• Title, Summary, Keyword: Carbothermal reduction

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Fabrication of WC/Co composite powder from oxide of WC/Co hardmetal scrap by carbothermal reduction process (WC/Co 초경합금 스크랩 산화물로부터 환원/침탄공정에 의한 WC/Co 복합분말 제조)

  • Lee, Gil-Geun;Lim, Young Soo
    • Journal of Korean Powder Metallurgy Institute
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    • v.25 no.3
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    • pp.240-245
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    • 2018
  • This study focuses on the fabrication of a WC/Co composite powder from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere for the recycling of WC/Co hardmetal. Mixed powders are manufactured by mechanically milling the oxide powder of WC-13 wt% Co hardmetal scrap and carbon black with varying powder/ball weight ratios. The oxide powder of WC-13 wt% Co hardmetal scrap consists of $WO_3$ and $CoWO_4$. The mixed powder mechanically milled at a lower powder/ball weight ratio (high mechanical milling energy) has a more rapid carbothermal reduction reaction in the formation of WC and Co phases compared with that mechanically milled at a higher powder/ball weight ratio (lower mechanical milling energy). The WC/Co composite powder is fabricated at $900^{\circ}C$ for 6 h from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere. The fabricated WC/Co composite powder has a particle size of approximately $0.25-0.5{\mu}m$.

Growth of SiC Nanowire Using Carbothermal Reduction Method (열탄화법을 사용한 탄화규소 나노와이어의 성장)

  • Rho, Dae-Ho;Kim, Jae-Soo;Byun, Dong-Jin;Yang, Jae-Woong;Kim, Na-Ri
    • Korean Journal of Materials Research
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    • v.13 no.10
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    • pp.677-682
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    • 2003
  • SiC nanowires were synthesized by carbothermal reduction using metal catalysts. Synthesized nanowires had mean diameters of 30∼50 nm and several $\mu\textrm{m}$ length. The kind of catalysts affects form of SiC nanowire because of difference of growth mechanisms. These differences were made by catalyst's physical property and relative activities to the source gas. Ni acted a conventional catalyst of VLS growth mechanism. But, Case of Fe, SiC nanowire was grown by stable VLS growth mechanism without relation of growth conditions. SiC nanowire was grown by two step growth model using Cr catalyst. Conversion ratios to the SiC nanowire were increased with growth conditions. Case of Cr, conversion ratio was about 45% that was higher than other catalyst used. This high conversion ratio was obtained by the addition VS growth to radial direction on the as-grown nanowires.

Synthesis of Aluminum Nitride Powder from Aluminum Hydroxide by Carbothermal Reduction-Nitridation (알루미나 수화물로부터 탄소환원질화법에 의한 질화알루미늄 분말의 합성)

  • 황진명;정원중;최상욱
    • Journal of the Korean Ceramic Society
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    • v.31 no.8
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    • pp.893-901
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    • 1994
  • In this study, AlN powder of fine particle size and of high purity was synthesized by the carbothermal reduction-nitridation of monodisperse, spherical Al(OH)3 which had been prepared by sol-gel method using Al(O-sec-C4H9)3 as the starting material. Depending on the mixing order and kinds of reducing agents, the optimum condition for the preparation of AlN was determined as follows. AlN single-phase was produced by the carbothermal reduction-nitridation of (1) Benzene-washed Al(OH)3 and the reducing agent, carbon, which was mixed in a ball mill: for 5 hours at 140$0^{\circ}C$ under NH3 atmosphere; (2) The mixture prepared by hydrolysis of alkoxide solution into which carbon had been dispersed beforehand: for 5 hours at 135$0^{\circ}C$ ; (3) Al(OH)3 Poly(furfuryl alcohol) composite powder: for 2.5 hours at 135$0^{\circ}C$; (4) The mixture of Al(OH)3 and polyacrylonitrile: for 5 hours at 140$0^{\circ}C$. Addition of CaF2 increased the nitridation rate when carbon or polyacrylonitrile was used as the reducing agent; but it had no effect on the nitridation rate when furfuryl alcohol was used as the reducing agent.

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Production of Fine ZnO Powders by Carbothermal Reduction

  • Choi, Heon-Jin;Lee, June-Gunn;Jung, Kwang-Taik;Kim, Ki-Hwan
    • The Korean Journal of Ceramics
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    • v.4 no.4
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    • pp.304-310
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    • 1998
  • Carbothermal reduction has been one of the important processes for the production of ceramic raw materials such as silicon carbide, silicon nitride, boron carbide, etc. The process has also been one of several trials for the recovery of ZnO from ZnO-containing waste. It usually involves two consecutive steps: the evolution of Zn vapor and its oxidation with air. In this study a ZnO-containing raw material is reduced by carbon at $1250^{\circ}C$ and the evolved Zn vapor is oxidized with air, resulting in fine powders of ZnO. computer programs, THERMO and PYROSIM developed by MINTEK, are used to simulate the process thermodynamically and the results are compared with the experimental results. It is shown that the ZnO-containing raw material can be reduced and can form fine ZnO with the yield as high as 98.7% under a proper condition. Based on these results, a process is engineered for the production of ZnO in a rotary kiln at a rate of 3 tons/day. The produced ZnO powders show properties suitable to the usual applications in ceramic industries with a purity of > 95wt% and an average particle size of ∼3${\mu}m$.

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Decomposition Behavior of Ferro-Si3N4 for High Temperature Refractory Application (고온 내화물 응용을 위한 질화규소철 (Ferro-Si3N4)의 분해거동)

  • Choi, Do-Mun;Lee, Jin-Seok;Choi, Sung-Churl
    • Journal of the Korean Ceramic Society
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    • v.43 no.9
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    • pp.582-587
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    • 2006
  • Decomposition behavior of $ferro-Si_3N_4$was investigated with varying temperature and holding time in mud components for high temperature refractory applications. Porosities gradually increased with increasing temperature and holding time due to the carbothermal reduction of $Si_3N_4\;and\;SiO_2$. Silicon monoxide (SiO) as a intermediate resulted from evaporation of $Si_3N_4\;and\;SiO_2$ reacted with C sources to generate needle-like ${\beta}-SiC$ and Fe in $Si_3N_4$ acted as a catalyst in order to enhance growth of SiC grain with the preferred orientation. SiC generation yield increased with increasing holding time, all of the $Si_3N_4\;and\;SiO_2$ affected on SiC formation up to 2h. However, SiC generation was only dependent on residual $SiO_2$ over 2h, because the carbothermal reduction reaction of $Si_3N_4$ was no longer possible at that time.

Low Temperature Processing of Porous Silicon Carbide Ceramics by Carbothermal Reduction (탄소열환원 공정을 사용한 다공질 탄화규소 세라믹스의 저온 제조공정)

  • Eom, Jung-Hye;Jang, Doo-Hee;Kim, Young-Wook;Song, In-Hyuck;Kim, Hai-Doo
    • Journal of the Korean Ceramic Society
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    • v.43 no.9
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    • pp.552-557
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    • 2006
  • A low temperature processing route for fabricating porous SiC ceramics by carbothermal reduction has been demonstrated. Effects of expandable microsphere content, sintering temperature, filler content, and carbon source on microstructure, porosity, compressive strength, cell size, and cell density were investigated in the processing of porous silicon carbide ceramics using expandable microspheres as a pore former. A higher microsphere content led to a higher porosity and a higher cell density. A higher sintering temperature resulted in a decreased porosity because of an enhanced densification. The addition of inert filler increased the porosity, but decreased the cell density. The compressive strength of the porous ceramics decreased with increasing the porosity. Typical compressive strength of porous SiC ceramics with ${\sim}70%$ porosity was ${\sim}13 MPa$.

Synthesis of TiC/Co Composite Powder by the Carbothermal Reduction Process (환원/침탄공정에 의한 TiC/Co 복합분말 합성)

  • Lee, Gil-Geun;Ha, Gook-Hyun
    • Journal of Korean Powder Metallurgy Institute
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    • v.16 no.5
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    • pp.310-315
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    • 2009
  • Ultra-fine TiC/Co composite powder was synthesized by the carbothermal reduction process without wet chemical processing. The starting powder was prepared by milling of titanium dioxide and cobalt oxalate powders followed by subsequent calcination to have a target composition of TiC-15 wt.%Co. The prepared oxide powder was mixed again with carbon black, and this mixture was then heat-treated under flowing argon atmosphere. The changes in the phase, mass and particle size of the mixture during heat treatment were investigated using XRD, TG-DTA and SEM. The synthesized oxide powder after heat treatment at 700$^{\circ}C$ has a mixed phase of TiO$_2$ and CoTiO$_3$ phases. This composite oxide powder was carbothermally reduced to TiC/Co composite powder by the solid carbon. The synthesized TiC/Co composite powder at 1300$^{\circ}C$ for 9 hours has particle size of under about 0.4 $\mu$m.

Synthesis of W18O49 Phase by Carbothermal Reduction of Tungsten Oxide and its Field Emission Characteristics

  • Yang, Hyo-Seung;Park, Hoon;Kim, Hyoung-chul;Ahn, Jae-Pyoung;Huh, Moo-Young;Park, Jong-Ku
    • Journal of Korean Powder Metallurgy Institute
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    • v.11 no.3
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    • pp.253-258
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    • 2004
  • We report a carbothermal reduction process for massive synthesis of monolithic W$_{18}$O$_{49}$ phase from tungsten oxide in the presence of carbon source. Carbon black powder was used as a carbon source and added to WO$_3$ by 40 weight percent. Bundles of W$_{18}$O$_{49}$ rods were formed over the temperature range of 80$0^{\circ}C$$^{\circ}C$ to 90$0^{\circ}C$. Pure W$_{18}$O$_{49}$ bundles could be separated from the mixture of W$_{18}$O$_{49}$ and residual carbon black powder. Field emission character of W$_{18}$O$_{49}$ phase was determined using the extracted W$_{18}$O$_{49}$ rods. Flat lamp fabricated from the W$_{18}$O$_{49}$ rods showed the turn-on field of 9.3 V/${\mu}m$.

High Temperature Reaction Behaviors of Oxide Materials with Carbon for Refractory Application (내화물 응용을 위한 산화물 재료들과 탄소와의 고온 반응거동)

  • Choi, Do-Mun;Lee, Jin-Seok;Kim, Nam-Hoon;Choi, Sung-Churl
    • Journal of the Korean Ceramic Society
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    • v.44 no.6
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    • pp.331-337
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    • 2007
  • High temperature reaction behaviors of various oxide materials (such as bauxite, pyrophyllite, mullite and fused silica powders) used in the refractory materials for tap-hole plugging of blast furnace were investigated with varying temperature in the carbon surrounding. Kinetics of carbothermal reduction of $SiO_2$ for forming SiC with high corrosion resistance were strongly dependent on it's crystalline phase. SiC generation yield increased with increasing catalyst amount in oxide regardless of generated SiO gas amount at temperature of $<1500^{\circ}C$. However, in case of fused silica over $1500^{\circ}C$, SiC generation yield was dominantly influenced by SiO amount without catalyst effect. Bauxite showed the most effective carbothermal reduction reaction, since bauxite have a large amount of catalyst and well-dispersed $SiO_2$ phase in oxide matrix.

Synthesis of TiC/Co Composite Powder by the Spray Thermal Conversion of Metallic Salt Solution (금속염용액의 분무열분해에 의한 TiC/Co복합분말 제조)

  • 이길근;문창민;김병기
    • Journal of Korean Powder Metallurgy Institute
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    • v.10 no.4
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    • pp.228-234
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    • 2003
  • In the present study, the focus is on the synthesis of titanium carbide/cobalt composite powder by the spray thermal conversion process using metallic salt solution as the raw materials. Two types of oxide powders of Ti-Co-O system were prepared by the spray drying of two types of metallic salt solutions : titanium chloride-cobalt nitrate and $TiO_2$ powder-cobalt nitrate solutions. These oxide powders were mixed with carbon black, and then these mixtures were carbothermal reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixtures during carbothermal reduction were analysed using XRD and TG-DTA. In the case of using the titanium chloride-cobalt nitrate solution, it could not be obtained TiC/Co composite powder due to contamination of the impurities during the spray drying of the solution. However, in tile case of using the $TiO_2$ powder-cobalt nitrate scullion, TiC-15 wt. %Co composite powder could be synthesized by the spray thermal conversion process. The synthesized TiC-15 wt. %Co composite powder at 120$0^{\circ}C$ for 2 hours has average particle size of 150 nm.