Preparation and characterization of Co-Ru/TiO2/MWCNTs electrocatalysts in PEM hydrogen electrolyzer

The subject of this study is preparation and characterization of hypo-hyper d-electrocatalysts with reduced amount of precious metals aimed for water electrolysis. The studied electrocatalysts contain 10% mixed metallic phase (Co:Ru = 1:1 wt., Co:Ru = 4:1 wt. and Co:Ru:Pt = 4:0.5:0.5 wt.), 18% TiO₂ as a crystalline anatase deposited on multiwalled carbon nanotubes (MWCNTs). Previously, MWCNTs were activated in 28% nitric acid. As a reference electrocatalyst for hydrogen evolution reaction, corresponding electrocatalysts with pure Pt metallic phase and mixed CoPt (Co:Pt = 1:1 wt.) metallic phase were prepared. Also, as a reference electrocatalyst for oxygen evolution reaction, electrocatalyst with pure Ru metallic phase was prepared.The prepared electrocatalysts were structurally characterized by means of XPS, XRD, TEM, SEM and FTIR analysis.Electrochemical characterization was performed by means of cyclic voltammetry and potentiodynamic method in the PEM hydrogen electrolyzer. The range of the catalytic activity for hydrogen evolution of studied electrocatalysts was the following: CoRuPt (4:0.5:0.5) > CoPt (1:1) > Pt > CoRu (1:1) > CoRu (4:1). The order of the catalytic activity for oxygen evolution was the following: CoRu (1:1) > Ru > CoRu (4:1) > Pt > CoRuPt (4:0.5:0.5) > CoPt (1:1).     

Multiexcitonic dual emission in CdSe/CdS tetrapods and nanorods

CdSe/CdS semiconductor nanocrystal heterostructures are currently of high interest for the peculiar electronic structure offering unique optical properties. Here, we show that nanorods and tetrapods made of such material combination enable efficient multiexcitonic emission, when the volume of the nanoparticle is maximized. This condition is fulfilled by tetrapods with an arm length of 55 nm and results in a dual emission with comparable intensities from the CdS arms and CdSe core. The relative intensities of the dual emission, originating from exciton phase-space filling and reduced Auger recombination, can be effectively modulated by the photon fluence of the pump laser. The results, obtained under steady-state detection conditions, highlight the properties of tetrapods as multiexciton dual-color emitters.     

Hydro energy potential of cooling water at the thermal power plant

The hydro energy of the gravity water flow from the coal-fired thermal power plant units to the river in an open cooling system of turbine condensers is determined. On the basis of statistical data for a long time period, the water net head duration curve due to the river annual level change, as well as the reduction of the hydro energy potential due to the thermal power plant overhauls periods, are evaluated in the case study of the Thermal Power Plant “Nikola Tesla B” in Serbia. A small hydro power plant is designed for the utilization of this hydro energy, and the economic benefits of the project are calculated. The internal rate of returns and pay back periods are calculated in dependence of the electricity price and total investment costs. The increase of profitability is assessed, bearing in mind that the plant might be realized as the Clean Development Mechanism project according to the Kyoto protocol. The obtained results show that the project is economically attractive, and it can be carried out with standard matured solutions of hydro turbines available at the market. Even for the relatively low electricity price from small hydro power plants in Serbia of 0.08 €/kW h the internal rate of return and the pay back period are 17.5% and 5.5 years.     

Influence of T4 Heat Treatment on Tribological Behavior of Za27 Alloy Under Lubricated Sliding Condition

The effects of heat treatment on the microstructure, hardness, tensile properties, and tribological behavior of ZA27 alloy were examined. The alloys were prepared by conventional melting and casting route. The heat treatment of samples included the heating up to 370 °C for 3 or 5 h, quenching in water, and natural aging. Lubricated sliding wear test were conducted on as-cast and heat-treated ZA27 samples using block-on-disc machine. The friction and wear behavior of alloys were tested in contact with steel discs using combinations of three levels of load (10, 30, and 50 N) and three levels of linear sliding speeds (0.26, 0.50, and 1.00 m/s). To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, under all combinations of sliding speeds and contact loads. The rate of improvement increased with duration of solutionizing process before quenching in water. Obtained tribological results were related to the effects of heat treatment on microstructure changes of alloy.     

Review of the Application of Ion Exchange Resins for the Recovery of Platinum-Group Metals From Hydrochloric Acid Solutions

Platinum-group metals (PGMs) have become one of the most sought after rare metals in this modern age of science and they will continue to increase in importance as a result of their advantageous use in clean-air technology. Due to the scarcity of these precious metals, the application of ion exchange processes to recover PGM ions from relatively uncontaminated aqueous solutions, such as produced by the leaching of secondary sources including used automotive catalytic converters and electronic scrap, is becoming an increasingly cost-effective option and hence an important topic for the PGM production industry. This paper provides a general overview of the basic principles and theories relevant to the hydrometallurgical recovery of PGMs using ion exchange resins, along with a review and discussion of the most important factors that affect the separation and purification of PGMs present initially in predominantly ionic state in an aqueous hydrochloric acid solution. It is shown that in these acidic chloride solutions, the current system of choice for the leaching of PGMs, the adsorption behavior of the PGM ions onto chelating ion exchange resins is strongly dependent on the anionic PGM chloro-complex species present. In addition, it is revealed that the main factors affecting this complexation are (i) acidity and chloride ion concentration of the contacting aqueous chloride solution, (ii) “ageing” of the solution, and (iii) temperature of the solution.     

Efficiency of high‐order elements for continuous and discontinuous Galerkin methods

To evaluate the computational performance of high‐order elements, a comparison based on operation count is proposed instead of runtime comparisons. More specifically, linear versus high‐order approximations are analyzed for implicit solver under a standard set of hypotheses for the mesh and the solution. Continuous and discontinuous Galerkin methods are considered in two‐dimensional and three‐dimensional domains for simplices and parallelotopes. Moreover, both element‐wise and global operations arising from different Galerkin approaches are studied. The operation count estimates show, that for implicit solvers, high‐order methods are more efficient than linear ones. Copyright © 2013 John Wiley & Sons, Ltd.     

Short Electrospun Fibers by UV Cutting Method

Short electrospun fibers were obtained by using UV cutting method. Either polymers with double bonds with a photocross‐linker (CL) and photoinitiator (PI) or known photochemistry of coumarin ([2 + 2] cycloaddition reaction) without the addition of CL and PI is utilized for making short electrospun fibers. The electrospun fibers were irradiated by UV light in the presence of a mask with a defined width of slits. The uncovered parts of fibers were cross‐linked and therefore became insoluble. The non‐cross‐linked parts were removed by immersion of the fibers into an appropriate solvent. The length of obtained short fibers can be controlled by changing the width of the slits of the employed mask.

     

The contribution of fractal nature to BaTiO3-ceramics microstructure analysis

The structure of BaTiO₃ based materials can be controlled by using different technological parameters and different additives. In this paper, microstructure and dielectrical properties of Er₂O₃ doped BaTiO₃-ceramics, sintered from 1320 °C to 1380 °C have been investigated. Microstructural investigations were carried out using scanning electron microscope equipped with energy dispersive spectrometer. Grain size distribution was determined by quantitative metallography method.The new correlation between microstructure and dielectric properties of doped BaTiO₃-ceramics, based on fractal geometry and contact surface probability, has been developed. Using the fractals and statistics of the grains contact surface, a reconstruction of microstructure configurations, as grains shapes or intergranular contacts, has been successfully done. Obtained results indicated that fractal analysis and statistics model for contact surfaces of different shapes were very important for the prognosis of BaTiO₃-ceramics microstructure and dielectric properties.The morphology of ceramics grains pointed out the validity of developing new structure analytical methods, based on different grains’ shape geometries. The grains contact model based on ellipsoidal geometry is presented as new modeling tool for structure research of BaTiO₃-ceramics materials. The directions of possible materials properties prognosis are determined according to the correlations synthesis-structure-property.The statistical approach to the investigation of BaTiO₃-ceramic grains concerning the relationship between the temperature and the area of the contact surface is also introduced.