• 제목/요약/키워드: Vanadium carbide

검색결과 28건 처리시간 0.022초

바나듐 탄화물 촉매를 이용한 수소생성용 암모니아 분해반응 (NH3 Decomposition Reaction for Hydrogen Formation Using Vanadium Carbide Catalysts)

  • 김정수;최성신;최정길
    • 한국수소및신에너지학회논문집
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    • 제31권1호
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    • pp.1-7
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    • 2020
  • The synthesis and catalytic activities over vanadium carbides were examined for ammonia decomposition reaction to produce the hydrogen. In particular, the comparison of vanadium nitrides were made on the ammonia decomposition reaction. The experimental data exhibited that BET surface areas ranged from 5.2 ㎡/g to 25.6 ㎡/g and oxygen uptake values varied from 3.8 μmol/g to 31.3 μmol/g. It is general that vanadium carbides (VC) were observed to be superior to vanadium nitrides for ammonia decomposition reaction. The primary reason for these differences were thought to be related to the extent of electronegativity between these materials. Most of vanadium carbide crystallites were exceeded by Pt/C crystallite. We assumed that the activities for vanadium carbide crystallites (VC) were comparable to or even higher than that determined for the Pt/C crystallite.

Characterization of vanadium carbide coating deposited by borax salt bath process

  • Aghaie-Khafri, M.;Daemi, N.
    • Advances in materials Research
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    • 제1권3호
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    • pp.233-243
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    • 2012
  • Thermal reactive diffusion coating of vanadium carbide on DIN 2714 steel substrate was performed in a molten borax bath at $950-1050^{\circ}C$. The coating formed on the surface of the substrate had uniform thickness ($1-12{\mu}m$) all over the surface and the coating layer was hard (2430-2700 HV), dense, smooth and compact. The influence of the kinetics parameters, temperature and time, has been investigated. Vanadium carbide coating was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction analysis (XRD). The corrosion resistance of the coating was evaluated by potentiodynamic polarization in 3.5% NaCl solution. The results obtained showed that decrease of coating microhardness following increasing time and temperature is owing to the coarsening of carbides and coating grain size.

용융 붕사욕 침지법에 의해 금형용 강에 형성된 VC coating층의 밀착성과 내마모성에 관한 연구 (A study on Adhesion and Wear Resistance of Vanadium Carbide Coating on Die Steels by Immersing in Molten Borax Bath)

  • 이병권;남태운
    • 열처리공학회지
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    • 제13권2호
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    • pp.71-84
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    • 2000
  • A study on adhesion and wear resistance of VC(vanadium carbide) coating on die steels, STD11 and STD61, has been carried out. The VC coating on the die steels was made by immersing them in molten borax bath, a kind of TRD(thermo-reactive deposition and diffusion). Adhesion strength and wear resistance were investigated using scratch test, indentation test and plate-disc test(Ogoshi type) respectively. The influence of sliding distance on the amount of wear has been determined and dominant wear mechanisms has been characterized using optical microscopy, scanning electron microscopy and EDS spectroscopy. The critical adhesion strength($L_c$) between VC coating layer and substrate(STD11) was increased to 60N($L_c$) in the scratch test. In the case of STD61, the strength increased to 24N. The wear resistance of VC coated die steels was excellent because the diffusion layer formed just below the coating layer. The dominant wear mechanism was identified as adhesive wear for VC coating die steels which were worn by combination of cracking and plucking of VC fragments and disc.

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다공성 흑연 소재를 이용한 바나듐 도핑된 반절연 SiC 단결정 성장의 특성 연구 (Vanadium-doped semi-insulating SiC single crystal growth by using porous graphite)

  • 이동훈;김황주;김영곤;최수훈;박미선;장연숙;이원재;정광희;김태희;최이식
    • 한국결정성장학회지
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    • 제26권6호
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    • pp.215-219
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    • 2016
  • 본 연구에서는 다공성 흑연 캡슐에 Vanadium carbide(VC) 분말을 채워 성장시킨 방법과 SiC 분말과 VC 분말을 혼합하여 다공성 흑연판을 그 위에 덮은 후 성장시키는 방법으로 진행하였으며, 성장된 결정들은 여러 분석방법을 사용하여 각각의 특성들을 관찰하였다. 반절연 SiC 성장은 6H-SiC 종자 결정을 사용하여 PVT(Physical Vapor Transport)법으로 성장을 진행하였다. 반절연으로 성장된 SiC 결정은 XRD를 이용하여 6H-SiC인 것을 확인하였으며, SIMS 분석결과 바나듐 도핑 농도가 바나듐 용해의 한계값 보다 높을 경우 석출물이 발생되며, 결정 품질 저하의 원인이 됨을 확인할 수 있었다.

질화후 붕사욕 침적에 의한 강의 내마모성 피복층 형성에 관한 연구 (Formation of Wear Resistant Layer on Steel by Immersion in Borax Bath After Nitriding)

  • 김선규;유정광
    • 한국표면공학회지
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    • 제28권6호
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    • pp.361-367
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    • 1995
  • When steels are heated at $1000^{\circ}C$ in a fused borax bath containing $V_2O_5$ and $B_4C$powders, vanadium carbide layers are formed on the steel surfaces. Since a decrease in carbon concentration and in microhardness in the substrate just below the carbide layer has been observed, gas nitrocarburizing and vanadium carbide forming processes were combined to form a V(C,N) type layer which prevented the decrease in carbon concentration in the substrate. EPMA analysis was done for this V(C,N) type layer. Hardness just below the layer and wear resistance properties of such treated specimens were investigated.

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주강계 저열팽창 주조합금의 열팽창 계수와 경도에 미치는 Mo, V 첨가의 영향 (Effects of Mo, V addition on Linear Thermal Expansion Coefficient and Hardness of Low Thermal Expansion Cast Steel)

  • 김영한;윤의박;문병문;홍영명
    • 한국주조공학회지
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    • 제18권5호
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    • pp.467-473
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    • 1998
  • For enhancing the mechanical properties of LTE (low thermal expansion) cast steel, systematic researches have been carried out. The effects of alloying elements such as vanadium, molybdenum and carbon on the hardness and linear thermal expansion coefficient were investigated. In the range of $0.5{\sim}2.3\;wt%$ carbon, addition of 1.73 wt% carbon caused hardness increase due to the formation of eutectic carbide having high hardness but over the range of 1.73 wt% carbon, hardness was decreased. Thermal expansion coefficient increases with carbon contents. In the LTE cast steel containing 0.6 wt% carbon, hardness increased up to 1.96 wt% vanadium addition. But over the range of 1.96 wt% vanadium hardness was decreased by coarse eutectic carbide. Thermal expansion coefficient of LTE cast steel containing 0.6 wt%carbon moderately increased with increasing vanadium contents. There was no significant variation of hardness and thermal expansion coefficient according to molybdenum content in LTE cast steel.

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1.0Cr-1.0Mo-0.25V 터어빈 로터강의 열영향부 연화층이 크립 파단 특성에 미치는 영향 - Part II : 탄화물 형태 - (Effect of HAZ Softening Zone on Creep Rupture Properties of 1.0Cr-1.0Mo-0.25V Turbine Steels -Part II : Carbide Morphology-)

  • 오영근
    • Journal of Welding and Joining
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    • 제15권1호
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    • pp.101-108
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    • 1997
  • 손상된 터어빈 로터강의 보수 용접에 있어서 용접부의 크립 파단 수명과 탄화물간의 관계가 연구되었다. 탄화물은 탄화물 추출 복제법을 이용하여 확인되었으며 로터강에는 Molybdenum 주성분의$M_2C$, Vanadium 주성분의 $M_4C_3$, 및 Chromium 주성분의 $M_{23}C_6$$M_7C_3$ 탄화물이 존재하였다. 한편 ICHAZ에서 파단된 시험편의 파단면에서는 구상의 조대한 Molybdenum 주성분의 $M_6C$ 탄화물이 발견되었다. 조대한 Molybdenum 주성분의 $M_6C$ 탄화물의 석출은 탄화물 주위에 고용경화 원소인 Molybdenum 농도를 떨어뜨려 기공 발생 원인을 제공하였다. CGHAZ에서 파단된 용접부의 파단면에서는 조대한 $M_6C$$M_{23}C_6$가 발견되었다.

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Effects of experimental conditions on synthesis of titanium carbide crystallites

  • Choi, Jeong-Gil
    • 한국결정성장학회지
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    • 제20권2호
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    • pp.80-84
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    • 2010
  • The temperature-programmed reduction of titanium oxide ($TiO_2$) with pure $CH_4$ was used for the preparation of titanium carbide crystallites. The synthesized materials had the different surface areas, indicating that the structural properties of these materials were strong functions of two different heating rates and space velocity employed. The titanium carbide crystallites were active for $NH_3$ decomposition. Since the reactivity varied with changes in the particle size, ammonia decomposition reactivity over the titanium carbides crystallites appeared to be related to the different active species. The reactivities of titanium carbide crystallites were two and three times lower than those of the vanadium and molybdenum carbide crystallites, respectively. These results suggested that the difference in activities might be related to the degree of electron transfer between metals and carbon.

EVALUATION OF HYDROGEN INDUCED DISBONDING FOR CR-MO-V STEEL/AUSTENITIC STAINLESS OVERLAY

  • Kim, Byung-Hoon;Kim, Dong-Jin;Kim, Jeong-Tae
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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    • pp.211-216
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    • 2002
  • To investigate transition region in welded overlay relating to disbonding crack, the effect of vanadium addition on disbonding of Cr-Mo steels overlay welded with austenitic stainless steel was studied. V modified Cr-Mo steels have a higher resistance to disbonding than V free Cr-Mo steel. One reason is due to the fact that fine vanadium carbide precipated in base metal traps hydrogen and thus decreases the susceptibility to the disbonding. The second is related to the higher stability of the vanadium and stable carbides formed during PWHT, in which the carbon diffusion to the interface is lower than for V free Cr-Mo steel. Decreasing the carbon content at the interface of the weld overlay shows good resistance to the disbonding. Hence, it is important to control the carbon content at the interface of the weld overlay.

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Fe-Cr-Ni-Si-C계 경면처리 합금의 Cavitaon Erosion 저항성에 미치는 Vanadium 첨가의 영향 (Effect of Vanadium Addition on the Cavitation Erosion Resistance of Fe-Cr-Ni-Si-C Hardfacing Alloy)

  • 김경오;김준기;장세기;김선진;강성군
    • 한국표면공학회지
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    • 제31권5호
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    • pp.297-303
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    • 1998
  • The influences of vanadium addition on the cavitation erosion resistance pf Fe-Cr-Ni-Si-C hardfacing alloy were investigated using a vibratory apparatus up to 30 hrs. It was shown that 1wt.%V additioned alloy improved the resistance to cavitation damage. However, further increase in V content up to 2wt.% reduced the cavitation erosion resistance. It was considered that the addition of V developed the cavitation erosion resistance by reducing the stacking fault energy of Fe-Cr-Ni-Si-C alloy. However, the further increase in V content seemed to reduce the cavitation erosion resistance by increasing the matrix/carbide interfacial area, which was the preferential sites of the cavitation damage.

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