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Content available Synthesis and Characterization of W Composite Powder with La2O3-Y2O3 Nano-Dispersoids by Ultrasonic Spray Pyrolysis
Heo Youn Ji, Lee Eui Seon, Kim Jeong Hyun, Lee Young-In, Jeong Young-Keun, Oh Sung-Tag
Archives of Metallurgy and Materials
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2022
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Vol. 67, iss. 4
1507--1510
EN
An optimum route to synthesis the W-based composite powders with homogeneous dispersion of oxide nanoparticles was investigated. The La2O3 dispersed W powder was synthesized by ultrasonic spray pyrolysis using ammonium metatungstate hydrate and lanthanum nitrate. The dispersion of Y2O3 nanoparticles in W-La2O3 powder was carried out by a polymer addition solution method using yttrium nitrate. XPS and Tem analyses for the composite powder showed that the nano-sized La2O3 and Y2O3 particles were well distributed in W powder. This study suggests that the combination processing of ultrasonic spray pyrolysis and polymeric additive solution is a promising way to synthesis W-based composite powders.
2
Content available Simple synthesis of Black TiO2 Nanofibers Via Calcination in Inert Atmosphere
Ji Myeongjun, Kim Eung Ryong, Park Mi-Jeong, Jeon Hee Yeon, Moon Jaeyun, Byun Jongmin, Lee Young-In
Archives of Metallurgy and Materials
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2022
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Vol. 67, iss. 4
1481--1486
EN
Black TiO2 nanofibers have recently emerged as a promising material that has both advantages of black metal oxide and one-dimensional nanostructure. However, current reduction-based synthesis approaches are not compatible with practical applications because these processes require high process costs, complicated processes, and sophisticated control. Therefore, it is still necessary to develop a simple and facile method that can easily introduce atomic defects during the synthesis process. This work suggests an electrospinning process with an antioxidant and subsequent calcination process for the facile synthesis of black TiO2 nanofibers. The synthesized black TiO2 nanofiber has an average diameter of 50.3 nm and a rutile structure. Moreover, this nanofiber represented a noticeable black color and a bandgap of 2.67 eV, clearly demonstrating the bandgap narrowing by the introduced atomic defects.
3
Content available Synthesis of Y2O3-Dispersed W Powders Prepared by Ultrasonic Spray Pyrolysis and Polymer Solution Route
Jo Hyeonhui, Lee Young-In, Suk Myung-Jin, Jeong Young-Keun, Oh Sung-Tag
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 3
799--802
EN
The nano-sized Y2O3 dispersed W composite powder is prepared by ultrasonic spray pyrolysis of a tungsten precursor using ammonium metatungstate hydrate and a polymer addition solution method using Y-nitrate. XRD analysis for calcined powder showed the formation of WO2 phase by partial oxidation of W powder during calcination in air. The TEM and phase analysis for further hydrogen reduction of calcined powder mixture exhibited that the W powder with a uniform distribution of Y2O3 nanoparticles can be successfully produced. These results indicate that the wet chemical method combined with spray pyrolysis and polymer solution is a promising way to synthesis the W-based composites with homogeneous dispersion of fine oxide particles.
4
Content available Morphology Control of One-Dimensional Gallium Nitride Nanostructures by Modulating the Crystallinity of Sacrificial Gallium Oxide Templates
Ko Yun Taek, Park Mijeong, Park Jingyeong, Moon Jaeyun, Choa Yong-Ho, Lee Young-In
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 3
709--712
EN
In this study, we demonstrated a method of controllably synthesizing one-dimensional nanostructures having a dense or a hollow structure using fibrous sacrificial templates with tunable crystallinity. The fibrous Ga2O3 templates were prepared by calcining the polymer/gallium precursor nanofiber synthesized by an electrospinning process, and their crystallinity was varied by controlling the calcination temperature from 500°C to 900°C. GaN nanostructures were transformed by nitriding the Ga2O3 nanofibers using NH3 gas. All of the transformed GaN nanostructures maintained a one-dimensional structure well and exhibited a diameter of about 50 nm, but their morphology was clearly distinguished according to the crystallinity of the templates. When the templates having a relatively low crystallinity were used, the transformed GaN showed a hollow nanostructure, and as the crystallinity increased, GaN was converted into a denser nanostructure. This morphological difference can be explained as being caused by the difference in the diffusion rate of Ga depending on the crystallinity of Ga2O3 during the conversion from Ga2O3 to GaN. It is expected that this technique will make possible the tubular nanostructure synthesis of nitride functional nanomaterials.
5
Content available Homogeneous Dispersion of Yttrium Oxide Particles in Nickel-Based Superalloy by High Pressure Homogenizing and Ball Milling Method
Byun Jongmin, Lee Young-In, Oh Sung-Tag
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 4
1055--1058
EN
An optimum route to fabricate the Ni-based superalloy with homogeneous dispersion of Y2O3 particles is investigated. Ni-based ODS powder was prepared by high-energy ball milling of gas-atomized alloy powders and Y2O3 particles treated with a high-pressure homogenizer. Decrease in particle size and improvement of dispersion stability were observed by high-pressure homogenization of as-received Y2O3 particles, presumably by the powerful cavitation forces and by collisions of the particles. Microstructural analysis for the ball-milled powder mixtures reveal that Ni-based ODS powders prepared from high-pressure homogenization of Y2O3 particles exhibited more fine and uniform distribution of Ni and Y elements compared to the as-received powder. These results suggested that high-pressure homogenization process is useful for producing Ni-based superalloy with homogeneously dispersed oxide particles.
6
Content available Effect of Pyrolysis Conditions on the Physicochemical Properties of Graphitic Carbon Nitride for Visible-Light-Driven Photocatalytic Degradation
Kim Jeong Hyun, Ji Myeongjun, Ryu Cheol-Hui, Lee Young-In
Archives of Metallurgy and Materials
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2020
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Vol. 65, iss. 3
1111--1116
EN
Graphitic carbon nitride (g-C3 N4 ) is an attractive photocatalyst, however, its practical photocatalytic applications are still faced with huge challenges. The aim of this research is to identify the correlation between synthetic conditions and properties of the g-C3 N4 and derive an optimum synthesis condition for improving photocatalytic activities of the g-C3 N4. In this study, novel and versatile g-C3 N4 nanosheets were synthesized by the simple thermal pyrolysis of urea. In the synthesis process, the pyrolysis temperature and the heating rate, which can have the most significant influence on the structures and properties of g-C3 N4, were set as variables, and the effects were systematically investigated. When synthesized at a relatively high temperature, the amount of material being synthesized is reduced, however it has been found to represent optical properties suitable for highly efficient photo-catalyst by the increase in the thickness and defects formed in the g-C3 N4nanosheets. The photocatalytic degradation experiment of MB dyes indicated that the highest degradation of 95.2% after the reaction for 120 min was achieved on the g-C3 N4 nanosheets synthesized at 650°C.
7
Content available Dilatometric Analysis of the Sintering Behavior of Bi2Te3 Thermoelectric Powders
Han Ju-Yeon, Byun Jong Min, Lee Young-In, Choi Byung Joon, Kim Hogyoung, Oh Sung-Tag
Archives of Metallurgy and Materials
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2020
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Vol. 65, iss. 3
1117--1120
EN
The sintering behavior of p-type bismuth telluride powder is investigated by means of dilatometric analysis. The alloy powders, prepared by ball milling of melt-spun ribbons, exhibit refined and flake shape. Differential thermal analysis reveals that the endothermic peak at about 280°C corresponds to the melting of bismuth, and peaks existing between 410°C and 510°C are presumably due to the oxidation and crystallization of the powder. The shrinkage behavior of ball-milled powders was strongly dependent of heating rate by the thermal effect exerted on specimens. In the case of 2°C/min, the peak temperature for the densification is measured at 406°C, while the peak temperature at a heating rate of 20°C/min is approximately 443°C. The relative density of specimen pressureless-sintered at 500°C exhibited relatively low value, and thus further study is required in order to increase the density of sintered body.
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