| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 91 === In this study, the PAN stabilized fiber felt was impregnated with phenolic resin with the liquid impregnation method. After curing and hot-pressing, the phenolic resin becomes the precursor of the carbon/carbon composites. The carbon/carbon composites are densified by using the process repeated impregnation for different times. After the process of the thermal treatment of the carbonization and graphitization, the precursor transferred into the carbon/carbon composites. The purpose of this research is aimed at different repeated impregnation times, and during the process of the thermal cracking of the carbon/carbon composites, we discuss the influence about the property, microstructure and electrical conductivity.
First of all, for the analysis of the basic property of the carbon/carbon composites, the outcome of the shrinkage shows that the shrinkage of the carbon/carbon composites tends to increase while the repeated impregnation times increase. For the weight loss of the carbon/carbon composites, in carbonization at 1000℃and in graphitization at 2500℃, the weight loss of R1 and R2 both decrease while the repeated impregnation times increase. For the open pore of the carbon/carbon composites, in 1000℃and 2500℃, the open pore of R1 and R2 both tends to decrease. And the flexural strength of the carbon/carbon composites is relatively enhanced. For the density of the carbon/carbon composites, in 1000℃and 2500℃, R1 and R2 both tend to increase. In 1000℃and 2500℃, the flexural strength of R1 and R2 tends to increase. Especially in 1000℃, the increase of the flexural strength of R1 and R2 is more obvious, the percentage of increase is 59.8 % and 53.1% each other.
For the microstructure analysis of the carbon/carbon composites, from the microscopic images of the SEM, we can observe that the carbon/carbon composites almost display the mode of the brittle fracture after the flexural test. It is because that the interface of the PAN stabilized fiber felt and the phenolic resin forms the strong bonding. From the same picture, we can also obverse that its range of increase in pore is quite obvious in 600℃. Therefore, it causes that the flexural strength in this temperature shows the lowest value. We can observe from the micro image of the OM that the voids and cracks of the carbon/carbon composites would gradually become bigger and more while the repeated impregnation times increase. Through the technique of the polarized micro image, I am aimed at observing the situation of the voids and cracks that the phenolic resin repeated impregnates the carbon/carbon composites. We can observe the phenolic resin permeate the cracks indeed. But for the reason that the resin and the crack’s surface have a bad agglutination, the resin would solidify inside the cracks because the resin generates shrinkage in the thermal treatment processes between the carbonization processes. So the resin can’t permeate the most top of the cracks, and the original open pore is obstructed to become the closed pore which is the main reason to cause the density’s decrease for the end composites. In the meanwhile, I am also observe that there are some cracks’ certain phenolic resin permeate the top of the cracks, and that don’t fill up overall the crack. This is the main reason to cause the deflection flexural strength decrease.
For the analysis of the electrical conductivity of the carbon/carbon composites, some resin which certainly permeates into the voids of the surface and the cracks of the fiber results in the densification of the structure of the carbon/carbon composites and makes the network of the electric conduction more complete. Therefore, in 1000℃and 2500℃, the DC resistivity and the value of the chip resister of R1 and R2 both tend to decrease.
|
|---|
