Structural investigations of Si/C/N-ceramics from polysilazane precursors by nuclear magnetic resonance

Thermal cross‐linking and pyrolytic conversion of poly(ureamethylvinyl)silazanes to silicon‐based ceramics

“…Continuous shifting of 13 C peaks with annealing temperature was previously observed for PHMS precursors and was explained as follows: Si-CH 3 (5 ppm) → SiCH 2 Si (12 ppm) → Si 2 CH-Si (18 ppm) → Si 4 C (24 ppm). 13,31 At 270°C, a small peak appears at 12 ppm as a shoulder of the main peaks centered at 3.5 ppm. This small peak is assigned to methyleneor ethylene-bridged silicon configurations (SiCH 2-Si or SiCH 2 CH 2 Si) 13,32 formed from hydrosilylation of vinyl groups or Kumada-like rearrangement reactions during cross-linking (see also Section 4.1).…”

“…Moreover, the formation of Si-N bonds is favored thermodynamically compared with, for example, the generation of weak Si-Si or N-N bonds in Eqns [7] and [9]. 31 However, several other reactions may also contribute to the total amount of hydrogen, but to a smaller extent. At higher temperatures the C-H bonds are certainly involved in the formation of hydrogen.…”

Compressive Deformation of Precursor-Derived Si-C-N Ceramics at Elevated Temperatures

“…This treatment results in black ceramic powders with a chemical composition of Si 1:0 C 1:6 N 1:3 in atomic ratio. Details of the preparation process and the ceramization behavior are described by Seitz et al 15) The hot isostatic pressing of pyrolyzed powder compact was conducted at 1500 C and 950 MPa without any sintering additives. Details of the consolidation process and the densification behavior are described in Ref.…”

Low Temperature Crystallization Behavior of .ALPHA.-Si3N4 from Ti-Doped Amorphous Silicon Nitride Derived from Polytitanasilazanes

“…7b, the 1273 K-pyrolyzed TNPHPS exhibited an additional small broad peak centered at ࢬ18 ppm assigned to SiC 3 H or SiC 4 unit. 16 This unit formation could be due to the small amount of the residual carbon derived from TiNCH 3 2 4 . The changes in the NMR spectra of the TNPHPS TiSiࢼ0.003 during pyrolysis at 543 to 1273 K were basically the same as those of as-received PHPS.…”

“…The spectrum showed another new broad peak centered at ࢬ48 ppm assigned to SiN 4 unit. 15,16 After pyrolysis at 1273 K, the relative peak intensity of the SiN 4 unit at ࢬ48 ppm was higher …”