Charles E. Bronnimann

Solid-state 29Si NMR of TEOS-based multifunctional sol-gel materials

Abstract Solid-state 29 Si NMR experiments were carried out on multifunctional TEOS-based sol-gel materials to determine the types of silicate structures formed as well as the degree of reaction attained under previously established acid-catalyzed conditions. The degree of reaction attained and the final functionality of the gels were found to correlate with a flexible/brittle transition which was observed to be a function of the gel composition. Both FT/MAS and CP/MAS experiments were conducted which allowed a comparison of the two methods in terms of their quantitative results. It was found that the CP/MAS experiment run under the proper conditions provides (with the exception of pure TEOS gels) quantitatively similar spectra to those obtained by FT/MAS experiments.

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.

Effects of drying, heating, annealing, and roasting on carbonate skeletal material, with geochemical and diagenetic implications

Abstract Carbonate skeletons subjected to drying, heating, annealing, or roasting at elevated temperatures as part of routine sample preparation for chemical analyses or geochemical experiments differ significantly from skeletal materials as they occur in nature. Heating of skeletal samples can degrade organic material, expel H2O and OH−, reduce the concentration of some trace elements, and change the mineralogy and texture of the material. Thermal degradation of organics and expulsion of water in inclusions, which can occur at temperatures of 100–105°C, cause fracturing and pitting of skeletal samples; areas of pitting reflect original concentrations of volatile phases within the skeleton. Coralline aragonites are partially or completely altered to calcite at temperatures of 150°C or higher; the degree of alteration varies with temperature and duration of heating, and genus of the coral. High Mg calcites (HMCs) tend to form calcian dolomite and multiple HMCs of lower Mg content on heating, but the rate of alteration is related to the taxonomic group rather than the Mg content; echinoids alter very rapidly (dolomite detectable by X-ray diffraction formed in Clypeaster heated for 6 h at 200°C), while the coralline red alga Neogoniolithon showed no alteration after heating at 400°C for 23 h. Mineralogical alteration of coralline aragonites and echinoid HMCs is positively correlated with water loss. Skeletal carbonates comprise a very diverse and heterogeneous suite of materials, and their diversity and heterogeneity are reflected in their responses to heating. Variations in rate and degree of alteration on heating, in many cases between different subsamples of material produced by the same organism, make it difficult to obtain a consistent product from heat treatment. Many workers have used high temperature experiments to model diagenetic processes, and the results of this study have implications for diagenetic alteration as well as for laboratory analyses and experiments.

1H CRAMPS n.m.r. study of the molecular-macromolecular structure of coal

Abstract A 1 H CRAMPS n.m.r. investigation has been carried out on a subbituminous coal and on the coal saturated with deuterated pyridine. The presence of pyridine significantly improved the resolution of the CRAMPS spectra. The intensity decay in a dipolar-dephasing CRAMPS experiment on the original coal consists of two components, corresponding to Gaussian and Lorentzian line shapes. The intensity decay in the same type of experiment on the coal saturated with pyridine consists of a mixture of Gaussian, intermediate-decay Lorentzian and slow-decay Lorentzian components. Different resonance frequencies correspond to different contributions from the different types of decay. However, only methyl groups contain a slow-decay Lorentzian component that indicates a high degree of rotational mobility. Thus, a correlation between highly mobile species and a molecular component cannot be made directly for this coal on the basis of these data.

2D 1H-133C heteronuclear correlation spectra of representative organic solids

Abstract A solid-state 2D 1 H- 13 C chemical-shift correlation experiment has been developed, refined, and applied to representative organic solids ranging from pure, powdered, crystalline compounds to lignite. During the 1 H chemical-shift evolution period a 48-pulse elaboration of a recently reported windowless 12-pulse sequence (BB-12) was applied in the 13 C channel for decoupling the 1 H- 13 C dipolar interaction, along with the windowless BLEW-48 for 1 H- 1 H dipolar decoupling. For 1 H → 13 C polarization transfer, the previously reported WIM-24 windowless sequence was used in both the 1 H and 13 C channels. Excellent 2D results are obtained, permitting 1 H peaks to benefit in resolution from the spread of 13 C chemical shifts. Prospects for future techniques and applications are discussed.

Recent advances in coal characterization by 13C and 1H n.m.r.

Abstract Ultralarge magic-angle spinning (MAS) systems (2.4–6.5 cm3) provide a sufficiently large increase in signal-to-noise ratio that 13C MAS experiments without cross-polarization (CP), as well as time-domain 13C CP/MAS studies, can be carried out expeditiously. The non-CP approach allows one to circumvent the uncertainties in quantitation by 13C CP/MAS techniques; however, a more direct determination of TH1ϱ values than by variable contact-time experiments yields promising results on 13C spin counting in coal. The 1H combined rotation/multiple-pulse spectroscopy technique, based on multiple-pulse dipolar line narrowing and MAS, provides a useful complement to 13C MAS techniques, typically yielding poorly resolved 1HCsp2 and 1HCsp3 peaks from which deconvolution nevertheless provides at least a semiquantitative assessment of amounts. A dipolar-dephasing approach and imbibing with perdeutero-pyridine, employed either separately or together, dramatically improve resolution and provide strategies for examining the mobilities of individual coal components.

1H CRAMPS studies of molecular dynamics of a premium coal

Abstract Premium coal No. 601 supplied by the Argonne National Laboratory has been studied under extraction with perdeuterated pyridine. The proton CRAMPS technique was applied to the study of the molecular dynamics of the untreated coal, its evacuated residue following extraction and the extracted material. Saturation using deuterated pyridine improved spectral resolution, resulting in the identification of two aliphatic resonances (0.9 and ≈1.7ppm) and three aromatic resonances (≈6.9, ≈8.1 and ≈9 ppm). The CRAMPS dipolar dephasing experiment showed that the spectral intensity decay consists of two or possibly three components, which can be described by a combination of Gaussian and/or Lorentzian curves. The initial amplitudes of these components and their respective decay time constants are changed with extraction. A correlation between the behaviour in the dipolar dephasing experiment and the molecularmacromolecular structure of coal is observed.

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.

A nuclear magnetic resonance study of the pyridine extraction of coal

Abstract Coal extracts prepared using different pyridine extraction methods have been investigated using 13 C CP/MAS, 1 H CRAMPS and 1 H liquid-state nuclear magnetic resonance spectroscopy. The results show that short and straight alkyl groups are transferred preferentially to the extract of the coal, but for the most part, the structural distribution in the extract resembles that of the original coal. Incorporation of the solvents, pyridine and THF, was observed to occur during the extraction procedure and/or the subsequent workup to isolate the extract. The information obtained from the different n.m.r. techniques was complementary.

1H NMR spectra of coals of various rank, obtained by the CRAMPS technique

Abstract 1 H NMR spectra were obtained of ten U.S. coals of various rank, ranging from a lignite to an anthracite. The CRAMPS technique was employed to average the line broadening effects of 1 H- 1 H dipolar interactions and 1 H chemical shift anisotropy. The spectra consist primarily of two partially resolved peaks, one identified with protons attached to aromatic rings and the other with protons attached to sp 3 carbons. A quantitative analysis of the spectra by simple deconvolution into two (or more) components is at the present time precluded by the difficulty of reproducing experimentally the exact shapes of the 1 H CRAMPS resonance patterns in coals.