• Title/Summary/Keyword: SiC boundary

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Observation of Densification Behavior during the Sintering of Ni-added $MoSi_2$ Powder Compacts (Ni을 첨가한 $MoSi_2$분말성형체의 소결시 치밀화거동의 관찰)

  • 이승익
    • Journal of Powder Materials
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    • v.4 no.4
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    • pp.298-303
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    • 1997
  • The activated sintering behavior of $MoSi_2$ powder compacts with addition of 0.5 and 1.0 wt.%Ni during the sintering under As atmosphere was studied. The shrinkage was measured and the microstructures were observed by SEM (scanning electron microscopy) and BEI (backscattered electron image) along with the phase analysis by EDS during heating up to 155$0^{\circ}C$ and holding for various time at 155$0^{\circ}C$. The most of shrinkage occurred upon heating and 92% of theoretical density was attained after sintering for 1 hr at 155$0^{\circ}C$. However, little shrinkage ensued even for prolonged sintering over 1 hr at 155$0^{\circ}C$. A liquid film formed at about 135$0^{\circ}C$ along necks and grain boundaries. The polyhedral grain structure composed of $(Mo,Ni)_5Si_3$and $Ni_2Si$ across the $MoSi_2$ grain boundary developed at 155$0^{\circ}C$. It was concluded that the activated sintering of $MoSi_2$ powder by Ni led to the diffusion of Si into Ni decreasing the liquidus temperature and the enhanced diffusion of Mo and Si through such a liquid phase and/or interboundary of $(Mo,Ni)_5Si_3$.

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Radiation damage analysis in SiC microstructure by transmission electron microscopy

  • Idris, Mohd Idzat;Yoshida, Katsumi;Yano, Toyohiko
    • Nuclear Engineering and Technology
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    • v.54 no.3
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    • pp.991-996
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    • 2022
  • Microstructures of monolithic high purity SiC and SiC with sintering additives after neutron irradiation to a fluence of 2.0-2.5 × 1024 n/m2 (E > 0.1 MeV) at 333-363 K and after post-irradiation annealing up to 1673 K were observed using a transmission electron microscopy. Results showed that no black spot defects or dislocation loops in SiC grains were found after the neutron irradiation for all of the specimens owing to the moderate fluence at low irradiation temperature. Thus, it is confirmed that these specimens were swelled mostly by the formation of point defects. Black spots and small dislocation loops were discovered only after the annealing process in PureBeta-SiC and CVD-SiC, where the swelling almost diminished. Anomalous-shaped YAG grains were found in SiC ceramics containing sintering additives. These grains contained dense black spots defects and might lose crystallinity after the neutron irradiation, while these defects may annihilate by recrystallization during annealing up to 1673 K. Amorphous grain boundary phase was also presented in this ceramic, and a large part of it was crystallized through post-irradiation annealing and could affect their recovery behavior.

Friction and Wear of Ceramic-Steel Pairs in Boundary-Lubricated and Unlubricated Line-Contact Sliding (경계윤활 및 무윤활 상태에서 선접촉을 하는 세라믹과 강의 마찰과 마멸 특성)

  • 이영제;김영호;장선태
    • Tribology and Lubricants
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    • v.12 no.3
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    • pp.12-25
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    • 1996
  • The friction and wear behaviors of ceramics against steels with lubricants were investigated and compared with those observed in air. Lubrications wbre done by a water and a commercial engine oil as received. The investigated ceramics were $Al_{2}O_{3}$, SiC, and $Si_{3}N_{4}$. Steels with 0.2 wt.% C were heat treated to obtain tempered structure. A cylinder-on-plate tribometer with rotated sliding motion was used to carry out the experiments. In the experiments reported here, the ranges of different testing speeds and loads were used. It was found that the friction and wear characteristics of tested pairs were significantly influenced by environments. In water and oil environments the wear of ceramics was reduced from 10$^{-6}$ g/s down to 10$^{-8}$ g/s in dry sliding at the same values of the frictional power which are the products of the friction coefficient, the load and the sliding speed. SiC showed excellent wear resistant behavior in water sliding, which was the lowest among tested ceramics, but it was, very poor in oils. In case of $Si_{3}N_{4}$, the wear rates were very low under oil environment, but the highest in water. The wear rates of $Al_{2}O_{3}$ were very low in both lubricating conditions at low values of the frictional power, but high at high values of the frictional power.

Measurement of Elastic Modulus of Structural Ceramics by Acoustic Resonance Method (공진법을 이용한 구조용 세라믹의 탄성계수 측정)

  • An, Bong-Yeong;Kim, Yeong-Gil;Lee, Seung-Seok
    • Korean Journal of Materials Research
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    • v.5 no.3
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    • pp.268-274
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    • 1995
  • 세라믹재료의 동탄성계수 측정을 위한 공진주파수 측정장치를 구성하였다. 구조용 세라믹 재료로 이용되는 $Al_{2}$O_{3}$, SiC, $Si_{3}$N_{4}$의 온도를 120$0^{\circ}C$까지 5$0^{\circ}C$의 온도간격으로 올리면서 torsional resonant frequency와 flexural resonant frequency를 측정하고, 측정된 공진주파수로부터 각 재료의 탄성계수를 구하였다. SiC의 경우는 120$0^{\circ}C$의 온도까지 탄성계수가 선형적으로 감소하였으나, $Al_{2}$O_{3}$와 $Si_{3}$N_{4}$의 경우에는 각각 100$0^{\circ}C$와 80$0^{\circ}C$까지는 선형적으로 감소하나, 그 이상의 온도에서는 탄성게수의 감소폭이 증가하는 현상을 보였다. 이러한 현상은 다결정재료에서의 grain boundary sliding에 의한 것으로 알려져 있다. 상온에서 공진법으로 측정된 동탄성계수의 측정결과는 초음파법으로 측정한 결과와 비교하였는데, 4% 내에서 서로 일치하는 결과를 보였다.

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Degradation Mechanism of single grain boundary in Zno Varistor (ZnO 바리스터 단입계의 열화 메카니즘)

  • Kim, Jong-Ho;Lim, Keun-Young;Kim, Jin-Sa;Park, Choon-Bae
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.07b
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    • pp.784-789
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    • 2004
  • Bulk ZnO varistor based on Matsuoka, which varied $SiO_2$ addition has fabricated by standard ceramic process. The micro-electrode, which fabricated for investigation on degradation property of the Single Grain Boundary of ZnO varistor, has sticked by lithography semiconductor process. The values of AC degradation has measured with 150% operating voltage in varistor threshold with 120 minute in 60Hz. In here we observed V-I and V-C property in every 30minute. The operating voltage of Single Grain Boundary has shown in variable patterns in the characteristic of V-I Property. By increasing the $SiO_2$ contents, operating value has also increased and dominated on degradation proper. In EPMA analysis, we know that added $SiO_2$ was nearly distributed at the Grain Boundary. $SiO_2$ has gradually distributed in Grain Boundary condition during the process of crystal growth. It contributes to degradation depression and decision of operating voltage. We also demonstrated for using practical application and performance on distribution random loop based on V-I Properties in Single-Grain-Boundary.

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Application of 3-dimensional phase-diagram using FactSage in C3H8-SiCl4-H2 System (C3H8-SiCl4-H2 시스템에서 FactSage를 이용한 압력-조성-온도 3차원 상평형도의 응용)

  • Kim, Jun-Woo;Kim, Hyung-Tae;Kim, Kyung-Ja;Lee, Jong-Heun;Choi, Kyoon
    • Journal of the Korean Ceramic Society
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    • v.48 no.6
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    • pp.621-624
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    • 2011
  • In order to deposit a homogeneous and uniform ${\beta}$-SiC films by chemical vapor deposition, we constructed the phase-diagram of ${\beta}$-SiC over graphite and silicon via computational thermodynamic calculation considering pressure(P), temperature(T) and gas composition(C) as variables in $C_3H_8-SiCl_4-H_2$ system. During the calculation, the ratio of Cl/Si and C/Si is maintained to be 4 and 1, respectively, and H/Si ratio is varied from 2.67 to 15,000. The P-T-C diagram showed very steep phase boundary between SiC+C and SiC region perpendicular to H/Si axis and also showed SiC+Si region with very large H/Si value of ~6700. The diagram can be applied not only to the prediction of the deposited phase composition but to compositional variation due to the temperature distribution in the reactor. The P-T-C diagram could provide the better understanding of chemical vapor deposition of silicon carbide.

Reaction Synthesis and Mechanical Properties of $B_4C$-based Ceramic Composites

  • Han, Jae-Ho;Park, Sang-Whan;Kim, Young-Do
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1080-1081
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    • 2006
  • In this investigation, $B_4C$ based ceramic composites were fabricated by in-situ reaction hot pressing using $B_4C$, TiC SiC powder as starting materials. The reaction synthesized composites by hot pressing at $1950^{\circ}C$ was found to posses very high relative density. The reaction synthesized $B_4C$ composites comprise $B_4C$, $TiB_2$, SiC and graphite by the reaction between TiC and $B_4C$. The newly formed $TiB_2$ and graphite was embedded both inside grain and at grain boundary $B_4C$. The mechanical properties of reaction synthesized $B_4C-TiB_2-SiC$-graphite composites were more enhanced compared to those of monolithic $B_4C$.

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A Study on the Grain Growth and Structure Properties of LPCVD Films Using $Si_2H_6$ GAS ($Si_2H_6$를 이용한LPCVD 실리콘 박막의 결정 성장 및 구조적 성질에 관한 연구)

  • 홍찬희;박창엽
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.40 no.7
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    • pp.670-674
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    • 1991
  • This paper presents the material properties of LPCVD silicon films formed using Si2H6 gas at various deposition temperatures. To study the structural properties depending on the deposition temperature, XRD, EBD and TEM analyses were used. The maximum grain size in this experiment was obtained at the deposition temperature of 485ø C. It is discussed that LPCVD films formed below the deposition temperature of 485ø C are promising for low temperature TFT applications. The enhancement of the film characteristics results from the reduction of grain boundary density. We also observed that the film properties of Si2H6 at 600ø C was quite different from those of Si H4 at 600ø C. It has shown that the grain structure from a TEM analysis was elliptical and not dependent on the deposition temperature.

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Effect of Alumina Content on the Hot Corrosion of SiC by NaCl and Na2SO4 (NaCl과 Na₂SO₄에 의한 SiC 고온 부식에 미치는 Alumina 첨가량의 영향)

  • 이수영
    • Journal of the Korean Ceramic Society
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    • v.28 no.8
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    • pp.625-625
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    • 1991
  • The specimens for the corrosion test were made by hot-pressing of SiC power with 2 wt% Nl2O3 and 10wt% Al2O3 additions at 2000℃ and 2050℃. The specimens were corroded in 37 mole% NaCl and 63 mole% Na2SO4 salt mixture at 1000℃ up to 60 min. SiO2 layer was formed on SiC and then this oxide layer was dissolved by Na2O ion in the salt mixture. The rate of corrosion of the specimen containing 10 wt% Al2O3 was slower than that of the specimen containing 2 wt% Al2O3. This is due to the presence of continuous grain boundary phase in the specimen containing 10 wt% Al2O3. The oxidation of SiC produced gas bubbles at the SiC-SiO2 interface. The rate of corrosion follows a linear rate law up to 50 min. and then was accelerated. This acceleration is due to the disruption oxide layer by the gas evolution at SiC-SiO2 interface. Pitting corrosion has found at open pores and grain boundaries.

$MgB_2$ Thin Films on SiC Buffer Layers with Enhanced Critical Current Density at High Magnetic Fields

  • Putri, W.B.K.;Tran, D.H.;Kang, B.;Lee, N.H.;Kang, W.N.
    • Progress in Superconductivity
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    • v.14 no.1
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    • pp.30-33
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    • 2012
  • We have grown $MgB_2$ superconducting thin films on the SiC buffer layers by means of hybrid physical-chemical vapor deposition (HPCVD) technique. Prior to that, SiC was first deposited on $Al_2O_3$ substrates at various temperatures from room temperature to $600^{\circ}C$ by using the pulsed laser deposition (PLD) method in a vacuum atmosphere of ${\sim}10^{-6}$ Torr pressure. All samples showed a high transition temperature of ~40 K. The grain boundaries of $MgB_2$ samples with SiC layer are greater in amount, compare to that of the pure $MgB_2$ samples. $MgB_2$ with SiC buffer layer samples show interesting change in the critical current density ($J_c$) values. Generally, at both 5 K and 20 K measurements, at lower magnetic field, all $MgB_2$ films deposited on SiC buffer layers have low $J_c$ values, but when they reach higher magnetic fields of nearly 3.5 Tesla, $J_c$ values are enhanced. $MgB_2$ film with SiC grown at $600^{\circ}C$ has the highest $J_c$ enhancement at higher magnetic fields, while all SiC buffer layer samples exhibit higher $J_c$ values than that of the pure $MgB_2$ films. A change in the grain boundary morphologies of $MgB_2$ films due to SiC buffer layer seems to be responsible for $J_c$ enhancements at high magnetic fields.