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 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.