High-Yield Molecular Borazine Precursors for Si−B−N−C Ceramics

Abstract

The synthesis of Si-B-N-C ceramic materials can be accomplished via two different routes using B-tris(trichlorosilylvinyl)borazine (2) as starting material. This silyl-functionalized ethinylborazine is obtained by Pt-catalyzed hydrosilylation of B, B′, B′′-tri-ethynylborazine (1) with HSiCl 3 in quantitative yield with a selectivity of 80% β-substituted product. Amminolysis of 2 with methylamine leads to the soluble silazane polymer P3 which contains intact borazine rings connected by sCHdCHsSisNMe linkages. In a second approach, the trichlorosilyl groups of 2 are hydrogenated to yield the B-tris(hydrosilylvinyl)borazine (4). With polymer P3 or 4, a highly durable Si-B-N-C ceramic is obtained after pyrolysis under inert atmosphere. The composition SiBN 1+x C 2 of the ceramic material corresponds exactly to the backbone of the precursor molecules 2 or 4, and very compact materials are obtained in each case. The ceramic yield of approximately 94% starting from the silane precursor 4 sets a new standard for this type of ceramics using the pyrolysis of a single site molecular precursor. Conductivity measurements show a semiconductor behavior of the ceramic at about 10 2 (Ωm) -1 at room temperature. The composition of the ceramic was characterized by laser-ablation ICP-MS, which was used for that purpose for the first time. The very satisfying results demonstrate the high potential of this direct solid sampling technique.

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.…”

Borazine Based Molecular Single Source Precursors for Si/B/N/C Ceramics

“…In the borazine based precursors studied so far, boron and silicon are linked by carbon atoms or chains [19][20][21] linkage that is not constitutive of the first generation of Si/B/N/C ceramics. Thus, during the process of condensing a respective polymer by pyrolysis manifold rearrangements of B-C and Si-C bonds would be required, most probably resulting in a higher concentration of dangling bonds.…”

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.…”