On hydrogen bonding in 1,6-anhydro-beta-D-glucopyranose

The geometry of hydrogen bonds in 1,6-anhydro-β-D-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O-H...O and supporting weaker C-H...O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O-H and associated blue shifts of C-H stretching frequencies due to the formation of hydrogen bonds in this system

The use of passive initiation aids in self-propagating high-temperature synthesis

A modification to initiation aid-assisted ignition in bomb calorimetry that involves systemically blending boron and potassium nitrate adjacent to, and within, a bulk structural energetic elemental power blend was developed. Linear regression was used to estimate the nominal heat of reaction for the primary reaction. The technique was applied to the synthesis of TiB2 as a validation study to see if proximity to the literature values could be achieved. X-ray diffraction was used to characterize the product phases of the reactions to determine the extent and the identity of the product phases and any by-products that may have formed as a result of adding the initiation aid. The experimental data indicate the technique approximates the heat of reaction value for the synthesis of TiB2 from Ti/B powder blends and the formation of TiB2 is supported by volume fraction analysis by X-ray diffraction. Some experimental uncertainty remains as X-ray diffraction revealed that the commercially labeled amorphous boron reactant exhibited some crystalline character and may be semicrystalline, as opposed to being completely amorphous. © 2013 The Minerals, Metals & Materials Society and ASM International

Thermodynamics of Condensed Phases: Formula Unit Volume, Vm, and the Determination of the Number of Formula Units, Z, in a Crystallographic Unit Cell

Formula unit (or molecular) volume, Vm, is related to many thermodynamic and physical properties of materials, so that knowledge of Vm is useful in prediction of such properties for known and even hypothetical materials. The symbol Z represents the number of formula units in a crystallographic unit cell; Z thus permits calculation of Vm from the unit-cell volume. Unfortunately, Z is sometimes omitted from published crystal constants (for obscure reasons).We discuss methods for evaluation of Z and Vm, and some of the complications in the assessment of Z. We show how entropy, lattice energy, and bulk isothermal compressibility (a thermoelastic property) are calculated using thermodynamic correlations, with the chalcopyrite CuAlS2 as an example