W₂C is synthesized through a reaction-sintering process from an ultrafine-W and WC powder mixture using spark plasma sintering (SPS). The effect of various parameters, such as W:WC molar ratio, sintering temperature, and sintering time, on the synthesis behavior of W₂C is investigated through X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis of the microstructure, and final sintered density. Further, the etching properties of a W₂C specimen are analyzed. A W₂C sintered specimen with a particle size of 2.0 μm and a relative density over 98% could be obtained from a W-WC powder mixture with 55 mol%, after SPS at 1700°C for 20 min under a pressure of 50 MPa. The sample etching rate is similar to that of SiC. Based on X-ray photoelectron spectroscopy (XPS) analysis, it is confirmed that fluorocarbon-based layers such as C-F and C-F2 with lower etch rates are also formed.

SiAlON ceramics are used as ceramic cutting tools for heat-resistant super alloys (HRSAs) due to their excellent fracture toughness and thermal properties. They are manufactured from nitride and oxide raw materials. Mixtures of nitrides and oxides are densified via liquid phase sintering by using gas pressure sintering. Rare earth oxides, when used as sintering additives, affect the color and mechanical properties of SiAlON. Moreover, these sintering additives influence the cutting performance. In this study, we have prepared Yb_m/3Si_12-(m+n)Al_m+nO_nN_16-n (m = 0.5; n = 0.5, 1.0) ceramics and manufactured SiAlON ceramics, which resulted in different colors. In addition, the characteristics of the sintered SiAlON ceramics such as fracture toughness and microstructure have been investigated and results of the cutting test have been analyzed.

SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as Si₃N₄, AlN, Al₂O₃, and Yb₂O₃. In this study, we fabricate Yb_m/3Si_12-(m+n)Al_m+nO_nN_16-n (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with β- SiAlON after gas-pressure sintering at 1820°C for 90 min. under 10 atm N₂ pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of 1300°C or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. Yb₂O₃ and SiO₂ are used as the raw starting materials to form ytterbium disilicate (Yb₂Si₂O₇). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., SiO₂, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

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• Fabrication, Microstructure and Adhesive Properties of BCuP-5 Filler Metal/Ag Plate Composite by using Plasma Spray Process
  Seong-June Youn, Young-Kyun Kim, Jae-Sung Park, Joo-Hyun Park, Kee-Ahn Lee
  Journal of Korean Powder Metallurgy Institute.2020; 27(4): 333.     CrossRef

Aluminum nitride (AlN) powder specimens are treated by high-energy bead milling and then sintered at various temperatures. Depending on the solvent and milling time, the oxygen content in the AlN powder varies significantly. When isopropyl alcohol is used, the oxygen content increases with the milling time. In contrast, hexane is very effective at suppressing the oxygen content increase in the AlN powder, although severe particle sedimentation after the milling process is observed in the AlN slurry. With an increase in the milling time, the primary particle size remains nearly constant, but the particle agglomeration is reduced. After spark plasma sintering at 1400°C, the second crystalline phase changes to compounds containing more Al₂O₃ when the AlN raw material with an increased milling time is used. When the sintering temperature is decreased from 1750°C to 1400°C, the DC resistivity increases by approximately two orders of magnitude, which implies that controlling the sintering temperature is a very effective way to improve the DC resistivity of AlN ceramics.

Reaction-bonded silicon carbide (RBSC) is a SiC-based composite ceramic fabricated by the infiltration of molten silicon into a skeleton of SiC particles and carbon, in order to manufacture a ceramic body with full density. RBSC has been widely used and studied for many years in the SiC field, because of its relatively low processing temperature for fabrication, easy use in forming components with a near-net shape, and high density, compared with other sintering methods for SiC. A radiant tube is one of the most commonly employed ceramics components when using RBSC materials in industrial fields. In this study, the mechanical strengths of commercial RBSC tubes with different sizes are evaluated using 3-point flexural and C-ring tests. The size scaling law is applied to the obtained mechanical strength values for specimens with different sizes. The discrepancy between the flexural and C-ring strengths is also discussed.

Lanthanum zirconate, La₂Zr₂O₇, is one of the most promising candidates for next-generation thermal barrier coating (TBC) applications in high efficient gas turbines due to its low thermal conductivity and chemical stability at high temperature. In this study, bulk specimens and thermal barrier coatings are fabricated via a variety of sintering processes as well as suspension plasma spray in lanthanum zirconates with reduced rare-earth contents. The phase formation, microstructure, and thermo-physical properties of these oxide ceramics and coatings are examined. In particular, lanthanum zirconates with reduced rare-earth contents in a La₂Zr₂O₇-4YSZ composite system exhibit a single phase of fluorite or pyrochlore after fabricated by suspension plasma spray or spark plasma sintering. The potential of lanthanum zirconate ceramics for TBC applications is also discussed.

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• Phase Formation and Thermo-physical Properties of Lanthanum/Gadolinium Zirconate with Reduced Rare-earth Contents for Thermal Barrier Coatings
  Sujin Lee, Chang-Sup Kwon, Sung-Min Lee, Yoon-Suk Oh, Hyung-Tae Kim, Sahn Nahm, Seongwon Kim
  Journal of Korean Powder Metallurgy Institute.2015; 22(6): 420.     CrossRef

Rare-earth zirconates, such as lanthanum zirconates and gadolinium zirconates, have been intensively investigated due to their excellent properties of low thermal conductivity as well as chemical stability at high temperature, which can make these materials ones of the most promising candidates for next-generation thermal barrier coating applications. In this study, three compositions, lanthanum/gadolinium zirconates with reduced rare-earth contents from stoichiometric RE₂Zr₂O₇ compositions, are fabricated via solid state reaction as well as sintering at 1600°C for 4 hrs. The phase formation, microstructure, and thermo-physical properties of three oxide ceramics are examined. In particular, each oxide ceramics exhibits composite structures between pyrochlore and fluorite phases. The potential of lanthanum/ gadolinium zirconate ceramics for TBC applications is also discussed.

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• Rare earth zirconate nanostructures: Recent development on preparation and photocatalytic applications
  Sahar Zinatloo-Ajabshir, Masoud Salavati-Niasari, Azam Sobhani, Zahra Zinatloo-Ajabshir
  Journal of Alloys and Compounds.2018; 767: 1164.     CrossRef
• A novel Co-ions complexation method to synthesize pyrochlore La 2 Zr 2 O 7
  Chunhui Xu, Hongyun Jin, Qifeng Zhang, Can Huang, Daifeng Zou, Fujian He, Shuen Hou
  Journal of the European Ceramic Society.2017; 37(8): 2871.     CrossRef
• Fabrication and Characteristics of Thermal Barrier Coatings in the La2O3-Gd2O3-ZrO2System by Using Suspension Plasma Spray with Different Suspension Preparations
  Soyul Lee, Sung-Min Lee, Yoon-Suk Oh, Hyung-Tae Kim, Sahn Nahm, Seongwon Kim
  Journal of the Korean institute of surface engineering.2016; 49(6): 595.     CrossRef

RBSC (reaction-bonded silicon carbide) represents a family of composite ceramics processed by infiltrating with molten silicon into a skeleton of SiC particles and carbon in order to fabricate a fully dense body of silicon carbide. RBSC has been commercially used and widely studied for many years, because of its advantages, such as relatively low temperature for fabrication and easier to form components with near-net-shape and high relative density, compared with other sintering methods. In this study, RBSC was fabricated with different size of SiC in the raw material. Microstructure, thermal and mechanical properties were characterized with the reaction-sintered samples in order to examine the effect of SiC size on the thermal and mechanical properties of RBSC ceramics. Especially, phase volume fraction of each component phase, such as Si, SiC, and C, was evaluated by using an image analyzer. The relationship between microstructures and physical properties was also discussed.

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• Structural and Mechanical Properties of SiC-Rich By-Products of the Metal Grade Si Process
  Thomas Hafner, Jonas Hafner, Frank Kimm, Vira Bovda, Oleksandr Bovda, Oleksandr Kuprin, Anatoliy Pikalov, Kostiantyn Lentsov, Pavlo Schikhaylo, Yriy Onyschuk, Andriy Tarasuk, Viktoriya Podhurska, Bogdan Vasyliv, Oleksandr Shcheretsky, Ihor Vorona, Roman Y
  Materials Science Forum.2024; 1113: 87.     CrossRef
• Effect of Y2O3 Additive Amount on Densification of Reaction Bonded Silicon Carbides Prepared by Si Melt Infiltration into All Carbon Preform
  Kyeong-Sik Cho, Min-Ho Jang
  Korean Journal of Materials Research.2021; 31(5): 301.     CrossRef
• Mechanical Strength Values of Reaction-Bonded-Silicon-Carbide Tubes with Different Sample Size
  Seongwon Kim, Soyul Lee, Yoon-Suk Oh, Sung-Min Lee, Yoonsoo Han, Hyun-Ick Shin, Youngseok Kim
  Journal of Korean Powder Metallurgy Institute.2017; 24(6): 450.     CrossRef

The effects of particle size of Li-Si alloy and LiCl-KCl addition as a binder phase for raw material of anode were investigated on the formability of the thermal battery anode. The formability was evaluated with respect to filling density, tap density, compaction density, spring-back and compressive strength. With increasing particle size of Li-Si alloy powder, densities increased while spring-back and compressive strength decreased. Since the small spring-back is beneficial to avoiding breakage of pressed compacts, larger particles might be more suitable for anode forming. The increasing amount of LiCl-KCl binder phase contributed to reducing spring-back, improving the formability of anode powder too. The control of particle size also seems to be helpful to get double pressed pellets, which consisted of two layer of anode and electrolyte.

FeS₂ has been widely used for cathode materials in thermal battery because of its high stability and current capability at high operation temperature. Salts such as a LiCl-KCl were added as a binder for improving electrical performance and formability of FeS₂ cathode powder. In this study, the effects of the addition of Li₂O in LiCl-KCl binder on the formability of FeS₂ powder compact were investigated. With the increasing amount of Li₂O addition to LiCl-KCl binder salts, the strength of the pressed compacts increased considerably when the powder mixture were pre-heat-treated above 350°C. The heat-treatment resulted in promoting the coating coverage of FeS₂ particles by the salts as Li₂O was added. The observed coating as Li₂O addition might be attributed to the enhanced wettability of the salt rather than its reduced melting temperature. The high strength of compacts by the Li₂O addition and pre-heat-treatment could improve the formability of FeS₂ raw materials.

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• Effects of Particle Size and Binder Phase Addition on Formability of Li-Si Alloy Powder for Thermal Battery Anode
  Sung-Soo Ryu, Hui-Sik Kim, Seongwon Kim, Hyung-Tae Kim, Hae-Won Cheong, Sung-Min Lee
  Journal of Korean Powder Metallurgy Institute.2014; 21(5): 331.     CrossRef