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[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] A series of phosphors of Sm and Eu single-doped or co-doped NaLa(WO) matrix are synthesized with the hydrothermal method. The structure, morphology, luminescent properties, quantum efficiency and CIE coordinates of sample are characterized and analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM and EDS), transmission electron microscope (TEM), fluorescence spectrophotometer (FL) and UV-Vis (UV) absorption spectra. The results show that all the obtained products have the scheelite structure with spherical or ellipsoidal shapes. The morphology formation mechanism is proposed as follows: nucleation - dissolution - recrystallization - crystal growth (self-assembly process). Under 393- and 403-nm photoexcitation, NaLa (WO):Sm:Eu emits intense red and orange red light. In NaLa (WO): Sm:Eu sample, the energy transfer can occur from Sm to Eu, and the critical distance of energy transfer is between 1.655 and 2.362 nm. The energy transfer mechanism is electric dipole–electric dipole interaction. The energy transfer efficiency can be over 70%. The best product NaLa(WO):2%Sm:4%Eu has a luminous efficiency of 54.70%. The CIE coordinates are X = 0.6585, Y = 0.3404.
[en] Polycrystalline HoMnO (HMO) samples were prepared through the solid-state reaction method to study their magnetic, thermal and magnetocaloric properties. X-ray diffraction studies revealed that the sample crystallized in hexagonal structure with P63cm space group. Low-temperature magnetization measurements showed an anomaly at 4 K, whereas the heat capacity measurements carried out under 0 T, 2 T, 5 T and 9 T fields in the temperature region of 2-150 K exhibited three different transitions at 72 K, 33 K and 5 K. These transitions are attributed to the ordering of Mn, spin reorientation of Mn ions and Ho ions, respectively. Magnetic contribution to the total entropy change was also evaluated at different magnetic fields. Magnetocaloric effect (MCE) parameters such as isothermal entropy change of 2 J/kg-K, 9 J/kg-K and 16 J/kg-K were obtained at around 10 K for a magnetic field change of 2T, 5T and 9T, respectively. The adiabatic temperature change (ΔT) values are found to be 0.6 K, 3.5 K and 8.5 K, whereas the relative cooling power (RCP) is found to be 4 J/kg, 120 J/kg and 360 J/kg under 2T, 5T and 9T magnetic field change, respectively.
[en] The results of a study carried out in the shaping of a clay located at Zulia (North of Santander, Colombia) and the influence of wet milling on the structural and mechanical performance are presented. The study was carried out by shaping the material by extrusion as this is the technique most used in the ceramic industry of the region and subsequent sintering treatment between 900°C to 1200°C. For the development of the analyzes, the specimens were formed with two pastes prepared by dry and wet milling. The structural behavior, its mechanical resistance and technological aspects such as contraction and densification, among others, were evaluated. The results indicate improvements in structural and mechanical properties decreases to 18.8% in porosity and increases up to 72.1% in resistance to external loads increasing the commercial value for coating products and masonry. The results showed that the wet milling can be used to improve the extrusion process, the technological characteristics of the materials and the commercial value of the same, an important aspect in regional companies.
[es]Se presentan los resultados de un estudio realizado en el conformado de una arcilla del Zulia (Norte de Santander, Colombia) y la influencia de la molienda húmeda en el comportamiento estructural y mecánico. El estudio se llevó a cabo conformando el material por extrusión por ser esta la técnica más utilizada en la industria cerámica de la región y posterior tratamiento de sinterización entre 900°C hasta 1200°C. Para el desarrollo de los análisis se conformaron probetas con dos pastas preparadas por molienda en seco y en húmedo. Se evaluó el comportamiento estructural, resistencia mecánica y aspectos tecnológicos como contracción y densificación, entre otros. Los resultados obtenidos indican mejoras en propiedades estructurales y mecánicas con descensos hasta del 18,8% en la porosidad e incrementos hasta de un 72,1% en resistencia a cargas externas, incrementando el valor comercial para productos de revestimiento y mampostería. Se evidenció que la molienda en húmedo puede ser usada para mejorar el proceso de extrusión, las características tecnológicas de los materiales y el valor comercial de lo mismos, aspecto importante en las empresas regionales.