Bernard G. Silbernagel

An NMR study of the alkali metal intercalation phase LixTiS2: Relation to structure, thermodynamics, and ionicity

The Knight shift and electric quadrupole coupling constant have been measured as a function of lithium concentration in the continuous intercalation phase LixTiS2 where 0⩽x⩽1. These NMR data, when compared with observations of c axis dilation and thermodynamics of this phase, suggest the donation of an appreciable fraction of the Li 2s electron to the TiS2 layers during intercalation, with the fraction diminishing as x increases. The relation of the charge donated to each of the observed quantities is discussed.

Anisotropy of the proton spin–lattice relaxation time in the superconducting intercalation complex TaS2(NH3): Structural and bonding implications

The nature of the interaction responsible for the formation of molecular intercalation complexes between Lewis bases and layered transition metal dichalcogenides is not well understood. To some extent this is due to a lack of structural information. A prototype of these complexes is TaS2(NH3), in which monolayers of ammonia are inserted between the metallic, superconducting layers of TaS2. The compound is crystalline and stoichiometric. Measurement of the anisotropy of the proton spin–lattice relaxation time at 300 °K indicates that the molecular threefold symmetry axis is not perpendicular to the disulfide layers as suggested by other workers, but is parallel to the layers. This orientation precludes direct interaction between the molecular lone pair orbital and the transition metal atoms. The interactions governing the structure of this complex may be similar to those obtaining in the intercalation complexes between TaS2 and a number of substituted pyridines, in which complexes the axis of the lone pair...

Electron spin resonance of isolated coal macerals

Abstract The g-value, linewidth, lineshapes, carbon radical densities and microwave saturation response have been measured for over 50 exinite, vitrinite, and inertinite maceral samples of coals varying in rank from subbituminous type C to anthracite. The process of maceral isolation has also been examined by comparing carbon radical properties of the starting coal with those of intermediates in the separation procedure: after comminution, demineralization and centrifugation. The g-values, linewidths and lineshapes appear unaltered by the separation steps, while there is some decrease in carbon radical density upon comminution and an increase upon demineralization. Carbon radical g-values fall with increasing coal rank for both vitrinites and exinites, a change associated with loss of oxygen at higher rank. Linewidths generally increase with rank for both vitrinites and exinites, but are extremely narrow (≈1G) for some inertinites, suggesting exchange narrowing between radicals. Radical densities and the ability to absorb microwave radiation increase with coal rank for exinites and vitrinites, reflecting stronger inter-radical interactions at higher radical densities.

Wideline NMR studies of ammonia intercalation complexes. I. TaS2 (NH3) and TiS2 (NH3)

Wideline NMR observations of the 1H and 15N nuclei in the intercalation complexes TaS2(NH3) and TiS2(NH3) have been made at temperatures from 5 to 300 K. Changes in the dynamics of the intercalated NH3 molecules have been traced by determining the temperature dependence of the linewidths and second moments of the 1H resonance. Above 160 K, molecular motions average the proton dipolar interactions to zero, which requires that molecular diffusion and reorientation occur at rates in excess of 105 s−1. The residual proton shifts reflect the magnetic properties of the complexes. Around 125 K, a strong line broadening indicates that translation and reorientation have slowed to this rate. Although translation and reorientation are correlated, the data suggests that they are not tightly coupled to one another. The molecules continus to spin about their threefold (C3) symmetry axes at 5 K, and saturation studies of the resonance line suggest that the rate for this spinning is still ∼108 s−1 at this temperature. In...

Molecular dynamics of linear and branched alkanes: Simulations and nuclear magnetic resonance results

We have extended two previously introduced models of n‐alkanes to numerically investigate the liquid‐state dynamics of branched alkanes. We compare our results with new experimental measurements of diffusion and 13C‐NMR T1 relaxation. Significant systematic and quantitative agreement is found between simulated and experimental values. We demonstrate the role of branching in controlling the temperature dependence of diffusion and point out the effect of global single‐chain relaxation processes on the local intramolecular dynamics probed by the 13C‐NMR experiment.

Coal Science: Basic Research Opportunities

More fundamental knowledge of coal (knowledge of its structure and its behavior during conversion processes) is essential before we can generate new technologies necessary for the efficient use of coal in the future. Herein are suggested specific basic research opportunities in the areas of coal characterization, gasification, combustion, and liquefaction, along with an assessment of the impact such research programs could have. Critical characterization needs include qualitative and quantitative determination of the chemical forms of carbon, oxygen, nitrogen, and sulfur and reliable methods for the measurement of surface area, pore volume, and weight-average molecular weights. Mechanistic studies aimed at increasing understanding of the thermal breakdown of the functionalities in coal, the behavior of coal in the presence of molecular and donor hydrogen environments, and carbon gasification and hydrocarbon synthesis reactions starting from carbon monoxide and hydrogen will lay the scientific foundation for the development of new processes for converting coal into clean usable fuels and chemicals.

Alkali intercalation compounds of vanadium and chromium sulfides: An NMR study

Abstract NMR techniques have been used to study a series of materials, LiVS 2 , NaVS 2 , LiCrS 2 , and NaCrS 2 , which, while isostructural with the titanium intercalation compounds, are much less well understood because the formation of CrS 2 and VS 2 have only recently been reported. The resonance shifts and quadrupolar coupling strengths of the alkali metal atoms in LiVS 2 and NaVS 2 are very similar to those in the corresponding TiS 2 intercalation compounds; the vanadium NMR properties are independent of the choice of alkali metal atoms. A transferred hyperfine interaction between the Na nuclei and the localized Cr electronic moment is observed in NaCrS 2 . The absence of an analogous interaction in LiCrS 2 is explained on the basis of the electronic character of the Li atom.

ESR of Carbon Radicals in Isolated Coal Macerals

ESR g-values, linewidths, and radical densities are compared with elemental analyses and other properties of a series of coal macerals isolated by the gravity centrifugation technique. Increases in g-values are attributed to the presence of phenolic oxygen pendant to the condensed ring structures of the coal. For vitrinites, all three ESR parameters vary with increasing coal rank: g-values fall, while linewidths and radical densities increase. Linewidths decrease and radical densities increase for more condensed inertinite forms having lower H/C values. Exchange between radicals is suggested to explain the observed narrowing phenomenon.

Evaluation of solid electrolytes for high temperature lithium batteries: A preliminary study☆

Abstract The lithium ionic conductivity of materials prepared by reaction of lithium iodide with anhydrous and hydrated aluminum sulfate has been investigated b