Nuclear magnetic resonance, 29Si

In earlier literature reports, x-ray data of a-based ceramics, the /3-like phase observed in certain silica minerals was explained by a structural model based on disordered Q -tridymite. However, others have suggested that the structure of the stabilized jS-cristobalite-like ceramics is closer to that of a-cristobalite than that of Q -tridymite, based on the 29Si nuclear magnetic resonance (NMR) chemical shifts (Perrota et al 1989). Therefore, in the absence of ED data it is impossible to determine the microstructure of the stabilized jS-cristobalite-like phase. ED and HRTEM have provided details of the ceramic microstructure and NMR has provided information about the environments of silicon atoms in the structure. Infrared spectroscopy views the structure on a molecular level. 

However, 29Si nuclear magnetic resonance shows experimental gel conversions,... 

Figure 1 29Si nuclear magnetic resonance spectra of different polycarbosilane precursors (molecular weight distributions Mn ranging from 320 to 1750) with respect to treatment temperatures. 

Zhang P, Dunlap C, Florian P, Grandinetti PJ, Faman 1, Stebbins JF (1996) Silicon site distributions in an alkali silicate glass derived by two-dimensional 29Si nuclear magnetic resonance. J Non Cryst Sol 204 294-300... 

The presence of four kinds of nuclear magnetic resonance (NMR) observable nuclei ( H, uB, 13C, and 29Si) allows poly(m-carborane-siloxane) to be readily investigated using NMR spectroscopy. In addition, H spin-echo NMR relaxation techniques can provide an insight into polymer segmental chain dynamics and therefore useful information on material viscoelastic characteristics. 

The bulky, stable silenes of Brook et al. (104,122-124,168) and Wiberg et al. (166,167) have been the only systems capable of being studied by nuclear magnetic resonance (NMR) spectroscopy to date. Table III lists the 13C and 29Si chemical shifts and the relevant coupling constants of these compounds. 

Nuclear magnetic resonance (NMR) spectroscopy is most frequently used to analyze liquid samples, but in the magic angle spinning (MAS) mode, this spectroscopy can also be employed to characterize solid catalysts, zeolites in particular [116-120], For example, the 29Si NMR signal can... 

Nuclear magnetic resonance (NMR) is used for a variety of purposes in this area, most of which parallel those used to characterize small-molecule systems.17,24 In addition to II and 13C NMR, 29Si NMR is very frequently employed. These methods are used to characterize chemical composition, structural features, and conformational preferences. They are also used to characterize hybrid inorganic composites, and silica-type ceramics, in general. 

Various methods may be used to examine configurations of polysilanes, but 29Si NMR spectroscopy has been the most useful. Silicon-29, like carbon-13, has spin 1/2 and a relatively low abundance, 4.7%. Nuclear magnetic resonance (NMR) spectroscopy using 29Si has been important for the characterization of siloxane polymers, and is proving to be equally useful for polysilanes. 

I.W.M. Brown, K.J.D. MacKenzie, M.E. Bowden, and R.H. Meinhold, Outstanding problems in the kaolinite-mullite reaction sequence investigated by 29Si and 27 AI solid-state nuclear magnetic resonance II, high temperature transformations of meta-kaolin, J. Am Ceram. Soc. 68(6), 298-301 (1985). 

---