2007 Fiscal Year Final Research Report Summary
Research on Nano-scale sintering
| Project/Area Number |
17360345
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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 |
Structural/Functional materials
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| Research Institution | National Institute for Materials Science |
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Principal Investigator |
TOSHIYUKI Nishimura National Institute for Materials Science, Nano Ceramics Center, Senior Researcher (50354428)
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| Co-Investigator(Kenkyū-buntansha) |
NISHIMURA Toshiyuki National Institute for Materials Science, Nano Ceramics Center, Group leader (40343868)
HIROSAKI Naoto National Institute for Materials Science, Nano Ceramics Center, グループリーダー (80343838)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Structural and functional materials / Ceramics / Nano materials |
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| Research Abstract |
After mixing silicon nitride powder with sintering additives by conventional planetary milling under wet conditions, the powder mixture was dried and milled by high-energy milling. Planetary milling was carried out at 475 rpm for 4 h. A pot lined with silicon nitride ceramics and silicon nitride balls as milling media were used for minimizing contamination. The introduction of the powder mixture into the pot and the extraction of the milled powder were performed in a glove box filled with nitrogen gas to avoid oxidation. The high-energy-milled powder mixture of Si_3N_4, Y_2O_3 and Al_2O_3 was observed using a transmission electron microscope. Particles with size<100 nm can be observed. The powder mixture was analyzed by XRD before and after high-energy milling. The peak height of Si_3N_4 decreased and the peaks ofY_2O_3 and Al_2O_3 disappeared in the XRD pattern of the milled powder. Background height of the pattern for milled powder increased. These results indicate the vitrification of Si_3N_4, Y_2O_3, and Al_2O_3, and the decrease in the particle size of Si_3N_4. Spark plasma sintering of the milled powder was carried out in nitrogen at a compressive stress of 30 MPa for 5 min. The heating rate was about 300 ℃/min. The high-energy-milled powder of Si_3N_4, Y_2O_3, and Al_2O_3 sintered at 1600℃ was almost fully densified. Grain diameter of the ceramic was about 60-90 nm. The shrinkage during sintering of the as-mixed powder starts at a temperature lower than the temperature at which the high-energy-milled powder starts shrinking. After the start of shrinkage, degree and rate in the shrinkage of milled powder became much higher than those of as-mixed powder. The difference in densification may be caused by the small grain size of Si_3N_4 and the vitrification of Si_3N_4, Y_2O_3, andAl_2O_3.
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