2002 Fiscal Year Final Research Report Summary
The elucidation of changes in electrical properties and water adsorption mechanism of wood by heat treatment
| Project/Area Number |
13460077
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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 |
林産学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
NORIMOTO Misato Kyoto Univ., Wood Res. Inst., Prof., 木質科学研究所, 教授 (20027163)
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| Co-Investigator(Kenkyū-buntansha) |
MOROOKA Toshirou Kyoto Univ., Wood Res. Inst., Assoc. Prof., 木質科学研究所, 助教授 (00192378)
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| Project Period (FY) |
2001 – 2002
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| Keywords | Heat Treatment / Dielectric Relaxation / Methylol Group / Sorption Isotherm / Adsorbed Water / Heterogeneous Dielectric / Interfacial Polarization / Maxwell-Wagner's Theory |
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| Research Abstract |
To investigate changes in electrical properties of wood by heat treatment, the longitudinal dielectric properties of wood specimens treated in the presence of nitrogen gas at various temperatures up to 800℃ were measured in a frequency range from 20Hz to 1MHz over a temperature range from -150℃ to 20℃. Changes in the water adsorption mechanism of wood specimens by heat treatment were also investigated. The yield by heat treatment remained unchanged up to 200℃, decreased remarkably between 200℃ and 300℃, then decreased gradually, and leveled off above 600℃. The magnitude of the dielectric relaxation due to the orientation of methylol groups was calculated from the Cole-Cole plots at -30℃. It remained unchanged in the treatment up to 200℃, but decreased remarkably above 200℃ and became 0 at 300℃. Any dielectric relaxation was not detected for the specimens treated at temperatures between 300℃ and 450℃. However, one large relaxation was recognized for the specimens treated at temperatures between 500℃ and 600℃. The relaxation magnitude obtained from the Cole-Cole plots at 20℃ was a large value of about 65 and the locus of plots became almost a semicircle. The Maxell-Wagner's theory on a heterogeneous dielectric was applicable to the experimental results. This fact suggested that the mechanism of this relaxation had some connection with the interfacial polarization in a system in which a small amount of a conductor disperses in the medium of an insulator. On the other hand, the shape of the sorption isotherm for specimens treated at temperatures up to 300℃ was sigmoid, although the moisture content decreased with increasing treatment temperature over all relative humidity range. The shape of the isotherm changed above 400℃. A remarkable change in the dielectric relaxation related to the adsorbed water was also recognized when the treatment temperature exceeded 300℃. These facts suggested that a drastic change in the sorption mechanism occurred above 300℃.
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