• Journal of Powder Materials
• /
• v.30 no.4
• /
• pp.318-323
• /
• 2023

The thermoelectric effect, which converts waste heat into electricity, holds promise as a renewable energy technology. Recently, bismuth telluride (Bi2Te3)-based alloys are being recognized as important materials for practical applications in the temperature range from room temperature to 500 K. However, conventional sintering processes impose limitations on shape-changeable and tailorable Bi₂Te₃ materials. To overcome these issues, three-dimensional (3D) printing (additive manufacturing) is being adopted. Although some research results have been reported, relatively few studies on 3D printed thermoelectric materials are being carried out. In this study, we utilize extrusion 3D printing to manufacture n-type Bi_1.7Sb_0.3Te₃ (N-BST). The ink is produced without using organic binders, which could negatively influence its thermoelectric properties. Furthermore, we introduce graphene oxide (GO) at the crystal interface to enhance the electrical properties. The formed N-BST composites exhibit significantly improved electrical conductivity and a higher Seebeck coefficient as the GO content increases. Therefore, we propose that the combination of the extrusion 3D printing process (Direct Ink Writing, DIW) and the incorporation of GO into N-BST offers a convenient and effective approach for achieving higher thermoelectric efficiency.

• Journal of the Korean Society for Heat Treatment
• /
• v.26 no.4
• /
• pp.165-172
• /
• 2013

In the present study, the microstructure and solution treatment response of Al-Zn-Mg alloys bars by thixo-extrusion was investigated. The alloy bars were solution treated at 400, 430, 460 and $490^{\circ}C$ for various times. In order to examine the microstructures and phase analysis of the samples after solution treatment, it was performed by optical and scanning electron microscopy. And, Vickers hardness and electrical conductivity was measured on the solution treated samples for each condition to investigate the solution treatment response of extruded bars during solution treatment. The results show that the optimum solution heat treatment conditions of thixo-extruded Al-Zn-Mg alloy for minimization of the grain growth and degradation promotion of the second phase is a temperature of $460^{\circ}C$ and holding time of 0.5 to 2 h.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.05a
• /
• pp.93-98
• /
• 1999

Generally, the - life of die is limited by fatigue fracture or dimensional inaccuracy originated from wear. In this paper, to predict the fatigue life of the dissimilar materials die, the stress and stxain histories of die can be predicted by the analysis of elasto-plastic finite element neth hod and the elastic analysis of die during the process analysis of workpiece. Using heat shrink fit analysis, initial stress of the k r t die is computed. Also, the stress-life curve of die material can be obtained through experiment. With the above two facts, we propose the analysis method of predicting fatigue life in die. In the proposed model, tlz analysis of elastic-plastic finite element method for material is carried out by using ABAQUS. Surface force resulted from the contacting border of the die and workpiece is tmnsformed into the nodal force of die to implement elastic analysis. Besides, the proposed analysis model of die is applied to the one material and the dissimilar materials extrusion die.

• Korean Journal of Food Science and Technology
• /
• v.25 no.6
• /
• pp.703-709
• /
• 1993

The changes in molecular size distribution of rice starch during extrusion cooking and simple heating of rice flour were compared and the effect of subsequent enzyme treatment on the molecular size was examined. A single-screw extruder was used with varing feed moisture contents ($17{\sim}29%$) and barrel temperatures ($100{\sim}150^{\circ}C$). An aluminium capsule immersed in oil bath ($100{\sim}200^{\circ}C$) was used for the simple heat treatment of rice flour. In case of extrusion cooking the mechanical energy input varied sharply at around 23% moisture content of the feed. At the feed moisture content of $17{\sim}23%$, a significant molecular size reduction of rice starch was observed by the gel permeation chromatography using Sephacryl S-1000 gel. The intact starch molecules of above $4{\times}10^{7}$ dalton were largely disintergrated by extrusion cooking of rice flour containing the moisture content less than 23%. It was mostly degraded further into the molecules having below $5{\times}10^{6}$ dalton by ${\alpha}-amylase$ treatment. But at the feed moisture content above 26% the starch did not show molecular size reduction either by extrusion cooking or by subsequent enzyme treatment. On the contrary little changes in molecular size of starch was occured by simple heating of rice flour containing the moisture less than 20%. but slight size reduction was observed at the moisture content above 23%, where the effect of ${\alpha}-amylase$ was also observed.

• Agricultural and Biosystems Engineering
• /
• v.6 no.1
• /
• pp.27-33
• /
• 2005

Soy protein meat analog was produced using a twin-screw extruder attached with a cooling die. Heat transfer analysis was performed for cooling dies with various die sizes at the four different moisture contents of feed during extrusion process. The experimental design consisted of two cooling die widths (30 and 60 mm), three cooling die lengths (100, 200, and 300 mm), four product moisture contents (71.2, 67.0, 61.6 and 55.8%), and water and water plus ethylene glycol as cooling material. When water was used as cooling medium, the values of equivalent overall heat transfer coefficient $(U_e)$ for each die width of 30 and 60 mm were in the range of 187.0 - 341.4 and $358.5-191.6W/m^2^{\circ}C$ depending on the size of die length. Convective heat transfer coefficients between cooling water and inside die wall of cooling channel $(h_c)$ for both die widths of 30 and 60 mm were 588.5, 416.1, and $339.8W/m^2^{\circ}C$ for each die length of 100, 200, and 300 mm. Convective heat transfer coefficients between product and inside die wall of product channel $(h_p)$ for each die width of 30 and 60 mm were in the range of $434.6-888.1W/m^2^{\circ}C$ and $460.7-1014.5W/m^2^{\circ}C$ depending on the size of die length. When water plus ethylene glycol was used as cooling medium, the values of $U_e$ were in the range of $143.9-319.6W/m^2^{\circ}C$ and $177.8-332.7W/m^2^{\circ}C$ for each die width of 30 and 60 mm depending on the size of die length.

• Journal of the Korean Society of Safety
• /
• v.14 no.4
• /
• pp.78-84
• /
• 1999

A compact air-preheating type heat exchanger was developed and tested for the ultra-high temperature heat recovery applications. For the direct use of exhaust gases up to $1200^{\circ}C$, the heat exchanger adopted a ceramic core with high strength and low thermal expansion coefficient less than $1{\times}10^{-6}^{\circ}C^{-1}$. The ceramic core was fabricated by special extrusion and bonding techniques. To minimize thermal stresses in the core, spring-loaded sealing mechanism was designed and successfully installed. 1-pass air flow scheme was adopted for the compactness and cost-savings. The pressure test for the ceramic core showed no failure under 35 kPa and less than 3% leak under 7 kPa. Flue gas simulation system was developed to investigate the performance of the heat exchanger. The test results showed normal operations of the heat exchanger up to $1200^{\circ}C$ of exhaust gases and relatively high heat recovery efficiencies of 31～39% depending upon exhaust gas temperatures..

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.8 no.1
• /
• pp.24-30
• /
• 2009

In this paper, the effect of heat treatment on forgeability is investigated and an improved heat treatment cycle is proposed for the bearing steel, SUJ2. An application example of a bearing inner race cold forging, which has small cracks in the bottom after backward extrusion and piercing, is found from a cold forging industry. The process is evaluated by finite element analysis and several heat treatment cycles are examined in order to propose an improved heat treatment cycle. The effect of heat treatment on material hardness and tool life, dimensional accuracy and forming load is revealed through experiment.

• Journal of Powder Materials
• /
• v.13 no.6 s.59
• /
• pp.421-426
• /
• 2006

The microstructural and mechanical properties of Al-Si alloyed powder, prepared by gas atomization fallowed by hot extrusion, were studied by optical and scanning electron microscopies, hardness and wear testing. The gas atomized Al-Si alloy powder exhibited uniformly dispersed Si particles with particle size ranging from 5 to $8{\mu}m$. The hot extruded Al-Si alloy shows the average Si particle size of less than $1{\mu}m$. After heat-treatment, the average particle size was increased from 2 to $5{\mu}m$. Also, mechanical properties of extruded Al-Si alloy powder were analyzed before and after heat-treatment. As expected from the microstructural analysis, the heat-treated samples resulted in a decrease in the hardness and wear resistance due to Si particle growth. The friction coefficient of heat-treated Al-Si alloyed powder showed higher value tough all sliding speed. This behavior would be due to abrasive wear mechanism. As sliding speed increases, friction coefficient and depth and width of wear track increase. No significant changes occurred in the wear track shape with increased sliding speed.

• Journal of the Korean Society for Heat Treatment
• /
• v.17 no.3
• /
• pp.165-172
• /
• 2004

Compared with the hydroforming technology for steel, the hydroforming technology for aluminum has not been actively investigated. Recently, the hydroforming of high strength aluminum tubes has attracted great interest because of its good strength to weight ratio. In this study, front side member (FSM) is fabricated with the hydroforming of aluminum tube and the mechanical properties and dimensional accuracy of the hydroformed FSM is investigated. For hydroforming process, extruded aluminum tubes with ribs to improve the structural rigidity are used. To ensure the mechanical properties, the aluminum tubes are T6 heat-treated before hydroforming.

• Journal of the Korean Society for Heat Treatment
• /
• v.31 no.3
• /
• pp.126-134
• /
• 2018

In this research, we produced polycrystalline n-type $Bi_2Te_{2.7}Se_{0.3}$ powder using water atomization. To obtain full benefit through water atomized powder, we have implemented spark plasma sintering and hot extrusion for powder compaction. The microstructure and thermoelectric properties were investigated and compared. The average grain size of SPS and extruded bulks were 3.08 and $3.86{\mu}m$ respectively. The extruded material microstructure contains layered grains with less grain boundaries and its counter-part SPS displays dense packed grains with high grain boundaries. Among both bulks, extrusion sample exhibited high power factor (PF) of $2.96{\times}10^{-3}Wm^{-1}K^{-2}$ which is 38% higher than SPS ($2.14{\times}10^{-3}$) bulk sample. Due to variations in grain size and grain boundaries, the SPS bulk shows low thermal conductivity than extruded bulk. However, the extruded bulk sample exhibited a peak ZT of 0.69 at 400 K, which is 19% higher than SPS bulk sample, due to its higher power factor.