Metallic Si 첨가가 SiC 분말 합성에 미치는 영향

Abstract

SiC는 우수한 열, 기계적 특성으로 널리 사용되는 비 산화물계 세라믹 재료중 하나이다. 또한, 최근 고 순도 SiC는 고출력, 고주파, 고온 전자재료 로의 적용이 연구되고 있으며, 거의 모든 SiC 제품이 SiC 분말로부터 제조되기 때문에 입도, 크기 등이 제어된 고 순도 SiC 분말의 중요성이 커지고 있다. 본 연구는 Sol-gel공정과 carbothermal reduction공정을 이용한 SiC 분말 합성공정에서 SiC 합성온도를 감소시키며 합성되는 SiC분말의 크기 및 응집을 효과적으로 제어할 수 있는 SiC 분말 합성 공정을 개발하는 것을 목적으로 진행되었다. Carbon 및 Si source로 각 각 페놀레진과 Tetraethyl orthosilicate ( TEOS )를 사용하여 sol-gel 공정을 사용하여 다양한 C/Si 몰비를 갖는 SiO2-C hybrid precursor를 제조하였으며, carbothermal reduction 공정을 이용하여 SiC 분말을 합성하였다. 또한 carbothermal reduction 반응에서 excess carbon 및 metallic silicon 분말의 첨가가 합성되는 SiC 분말의 크기와 응집 및 SiC 합성온도에 미치는 영향을 조사하였다. SiO2-C hybrid precursor를 사용하여 carbothermal reduction 공정에 의한 β-SiC 분말 합성공정에서는 C/Si 몰비가 1.6인 SiO2-C hybrid precursor을 사용하여 1600℃ 이상의 온도에서 carbothermal reduction이 이루어졌을 때 순수한 β-SiC 분말이 합성 되었으며 합성된 분말의 크기는 합성온도가 증가될수록 증가되었다. C/Si 몰비가 1.8~2.5인 SiO2-C hybrid precursor에 Si 분말의 첨가는 Si 과 C 사이에서 직접 탄화 반응에 의해 β-SiC 분말의 합성 온도를 감소시켰으며, SiO2-C hybrid precursor 내 C/Si 몰비가 증가될수록 Si 분말의 첨가 효과는 크게 나타났다. Si 분말이 혼합된 C/Si 몰비가 2.5인 SiO2-C hybrid precursor에서는 1350℃에서 미량의 β-SiC 분말이 합성되며 1400℃ 이상의 온도에서 β-SiC 분말 합성이 이루어졌으며 합성시간이 증가됨에 따라 합성된 β-SiC 결정상의 결정도는 증가하였다.| Silicon carbide (SiC) is the most widely applied non-oxide ceramic to industries due to its good thermo-mechanical properties such as high melting point, high temperature strength, high wear resistance, high chemical resistance and high thermal shock resistance. In addition, SiC with high purity has been recently noticed as an attractive material for high power, high frequencies and high temperature electronics applications since SiC has excellent unique physical and chemical properties even under severe conditions such as wide band gap, high thermal conductivity, high breakdown voltage and high forward current density. The objectives of this study is the development of the synthesis process for β-SiC powders using a sol-gel process and a carbothermal process to reduce the synthesis temperature and to control the particle size and particle agglomeration of synthesized β-SiC powders. The phenol resin and TEOS were used as the starting materials for carbon and Si source. The SiO2-C hybrid precursor with various C/Si mole ratio were fabricated using a sol-gel process. β-SiC powders were synthesized using SiO2-C hybrid precursor with various C/Si mole ratios by a carbothermal reduction process. The effects of excess carbon and the additions of Si to the SiO2-C hybrid precursor on the synthesis temperature and particle size of β-SiC were examined. β-SiC powders were synthesized using SiO2/C hybrid precursor with and without the addition of metallic Si powders. The SiO2/C hybrid precursor with various C/Si mole ratios(1.6~2.5)were prepared by the sol-gel process using TEOS and phenol resin as starting materials. The single phase β-SiC powders were obtained by the carbothermal reduction of the SiO2/C hybrid precursor with C/Si mole ratio of 1.6 above 1600℃ under vacuum atmosphere. Fine β-SiC powders were started to be synthesized by the carbothermal reduction of the SiO2/C hybrid precursor with the addition of metallic Si powders at the temperature above 1350℃ under the vacuum atmosphere. The single phase β-SiC powders were obtained by the carbothermal reduction of the SiO2/C hybrid precursor with C/Si mole ratios of 1.8 and 2.5 above 1500oC under vacuum atmosphere. It was found that the addition of metallic Si powders to the SiO2/C hybrid precursor with excess carbon reduced the temperature for the synthesis of β-SiC powders as low as 1350℃. The synthesis temperature for β-SiC were seemed to be reduced with increasing the C/Si mole ratio in SiO2-C hybrid precursor by a direct carburization reaction between Si and excess carbon. The particle sizes of synthesized β-SiC powders using SiO2-C hybrid precursors with excess carbon were reduced with increasing C/Si mole ratio. With increasing carbothermal reduction time, the particle size of synthesized β-SiC powders were reduced and the crystallinity of synthesized β-SiC powders were increased.; Silicon carbide (SiC) is the most widely applied non-oxide ceramic to industries due to its good thermo-mechanical properties such as high melting point, high temperature strength, high wear resistance, high chemical resistance and high thermal shock resistance. In addition, SiC with high purity has been recently noticed as an attractive material for high power, high frequencies and high temperature electronics applications since SiC has excellent unique physical and chemical properties even under severe conditions such as wide band gap, high thermal conductivity, high breakdown voltage and high forward current density. The objectives of this study is the development of the synthesis process for β-SiC powders using a sol-gel process and a carbothermal process to reduce the synthesis temperature and to control the particle size and particle agglomeration of synthesized β-SiC powders. The phenol resin and TEOS were used as the starting materials for carbon and Si source. The SiO2-C hybrid precursor with various C/Si mole ratio were fabricated using a sol-gel process. β-SiC powders were synthesized using SiO2-C hybrid precursor with various C/Si mole ratios by a carbothermal reduction process. The effects of excess carbon and the additions of Si to the SiO2-C hybrid precursor on the synthesis temperature and particle size of β-SiC were examined. β-SiC powders were synthesized using SiO2/C hybrid precursor with and without the addition of metallic Si powders. The SiO2/C hybrid precursor with various C/Si mole ratios(1.6~2.5)were prepared by the sol-gel process using TEOS and phenol resin as starting materials. The single phase β-SiC powders were obtained by the carbothermal reduction of the SiO2/C hybrid precursor with C/Si mole ratio of 1.6 above 1600℃ under vacuum atmosphere. Fine β-SiC powders were started to be synthesized by the carbothermal reduction of the SiO2/C hybrid precursor with the addition of metallic Si powders at the temperature above 1350℃ under the vacuum atmosphere. The single phase β-SiC powders were obtained by the carbothermal reduction of the SiO2/C hybrid precursor with C/Si mole ratios of 1.8 and 2.5 above 1500oC under vacuum atmosphere. It was found that the addition of metallic Si powders to the SiO2/C hybrid precursor with excess carbon reduced the temperature for the synthesis of β-SiC powders as low as 1350℃. The synthesis temperature for β-SiC were seemed to be reduced with increasing the C/Si mole ratio in SiO2-C hybrid precursor by a direct carburization reaction between Si and excess carbon. The particle sizes of synthesized β-SiC powders using SiO2-C hybrid precursors with excess carbon were reduced with increasing C/Si mole ratio. With increasing carbothermal reduction time, the particle size of synthesized β-SiC powders were reduced and the crystallinity of synthesized β-SiC powders were increased.