High temperature structure evolution of SiBZrOC quinary polymer derived ceramics

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 sp(3)–C/Si ratio of SiBZrOC ceramics was between the values for SiZrOC and SiBOC. The presence of B promotes the crystallization of t-ZrO(2), which precipitated at 1000 °C and transformed to m-ZrO(2) at 1400 °C. At 1600 °C, ZrO(2) reacted with the matrix and formed ZrSiO(4), which consumed SiO(2) 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 ZrSiO(4) and the highly graphitized free carbon play important roles in inhibiting the carbothermal reaction and thus improving the thermal stability of SiBZrOC ceramics.