Materials Science Forum Vols. 636-637

Abstract: Dyeing of polyamide fibers is normally made with acid dyes, however, it is somewhat difficult to achieve uniformity and control of pH and temperature must be carefully made. The possibility to dye polyamide 6.6 in a larger gamut of colours with good properties may be achieved using other classes of dyes after plasmatic modifications in textile substrates. Polyamide 6.6 fabrics were treated with Double Barrier Discharge (DBD) plasma obtained at atmospheric conditions in a semi-industrial machine and very positive results were obtained when dyeing is made with direct dyes. Surface modifications were evaluated, namely, roughness in terms of Atomic Force Microscopy, changes in chemical composition by X-Ray Photoelectron Spectroscopy (XPS) and microstructural analysis by SEM. In order to optimize dyeing process, different dye concentrations, pH and temperatures were attempted on dyeing with DBD treated fabrics. Important parameters were studied such as exhaustion, colour strength (K/S) and washing fastness. Chemical and physical effects of plasmatic discharge contribute to excellent results obtained in yield, exhaustion and fastness of dyeing of polyamide with direct dyes demonstrating extensive improvement of dye exhaustion from baths, easily achieving 100% in shorter dyeing times. These results mean less dyes in effluents and less time for dyeing processes. The cleanness of the processes and lower cost of direct dyeing are additional advantages when compared to difficulties in acidic dyeing of polyamide.

Abstract: Enhancing absorption of solar cells over the solar spectrum is one of the most important ways to improve such devices’ performances. In this research, two-dimensional surface photonic designs were suggested to introduce rotationally distributed reciprocal vectors, which will match the guiding modes of the thin planar layer of an active material, and thus to further couple the incident light laterally into the layer. This allows the use of a fewer amount of active materials, increases the devices’ angle acceptance, and reduces costs for both fabrication and system installation.

Abstract: Increasing spectral coverage of a solar cell over the entire solar spectrum is one of the most important energy harvesting ways. In this research, an alternative approach of using plasmon-enhanced luminescence to realize an efficient wavelength shifting potentially useful for solar cells was discussed. Plasmon-enhanced luminescence was experimentally shown in erbium-doped yttria films integrated with arrays of metallic nanostructures having different sizes, in which a strongly enhanced and nanoparticle size-dependent luminescent behavior was observed.

Abstract: Anodes composed of Ni-YSZ (yttria-stabilised zirconia) cermets are the key material to allow direct biofuel feeding to Solid Oxide Fuel Cell (SOFC) devices due to its internal reforming capability. The main challenge among these materials is related to carbon deposition poisoning effect when C-bearing fuels are feed. The work deals with these issues by alloying Ni with some metals like Cu to conform a multi-metallic anode material. Mechanical alloying (MA) at shaker mills is chosen as the route to incorporate the metal and ceramic powders in the anode material, also leading to better sintering behaviour. A projected cermet material is conceived where a third metal can be added based on two criteria: low Cu solubility and similar formation enthalpy of hydrides regarding Ni. Refractory metals like Nb, W and Mo, seems to fulfil these characteristics, as well as Ag. The MA resulted powder morphology is highly homogeneous showing nanometric interpolated metal lamellae. The sintering behaviour is investigated by conventional dilatometry as well as by stepwise isothermal dilatometry (SID) quasi-isothermal method to determine the sintering kinetic parameters. Based on these tools, it is found the Cu additive promotes sintering to obtain a denser anode and therefore allowing lower process temperatures. The consolidation is achieved through the sintering by activated surface (SAS) method allied to liquid phase sintering process, where the third metal additive also has influenced. The final cermet can be obtained at one sole process step, dispensing pore-forming additives and reduction treatments. The sintered microstructure demonstrates the material is homogeneous and possesses suitable percolation networks and pore structure for SOFC anode applications.

Abstract: Single phase La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM9182) was synthesized by a polymeric precursor route. The XRD pattern after calcination at 1300 °C for 6h indicates the formation of the perovskite without the presence of secondary phases. XRD, FTIR and TG-DTG measurements were used to examine the powder precursor as well as the intermediate and final products. SEM images indicated the small grain size of the final product. The conductivity of the sintered sample was examined by means of a.c. impedance spectroscopy and was found to be 9.10-2 S/cm at 800 °C similar to the typical value of LSGM materials.

Abstract: The goal of our studies is to find alloy compositions capable of high H capacity and reversible low temperature hydrogenation. In the present research work, specimens with nominal compositions Zr0.9Ti0.1Cr1.2V0.8 and Zr0.9Ti0.1Cr0.8V0.8Ni0.4 have been prepared by arc–melting under argon atmosphere. The microstructural properties of the samples were analyzed by XRD and SEM, while the corresponding microchemistry was determined by EDAX measurements. A two phase system was regularly obtained, with the main component being the hexagonal (C14) Laves phase. The presence of small amounts of Ni has been found to increase the alloy activity on hydrogen. Hydrogen activation was performed for both samples and charging-discharging properties were investigated in the temperature range between 20 oC and 100 oC by using a Sievert-type apparatus.

Abstract: Hydrogen storage in reversible metal hydrides is attractive because it can be stored at relatively low pressures with a high volumetric density. In the present research work have been investigated compounds with nominal compositions Zr0.8Ti0.2Cr1.2V0.4Ni0.4 and Zr0.8Ti0.2Cr0.8V0.8Ni0.4 that have been prepared by arc-melting under argon atmosphere. Structural characteristics have been studied by using X-ray powder diffraction while the patterns have been analyzed by using the Rietveld analysis. A main hexagonal Laves phase MgZn2 (C14) and a secondary MgCu2 (C15)-type of, have been found in the powdered compounds. The bulk samples have composite microstructures but the V-rich is characterized by a dendritic microstructure. The high resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray analysis (EDAX) have been used for the morphology and quantitative analysis, respectively. Hydrogenations and dehydrogenations have been obtained after crucial activation procedure. The alloys were found to be more active under hydrogen after activation while the desorbed amount of hydrogen has been measured by using a Sievert-type apparatus.

Abstract: Intermetallic Ni3Al–based alloys (doped with zirconium and boron) represent a group of advanced materials with potential outstanding physical and chemical properties (such as high catalytic activity and structural stability in corrosive environments) that make them a considerable candidate for many high-tech applications. In this paper, the catalytic activity of fully dense Ni3Al-based thin foils (as thin as 50 m) possessing structures with micrometer or nanometer grain sizes is discussed. The examined material, without any additional catalytic coating, was successfully produced from as-cast coarse-grained sheets by heavy cold rolling and recrystallisation with an appropriately chosen set of parameters. The examination focuses on methanol and methanol/water mixture decomposition into H2 and CO at temperatures up to 530OC in a quartz reactor. Except for these products, a small amount (below 1%) of CO2 and dimethyl ether was observed. The catalyzed reaction began effectively at about 400OC, with a methanol conversion of about 90% or higher.

Abstract: La1-xSrxCoO3-δ (x=0, 0.2, 0.5) powders were prepared by a polymeric precursor route, with the application of microwave heating for the precursor preparation. Single-phase oxide powders are obtained after calcination at 700°C for x=0, 0.2 and 1300 °C for x=0.5. XRD, FTIR and TG-DTG measurements were used to examine the powder precursors as well as the intermediate and final products. SEM images indicated the small grain size of samples with x=0, 0.2. Conductivity and thermal expansion were measured by means of DC method and dilatometry respectively. The end member LaCoO3-δ showed a semiconducting behaviour, while doped samples showed a metallic behaviour at high temperatures. La0.8Sr0.2CoO3-δ showed the highest conductivity of all samples investigated, at temperatures higher than 300 °C.

Abstract: In the present work a modified polymeric precursor route is applied for the preparation of La1-xSrxGa0.8Mg0.2O3-δ (x=0.1, 0.2, 0.3). Citric acid and ethylene glycol are used as chelating and complexing agents respectively and microwave heating is used for the preparation of the precursors. The sintering reactions are recorded using TG/DTG measurements, while XRD, FTIR and SEM are used for the characterization of the intermediate and final products. As it is concluded, pure La0.9Sr0.1Ga0.8Mg0.2O3 can be prepared after sintering at 1300 °C for 6h. As the doping level of Sr increases, the formation of single phase perovskite is hindered. La0.8Sr0.2Ga0.8Mg0.2O3 contains minor amounts of SrLaGa3O7, while single-phase La0.7Sr0.3Ga0.8Mg0.2O3 can not be prepared at all. In all cases, the intermediate products at lower temperatures are mainly SrLaGa3O7, SrLaGaO4, La4Ga2O7 and La carbonates.