Results 1 - 10 of 107523
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[en] The objective of this work was to search for possible uses of the raw-material agalmatolite in ceramics considering the prince and the possible enhancement of the properties of the products. (author)
[en] Recent work has been devoted to develop a simplified bolometer type device which would enable in-reactor testing of more radiation resistant substrates, meander materials, and electrical contacts. The bolometer configurations based on a thin sandwich structure, make possible more reliable electrical connections, as well as facilitating PIE. Different materials for use as the insulating support frame for the delicate sensor substrate have been examined. Initially machineable glass ceramic (MACOR) was considered, and trial supports fabricated to test different configurations and electrical contact designs, however the high boron content makes this material unsuitable for a nuclear environment. Similar support frames were then made from alumina, this being the perfect choice for the application. But alumina was rejected due to cost of machining and fragility. Finally support frames of anodized aluminium were tested. These gave more than adequate electrical insulation for operating temperatures up to at least 400 deg. C. Ionizing radiation at high temperature and dose has no effect on the sensor resistance values. Several prototypes are now awaiting final in-reactor (BR2) characterization at SCK-CEN, Mol.
[en] The study intends to look at the most suitable aluminium salt to produce a single-phase a-alumina by the hydrothermal method. In the process to produce alumina from the calcination of aluminium hydroxide (Al(OH)3), three different aluminium salts namely aluminium sulfate (Al2(SO4)2), aluminium nitrate (A(NO3)3) and aluminium chloride (AlCl3) were tried. The process involved the used of NH4OH as the precipitating medium. Aluminium hydroxide produced from each of these salts were characterised by x-ray diffraction (XRD) technique to identity the crystalline phase. Aluminium hydroxide produced by all the different aluminium salts is present as boehmite or pseudo-boehmite phase. Aluminium hydroxide produced from Al2(SO)2, Al(NO)3 and AlCl3 shows the transformation of the boehmite phase to a α-alumina phase at 500 0C. On further heating, the α-alumina continuously formed at 800 oC followed soon at 1000 oC. But for the Al(NO3)3 salts a different phase transitions occurs on heating especially at 1000 oC. Here it was observed not a single alumina phase is presence but the presence of both α and γ--alumina phases. At 1300 oC, the single α-alumina phase was formed. The study concluded that aluminium sulphate is recommended in order to obtain a single-phase α-alumina with the required characteristics. (Author)
[en] Highlights: • The addition of Al changed the segregation of Cr element. • Y could promote the selective oxidation of Cr. • The selective oxidation of Al was promoted with addition of Y and Al. • The oxidation resistance of T-700 was improved with addition of Y and Al. - Abstract: The oxidation behavior of Tribaloy T-700 alloys with the additions of 0.5 wt.% yttrium, 5 wt.% Al and a combination of the two have been studied. Addition of yttrium decreased the oxidation rate and the selective oxidation of Cr was promoted. Oxidation rate also decreased with the Al addition and the selective oxidation of both Cr and Al was occurred simultaneously. The selective oxidation of Al was promoted more significantly with the addition of yttrium plus aluminum. The benefit was especially pronounced at 1000 °C, with a continuous external Al2O3 scale developed at the scale/alloy interface without any noticeable internal oxides
[en] An Al-AlN core-shell structure is beneficial to the performance of Al-Al2O3 composites. In this paper, the phase evolution and microstructure of Al-Al2O3-TiO2 composites at high temperatures in flowing N2 were investigated after the Al-AlN core-shell structure was created at 853 K for 8 h. The results show that TiO2 can convert Al into Al3Ti (~1685 K), which reduces the content of metal Al and rearranges the structure of the composite. Under N2 conditions, Al3Ti is further transformed into a novelty non-oxide phase, TiCN. The transformation process can be expressed as follows: Al3Ti reacts with C and other carbides (Al4C3 and Al4O4C) to form TiCx (x < 1). As the firing temperature increases, Al3Ti transforms into a liquid phase and produces Ti(g) and TiO(g). Finally, Ti(g) and TiO(g) are nitrided and solid-dissolved into the TiCx crystals to form a TiCN solid solution.
[en] Aluminum samples have been investigated during and after exposure to well-controlled amounts of NaCl and humidified air. With infrared reflection absorption spectroscopy the deliquescence of NaCl crystallites could be followed in situ at high relative humidity (RH), as well as the growth of different aluminum oxide, hydroxide and chloride corrosion products. Investigations with scanning electron microscopy and energy dispersive X-ray analysis after exposure revealed the growth of filaments representative of filiform corrosion and chlorine enrichment in the filament heads. The exposed samples were further investigated with synchrotron based photoelectron microscopy/spectroscopy. Spectra taken of the Al 2p core level showed an intricate structure with multiple components in the core level. By means of mapping the intensity of the different chemical states within the core level the distribution of compounds over the surface could be determined. An enrichment of aluminum chloride containing compounds was found in the heads of the filaments, whereas aluminum oxides or hydroxides were observed both inside and outside the filaments
[en] Mixed aluminium chloro/fluoro anions are formed in dichloromethane solution by the interaction of AlCl3 and [Ph3PhCH2P] [H2F3]. Aluminium-27 n.m.r. studies are restricted to the stoichiometric ranges F/Al from 1:1 to 3:1 and F/Al>8:1. Between these limits rapid precipitation reactions occur. In the fluoride-rich stoichiometric range there is rapid exchange on the n.m.r. time scale between the aluminium fluoro anion and free fluoride, so that a direct identification of the species by the multiplicity of the resonance is not possible. Indirect evidence strongly suggests that the aluminium species is [AlF4]-. In the F/Al stoichiometry range from 1:1 to 3:1 aluminium-27 resonances were observed for all the other possible [AlClχF4-χ]- species. Studies on the aluminium iodo/fluoro system support the identification of [AlF4]-, but the system is labile and the mixed iodo/fluoro species undergo rapid disproportionation. 12 refs., 1 fig
[en] A process is disclosed for producing an anhydrous aluminum chloride composition from a water-based aluminous material such as a slurry of aluminum hydroxide in a multistage extraction process in which the aluminum ion is first extracted into an organic liquid containing an acidic extractant and then extracted from the organic phase into an alkali metal chloride or chlorides to form a melt containing a mixture of chlorides of alkali metal and aluminum. In the process, the organic liquid may be recycled. In addition, the process advantageously includes an electrolysis cell for producing metallic aluminum and the alkali metal chloride or chlorides may be recycled for extraction of the aluminum from the organic phase
[en] Both α-alumina and aluminium nitride are insulators. They are widely applied as tunnel barriers. On the basis of first-principles calculations, it is shown here that the conduction band of these two compounds is of fundamentally different origin than generally assumed. The bottom of the conduction band of both compounds is primarily derived from oxygen/nitrogen 3s states with an admixture of a small amount of aluminium s character only. The presence of the anion 3s states is of importance for the size of the band gap: without them they would be significantly larger. The consequences of these differences are discussed