• Title/Summary/Keyword: Vanadium carbide

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

  • KIM, JUNG-SU;CHOI, SEONG-SHIN;CHOI, JEONG-GIL
    • Transactions of the Korean hydrogen and new energy society
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    • v.31 no.1
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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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    • v.1 no.3
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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.

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

  • Lee, B.K.;Nam, T.W.
    • Journal of the Korean Society for Heat Treatment
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    • v.13 no.2
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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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Vanadium-doped semi-insulating SiC single crystal growth by using porous graphite (다공성 흑연 소재를 이용한 바나듐 도핑된 반절연 SiC 단결정 성장의 특성 연구)

  • Lee, Dong-Hun;Kim, Hwang-Ju;Kim, Young-Gon;Choi, Su-Hun;Park, Mi-Seon;Jang, Yeon-Suk;Lee, Won-Jae;Jung, Kwang-Hee;Kim, Tae-Hee;Choi, Yi-Sik
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.26 no.6
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    • pp.215-219
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    • 2016
  • Vanadium-doped SiC crystals have been grown by using a porous graphite inner crucible filled with vanadium carbide (VC) and by using a porous graphite plate and SiC + VC powders, respectively. Semi-insulating SiC crystals were grown onto the 6H-SiC seed crystals by PVT (Physical Vapor Transport) method. The grown crystals were indicated to be 6H-SiC polytype by XRD. As result of SIMS analysis, vanadium-rich precipitates were observed when the vanadium concentration was relatively higher than the maximum solubility of vanadium ($3-5{\times}10^{17}cm^{-3}$) in vanadium-doped SiC crystals, which resulted in degradation of crystal quality.

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

  • 김선규;유정광
    • Journal of the Korean institute of surface engineering
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    • v.28 no.6
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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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Effects of Mo, V addition on Linear Thermal Expansion Coefficient and Hardness of Low Thermal Expansion Cast Steel (주강계 저열팽창 주조합금의 열팽창 계수와 경도에 미치는 Mo, V 첨가의 영향)

  • Kim, Young-Han;Yoon, Eui-Park;Moon, Byoung-Moon;Hong, Young-Myung
    • Journal of Korea Foundry Society
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    • v.18 no.5
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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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Effect of HAZ Softening Zone on Creep Rupture Properties of 1.0Cr-1.0Mo-0.25V Turbine Steels -Part II : Carbide Morphology- (1.0Cr-1.0Mo-0.25V 터어빈 로터강의 열영향부 연화층이 크립 파단 특성에 미치는 영향 - Part II : 탄화물 형태 -)

  • ;Indacochea, J. E.
    • Journal of Welding and Joining
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    • v.15 no.1
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    • pp.101-108
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    • 1997
  • In repaired weldment of ASTM A-470 class 8 high pressure stream turbine rotor steel, creep rupture life was studied in relation with carbide morphology. Carbides were identified using carbide extraction replica method. A retired rotor has molybdenum rich carbide $M_2C$, lndacochea vanadium rich carbide $M_4C_3$, and chromium rich carbides $M_{23}C_6$and $M_7C_3$. Weldments ruptured at ICHAZ showed that some of carbides have been transformed into spherical types of coarsened carbides at ruptured area. Those carbides were revealed as molybdenum rich $M_6C$ carbide and they provided cavitation sites due to molybdenum depletion around $(M_6C)$ carbide. However coarsened $M_6C$ and $M_{23}C_6$ carbides were observed at ruptured area in case of ruptured at CGHAZ.

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Effects of experimental conditions on synthesis of titanium carbide crystallites

  • Choi, Jeong-Gil
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.20 no.2
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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
    • Proceedings of the KWS Conference
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    • 2002.10a
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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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Effect of Vanadium Addition on the Cavitation Erosion Resistance of Fe-Cr-Ni-Si-C Hardfacing Alloy (Fe-Cr-Ni-Si-C계 경면처리 합금의 Cavitaon Erosion 저항성에 미치는 Vanadium 첨가의 영향)

  • 김경오;김준기;장세기;김선진;강성군
    • Journal of the Korean institute of surface engineering
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    • v.31 no.5
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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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