Nickel Phase Research Articles

Molybdenum doped induced amorphous phase in cobalt acid nickel for supercapacitor and oxygen evolution reaction

Reasonable structural design and metal-doping play significant roles in the optimization of electrochemical energy storage and conversion. Herein, in situ growth of Molybdenum-doped amorphous cobalt acid nickel nanoneedles on Ni foam (Mo-NiCo2O4/NF) has been successfully synthesized by a simple hydrothermal-annealing strategy. Benefiting from the unique hierarchical nanostructures and doping-optimized electronic structural configuration, the cross-link network structure of Mo-doped amorphous NiCo2O4 with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, the optimized Mo-doped NiCo2O4 samples possess a specific capacitance of 3970 mF cm−2 at 1 mA cm−2 and remarkable rate performance. The assembled hybrid supercapacitor obtains a maximum energy density of 35 Wh kg−1 (420 W kg−1) and keeps a capacitance retention of 107% after 5000 cycles. As an electrocatalyst, Mo-NiCo2O4/NF shows a rapid self-reconstruction process during oxygen evolution reaction (OER) that produces rich oxygen vacancies and thus exhibits remarkable long-term stability. The nanocomposites exhibit small overpotential (280 mV at 10 mA cm−2) and Tafel slope (43 mV dec-1). These results strongly demonstrate that both local amorphous phase and porous hierarchical structure design from Mo dopant provide superiorities for the synthesis of efficient and stable multifunctional electrode materials for energy storage and conversion.

Transformation of residual fatty raw materials into third generation green diesel over a nickel catalyst supported on mineral palygorskite

The transformation of residual fatty raw materials (RFRMs) (waste cooking oils (WCO), fatty acid distillate (FAD), oil extracted from spent coffee grounds (SCGO) and oil from chicken fat (CHO)) into third generation green diesel was studied over a very active nickel catalyst supported on mineral palygorskite. The transformation of biodiesel into green diesel was also studied. The physicochemical characteristics of the RFRMs were correlated with their composition and the conditions and procedure of their preparation. The composition of the reaction liquid mixture in total green diesel follows the order: 98% (CHO), 83% (WCO), 68% (FAD) and 10% (SCGO). Biodiesel is transformed much faster into green diesel than RFRMs. The catalyst use does not affect its main physicochemical characteristics. The activity trend was rationalized in terms of the relative surface concentrations of the supported nickel phases and on the basis of some molecules present in the RFRMs which may bring about catalyst deactivation.

Dry methane reforming with nickel–cobalt bimetallic catalysts based on halloysite nanoclay modified by alkaline melting method

AbstractCatalysts, including (10% Ni)/AMHA, (10% Ni + 5% Co)/AMHA, (5% Ni + 5% Co)/AMHA, and (5% Ni + 10% Co)/AMHA, were prepared by simultaneous impregnation of Ni and Co on alkaline molten halloysite (AMHA) and characterized by X‐ray diffraction (XRD), field diffusion scanning electron microscopy (FESEM), temperature‐programmed reduction (TPR), temperature‐programmed oxidation (TPO), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), atomic force microscopy (AFM), and Brunauer–Emmett–Teller (BET). The catalysts were evaluated in dry reforming of methane (DRM) at temperatures of 700 to 850°C and with a volumetric composition of a feed gas of 40% CH4, 40% CO2, and 20% Ar in a fixed bed reactor. Catalyst performance tests showed that the nickel catalyst based on milled and alkaline molten nano‐halloysite had a relatively poor performance. After impregnation of cobalt metal with different concentrations in the presence of nickel, the functional properties increased. Characteristic observations and experiments showed a very positive effect of cobalt metal on the catalyst performance. The presence of cobalt reinforcing metal along with nickel improves the activity and stability and reduces catalyst coking. Moreover, increasing cobalt along with nickel leads to better dispersion of the active phase of nickel, improved catalyst regeneration, and stable production of synthetic gas from methane and carbon dioxide. The effect of cobalt and nickel ratio on the catalyst structure, conversion rate of methane and carbon dioxide, stability, and carbon deposition rate were investigated. The conversion rate increases at high temperatures. Also, the resulting gas composition is suitable for Fischer–Tropsch reactions.

Triphenylphosphine-Assisted Transformation of NiS to Ni2P through a Solvent-Less Pyrolysis Route: Synthesis and Electrocatalytic Performance.

Straightforward synthetic routes to the preparation of transition metal phosphides or their chalcogenide analogues are highly desired due to their widespread applications, including catalysis. We report a facile and simple route for the preparation of a pure phase nickel phosphide (Ni2P) and phase transformations in the nickel sulfide (NiS) system through a solvent-less synthetic protocol. Decomposition of different sulfur-based complexes (dithiocarbamate, xanthate, and dithiophosphonate) of nickel(II) was investigated in the presence and absence of triphenylphosphine (TPP). The optimization of reaction parameters (nature of precursor, ratio of TPP, temperature, and time) indicated that phosphorus- and sulfur-containing inorganic dithiophosphonate complexes and TPP (1:1 mole ratio) produced pure nickel phosphide, whereas different phases of nickel sulfide were obtained from dithiocarbamate and xanthate precursors in the presence or absence of TPP. A plausible explanation of the sulfide or phosphide phase formation is suggested, and the performance of Ni2P was investigated as an electrocatalyst for supercapacitance and overall water-splitting reactions. The performance of Ni2P with the surface free of any capping agents is not well explored, as common synthetic methods are solution-based routes; therefore, the electrocatalytic performance was also compared with metal phosphides, prepared by other routes. The highest specific capacitance of 367 F/g was observed at 1 A/g, and the maximum energy and power density of Ni2P were calculated to be 17.9 Wh/kg and 6951 W/kg, respectively. The prepared nickel phosphide required overpotentials of 174 and 316 mV along with Tafel slopes of 115 and 95 mV/dec to achieve a current density of 10 mA/cm2 for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively.

First-principles study of electron and hole doping effects in perovskite nickelates

Rare-earth nickelates ${R}^{3+}{\mathrm{Ni}}^{3+}{\mathrm{O}}_{3}$ ($R=\mathrm{Lu}\text{\ensuremath{-}}\mathrm{Pr}$, Y) show a striking metal-insulator transition in their bulk phase whose temperature can be tuned by the rare-earth radius. These compounds are also the parent phases of the newly identified infinite layer $R\mathrm{Ni}{\mathrm{O}}_{2}$ superconductors. Although intensive theoretical works have been devoted to understand the origin of the metal-insulator transition in the bulk, there have only been a few studies on the role of hole and electron doping by rare-earth substitutions in $R\mathrm{Ni}{\mathrm{O}}_{3}$ materials. Using first-principles calculations based on density functional theory (DFT) we study the effect of hole and electron doping in a prototypical nickelate $\mathrm{SmNi}{\mathrm{O}}_{3}$. We perform calculations without Hubbard-like $U$ potential on Ni $3d$ levels but with a meta--generalized gradient approximation better amending self-interaction errors. We find that at low doping, polarons form with intermediate localized states in the band gap resulting in a semiconducting behavior. At larger doping, the intermediate states spread more and more in the band gap until they merge either with the valence (hole doping) or the conduction (electron doping) band, ultimately resulting in a metallic state at 25% of $R$ cation substitution. These results are reminiscent of experimental data available in the literature and demonstrate that DFT simulations without any empirical parameter are qualified for studying doping effects in correlated oxides and exploring the mechanisms underlying the superconducting phase of rare-earth nickelates.

Assessment of possibility of obtaining alloying components in the process of desalting of heavy hydrocarbon raw materials. Part 2

Earlier, the authors had already successfully proposed a method for extracting minerals from crude oil as a first step, to be further developed in this second step in the direction of obtaining solid (metallic and / or oxide) phases of nickel and vanadium. The scientific, practical and strategic importance of the work is clearly-underlined with a general depletion of vanadium and nickel ores. In the current situation of mineral resources with a general depletion of vanadium and nickel ores, it becomes necessary to search for new and alternative resources to obtain these strategic and important metals and their compounds from available resources. Taking into account that vanadium and nickel ores are practically absent in the raw material resources base of some countries, such as Middle East’s countries. Thus, a high percentage of imports of this metal product remains, which worsens the economic situation that has developed during political conflicts. The scientific approach was based on a combination of hydrometallurgical and electrometallurgical experiments, consistently carried out through the processes of sorption and desorption during cathodic electrodeposition. Sorption processes for vanadium and nickel were carried out using a mixture of Syrian sorbing materials (incense-type resins and surface-activated natural clays) with finely ground glass SiO2. Cathodic electrodeposition experiments were carried out on a copper cathode plate, and on the other hand, an insoluble glassy carbon electrode was used as the anode. All batch experiments were carried out to determine the best conditions for vanadium and nickel sorption by studying six different parameters affecting the sorption capacity of vanadium and nickel. As a result, the maximum sorption capacity of vanadium and nickel was 87.5 % and 91.3 % consistently under the predetermined conditions. Eventually, 7.6 % Ni (with a purity of 97 %) was recovered from the solution after the desorption process by the electrolytic method (during electrolysis); 15.6 % (99.3 % pure) V2O5 and 11.5 % (79 % pure) NiO chemically.

Role of nickel in the phase change from nanocrystalline Cu2O to CuO sputtered films and the formation of a metastable phase of Cu4O3

Copper oxide thin films doped with nickel were prepared by sputtering. The ratio of elements to the silicon substrate was measured by energy- dispersive X-ray spectroscopy. By the change in the power from 20 W to 50 W for sputtering nickel, the content of nickel intercalated in the copper-oxide lattice increased from 2.13 wt% to 7 wt%, respectively. The base sample and 2.13 wt% Ni sample exhibited the cubic Cu2O phase, while the increase in the nickel content to 3.54 wt% and 6.21 wt% led to the change in the tetragonal metastable structure of the Cu4O3 phase. The high doping of Ni at 7 wt% in the copper-oxide lattice transformed the metastable phase to stable monoclinic CuO. The lattice strain and dislocation density of the prepared samples depended on the nickel content. The lattice strain of the 6.21 wt% nickel sample ( ̴ 7.90 ×10−3) was greater than those of the stable phases of Cu2O (~2.5 × 10−3) and CuO (~3.65 × 10−3). The copper-oxide thin film nanostructure was confirmed by atomic-resolution transmission electron microscopy. With the change in the nickel content, the average grain size of the prepared films ranged between 16.57 nm and 20.76 nm. The films roughness was correlated to the nickel content and phase change in the copper-oxide lattice. The optical properties were analyzed and calculated. The optical band gap of the films were affected by the phase change and the nickel content, which decreased from 2.535 eV (Cu2O) to 2.090 eV (CuO).

Preparation, Properties and Applications of the Hybrid Organic/Inorganic Nanocomposite Based on Nanoporous Carbon Matrix

Nanoporous carbon matrix was prepared by the sol–gel process from pyrogallol-formaldehyde (PF) mixtures in water using picric acid as catalyst. For the second sample, nickel oxide nanoparticles were added in the PF matrix to get a PF/NiO hybrid organic/inorganic nanocomposite. After a drying step, the samples were heat treated for two hours at 650 °C in tubular furnace under open nitrogen atmosphere. The XRD analysis shows that PF matrix is amorphous while PF/NiO nanocomposite exhibited a metallic phase of nickel. The average value of the metallic nickel crystallites deduced from the Scherrer’s equation was found to be about 35 nm. TEM images indicate the existence of nanopores in the PF matrix and the presence of nickel nanoparticles in the PF/NiO nanocomposite which are dispersed randomly in the carbon matrix. The adsorption–desorption of nitrogen revealed that the pore size equal to 1.9 nm for PF matrix and 2.6 nm for PF/NiO nanocomposite. So, the adsorption capacities of carbon dioxide (CO2) and methane (CH4) show that the PF matrix has the highest adsorption at low pressures where micropores are dominant and the PF/NiO nanocomposite tends to adsorb gases better at high pressure where the presence of mesopores. The V(I) characteristics showed that the PF/NiO nanocomposite can be considered as a smart material. Indeed, the characteristic behavior can be adjusted according to the maximum applied current. Electrochemical measurements have shown that the PF/NiO nanocomposite is very promising for the detection of non-enzymatic glucose with a sensitivity of 76 µA/mM.cm−2 and a detection limit lower than 0.03 µM. The absorption spectra showed that the addition of the NiO nanoparticles increased the Urbach energy and the disorder in the PF/NiO nanocomposite.

Techno-Economic Analysis of CO2-to-Fuel with a Proton-Conducting Ceramic Sabatier Electrolyzer

As intermittent renewable electricity generation achieves higher market penetration, the need for robust storage and dispatch capabilities become more pronounced. In this report, we present a techno-economic analysis based around a levelized cost of storage (LCOS) calculation for a Sabatier Electrolyzer to illustrate the value proposition of electrolyzer technology. The Sabatier Electrolyzer is illustrated in Figure 1A; the CO2 feed to the fuel electrode is upgraded to CH4 through heterogeneous catalysis with hydrogen. The hydrogen is produced through water electrolysis at the steam electrode. When driven by surplus electricity, the Sabatier Electrolyzer presents an energy-storage option with CO2-to-fuels.The electrolyzer features a proton-conducting ceramic electrolyte (BaCe0.4Zr0.4Y0.1Yb0.1O3-d) that has shown encouraging performance under fuel-cell and H2O-electrolysis applications. The Sabatier chemistry (CO2 + 4 H2 = CH4 + 2 H2O) occurs within the porous fuel electrode, a nickel-ceramic composite, where protons emerging from the ceramic phase react with CO2 or recombine to form H2 over the nickel phase. The exothermic Sabatier reaction can be balanced by the endothermicity of H2O electrolysis improving plant-level thermal balance and higher efficiency.This report explores the economic potential of a commercial-scale Sabatier electrolyzer plant from the perspective of levelized cost of storage (LCOS). This LCOS is based on similar analyses conducted for lithium-ion batteries, flow batteries, flywheels, and pumped-hydro facilities. The model combines plant-level round-trip efficiency (RTE), overnight capital costs, variable operations and maintenance (O&M) costs, and charging costs into a time value of money (TVM) financial model. The model is exercised to estimate the lifetime cost of energy storage for the plant.The protonic-ceramic electrolyzer presents a perhaps unusual materials set. While protonic-ceramic fuel cells have demonstrated high performance and encouraging durability at the lab scale, the materials have also shown undesirable electronic conduction that can substantially decrease electrolysis efficiency, boosting costs. The electrochemical model captures the substantial impact of protonic-ceramic electrochemical performance on LCOS, and is validated by lab-scale experimental measurements of protonic-ceramic Sabatier Electrolyzer cells. Results were scaled to yield the commercial-scale LCOS.Sensitivity analyses demonstrate the primary cost drivers behind the commercial-scale Sabatier Electrolyzer plant. Key cost drivers include Faradaic efficiency, methane yield, utility cost of electricity, and cost of sequestered CO2. Depending on operational parameters, the LCOS of the commercial-scale Sabatier Electrolyzer plant ranges from $4,319 down to $348 per MWh of storage potential. Figure 1

Selective Cobalt Precipitation for the Synthesis of Precursors for Cathode Materials of Li-Ion Batteries

Due to the increase in energy storage for consumer electronics, stationary application and above all for electrical vehicles, the manufacturing of Li-ion batteries has dramatically increased in the past few years. Unfortunately, cathode materials still often use cobalt, and consequently, an increase of 10% per year of the world’s cobalt consumption has been observed. Li-ion batteries represent 60% of the use of extracted cobalt today (more than 80% expected in 2030), which is classified as a critical material since 2011 by the European Commission. Battery grade cobalt is produced by only few countries. 60% is provided by the Democratic Republic of Congo. In order to avoid reliance on cobalt supplying, European industry should have to develop alternative solution.We present here a new way to extract cobalt from a solution of battery-waste materials. Through a one-step process, it is possible to recover the cobalt, selectively, in a solution composed in majority of cobalt, nickel and manganese.The goal of the process is to form a cobalt-based Metal Organic Framework compounds (MOF) from a multi-metals based solution. The contact of a well-designed ligand with model multi-metallic solution of nickel, manganese and cobalt, under specific conditions, creates a precipitate, which is recovered by centrifugation or filtration. The XRD analysis of the resulting material demonstrates a crystalline structure, and its ICP analysis shows up to 99% of cobalt composition of the metallic nodes of the material. The same process with a real battery waste solution enables the formation of a precipitate made of 94% of cobalt (among the metallic centers).The resulting MOF can be used as a precursor for synthetizing cathode materials. In order to complete the described closed-loop concept, it is indeed possible to assemble a coin-cell from those products. The well define crystalline structure of the MOF makes them suitable for other industrial application, such as separation or catalysis (open-loop concept).We are focusing on better understanding of this selectivity process. Density Functional Theory (DFT) calculations are performed, as a tool to evaluate the energy of the different complexes in solution at all states of the nucleation and growth of the MOF. Moreover, the ligand used can form a MOF with each of the metals present in solution. Some nickel and manganese phases (more or less soluble) are involved during the process as a function of the reaction conditions. Identifying their nature and formation is another axis for the understanding of the presented work. Modelling these phenomena could help to determine the reaction that occurs, how the selectivity happens, and why the growing material is made of cobalt only (no other metal).

An Earth‐Abundant Ni‐Based Single‐Atom Catalyst for Selective Photodegradation of Pollutants

Highly efficient catalytic technologies are urgently needed to remove pharmaceutical pollutants from water. In this work, the preparation, characterization, and photocatalytic performance of an earth‐abundant Ni‐based heterogeneous catalyst featuring highly dispersed Ni species over nanosheets of carbon nitride are reported. The absence of any metallic nickel phase has been confirmed by spectrometric analyses, unveiling the NiN environment for the metal centers and attaining synergistic interfacial carrier transfer via NNiN coordination. By combining advanced characterizations with kinetic investigations, it is demonstrated that these newly formed isolated single atoms of Ni act as a bridge, facilitating faster electron transfer, increasing the charge density on Ni, and reducing the photocarrier transfer barrier. Compared to literature precedents, this substantially enhances the degradation of gemfibrozil, a model pharmaceutical pollutant found in wastewater, reducing the formation of toxic benzenic byproducts during photooxidation. This effect, which is not observed over conventional nanoparticle‐based materials, discriminates the role of single‐atom and nanoparticle‐based catalysis during degradation of pollutants. This work opens new avenues in designing selective and earth‐abundant photocatalysts for advanced oxidation processes, showing the importance of atom coordination to control the surface and catalytic properties of single‐atom materials.

Amorphous Alloys Atomic Structure Investigation by Means of Electron Microscopy and Diffraction

In the paper, the atomic structure of amorphous and nanocrystalline alloys of the electrolytically obtained CoP, NiP, CoNiP, CoW, and CoNiW systems has been studied. The structure was investigated by electron microscopy and diffraction using a Libra 200 HR FE transmission electron microscope at an accelerating voltage of 200 kV within a temperature range of 50-35 °C. The obtained radial atom distribution function and the coordination sphere radii are in good agreement with the data for the cobalt structure in the cubic and hexagonal modifications. The high coordination numbers of the third and fourth coordination spheres allow suggesting a predominantly cubic structure of the local atom environment in CoP samples but somewhat lower, which is explained by the presence of free volume and phosphorus atoms distorting the local structure. When heating, the near atomic order also corresponds to the cubic phase of cobalt, and the ordering occurs in the second, third, and fourth coordination spheres. The data obtained for CoNiP alloys indicate that by configuration, the local atomic environment is closer to the hexagonal structure of nickel. In general, the structure of the CoP-CoNiP system alloy films obtained by electrolytic deposition is already in one of the local minima of the total system energy, which is confirmed by the near atomic order similar to the cubic phase of cobalt or hexagonal phase of nickel. This determines the good stability of the structure and properties during thermal exposure.

Structural, magnetic and electrical properties of nickelthin films deposited on Si (100) substrates by pulsed laser deposition

Nickel thin films have been deposited on silicon (100) substrates by pulsed laser deposition at various substrate temperatures, Ts , in the range 100 - 700 ºC. X-ray diffraction analysis confirms nickel phases are present for Ts in the range 100 - 300 ºC, while above 500 ºC Ni-Si phases were observed. The grain size and roughness of thin films were in the range 30 nm - 590 nm and 4.3 - 15.7 nm respectively for thickness of the films is in the range 45 nm - 100 nm. Systematic variation with Ts was found for these morphological parameters, as well as the ratio of the remnant to saturation magnetic moment, magnetic coercivity and magnetoresistance.

Performance of Carbon-Nickel Composite Coatings on Laser Surface Roughened Aluminum Foils for Supercapacitor Current Collectors

Surface-engineered aluminum current collectors were developed through laser-based surface modification methods. Their performances as current collectors in supercapacitors clearly outperformed state-of-the-art carbon-coated commercial foils and were close to ideal gold foils, thanks to the enhanced interfaces provided by their engineered surfaces. Surface modifications included roughening by laser ablation in high vacuum, and coating with a carbon-nickel (C0.97Ni0.03) composite thin film deposited using pulsed laser deposition. The main improvement was obtained after coating the aluminum foil with the carbon-nickel protective layer, which was attributed to the almost pure sp2 bonding state of the carbon and a mostly metallic nickel phase. The surface roughening treatment further decreased the interface resistance by providing a higher contact surface and a better mechanical anchorage of the active materials layer. The combination of laser roughening in vacuum conditions and subsequent deposition of an electronically conductive protective coating was therefore demonstrated as an efficient approach to improve the performance of current collectors for supercapacitors.

Characterisation of Ni-cermet degradation phenomena II. Relationship between connectivity and resistivity

The present work is related to numerical modelling and electrical conductivity monitoring of Ni-cermet supports with YSZ ceramic components in wide range of temperatures (700, 750, and 800 °C) and water content (3, 45, and 80 vol%) in hydrogen atmospheres. The experimentally evaluated resistivity of the Ni-YSZ supports has exponential type dependence on time. The microstructure can be characterized by the special parameters, which were determined using SEM image analyses of supports made of Ni-YSZ. Three-dimensional modelling of the sample microstructure was done by means of the original algorithm. Estimation of the volume contribution of interlinked clusters of nickel phase was carried out. The electrical resistivity of the Ni-YSZ cermet microstructure model was simulated before and after exposure by means of the finite element method. It was revealed that the relative effective resistivity of the Ni-YSZ supports is directly proportional to the connectivity of Ni phase. This relationship between connectivity and resistivity is fulfilled in a whole range of experimental conditions. The effective resistivity as a function of exposure time obtained experimentally was consistent with the simulation results.

Study of the degradation of a fine-grained YSZ–NiO anode material during reduction in hydrogen and reoxidation in air

In this work, the high-temperature reduction of nickel oxide and reoxidation of metallic nickel in the YSZ–NiO anode material have been studied. As-sintered material (of mode 1) manufactured by tape casting underwent two treatment modes: one-time reduction (mode 2) in pure hydrogen for 4 h at 600 °C under a pressure of 0.15 MPa; reduction/oxidation (redox) for five cycles in hydrogen/air atmospheres at 600 °C (mode 3). The material of mode 1 exhibited a bending strength of about 209 MPa. This level is high enough for anode materials. Significant changes have been detected in the microstructure of the material reduced in hydrogen (mode 2). Agglomerates of particles (average size about 5 µm) with a predominance of the zirconium phase as well as regions of small particles (1 µm) with uniformly distributed both the nickel and zirconium phases were revealed. The intergranular fracture micromechanism prevailed in the specimens tested. The material strength (40 MPa) did not satisfy the requirements for anode materials. Despite too “rigid” redox treatment mode in pure hydrogen and air at 600 °C (mode 3), the cermet is not inferior in strength (85 MPa) to those fabricated using other techniques. On the specimen fracture surface, a porous core and dense outer layers have been revealed. An increased amount of nickel in the surface layer is probably a consequence of the microstructural transformation due to the diffusion of nickel from the subsurface region towards the surface. The redox treatment caused the specimen core degradation due to forming large pores, their coalescence into cracks, and loss of material integrity. In contrast to the mixed fracture micromechanism noted in the specimen surface layer, the intergranular one in the core was revealed. The reached level of electrical conductivity and a positive effect of the treatment on the material strength indicate the potential of the tape cast material, especially, in the case of reduction in Ar–5 vol% H2 gas mixture instead of pure hydrogen.

Mineralogical Tracers of Gold and Rare-Metal Mineralization in Eastern Kazakhstan

Replenishment of mineral resources, especially gold and rare metals, is critical for progress in the mining and metallurgical industry of Eastern Kazakhstan. To substantiate the scientific background for mineral exploration, we study microinclusions in minerals from gold and rare-metal fields, as well as trace-element patterns in ores and their hosts that may mark gold and rare-metal mineralization. The revealed compositions of gold-bearing sulfide ores and a number of typical minerals (magnetite, goethite, arsenopyrite, antimonite, gold and silver) and elements (Fe, Mn, Cu, Pb, Zn, As, and Sb) can serve as exploration guides. The analyzed samples contain rare micrometer lead (alamosite, kentrolite, melanotekite, cotunnite) and nickel (bunsenite, trevorite, gersdorffite) phases and accessory cassiterite, wolframite, scheelite, and microlite. The ores bear native gold (with Ag and Pt impurities) amenable to concentration by gravity and flotation methods. Multistage rare-metal pegmatite mineralization can be predicted from the presence of mineral assemblages including cleavelandite, muscovite, lepidolite, spodumene, pollucite, tantalite, microlite, etc. and such elements as Ta, Nb, Be, Li, Cs, and Sn. Pegmatite veins bear diverse Ta minerals (columbite, tantalite-columbite, manganotantalite, ixiolite, and microlite) that accumulated rare metals late during the evolution of the pegmatite magmatic system. The discovered mineralogical and geochemical criteria are useful for exploration purposes.

Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study.

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO2 emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO2 by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO2 with H2 was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO2 reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH4 formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H2O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions.

Kinetic control of zinc cyamelurate crystal formations

The dynamic combinatorial library (DCL) of cyamelurates consists of 17 tautomers of cyameluric acid and their ions, as well as metal aqua complexes. That leads to a variety of compounds in the Zn(NO3)2 – K3(C6N7O3) – H2O system. All compounds are obtained with impurity amorphous and crystalline phases, which complicates their study. In this work, metastable phases of zinc, nickel, and iron cyamelurates were obtained and their crystal structures were determined for the first time. Kinetic control of chemical reactions allowed us to isolate two zinc cyamelurate metastable phases. The metastable compound K2Zn(C6N7O3H)2∙8H2O is formed immediately after mixing the precursor solutions, and after two hours, it is converted to another metastable compound Zn(C6N7O3H)∙5H2O. Due to hydrate isomerization, after 12 hours in the mother liquor, the latter transforms into a thermodynamically stable compound of the same composition. The features of the synthesis and crystalline structure of zinc cyamelurates can be interpreted from the standpoint of the nonclassical nucleation theory. The crystal structures of the synthesized compounds K2Zn(C6N7O3H)2∙8H2O, Zn(C6N7O3H)∙5H2O, and Zn(C6N7O3H2)2∙8H2O allowed us to conclude that decomposition of supersaturated zinc solution leads to the formation of double electric micelles (DEM). They can be considered nanoreactors playing an important role in crystal nucleation.

Effects of sintering temperature on dihedral angle of NiTiCu SMA fabricated using spark plasma sintering

Abstract Applications of shape memory alloys can be designated based on the transformation temperatures which could be dominated by the chemical composition of nickel, processing temperature and secondary phase precipitates. The existence of secondary phase precipitates can be mainly affected by the grain surface and boundary energy which could be calculated by the dihedral angle. In this work, nickel-titanium-copper shape memory alloy has been fabricated using spark plasma sintering technique at various temperatures such as 700 °C, 800 °C and 900 °C. The influence of sintering temperature has been investigated on the occurrence of dihedral angle. Grain boundary and surface energy have been suppressed while energy of triple junctions has been improved with the sintering temperature. The reason behind this was observed by the enhancement of fraction of triple junctions with dihedral angle. Results suggest that the dihedral angle can be improved with the sintering temperature which led to enhance the density of the NiTiCu SMA.