Synthesis and characterization of zirconium diboride precursor based on polycentric bridge bonds

Zirconium diboride (ZrB₂) is one of the most important ultrahigh temperature ceramics (UHTCs). ZrB₂ precursor was synthesized with bis(cyclopentadienyl)zirconium dihydride (Cp₂ZrH₂) and borane-dimethyl sulfide complex (BH₃·S(CH₃)₂). The influences of molar ratio of reactants and reaction temperature on the solubility of the as-synthesized precursors were investigated. The molecular structure of the precursor, pyrolysis behavior, and the composition of the derived ceramics were investigated by X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infrared Spectroscopy (FT IR), Raman Spectroscopy (RMS), ¹H Nuclear Magnetic Resonance Spectroscopy (¹H NMR), ¹¹B Nuclear Magnetic Resonance Spectroscopy (¹¹B NMR), Thermogravimetric-Mass Spectroscopy (TG-MS), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The results showed that, the precursor was an oligomer based on Zr–H–B polycentric bridge bonds with molecular weight of 750 and formula as (Cp₂Zr(BH₄)₂)₃. The precursor would probably further polymerize under vacuum or at high temperature and lead to an insoluble polymer. The ceramic yield of the precursor at 1000 °C was around 66% under N₂ atmosphere. After pyrolyzed at 1800 °C, the derived ceramics were composed of h-ZrB₂, ZrC, and free carbon with a formula as ZrB_1.38C_2.18. - Highlights: • ZrB₂ precursor based on Zr–H–B polycentric bridge bonds was synthesized. • The ceramic yield of the precursor at 1000 °C was around 66% under N₂ atmosphere. • After pyrolyzed at 1800 °C, the derived ceramics were composed of h-ZrB₂, ZrC and free carbon with a formula as ZrB_1.38C_2.18