Defect and Diffusion Forum Vols. 297-301

Abstract: The aim of this research is to clarify a quantitative evaluation in the structural relaxation processes focusing on the activation energy on the addition of B to Cu-based amorphous alloys. The activation energy for structural relaxation process in a metal type amorphous CuHfTi ternary and CuHfTiB quaternary alloys, with cross sections of typically 0.03 mm x 2.0 mm, prepared by chill-block melt spinning has been investigated by Differential Scanning Calorimetry (DSC) with a cyclically heating technique. Activation energies for structural relaxation with a spatial quantity in amorphous materials have been discussed by use of a total relaxed ratio function that depends on annealing temperature and time. In the present work on CuHfTi ternary and CuHfTiB quaternary alloys, the distributions for the Activation Energy Spectrum (AES) by calculation with derivative-type relaxed ratio function were observed almost 160 kJmol-1, whereas in difference for shape only in the CuHfTi-B3% quaternary alloy. Another result has been also established that the ‘reversible’ AES model energy distribution though the cyclically structure relaxation occurs even in amorphous CuHfTiB alloy system.

Abstract: In a universe in indefinite expansion, undetermined amounts of dark material suspended in the space-time continuum exist. The case of ‘sufficient’ amount of material contracted throughout time due to its density can occur. Using relativistic equations, in the present work a thermodynamic system was considered whose volume of control is limited by a gigantic mass that is suspended in space in order to predict its behavior. Given the obtained results, evidence of a certain quantized dark material in process of collapse or collapsed into a black hole can be argued. The heat transfer of the black hole was measure through entropy change with respect to the time and other forms of energy, it was determined that the hole emits particles to surroundings from its event horizon (black hole ‘shining’). The emissions are proportional to the disappearance of the hole; they are candidates to integrate the “baby universes" of Hawking with new histories that satisfy the theorem "a black hole has no hair".

Abstract: Internally oxidized (I.O.) Pd0.97Zr0.03 and Pd0.97Nb0.03 alloys were submitted to gas permeation tests with temperatures in the range of 473-873 K. The internal oxidation was kept in a conventional furnace at 1073 K for 24 hours in air contact. The formation of nano-oxides, ZrO2 and Nb2O5, dispersed in the Pd matrix was observed. SEM images showed a preferential segregation of these oxides in the grain boundaries. It was observed that the diffusion coefficient in the sample containing Nb oxide was smaller than that in the Pd-Zr oxide. The effect of hydrogen pressure was investigated in the Pd-Nb samples. It was observed that the hydrogen diffusion coefficient increases with increasing the pressure. The hydrogen solubility is bigger for the Pd-Zr internally oxidized. This effect is attributed to the Zr nanoxides, which are smaller than Pd-Nb precipitates and then offer more interface for trapping the hydrogen.

Abstract: Hydrogen gas permeation tests were performed on two Nb-modified Zr alloys used in the nuclear industry. The influence of the microstructure on hydrogen diffusivity in each alloy is discussed and a mechanism of hydride formation is presented. The hydrogen binding energy for different trap sites was calculated in the M5 alloy as well as hydrogen diffusivity value in the Zirlo alloy at 300oC, D = 2.5 x 10-13 m2/s.

Abstract: A 3D numerical analysis is carried out to investigate heat and mass transfer in a partly porous cavity of high aspect ratio. The goal is to determine the best physical and geometrical parameters that allow optimal heat and mass transfer rate in such domain used in a solar adsorption cooling system. The computational domain consists of a tall cavity heated on the left vertical wall and cooled on the opposing wall. The SIMPLE algorithm is used to handle the velocity pressure coupling. Simulation results allow determining the optimal configuration of the used porous substrate and plain fluid position in the cavity in order to optimize the performance of such solar adsorption cooling installation.

Abstract: In some applications involving aggressive environments, common in oil and gas industries, superalloys 718 may suffer hydrogen embrittlement, resulting in degradation of mechanical properties. The aim of this work is to study the interaction of hydrogen with different microstructures in a 1 mm thick plate, annealed and age hardened superalloy 718. In this way, the effects of hydrogen interaction on microstructure were studied via thermal programmed desorption (TPD), tensile tests and scanning electron microscopy (SEM). Samples were studied in as-received, artificially aged and overaged conditions. Hydrogenated samples submitted to tensile tests presented ductility loss when compared to hydrogen free samples, showing the hydrogen embrittlement sensitivity of this alloy. The influence of  phase precipitation on hydrogen diffusivity, as a result of aging treatment, was also discussed in this work.

Abstract: We describe a study conducted to examine the influence of turbulence on the flow and heat transfer in graphitic foams. In this study, a Large Eddy Simulation (LES) model was used to characterize turbulence in the momentum and energy balances, and calculations were done to produce transient results of the velocity and temperature fields inside the spherical pores of the foam. The LES simulations enable excellent insight into the pore-level heat transfer mechanisms for the spherical void shape, and show that the heat transfer increases by a factor of 4.7 for an order of magnitude increase in the Reynolds number.

Abstract: Nanostructured Mg2Ni, Fe-doped and Ti-doped Mg2Ni alloys for hydrogen storage applications have been produced by means of Mechanically Activated Self-propagating High temperature Synthesis (MASHS). Different molar compositions of Fe and Ti (0.1; 0.3 and 0.5) have been studied in order to determine their influence in the hydrogen sorption properties. Different Mg-Ni based alloys have been tested in order to study their hydrogen sorption behavior. The hydrogenation was carried out in a Pressflow Gas Controller. Subsequently, the dehydrogenation process was conducted by means of a Differential Scanning Calorimetry (DSC) equipped with an H2 detector of the purged gas. The MASHS method has been demonstrated to be effective for the obtainment of nanostructured pure and doped Mg2Ni intermetallics. In addition, the materials produced showed hydrogen storage capacities superior to 4wt%, especially in the case of Fe-doped Mg2Ni and a slight reduction of desorption temperature was reached with Ti-doped Mg2Ni. Finally, the activation energy of the dehydrogenation process was evaluated and Ti-doped sample exhibited the lower activation energy value. Obtained results are promising for technological applications of Mg-based alloys.

Abstract: This paper investigates the surface texture evolution after a short phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components <100>//ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon.

Abstract: M-CNTs (Multiwall Carbon Nano Tubes) can be used as an electrode, transferring electrons and heat very easily. This property helps transfer electrons created in TiO2 layer of DSSC (Dye-sensitized Solar Cell). CNTs layer with TiO2 utilized for the photocatalyst is expected to contribute to improve the efficiency of the solar cell. The Photocatalyst of TiO2 thin film was manufactured from titanium isopropoxide, ethanol, and HCl by a sol-gel process. To determine the property of TiO2 thin film with CNT, we performed to mix acid dispersed CNT in TiO2 Sol-gel and make coating membranes using sol-gel with different densities of CNT. It was found that the crystal structure changed from the anatase phase to the rutile phase having higher efficiency by XRD measure after treatment of high temperature sintering. To demonstrate the property of each sample, the transmittance of the TiO2 thin film was measured by a spectrometer and dispersion of CNT of the thin film was measured by SEM. In conclusion, the capacitance as the parameter which can affect performance of DSSC was investigated.