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.