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[en] The Cape Coast granite complex, which is associated with the metasedimentary basin rocks of Birimian in Ghana are, also referred to as the basin - type granitoids, and forms part of the two major types of Eburan granitoids in Ghana. The Cape Coast granite complex is characterized by various intrusions such as acid intrusion and pegmatites. The pegmatites associated with the Cape Coast granite complex are noted to be related to the margin of the granite batholiths. The mineralogical characteristics of the pegmatites have been documented, but there is little published information on the geochemical characteristics, source and tectonic settings and mode of emplacement of these pegmatites as compared to the Cape Coast granite complex. The objectives of this project were therefore to determine the compositions and geochemistry of the pegmatite and use the data to infer the possible source of these pegmatites. The geochemical data indicates that the pegmatites of the Egyaa, Saltpond and Akim Oda areas consist of a low to high-K, S-type characteristics, with three samples from Saltpond having metaluminous character. Lower values of molar CaO/ (MgO + FeOtot) coupled with higher values of molar Al2O3/ MgO + Fetot) suggest their derivation from partial melting from metabalistic source. The data suggests the rocks so have emplaced in a volcanic arc and ocean ridge geotectonic environment. (au)
[en] The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl2O4·10H2O converted to Ca3Al2(OH)12 and amorphous aluminum hydroxide. Ca2Al2O5·8H2O transformed via the intermediate phase Ca4Al2O7·13H2O to Ca3Al2(OH)12 and gibbsite, Al(OH)3. The phase Ca4Al2O7·19H2O reacted via the same intermediate phase to Ca3Al2(OH)12 and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported
[en] High-quality in situ synchrotron powder diffraction data have been used to investigate the decomposition products of bischofite in the temperature range 298 ≤ T ≤ 873 K. At least eight phases could be identified: MgCl2·nH2O (n = 1, 2, 4 and 6), MgOHCl·nH2O (0 ≤ n ≤ 1.0), MgCl2 and MgO. The crystal structures of three magnesium chloride hydrates MgCl2·nH2O (n = 1, 2, 4) were determined ab initio, replacing published Rietveld refinements from low-quality powder diffraction data based on similarity criteria. MgCl2·4H2O was found to be disordered and has been correctly determined for the first time. The crystal structures of bishcofite and MgCl24H2O consist of discrete Mg(H2O)6 and MgCl2(H2O)4 octahedra, respectively. The crystal structure of MgCl2·2H2O is formed by single chains of edge-sharing MgCl2(H2O)4 octahedra, while in the case of MgCl2H2O double chains of edge-sharing MgCl(H2O)5 octahedra are found. The phases in the system MgCl2-H2O are intermediates in the technologically important process of MgO and subsequently Mg production. The same phases were recently found to be of key importance in the understanding of cracks in certain magnesia concrete floors
[en] The main objective of this project is to develop an advanced fuel matrix capable of achieving extended burnup while improving safety margins and reliability for present operations. In the course of this project, the authors improve understanding of the mechanism for high burnup structure (HBS) formation and attempt to design a fuel to minimize its formation. The use of soluble dopants in the UO2 matrix to stabilize the matrix and minimize fuel-side corrosion of the cladding is the main focus
[en] Calcium aluminate decahydrate is hexagonal with the space group P63/m and Z = 6. The compound has been named CaAl2O4·10H2O (CAH10) for decades and is known as the product obtained by hydration of CaAl2O4 (CA) in the temperature region 273-288 K - one of the main components in high-alumina cements. The lattice constants depend on the water content. Several sample preparations were used in this investigation: one CAH10, three CAD10 and one CA(D/H)10, where the latter is a zero-matrix sample showing no coherent scattering contribution from the D/H atoms in a neutron diffraction powder pattern. The crystal structure including the positions of the H/D atoms was determined from analyses of four neutron diffraction powder patterns by means of the ab initio crystal structure determination program FOX and the FULLPROF crystal structure refinement program. Additionally, eight X-ray powder diffraction patterns (Cu K[alpha]1 and synchrotron X-rays) were used to establish phase purity. The analyses of these combined neutron and X-ray diffraction data clearly show that the previously published positions of the O atoms in the water molecules are in error. Thermogravimetric analysis of the CAD10 sample preparation used for the neutron diffraction studies gave the composition CaAl2(OD)8(D2O)2·2.42D2O. Neutron and X-ray powder diffraction data gave the structural formula CaAl2(OX)8(X2O)2·[gamma]X2O (X = D, H and D/H), where the [gamma] values are sample dependent and lie between 2.3 and 3.3.
[en] Hausmannite (Mn3O4) nanoparticles have been prepared by mixing aqueous solutions of manganese nitrate and hexamethylenetetramine from 20 to 80 C. Activation energy for the particle formation increases from 0.5 to 0.8 kJ/mol with nitrate concentration. Nanoparticles (18-41 nm) with a faceted structure are prepared by this method. We describe synchrotron in-situ time-resolved XRD experiments in which Mn3O4 nanoparticles are reduced to MnO and subsequently reoxidized in ramping temperature conditions. The temperature of Mn3O4 to MnO reduction decreases as Mn3O4 particle size decreases. On oxidation, 18 nm and smaller MnO nanoparticles formed the intermediate phase Mn5O8 (MnO Mn3O4 Mn5O8 Mn2O3), while larger MnO particles oxidized to Mn3O4 then directly to Mn2O3. Formation of Mn3O4 occurred at lower temperature for smaller MnO nanoparticles. Further oxidation to Mn2O3 required higher temperatures for the initially smaller MnO nanoparticles, indicating that the kinetics of forming the new oxide phases is not controlled by diffusion, where smaller distance favors faster reaction, but by nucleation barrier.
[en] In November 2000, the U.S. Department of Energy (DOE) Richland Operations Office (RL) initiated an effort to produce a single, strategic perspective of RL Site closure challenges and potential Science and Technology (S and T) opportunities. This assessment was requested by DOE Headquarters (HQ), Office of Science and Technology, EM-50, as a means to provide a site level perspective on S and T priorities in the context of the Hanford 2012 Vision. The objectives were to evaluate the entire cleanup lifecycle (estimated at over $24 billion through 2046), to identify where the greatest uncertainties exist, and where investments in S and T can provide the maximum benefit. The assessment identified and described the eleven strategic closure challenges associated with the cleanup of the Hanford Site. The assessment was completed in the spring of 2001 and provided to DOE-HQ and the Hanford Site Technology Coordination Group (STCG) for review and input. It is the first step in developing a Site-level S and T strategy for RL. To realize the full benefits of this assessment, RL and Site contractors will work with the Hanford STCG to ensure: identified challenges and opportunities are reflected in project baselines; detailed S and T program-level road maps reflecting both near- and long-term investments are prepared using this assessment as a starting point; and integrated S and T priorities are incorporated into Environmental Management (EM) Focus Areas, Environmental Management Science Program (EMSP) and other research and development (R and D) programs to meet near-term and longer-range challenges. Hanford is now poised to begin the detailed planning and road mapping necessary to ensure that the integrated Site level S and T priorities are incorporated into the national DOE S and T program and formally incorporated into the relevant project baselines. DOE-HQ's response to this effort has been very positive and similar efforts are likely to be undertaken at other sites. Hanford was the first site where such a unique, comprehensive assessment was performed. This paper provides a means to share this approach with other sites and to introduce Hanford's S and T challenges to potential technology providers and other interested parties