction layer was also investigated. The converter slag reagent-grade $SiO_2$ added was melted and hold for 30 minutes in MgO crucible between $1350∼1500 ^{\circ}C$. Then sintered CaO pellet heated at the same temperature was dipped into the molten slag and hold for 10∼30 min. After the reaction, the crucible was cooled in air and the specimen was cut off to the horizontal direction of the crucible. The dissolution rate of CaO pellet was measured by the change of the radius of sintered CaO pellet and the interface layer was observed by SEM/EDX and XRD. The dissolution rate of sintered CaO pellet contacted with the slag of basicity 1 was 9.8 $\mu\textrm{m}$/min at $1350^{\circ}C$ and increased to 18.0 $\mu\textrm{m}$/min at $1500^{\circ}C$. The rate was slightly decreased to 7.6 $\mu\textrm{m}$/min at $1350^{\circ}C$ and 15.0 $\mu\textrm{m}$/min at $V^{\circ}C$ in the slag of basicity 2. The dissolution rate of CaO in converter slag was followed to the rule of Arrhenius' temperature dependency, and the apparent activation energy of the dissolution of CaO was 36 kcal/mole. In case of the slag basicity of 1, the thickness of $C_2$S layer was 64-118 $\mu\textrm{m}$ and the thickness of $C_3$S was 28∼90 $\mu\textrm{m}$ for 10∼30 minutes at $1500^{\circ}C$. And the thickness of the $C_3$S layer was 90∼120 $\mu\textrm{m}$ at the same conditions in the slag basicity of 2.

Effect of Grain Size and Drying Temperature on Drying Characteristics of Soybean (Glycine max) Using Hot Air Drying (열풍건조 시의 건조 온도와 입경에 따른 콩(Glycine max)의 건조 특성)

  • Park, Hyeon Woo;Han, Won Young;Yoon, Won Byong
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.44 no.11
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    • pp.1700-1707
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    • 2015
  • The effects of drying temperature on drying characteristics of soybeans with different grain sizes [6.0 (S), 7.5 (M), and 9.0 mm (L) (${\pm}0.2$)] with 25.0% (${\pm}0.8$) initial moisture content were studied. Drying temperatures varied at 25, 35, and $45^{\circ}C$, with a constant air velocity (13.2 m/s). Thin-layer drying models were applied to describe the drying process of soybeans. The Midilli-Kucuk model showed the best fit ($R^2$ >0.99). Based on the model parameters, drying time to achieve the target moisture content (10%) was successfully estimated. Drying time was strongly dependent on the size of soybeans and the drying temperature. The effective moisture diffusivity ($D_{eff}$) was estimated by the diffusion model based on Fick's second law. $D_{eff}$ values increased as grain size and drying temperature increased due to the combined effect of high temperatures and high drying rates, which promote compact tissue. Deff values of S, M, and L estimated were in the range of $0.83{\times}10^{-10}$ to $1.51{\times}10^{-10}m^2/s$, $1.17{\times}10^{-10}$ to $2.17{\times}10^{-10}m^2/s$, and $1.53{\times}10^{-10}$ to $2.95{\times}10^{-10}m^2/s$, respectively, whereas activation energy ($E_a$) based on drying temperature showed no significant differences in the size of soybeans.

Persistence of Fungicide Pencycuron in Soils (토양 중 살균제 Pencycuron의 잔류 특성)

  • An, Xue-Hua;An, Wen-Hao;Im, Il-Bin;Lee, Sang-Bok;Kang, Jong-Gook
    • The Korean Journal of Pesticide Science
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    • v.10 no.4
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    • pp.296-305
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    • 2006
  • The adsorption and persistence of pencycuron {1-(4-chlorobenzyl) cyclopentyl-3-phenylurea} in soils were investigated under laboratory and field conditions to in order to assess the safety use and environmental impact. In the adsorption rate experiments, a significant power function of relation was found between the adsorbed amount of pencycuron and the shaking time. Within one hour following the shaking, the adsorption amounts in the SCL and the SiCL were 60 and 65% of the maximum adsorption amounts, respectively. The adsorption reached a quasi-equilibrium 12 hours after shaking. The adsorption isotherms followed the Freundlich equation. The coefficient (1/n) indicating adsorption strength and degree of nonlinearity was 1.45 for SCL and 1.68 to SiCL. The adsorption coefficients ($K_d$) were 2.31 for SCL and 2.92 to SiCL, and the organic carbon partition coefficient, $K_{oc}$, was 292.9 in SCL and 200.5 inSiCL. In the laboratory study, the degradation rate of pencycuron in soils followed a first-order kinetic model. The degradation rate was greatly affected by soil temperature. As soil incubation temperature was increased from 12 to $28^{\circ}C$, the residual half life was decreased from 95 to 20 days. Arrhenius activation energy was 57.8 kJ $mol^{-1}$. Furthermore, the soil moisture content affected the degradation rate. The half life in soil with 30 to 70% of field moisture capacity was ranged from 21 to 38 days. The moisture dependence coefficient, B value in the empirical equation was 0.65. In field experiments, the half-life were 26 and 23 days, respectively. The duration for period of 90% degradation was 57 days. The difference between SCL and SiCL soils varied to pencycuron degradation rates were very limited, particularly under the field conditions, even though the characteristics of both soils are varied.

Prediction of Propylene/Propane Separation Behavior of Na-type Faujasite Zeolite Membrane by Using Gravimetric Adsorption (중량식흡착 거동에 기초한 Na형 Faujasite 제올라이트 분리막의 프로필렌/프로페인 분리 거동 예측 연구)

  • Hwang, Juyeon;Min, Hae-Hyun;Park, You-In;Chang, Jong-San;Park, Yong-Ki;Cho, Churl-Hee;Han, Moon-Hee
    • Membrane Journal
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    • v.28 no.6
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    • pp.432-443
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    • 2018
  • In this study, propylene/propane separation behavior of Na-type faujasite zeolite membranes is predicted by observing gravimetric adsorptions of propylene and propane on zeolite 13X. The gravimetric adsorptions were measured by using a magnetic suspension balance (MSB) at temperatures of 323, 343, 363 K and a pressure range of 0.02-1 bar. The pressure was increased at 0.1 bar intervals. As adsorption temperature increased, adsorptions of propylene and propane decreased and propylene/propane adsorption selectivity increased. Also, the diffusion coefficients of propylene and propane were increased as the adsorption temperature increased, following the Arrhenius equation. The maximum propylene/propane diffusion selectivity was 0.9753 at 323 K. The perm-selectivity was calculated from the adsorption data of zeolite 13X and compared with the perm-selectivity measured in the single gas permeation experiment for the Na-type faujasite zeolite membrane. The maximum values for the calculated and measured perm-selectivities were observed at a temperature of 323 K. It could be concluded that the prediction of propylene/propane separation of surface diffusion-based membrane by using gravimetric adsorption data is reasonable. Therefore, it is expected that this prediction method can be applied to the screening of adsorption-based microporous membrane for propylene/propane separation.