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Effects of after-curing in the air and in N₂ gas on properties of the carbon-glass fiber composite are described.
The after-curing temperatures are 230, 250 and 300°C., and after-curing period is about 24 hours.
After-cured composites are carbonized at 1000°C in coke powder. The heating rates are as follows: 5°C/min for the temperatures ranging from the room temperature to 200°C, 10°C/hr for temperature ranging from 200 to 280°C, 2.5°C/hr from 280 to 500°C, and 7.5°C/hr for temperature ranging from 500 to 1000°C.
Two kinds of glass-cloth phenol resin laminates are used as the samples; resin content of the sample I is about 30%, and that of the sample II is about 51%.
The effects of after-curing are as follows: No difference of the sample shrinkage by both after-curing and carbonization is observed between the specimen cured in the air and that in N₂ gas at all after-curing tempera tures. Moreover, there is no significant difference of glass content, real density, bulk density, and porosity between these samples cured in different atmospheres. The weight loss by after-curing for the sample I in the air is smaller than that in N2 gas to 250°C, but for the sample II, no difference is observed.
Flexural strength of the carbonized sample increases with the after-curing temperature . Flexural strength of the sample after-cured in the air is larger than that after-cured in N₂ gas throughout the curing temperatures investigated.

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Theoretical analysis is made of the change in the Hall coefficient and magnetoresistance of impurity -doped carbons with the aid of the quasi three dimensional band model proposed by K . Yazawa. Our analysis is successful when it is assumed that the energy levels of the chemical impurities are located deep from the band edge whereas the acceptors originating from defects are located shallow below the band edge . It is also cleared that the change in the field dependence of the carrier concentration is responsible for the magnetoresistance.

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