Solid‐State 29Si NMR Analysis of Amorphous Silicon Nitride Powder

Abstract

Solid‐state 29Si NMR techniques were used to characterize laser‐synthesized silicon nitride powder prepared from the reaction of silane with ammonia. When the powder is exposed to water vapor, a hydrated layer rapidly forms at the surface. A comparison of 29Si cross polarization (CP) and Bloch decay (BD)‐MAS‐NMR spectra revealed differences between surface and bulk compositions. CP‐NMR identified Si‐NHx (x = 1, 2) species with a chemical shift of −45 ppm in the as‐synthesized (unexposed) powder. In BD‐NMR spectra, the nitride resonance is observed at −48 ppm. For the hydrated powder, CP‐NMR identified additional =Si‐OH (Q3), =Si‐(OH)2 (Q2), and SiO2 (Q4) species present at the surface. The CP‐NMR spectra were corrected for TlpH relaxation effects and deconvoluted into individual components in order to extract quantitative measurements of the various species present.

Nanostructured Aniline Formaldehyde Resin/Polysilazane Hybrid Materials by Twin Polymerization

“…The 29 Si‐NMR signal position of the hybrid material derived from 1 appears at −45 ppm compared to that from 2 /HMTA which occurs at −43 ppm when both products are synthesized at similar polymerization temperatures. This result indicates that hybrid materials of 2 /HMTA could contain more available amino functionalities for hydrolysis …”

“…The hybrid materials obtained at temperatures below 500 °C are very sensitive to air and moisture due to Si−N bonds which are not stable to hydrolysis . The reaction of silicon nitride surface functionalities with oxygen or moisture to silicone dioxide (Q‐signals in 29 Si spectra) and intermediate stages of SiN y O x are observed in the solid state 29 Si‐NMR and XPS spectra (Figure ; Figure S5 and Tables S4 and S5, Supporting Information) . Interestingly, there is a significant difference in hydrolysis rate of hybrid materials resulting from 1 or 2/ HMTA, the latter one being far more reactive.…”

“…The chemical shifts of the 29 Si‐NMR signals indicate the formation of amorphous inorganic polysilazane networks with active amino groups at reaction temperatures below 400 °C. Very broad 29 Si‐NMR signals centered at −47 ppm show the formation of amorphous silicon nitride after pyrolysis at 1100 °C …”

Rivalry under Pressure: The Coexistence of Ambient‐Pressure Motifs and Close‐Packing in Silicon Phosphorus Nitride Imide SiP2N4NH

“…Thepresence of both signals in the 31 P{ 1 H} spectrum and the absence of asignificant change in the integral ratio confirmed the presence of Hi n bulk SiP 2 N 4 NH and proved both Pp ositions to be in almost equidistant spacing from H. The 29 Si{ 1 H} spectrum shows one major resonance at d = À205 ppm (Figure 3b), in line with one crystallographic Si site in SiP 2 N 4 NH and in good agreement with the 29 Si resonance reported for Si [6] in g-Si 3 N 4 (d = À225 ppm). [37] In the 1 HNMR spectrum, one resonance at 6.6 ppm was observed, exhibiting aw eak shoulder (Figure 3c), which most likely originates from the Si/O/H species mentioned above.T hus,o ne crystallographic Hposition is suggested for SiP 2 N 4 NH, as presented by selective N1 À H1 bonding above.T oc onfirm the experimental findings and conclusions from XRD and NMR investigations,S iP 2 N 4 NH was analyzed by the CHARDI method (see the Supporting Information, Figure S21, Tables S22 and S23). [37] In the 1 HNMR spectrum, one resonance at 6.6 ppm was observed, exhibiting aw eak shoulder (Figure 3c), which most likely originates from the Si/O/H species mentioned above.T hus,o ne crystallographic Hposition is suggested for SiP 2 N 4 NH, as presented by selective N1 À H1 bonding above.T oc onfirm the experimental findings and conclusions from XRD and NMR investigations,S iP 2 N 4 NH was analyzed by the CHARDI method (see the Supporting Information, Figure S21, Tables S22 and S23).…”

Pore-Size Engineering of Silicon Imido Nitride for Catalytic Applications

“…Such a broadening originates from the amorphous character of preceramic silicon nitride powders, in which various different coordination spheres are present. [10] Silicon imido nitride with high accessible surface area can be used as a solid base catalyst in Michael addition reactions due to the presence of basic sites. For example, moderately acidic substrates like malononitrile (pK a 11) are activated to form addition products with substrates like acrylonitrile (Scheme 1).…”