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 ZrB1.38C2.18.