Advanced Materials Forum III

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Authors: Victoria Corregidor, Nuno Franco, Eduardo Alves, Nuno P. Barradas
Abstract: Ga0.81In0.19As0.14Sb0.86 layers were grown on (100)-Te doped GaSb substrates 2º missoriented towards (110), (111)A and (111)B directions by metalorganic vapour deposition (MOVPE) at 540 °C. X-ray reciprocal space maps done in symmetric (224) and asymmetric (115) directions show a super-lattice structure due to the phase separation with a 5 nm period and independent of substrate orientation. The x-ray maps show different stage of relaxation of the films and in same cases an interdiffusion region near the substrate. Despite of the phase separation, channelling experiments with H ions as projectiles showed a good quality of the films. Channelling experiments show that the crystalline quality gets worse with increasing the In and As concentration.
Authors: Yun Chen, César A.C. Sequeira
Abstract: With the goal to find hydride electrodes, the phase structure and electrochemical characteristics of the as-cast and ball-milled La2Mg17 alloy with Ni additions were investigated. The addition of Ni was found to be an important factor for the earlier transformation to an amorphous alloy. When the addition of Ni reached 100 wt%, the ball-milled La2Mg17 alloy transformed into a homogeneous phase with high discharge capacity of 1060 mAh/g(La2Mg17) [530 mAh/g(La2Mg17+100 wt% Ni)]. The exchange current density and the kinetics of the amorphous alloy were also found experimentally noticeably higher than those of corresponding crystal alloy.
Authors: Maria Cristina F. Oliveira
Abstract: Spontaneously-deposited Pd-black films were prepared on a Ni mesh. Characterization of the films morphology was performed by Scanning Electron Microscopy. Cyclic voltammetry in 0.1 M NaOH was used to characterize the voltammetric profile in the H-adsorption/absorption region. Contrasting to smooth Pd, the results revealed that the H-adsorption peak can be detected using this electrode. It was found that the displacement metal reaction leads to codeposition of Ni during the Pd-black film preparation. The ability of these electrodes to be used on the electrohydrogenation of organic molecules was evaluated using 3-buten-1-ol as a test molecule. It was also analysed the stability of the electrodes upon reusing the same electrode in repetitive electrolysis. It was concluded that the films present a very good catalytic activity to electrohydrogenation but show poor adherence to the substrate when are re-used.
Authors: Magdalena Popczyk, Antoni Budniok, Henryk Scholl, Tadeusz Blaszczyk
Abstract: Ni-P, Ni-Co-P and Ni-W-P layers were obtained in galvanostatic conditions, at the current density jdep= 0.200 A cm-2. The X-ray diffraction method was used to determine phase composition of the layers and the atomic absorption spectrometry was applied to specify their chemical composition. A metallographic, stereoscopic and tunneling microscope and also Form Talysurf-type profilograph were used for cross-section and surface morphology characterization of the layers. The behaviour of obtained layers was investigated in the processes of hydrogen and oxygen evolution from 5 M KOH using voltammetry method. It was ascertained that, introduction of cobalt or tungsten into Ni-P matrix, lead to obtain the layers about very developed surface. Thus obtained layers may be useful in application as electrode materials in electrochemistry.
Authors: Jolanta Niedbała
Abstract: The electrochemical layers with molybdenum were obtained by electrodeposition from citrate bath. The process was carried out under galvanostatic conditions. Structural investigations were conducted by X-ray diffraction method. It was ascertained that electrodeposited Ni-Mo-P alloys are characterized by amorphous structure, Ni-Mo alloys are characterized by nanocrystalline structure whereas Ni+Mo composite layers have a crystalline structure. The chemical composition was determined using X-ray fluorescence spectroscopy method. It was stated that Ni-Mo-P alloys contain 75%Ni, 10%Mo and 15%P, the Ni-Mo alloys contain 90%Ni and 10%Mo, Ni+Mo composite layers contain 90%Ni and 10%Mo. These layers were characterized by electrochemical methods (j=f(E) voltammetry and corrosion resistance by Stern method). The results of corrosion tests show that from among obtained layers the highest corrosion resistances exhibit nanocrystalline Ni-10%Mo alloys.
Authors: P. Ferreira, C.D. Nunes, João Pires, Ana P. Carvalho, P. Brandão, João Rocha
Abstract: A new porous benzene-silica hybrid clay heterostructure has been prepared by a template-assisted method. The synthesis of Hybrid Porous Clay Heterostructures (HPCH) has been performed via the intercalation of a quaternary ammonium cation surfactant (cetyltrimethylammonium bromide) and a neutral amine (octylamine) as cosurfactant, in a Portuguese clay, to direct the interlamellar hydrolysis and condensation polymerisation of neutral inorganic etraethylorthosilicate (TEOS) together with an organic precursor, the 1,4- bis(triethoxysilyl)benzene (BTEB). The material has been characterised by elemental analysis, powder X-ray diffraction, nitrogen adsorption, 13C CP MAS, 29Si MAS and CP MAS NMR spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermal analyses. The hydrophobicity of the material was tested by water adsorption. Its potential application as adsorbent of volatile organic compounds was studied by the adsorption of methanol, methyl ethyl ketone, toluene and trichloroethylene.
Authors: Ana Sofia Ramos, M. Teresa Vieira, Manuel F. Vieira, Filomena Viana
Abstract: The optimisation of joining technologies is essential to the application of advanced materials in the design of parts and devices. The development of intermetallic compounds, as structural materials, inevitably requires a new approach to join these compounds to themselves or to other materials. Among different intermetallic classes, titanium aluminides are one of the most studied. However, the industrial application is far from being proportional to the research, due to different problems, where joining processes have an important role. The present paper highlights the state of art on joining γ-TiAl alloys. A review is presented with special emphasis on solid-state diffusion bonding process, because it seems to be the most suitable technique to produce high quality joints of advanced materials. The influence of the bonding conditions on the physical and mechanical properties of the joints is highlighted and the introduction of single or multiple interlayers to assist in the bonding process is discussed. A novel approach developed by the authors to the solid-state diffusion bonding of γ-TiAl alloys using Ti/Al multilayer thin films as bonding materials is proposed. The improvement of the solid-state diffusion bonding will induce sound joints at lower temperatures or pressures.
Authors: Amélia Almeida, Patrícia Almeida Carvalho, Rui Vilar
Abstract: Surface alloys with composition ranging from 10 to 20% Cr were produced by laser surface alloying. Their microstructure consists of faceted plate-like Al4Cr intermetallic compound particles dispersed in a matrix of α-Al solid solution. During remelting, heterogeneous nucleation of eutectic Al7Cr/α-Al occurred in the undercooled liquid ahead of the columnar solid-liquid interface, followed by equiaxial solidification, resulting in a microstructure formed of equiaxed cells. Al-Cr alloys present Young’s modulus and hardness values that increase with increasing volume fraction of intermetallic compounds. Wear resistance, measured in dry sliding conditions, increases with increasing load due to the protective effect of a stable mechanically mixed layer that forms at the surface of the samples and the steel counterbody. Alloys formed of equiaxed eutectic cells provide better wear resistance than those formed of large plate-like particles since a thinner, more stable and harder mechanically mixed layer is formed, which offers best protection against wear.
Authors: José M. Silva, Ricardo A. Cláudio, A. Sousa e Brito, Carlos M. Branco, Jim Byrne
Abstract: During the last decade, some major improvements have been achieved concerning the evaluation of new types of materials suitable for aeronautical components exposed to severe operational conditions, such as turbine disks. Due to their outstanding mechanical properties, nickel base superalloys assumed a preferential position when compared with other conventional metallic alloys, benefiting from both their superior fatigue strength and high temperature behaviour. However, these alloys evince a high sensibility concerning possible defects that can arise due to certain types of loading, such as porosities and cavities associated with creep-fatigue at high temperatures. The present paper compiles some experimental results obtained for two types of recent nickel base superalloys. Some fatigue tests were performed using two configurations of these materials: a set of Udimet 720Li specimens (CT geometry) and a set of RR1000 specimens (CN geometry). A maximum temperature of 650°C was considered in both types of materials. The mechanical properties of these alloys were inferred via typical FCGR parameters, such as da/dN vs K curves, complemented with detailed analyses of the cracking mechanisms based on SEM observations. Finally, some metallographic characterization tests were carried out in order to determine the average grain size of these PM alloys and to confirm the presence of important microstructural constituents that can influence the overall fatigue performance of these materials.

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