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[en] Thermally Stimulated Depolarization Current measurements between 100 K and 350 K have been performed in ZrO2:MgO ceramic samples to discriminate the several kinds of polarization (orientational and interfacial polarization, and extrinsic and intrinsic space charge effects) to allow for the use of the technique in the study of solid solution formation in partially stabilized zirconia. The samples were prepared by conventional ceramic processing methods. Different electrode materials have been used: colloidal graphite, silver, gold, and also insulating electrodes (e.g. mylar foils). The current spectra obtained are strongly dependent upon the electrode material showing the presence of spacial charge phenomenon in these ceramics. (Author)
[pt]Medidas de Correntes de Despolarizacao Termicamente Estimuladas entre 100 K e 350 K foram feitas em amostras ceramicas de ZrO2:MgO para discriminar os diferentes tipos de polarizacao (polarizacao orientacional, interfacial e de carga espacial intrinseca e extrinseca), com o objetivo de usar essa tecnica para o estudo de formacao de solucao solida em zirconia parcialmente estabilizada. As amostras foram preparadas por processamento ceramico convencional. Foram empregados diferentes materiais como eletrodos, tais como grafite coloidal, ouro e prata, alem de eletrodos isolantes (p. ex. mylar). Os espectros de correntes obtidos sao fortemente dependentes do material que compoe os eletrodos, evidenciando a ocorrencia de fenomenos de carga espacial nessas ceramicas. (Autor)
[en] We have carefully measured the hydrostatic compressibility and thermal expansion for a series of magnesia nanoparticles. We found a strong variance in these mechanical properties as crystallite size changed. For decreasing crystallite sizes, bulk modulus first increased, then reached a modest maximum of 165 GPa at an intermediate crystallite size of 14 nm, and then decreased thereafter to 77 GPa at 9 nm. Thermal expansion, meanwhile, decreased continuously to 70% of bulk value at 9 nm. These results are consistent to nano-ceria and together provide important insights into the thermal-mechanical structural properties of oxide nanoparticles.
[en] Full text: The sorption of boron on the oxide of magnesium obtained by tempering easily decomposed combinations of magnesium has been studied. By the experiments there have been determined the following optimal parameters of boron sorption process by the oxide of magnesium (having been tempered at 700 ) from the imitating solutions at the starting concentration, time of concentrating-4 hours, and multiple of sorbet portion processing equal 5.
[en] As the lead temperature of a mineral insulated thermocouple is raised, the resistance of the insulator decreases and acts as a resistive shunt on any thermoelectric emf which is generated, thereby leading to errors in temperature measurement. Furnace tests are described in which such errors are demonstrated and a computer code has been used to predict the magnitudes of the errors. A method of predicting the performance of a thermocouple under high lead temperature conditions is proposed, which could be used as a selection process by a thermocouple manufacturer. The work has applications in the field of nuclear reactor in-core temperature instrumentation, in high temperature test rigs and in fire test facilities, where long thermocouple leads pass through high temperature environments. (author)
[en] A sample with a composition of 90 wt% Mg-10 wt% TaF_5 (named Mg-10TaF_5) was prepared by reactive mechanical grinding, and its hydriding and dehydriding properties were examined. The activation of Mg-10TaF_5 was not required. At n=1, the sample absorbed 3.63 wt% H for 5 min, 4.03 wt% H for 10 min, and 4.53 wt% H for 30 min at 593 K under 12 bar H2. At n=1, the sample desorbed 0.59 wt% H for 5 min, 1.46 wt% H for 10 min, 3.42 wt% H for 30 min, and 4.24 wt% H for 60 min at 593 K under 1.0 bar H2. Mg-10TaF_5 after reactive mechanical grinding contained MgH_2, Mg, and very small amounts of MgF_2 and Ta_2H. The XRD pattern of Mg-10TaF_5 dehydrided at n=3 revealed Mg, MgH_2, a small amount of MgO, and very small amounts of MgF_2 and Ta_2H phases. Mg-10Fe_2O_3 and Mg-10MnO were reported to have quite high hydriding rate and dehydriding rates, respectively. Mg-10TaF_5 had a larger initial hydriding rate but a lower quantity of hydrogen absorbed for 60 min than Mg-10Fe_2O_3. However, Mg-10TaF_5 had a higher initial dehydriding rate (after the incubation period) and a larger quantity of hydrogen desorbed for 60 min than Mg-10MnO.
[en] The high-temperature rheological behavior of polycrystalline periclase, MgO, has been investigated using the deformation-DIA on a synchrotron beamline at pressures up to 10 GPa. Significant experimental scatter in stress measurement illustrates current limitations of this technique. Although temperature and stress sensitivities are not well constrained, there is a clear dependence of creep rate on pressure. Based on our results, the creep rate of MgO depends on confining pressure with an activation volume of V* e 2.4 x 10-6 m3/mol. The grain-scale view of deformation processes reveals, as other D-DIA studies have, that subpopulations of grains, grouped by orientation, obey slightly different flow laws. The measurements also reveal that stress heterogeneity in the sample, whether caused by external conditions or processes internal to the sample itself, contribute a significant portion of the overall uncertainty in stress measurement.
[en] Highlights: • MGO nanocarrier was prepared by loading Fe3O4 on GO sheet. • MGO was observed to be biocompatible having superparamagnetic characteristics. • MGO has showed a very good drug loading performance and pH-responsive release. • Aptamer conjugated MGO was found to be specifically targeting MCF-7 cancer cell.
[en] Carbon nanotube junctions are of great interest in the fundamental research and nanoelectronic applications. Identical carbon nanotube Y junctions have been successfully synthesized by pyrolysis of methane over cobalt supported on magnesium oxide. The Y junctions have very straight arms with uniform diameters, and the angles between the three arms are close to 120o. Based on the analysis on the structure of the Y junctions the growth mechanism has been discussed. The fact that all the Y junctions grow in a similar way may be very important in the development of nanoelectronic devices
[en] Magnesium oxide nanofibers (MgO NF) were prepared with poly(vinyl acetate) as template using electrospinning technique. The role of solution concentration and collector design on the preparation of nanofibers was presented. This study offered a cost-effective catalyst and its easy method of preparation for the reduction of nitrocompounds. The complete material and product characterization was reported with appropriate analytical evidences. The possible mechanism for the reduction process was reported in detail. Further, an attempt was made to re-use the catalyst for next few cycles. (paper)
[en] A molten core/material interaction experiment was performed at the Large-Scale Melt Facility (LMF) at Sandia National Laboratories. The experiment involved the release of 230 kg of core melt at 2923 K (26500C), into a magnesia brick crucible. The facility, the melting technology, and results of the experiment, are described. Preliminary evaluations of the results indicate that magnesia brick can be a suitable material for core ladle construction. A brief description of IRIS, a new method for producing large quantities of melt using internal susceptors buried in a matrix of the melt charge is also presented