Research On SiBOC Ceramic Precursor Containing Carborane And Its High Temperature Crystal Phase Transformation

Polymer precursor-derived ceramics（PDCs）are ceramics obtained by cracking and removing small organic molecules under high temperature conditions after polymer precursors are cured and cross-linked.PDCs were widely used in various fields due to their simple preparation technology,designable molecular structure and low preparation temperature.Among various PDCs,silicon boron oxycarbide（SiBOC）ceramics have attracted much attention due to their excellent high temperature resistance,creep resistance and chemical stability.However,the yield of SiBOC ceramics prepared by the existing PDCs method can only reach 60-70%,resulting in the inability of industrial production.In this paper,high-yield SiBOC ceramics were prepared from the molecular structure design,and the crystal phase transition at 1000-1500^oC was studied.The main research contents and conclusions are as follows:First,1,2-bis（4-methoxyphenyl）-acetylene monomer was prepared by Sonogashira coupling reaction;then,it was reacted with B₁₀H₁₂（CH₃CN）₂ to obtain 1,2-bis（4-methoxybenzene）Group)-carborane monomer;finally reduced by boron tribromide to obtain 1,2-bis（4-hydroxyphenyl）-carborane monomer.Liquid phase test results prove that the purity of the three compounds after purification are above 99%.The FT-IR,¹H-NMR and¹³C-NMR spectrums proved that the three monomer structures were correct.The precursor polyvinyl siloxane carborane V-PMSCB was designed and synthesized,and its structure was verified by FT-IR,¹H-NMR,and ¹³C-NMR spectra;The reaction at 80^oC for 44h and the reaction material ratio at 1:1 are the best reaction conditions.The residual carbon rates at 1000 ^oC under air and nitrogen conditions are 89.69 and 84.23%,respectively;XRD test results prove that the resin has certain crystal.Performance and solubility test results showed that the resin was soluble in most common organic solvents at room temperature.The kinetics of non-isothermal curing reaction of V-PMSCB was studied by DSC,and the curing process of V-PMSCB was determined to be 60 ^oC 3h,115 ^oC 2h,140 ^oC 1h;P-MSCB resin with good thermal performance was prepared;P-MSCB resin was pyrolyzed at1000 ^oC for 2h to obtain a SiBOC ceramic with a ceramic yield of 90.24%;XRD,XPS and Raman proved that the pyrolysis of SiBOC at 1500 ^oC for 2h changed from the original amorphous structure to a complex ceramic structure containing graphite crystals,boron carbide crystals and silicon carbide crystals.