Polyborosilazane with Broadly Tunable Boron Content for SiBCN Ceramics

Thehigh-temperature durability of SiBCN ceramics is significantlyinfluenced by the boron concentration and synthesis methods. Althoughsingle-source synthetic routes allow one to obtain homogeneous ceramicsat the atomic level, the content of the boron element therein is limitedby borane (BH3). In this study, the synthesis of carborane-substitutedpolyborosilazanes was performed via a simple one-pot reaction of polysilazaneswith alkyne bonds on the main chain and decaborododecahydrodiacetonitrilecomplexes with different molar ratios. This enabled one to vary theboron content from similar to 0 to 40.00 wt %. The ceramic yields werein the range of 50.92-90.81 wt %. Independently of the boraneconcentration, SiBCN ceramics started to crystallize at 1200 degrees C,and B4C appeared as a new crystalline phase with increasingboron content. The introduction of boron inhibited the crystallizationof Si3N4 and increased the crystallization temperatureof SiC. The presence of the B4C phase improved both thermalstability and functional properties such as neutron-shielding characteristicsof the ceramics. Therefore, this research opens up new prospects forthe design of novel polyborosilanzes with great application potential. Polyborosilizanes containing carboranesegments were synthesizedand the boron content could be broadly tuned up to 40 wt % theoretically.High boron content contributes to the formation of B(4)Cand the inhibition of Si3N4 crystallization.

Automated summary

The high-temperature durability of SiBCN ceramics is significantly influenced by boron concentration and synthesis methods. Carborane-substituted polyborosilazanes were synthesized with a broad range of boron content up to 40 wt %, which improved the thermal stability and functional properties of the ceramics. The introduction of boron inhibited Si3N4 crystallization and increased the crystallization temperature of SiC, while B4C appeared as a new crystalline phase.