Search

Thermochemical heat storage (THS) systems have recently attracted a lot of attention in research and development. In this study, an anodic aluminum oxide (AAO) template, fabricated by a two-step anodization method, was used for the first time as the matrix material for a THS system. Different salts were studied as thermochemical materials for their suitability in low-grade heat storage application driven by solar energy for an open system. Compositions were prepared by absorbing CaCl2, MgCl2, LiCl, LiNO3 and mixtures of these salts under a vacuum in an AAO matrix. Field Emission Scanning Electron Microscopy was used to examine the morphology of the produced AAO composites. Thermal energy storage capacities of the composites were characterized using a differential scanning calorimeter. Characterization analysis showed that anodized Al plates were suitable matrix materials for THS systems, and composite sorbent prepared with a 1:1 ratio LiCl/LiNO3 salt mixture had the highest energy value among all composites, with an energy density of 468.1 kJ·kg−1. [ABSTRACT FROM AUTHOR]

In this study, NiCu alloy coatings were electrochemically deposited on a copper electrode (Cu/NiCu). The effects of Ni/Cu mole ratio in the electrolyte and the current density on alloy composition and morphology as well as on the hydrogen evolution reaction (HER) in the alkaline solution for electrodeposited NiCu were investigated. The electrocatalytic activity of the fabricated NiCu alloys for the HER in alkaline solutions at 30°C was investigated by the polarization measurements and electrochemical impedance spectroscopy techniques. The morphology and chemical composition of the electrodeposited NiCu were characterized by scanning electron microscopy and atomic absorption spectroscopy. It was found that a NiCu electrode with copper content of ca. 14 wt % and a large surface area show a high electrocatalytic activity for the HER. The experiments were carried out in a bath with a pH of 8.0, Ni/Cu mol ratio of 1/20 and 0.2 M sodium citrate concentration at a current density of 50 mA cm–2. The fabricated alloys stability was tested by polarization measurements after different anodic and cathodic treatments in 1 M NaOH solution. Moreover, the corrosion behavior of Cu/Ni and Cu/NiCu electrodes at an open circuit potential was also investigated and their corrosion resistances were compared. [ABSTRACT FROM AUTHOR]

Corrosion behavior of A356 aluminum alloy with different grain refiners was evaluated. For this purpose, the Sr-modified A356 alloy was grain refined with Al5Ti1B and Al3B, and then, the corrosion characteristics were determined. For the mechanical properties, impact and Vickers hardness tests were carried out. To determine the corrosion behavior, both the electrochemical impedance spectroscopy technique and by potentiodynamic polarization plots were carried out in a 3.5 wt.% NaCl solution at 25 °C. The corrosion resistance of A356 alloy was dramatically improved in sequence with the following modifications compared to the unmodified castings: Sr, Ti and B additions. This situation applies to both different cooling rates, namely die and sand casting. The increase in corrosion rate was more than 80% for all alterations of the microstructure. Additionally, charge transfer resistance was increased ten times in die cast samples, while this value was 2.5 for sand cast samples compared to the unmodified alloy. It is important to note that sand casting of the unmodified alloy was improved four times with regard to the die cast unmodified A356. [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]

In this study, Ni-Mo alloy coatings were electrochemically deposited on a copper plate in citrate solutions. The effects of Ni/Mo mole ratio in the electrolyte and pH value on hydrogen evolution reaction (HER) as well as the electrochemical stability were investigated in the alkaline solution for electrodeposited NiMo. The electrocatalytic activity of the fabricated NiMo alloys for HER in alkaline solutions was investigated by the polarization measurements and electrochemical impedance spectroscopy techniques. The morphology and chemical composition of the electrodeposited Ni-Mo were investigated using SEM and EDS analyses. It was found that NiMo electrode with the highest molybdenum content (ca. 38 wt.%) and high surface area show high electrocatalytic activity in the HER. This was produced from a bath with a pH of 9.5, Ni/Mo ratio of 1/10 and 0.5 M sodium citrate concentration. The stability of this coating was tested by polarization measurements after different anodic and cathodic treatment in 1 M NaOH solution. The open circuit potential ( E) of the electrode as a function of immersion time was also measured. [ABSTRACT FROM AUTHOR]

Pure nickel and nickel matrix composite coatings containing nano-TiO particles were produced under both direct and pulse current conditions from an additive-free nickel Watts' type bath. The surface morphology, crystal size, crystallographic orientation, and microhardness of nickel matrix and the amount of embedded nano-TiO particles in the composite coatings were investigated. The corrosion performance of the coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods. The TiO particles embedded in the nickel matrix exerted strong influence on the texture of the growing nickel layer, changing its texture under both direct and pulse current conditions. The textural perfection of the deposits revealed that the presence of TiO particles led to the deteriorating of [100] preferred orientation. Under direct current conditions, the composite coating exhibited clearly [211] fiber orientation, while pulse current working exhibited a mixed crystal orientation through [100] and [211] axes. It is concluded that in the presence of TiO nanoparticles, the adsorption-desorption phenomena occurring on the metal surface are altered. The experimental results show that composite electrodeposits prepared under pulse plating conditions exhibited higher incorporation percentages than those obtained under direct plating conditions, at particularly 10 Hz and low duty cycles. The results revealed that pulse-plated Ni/TiO nanocomposite coating provided excellent anti-corrosion performance and presented higher microhardness. [ABSTRACT FROM AUTHOR]