Results 1 - 10 of 16170
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[en] Full text: Multi-phase ceramic waste forms were fabricated by melt-processing and hot isostatic pressing (HIP) to immobilize alkaline/alkaline earth (Cs/Sr-CS) + lanthanide (LN) + transition metal (TM) fission product waste streams from nuclear fuel reprocessing. Al2O3 and TiO2 were combined with these waste components to produce multi-phase crystalline ceramics containing hollandite-type phases, perovskites, zirconolite/pyrochlores and other minor phases. In this study, ion irradiations are performed to test and compare radiation tolerance of multi-phase ceramics produced via melting processing and HIP techniques. For the radiation stability test, selected crystalline ceramic samples are exposed to charge particles generated by an ion accelerator, which is used to simulate self-radiation in a waste form. Ion irradiation-induced microstructural modifications, volume swelling and microcracking are examined using X-ray diffraction, transmission electron microscopy, scanning electron microscopy and other characterization methods. Our preliminary results reveal similar radiation tolerance in these multi-phase ceramics with different fabrication techniques.
[en] A new type of composite based on the high-tensile aluminum alloy 7075 strengthened with nanoparticles of diamond powder and tungsten is developed. The resulting new composite was stored in two different environmental conditions for 28 months. One sample was stored on Earth at room temperature and second one was mounted on the outer side of the International Space Station. The effect of outer space on the microstructure of this new alloy was investigated by means of powder X-ray diffraction (XRD), X-ray photoelectron microscopy (XPS) and EDAX microprobe analysis. Key words: aluminum alloy (7075), cosmic ray and gamma radiation, crystalline structure, X-ray diffraction, X-ray photoelectron microscopy (XPS) and EDAX microprobe analysis
[en] As-cast and as-extruded Mg-[x]Zn-0.3Mn (x=1.5, 2.0 wt.%) alloys were prepared by means of medium-frequency induction-heating technique and extrusion process, respectively. The microstructural characteristics, thermal conductivity and mechanical properties of the samples were characterized. The research results show that the samples are composed of major α-Mg and minor second phases MgZn2 . For the as-extruded samples, the grain size is refined. After extrusion, much more second phases were precipitated from α-Mg matrix and the dislocations were reduced. The degree of lattice distortion was decreased for as-extruded samples. Because of the decline of lattice distortion degree, the as-extruded samples display much higher thermal conductivity than the as-cast samples. Additionally, on account of lower lattice distortion, Mg-1.5Zn-0.3Mn alloy has a bit larger thermal conductivity than Mg-2Zn-0.3Mn alloy. Finally, the as-extruded alloys present good mechanical properties based on the fine-grained strengthening and second-phase strengthening mechanism. (author)
[en] In this paper, preliminary experimental results on the changes occurring at the interface between Boom clay and cementitious materials due to chemical/physical interaction are presented. 14 years old in-situ interfaces as well as laboratory manufactured interfaces are currently under investigation. The in-situ interfaces were sampled using resin anchor concept both in mid-2016 and early 2017. A μ-tomography acquisition of the full size samples ( 10 x 20 cm) were then performed to visualize the quality of the contact at the interfaces. Both in-situ interface samples have been impregnated with C PolyMethyl MethAcrylate (PMMA) in order to perform autoradiography and examine the porosity change. Mineralogical maps done with an Electron Probe Micro-Analyser (EPMA) were also performed on concrete and Boom clay in the undisturbed area (distant from the interface). The same will be done in the near future at the interface to follow the mineralogical evolutions. In addition, microstructural characterization from nano to micrometer scale will be achieved using Transmission Electron Microscopy (TEM) and Focused Ion Beam / Scanning Electron Microscope (FIB / SEM). The lab manufactured interfaces were created by putting backfill concrete (high porosity) and Boom clay in contact in either accelerated percolation or batch-type experiments. The transport properties of concrete and clay (both newly made and in-situ samples) were measured by water permeability, diffusion of dissolved gases and water sorptivity using newly developed techniques.
[en] Carbon steel, compacted bentonite and concrete will come in contact with each other in the near field of deep geological repositories (DGR) for high-level radioactive waste (HLW) in clay formations. The bentonite barrier could be affected by the corrosion products at the canister-bentonite interface and the hyper-alkaline conditions caused by the degradation of concrete at the bentonite-concrete interface. Additionally, the host clay formation could also be affected by the hyper-alkaline conditions at the concrete-clay interface. Here we present a non-isothermal multicomponent reactive transport model of the long-term (1 Ma) interactions of compacted bentonite with the corrosion products of a carbon-steel canister and the concrete liner of the engineered barrier of a high-level radioactive waste repository in clay. The degradation of the concrete liner leads to the precipitation of secondary minerals and a reduction of the porosity of concrete, bentonite and the clay formation at their interfaces with the concrete liner. The reduction of porosity becomes especially relevant after t = 10 years. The zones affected by pore clogging at the concrete-clay interface after 1 My are approximately equal to 3.3 cm thick. The hyper-alkaline front (pH > 8.5) spreads 2.5 cm into the clay formation after 1 My. The thickness of the zones affected by a reduction of porosity and high pH computed with a coarse grid are significantly larger than those computed with a fine grid. Therefore, the finite element grid should be properly optimized to prevent numerical errors in the prediction of pore clogging and high-pH zones. The numerical results show that the porosity feedback starts to be relevant after t > 10 years. By neglecting the porosity feedback one may overestimate the thickness of the pore clogging zones for t = 2.5·10 years. The relevance of porosity feedback could increase for larger times.
[en] PbZrxTi(1-x)O3 (PZT) material is currently one of the highest quality piezoelectric materials and has been widely used in various applications, including as sensors in the observation system in nuclear reactor cores. In this study, a solid state reaction method was used to synthesize PbZrxTi(1-x)O3 (PZT) material with variations in compaction pressure of 7000 and 5000 psi. The sample synthesized was analyzed by the crystal structure system using Rietveld method of X-ray diffraction (XRD) pattern. The fitting results from High score program showed compounds with perovskite crystals system of tetragonal (PbZr0.52Ti0.48O3 ) and rhombohedral (PbZr0,58Ti0,42O3) and PbTiO3 (tetragonal). The electrifying process using an electrical voltage of kv DC has been successfully carried out on synthesis products. The voltage source used is from the electronic circuit Television (TV) 14-21 inches which has a fly back component and then continues with a voltage drop by making a voltage divider. The polling results can be identified by measuring the piezoelectric constant with the d33 meter device. Optimization of polling parameters to the material temperature was obtained at 100 °C, then applied polling sample of PbZrxTi(1-x)O3 (PZT) material added by PVDF (1.5, 2.5 and 5 % weight percent) to samples with the compaction of 7000 and 5000 psi. Maximum d33 measurement (61 x 10-12 C/N) was obtained on PZT material with a pellet pressure of 7000 psi. Increasing the addition of PVDF results in a reduction of d33. (author)
[en] Two-parametric asymptotic analysis of the equilibrium of an elastic half-space coated by a thin soft layer is developed. The initial scaling is motivated by the exact solution of the plane problem for a vertical harmonic load. It is established that the Winkler–Fuss hypothesis is valid only for a sufficiently high contrast in the stiffnesses of the layer and the half-space. As an alternative, a uniformly valid non-local approximation is proposed. Higher-order corrections to the Winkler–Fuss formulation, such as the Pasternak model, are also studied.