Search

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, µ-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO2 in two materials, and as a mixture of UO2, U3O8 and an intermediate species U3O7 in the third material. [ABSTRACT FROM AUTHOR]

A new class of materials, which rely on the dispersion strengthening of SiC particles in addition to precipitation strengthening by nano-precipitates is being developed for the application in molten salt nuclear reactors. A battery of dispersion and precipitation strengthened (DPS) NiMo-based alloys containing varying amount of SiC (0.5–2.5 wt.%) was prepared via a mechanical alloying (MA) route followed by spark plasma sintering (SPS), rapid cooling, high-temperature annealing and water quenching. Lab X-ray Diffraction (XRD), Electron Back Scattering Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were employed in the microstructural characterization of this new type of alloys. It is shown that the NiMo matrix of these alloys is effectively reinforced by dispersion of SiC from the initial powder mixture and nano-Ni 3 Si precipitates, which precipitated during the sintering/annealing process. Furthermore, the matrix is strengthened by solid-solution of Mo in Ni. As a result, these newly developed NiMo alloys take advantage of dispersion, precipitation and solid solution strengthening, which leads to their superior mechanical properties. [ABSTRACT FROM AUTHOR]

The structures of some A UO 4 ( A =Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L 3 -edge. The smaller Ca cation favours a rhombohedral A UO 4 structure with 8-coordinate UO 8 moieties whilst an orthorhombic structure based on UO 6 groups is found for BaUO 4 . Both the rhombohedral and orthorhombic structures can be stabilised for SrUO 4 . The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In the rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably overbonded, which, in the case of rhombohedral α-SrUO 4 , is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction. [ABSTRACT FROM AUTHOR]

Copper-doped nanosized zeolite A crystals were synthesized by an in situ templating approach using [Cu(EDTA)] 2− -complex. The structural properties of the copper containing zeolite crystals were characterized by a suite of different techniques including SEM–EDX, ESR, mid-IR and Far-IR, Raman, in situ XRD and non-ambient neutron powder diffraction. The SEM investigations on the morphology show spheroidal zeolite A crystals with average size ∼200 nm. The asymmetric ESR spectrum shows that the Cu 2+ ion is in a tetragonal-distorted octahedral crystal field. FT-IR and Raman spectroscopies provide information on coordination environment of the copper ion. The band due to stretching vibration of C–N bond, where N is coordinated to the copper ion (C–N–Cu), was observed at 1109 cm −1 in the mid-infrared region. The Raman band due to the Cu–O bond is present at 630 cm −1 indicating the coordination of the Cu 2+ -cation to COO − -group of the EDTA-ion. The XRD data shows an enlarged d -spacing between the adjacent zeolite lattice planes due to the presence of the [Cu(EDTA)] 2− -complex in comparison to template-free LTA zeolite structure. LeBail fitting approach on temperature-dependent in situ X-ray and neutron diffraction profiles have demonstrated the expansion of the zeolite cell during the thermal treatment followed by subsequent contraction with the decomposition of the organic template. [ABSTRACT FROM AUTHOR]

The β -phase of Au 7 Cu 5 Al 4 undergoes a reversible shape-memory phase transformation for which several conflicting martensite phases have been reported. Here we show the significance of the cooling temperature used to obtain the martensite. If Au 7 Cu 5 Al 4 is cooled from the parent phase condition to cryogenic temperatures, e.g. below 200 K, the martensitic phase is orthorhombic (space group Pcmn , a = 4.4841 Å, b = 5.8996 Å, c = 17.8130 Å); however, when this composition is cooled to only ∼260 K it will in general consist of a mixture of orthorhombic and monoclinic phase (the latter has space group P 2 1 / m , a = 4.4742 Å, b = 5.9265 Å, c = 13.3370 Å, β = 91.425°). In contrast, a sample with decreased Al content (Au 7 Cu 5.7 Al 3.3 ) transforms fully to monoclinic phase if cooled to ∼260 K. [ABSTRACT FROM AUTHOR]