X-rays in situ investigations on mesophase formation during carbonization of decacyclene

Abstract

An in situ X-ray diffraction method has been developed, permitting one to follow all the steps preceding the formation of mesophase spherules during the decacyclene carbonization. Results have been compared with those obtained from differential thermal analysis (D.T.A.), thermogravimetric analysis (T.G.A.) and transmission electron microscopy (T.E.M.). We have established that decacyclene undergoes, near 300°C, a phase transition: ϑ 1→ ϑ 2. This transition is reversible and purely physical; however if temperature is maintained at 300°C the decacyclene molecule is damaged and when the weight loss reaches 5% the transition ϑ 1→ ϑ 2 becomes irreversible, and the ϑ 2 high temperature phase remains stable at the room temperature. This ϑ 2 decacyclene phase is the principal stable intermediate compound in the mesophase formation: at 300°C the ϑ 2 phase has a well organized structure; at 410°C it begins to melt slowly into a pitch in which spherules appear at 530°C. T.E.M. investigations assign the Brooks and Taylor structure to these spheres.