• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.324-332
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• 1998

The grain growth characteristics of dual-phase (${\alpha}+{\gamma}$) containing high Cr-steel have investigate using ${\alpha}$-, ${\gamma}$-single phases and (${\alpha}+{\gamma}$)dual-phase of 12%Cr Steel. The heat treatment has performed at $1000-1200^{\circ}C$ for 1-100hr. The results are as follows : 1) The grain growth rate in (${\alpha}+{\gamma}$) dual phase was substantially slower than that of single grain. 2) The relation between mean grain radius $\bar{{\gamma}}$ and annealing time t is, in general, described as following equation : $$(\bar{{\gamma}})^n-(\bar{{\gamma}_o})^n=K_n{\cdot}t{\cdots}{\cdots}(1)$$ i) In the case of single phase of high Cr steel, Eq.(1) is described as $(\bar{{\gamma}})^2-(\bar{{\gamma}_o})^2=K_2{\cdot}t$ and the grain growth is controlled by boundary migration. ii) In dual phase, the grain growth needs diffusion of alloying elements because the chemical composition of ${\alpha}$- and ${\gamma}$- phases differs from each other. When the volume fraction of ${\alpha}$-, ${\gamma}$-phase was almost equal and ${\gamma}$-phase in the case of 80 and $90%{\gamma}$. Eq.(1) is described as $(\bar{{\gamma}})^3-(\bar{{\gamma}_o})^3=K_3{\cdot}t$ because the grain growth is controlled by volume diffusion iii) In the case of ${\gamma}$-rich phase (80 and $90%{\gamma}$), the grain growth of minor phase (10 and $20%{\alpha}$) is described as $(\bar{{\gamma}})^4-(\bar{{\gamma}_o})^4=K_4{\cdot}t$ because the boundary diffusion is predominent rather than volume diffusion.

• Membrane and Water Treatment
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• v.10 no.5
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• pp.361-372
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• 2019

Effect of different alkane based solvents on the stability of emulsion liquid membrane was investigated using normal alkanes (n-hexane, n-heptane, n-octane and n-decane) under various operating parameters of surfactant concentration, emulsification time, internal phase concentration, volume ratio of internal phase to organic phase, volume ratio of emulsion phase to external phase and stirring speed. Results of stability revealed that emulsion liquid membrane containing n-octane as solvent and span-80 (5 % (w/w)) as emulsifying agent presented the highest amount of emulsion stability (the lowest breakage) compared with other solvents; however, operating parameters (surfactant concentration (5% (w/w)), emulsification time (6 min), internal phase concentration (0.05 M), volume ratio of internal phase to organic phase (1/1), volume ratio of emulsion phase to external phase (1/5) and stirring speed (300 rpm)) were also influential on improving the stability (about 0.2% breakage) and on achieving the most stable emulsion. The membrane with the highest stability was employed to extract acridine orange with various concentrations (10, 20 and 40 ppm) from water. The emulsion liquid membrane prepared with n-octane as the best solvent almost removed 99.5% of acridine orange from water. Also, the prepared liquid membrane eliminated completely (100%) other cationic dyes (methylene blue, methyl violet and crystal violet) from water demonstrating the efficacy of prepared emulsion liquid membrane in treatment of dye polluted waters.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.8
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• pp.1047-1054
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• 2018

This paper proposed the strategies for controlling both the heater temperature and the output voltage of a single-phase inverter for the heat treatment. The single-phase inverter system for the heat treatment controls the heater temperature to its reference one, and also it limits the inverter output voltage to 60 V for safety. The stability may be deteriorated due to the large time constant difference between the heater temperature and inverter output voltage. In order to ensure the stability, a hysteresis on/off control approach for the heater temperature control is adapted, and both the open-loop and the closed-loop control strategies of the output voltage are suggested. The performances for the proposed strategies are demonstrated with the experiments.

• Fisheries and Aquatic Sciences
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• v.1 no.2
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• pp.242-249
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• 1998

The engineering aspect of water treatment processes in the recirculating aquaculture system was studied. To recycle the water in the aquaculture system, a wastewater treatment process was required to maintain high water quality for the growth and health of the cultured fish. In this study, three different biofilm processes were used to reduce the concentration of organic matters and ammonia from the recirculating water - two phase fluidized bed, three phase fluidized bed, and trickling filter. The objectives of this research were to evaluate the optimum treatment conditions of the biofilm processes for the recirculating aquaculture system, and thereby reduce the volume of biofilm processes, which are commonly used for the recycle water treatment processes for aquaculture. The result of this study showed that the removal efficiency of organic matters by trickling filter was found to be lower than that of the fluidized bed. In the trickling filter system, anthracite showed better organic removal efficiency than crushed stone as a media. In the two phase fluidized bed, the maximum removal efficiency of either organics or ammonia was obtained when both the packing rate of media was maintained to $40\%$ of total reactor depth excepting sediment zone and the bed expansion rate was maintained to $100\%$. When 100 tilapia (Oreochromis niloticus) of each average 200g was reared, the pollutant production rate was 0.07g $NH_4\;^+-N/kg$ fish/day and 0.06g P04-3-P/kg fish/day, and sludge production rate was 0.39 g SS/kg fish/day. In the two phase and three phase fluidized bed, the volume of water treatment tank could be calculated from an empirical equation by using the relationship between the influent COD to $NH_4\;^+-N$ ratio (C/N, -), media concentration (Cm, g/L), influent ammonia nitrogen concentration (Ni, mg/L), effluent ammonia nitrogen concentration (Ne, mg/L), bed expansion rate $(E,\;\%)$, and influent flowrate $(Q,\;m^3/hr)$. The empirical equation from this study is $$V_2\;=\;10^{3.1279}\;C/N^{3.5461}\;C_m\;^{-3.7473}\;N_i\;^{4.6477}\;E^{0.0326}\;N_e\;^{-0..8849}\;Q\;(Two\;Phase\;FB) V_3\;=\;10^{11.7507}\;C/N^{-1.2330}\;C_m\;^{-6.5715}\;N_i\;^{1.5091}\;N_e\;^{-1.8489}\;Q (Three\;Phase\;FB)$$

• Journal of the Korean Society for Heat Treatment
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• v.26 no.6
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• pp.306-316
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• 2013

Microstructure and fracture behavior of a multi-phase low-density steel were investigated. After hot-rolling and heat treatment, the microstructure of low-density steel was composed of coarse ferrite grains and elongated bands which include second phases such as austenite, martensite and ${\kappa}$-carbide depending on holding time during isothermal heat treatment. After tensile test, microcracks were observed at martensite or ${\kappa}$-carbide interface in the elongated bands. Coarse ferrite grains showed cleavage fracture behavior regardless of second phase. The cleavage fracture of ferrite could be attributed to their coarse grain size and solute atoms that increase ductile-to-brittle transition temperature of ferrite. Despite of the tendency of cleavage fracture in coarse ferrite grains, a specimen having coarse spheroidized ${\kappa}$-carbide particles in the elongated bands showed high total elongation of 30%. Thus, the easiness of plastic deformation in the elongated band seems to play an important role in retardation of cleavage crack formation in coarse ferrite grains.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.4
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• pp.503-510
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• 1998

Effects of cadmium exposure on renal $Na^+$ and $K^+$ transports were studied in rats. During the course of cadmium treatment (2 mg Cd/kg/day, s.c. injections for 3 weeks) renal tubular transports of $Na^+$ and $K^+$ were evaluated by lithium clearance technique. During the early phase (first week) of cadmium treatment, urinary $Na^+$ excretion decreased drastically and this was due to an increased $Na^+$ reabsorption both in the proximal and distal nephrons. During the late phase (third week) of cadmium treatment, filtered $Na^+$ load was decreased by reduction in GFR, but the renal $Na^+$ excretion returned to the control level due to impaired $Na^+$ transport in the proximal tubule. Urinary excretion of $K^+$ did not change during the early phase, but it rose markedly during the late phase of cadmium treatment. These results indicate that a light cadmium intoxication induces a $Na^+$ retention, and a heavy intoxication results in a $K^+$ loss. Possible mechanisms for these changes are discussed.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.262-266
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• 2011

The aim of this study is to investigate aging behavior of A356 alloy for turbo charger part. The specimen was fabricated by investment casting. Solution heat treatment was performed at $525^{\circ}C$ for 8h and followed by aging treated at $160^{\circ}C$, $170^{\circ}C$ for 0.5~20h. And their microstructures and mechanical properties of the aged specimens were analyzed by scanning electron microscope and hardness tester, respectively. All the cast A356 alloy included eutectic Si particles. In the cast A356 alloy, eutectic Si phase mainly was formed along Chinese script phase. Vickers hardness of the cast was improved by aging treatment due to formation of ${\beta}$" phase and ${\beta}$' phase.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.10
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• pp.1210-1216
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• 2011

The purpose of this study is to establish the analysis method for prediction of temperature during cryogenic heat treatment. Experimental cryogenic heat treatment is conducted to observe the phenomena such as boiling of fluid, ice layer on the material surface and to measure the temperature distribution of Al6061 tube. The CFD analysis considering the observed phenomena in the experiment is performed to predict the temperature distribution and convection heat transfer coefficient at each stage of cryogenic heat treatment, in which the boiling of fluid is considered as the multi-phase condition of vapour and liquid. The formation of ice layer on the tube surface is also modeled between material and fluid. The predicted results are in good agreement with the experimental ones. From the results, it is shown that the analysis method can predict the temperature distribution and convection heat transfer coefficient during cryogenic heat treatment.

• Journal of Korea Foundry Society
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• v.26 no.1
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• pp.17-26
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• 2006

The substitution of cooling method from water quenching to air cooling after solution heat treatment was aimed for the development of a convenient and economical heat treatment process of duplex stainless steels without deterioration of mechanical and corrosion resistant properties for the industry. In order to achieve this goal, the mechanical properties and corrosion properties of a ASTM A890-4A duplex stainless steel were systematically investigated as functions of casting condition and cooling method after solution heat treatment. A 3-stepped sand mold and a permanent Y-block mold were used to check the effects of solidification structure and cooling rate after solution heat treatment. The microstructural characteristics such as the ferrite/austenite phase ratio and the precipitation behavior of ${\sigma}$ phase and carbides were investigated by combined analysis of OM and SEM-EDX with an aid of TTT diagram. Hardness and tension test were performed to evaluate the mechanical properties. Impact property at $-40^{\circ}C$ and corrosion resistance were also examined to check the possibility of the industrial application of this basic study. Throughout this investigation, air-cooling method was proved to effectively substitute for water-quenching process after the solution heat treatment, when the duplex stainless steel was sand mold cast with a thickness below 15 mm or permanent mold cast with a thickness below 20 mm.

• Journal of Korean Society on Water Environment
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• v.18 no.2
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• pp.151-157
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• 2002

Landfill leachate is one of highly contaminated and heterogeneous wastewater. The leachate from initial landfill can be treated by anaerobic process because it contains biodegradable matters, particularly, volatile fatty acids (VFAs). However, the anaerobic treatment of leachate is generally required longer hydraulic retention time (HRT) than aerobic process and another treatment process to satisfy effluent concentration. Therefore the modification of conventional anaerobic treatment is needed. Two phase anaerobic membrane process (TPAMP) is an integrated membrane process to be able to separate anaerobic metabolism into two phase which are acidogenesis and methanogenesis for improvement of anaerobic treatment efficiency. In this study, the efficiency of TPAMP and conventional anaerobic treatment were compared in terms of HRT, effluent SCOD, VFAs Membrane used in TPAMP was the UF of capillary type with the surface area of $0.048m^2$. The average effluent SCOD of conventional anaerobic treatment was 1352 mg/L and the removal was 96 % at HRT 60 days, while in TPAMP, 927 mg/L and 98% at HRT 30 days.