Materials Science Forum Vols. 480-481

Abstract: Binary and ternary TeO2 based oxy-chloride glass systems have been prepared and characterised by absorption and low-temperature photoluminescence spectroscopy, and by the measurements of dc electrical conductivity. Prepared glasses exhibit transmittance 75-80% in a broad transmission range 0.3 – 6.5µm with modest shift of upper absorption edge to longer wavelength as heavier ions are introduced into the system. Electronic transitions between 4f-4f inner shells of Pr3+ ions embedded into the host glass have been investigated in a wide temperature range as a function of used precursors used for doping. The temperature dependence of dc electrical conductivity exhibits Arrhenius plots with the single activation energy. PACS codes 81.05.Kf, 78.20.Ci, 78.55.Hx

Abstract: Radiation-induced losses and paramagnetic centers were investigated in phosphorusdoped and P-free multimode germanosilicate optical fibers after g-rays (~1 MeV) and ultraviolet (5 eV) exposures. After both types of irradiation, the same defects seem to be responsible of the fiber absorption in the spectral range 400 to 1650 nm. In particular, the P1 centers and the Phosphorus Oxygen Hole centers are created in both cases in the phosphorus-doped fibers and explain the high permanent radiation-induced attenuation levels observed in this fiber type. Luminescence and electron spin resonance measurements (77 K, ~9.38 GHz) on irradiated samples confirm that the GeE’, SiE’ and NBOHC defects are also generated in the different irradiated samples. From this study, it seems that the pertinence of a multimode fiber for nuclear space or civil applications could be estimated through low-cost ultraviolet measurements.

Abstract: We studied the defects at the origins of the permanent radiation-induced attenuation in four g-rays irradiated single-mode germanosilicate optical fibers (~1 MeV; 1.2 kGy; 0.3 Gy/s) in the spectral range 400 - 1700 nm. We determined the wavelength dependence of the following cladding codopant influences: germanium (0.3 %), phosphorus (0.3 %), fluorine (0.3 %) on the germanosilicate (13 %) fiber radiation responses. We identified some of the different color centers produced by g-rays and we evaluated their localization in the fiber cross-section through the determination of the radial distribution of the radiation-induced absorption at 633 nm. We also evidenced the strong interactions between these three codopants. In particular, our results showed that the properties of the phosphorus-related color centers, which mainly determine the fiber infrared radiation sensitivity, are strongly influenced by the germanium- and fluorine-codoping.

Abstract: Thermoplastic vulcanizates nanocomposites based on polypropylene (PP) and ethylene–propylene-diene terpolymer rubber (EPDM) blends reinforced with organoclay modified montmorillonite have been prepared via melt intercalation. The silicate layers of the clay were intercalated and dispersed at a nanometer level in the matrix blends. The nanocomposites exhibit improved mechanical properties, this effect being more evident at high EPDM contents in the blend (above 80%). This behavior is attributed to the fact that the EPDM chains are more easily inserted into the galleries silicate, giving rise to a more intercalated structure as was observed by X-ray diffraction.

Abstract: By using photoacoustic (PA) spectroscopy it was performed a study about bone consolidation in fractures. It was obtained the optical absorption spectra of callus of male rat fractured bones at different consolidation times. From these spectra it was possible to observe the presence of alkaline phosphatase through their absorption peaks which were compared with characteristic peaks reported in the literature for this phosphatase. In this study we showed that alkaline phosphatase could be considered as an indicator of the repair process of bone fractures.

Abstract: Zinc anodic dissolution has been studied according to the steel galvanized method by means of the electrochemical impedance spectroscopy (EIS) and microscopic observations. Relevant information on the galvanized method is provided by the analysis of experimental data. The galvanized method has no influence on the kinetics parameters of the zinc anodic dissolution process. The galvanized method only changes the surface texture of the working electrode. Thus, the EIS fitting allows to calculate the fractal dimension of the surface of the working electrode.

Abstract: A new diatomic molecule-containing endohedral fullerenes were prepared by ion implantation technique (introducing negatively charged C70 into a low temperature lithium plasma column by a strong exial magnetic field).The species prepared were Li@C70 and Li2@C70 and ionized by surface ionization. Their existance was demonstrated through high sensitivity, magnetic mass spectrometer. The corresponding endohedral ions undergo the Rice shrinkwrap mechanism: a mass –analyzed ion spectrum demonstrates the loss of a C2 unit from the cage. The observed ionization energies of endohedral molecules were 5.1 " 0.1 eV and 5.3 " 0.1 eV, respectively.

Abstract: The viscoelastic behavior of different ceria gelling systems prepared through sol-gel transition were investigated by the rheological measurement. The gelation time was observed by the frequency independence of tand, and increased with increasing acid:alkoxide molar ratio. At the gel point, both storage and loss moduli (G’µ wn, G” µ wn)exhibited a power law dependence of applied frequency with n’ = n” = n. The viscoelastic exponents and gel strength parameter were dependent on the composition of system. The increase in HCl:alkoxide molar ratio increased the n value while decreased the S parameter.

Abstract: Thixocasting or semi-solid casting is an alternative to the traditional casting processes. A numerical simulation of these methods is useful to define the real process. A new test concept will be presented to determine parameters, such as temperature and rates, as well as the die filling and solidification processes. The simulation tools permit us to understand better the processes, to predict and to eliminate potential defects before they take place. The studied component is a steering knuckle made of an A357 aluminium alloy. The microstructure is characterized by optical microscopy. It has been preceded to the development of a model based on the experimental data, it has been defined to the semi-solid as an homogeneous material with thixotropic properties, and the microstructure is a structural parameter. The results are compared with real tests.

Abstract: This paper describes the heat treatment effect on the eutectic silicon evolution in the A357 alloy, obtained by semisolid forming process (SSM). The coarsening rate of the silicon was determined by Image Analysis Technique in specimens from rheocasting ingots and thixocasting components. The study was realized in the temperature range from 450 to 550°C by applying heating times between 1 and 24 hours. The results show that during the heat treatment the coarsening and sphereodization of the silicon particles is produced and the fragmentation stages, which are observed in conventional alloys, do not appear. Kinetic silicon growth has been adjusted to the Oswald’s ripening equation.