Search Results (6,340)

Three nickel, copper, and zinc complexes with dicarboxylic acids (3,3′-dithiodipropionic acid (H₂dtdp) and fumaric acid (H₂fu)) and N-donor ligands (1,10-phenanthroline (phen), N′–methyldipropylenetriamine (mdpta), and N,N,N′,N″,N″-pentamethyldiethylenetriamine (pmdien)) were synthesized. These complexes were characterized using elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Interestingly, [Ni(dtdp)(phen)(H₂O)₃]∙0.5H₂O (1) is a mononuclear complex, where the dtdp dianion employs only one carboxylate group for coordination to the central nickel atom. [(ClO₄)(mdpta)Cu(μ-dtdp)Cu(mdpta)(H₂O)](ClO₄) (2) is a dinuclear copper complex with a dtdp bridge and different coordination on the copper center. [{Zn(pmdien)(H₂O)}₂(μ-fu)](ClO₄)₂ (3) is a symmetric dimer with a bridging fumarate ligand. These coordination compounds were tested for their antibacterial activities on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis bacteria strains. All the complexes show moderate activities on the mentioned strains. Full article

The extraction of nickel and cobalt from a limonitic laterite sample, derived from a mine area in the Greek island of Euboea, was studied via an acid agitation leach process with nitric acid as the leaching agent, to determine the optimal conditions at which the highest possible extractions of nickel and cobalt were obtained in the pregnant solution. Two series of experiments were carried out. In the first series, the extractability of metals was studied by varying the leaching temperature at values of 60 °C, 80 °C and 100 °C. For the second series of tests, the metals’ extraction at different values of initial nitric acid concentrations of 1M, 2M and 4M was examined. Based on the results, the effect of temperature is characterized as particularly significant, as with its increase, the final recoveries of nickel and cobalt were particularly high. The variation in acid concentration had a significant effect but not like that of temperature. For extraction conditions of an S/L ratio of 20%, a temperature of 100 °C and a 2M HNO₃ concentration, the highest recoveries of nickel and cobalt were obtained, namely 94.4% and 83.6%, respectively. Iron in all tests did not exceed dissolutions of more than 7.2% in the pregnant solution. Full article

This work studied the effect of sequential irradiation by krypton and helium ions at room temperature on the composition and structure of CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Irradiation of the HEAs by 280 keV Kr¹⁴⁺ ions up to a fluence of 5 × 10¹⁵ cm^–2 and 40 keV He²⁺ ions up to a fluence of 2 × 10¹⁷ cm^–2 did not alter their elemental distribution and constituent phases. Blisters formed on the nickel surface after sequential irradiation, where large blisters had an average diameter of 3.8 μm. The lattice parameter of the (Co, Cr, Fe and Ni) and (Co, Cr, Fe, Mn and Ni) solid solutions increased by 0.17% and 0.37% after sequential irradiation, respectively. Irradiation by Kr ions led to a decrease in tensile macrostresses in the HEAs in the region of krypton ion implantation (Region I) and the formation of compressive macrostresses in the region behind the peak of implanted krypton (Region II). Sequential irradiation formed large compressive stresses in Ni and HEAs equal to −131.5 MPa, −300 MPa and −613.5 MPa in Ni, CoCrFeNi and CoCrFeMnNi, respectively, in the Region II. Irradiation by krypton ions decreased the dislocation density by 1.6–2.3 times, and irradiation with helium ions increased it by 11–15 times relative to unirradiated samples for CoCrFeNi and CoCrFeMnNi, respectively. Sequentially irradiated CoCrFeMnNi HEA had higher macrostresses and dislocation density than CoCrFeNi. Full article

Background: Rotary Ni-Ti files are susceptible to sudden intra-canal separation due to cyclic fatigue stress, particularly in curved canals. To increase resistance to cyclic fatigue, new heat-treated files have been introduced. This study aimed to compare the performance of four heat-treated Ni-Ti files in two simulated curved root canals by evaluating the effect of the alloy, rotation speed, and diameter of the files on their resistance to cyclic fatigue. Methods: The Ni-Ti files included in the study were the ProTaper Gold^® (Dentsply Sirona) F2, ProTaper Ultimate^® (Dentsply Sirona) F2, FQ^® (Komet) 25.06, and Blueshaper^® (Zarc4Endo) Z4 25.06. Two groups of 30 files were selected for each system and were tested in two simulated canals milled in a specific metal template. One group was tested in a 60° curved canal and the other in a 90° curved canal. Results: In the 60° simulated canal, there were no instrument fractures within the 15 min time limit. In the 90° simulated canal, the Blueshaper Z4 demonstrated a lower resistance to cyclic fatigue, while FQ 25.06 showed statistically higher fatigue resistance based on both the Kruskal–Wallis and Games–Howell tests (p < 0.05). Conclusions: No differences were found between files when tested in a 60° curved canal for up to 15 min. However, in a 90° canal, the FQ^® files showed significantly higher resistance to cyclic fatigue, especially compared to the Blueshaper^® Z4. The ProTaper Ultimate and ProTaper Gold produced intermediate results, with the ProTaper Ultimate F2 slightly outperforming the ProTaper Gold F2. Full article

In the field of petroleum extraction, the welding technology of the core wire (the hybrid structure of copper and the Ni-Cr alloy) in high-power oilfield heaters is a key process that determines the efficiency of the heater. Using the tungsten inert gas (TIG) welding method of filling pure copper wire, this work effectively joins the dissimilar metals of red copper and the Cr₂₀Ni₈₀ nickel–chromium alloy. The microstructure, mechanical properties, and conductivity of the joint were analyzed. The results showed that the surface of the welded dissimilar metal joint was smooth and uniform; radiographic nondestructive testing did not reveal any macroscopic forming defects such as pores or cracks. The microstructure of the joint fusion zone exhibits an equiaxed grain morphology. The interface between the copper and the fusion zone displays a columnar grain structure, growing perpendicular to the fusion line. An interdiffusion layer of elements was formed at the interface between the Ni-Cr alloy and the fusion zone. The microhardness of the joint shows a stepwise decreasing trend, with the highest hardness on the nickel–chromium alloy side, followed by the fusion zone, and the lowest on the copper side. The joint fractures at the copper base material, with a tensile strength greater than 220 MPa, indicating a ductile fracture mode. During the electrical heating process, the joint temperature does not significantly increase compared to the copper side, demonstrating good thermal stability. Full article

A new cage-like dimeric nickel(II) complex Ni₂L₂(DMSO)₄ based on a ditopic redox-active hydroxy-para-iminobenzoquinone type ligand LH₂ (L is 4,4′-(1,3-phenylene-bis(azaneylylidene))-bis(3,6-di-tert-butyl-2-oxycyclohexa-2,5-dien-1-one dianion) was synthesized in DMSO at 120 °C. The molecular structure of the synthesized compound was determined by X-ray diffraction analysis. The complex Ni₂L₂(DMSO)₄ is almost insoluble in all organic solvents, probably due to the presence of a large number of intermolecular contacts in its structure. The electronic spectrum and thermal stability of the crystalline compound have been studied. Full article

The aim of this work was to determine the concentrations, distribution, and fate of potentially toxic elements [lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), mercury (Hg), arsenic (As), and cadmium (Cd)] in sediments of a hydropower plant water reservoir located in the Brazilian Cerrado biome (used as system model). The purpose of this study was achieved with an analysis of the level of contamination based on the geoaccumulation index (Igeo) and factor contamination (FC) and comparisons with values established by environmental legislation. The physical–chemical–biological properties of sediment samples, the distribution, and the fate of potentially toxic elements (PTEs) in the basin of the stream studied were also investigated using Pearson’s correlation coefficient (r) and principal component analysis (PCA). Cu, Hg, and Cd concentrations in the sediment samples from most of the points analyzed were above level II of the categorization stipulated in environmental legislation, characterizing sediments of poor quality. Moreover, Igeo and FC values indicated potential pollution of the water reservoir sediment by Cd. Concentrations of Cd exceeding 0.34 mg kg⁻¹ surpassed the reference values for water quality established by Conama Resolution No. 454/2012, highlighting the urgent need for ongoing sediment quality monitoring strategies. Hence, the study water reservoir was classified as being moderately to extremely polluted due to the fate of potentially toxic metals in the sediment samples. Frequent monitoring of the sediment quality in watersheds with hydropower plants is indispensable for the assessment of water resources, considering the importance of the water supply and power generation for the population. Moreover, water contaminated by PTEs poses potential risks to river basins, as well as to human and animal health. The results of this work can assist in the investigation of other water reservoirs around the world. Full article

This paper describes the principles of obtaining wear-resistant coatings based on titanium diboride that are deposited on the cutting tool for use in the machining of chromium–nickel alloys. The spark plasma sintering of samples from the TiB₂/Ti powder composition was studied, and the influence of sintering modes on the characteristics of the ceramic targets was analyzed. The regularities of the magnetron sputtering of sintered targets were revealed. The dependences of the physical and mechanical properties of coatings formed on hard alloy substrates on deposition conditions were established. The wear resistance of carbide samples with TiB₂-based coatings under friction-sliding conditions and coated carbide ball-end mills in milling Inconel 718 chromium–nickel alloy that is widely used in the industry was assessed. Full article

In Slovakia, around 200 environmental burdens that contain a significant amount of usable raw materials were created by the extraction of ores or the dumping of industrial waste. In this research, the hydrometallurgical metal recovery method from a metal-bearing environmental landfill in Sereď was investigated. The analysis of a representative sample of waste obtained from this landfill proved the presence of significant amounts of metals (43.45% Fe; 1.3% Cr; 0.09% Co, and 0.23% Ni). A thermodynamic study of the metals’ (Fe, Cr, Ni, and Co) leaching probability confirmed the possibility of metal extraction in an acidic environment. Subsequently, the effect of the most important factors on the leaching process (stirring intensity, temperature, liquid-to-solid phase ratio, and acid concentration) was experimentally tested. The analysis of the results determined the optimal leaching conditions. The extraction of 90.35% Fe and 59.62% Cr was ensured at a stirring intensity of 400 rpm, a leaching temperature of 80 °C, a liquid-to-solid phase ratio of 40, and a H₂SO₄ concentration of 3 mol/dm³. Various techniques, including SEM, EDX, XRD, Eh-pH diagrams, and AAS analysis, were used to analyze samples and products after leaching. The possibility of precipitating metals/compounds from the leachate to obtain a marketable product was theoretically proposed and proven. Full article

Converting CO₂ into methane is considered a promising and economically viable technology for global transportation and utilization of this greenhouse gas. This study involves the preparation of a Ni-CZ (CeO₂-ZrO₂)/ATP (attapulgite) catalyst through the co-precipitation and impregnation methods. XRD, SEM, TEM, N₂ absorption-desorption isotherms, XPS, H₂-TPR, CO₂-TPD, TG/DSC, and Raman were adapted to characterize the obtained samples. Real-time GC was used to measure the catalytic performances and to intensively study the impact of Ni loading content and ATP to CZ ratio on the catalytic performance of the products. DRIFTs was used to monitor the interstitial radicals in the catalytic reactions and to deduce the catalytic mechanisms. The results indicate that the composite catalytic matrix composed of CZ assembled on ATP demonstrated higher CO₂ methanation stability and better carbon deposition resistance ability than the single CZ or ATP as the carrier, which should be attributed to the improved specific surface area and pore volume of the ATP assembled matrix and the enhanced dispersibility of the CZ and Ni species. The adoption of CZ solid solutions improves the oxygen storage capability of the catalyst, thereby providing continued mobile O²⁻ in the matrix and accelerating the molecular exchange rate in the catalytic reactions. The ideal loading quantity of nickel contents on the CZA matrix is 15%, as the CO₂ conversion decreases at elevated temperatures when the Ni loading content reaches 20%. Among the tested samples, the 15Ni-0.8CZA sample showed the best catalytic performance of 75% CO₂ conversion and 100% CH₄ selectivity at 400 °C. After 50 h of stability tests, the CO₂ conversion rate still remained 70.84%, and the CH₄ selectivity obtained 97.46%. No obvious coke was detected according to the Raman spectra of the used catalyst. The in situ DRIFTS experiment showed that formate is the main intermediate of the CO₂ hydrogenation reaction on the 15Ni-0.8CZA catalyst. Full article

The room temperature ionic liquid trihexyl(tetradecyl)phosphonium decanoate ([P₆₆₆₁₄][Dec]) was employed in the liquid-liquid extraction of Co(II) from hydrochloric acid solutions in the presence of Ni(II). The extraction performance in liquid-liquid separations showed a strong dependence on the acid content of the feed aqueous solution. The best performance in terms of extracted cobalt and selectivity was obtained when the feed contained a HCl concentration above 6 M On the contrary, when the experiment was performed in absence of HCl, a lower extraction and Co/Ni selectivity were obtained. This behavior has been rationalized by considering the protonation of the [Dec]⁻ anion and the different Co(II)/Ni(II) speciation in HCl media. Moreover, polymer inclusion membranes (PIMs) were prepared using PVC and [P₆₆₆₁₄][Dec] at different weight rations. Only the PIM formulated with a 30:70/PVC:[P₆₆₆₁₄][Dec] weight ratio demonstrated effective extraction of Co(II) from the HCl solution. The extraction efficiency and selectivity of the PIM was comparable to that from biphasic liquid experiments at 8 M HCl. The results of this study constitute a promising background for further practical developments of carboxylate-based ILs applied in Co/Ni separations. Full article

Nickel is an important raw metal material in industry, which has been identified as a strategic mineral resource by the Chinese Ministry of Land and Resources. Nickel sulfide ore accounts for 40% of all nickel ores worldwide. However, magnesium silicate gangue minerals in sulfide nickel ores, particularly serpentine, pose significant challenges to the flotation of nickel sulfide ores. The presence of magnesium silicate gangue leads to a series of issues, including increased energy consumption in subsequent smelting processes, accelerated equipment wastage, and increased SO₂ emissions, which severely impact the comprehensive utilization of nickel resources in sulfide nickel ores. In this regard, flotation depressants are the most direct and effective method to reduce adverse influences caused by magnesium silicate gangue in the flotation of nickel sulfide ore concentrate. Based on the characteristics of the typical magnesium-containing nickel sulfide ore, this review illustrates the difficulties of the depression of magnesium silicate gangue during the flotation of nickel sulfide ore and gives an overview of the common depressants from six aspects (chelation depressants, dispersion depressants, flocculation depressants, depressants for grinding, depressants for slurry adjustment and combination depressants). Each section summarizes the relevant depression mechanisms and analyzes the advantages and disadvantages of various reagents, providing a reference for designing depressants specifically targeting serpentine. Full article

The development of a suitable catalytic system for methane pyrolysis reactions requires a detailed investigation of the activation energy of C-H bonds on catalysts, as well as their stability against sintering and coke formation. In this work, both single-metal Ni atoms and small clusters of Ni atoms deposited on titanium nitride (TiN) plasmonic nanoparticles were characterized for the C-H bond activation of a methane pyrolysis reaction using ab initio spin-polarized density functional theory (DFT) calculations. The present work shows the complete reaction pathway, including energy barriers for C-H bond activation and dehydrogenated fragments, during the methane pyrolysis reaction on catalytic systems. Interestingly, the C-H bond activation barriers were low for both Ni single-atom and Ni-clusters, showing the energy barriers of ~1.10 eV and ~0.88 eV, respectively. Additionally, single-atom Ni-TiN showed weaker binding to adsorbates, and a net endothermic reaction pathway indicated that the single-atom Ni-TiN was expected to resist coke formation on its surface. However, these Ni single-atom catalysts can sinter, aggregate into a small cluster, and form a coke layer from the highly exothermic reaction pathway that the cluster takes despite the facile reaction pathway. Full article

Nickel catalysts promoted with Mo and supported on silica were studied for renewable diesel production from triglyceride biomass, through the selective deoxygenation process. The catalysts were prepared by wet co-impregnation of the SiO₂ with different Ni/(Ni + Mo) atomic ratios (0/0.84/0.91/0.95/0.98/1) and a total metal content equal to 50%. They were characterized by XRD, XPS, N₂ physisorption, H₂-TPR, and NH₃-TPD. Evaluation of the catalysts for the transformation of sunflower oil to renewable (green) diesel took place in a high-pressure semi-batch reactor, under solvent-free conditions. A very small addition of Mo, namely the synergistic Ni/(Ni + Mo) atomic ratio equal to 0.95, proved to be the optimum one for a significant enhancement of the catalytic performance of the metallic Ni/SiO₂ catalyst, achieving 98 wt.% renewable diesel production. This promoting action of Mo has been attributed to the significant increase of the metallic Ni active phase surface area, the suitable regulation of surface acidity, the acceleration of the hydro-deoxygenation pathway (HDO), the creation of surface oxygen vacancies, and the diminution of coke formation provoked by Mo addition. Full article

Transition metal phosphate is the prospective electrode material for supercapacitors (SCs). It has an open frame construction with spacious cavities and wide aisles, resulting in excellent electric storage capacity. However, the inferior rate behavior and cycling stability of transition metal phosphate materials in alkaline environments pose significant barriers to their application in SCs. Herein, Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂ heterostructured materials synthesized through a one-step hydrothermal process exhibiting remarkable rate capability coupled with exceptional cycling endurance. Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂ samples exhibit a micron-scale structure composed of sheet-like compositions and unique pore structure. The multistage pore structure is favorable for promoting the diffusion of protons and ions, enhancing the sample’s electrochemical storage capacity. Upon conducting electrochemical tests, it was observed that Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂ composite electrode surpassed both the standalone Ni₁₁(HPO₃)₈(OH)₆ and Co₃(HPO₄)₂(OH)₂ electrode, achieving a remarkable specific capacity of 163 mAh g⁻¹ with exceptional stability and efficiency at 1 A g⁻¹. Notably, this electrode also exhibits superior rate performance, maintaining 82.5% and 71% of its original full capacity even at 50 A g⁻¹ and 100 A g⁻¹, respectively. Furthermore, it demonstrates superior stability in cycling, retaining a capacity of 92.7% at 10 A g⁻¹ after 5000 cycles. Moreover, Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂ and porous carbon (PC) were assembled into a hybrid supercapacitor (HSC). Electrochemical tests reveal an impressive power density of up to 36 kW kg⁻¹ and an exceptional energy density of up to 47.4 Wh kg⁻¹ for the HSC. Moreover, Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂//PC HSC exhibits robust capacity retention stability of 92.9% after enduring 10,000 cycles at 3 A g⁻¹, demonstrating its remarkable durability. This work imparts viewpoints into the design of transition metal phosphate heterostructured materials. Full article