Pub Date : 2023-04-05DOI: 10.3365/kjmm.2023.61.4.261
S. Ham, Junho Park, C. Jo, Seung-Ho Yang, Y. Joo, J. Gu, Jehyun Lee
The solidification and phase transformation behaviors of IN625 with low C and Fe were investigated through directional solidification and quenching experiments. The primary and secondary dendrite arm spacing decreased exponentially as the solidification rate increased, demonstrating good agreement with theoretical equations. The MC carbide formed at a constant temperature gradient regardless of the solidification rate. It is reasonable to assume that the Laves phase solidified in the final stage of solidification, as it was found at the bottom of the mushy zone. The morphologies and sizes of the MC carbide and the Laves phase were closely related to the solidification rate. Increasing the solidification rate at a constant thermal gradient resulted in the development of the MC carbide from blocky to Chinese script, and eventually spotty shapes, along with decreasing size. As a result of this research, it is believed that the weldability of the alloy could be improved at the expense of mechanical properties, especially with low C and Fe contents and a relatively high solidification rate, which are able to generate the finely distributed MC and Laves phase.
{"title":"Study on Solidification and Phase Transformation Behaviors in Ni-based Superalloy IN625","authors":"S. Ham, Junho Park, C. Jo, Seung-Ho Yang, Y. Joo, J. Gu, Jehyun Lee","doi":"10.3365/kjmm.2023.61.4.261","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.4.261","url":null,"abstract":"The solidification and phase transformation behaviors of IN625 with low C and Fe were investigated through directional solidification and quenching experiments. The primary and secondary dendrite arm spacing decreased exponentially as the solidification rate increased, demonstrating good agreement with theoretical equations. The MC carbide formed at a constant temperature gradient regardless of the solidification rate. It is reasonable to assume that the Laves phase solidified in the final stage of solidification, as it was found at the bottom of the mushy zone. The morphologies and sizes of the MC carbide and the Laves phase were closely related to the solidification rate. Increasing the solidification rate at a constant thermal gradient resulted in the development of the MC carbide from blocky to Chinese script, and eventually spotty shapes, along with decreasing size. As a result of this research, it is believed that the weldability of the alloy could be improved at the expense of mechanical properties, especially with low C and Fe contents and a relatively high solidification rate, which are able to generate the finely distributed MC and Laves phase.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48138343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.157
S. Lim, J. Huh
Carbon-based thin film tool coatings, such as diamond-like carbon (DLC), have excellent lowfriction and anti-sticking properties. These thin films are widely used for the cutting and machining of increasingly widely-used lightweight non-metallic and non-ferrous metal materials, as a part of countermeasures against global warming. However, non-metallic and non-ferrous metal materials are significantly inferior in strength and heat resistance compared to iron-based metals. Therefore, they are primarily employed in high-content fiber reinforced composite materials, which significantly improves their mechanical and thermal properties. Tetrahedral amorphous carbon (TAC) coating has a hardness level similar to diamond coating. However, when TAC is deposited as a thick film, delamination of the coating layer may occur because of the high internal compressive stress between the carbide-based substrate and coating layer, thereby restricting its scalability to other applications. Other factors to be controlled for thick film TAC deposition include minimizing droplets generated during the coating process, and improving interfacial properties like hardness and fatigue resistance. Here, C in the form of CH4, which has high solubility over Cr and forms various compounds, was added during the interfacial deposition process, between the carbide and TAC, to improve interfacial strength and adhesion by precipitation of carbide at the interface. This eventually led to thick TAC film with the thickness and adhesion of commercially viable thick film.
{"title":"Interfacial Layer Effect on the Adhesion of the Ultra-Hard Thick TAC Film Deposition","authors":"S. Lim, J. Huh","doi":"10.3365/kjmm.2023.61.3.157","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.157","url":null,"abstract":"Carbon-based thin film tool coatings, such as diamond-like carbon (DLC), have excellent lowfriction and anti-sticking properties. These thin films are widely used for the cutting and machining of increasingly widely-used lightweight non-metallic and non-ferrous metal materials, as a part of countermeasures against global warming. However, non-metallic and non-ferrous metal materials are significantly inferior in strength and heat resistance compared to iron-based metals. Therefore, they are primarily employed in high-content fiber reinforced composite materials, which significantly improves their mechanical and thermal properties. Tetrahedral amorphous carbon (TAC) coating has a hardness level similar to diamond coating. However, when TAC is deposited as a thick film, delamination of the coating layer may occur because of the high internal compressive stress between the carbide-based substrate and coating layer, thereby restricting its scalability to other applications. Other factors to be controlled for thick film TAC deposition include minimizing droplets generated during the coating process, and improving interfacial properties like hardness and fatigue resistance. Here, C in the form of CH4, which has high solubility over Cr and forms various compounds, was added during the interfacial deposition process, between the carbide and TAC, to improve interfacial strength and adhesion by precipitation of carbide at the interface. This eventually led to thick TAC film with the thickness and adhesion of commercially viable thick film.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42445565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.206
Ok Kyu Park, Taewan Kim, M. Heo, S. Park, Se Woong Lee, Hyunmin Cho, Sang‐il Kim
Bi2Te3-based alloys have been extensively studied as thermoelectric materials near room temperature. In this study, the electrical, thermal, and thermoelectric transport properties of a series of Co-doped n-type Cu0.008Bi2Te2.6Se0.4 polycrystalline alloys (Cu0.008Bi2−xCoxTe2.6Se0.4, x = 0, 0.03, 0.06, 0.09 and 0.12) are investigated. The electrical conductivity of the Cu0.008Bi1.97Co0.03Te2.6Se0.4 (x = 0.03) sample was significantly enhanced, by 34%, to 1199 S/cm compared to 793 S/cm of the pristine Cu0.008Bi2Te2.6Se0.4 (x = 0) sample at 300 K, and gradually decreased to 906 S/cm for x = 0.12 upon further doping. Power factors of the Co-doped samples decreased compared to the 3.26 mW/mK2 of the pristine Cu0.008Bi2Te2.6Se0.4 sample at 300 K. Meanwhile, the power factor of the Cu0.008Bi1.97Co0.03Te2.6Se0.4 (x = 0.03) sample became higher at 520 K. The lattice thermal conductivities of the Co-doped samples decreased due to additional point defect phonon scattering by the Co dopant. Consequently, the zT for the Cu0.008Bi1.97Co0.03Te2.6Se0.4 alloy at 520 K was 0.83, which is approximately 15% larger than that of pristine Cu0.008Bi2Te2.6Se0.4, while the zT of the Cu doped samples at 300 K was smaller than that of the pristine Cu0.008Bi2Te2.6Se0.4 sample. Electrical transport properties of the Co-doped Cu0.008Bi2−xCoxTe2.6Se0.4 samples were analyzed by experimental phenomenological parameters, including the density-of-state, effective mass, weighted mobility, and quality factor.
{"title":"Electrical, Thermal, and Thermoelectric Transport Properties of Co-Doped n-type Cu0.008Bi2Te2.6Se0.4 Polycrystalline Alloys","authors":"Ok Kyu Park, Taewan Kim, M. Heo, S. Park, Se Woong Lee, Hyunmin Cho, Sang‐il Kim","doi":"10.3365/kjmm.2023.61.3.206","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.206","url":null,"abstract":"Bi<sub>2</sub>Te<sub>3</sub>-based alloys have been extensively studied as thermoelectric materials near room temperature. In this study, the electrical, thermal, and thermoelectric transport properties of a series of Co-doped <i>n</i>-type Cu<sub>0.008</sub>Bi<sub>2</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> polycrystalline alloys (Cu<sub>0.008</sub>Bi<sub>2−x</sub>Co<sub>x</sub>Te<sub>2.6</sub>Se<sub>0.4</sub>, <i>x</i> = 0, 0.03, 0.06, 0.09 and 0.12) are investigated. The electrical conductivity of the Cu<sub>0.008</sub>Bi<sub>1.97</sub>Co<sub>0.03</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> (<i>x</i> = 0.03) sample was significantly enhanced, by 34%, to 1199 S/cm compared to 793 S/cm of the pristine Cu<sub>0.008</sub>Bi<sub>2</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> (<i>x</i> = 0) sample at 300 K, and gradually decreased to 906 S/cm for <i>x</i> = 0.12 upon further doping. Power factors of the Co-doped samples decreased compared to the 3.26 mW/mK<sup>2</sup> of the pristine Cu<sub>0.008</sub>Bi<sub>2</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> sample at 300 K. Meanwhile, the power factor of the Cu<sub>0.008</sub>Bi<sub>1.97</sub>Co<sub>0.03</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> (<i>x</i> = 0.03) sample became higher at 520 K. The lattice thermal conductivities of the Co-doped samples decreased due to additional point defect phonon scattering by the Co dopant. Consequently, the <i>zT</i> for the Cu<sub>0.008</sub>Bi<sub>1.97</sub>Co<sub>0.03</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> alloy at 520 K was 0.83, which is approximately 15% larger than that of pristine Cu<sub>0.008</sub>Bi<sub>2</sub>Te<sub>2.6</sub>Se<sub>0.4</sub>, while the <i>zT</i> of the Cu doped samples at 300 K was smaller than that of the pristine Cu<sub>0.008</sub>Bi<sub>2</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> sample. Electrical transport properties of the Co-doped Cu<sub>0.008</sub>Bi<sub>2−x</sub>Co<sub>x</sub>Te<sub>2.6</sub>Se<sub>0.4</sub> samples were analyzed by experimental phenomenological parameters, including the density-of-state, effective mass, weighted mobility, and quality factor.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43045730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.198
Seung-Hwan Kwon, Sang‐il Kim, M. Heo, W. Seo, J. Roh, Heesun Yang, Hyun-sik Kim
YbCd2Sb2 is a promising Zintl compound for waste heat recovery applications due to its low thermal conductivity, originating from its complex crystal structure. Many strategies such as alloying or doping have been suggested to further reduce the thermal conductivity of YbCd2Sb2 to improve its thermoelectric performance. However, the effects of alloying or doping on the electronic transport properties of YbCd2Sb2 have not been evaluated in detail. Here, previously reported thermoelectric properties of YbCd2-xMgxSb2 (x = 0, 0.2, 0.4) with drastic thermal conductivity suppression were evaluated using the Single Parabolic Band (SPB) model and Callaway von Bayer (CvB) model. The SPB and CvB models evaluate any changes in electronic band parameters and phonon scattering strength, respectively, due to Mg alloying. Based on the SPB model, Mg alloying deteriorated the weighted mobility, mostly due to non-degenerate mobility reduction. However, the magnitude of point-defect phonon scattering significantly increased with Mg alloying, as evaluated by the CvB model. As a result, the maximum zT is achieved when x = 0.4 at 700 K despite the decreased electronic transport properties from Mg alloying. Our work suggests that carefully designed alloying can improve the thermoelectric performance of the Zintl compound even when it changes its electronic and thermal transport properties in opposite directions.
{"title":"The Mechanism behind the High Thermoelectric Performance in YbCd2-xMgxSb2","authors":"Seung-Hwan Kwon, Sang‐il Kim, M. Heo, W. Seo, J. Roh, Heesun Yang, Hyun-sik Kim","doi":"10.3365/kjmm.2023.61.3.198","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.198","url":null,"abstract":"YbCd2Sb2 is a promising Zintl compound for waste heat recovery applications due to its low thermal conductivity, originating from its complex crystal structure. Many strategies such as alloying or doping have been suggested to further reduce the thermal conductivity of YbCd2Sb2 to improve its thermoelectric performance. However, the effects of alloying or doping on the electronic transport properties of YbCd2Sb2 have not been evaluated in detail. Here, previously reported thermoelectric properties of YbCd2-xMgxSb2 (x = 0, 0.2, 0.4) with drastic thermal conductivity suppression were evaluated using the Single Parabolic Band (SPB) model and Callaway von Bayer (CvB) model. The SPB and CvB models evaluate any changes in electronic band parameters and phonon scattering strength, respectively, due to Mg alloying. Based on the SPB model, Mg alloying deteriorated the weighted mobility, mostly due to non-degenerate mobility reduction. However, the magnitude of point-defect phonon scattering significantly increased with Mg alloying, as evaluated by the CvB model. As a result, the maximum zT is achieved when x = 0.4 at 700 K despite the decreased electronic transport properties from Mg alloying. Our work suggests that carefully designed alloying can improve the thermoelectric performance of the Zintl compound even when it changes its electronic and thermal transport properties in opposite directions.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41341692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.145
Hye Rin Bang, Jin Sung Park, Sang Heon Kim, T. Kim, M. Oh, Sung Jin Kim
The effects of the electrogalvanizing conditions (a combination of plating current and time) on hydrogen infusion, embrittlement, and corrosion-induced hydrogen embrittlement (HE) behaviors of ultra-high strength steel were examined. A range of experimental and analytical methods, including electrochemical impedance spectroscopy, hydrogen permeation, polarization, and slow strain rate test, were employed. The results showed that the applied cathodic current density during electrogalvanizing had an inverse relationship with the Zn crystalline size. A smaller cathodic current density and longer plating time led to a larger crystalline size, resulting in a higher infusion rate of hydrogen atoms, and HE-sensitivity (i.e., mechanical degradation with larger density of secondary crack in fracture surface). On the other hand, a larger cathodic current density and shorter plating time caused a higher anodic dissolution rate and smaller polarization resistance of the coating when exposed to neutral aqueous environments. Hence, a higher rate of galvanic corrosion between the coating and exposed steel substrate (e.g., locally damaged areas around coating layer) resulted in a higher infusion rate of hydrogen atoms and HE-sensitivity. This study provides insight into the desirable plating conditions for electro-Zn plating on ultra-high strength steels with enhanced resistance to hydrogen infusion and embrittlement, induced by aqueous corrosion.
{"title":"Effects of Applied Cathodic Current on Hydrogen Infusion, Embrittlement, and Corrosion-Induced Hydrogen Embrittlement Behaviors of Ultra-High Strength Steel for Automotive Applications","authors":"Hye Rin Bang, Jin Sung Park, Sang Heon Kim, T. Kim, M. Oh, Sung Jin Kim","doi":"10.3365/kjmm.2023.61.3.145","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.145","url":null,"abstract":"The effects of the electrogalvanizing conditions (a combination of plating current and time) on hydrogen infusion, embrittlement, and corrosion-induced hydrogen embrittlement (HE) behaviors of ultra-high strength steel were examined. A range of experimental and analytical methods, including electrochemical impedance spectroscopy, hydrogen permeation, polarization, and slow strain rate test, were employed. The results showed that the applied cathodic current density during electrogalvanizing had an inverse relationship with the Zn crystalline size. A smaller cathodic current density and longer plating time led to a larger crystalline size, resulting in a higher infusion rate of hydrogen atoms, and HE-sensitivity (i.e., mechanical degradation with larger density of secondary crack in fracture surface). On the other hand, a larger cathodic current density and shorter plating time caused a higher anodic dissolution rate and smaller polarization resistance of the coating when exposed to neutral aqueous environments. Hence, a higher rate of galvanic corrosion between the coating and exposed steel substrate (e.g., locally damaged areas around coating layer) resulted in a higher infusion rate of hydrogen atoms and HE-sensitivity. This study provides insight into the desirable plating conditions for electro-Zn plating on ultra-high strength steels with enhanced resistance to hydrogen infusion and embrittlement, induced by aqueous corrosion.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48751481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.213
Jeong Yun Hwang, Rahidul Hasan, Kyu Hyoung Lee
Herein we report the optimized processing conditions of hot extrusion for fabricating an n-type Bi2Te2.7Se0.3 thermoelectric compound, with high electronic transport properties as well as improved mechanical reliability. We fabricated a Bi2Te2.7Se0.3 extrudate that was 3.8 mm in diameter and 700 mm in length by controlling the processing parameters of temperature and pressure. A 3-point bending strength of over 70 MPa, which is 7 times higher that of the commercial zone melting ingot, was obtained in the samples prepared at 460 oC temperature under 6–6.5 MPa pressure. The samples benefitted from the formation of a highly-dense microstructure (relative density > 98%). It is noted that the electronic transport properties (electrical conductivity and Seebeck coefficient) could be manipulated by controlling the applied pressure of hot extrusion at 460 oC, mainly due to the change in the characteristics of the 00l crystal orientation, which originated from grain rotation and rearrangement. Power factor values of ~2.9 mW/mK2 at 300 K and ~2.95 mW/mK2 at 320 K, similar to those of sintered bulks, were obtained in the hot extrudate fabricated under processing parameters of 460 oC and 6 MPa. Moreover, a high power factor value of 2.25 mW/mK2 was observed even at the high temperature of 480 K, which is 70% higher than that of Bi2Te2.7Se0.3 bulk fabricated by hot pressing.
{"title":"Electronic Transport Properties of Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> Fabricated by Hot Extrusion","authors":"Jeong Yun Hwang, Rahidul Hasan, Kyu Hyoung Lee","doi":"10.3365/kjmm.2023.61.3.213","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.213","url":null,"abstract":"Herein we report the optimized processing conditions of hot extrusion for fabricating an <i>n</i>-type Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> thermoelectric compound, with high electronic transport properties as well as improved mechanical reliability. We fabricated a Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> extrudate that was 3.8 mm in diameter and 700 mm in length by controlling the processing parameters of temperature and pressure. A 3-point bending strength of over 70 MPa, which is 7 times higher that of the commercial zone melting ingot, was obtained in the samples prepared at 460 <sup>o</sup>C temperature under 6–6.5 MPa pressure. The samples benefitted from the formation of a highly-dense microstructure (relative density > 98%). It is noted that the electronic transport properties (electrical conductivity and Seebeck coefficient) could be manipulated by controlling the applied pressure of hot extrusion at 460 <sup>o</sup>C, mainly due to the change in the characteristics of the 00<i>l</i> crystal orientation, which originated from grain rotation and rearrangement. Power factor values of ~2.9 mW/mK<sup>2</sup> at 300 K and ~2.95 mW/mK<sup>2</sup> at 320 K, similar to those of sintered bulks, were obtained in the hot extrudate fabricated under processing parameters of 460 <sup>o</sup>C and 6 MPa. Moreover, a high power factor value of 2.25 mW/mK<sup>2</sup> was observed even at the high temperature of 480 K, which is 70% higher than that of Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> bulk fabricated by hot pressing.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"89 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135130718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.183
Jae-Hee Heo, Young-Min Kang
Perovskite manganese La0.7Sr0.3MnO3 (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (T) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at T ≥ 600 oC. The average grain size was ~15 nm at the calcination temperature (Tcal) = 600 oC and it increased to ~1 μm when T cal increased up to 1200 oC. M-H curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing Tcal. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ f ≤ 18GHz. The complex permittivities (ε', ε") increased significantly in samples calcined above 800 oC because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the MS value increased significantly. As the Tcal increased, the height of the μ' and μ" spectra also gradually increased. The large values of ε', ε" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.
{"title":"Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of La0.7Sr0.3MnO3","authors":"Jae-Hee Heo, Young-Min Kang","doi":"10.3365/kjmm.2023.61.3.183","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.183","url":null,"abstract":"Perovskite manganese La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (<i>T</i>) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at <i>T</i> ≥ 600 <sup>o</sup>C. The average grain size was ~15 nm at the calcination temperature (T<sub>cal</sub>) = 600 <sup>o</sup>C and it increased to ~1 μm when T cal increased up to 1200 <sup>o</sup>C. <i>M</i>-<i>H</i> curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing <i>T</i><sub>cal</sub>. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ <i>f</i> ≤ 18GHz. The complex permittivities (ε', ε\") increased significantly in samples calcined above 800 <sup>o</sup>C because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the <i>M</i><sub>S</sub> value increased significantly. As the <i>T</i><sub>cal</sub> increased, the height of the μ' and μ\" spectra also gradually increased. The large values of ε', ε\" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49581058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.190
Eun Been Lee, S. Jo, Sang Jun Kim, Gil-Ryeong Park, Jung Woo Lee
Green hydrogen has attracted significant attention as one of the future energy sources because no greenhouse gases are emitted during production and its energy density is much higher than fossil fuels. Precious metals such as platinum (Pt) and iridium (Ir)-based catalysts are commonly used for water splitting catalysts. However, because of high cost of these precious metals, the mass production of green hydrogen is restricted. In this study, water splitting catalysts based on relatively inexpensive ruthenium (Ru), cobalt (Co), and iron (Fe) were synthesized. The metal nanoparticles were anchored on reduced graphene oxide (rGO) by a microwave-assisted process. The nanoparticles were uniformly distributed on the rGO supports with sizes of about 1.5 and 2 nm in Ru/rGO and RuCoFe/rGO, respectively. This promoted the reaction by further increasing the specific surface area of the catalysts. In addition, it was confirmed by EDS mapping results that the nanoparticles were made of RuCoFe alloy. Among the prepared catalysts, Ru/rGO was excellent toward the hydrogen evolution reaction (HER), which required an overpotential of 50 mV to reach a current density of −10 mA cm−2. In addition, RuCoFe/rGO, which contained the RuCoFe alloy, was the best for the oxygen evolution reaction (OER), and it required 362 mV at the current density of 10 mA cm−2.
由于生产过程中不排放温室气体，且能量密度远高于化石燃料，绿色氢作为未来能源之一备受关注。铂基催化剂(Pt)和铱基催化剂(Ir)等贵金属通常用于水裂解催化剂。然而，由于这些贵金属的高成本，限制了绿色氢的大规模生产。在本研究中，合成了基于相对便宜的钌(Ru)、钴(Co)和铁(Fe)的水裂解催化剂。通过微波辅助工艺将金属纳米颗粒固定在还原氧化石墨烯(rGO)上。在Ru/rGO和RuCoFe/rGO中，纳米颗粒均匀分布在rGO载体上，尺寸分别为1.5 nm和2 nm。这通过进一步增加催化剂的比表面积来促进反应。此外，能谱图结果证实了纳米颗粒是由RuCoFe合金制成的。在制备的催化剂中，Ru/rGO对析氢反应(HER)表现优异，该反应需要50 mV的过电位才能达到−10 mA cm−2的电流密度。此外，含有RuCoFe合金的RuCoFe/rGO在10 mA cm−2的电流密度下需要362 mV才能进行出氧反应(OER)。
{"title":"Fabrication of Ruthenium-Based Transition Metal Nanoparticles/Reduced Graphene Oxide Hybrid Electrocatalysts for Alkaline Water Splitting","authors":"Eun Been Lee, S. Jo, Sang Jun Kim, Gil-Ryeong Park, Jung Woo Lee","doi":"10.3365/kjmm.2023.61.3.190","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.190","url":null,"abstract":"Green hydrogen has attracted significant attention as one of the future energy sources because no greenhouse gases are emitted during production and its energy density is much higher than fossil fuels. Precious metals such as platinum (Pt) and iridium (Ir)-based catalysts are commonly used for water splitting catalysts. However, because of high cost of these precious metals, the mass production of green hydrogen is restricted. In this study, water splitting catalysts based on relatively inexpensive ruthenium (Ru), cobalt (Co), and iron (Fe) were synthesized. The metal nanoparticles were anchored on reduced graphene oxide (rGO) by a microwave-assisted process. The nanoparticles were uniformly distributed on the rGO supports with sizes of about 1.5 and 2 nm in Ru/rGO and RuCoFe/rGO, respectively. This promoted the reaction by further increasing the specific surface area of the catalysts. In addition, it was confirmed by EDS mapping results that the nanoparticles were made of RuCoFe alloy. Among the prepared catalysts, Ru/rGO was excellent toward the hydrogen evolution reaction (HER), which required an overpotential of 50 mV to reach a current density of −10 mA cm−2. In addition, RuCoFe/rGO, which contained the RuCoFe alloy, was the best for the oxygen evolution reaction (OER), and it required 362 mV at the current density of 10 mA cm−2.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44462349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.170
Eui Seon Lee, Youn-Ji Heo, Ji Young Kim, Young-In Lee, M. Suk, Sung-Tag Oh
The effects of fabrication method on the microstructure and sinterability of W-1 wt% Y2O3 were analyzed. W composite powders dispersed with Y2O3 particles were synthesized by the ultrasonic spray pyrolysis process or the ultrasonic spray pyrolysis/polymer solution process. A dense composite was fabricated by a combination of spark plasma sintering and final hot isostatic pressing. The powder synthesized by the ultrasonic spray pyrolysis had fine dispersed particles on the surface of the cubic powder and was composed of W, Y2O3 and W-oxides. On the other hand, in the case of the ultrasonic spray pyrolysis/polymer solution process, the nano-sized particles formed agglomerates and existed only as pure W and Y2O3 phases. All the sintered compacts treated with HIP showed an increase in relative density, and the sintered compacts of the powder synthesized by the ultrasonic spray pyrolysis/polymer solution process showed a maximum relative density of 97~99% and a fine grain size. The change in microstructure with different powder processing was explained by the presence of W-oxide and the size and distribution of Y2O3 particles. The Vickers hardness of the sintered compact reached the largest value of about 5 GPa in the powder synthesized by the ultrasonic spray pyrolysis/polymer solution process, which was interpreted to be a result of the relatively high density and decreased grain size.
{"title":"Properties of Y2O3 Dispersion Strengthened W Fabricated by Ultrasonic Spray Pyrolysis and Pressure Sintering","authors":"Eui Seon Lee, Youn-Ji Heo, Ji Young Kim, Young-In Lee, M. Suk, Sung-Tag Oh","doi":"10.3365/kjmm.2023.61.3.170","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.170","url":null,"abstract":"The effects of fabrication method on the microstructure and sinterability of W-1 wt% Y2O3 were analyzed. W composite powders dispersed with Y2O3 particles were synthesized by the ultrasonic spray pyrolysis process or the ultrasonic spray pyrolysis/polymer solution process. A dense composite was fabricated by a combination of spark plasma sintering and final hot isostatic pressing. The powder synthesized by the ultrasonic spray pyrolysis had fine dispersed particles on the surface of the cubic powder and was composed of W, Y2O3 and W-oxides. On the other hand, in the case of the ultrasonic spray pyrolysis/polymer solution process, the nano-sized particles formed agglomerates and existed only as pure W and Y2O3 phases. All the sintered compacts treated with HIP showed an increase in relative density, and the sintered compacts of the powder synthesized by the ultrasonic spray pyrolysis/polymer solution process showed a maximum relative density of 97~99% and a fine grain size. The change in microstructure with different powder processing was explained by the presence of W-oxide and the size and distribution of Y2O3 particles. The Vickers hardness of the sintered compact reached the largest value of about 5 GPa in the powder synthesized by the ultrasonic spray pyrolysis/polymer solution process, which was interpreted to be a result of the relatively high density and decreased grain size.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42179446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-05DOI: 10.3365/kjmm.2023.61.3.218
G. Kim, Han-Sang Oh, Jong Hyup Lee, Young Joo Park, Yu Bin Lee, Jae Hong Kwon, Byong-chul Kim
Technologies to reduce CO2 emissions in the steel industry have been actively developed since the early 1990s in order to deal with global climate change. In particular, the utilization of various types of biomass including wood, bamboo, grass, food and agricultural by-product are being attempted as carbon neutral fuels in the blast furnace process. In this study, an alternative reducing agent for coke and pulverized coal using biomass was developed and the effect on blast furnace performance and CO2 reduction was evaluated. The first investigation was whether a burden material made of torrefied biomass mixed with iron ore and coal (Iron-bearing Biomass Coke, IBC) could be used as a substitute for coke in the form of a carbonized briquette. In addition, a method of mixing torrefied biomass with pulverized coal (Bio-PC) to inject through tuyere in a blast furnace was examined. As a result, when coke was replaced with 10% of IBC, the reducibility of the sintered ore was improved in association with an increased CO gas utilization ratio, hence CO2 emissions decreased by 2.3%. Furthermore, the combustion efficiency of Bio-PC mixed with 10% of torrefied biomass was improved by 13.2%, thus, the amount of CO2 emissions was calculated to decrease by 4%. These results suggest that the possibility of using IBC and Bio-PC in blast furnaces, as they could effectively reduce CO2 emissions in the ironmaking process.
{"title":"Development of Alternative Reductant using Biomass for Reducing CO2 in Ironmaking Process","authors":"G. Kim, Han-Sang Oh, Jong Hyup Lee, Young Joo Park, Yu Bin Lee, Jae Hong Kwon, Byong-chul Kim","doi":"10.3365/kjmm.2023.61.3.218","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.3.218","url":null,"abstract":"Technologies to reduce CO2 emissions in the steel industry have been actively developed since the early 1990s in order to deal with global climate change. In particular, the utilization of various types of biomass including wood, bamboo, grass, food and agricultural by-product are being attempted as carbon neutral fuels in the blast furnace process. In this study, an alternative reducing agent for coke and pulverized coal using biomass was developed and the effect on blast furnace performance and CO2 reduction was evaluated. The first investigation was whether a burden material made of torrefied biomass mixed with iron ore and coal (Iron-bearing Biomass Coke, IBC) could be used as a substitute for coke in the form of a carbonized briquette. In addition, a method of mixing torrefied biomass with pulverized coal (Bio-PC) to inject through tuyere in a blast furnace was examined. As a result, when coke was replaced with 10% of IBC, the reducibility of the sintered ore was improved in association with an increased CO gas utilization ratio, hence CO2 emissions decreased by 2.3%. Furthermore, the combustion efficiency of Bio-PC mixed with 10% of torrefied biomass was improved by 13.2%, thus, the amount of CO2 emissions was calculated to decrease by 4%. These results suggest that the possibility of using IBC and Bio-PC in blast furnaces, as they could effectively reduce CO2 emissions in the ironmaking process.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46010783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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