No description available.

No description available.

No description available.

Previous work by Heal had shown that X-irradiated sodium azide crystals dissolved in water produced small amounts of nitrogen gas, hydroxyl ion and ammonia, thereby indicating that some decomposition had occurred. Heal also observed colours in the material, similar to those of the X-irradiated alkali halides for which a whole series of colour centres responsible have been postulated. It was therefore decided to investigate the colour centres of the alkali azides, partly to extend the colour centre research, and partly to illuminate the X-ray decomposition processes. Crystalline plates of NaN₃, KN₃, RbN₃ and CsN₃ were irradiated at liquid nitrogen and room temperature, using a Machlett AEG-50 tungsten target X-ray tube, operated at 50 KVP. The absorption spectra of the irradiated samples were measured at liquid nitrogen temperature with a Cary model 14 recording spectrophotometer. The low temperature spectra consisted of three bands. The A band, peaking at 612, 568, 578 and 592 mu for NaN₃, KN₃, RbN₃ and CsN₃, respectively, is ascribed to F centres. The anomalous sodium azide band is related to its trigonal crystal structure, differing from the body centred tetragonal of the other azides. The B band, peaking at 361, 374 and 390 mu for KN₃, RbN₃ and CsN₃ respectively, was strong and triple, there being shoulders about 30 mu on each side of the main peak. For NaN₃ it was weak, single and peaked near 330 mu. Tentatively, it is ascribed to the centre. The C band, peaking about 740, 790, 820 and 850 mu for NaN₃, KN₃, RbN₃ and CsN₃ is weak and single. It may be due to F1 centres. The room temperature spectra were strikingly different from each other, except for RbN₃ and CsN₃. For NaN₃ five bands were observed at 342, 560, 630 , 730 and 860 mu; the latter four were weak and may be an electronic vibrational spectrum. The strong 342 mu band is ascribed to the presence of sodium metal in some non-colloidal form; a correlation between the band and the ionisation potential of the metal is noted. In KN₃ three bands at 760 (strong), 590 (strong shoulder) and 340 mu (weak) were obtained. The first two are ascribed to small F centre aggregates of the M,R type though no definite assignations are made. RbN₃ and CsN₃ spectra both consist of a broad peak showing fine structure, the highest peaks occurring at 330 mu and 375 mu respectively. It is considered uncertain that all the absorption is due to the impurity held responsible for the fine structure. / Science, Faculty of / Chemistry, Department of / Graduate

The structures of four compounds representing each of the organic (natural product), inorganic and organometallic classes of compounds have been determined by single-crystal X-ray diffraction, and the methods employed in solution of the structures have been discussed briefly. For all four structures, the intensity data were collected on a single-crystal diffractometer with [formula omitted] radiation and a scintillation counter. The structure of the alkaloid, daphmacrine methiodide (acetone solvate), was determined from heavy-atom Patterson and Fourier syntheses, and refined by block-diagonal least-squares methods to a final R value of 0.089 for 1834 observed reflections. The absolute configuration was determined by the anomalous dispersion method. The molecule consists of two cage-structures which are linked by a chain of two carbon atoms, and the bond lengths and valency angles do not differ from normal values. 2 4-, For both exo-tricyclo [formula omitted] silver nitrate and silver nitrate itself, the silver ion was determined from Patterson syntheses to be lying in a pseudo-special position, so that the resulting electron-density maps exhibited pseudo-symmetry. A trial-and-error method based on detailed study of the shape of the Ag-Ag Patterson peaks was adopted to find the exact location of the silver ions, and from the resulting electron-density maps the true light atom peaks could be discerned from their images. The refinement was carried out by full-matrix least-squares, and the final R for the complex of silver nitrate was 0.105 and for silver nitrate was 0.067. The structure of the complex consists of thick layers perpendicular to the a crystallographic axis, and separated by ½ a. The silver ion is coordinated roughly tetrahedrally to the double bond of the hydrocarbon (in the exo-position, [formula omitted]), and to three nitrate groups [formula omitted]. The layers are held together by van der Waals forces. The silver nitrate structure consists of layers of silver ions parallel to the b crystallographic axis, and separated by ½ b, with the nitrate groups bridging the gap between layers. Previously observed inequalities in the N—O distances have been removed, all three bond lengths in the nitrate ion being 1.26 (l)Ǻ. The anisotropic thermal motion has been described. The N,N-dimethyl(ferrocenylmethyl)ammonium tetrachlorozincate hydrate structure contains seven heavy atoms, and it was not possible to resolve the Patterson peaks because of the overlap. A direct sign-determining procedure was employed to locate the heavy atoms, and the light atoms were located from resulting electron-density maps. The structure was refined to a final R value of 0.068 for 2012 observed reflections. The mean bond distances are Fe-C = 2. 04Ǻ and C-C (cyclopentadienyl rings) = 1.43Ǻ. Groups of four cations, two anions and two water molecules (two formula units), are linked around centres of symmetry by N-H...Cl (3.11Ǻ), N-H...0 (2.76Ǻ) and 0-H...Cl (3.05, 3.17Ǻ) hydrogen bonds. / Science, Faculty of / Chemistry, Department of / Graduate

Acetyltriphenylgermane, (C₆H₅)₃GeCOCH₃, crystallizes in the monoclinic system with a = 15.30, b = 14.53, c = 7.68Å, and β = 94.8°. The space group is P2₁/c and there are four molecules per unit cell, thus each molecule forms an asymmetric unit in the cell. The intensities of 2537 reflections were measured by means of a scintillation counter using CuKα radiation. The structure was determined by heavy atom Patterson and Fourier synthesis and refinement was by least-squares methods. The final discrepancy, R, for 1834 observed reflections is 0.075. The compound was found to be tetrahedral about the germanium atom, with only small deviations caused by the spreading of the phenyl rings. The phenyl rings are planar with a mean C-C bond distance of 1.383 Å, mean C-C-C bond angle of 120.0°, and a mean C-H bond distance of 1.09 Å. Intermolecular interaction causes one ring to deviate from a symmetric propeller orientation. Two Ge-C bond distances were found: Ge-Cphenyl distance of 1.945 Å and Ge-Cacetyl distance of 2.011 Å. The longer Ge-C bond is attributed to contribution from a resonance structure in which there is no formal bond between germanium and the carbonyl carbon, resulting in a partial negative charge on the oxygen and a partial positive charge on the germanium. This is supported by the electronegativity difference between carbon and germanium. The C=O bond distance is 1.20 Å. / Science, Faculty of / Chemistry, Department of / Graduate

The techniques of x-ray diffraction of liquids are employed to study the salt TlCo(CO)4 in two solvents, tetrahydrofuran and dimethylsulfoxide. Radial distribution functions calculated from scattering data are analyzed in terms of the structure of these solutions, and the results are compared to those of other studies of the same and similar solutions investigated by infrared techniques. In tetrahydrofuran, a solvent of low dielectric constant, the evidence indicates close association of anion and cation, and contact ion pair and covalent models are presented and discussed. In dimethylsulfoxide, a solvent of high dielectric constant, the evidence indicates relatively loose association or no association of anion and cation, and solvent-separated ion pair and free ion models are presented and discussed.

by Cheung Man Kit. / Errata slip inserted / Bibliography: leaves 83-84 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 88-90.

X-ray diffraction (XRD) has become one of the most powerful techniques for crystal structure studies and phase composition identifications. In this thesis, using the quantitative XRD (QXRD) technique to assist the development of reliable engineering strategies of stabilizing hazardous lead pollutants into ceramic matrix and resource recovery will be introduced. Metal stabilization strategies have been sought to replace the traditional disposal methods for the management of waste metal sludge. To demonstrate the unique capability of QXRD in monitoring the lead incorporation behavior, different ceramic precursors was used to react with lead oxide to investigating metal transformation mechanisms during the sintering process. When heating with alumina, influences of Pb/Al molar ratio, temperature, and treatment time on lead incorporation efficiency on the formation of PbAl2O4and PbAl12O19phasesweresuccessfully revealed by QXRD. Moreover, the influence of silica on lead stabilization effect was analyzed by blending amorphous SiO2 and quartz with -Al2O3 as the precursors. The results suggest that both silica precursors could crystallochemically incorporate lead into the lead feldspar (PbAl2Si2O8) structure in significant quantities. In addition, by sintering clay-based precursors with lead oxide, a complete lead incorporation into lead feldspar occurred above 950℃. Lead glass-ceramics were produced by thermally treating waterworks sludge with lead oxide, and amorphous contents in the products were quantified using QXRD. When hematite was used as a Fe-rich precursor to treat lead oxide, three types of lead ferrite crystals were observed and quantitatively determined. Furthermore, the mechanism of incorporating lead-zinc tailing with P-rich municipal waste sludge ash was investigated under different thermal conditions. By detailed X-ray diffraction analysis, Pb was crystallochemically incorporated into the Ca5.5Pb4.5(PO4)6(OH)2 crystalline structure and Zn was stabilized into Zn(Al0.5Fe1.5)O4 spinel phase. The stability of lead in all the product phases was evaluated byprolonged acid leaching, and the results indicated the lower intrinsic lead leachability of the product phases. The progress in optimizing experimental parameters in resource recovery suggest an opportunity of using QXRD technique to investigate the feasibility of extracting Pb from CRT and recycling P by struvite precipitation. A novel process of thermal reduction treatment with the addition of metallic iron (Fe(0)) to recover lead from cathode ray tube (CRT) funnel glass was introduced. The optimal operational parameters for the thermal extraction of lead from CRT glass were determined by QXRD technique as 50 wt.% Fe addition, heating at 700 °C for 30 min. Struvite crystallization for phosphorus recovery from wastewaters has gained strong attention. While the aspects of application and modeling have been widely studied, the phase composition of recovered phosphorus products was rarely reported. The obtained high degree of accuracy supports the validity of Rietveld method for the quantification of both amorphous and crystal phases in the products. QXRD results suggest the amount of increase of struvite in the products with the elevated N/P molar ratio from 0.2/1 to 1.2/1. All the results have demonstrated the capability of QXRD in contributing to the advancements of both material and environmental technologies. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy