The influence of chronopotentiometry response on the morphology and structure of galvanostatically synthesized tin dendritic particles has been investigated. Sn dendrites were electrodeposited at the ...current density 1.5 times larger than the limiting diffusion current density (− 3 mA cm
−2
) with various amounts of the electricity (200 and 400 mC), and the obtained morphology and structure of the particles were characterized by SEM and XRD techniques, respectively. The strong effect of the amount of spent electricity on the morphology and structure of the particles was observed, and it is explained by morphological and structural analysis of Sn particles produced potentiostatically at various cathodic potentials selected to be in line with the recorded chronopotentiometry response. The strong correlation among chronopotentiometry response, morphology, and structure of the Sn dendrites was established. The spear-like and the dendrites with prismatic branches possessed the strong (200),(400) preferred orientation, and they were obtained with a chronopotentiometry response of about − 1200 mV vs. Ag/AgCl. The chronopotentiometry responses in the − 1210 ÷ − 1740 mV vs. Ag/AgCl range caused a formation of the fern-like dendrites with the strong (220),(440) preferred orientation. Based on the obtained results, it follows that the chronopotentiometry analysis represents good diagnostic criteria for obtaining Sn powder particles of desired morphology and structure.
In this review paper, morphologies of metal powders produced by the constant (potentiostatic and galvanostatic) regimes of electrolysis from aqueous electrolytes are correlated with their crystal ...structure at the semiquantitative level. The main parameters affecting the shape of powder particles are the exchange current density (rate of electrochemical process) and overpotential for hydrogen evolution reaction. Depending on them, various shapes of dendrites (the needles, the two-dimensional (2D) fern-like, and the three-dimensional (3D) pine-like dendrites), and the particles formed under vigorous hydrogen evolution (cauliflower-like and spongy-like particles) are produced by these regimes of electrolysis. By decreasing the exchange current density value, the crystal structure of the powder particles is changed from the strong (111) preferred orientation obtained for the needle-like (silver) and the 2D (lead) dendrites to the randomly orientated crystallites in particles with the spherical morphology (the 3D dendrites and the cauliflower-like and the spongy-like particles). The formation of metal powders by molten salt electrolysis and by electrolysis in deep eutectic solvents (DESs) and the crystallographic aspects of dendritic growth are also mentioned in this review.
This work highlights the potential for the synthesis of new PtSnZn catalysts with enhanced efficiency and durability for methanol oxidation reaction (MOR) in low-temperature fuel cells. In this ...research, PtZn and PtSnZn nanoparticles deposited on high surface area Vulcan XC-72R Carbon support were created by a microwave-assisted polyol method. The electrochemical performances of synthesized catalysts were analyzed by cyclic voltammetry and by the electrooxidation of adsorbed CO and the chronoamperometric method. The physicochemical properties of obtained catalysts were characterized by transmission electron microscopy (TEM), thermogravimetric (TGA) analysis, energy dispersive spectroscopy (EDS) and by X-ray diffraction (XRD). The obtained findings showed the successful synthesis of platinum-based catalysts. It was established that PtSnZn/C and PtZn/C catalysts have high electrocatalytic performance in methanol oxidation reactions. Catalysts stability tests were obtained by chronoamperometry. Stability tests also confirmed decreased poisoning and indicated improved stability and better tolerance to CO-like intermediate species. According to activity and stability measurements, the PtSnZn/C catalyst possesses the best electrochemical properties for the methanol oxidation reaction. The observed great electrocatalytic activity in the methanol oxidation reaction of synthesized catalysts can be attributed to the beneficial effects of microwave synthesis and the well-balanced addition of alloying metals in PtSnZn/C catalysts.
Three different forms of Cu powder particles obtained by either galvanostatic electrolysis or a non-electrolytic method were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) ...and particle size distribution (PSD). Electrolytic procedures were performed under different hydrogen evolution conditions, leading to the formation of either 3D branched dendrites or disperse cauliflower-like particles. The third type of particles were compact agglomerates of the Cu grains, whose structural characteristics indicated that they were formed by a non-electrolytic method. Unlike the sharp tips that characterize the usual form of Cu dendrites, the ends of both the trunk and branches were globules in the formed dendrites, indicating that a novel type of Cu dendrites was formed in this investigation. Although the macro structures of the particles were extremely varied, they had very similar micro structures because they were constructed by spherical grains. The Cu crystallites were randomly oriented in the dendrites and compact agglomerates of the Cu grains, while the disperse cauliflower-like particles showed (220) and (311) preferred orientation. This indicates that the applied current density affects not only the morphology of the particles, but also their crystal structure. The best performance, defined by the largest specific surface area and the smallest particle size, was by the galvanostatically produced powder consisting of disperse cauliflower-like particles.
The formation of tin dendritic nanostructures by electrolysis from the alkaline electrolyte has been investigated. Morphology and structure of Sn dendrites produced applying both potentiostatic and ...galvanostatic regimes of the electrolysis are characterized by SEM and XRD, respectively. Depending on the applied cathodic potentials, three types of Sn dendrites were obtained: (a) needle-like and spear-like, (b) fern-like, and (c) stem-like dendrites. The very branchy dendrites with branches of the prismatic shape obtained by the galvanostatic regime of electrolysis represented a novel type of Sn dendrites, not previously reported in the literature. To explain the formation of various dendritic forms, correlation with the polarization characteristics for this electrodeposition system is considered. The needle-like and the spear-like dendrites represented monocrystals of (200),(400) preferred orientation, the fern-like dendrites exhibited the predominant (220),(440) preferred orientation, while in the stem-like particles Sn crystallites were oriented to a greater extent in the (440) crystal plane than in other planes. The galvanostatically synthesized Sn particles possessed the strong (200),(400) preferred orientation. The strong influence of parameters and regimes of electrodeposition on structural characteristics of Sn dendrites is explained by the fundamental laws of electrocrystallization taking into consideration the concept of slow-growing and fast-growing crystal planes.
In this study, metal matrix-based composite (MMC) was subjected to Equal Chanel Angular Pressing (ECAP) in several passes to determine the influence of deformation on the hardness of the samples. ...Composite based on A356 aluminum alloy and reinforced with Fly Ash (FA) particles was obtained by the compo casting method. The microstructural analyses and microhardness measurements were performed on the cast and pressed samples. Vickers hardness measurement of composite samples was performed with different indentation load sizes: HV0.02, HV0.05, HV0.1 and HV0.2. Results showed that hardness increases after each ECAP pass. The lowest hardness value of 42 (HV0.02) as well as the lowest arithmetical mean value of 46 (HV0.2) was measured at the cast composite. The greatest composite hardness of 107 (HV0.1) and the highest arithmetical mean value of 94 (HV0.1) was measured at the three-time pressed sample. The mathematical model named Meyer’s law was used for data analysis. In the cast sample, a decrease in hardness was detected with increasing indentation load, termed Indentation Size Effect (ISE), was confirmed with Meyers index n = 1.9112 < 2. Pressed samples showed opposite behavior—an increase in hardness with increasing indentation load—where Meyers index n > 2 indicated Reverse Indentation Size Effect (RISE). For all samples, a high coefficient of determination R2 > 0.99 confirmed that Meyer’s law described this phenomenon well.
This paper presents the technological process for obtaining basalt-stainless steel composite materials and testing their physical and mechanical properties. The phases of the technological process ...consist of: milling, homogenization, pressing, and sintering to obtain composite materials with improved fracture toughness. Andesite basalt from the deposit site "Donje Jarinje", Serbia, was used as a matrix in the composites, while commercial austenitic stainless steel 316L in the amount of 0-30 wt.% was used as a reinforcement. Although the increase of 316L amount caused a continuous decrease in the relative density of sintered samples, the relative density of sample containing 30 wt.% of 316L was above 94%. The 316L grains, which possess a larger coefficient of thermal expansion than the basalt matrix, shrinking faster during cooling from sintering temperature resulting in the formation of compressive residual stress in the basalt matrix surrounding the spherical steel grains. The presence of this stress activated toughening mechanisms such as crack deflection and toughening due to compressive residual stress. The addition of 20 wt.% of reinforcing 316L particles increased the fracture toughness of basalt by more than 30%. The relative density of these samples was measured to be 97%, whereas macrohardness was found to be 6.2 GPa.
Production of copper powders by the potentiostatic electrolysis under different hydrogen evolution conditions was investigated. Copper powders were characterized by the scanning electron microscope ...(SEM), X-ray diffraction (XRD), particle size distribution (PSD), and by the determination of the specific surface area (SSA) of the formed powders. Depending on quantity of hydrogen generated during electrolysis, the two types of particles were formed: dendrites and cauliflower-like particles. The dendrites were formed without, while cauliflower-like particles with the quantity of evolved hydrogen enough to achieve strong effect on hydrodynamic conditions in the near-electrode layer. Although macro structure of the particles was very different, they showed similar micro structure. Namely, both types of the particles consisted of small agglomerates of approximately spherical Cu grains at the micro level. The existence of the spherical morphology was just responsible for random orientation of Cu crystallites in both types of particles. The SSA of cauliflower-like particles was more than two times larger than that of the dendrites, while their size was considerably smaller than that of the dendritic particles. In this way, the useful benefit of Cu powder formation in the conditions of vigorous hydrogen evolution is shown.
The aspartic protease (FeAP9) gene from buckwheat resembles the exon–intron structure characteristic for typical aspartic proteinases, including the presence of the leader intron in the 5′-UTR. RT ...PCR experiments and gel protein blot analysis indicated that FeAP9 was present in all analyzed organs: developing seeds, seedlings, flowers, leaves, roots and stems. Using Real-time PCR, we found that
FeAP9 expression is upregulated in buckwheat leaves under the influence of different abiotic stresses, including dark, drought and UV-B light, as well as wounding and salicylic acid.
Cobalt 3D powder particles were successfully prepared by the galvanostatic
electrodeposition. Electrodeposited cobalt powder were characterized by X-ray
diffraction (XRD), scanning electron ...microscope (SEM), Energy Dispersive
Spectroscopy (EDS) analysis and SQUID magnetometry. It has been shown that
morphology, structure and magnetic properties of cobalt particles are closely
associated and can be easily controlled by adjusting process parameters of
electrodeposition. Morphology of cobalt powder particles is strongly affected
by hydrogen evolution reaction as a parallel reaction to cobalt
electrodeposition. Depending on the applied current density, the two types of
powder particles were formed: dendrites at lower and spongy-like particles at
higher current densities. Morphologies and structures of powder particles are
correlated with their magnetic properties, and compared with those of the
bulk cobalt. In comparison with the properties of bulk cobalt, the obtained
3D structures exhibited a decreased saturation magnetization (MS), but an
enhanced coercivity (HC) which is explained by their peculiar morphology.
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