Steven F. Dec

Comparison of the 1H NMR analysis of solids by the CRAMPS and MAS-only techniques

1H NMR spectra are reported on eight representative solid samples, including pure powdered crystalline samples, synthetic organic polymers, a silica gel, HY zeolite, and a lignite. Spectra were obtained by the following three approaches: (1) single pulse on a static sample, (2) CRAMPS, and (3) single pulse with magic-angle spinning (MAS-only). The MAS-only results were obtained as a function of MAS speed. Although the MAS-only technique is capable of achieving a significant degree of line narrowing, even with modest MAS speeds, MAS-only spectra of the general quality of the apparently undistorted high-resolution 1H spectra obtained by the CRAMPS technique are not obtained at the highest MAS speeds examined (21 kHz for a polymethylmethacrylate sample), unless the 1H-1H dipolar interactions in the sample are rather weak, as with silica gel or a zeolite. Thus, caution should be exercised in interpreting 1H MAS-only spectra, especially if CRAMPS results are not available as a calibration.

Solid-state 27Al and 29Si NMR studies of the reactivity of the aluminum-containing clay mineral kaolinite

Abstract Solid-state 27 Al and 29 Si NMR spectroscopy, X-ray powder diffraction and other chemical analyses have been used to study the dealumination of uncalcined and calcined (850°C) kaolinite following extraction with aqueous HCI solutions at 98°C. The degree of the dealumination is dependent on the extraction stoichiometry and the temperature of calcination pretreatment of the kaolinite. Solid-state MASS 27 Al and CP/MASS 29 Si NMR studies provide unique information about the aluminum and silicon atoms in kaolinite samples before and following the dealumination process. The results are discussed in light of the current mechanisms proposed for the dehydration and dealumination processes of kaolinite.

The pyrolytic conversion of perhydropolysilazane into silicon nitride

Abstract Polymeric precursors to ceramics have the potential to enable production of ceramic articles in novel forms, with novel microstructures, and improved properties. The polymer-to-ceramic conversion process is not sufficiently understood for this approach to be widely utilised. Perhydropolysilazane converts to high purity silicon nitride (Si3N4), and has been shown to be a useful coating and matrix precursor. The conversion of PHPS to Si3N4 is being examined by Solid State, Magic Angle Spinning (MAS) NMR spectroscopy and other techniques. This paper summarises the results to date of this investigation.

Solid-State Emulsions: Evaluation by 1H and 13C Solid-State Nuclear Magnetic Resonance

The molecular environment of sucrose and mineral oil within sucrose and mineral oil solid state emulsions was investigated by NMR techniques. The 13C and 1H chemical shifts of sucrose and mineral oil to those observed in solid state emulsions (comprised of sucrose and mineral oil) were equivalent, indicating that the local structure of sucrose is unaffected by the presence of mineral oil in the solid-state emulsion. Cross-polarization, magic angle spinning 13C (CP-MAS) in conjuncton with single-pulse studies indicated that the 1H-13C dipole-dipole interactions are very weak, i.e., mineral oil is highly mobile. Spinning side bands were observed, however, in 1H single-pulse, magic angle spinning (SPMAS) spectra of the solid-state emulsion, indicating that the mineral oil has solid properties. Although the mineral oil was shown to be highly mobile, it also appears to be constrained or included by the sucrose.