Combined pyrolysis-ammonolysis treatment to retain C during nitridation of SiBOCN ceramics

Abstract

Two sets of solgel derived glass materials have been prepared and subjected to different thermal treatments. Pyrolysis in inert atmosphere lead to the formation of amorphous Si(B)CO ceramics whereas if the inert atmosphere is changed to NH 3 once the carbon substituents of the preceramic hybrid material transform to a glassy network, the nitrogen is incorporated efficiently while the carbon is retained into the structure, as revealed by 29 Si NMR analysis. Raman spectra show a less graphitized structure in the case of B-rich materials because of the reduced mobility of the C atoms due to the formation of mixed (B)CN bonds.

Defective structure of doped carbons obtained from preceramic polymers through Cl2‐ and NH3‐assisted thermolysis

“…The thermal treatment in ammonia atmosphere of polycarbosilanes leads to the formation of a tight network dominated by Si–N and Si–C bonds 35 . Treating preceramic precursors in ammonia hinders the formation of Si–C–Si structures at the intermediate pyrolysis stages and reduces the amount of free carbon in the material 36,37 . Moreover, in metal‐containing preceramic polymers heat treated in ammonia, the crystalline metal nitride formation temperature depends on the metal and varies approximately from 300 to 700°C, then metal nitrides formed in situ can easily be converted to metal silicides during further heat treatment up to 1000°C 38 …”

“…35 Treating preceramic precursors in ammonia hinders the formation of Si-C-Si structures at the intermediate pyrolysis stages and reduces the amount of free carbon in the material. 36,37 Moreover, in metal-containing preceramic polymers heat treated in ammonia, the crystalline metal nitride formation temperature depends on the metal and varies approximately from 300 to 700 • C, then metal nitrides formed in situ can easily be converted to metal silicides during further heat treatment up to 1000 • C. 38 In this manuscript, it has been explored the effect of using a combination of two reactive atmospheres in the microstructure of a preceramic polymer modified with different amounts of phosphorus. Cl 2 and NH 3 have been selected as reactive atmospheres.…”