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[en] Starch is the primary carbohydrate component in the human diet and the major storage polysaccharide in plants. Small angle scattering (SAS) techniques have an extensive track record in illuminating the semi-crystalline lamellar structure of the starch granule, however, there have been few attempts to use SAS techniques to characterise larger-scale structures reported from imaging techniques, such as growth rings, blocklets or pores. In this study, SAS data collected over an extended q range were gathered from dry and hydrated starch powders of various botanical origins. The use of neutrons and x-rays, as well as comparing dry and hydrated granules, allowed different levels of contrast in scattering length density to be probed and therefore selected structural regions to be highlighted. SAXS measurements were obtained with the Bruker Nanostar, whilst SANS measurements taken at the QUOKKA instrument, ANSTO. Data were analysed with the 'unified' method, which fits SAS curves from hierarchical structures, with each level consisting of a Guinier and Porod component which can be refined during fitting. The lowest q range, 0.002 - 0.04 Å-1, was found to be dominated by scattering from the starch granules themselves, especially in the dry powders; however an inflection point from a low contrast structure was observed at 0.035 Å-1. The associated scattering was interpreted within a unified scattering framework with the inflexion point correlating with a structure with radius of gyration -90 Å - a size comparable to small blocklets or superhelices. In hydrated starches, it is observed that there is an inflection point between lamellar and q-4 power-law scattering regions at approximately 0.004 Å-1 which may correlate with growth rings and large blocklets. The implications of these findings on existing models of starch lamellar scattering are discussed.
[en] Isothermal hot microhardness and multi-scan differential scanning calorimetry (DSC) experiments were carried out on an AlZnMgZr, 7000 series aluminum alloy to characterize the evolution and dissolution of GP zones and the formation of the η' phase. Three stages of hardness evolution with aging time were observed for aging in the 25-100 deg C temperature range corresponding to GP zone formation, simultaneous GP zone dissolution and η' formation, and η' formation and coarsening. The isothermal activation energy for the GP zone formation from hot microhardness measurements was about 0.35 eV per atom comparable with that from previous hardness measurements reported in the literature. From variable heating rate DSC scans, the activation energies for GP zone formation and dissolution were 0.75 and 0.92 eV per atom, respectively. The activation energy for η' phase formation and growth of the asquenched specimens as well as aged specimens was about 0.59 eV per atom, and the Avrami index for the transformation was inferred to be in the range 2.3-2.8 (±20%). The activation energies are discussed in terms of various diffusional processes in the Al matrix and are compared with values reported in the literature. (author). 37 refs., 3 tabs., 9 figs
[en] Small-angle x-ray scattering from oriented voids in pyrolytic graphite has been studied. The scattering is found equivalent to that from a dilute dispersion of ellipsoids of revolution called ''Guinier spheres'' of radius of gyration R=(3/5) H]/sup 1/2/=(3/5)(a2 sin2γ+b2 cos2γ)]/sup 1/2/, where γ is the angle between the common axis of revolution (semiminor axis b) and the scattering vector h. Analysis of the data using Hamzeh and Bragg's theory provides values of a, b, and a/b from the ''Guinier'' and the ''Porod'' regions, independently, with good agreement. The theoretically predicted angular dependence of H using ''best-fit'' values of a and b is in good agreement with the experimentally determined value of H, γ varying from 00 to 1800
[en] The addition of 0.3% Mn to a Mg–2Al–2Ca (mass%) alloy improves the minimum creep rate by one order of magnitude compared with the Mn-free alloy. Network-shaped Mg2Ca (C14 structure) and (Mg,Al)2Ca (C36 structure) compounds coexist in the interdendritic regions, while plate-shaped Al2Ca (C15 structure) phases are dispersed in the matrix. Ordered Guinier–Preston (GP) zones form dynamically on the basal plane of the α-Mg matrix during creep deformation. The number density of the fine GP zones in the Mn-containing alloy was found to be higher than that in the Mn-free alloy.
[en] Electron diffraction method has been used to study the structural changes occurring under friction conditions on the surface of carburized 12KhN3A steel. The specific features of the structural transformation under these conditions are attributed to the combined action of deformation and heating. Under the testing conditions a deformation texture forms initially on the surface of the carburized 12KhN3A steel. Under the action of frictional heat monocrystalline areas of frictional austenite (the white zone) appear in the textured α-phase. This austenite is stable when cooled down to room temperature, which is associated with the saturation of the friction surface with austenite-forming elements, i.e. nickel and carbon, on the process of friction. The high hardness of the white zone may be caused by the presence of the coherent depositions of the carbide phase
[en] The interaction of a moving edge dislocation with the Guinier-Preston zones is studied theoretically. An analytical expression for the contribution of this interaction to the value of the dynamic yield stress is obtained.(authors)