Key Engineering Materials Vol. 865

Abstract: The modern development of (PEMFCs) is still faced by several obstacles such as membrane cost and performance. Perfluorosulfonic acid membranes (e.g. Nafion of DuPont) are currently the most successful in PEMFCs. PEMFCs usually operate at temperatures around 80°C and at atmospheric pressure. Higher temperature operation (T >100°C) is preferred and has several advantages including enhanced fuel cell kinetics, improved catalysts tolerance for contaminants and recovery of useful heat. However, the high-temperature operation is not permitted using Nafion membranes as they dehydrate and their proton conductivity dramatically decreases, thus, lowering the fuel cell efficiency. Therefore, this work aims at developing a Nafion-free membrane that would successfully operate at higher temperatures and with reasonable proton conductivity (preferably higher than 10-3 S/cm). In this study, novel solid proton conductors based on polyaniline (PANI) and ionic liquids (ILs) are proposed as membranes in PEMFCs. PANI-IL composite membranes are fabricated using porous polytetrafluoroethylene (PTFE) as support. The composite membrane was evaluated for its proton conductivity. The results showed a high proton conductivity range of 0.01 to 0.02 S/cm when a 3.7 wt % of the ionic liquid (IL)[1-Hexyl-3-Methylimidazolium Tricyanomethanide] was used.

Abstract: In magnetoelectric sensors for the detection of weak magnetic fields, the magnetostrictivecomponent is required to show a high strain at small magnetic field changes. Co-Fe alloys, amongrare earth free materials, have one of the largest saturation magnetostriction and are magnetically softat the same time. In this study, Co-Fe alloy films with 66 at.-% Co are prepared by magnetron sputterdeposition of Co/Fe-multilayers which differ in their individual layer structure and in a subsequentrapid thermal annealing process. The influence of the initial bilayer period and the annealing temperatureon the phase formation and film structure are investigated. X-ray diffraction revealed a higherfraction of the desired face-centered cubic solid solution for thicker individual layers after the 800 °Cannealing. The change of the electrical in-plane resistivity reaches a minimum around 500 °C and iscorrelating well with the observed grain growth and solid solution phase formation. The investigationof magnetic properties with vibrating sample magnetometry shows coercive fields of 3.2 kA/m and2.2 kA/m for fully alloyed films with initial bilayer periods of 25 nm and 250 nm, respectively.

Abstract: In this paper, thermoelastic damping (TED) in a simply supported rectangular functionally graded material (FGM) micro plate with continuous variation of the material properties along the thickness direction is performed. The equations of motion and the heat conduction equation coupled with the thermal effects are derived based on the Mindlin plate theory and the one-way coupled heat conduction theory, respectively. The heat conduction equation with variable coefficients is solved by using the layer-wise homogenization approach. Analytical solution of TED is obtained by complex frequency method. Numerical results of TED are presented for the rectangular FGM micro plate made of ceramic-metal constituents with the power-law gradient profile. The effects of the shear deformation, the material gradient index, the plate thickness on the TED of the FGM micro plate are studied.

Abstract: The effect of mixing suspended nanoparticles into a bi-disperse magneto-rheological fluid on sedimentation phenomena is explored. A reference bi-disperse MRF has been modified using a ferrofluid containing magnetite nanoparticles of two shapes (spheres or hexagonal platelets) suspended in paraffin-oil as carrier fluid. The reference MRF was prepared with a mixture of two diameter sizes for the micrometric particles. The reference MRF was also prepared using two different grades of carbonyl-iron micrometric particles (herein these will be referred to as HARD and SOFT), which differ each other for their mechanical properties. The experiment monitored the evolution with time of the sediment-supernatant interface. This experiment showed that the presence of nanoparticles (particularly the spherical ones) slows down the sedimentation effects in terms of ratio and rate, independently of the other characteristics of the fluid. This study also showed that fluids based on SOFT carbonyl iron powders, in presence of nanospheres, are more stable than HARD carbonyl iron powder based fluids, since their sedimentation rate slows down in the long term. At the same time, HARD particle-based magnetorheological fluids show smaller sedimentation ratios than SOFT based fluids.

Abstract: Water scarcity is growing and in particularly in regions where population is high. It is estimated by world wild life organization that two thirds of human population may face water shortage by 2025. However, the amount of water available on earth covers approximately two thirds of the total surface area, but most of the water is seawater. Seawater cannot be used for any human use due to the high salinity levels. Desalination processes have been implemented on various scales whereby reverse osmosis is the most successful. However, such system is too complex and expensive. An alternative system utilizing humidification-dehumidification process for desalination is proposed in this paper. The process involves the use of a novel hydrophobic membrane allowing the humidification. Two configurations have been tested in a closed loop cycle, namely: static and moving membrane. The results from the experiments have shown that the efficiency of the moving membrane configuration is higher than the static by 46%. And based on 1 Litre brine feed, 50% of the volume has been successfully desalinated.

Abstract: Thorough analyses were focused on characterization of deformation behaviour of the component metals, orientations of their structural units, and development of intermetallic phases on the interfaces within Cu/Al clad composites produced by rotary swaging at 20 °C and 250 °C. The shapes of the cross-sections of Al wires within the composites were affected by the increasing total imposed strain more at 250 °C, the 250 °C composites also exhibited formation of intermetallics at higher swaging degrees. Intermetallics decreased the electric conductivity, which was generally higher for 20 °C samples, however, the conductivity was also affected by the occurring deformation hardening/softening. The average microhardness of Cu exceeded 100 HV for all the samples.

Abstract: The study investigates a W93Ni6Co1 tungsten heavy alloy rotary swaged at 20 °C and 900 °C with the aim to optimize its mechanical properties. Deformation behaviour was predicted via numerical simulations and subsequently verified via experimental swaging. The results showed that swaging at 900 °C led to substantial increase in ductility (24% elongation after the first pass), whereas swaging at room temperature primarily increased the UTS (up to 1800 MPa after the second pass). Among the key differences between both the swaging temperature modes were the different substructure developments; the higher swaging temperature imparted activation of softening processes within the γ matrix and homogenization of residual stress. The W agglomerates within both the swaged pieces featured the presence of <101> and <001> preferential orientations.

Abstract: This work presents a pilot study on the photoelectric effect of anatase titanium dioxide (TiO₂) deposited on grade 4 titanium discs on their antimicrobial properties, especially for dental implants applications. The prepared specimens are characterized by X-ray diffraction and Raman spectroscopy to ensure a homogenous coverage of the TiO₂ material on the discs. The samples were further tested to outline the photoelectric response of titanium dioxide to ultraviolet radiation in the form of electrical current within the discs. Six discs (three bare Ti, and three coated with TiO₂) were seeded with a 5 μl of Escherichia coli culture. One disc of each group was subjected to the same UV light source used for the opto-electrical analysis for 0, 1 or 5 minutes. Bacteria on the discs were then harvested and incubated to examine number of viable cells. The obtained electrical properties confirmed the suitability of the surface-coating to provide simultaneous oxidation-reduction driven reactions under the photoinduced catalytic activity. This activity highlighted the benefits of the added TiO₂ layer in reducing the numbers of active E-Coli bacteria in a microbial setup by as much as 21% after 5 minutes of UV exposure. This photoelectrical effect has a profound impact on the development of an in-situ oral disinfectant material deposited on titanium-based dental implants.

Abstract: During the electrolytic reduction of magnesium, it is very important to understand the mechanism of the digestion of the magnesium chloride dihydrate granules in the molten electrolyte throughout the chlorination process. This work aimed to investigate the kinetics of this digestion process. The results showed that the granules digestion is happening in two stages. The first stage is very fast, hence, results in the formation of MgOHCl during the dehydration and the hydrolysis of magnesium chloride dihydrate in the interior of the granules. The kinetic results for the first stage was best modeled using shrinking core model where the surface reaction was the rate controlling step. The second stage was best modeled as a first-order homogenous reaction. The kinetic parameters for the two stages were determined along with the Arrhenius plots. The results of this kinetics study are essential for the mathematical modeling of the chlorination process of the magnesium chloride dihydrate granules.

Abstract: The overall efficiency of a PV system is strongly affected by the PV cell raw materials. Since a reliable renewable energy source is expected to produce maximum power with longest lifetime and minimum errors, a critical aspect to bear in mind is the occurrence of PV faults according to raw material types. The different failure scenarios occurring in PV system, decrease its output power, reduce its life expectancy and ban the system from meeting load demands, yielding to severe consecutive blackouts. This paper aims first to present different core materials types, material based fault occurring on the PV cell level and consequently the fault detection techniques corresponding to each fault type.