Poly(borosilazane) Precursors to Ceramic Nanocomposites

Abstract

Single-component polymeric precursors to SiC/Si 3 N 4 /C/BN and Si 3 N 4 /BN ceramic nanocomposites were synthesized via hydroboration and dehydrocoupling of vinyl-containing cyclotrisilazanes. The polymer-to-ceramic conversion process was investigated by 13 C, 29 Si, and 11 B solid-state magic-angle spinning (MAS) NMR spectroscopy, FTIR spectroscopy, thermal analysis, elemental analysis, X-ray diffraction (XRD), and transmission electron microscopy. The yields, processibility, and resulting microstructure of the ceramics were dependent on the starting Si/B ratio in the polymers and the atmosphere used for pyrolysis. Thermal conversion of the polymers from 200 to 600 °C involved loss of vinyl functionality, an increase in the amount of B-N environments, and possibly some degradation of the silazane ring structure. Conversion of the polymeric environment to that of mixed-phase ceramic was complete between 600 and 1000 °C; XRD, however, showed the products to be amorphous even after heating to 1600 °C. Heating the N 2 pyrolyzed products to 1800 °C resulted in β-Si 3 N 4 , β-SiC, and t-BN peaks in the XRD powder patterns, while R-Si 3 N 4 and β-Si 3 N 4 peaks were observed for the NH 3 pyrolyzed products.

Silicon-Based Polymer-Derived Ceramics: Synthesis Properties and Applications-A Review

“…Many examples of ultra high temperature stable polymer-derived ceramics have been published [1][2][3][4][5][6][7][8][9][10] although the process is a relatively young area of research. A continuing series of workshops related to this topic take place regularly since 1998 at the University of Colorado at Boulder see http:me-www.colorado.eduà rajr ultratemp.…”

Polymer-Derived SiBCN Ceramic and their Potential Application for High Temperature Membranes Dedicated to Prof. Dr.-Ing. Dr.h.c. Hartmut Fuess on the occasion of his 65th birthday

“…[1][2][3][4][5][6][7][8][9] Indeed, the chemical modification of the silazane system by the incorporation of boron is reported to form ceramics in the quaternary system SiBCN with high thermal stability in inert or oxidative atmosphere. In particular, boron-modified polysilazanes interconnected via C-B-Cbridges, 4,7 pinacolborane and borazine-hydridopolysilazanes 10 as well as polysilazanes bridged via N-B-N-units 3,11 have been shown to be promising preceramic polymers for providing such materials.…”

“…The use of commercially available and vinyl groups containing cyclosilazanes opens the possibility to avoid time consuming filtration processes necessary to separate solid by-products such as ammonium salts. 6 As-synthesised polyborosilazanes are best suited to the preparation of materials which retain an amorphous ceramic structure above 1800c C and exhibit a high thermal and oxidation resistance at that temperature. Therefore, SiBCN ceramics should provide the possibility of extending the practical upper temperature limit for currently available ceramic membranes.…”

Preparation of high-temperature stable SiBCN fibers from tailored single source polyborosilazanes

“…[1][2][3][4][5][6][7][8][9] Indeed, the chemical modification of the silazane system by the incorporation of elemental B is reported to yield ceramics in the quaternary system Si−B−C−N with high thermal stability in inert or oxidative atmosphere. In particular, single source boron-modified polysilazanes such as C−B−C-bridged polysilazanes, 4,7 pinacolborane and borazine-hydridopolysilazanes 10 as well as N−B−N-bridged polysilazanes 3,11 have been shown to be promising pre-ceramic polymers for providing such materials.…”