In situ synthesis mechanism of ZrB2–ZrC–C composites

In situ ZrB2–ZrC–C composites were synthesized via pyrolysis of a boron and zirconium containing precursor (PBZC), which was prepared by using phenol, paraformaldehyde, boric acid, ZrOCl2·8H2O, and acetylacetone as raw materials. The structure and thermal properties of PBZC were characterized by Fourier transform infrared spectra (FTIR) and thermogravimetry–derivative thermogravimetry (TG–DTG), respectively. The synthesis mechanism of ZrB2–ZrC–C composites was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that boron and zirconium are successfully introduced into the polymer. Decomposition of PBZC is completed at about 800 °C with ZrO2, B2O3 and carbon as pyrolysis products. ZrB appears at 1350 °C as an intermediate phase and will transform into ZrB2 at a relatively high temperature. ZrB2 forms at about 1500 °C, followed by the appearance of ZrC when the amount of B2O3 is limited. The ZrB2–ZrC–C composites are hard and dense solids with ZrB2 and ZrC grains uniformly embedding in the carbon matrix.