1998 Fiscal Year Final Research Report Summary
IMPROVEMENT OF ENVIRONMENTAL DURABILITY AND STRENGTH OF SIALON CERAMICS BY TAILORING THE GRAIN-BOUNDARY PHASE DUE TO SOLID-SOLUTION NATURE
| Project/Area Number |
09650736
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | OKAYAMA UNIVERSITY |
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Principal Investigator |
YOSHIO Tetsuo OKAYAMA UNIVERSITY,FACULTY OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY,PROFESSOR, 環境理工学部, 教授 (70032943)
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| Project Period (FY) |
1997 – 1998
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| Keywords | sialon ceramics / solid solution / aqueous corrosion / forms of corrosion / uniform corrosion / pitting corrosion / corrosion resistance / strength degradation |
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| Research Abstract |
Hydrothermal corrosion and strength degradation of Si_3N_4-based ceramics has been investigated using an autoclave method in order to assure the tailoring effect of grain-boundary phase on corrosion resistance of alpha-sialon. The hydrothermal corrosion products in sialon ceramics can be removed easily from the substrate in an ultrasonic waterbath. SEM micrographs for corroded substrate after removal of corrosion products revealed the nature of forms of corrosion for each ceramics In Si_3N_4 ceramics, corrsion pits were clearly observed. In contrast, the corroded substrate of alpha-sialon revealed the surface with no identifiable corrosion pits, which could be designated as uniform corrosion.
Fracture strength degradation as a function of exposure time for these sialon ceramics is showed a rapid decrease in fracture strength occured in the early stage of corrosion, and then was almost cnstant up to 10 days. However, the degree of strength degradation was different between the uniform corrosion in alpha-sialon and the pitting corrosion in Si_3N_4. Although the strength decrease after extended exposure in the latter was 40%, thatin the firmer was only 15%. Formation of corrosion pits may explain the larger extent of strength reduction. Thus, it has been found that corrosion resistance and strength degradation in alpha-sialon are superior to other types of sialon due to the solid-solution nature.
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