No abstract

Details of the synthesis, physical and spectroscopic characterization, and thermal decomposition of tris(benzylthiolato)bismuth, (BnS)(3)Bi, Bn = CH(2)C(6)H(5), are presented. Results from pyrolysis of (BnS)(3)Bi demonstrate that this compound is a convenient precursor to phase-pure, polycrystalline Bi(2)S(3) with low carbon and hydrogen contamination under mild thermal conditions (ca. 275 degrees C). Flow-tube pyrolysis produces small ( approximately 1 &mgr;m) spherical particles, whereas sealed-tube pyrolysis produces 6-&mgr;m diameter spherical particles composed of radiating acicular crystallites. Bi(2)S(3) was characterized by X-ray powder diffraction and scanning electron microscopy.

Rietveld quantitative X-ray diffraction analysis of the fly ash Standard Reference Materials (SRMs) issued by the National Institute of Standards and Technologies was performed. A rutile (TiO 2 ) internal standard was used to enable quantitation of the glass content, which ranged from 65% to 78% by weight. The GSAS Rietveld code was employed. Precision was obtained by performing six replicates of an analysis, and accuracy was estimated using mixtures of fly ash crystalline phases and an amorphous phase. The three low-calcium (ASTM Class F) fly ashes (SRM 1633b, 2689 and 2690) contained four crystalline phases: quartz, mullite, hematite, and magnetite. SRM 1633b also contained a detectable level of gypsum, which is not common for this type of fly ash. The high-calcium (ASTM Class C) fly ash, SRM 2691, had eleven crystalline phases and presented a challenge for the version of GSAS employed, which permits refinement of only nine crystalline phases. A method of analyzing different groups of nine phases and averaging the results was developed, and tested satisfactorily with an eleven-phase simulated fly ash. The results were compared to reference intensity ratio method semiquantitative analyses reported for most of these SRMs a decade ago. © 2000 International Centre for Diffraction Data. [S0885-7156(00)00403-6] Powder Diffraction 15 (3),

Waxy wheats possess unique starch functional properties that may be useful in specific end‐uses. To assess the physicochemical, thermal, and pasting properties, starches from seven waxy genotypes originating from two wheat classes, tetraploid durum and hexaploid hard red spring (HRS), were evaluated and compared with their counterpart non‐waxy wild types. The amylose content ranged from 2.3% to 2.6% in waxy durum lines, compared to 29.2% in normal durum control, and 2.1% to 2.4% in waxy HRS, compared with 26.0% in normal HRS control. Significant differences in the degree of crystallinity were observed between the waxy and control starches, despite similar A‐type X‐ray patterns, although differences between the two wheat classes were non‐significant. Both, control and waxy starches displayed an X‐ray peak corresponding to the amylose‐lipid complex, but the intensity of the peak was markedly lower in the waxy starches. The waxy durum starches exhibited the highest transition temperatures as measured by Differential Scanning Calorimetry (DSC), whereas, the enthalpy of gelatinization of most waxy genotypes was statistically higher than that of the controls. All waxy starches displayed high peak viscosity, high breakdown, and low setback profile as measured by the Rapid Visco Analyser (RVA). Texture analysis of RVA gels revealed significant differences between waxy and non‐waxy wheats, as well as between waxy tetraploid and hexaploid wheats, confirming that the nature and class of wheat starch would play a significant role when using waxy wheat blends in different wheat‐based products.

The benzyl-substituted tin chalcogenides (Bn 3 Sn) 2 S (1), (Bn 2 SnS) 3 (2), (Bn 3 Sn) 2 Se (3), and (Bn 2 SnSe) 3 (4), prepared from the corresponding benzyltin chloride and anhydrous sodium chalcogenide in THF, are convenient single-source precursors for tin sulfide or tin selenide. Pyrolysis (450 °C) of these precursors gave gray or black powders and bibenzyl as the major products. X-ray diffraction (XRD) analysis of the powders from the linear compounds 1 and 3 showed that SnS and SnSe were produced along with elemental tin, as expected from the precursor stoichiometry. In contrast, the solids generated by cyclics 2 and 4 contained only SnS and SnSe respectively. Solid solutions of the formula Sn(S x Se 1-x ) were prepared by heating mixtures of 2 and 4. The value of x could be controlled by varying the ratio of 2 to 4. Combustion analysis showed less than 1% residual carbon in all tin sulfide and tin selenide samples.