| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === The effect of carbonization rate in a wide range (1, 100 and 1000 ℃/min) on the properties of a PAN/phenolic-based carbon/carbon (C/C) composite was studied. The results indicated that the composite processed at a higher carbonization rate had a higher porosity level, more large pores and a more graphitic structure than that processed at a lower carbonization rate. After second graphitization the bending properties of composites carbonized at 1 ℃/min and 1000 ℃/min were comparable. The composite carbonized at 1000 ℃/min had the highest fracture energy. The composite carbonized at 100 ℃/min showed the worst mechanical performance among three. The large increase in carbonization rate can be beneficial to the industry from an economic point of view.
Since C/C composite have been widely use for frictional materials, one purpose of the present study is to evaluate the tribological behavior of a fast-carbonized (1000℃/min) C/C composite. The results indicate that average coefficient of friction (COF) values of non-post-treated composites prepared with three different carbonization rates (1, 100 and 1000 ℃/min) are similar (0.40 - 0.45). The average wear rate of samples carbonized at 1000 ℃/min is about twice as large as samples carbonized at 1 and 100 ℃/min.
One other purpose of the study is to enhance the tribological performance of the composite by applying a post-treatment comprising re-impregnation of a carbonaceous additive-doped liquid precursor. Great majority of the samples demonstrate an increase in density and a decrease in porosity after the post-treatment. Pitch-group samples generally have larger changes in density and porosity than furan-group samples. After the post-treatment, all samples demonstrate decreases in both COF and specific wear rate coefficient. Pitch-group samples generally exhibit lower wear rate than furan-group samples. Samples post-treated with pitch/carbon black and pitch/mesophase pitch demonstrate the lowest wear rates among all samples tested (only half that of untreated samples carbonized at 1 ℃/min), while still maintaining relatively high COF values (close to 0.4). These results indicate that an appropriate post-treatment, especially a pitch treatment, may dramatically improve the tribological performance of fast-carbonized C/C composite.
One more experiment has been carried out to verify whether this simple treatment is also capable of improving the tribological performance, especially reducing wear rate, of two other 2D C/C formulae (PAN/CVI and pitch/phenolic/CVI) which are among the most-popularly-used C/C composites for aircraft brake disk today. The results indicated that with some certain combination of C/C and precursor/additive, there will have the effect that not only largely stabilized COF, but also effectively cut down by nearly half the wear rates without changing much the COF values.
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