Effect of Precursor on Speciation and Nanostructure of SiBCN Polymer‐Derived Ceramics

Abstract

A comparative structural study of silicon borocarbonitride polymer‐derived ceramics synthesized using polyborosilylcarbodiimide and polyborosilazane precursors is carried out using high‐resolution, multinuclear, one‐ and two‐ dimensional NMR spectroscopy. The polyborosilylcarbodiimide‐derived ceramics contain relatively pure Si3N4 and C nanodomains with the BN domains being present predominantly at the interface such that the bonding at the interface consists of Si–N–B, Si–N–C, and B–N–C linkages. In contrast, the structure of the polyborosilazane‐derived ceramics consists of significant amount of mixed bonding in the nearest‐neighbor coordination environments of Si and B atoms leading to the formation of SiCxN4−x (0 ≤ x ≤ 4) tetrahedral units and BCN2 triangular units. The interfacial region between the SiCN and C nanodomains is occupied by the BCN phase. These results demonstrate that the chemistry of the polymeric precursors exerts major influence on the microstructure and bonding in their derived ceramics even when the final chemical compositions of the latter are similar.

Synthesis and characteristic of SiBCN/HfN ceramics with high temperature oxidation resistance

“…In the spectra of PBSZHf, the signals at À3.7 ppm and À22.7 ppm are assigned to SiC 2 (sp 3 )N 2 and SiC(sp 3 )N 3 . Compared with that of PBSZ, the absence of Si(H)eCH 3 (1.6 ppm) and SiHC(sp 3 )N 2 (À18 ppm) [27,28] sites indicates that the SieH bonds are consumed in the metal substitution reaction, which is agreed with the inference of FTIR results. As the hafnium introduced into PBSZ, the dominating peak at À22.7 ppm for SiC(sp 3 )N 3 increases in its relative intensity, revealing that NeH groups in SiC 2 (sp 3 )N 2 sites are replaced the NeHf bonds or dehydrocoupling.…”

Single-source-precursor synthesis of dense SiC/HfCxN1−x-based ultrahigh-temperature ceramic nanocomposites

“…In Fig. 42,43 After annealing at 1300°C (Fig. In the materials heat-treated at higher temperatures, two types of sp 2 carbon sites were found (Fig.…”

Crystallization Behavior of Amorphous Si2BC3N Ceramic Monolith Subjected to High Pressure

“…They are greatly promising candidates for reentry aircraft nose cones, wing leading edge and turbine blades . Although the resulting amorphous Si–B–C–N materials are thermodynamically stable below a certain temperature, it can be expected to transform spontaneously at temperatures sufficiently high to initiate nucleation and growth processes leading to nanocrystalline materials …”