Determination of minor components in mixtures using EXAFS

An EXAFS spectrum, obtained by taking the difference between a weighted absorptivity spectrum of a known compound and that of a mixture containing this compound, contained information mainly on the remaining phase(s) in the mixture. The optimum weighting factor was that which gave the minimum value of the definite integral of the radial distribution function (RDF). The efficacy of this technique was demonstrated by the easy identification of Cu₂O, after removal of the CuO contribution, from the spectrum of a mixture of 5% Cu₂O in a ca. 1 + 1 mixture of CuO and ZnO. The method was also used to probe the minor component(s) of a CuO and ZnO calcined catalyst precursor; these showed features consistent with copper dissolved in the ZnO lattice.     

Sol-Gel Synthesis of Protoenstatite and a Study of the Factors That Affect Crystallization

Three different magnesium silicate sols were prepared from Mg(OMe)₂ and TEOS for which hydrolysis with H₂O₂ and H₂O was under stoichiometric, stoichiometric, or over stoichiometric. Xerogels were prepared from the sols by simple evaporation, spray-drying, or freeze-drying. The freeze-dried precursor formed mostly protoenstatite, a high-temperature polymorph of enstatite (MgSiO₃) that is generally not stable at room temperature; the other precursors formed mixtures of protoenstatite and clinoenstatite. The three xerogels and their calcined products were studied with XRD, HTXRD, BET, carbon analysis, TG/DTA and²⁹ Si-NMR. Residual carbon was found to be an important factor in the crystallization, and ²⁹Si-NMR spectroscopy was found to be a better tool than XRD to assess the phase purity of protoenstatite.     

Reactions of bis(η4-1,5-cyclooctadiene)nickel(0) with transition metal halides,and the crystal structure of μ-dichloro-bis(tetrahydrofuran)hexacarbonyldimanganese

Bis-(η⁴-1,5-cyclooctadiene)nickel(0) reacted with η⁵-C₅H₅Fe(CO)₂Cl, η³-C₅H₅Fe(CO)₃Cl, Mn(CO)₅Cl and {Mn[P(OMe)₃](CO)₄}₂ to form metal metal bonded coupling products. Partial reduction of Mn(CO)₅Cl gave [MnCl(CO)₃(THF)]₂ shown to have a chlorine-bridged C_2h structure by X-ray diffraction analysis. Ligand transfer also accompanied the reduction of Fe[P(OMe)₃]₂(CO)₂Br₂ and Fe(CO)₄Cl₂ to Fe[P(OMe)₃]₂(CO)₃ and Fe(CO)₅, respectively. Only partial reduction was observed for Ti(acac)₂Cl₂ and (η⁵-C₅H₅)₂TiCl₂ which gave [Ti(acac)₂Cl]₂ and (η⁵-C₅H₅)₂Ti(py)Cl, respectively.     

Electro-spray synthesis of titanium oxide nano-particles

Nano-particles of anatase (TiO₂) were prepared by pyrolyzing amorphous 20–150 nm precursor particles prepared by electrostatically spraying an ethanolic solution of a modified titanium alkoxide in a heated chamber from a needle to which a 20–30 kV electric potential was applied. By spraying the precursor solution at low Ti concentration in a multi-jet mode, nano-particles that were unimodal around 20 nm were prepared. In most experiments, the charged aerosol was heated to prevent coagulation of solidifying particles. Two competing processes occurred: disruption of droplets into smaller ones, and formation of a hard outer shell, which prevented the partially dried droplets from further disruption. It is suggested that heating provided a thermophoretic effect, which when combined with the influence of a counterfield formed near the inside wall of the chamber, focused the particles onto the collector. Low water content of the precursor solution produced smaller particles and improved drying. Weakening of the spray, attributed to back-ionization by collected, non-conducting particles, was alleviated by addition of ammonium acetate to the precursor solution. Strategies for fabricating nano-particles from gel-forming, reactive precursor solutions are discussed.