• Title/Summary/Keyword: ultrafine powder

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Rapid Heating of Ultrafine $Si_3N_4$ Powder Compacts under the Controlled Thermograms (가열이력 제어에 의한 $Si_3N_4$ 미분말 시편의 급속가열)

  • 이형직
    • Journal of the Korean Ceramic Society
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    • v.30 no.3
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    • pp.181-188
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    • 1993

  • The sintering and renitridation behaviors of ultrafine Si3N4 powder compacts, which were heavily oxidized and/or free-Si rich, were investigated with particular attentiion to microstructures. The specimens were heated without restoring to additives and pressure by controlling heating process attained a Xe image apparatus. The effect of particle size, free-Si contents, decomposition and renitridation, were investigated. When fired to 1$650^{\circ}C$ within 15 sec and then immediately held at 135$0^{\circ}C$ for 10min N2 atmosphere, significant densification took place in the limited region, in addition to decreasing oxygen contents to less than 0.3wt%. On the other hand, specimens decomposed due to overheating at the initial stage were rapidly renitridated at the relatively lower temperature of the holding stage. And, then, the activation energy for the renitridation was calculated to be 49kcal/mole.

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Synthesis of TiC-Ni Based Cermet Powders and Microstructures of Sintered Compacts Prepared by Reaction Milling (반응밀링법으로 제조한 TiC-NirP 서멧분말제조 및 소결성형체의 미세조직)

  • 최철진
    • Journal of Powder Materials
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    • v.6 no.2
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    • pp.139-144
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    • 1999

  • The pure Ti, Ni and carbon powders were reaction milled to synthesize the TiC-Ni based cermet powders with ultrafine microstructures. After milling, the ultrafine TiC or amorphous Ti-Ni phase was obtained, respectively, according to the milling condition. The effects of milling variables on the synthesizing behavior of the powders were investigated in detail. The sintered TiC-Ni based cermet of the reaction milled powders consisted of very fine TiC of 0.2~1.5$\mu$m, as compared with that of a commercial cermet of 3~5$\mu$m. This demonstrates the potenial of reaction milling as an effective processing route for the preparation of cermet materials.

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Process Control for the Synthesis of Ultrafine Si3N4-SiC Powders by the Hybrid Plasma Processing (Hybrid Plasma Processing에 의한 Si3N4-SiC계 미립자의 합성과정 제어)

  • ;吉田禮
    • Journal of the Korean Ceramic Society
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    • v.29 no.9
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    • pp.681-688
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    • 1992

  • Ultrafine Si3N4 and Si3N4+SiC mixed powders were synthesized through thermal plasma chemical vapor deposition(CVD) using a hybrid plasma, which was characterized by the supersposition of a radio-frequency plasma and arc jet. The reactant SiCl4 was injected into an arc jet and completely decomposed in a hybrid plasma, and the second reactant CH4 and/or NH3 mixed with H2 were injected into the tail flame through double stage ring slits. In the case of ultrafine Si3N4 powder synthesis, reaction efficiency increased significantly by double stage injection compared to single stage one, although crystallizing behaviors depended upon injection speed of reactive quenching gas (NH3+N2) and injection method. For the preparation of Si2N4+SiC mixed powders, N/C composition ratio could be controlled by regulating the injection speed of NH3 and/or CH4 reactant and H2 quenching gas mixtures as well as by adjusting the reaction space.

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