1998 Fiscal Year Final Research Report Summary
Control of Nano-Phase Separated Structure in Fine Amorphou Composite Partucles
| Project/Area Number |
09450247
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic materials/Physical properties
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
HOJO Junichi Kyushu Univ., Fac.Eng., Professor, 工学部, 教授 (20038079)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIDA Michie Kyushu Univ., Fac.Eng., Research Assistant, 工学部, 教務員
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| Project Period (FY) |
1997 – 1998
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| Keywords | Silicon nitride / Boron nitride / Titanium nitride / Composite particle / Phase separation / Nanocomposite |
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| Research Abstract |
(1)Structure of fine composite particles
Fine composite particles were prepared by a vapor phase reaction method : Si_3N_4-BN composite particles in SiCI_4-BCl_3-NH_3-H_2 system and Si_3N_4-TiN composite particles in SiCI4-TiCl4-NH3-H2 system. The particle size was 0.05-0.1mum. The Si_3N_4-BN composite particles were amorphous. It was suggested that Si3N4 and BN were mixed on molecular level. In Si_3N_4-TiN system, TiN crystallites with a size below 10nm were dispersed in amorphous Si_3N_4 particles.
(2)Phase change and crystallization of fine composite particles
The powder compact of fine composite particles was heat-treated at 1200-16000C in N2. The sintering aid of Y_2O_3(6wt%)-Al_2O_3(2wt%) system was used. In Si_3N_4-BN system, although the powder was amorphous even at 1 6000C without sintering aid, beta- Si_3N_4 crystallized at 16000C with sintering aid. IR analysis indicated that Si_3N_4 and BN phases separated with a rise of temperature, and the crystallization was accelerated by sintering aid. It was found from XPS analysis and TEM observation that BN was segregated on the surface of Si_3N_4 particles during phase separation.
In Si3N4-TiN system, TiN stimulated the crystallization of beta- Si_3N_4 with and without sintering aid. XPS analysis suggested that TiN was segregated on the surface of Si_3N_4 particles without sintering aid, whereas TIN particles were surrounded by Si_3N_4 particles with sintering aid.
(3)Mechanical properties of nanocomposites
The nanocomposites of Si_3N_4-BN and Si3N4-TiN systems were fabricated by hot pressing of fine composite particles. Fine BN dispersion improved the thermal shock resistance in Si_3N_4-BN system. The fracture toughness was improved in Si_3N_4-TiN system. It was found that fine TiN dispersion accelerated the growth of beta Si_3N_4 rod-like grains, resulting in the improvement of fracture toughness.
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