Search

In recent years, Thermochemical Heat Storage (THS) systems and storage materials are important for the development of these systems have attracted a great interest. In this study, composite materials were prepared by impregnating sorbent salts (MgCl2, LiNO3) into vermiculite (V). The cyclical heat storage behaviors of the obtained composite structures were investigated with the laboratory scale thermochemical heat exchanger prototype system. Accordingly, the stability of the V+MgCl2 composite during repeated cycles and the energy storage density (Ed) value calculated as a result of the measurements in the prototype were found to be higher than the V+LiNO3 composite, as in the DSC analysis results. [ABSTRACT FROM AUTHOR]

Mg Ni alloys are produced by molten salt electrolysis and diffusion method on a nickel plate in KCl NaCl based melts. Structure, alloy composition and electrochemical properties of these alloys are evaluated. Electrolyte composition and applied current density parameters are studied for the characterization of the alloys. It is found that Mg Ni alloys with 45 wt% to 49 wt% Ni content which can be defined as MgNi–type alloys, have both higher discharge capacity and good retaining rate (72%). These alloys are mainly composed of Mg 2 Ni phases and displayed a maximum discharge capacity of 384 mAhg −1 . Increased Ni content is advantageous for the enhancement of the cycle life. At the same time, the discharge capacity of Mg Ni alloy electrode is found to be decreasing. The highest capacity retaining (85%) rate is observed in the highest Ni content alloys (72 wt% Ni). Electrochemical impedance spectroscopy and potentiodynamic polarization measurements show that the controlling–step of the discharge process changed from a mixed rate–determining process at lower depth of discharge to a mass transfer controlled process at higher depth of discharge. The charge transfer resistance increases from 0.5 Ω to 23 Ω with increasing depth of discharge. [ABSTRACT FROM AUTHOR]

Mg–Ni hydrogen storage alloy electrodes with composition of Mg–33, 50, 67 Ni at. % in amorphous phase were prepared by means of mechanical alloying (MA) process using a planetary ball mill. The electrochemical hydrogen storage characteristics and mechanisms of these electrodes were investigated by electrochemical measurements, X–ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The relationship between alloy composition and electrochemical properties was evaluated. In addition, optimum milling time and composition of Mg–Ni hydrogen storage alloy with acceptable electrochemical performance were determined. XRD results show that the alloys exhibit dominatingly amorphous structures after milling of 20 h. The electrochemical measurements revealed that the discharge capacity of Mg 33 Ni 67 and Mg 67 Ni 33 alloy electrodes reached a maximum when alloys were prepared after 20 h of milling time (260 and 381 mAhg −1 , respectively). The maximum discharge capacity of Mg 50 Ni 50 alloy was observable after 40 h milling (525 mAhg −1 ). It was also found that the cyclic stability of the alloys increased with increasing Ni content. Among these alloys, the amorphous Mg 50 Ni 50 alloy presents the best overall electrochemical performance. In this paper, electrode process kinetics of Mg 50 Ni 50 alloy electrode was also studied by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The impedance spectra of electrodes were measured at different depths of discharge (DODs). The observed spectra were fit well with the equivalent circuit model used in the paper. The electrochemical parameters calculated from electrochemical impedance were also compared. The electrochemical discharge and cyclic performance of 20, 40 and 60 h milled Mg 50 Ni 50 alloy electrodes were demonstrated by the fitted charge transfer resistance and Warburg impedance obtained at various DODs. It was further observed that the controlling-step of the discharge process changed from a mixed rate-determining process at lower DODs to a mass-transfer controlled process at higher DODs. The fitted results demonstrated that charge–transfer resistance (R ct ) increased with DOD. The R ct of 40 h milled Mg 50 Ni 50 alloy (29.27 Ω) was lower than that of 20 h (41.89 Ω) and 60 h milled alloys (92.43 Ω) at fully discharge state. [ABSTRACT FROM AUTHOR]

The effects of copper ion concentrations and electrolyte temperature on the morphologies and on the apparent densities of electrolytic copper powders deposited at high current densities under galvanostatic control were examined. These parameters were evaluated by the current efficiency of hydrogen evolution. In addition, scanning electron microscopy was employed for analyzing the morphology of the copper powders. It was found that the morphology was dependent on the copper ion concentration and electrolyte temperature under same current density (CD) conditions. At 150 mA cm-2 and a potential of 1000±20 mV (vs. SCE), porous and disperse copper powders were obtained at low concentrations of Cu ions (0.120 M Cu2+ in 0.50 M H2SO4). Under these conditions, a high rate of hydrogen evolution occurred parallel to copper electrodeposition. The morphology was changed from porous, disperse and cauliflower-like to coral-like, shrub-like and stalk--stock-like morphology with increasing Cu ion concentrations from 0.120, through 0.155, 0.315 and 0.475 to 0.630 M Cu2+ in 0.5 M H2SO4, respectively, at the same CD. Similarly, with increasing temperature, the powder morphology and the apparent density changed. The apparent density values of the copper powders were suitable for many powder metallurgy applications. [ABSTRACT FROM AUTHOR]

Convention on Long Range Transboundary Air Pollution (LRTAP) and its protocols aim to tackle transboundary air pollution problems. LRTAP is the first binding international environmental regime and forerunner of other environmental regimes. It aims to solve regional air pollution problems through scientific collaboration and deliberation within the framework of détente and rising environmental movements. Started as a weak regime, LRTAP became a stronger regime with the addition of new protocols. At the beginning LRTAP focused on sulphur dioxide and nitrogen oxide emissions and later incorporated volatile organic compounds, heavy metals, persistent organic pollutants, eutrophication and ground level ozone pollution into its agenda and contributed to substantial cuts in emissions. Having signed the LRTAP and its first protocol concerning the financing of EMEP, Turkey hasn't been a party to other protocols without binding itself for cuts in emissions. Although a legal and institutional framework for air pollution control was introduced, Turkey lacks a comprehensive monitoring system and suffers from rising air pollution levels. Turkey's efforts towards harmonising its environmental legislation as a part of its EU membership process do not produce tangible results given the problems of implementation and discrepancies between the limit values and long transition periods. Prevailing developmentalist discourse that prioritises economic development over environmental concerns contributes to postponement of sound pollution control efforts until Turkey becomes a full member. Yet again rising pollution levels reminds us that Turkey should take LRTAP and its protocols into account to solve those problems left unattended for quite some time. [ABSTRACT FROM AUTHOR]

The effects of copper ion concentrations and electrolyte temperature on the morphologies and on the apparent densities of electrolytic copper powders at high current densities under galvanostatic regime were examined. These parameters were evaluated by the current efficiency of hydrogen evolution. In addition, scanning electron microscopy was used for analyzing the morphology of the copper powders. It was found that the morphology was dependent over the copper ion concentration and electrolyte temperature under same current density (CD) conditions. At 150 mA cm-2 and the potential of 1000±20 mV (vs. SCE), porous and disperse copper powders were obtained at low concentrations of Cu ions (0.120 M Cu2+ in 0.50 M H2SO4). Under this condition, high rate of hydrogen evolution reaction took place parallel to copper electrodeposition. The morphology was changed from porous, disperse and cauliflower-like to coral-like, shrub-like and stalk-stock like morphology with the increasing of Cu ion concentrations towards 0.120 M, 0.155 M, 0.315 M, 0.475 M and 0.630 M Cu2+ in 0.5 M H2SO4 respectively at the same CD. Similarly, as the temperature was increased, powder morphology and apparent density were observed to be changed. The apparent density values of copper powders were found to be suitable for many of the powder metallurgy applications. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, electrolysis method was used to produce copper powder particulates. The effects of parametric values, such as current density, concentration of copper ions, electrolyte temperature and rotation speed of cathode, on the morphologies and on the apparent densities of copper powders were examined. These parameters were evaluated by the current efficiency of hydrogen evolution. In addition, scanning electron microscopy (SEM) was used for analyzing the morphology of the copper powders. It was found that the increasing of the current density or the electrolyte temperature decreased the size of the powder particles promoting their morphology into dendritic structure. In contrast, the increase of copper ion concentration or rotation speed of cathode also increased the size of the particles resulting in a cauliflower-like morphology. All powder particles obtained were consisted of agglomerated copper grains. The most important difference was the size and the shape of the copper grains which were notably influenced by the electrolysis parameters. The apparent density values of copper powders were found to be suitable for many powder metallurgical applications. Attempts were also made in the later part of the paper to determine optimum process parameters for the production of electrolytic copper powders. [Copyright &y& Elsevier]

Abstract: Laboratory-scale research has focused on the treatment of EAF steel making dusts by an alkaline caustic leach process, combining both hydro- and environmentally suitable metallurgical methods to recover zinc and lead. Optimum conditions were found to be: 95 °C, 1/7 solid/liquid ratio, 10 M NaOH and 2 h leaching time. Under these conditions, 85% Zn and 90% Pb were recovered. The leachate was further purified by zinc cementation at 50 °C to remove the metallic impurities (Pb, Cu, Cd, etc.) and to make it suitable for alkaline zinc electrolysis. The cementation process was chemically controlled with an activation energy of 26.7 kJ mol−1. [Copyright &y& Elsevier]

An electrochemical method was applied for the recovery of copper both from the spent solutions and from the rinse waters of electroless copper plating baths, containing copper sulfate, formaldehyde, quadrol, and NaOH. Experiments were conducted in a rotating packed cell (Rollschichtzelle®) to investigate the effects of current density, electrolyte composition, temperature, and pH on the copper recovery. All the copper (final CCu = 0.1 ppm) was recovered from the waste and rinse waters of chemical copper plating plants with 70% current efficiency by the electrochemical treatment in a rotating packed cell at 130 A/m2 current density, room temperature, with 5 mm diameter cathode granules, with the presence of formaldehyde, and with a specific energy consumption of 3.2–3.5 kW h/kg Cu. On the other hand, final copper concentrations of 5 ppm were reached with 62% current efficiency and 5.5–5.8 kW h/kg Cu specific energy consumption, with electrolytes containing no formaldehyde. [Copyright &y& Elsevier]

Hydrometallurgy is an efficient and well-known method that is frequently used in metal extraction. However, due to the high amount of water used in these systems and the amount of waste acid released, alternative method research activities in the scientific world are increasing day by day. Furthermore, when the literature is examined, it is seen that the concepts of green chemistry and solvometallurgy come to the fore. In this study, green solvents used in solvometallurgical methods are defined and information about ionic liquids and deep eutectic solvents is given. Examples of solvometallurgical methods to primary raw materials are given, such as extraction of rare earth elements and copper from their ores. Also, detailed information is given about the recovery of metals from waste lithium-ion batteries, fluorescent lamp wastes, scrap NdFeB and SmCo magnets, and mine wastes by using solvometallurgical methods. In conclusion; the method is suggested as an efficient way to reduce the use of resources in production, especially the use of less water, and producing less amount of waste acid. It is expected to increase the number of publications related with solvometallurgy within following years. Also, studies about upscaling the method to industry is an ongoing process. [ABSTRACT FROM AUTHOR]

In this paper, NiMo coatings were electrochemically deposited on a copper electrode (Cu/NiMo) and on an electrodeposited nickel onto copper plate (Cu/Ni/NiMo) in citrate solutions. Effects of electrolyte composition, pH value, and temperature on hydrogen-evolution reaction (HER) as well as the electrochemical stability in alkaline solution were investigated, and the electrochemical activation energy was determined for the NiMo alloys. This was evaluated by the determination of kinetic and mechanism of HER in alkali medium by the polarization measurements, cyclic voltammetry, and electrochemical impedance spectroscopy techniques. The morphology and chemical composition of the electrodeposited Ni-Mo were investigated using SEM and EDS analyses. The results showed that the corresponding HER overpotential of the Ni-Mo film depends on alloy composition and surface morphology. As the wt% of Mo content in the alloy is increased, the onset potential of electrode for HER shifted in the positive direction favoring hydrogen generation with lower overpotential. The overall experimental data indicated that the porous Ni-Mo coating on electrodeposited nickel plate was obtained when the molybdenum content was ca. 41 wt%. This electrodes exhibited high catalytic activity in the HER ( η = −48 mV at 100 mA cm and 80 °C), and their stability was tested by polarization measurements after different anodic and cathodic treatments in 1 M NaOH solution. Moreover, the corrosion behaviors of Ni and Cu/Ni/NiMo electrodes at open-circuit potential were also investigated, and their corrosion resistances were compared. Graphical abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Ni/SiC nanocomposite coatings were obtained by electrochemical codeposition of SiC nanoparticles with nickel, from an additive-free Watts type bath. Pure Ni deposits were also produced under the same experimental conditions for comparison. The influences of the SiC nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were studied. It is shown that these parameters strongly affected the weight percentage of SiC nanoparticulates. The phase structures, the surface morphology, and the chemical composition of the coatings were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) respectively. The corrosion performance of the coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The wear resistance and the microhardness of the coatings were studied also on a ball-on-disk tribometer and Vickers hardness tester, respectively. Characterization experiments showed that the SiC nanoparticle incorporation promoted changes in the texture of the nickel matrix. Moreover, the presence of SiC inhibits Ni growth, enhances re-nucleation, and hence results in a microcrystalline metal matrix. The results revealed that Ni/SiC nanocomposite coating provided excellent anti-corrosion performance and presented higher microhardness and better anti-wear performance compared to pure Ni coating. [Copyright &y& Elsevier]

Purpose: This study aims to investigate the effect of different pore diameter and pore length on corrosion properties of anodic aluminum oxide (AAO) film. Design/methodology/approach: AAO layer was produced by two-step anodization aluminum in oxalic acid. The surface morphology was investigated using field emission scanning electron microscopy. The pore diameters were ranging from 25 ± 5 to 65 ± 5 nm and the pore length ranging from 5 to 17 µm. The corrosion properties of the AAO films was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy tests. Corrosion properties and morphology of the anodic films depending on anodization times and pore expansion times were evaluated. Findings: All highlights of this work can be summarized with the following specified below: more treatment with the protective barrier layer of the solution as the pore diameter increases depends on the morphology of the nanotube structured AAO layer. The excellent corrosion resistance renders AAO films without pore expansion very promising. The oxide layer thickness does not affect the corrosion resistance. The better corrosion resistance of AAO films at low pore length can be ascribed to the barrier layer thickness and the more homogeneous structure. The presence of defects for the higher pore length decreases its corrosion resistance. Originality/value: The AAO films were fabricated by a two-step anodization method in oxalic acid. The anodization times and pore expansion times affect the corrosion performance. The AAO film without pore expansion has good corrosion resistance. The corrosion resistance decreases as the pore length increases. [ABSTRACT FROM AUTHOR]

The relation between time-dependent corrosion behaviors and microstructural characteristics of Sr modified and unmodified AlSi9 alloy was studied. The melted alloys were cast into the permanent mold at 700 °C casting temperature. The Effect of holding time in the furnace on chemical compositions of alloys was determined. Sr content of the modified alloys was 200 ± 5 ppm after 4 h and 50 ± 2 ppm after 17 h holding time. Microstructural properties were analyzed after casting. The corrosion behavior of AlSi9 depending on Sr content was investigated by means of electrochemical impedance spectroscopy technique and potentiodynamic polarization plots in 3.5 wt% NaCl solution at 25 °C. The effect of immersion time was examined at 1, 24, 72 and 120 h. The results indicated that high Sr content in AlSi9 alloy contributes to the formation of a finer eutectic phase and more stable corrosion behavior during immersion time. • The effect of Sr modification on the AlSi9 is investigated. • The relation between corrosion and microstructural characteristics are evaluated. • 50 ppm Sr is enough to obtain fine and fibrous eutectic morphology. • Sr Modification contributes to formation of stable and less defective oxide layer. • The protective effect of denser oxide/hydroxide layer is evident up to 120 h. [ABSTRACT FROM AUTHOR]

Abstract In this study, it aimed to produce carbon fiber (CF) reinforced aluminum metal matrix composite by squeeze casting method. In order to overcome the wetting problem between the aluminum matrix and the reinforcing agent, carbon fibers were coated with Ni coating with electroless technique. Different bath pH values and hypophosphite (HP), coating durations and bath temperature were investigated. SEM, EDS and XRD methods used to determine the characterize the layers. It has been observed that increasing the pH of the bath, coating time, bath temperature and amount of hypophosphite increases the thickness of the Ni coatings on the carbon fibers. Two different thicknesses of coatings were used with different volume fractions of fiber used to reinforce the 6063 aluminum as matrix alloy. Squeeze casting process was used for the production of the composites to increase the connection between the matrix and the carbon fibers. After achieving a good bonding, three-point bending, Charpy impact, and Vickers hardness tests were carried out to investigate the difference of at the mechanical properties. It was observed from the mechanical tests that while the hardness and the three-point bending strength was increasing the impact strength was decreasing after the carbon fiber addition. Also coating, in general, helping the mechanical properties, mechanical properties of composites are badly affected by higher coating thicknesses. Highlights • Carbon fiber reinforced 6063 alloy was produced by squeeze casting method. • Ni−P were coated on carbon fibers by electroless technique to enhance the wettability. • Ni coated CF addition increased mechanical properties of 6063 alloy. • Ni thickness and distribution of fibers in the matrix affect the mechanical properties. • Incorporation of carbon fibers resulted in increased bending strength in 6063 alloy. [ABSTRACT FROM AUTHOR]

3XX series Al–Si alloys are generally used in corrosive environments open for oxidation such as rainwater and seawater. The dendrite size and characteristics of the eutectic Si are important factors determining the properties of A356 alloy. In this study, the microstructure of Sr modified A356 aluminum alloy and the changes in corrosion properties were investigated. The alloy was cast into die and sand molds to examine the effect of cooling parameters on the microstructure. Sr modification was carried out by adding four different weight percentages (0, 120, 170 and 250 ppm). Corrosion behavior of the produced alloys was investigated by two ways. One of them was electrochemical impedance spectroscopy technique and the other is potentiodynamic polarization plots that was carried out in 3.5 wt.% NaCl solution at 25 °C. The corrosion resistance of the alloy was found to be increasing as Sr content was increased which modified the morphology of the silicon in the alloy. [ABSTRACT FROM AUTHOR]