Optimizing Electrical and Mechanical Properties of Reaction-Sintered SiC by using Different-Sized SiC Particles in Preform

전영삼,신현호,박진수,강상원 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.8

A series of reaction-sintered SiC was fabricated from preforms with varying volume fractions of two resin-coated SiC particles of different sizes (63 and 18 μm). The electrical resistivity and mechanical strength were eventually optimized at the small particle volume fraction of 0.3~0.4, at which point the porosity of the preform was minimized. This study experimentally proves that additional processes after the formation of the preform, such as silicon infiltration and reaction sintering, do not apparently alter the optimum volume fraction of the preform packing, predicted by an existing analytical model based on solid packing. Thus, the volume fraction of particles of different sizes can be determined practically through the solid packing model to fabricate RSSCs with optimal properties. A series of reaction-sintered SiC was fabricated from preforms with varying volume fractions of two resin-coated SiC particles of different sizes (63 and 18 μm). The electrical resistivity and mechanical strength were eventually optimized at the small particle volume fraction of 0.3~0.4, at which point the porosity of the preform was minimized. This study experimentally proves that additional processes after the formation of the preform, such as silicon infiltration and reaction sintering, do not apparently alter the optimum volume fraction of the preform packing, predicted by an existing analytical model based on solid packing. Thus, the volume fraction of particles of different sizes can be determined practically through the solid packing model to fabricate RSSCs with optimal properties.

Synthesis and microwave dielectric properties of Li2ZnTi3O8 ceramics by the reaction-sintering process

G.G. Yao 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.1

Li2ZnTi3O8 ceramics were prepared by reaction-sintering process (calcination free). The crystal phase and microstructure were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). A pure phase of Li2ZnTi3O8 ceramics sintered at 1075 o C-1150 o C with cubic spinel structure was confirmed by XRD. The microwave dielectric properties (εr, Qxf) of Li2ZnTi3O8 ceramics were strongly dependent on the densification and grain size. The τf of Li2ZnTi3O8 ceramics was almost independent with the sintering temperatures. In particular, Li2ZnTi3O8 ceramics by reaction-sintering method sintered at 1125 o C for 5 hrs exhibited good combination microwave dielectric properties of εr = 21.7, Q × f = 70 500 GHz (at 7.5 GHz) and τf=−13 ppm/o C.

Fabrication and properties of reaction-bonded SiC prepared by gelcasting

Lifang Nie,Hongyu Gong,Tao Zhang,Yujun Zhang 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.1

The properties of green and reaction-bonded SiC (RBSC) samples prepared by a gelcasting technique are investigated in this paper. The results show that solid loading and monomer content of the suspension in the gelcasting process are the main factors that effect the density and shrinkage of the green bodies. A slurry with a solid loading of 58 vol% was solidified in situ to a green body with a linear shrinkage of 1.1% and flexural strength of 27 ± 2 MPa. SEM micrographs show that the SiC and C particles in the green body were closely compact by a connection of the polymer network. The maximum density and flexural strength of samples reaction sintered at 1700℃ in vacuum were 2.97 g/㎤ and 378 ± 12 MPa respectively. The properties of green and reaction-bonded SiC (RBSC) samples prepared by a gelcasting technique are investigated in this paper. The results show that solid loading and monomer content of the suspension in the gelcasting process are the main factors that effect the density and shrinkage of the green bodies. A slurry with a solid loading of 58 vol% was solidified in situ to a green body with a linear shrinkage of 1.1% and flexural strength of 27 ± 2 MPa. SEM micrographs show that the SiC and C particles in the green body were closely compact by a connection of the polymer network. The maximum density and flexural strength of samples reaction sintered at 1700℃ in vacuum were 2.97 g/㎤ and 378 ± 12 MPa respectively.

A study of a nano-structured Ni-YSZ anode substrate fabricated by a nickel oxidation reaction for SOFCs

Tae Wook Roh 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.6

The performance of solid oxide fuel cells is dominated by their microstructure in the reaction zone which is a three-phase boundary (TPB) among the electrolyte, the electrode and gas phase, which can act as an electrochemically active site for the electrode reaction. In order to improve the performance of the unit cell, a new method was proposed involving the oxidation reaction of nano nickel powder. Furthermore, the nano-microstructure of a nickel/yttria-stabilized zirconia (Ni/YSZ) cermet as an anode substrate was fabricated. The oxidation of nickel was completed at 900 ο C over 2 h; this sintering temperature of the anode substrate was much lower than that of anode substrates including NiO and YSZ starting powder which is about 1450 ο C. The anode substrate was nano-microstructured using Ni nano powder. There was no shrinkage or grain growth after sintering. A homogeneous pore channel was created by supplying air into the anode substrate during the oxidation reaction of nickel without additional pore formers, and the fuel was supplied excellently.

Effective synthesis to fabricate a giant dielectric-constant material CaCu3Ti4O12 via solid state reactions

Wen Xiang Yuan,Wai Ning Mei,Sui Kong Hark 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.5

In this study, we effectively synthesized a giant dielectric-constant material CaCu3Ti4O12 (CCTO) by using a solid-state reaction method that was composed of two main chemical reactions. Comparing with typical calcining conditions, our procedures are much less energy- and time-consuming. When preparing our CCTO, we applied a momentarily high temperature heating at the end of the calcination, then followed it by a typical sintering process. We found this additional heating converts the otherwise mixed-phase products into a pure phase and the CCTO samples prepared this special way possess a large dielectric constant, up to 19,000. In this study, we effectively synthesized a giant dielectric-constant material CaCu3Ti4O12 (CCTO) by using a solid-state reaction method that was composed of two main chemical reactions. Comparing with typical calcining conditions, our procedures are much less energy- and time-consuming. When preparing our CCTO, we applied a momentarily high temperature heating at the end of the calcination, then followed it by a typical sintering process. We found this additional heating converts the otherwise mixed-phase products into a pure phase and the CCTO samples prepared this special way possess a large dielectric constant, up to 19,000.

반응소결법으로 제조한 n형 β-SiC의 열전특성

배철훈(Chul-Hoon Pai) 한국산학기술학회 2019 한국산학기술학회논문지 Vol.20 No.3

SiC는 큰 에너지 밴드 갭을 갖고, 불순물 도핑에 의해 p형 및 n형 전도의 제어가 용이해서 고온용 전자부품 소재로 활용이 가능한 재료이다. 특히 N2 분위기, 2000℃에서 β-SiC 분말로부터 제조한 다공질 n형 SiC 반도체의 경우, 800~1000℃ 에서의 도전율 값이 단결정 SiC와 비교해서 비슷하거나 오히려 높은 값을 나타내었으며, 반면에 열전도율은 치밀한 SiC 세라믹스와 비교시 1/10∼1/30 정도로 낮은 값을 나타내었다. 본 연구에서는 소결온도를 낮추기 위해 n형 β-SiC에 함침 시킨 polycarbosilane (PCS)의 열분해에 의한 반응소결 공정 (1400~1600℃)으로 다공질 소결체를 제작하였다. 함침 및 소결공정(N2 분위기, 1600℃, 3시간)을 반복함에 따라 상대밀도는 크게 증가하지 않았지만 Seebeck 계수 및 도전율은 크게 증가하였다. 본 연구에서의 열전변환 효율을 반영하는 power factor는 고온에서 상압소결 공정으로 제작한 다공질 SiC 반도체에 비해 1/100~1/10 정도 작게 나타났지만, 미세구조 및 캐리어 밀도를 정밀하게 제어하면, 본 연구에서의 반응소결 공정으로 제작한 SiC 반도체의 열전물성은 크게 향상될 것으로 판단된다. Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its large energy band gap and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, electric conductivity of porous n-type SiC semiconductors fabricated from β-SiC powder at 2000℃ in N2 atmosphere was comparable to or even larger than the reported values of SiC single crystals in the temperature region of 800℃ to 1000℃, while thermal conductivity was kept as low as 1/10 to 1/30 of that for a dense SiC ceramics. In this work, for the purpose of decreasing sintering temperature, it was attempted to fabricate porous reaction-sintered bodies at low temperatures (1400-1600℃) by thermal decomposition of polycarbosilane (PCS) impregnated in n-type β-SiC powder. The repetition of the impregnation and sintering process (N2 atmosphere, 1600℃, 3h) resulted in only a slight increase in the relative density but in a great improvement in the Seebeck coefficient and electrical conductivity. However the power factor which reflects the thermoelectric conversion efficiency of the present work is 1 to 2 orders of magnitude lower than that of the porous SiC semiconductors fabricated by conventional sintering at high temperature, it can be stated that thermoelectric properties of SiC semiconductors fabricated by the present reaction-sintering process could be further improved by precise control of microstructure and carrier density.

Fabrication of β-SiAlONs by a Reaction-Bonding Process Followed by Post-Sintering

박영조,노은아,김해두,고재웅 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.5

A cost-effective route to synthesize β-SiAlONs from Si mixtures by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87, in Si6-zAlzOzN8-z without excess liquid phase were selected to elucidate the mechanism of SiAlON formation and densification. For RBSN (reaction-bonded silicon nitride) specimens prior to post-sintering, nitridation rates of more than 90% were achieved by multistep heating to 1400℃ in flowing 5%H₂/95%N₂; residual Si was not detected by XRD analysis. An increase in density was acquired with increasing z values in post-sintered specimens, and this tendency was explained by the presence of higher amounts of transient liquid phase at larger z values. Measured z values from the synthesized β-SiAlONs were similar to the values calculated for the starting compositions. Slight deviations in z values between measurements and calculations were rationalized by a reasonable application of the characteristics of the nitriding and post-sintering processes.

W-WC의 Spark Plasma Sintering에 의한 W₂C의 합성 및 식각특성

오규상,이성민,류성수,Oh, Gyu-Sang,Lee, Sung-Min,Ryu, Sung-Soo 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.4

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 ㎛ and a relative density over 98% could be obtained from a W-WC powder mixture with 55 mol%, after SPS at 1700℃ 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.

Fabrication of SiC Fiber-SiC Matrix Composites by Reaction Sintering

임광영,김영욱,박지연 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.4

This paper presents a new process for producing SiC fiber-SiC matrix (SiC/SiC) composites by reaction sintering. The processing strategy for the fabrication of the SiC/SiC composites involves the following: (1) infiltration of the SiC fiber fabric using a slurry consisting of Si and C precursors, (2) stacking the slurry-infiltrated SiC fiber fabric at room temperature, (3) cross-linking the stacked composites, (4) pyrolysis of the stacked composites, and (5) hot-pressing of the pyrolyzed composites. It was possible to obtain dense SiC/SiC composites with relative densities of >96% and a typical flexural strength of ~400 MPa. This paper presents a new process for producing SiC fiber-SiC matrix (SiC/SiC) composites by reaction sintering. The processing strategy for the fabrication of the SiC/SiC composites involves the following: (1) infiltration of the SiC fiber fabric using a slurry consisting of Si and C precursors, (2) stacking the slurry-infiltrated SiC fiber fabric at room temperature, (3) cross-linking the stacked composites, (4) pyrolysis of the stacked composites, and (5) hot-pressing of the pyrolyzed composites. It was possible to obtain dense SiC/SiC composites with relative densities of >96% and a typical flexural strength of ~400 MPa.

Fabrication of β-SiAlONs by a Reaction-Bonding Process Followed by Post-Sintering

Park, Young-Jo,Noh, Eun-Ah,Ko, Jae-Woong,Kim, Hai-Doo The Korean Ceramic Society 2009 한국세라믹학회지 Vol.46 No.5

A cost-effective route to synthesize $\beta$-SiAlONs from Si mixtures by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87, in $Si_{6-z}Al_zO_zN_{8-z}$ without excess liquid phase were selected to elucidate the mechanism of SiAlON formation and densification. For RBSN (reaction-bonded silicon nitride) specimens prior to post-sintering, nitridation rates of more than 90% were achieved by multistep heating to $1400^{\circ}C$ in flowing 5%$H_2$/95%$N_2$; residual Si was not detected by XRD analysis. An increase in density was acquired with increasing z values in post-sintered specimens, and this tendency was explained by the presence of higher amounts of transient liquid phase at larger z values. Measured z values from the synthesized $\beta$-SiAlONs were similar to the values calculated for the starting compositions. Slight deviations in z values between measurements and calculations were rationalized by a reasonable application of the characteristics of the nitriding and post-sintering processes.