High temperature structure evolution of SiBZrOC quinary polymer derived ceramics

Abstract

SiBZrOC quinary ceramics were obtained through the modification of a SiOC precursor with B(OH)₃ and Zr(OnPr)₄. The results showed that both B and Zr atoms were involved in the SiOC network through Si–O–B and Si–O–Zr bonds, respectively. The combined effects of B and Zr on the chemical structure and the thermal stability of the SiBZrOC system were investigated in detail. The sp³–C/Si ratio of SiBZrOC ceramics was between the values for SiZrOC and SiBOC. The presence of B promotes the crystallization of t-ZrO₂, which precipitated at 1000 °C and transformed to m-ZrO₂ at 1400 °C. At 1600 °C, ZrO₂ reacted with the matrix and formed ZrSiO₄, which consumed SiO₂ and thus inhibited the carbothermal reaction. The very small I(D)/I(G) ratio of 0.13 in the Raman spectra indicated the high graphitization of free carbon in SiBZrOC ceramics, which was observed by TEM with 10–20 graphene layers. The SiBZrOC ceramics showed excellent thermal stability in argon at 1600 °C for 5 h with a mass loss of 6%. Both the formation of ZrSiO₄ and the highly graphitized free carbon play important roles in inhibiting the carbothermal reaction and thus improving the thermal stability of SiBZrOC ceramics.