聚酰亚胺薄膜制备高定向石墨材料的研究

Research on the highly oriented graphite from polyimide films

将双向拉伸聚酰亚胺（PI）薄膜叠层、压制炭化、高温热处理后制得了高定向石墨材料。借助TG、元素分析、XRD等测试手段分析了PI薄膜层叠成型体在热处理过程中质量、尺寸、化学组成、微观结构的变化。结果表明成型体炭化期间薄膜面向收缩较大，层叠方向尺寸变化不大，对材料进一步加压石墨化后，发现材料沿层叠方向有较大收缩，沿径向收缩较小。XRD分析表明PI薄膜热处理过程中会发生从高分子定向膜到无定型炭，再到高有序石墨结构的转变。经2800℃处理后的材料具有高的取向性和传导性能，四探针法测得样品的电阻率为0．79μΩ·m，根据电阻率与热导率的相关公式推得其热导率为1000～1600W／m·K。

Highly oriented graphite was prepared from polyimide（PI）films with hi-oriented hy the processes including piled up several PI films to form a sheaf and the sheaf of the films was carbonized and then hot-pressed at high temperature. The variation of mass, dimension and microstructure for the PI sheaf were analyzed using TG,element analyses and XRD. Results show that the shrinkage of the sheaf mainly occurs in the a-b plane and the shrinkage along the c-axis is small during the carbonization. The sheaf has large shrinkage along the c-axis but small in the a-b plane after graphitization. The analysis of XRD for PI sheaf shows the transit of the microstructure of PI film from super molecular lamellar structure to the random state, and then to highly oriented graphite with the increment of heat treatment temperature. The sheaf has high orientation and conduction after high temperature heat treatment at 2800℃. The electrical resistivity of the sheaf at room temperature is 0.79μΩ·m measured with the four-probe method,and the thermal conductivity of that is 1000-1600W/m · K calculated by Mason formula.