Browsing by Author "Taylor, JC"

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    The composition of cement hydrating at 60 deg C from synchrotron radiation
    (Australian X-ray Analytical Association, 2002-07-01) Auld, J; Turner, KS; Thorogood, GJ; Ball, CJ; Aldridge, LP; Taylor, JC
    Cement consists of 5 phases C3S, C2S, C3A, C4AF (where C denotes CaO, S denotes SiO2, A denotes AI2O3 and F denotes Fe2O3) and gypsum. When cement hydrates it forms an amorphous calcium silicate hydrate (C-S-H) as well as the crystalline ettringite and calcium hydroxide. The x-ray diffraction pattern of the hydrated cement is difficult to interpret because of its complexity. In addition, the overlapping lines from the remaining cement compounds make it difficult to quantify the amount of the crystalline components present. Using Rietveld analysis we have been able to interpret the patterns obtained from synchrotron x-ray diffraction patterns obtained at the Photon Factory at the Australian National Beamline Facility using BIGDIF. The changes in the composition of the hydrated cement paste were determined as a function of time during hydration at 60 deg C. © 2002 Australian X-ray Analytical Association Inc
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    Fortran IV least squares computer program for the profile refinement of cubic powder diffraction patterns with cubic harmonic functions.
    (Australian Atomic Energy Commission, 1980-06) Taylor, JC
    A cubic harmonic least squares Fortran IV program has been written for the refinement of cubic structures with disordered or rotating groups, e.g. MX6, which cannot be refined satisfactorily with classical methods. The program has been used to refine neutron powder data for the plastic cubic phases of MoF6, WF6, SF6 and Na2UBr6. The anion density is assumed to lie on the surface of a sphere of radius the M-X distance. The powder pattern intensities and relevant crystal data are input and the program refines the M-X distance, a scale factor, an overall Debye-Waller factor and the cubic harmonic coefficients by a full matrix, least squares treatment. The program is adaptable, with small changes in the structure factor expression, to other disordered cubic structures.
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    General IBM360 computer program for determining the multiplicities of crystal forms, to be used in conjunction with the Rietveld powder profile refinement program.
    (Australian Atomic Energy Commission, 1978-01) Taylor, JC
    IBM360 computer program has been written which generates multiplicity data for the crystal forms in any space group. The input data consist of the unit cell dimensions, lattice centring indicator, system type, equivalent positions of the space group, and the range of h, k, l and 20. The program calculates structure factors for all reflexions over the powder pattern, and sorts hem into forms using the IBM OS SORT/MERGE program. The form indices {hkl} are taken as those of the last member of the form generated, and the multiplicity m{hkl} as the number of reflexions encountered through the form. The {hkl}, m{hkl} data serve as input for the Rietveld powder profile refinement program for the refining of structural parameters with powder data. Previously, these had to be deduced from the International Tables for X-Ray Crystallography Volume 1, which is difficult to use with the higher symmetry systems, As the {hkl} and multiplicity generation is a major part of the effort needed to set up the Rietveld program, the present program reduces significantly the work involved in these refinements. The program gives [{hkl}, m{hkl}] cards in about 30-50 seconds of CPU time.
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    A modified version of the Busing-Martin-Levy least squares program for the direct fitting of structures to powder diffraction patterns by the method of profile analysis
    (Australian Atomic Energy Commission, 1973-03) Taylor, JC; Cox, GW
    The Busing-Martin-Levy (BML) crystallographic least squares program has been modified to handle the case of the overlapping diffraction data encountered in powder patterns. Each count along the scan is treated as a single observation and the pattern is considered to be the superposition of the (h,k,l) Gaussian peaks, as in the method of Rietveld (Acta Cryst., 22, 151 (1967)). In this way the structure is fitted directly to the diffraction pattern, while details of the profiles are not lost. For this reason, together with the fact that a larger number of observations are used, the method is superior to conventional refinements with integrated intensities (which can also be done with the present program).
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    The structures of fluoride II - the structure of uranyl fluoride
    (Australian Atomic Energy Commission, 1973-01) Taylor, JC; Wilson, PW
    A neutron diffraction study of UO2F2 has been carried out. Previous workers have proposed that line broadening in the diffraction pattern of UO2F2 is due to puckering of the hexagonal fluorine atom rings and consequent stacking disorders. It is shown that, in our samples, most of the line broadening is due to the effects of particle size and shape. The puckering of the layers, if present, must be determined from a neutron analysis of the deviation of the z-coordinate of the fluorine atom from the value 0.333, using reflexions for which h-k = 3n. There are only two resolved lines of this type in the pattern, making it difficult to decide whether the previously proposed complex disorder structures are better than a simple model where the layers are unpuckered. It is shown that single crystal studies will be necessary to distinguish between the alternative models.