In situ mesophase transformation by zirconium chloride in fabrication of carbon/carbon composites

Carbon/carbon (C/C) composites were prepared using multiple cycle in situ mesophase densification in the presence of zirconium chloride. The mesophase transformation and the performance of C/C composites were investigated in detail. The results show that higher amount of ZrCl4 and longer soaking time accelerate the condensation of aromatic hydrocarbons. Additionally, the XRD pattern and ash contents show that the ZrCl4 is retained in the samples and transformed to t-ZrO2 and m-ZrO2 after carbonization. In all the composites, the bulk density increases with cycle times, and the flexural strength increases with bulk density. However, a decrease of flexural strength for low density composites was observed when increasing ZrCl4 concentrations. This tendency is attributed to more ZrO2 formation in the composites using 20 wt.% ZrCl4. Subsequently, these ZrO2 particles produce interface defects in the matrix which decreases its strength. Attributed to the very low content of ZrO2 in high density composites, there is no difference between the samples using 13 wt.% and 20 wt.% ZrCl4.