NiO Powders Research Articles

A direct CH4 metal-supported solid oxide fuel cell with an engineered Ni/Gd-doped CeO2 anode containing Ni and MnO nanoparticles

NiMn 2 O 4 (NMO) coated Gd-doped CeO 2 (GDC) and NiO powders are prepared by a hydrothermal method for the anode of a metal (Ni-10 at.% Fe)-supported solid oxide fuel cell fueled by wet CH 4 (3 vol.% H 2 O). NMO remains on NiO but dissolves into GDC at 1400 °C. Upon reduction in H 2 at 700 °C for 2 h, Ni nanoparticles exsolve on the doped-CeO 2 (DCO) substrate (DCO@Ni), while MnO nanoparticles form on Ni (Ni@MnO). DCO@Ni demonstrates high catalytic activity for reforming wet CH 4 and high resistance to carbon deposition with a yield of H 2 increasing from 11 (500 °C) to 33 (700 °C) ml min −1 and remaining around 25 ml min −1 at 600 °C for 30 h. The metal-supported single-cell with a Ni@MnO-DCO@Ni anode shows high initial and durable electrochemical performance with a maximum power density increasing from 160 (500 °C) to 720 (700 °C) mW cm −2 and a cell voltage remaining above 0.55 V at 600 °C for 200 h under 400 mA cm −2 and 20 ml min −1 . Such high performance is ascribed to the metal support with low ohmic resistance and the engineered anode with high catalytic activity and enhanced resistance to carbon deposition.

Evaluation of the thermodynamic possibility of in-situ composites fabrication in aluminum-metal and aluminum-metal oxide systems through friction stir processing

Thermodynamic evaluations of the possibility of the interaction reaction of aluminum with powders of Ti, Ni, Fe, TiO2, NiO and Fe2O3 leading to the formation of intermetallics and aluminum oxide Al2O3 during friction stir processing (FSP) were carried out. The Gibbs energy was considered as a determining parameter since its change resulted from chemical transformations makes it possible to establish the fundamental possibility of a chemical reaction proceeding under certain conditions. The change in the Gibbs free energy with temperature was calculated, and the Ellingham diagrams were plotted for the reactions observed experimentally during FSP in the systems Al+Ti, Al+TiO2, Al+Ni, Al+NiO, Al+Fe and Al+Fe2O3. The evaluations were performed for 1 mole of aluminum. The selected temperature range was 620 – 720 K because during FSP of aluminum and its alloys the peak temperatures usually fall into this temperature range. It was shown that all considered reactions of aluminum interaction with both pure metals (Ti, Ni, Fe) and oxides (TiO2, NiO, Fe2O3) were thermodynamically possible. However, chemical reactions involving aluminum interaction with TiO2, NiO and Fe2O3 gave higher absolute values of ΔG than those with Ti, Ni, and Fe. In the systems Al+NiO and Al+Fe2O3 in reactions involving the formation of intermetallics of MeAl3 type and oxide Al2O3 the absolute values of ΔG were approximately the same and in two times higher than that for the system Al+TiO2. It was concluded that for manufacturing of the in-situ Al-based composites by FSP the use of nickel and iron oxides (NiO and Fe2O3) is preferable to the pure metals (Ti, Ni, Fe) and the titanium oxide (TiO2).

Experimental investigation on the effect of anode functional layer on the performance of anode supported micro-tubular SOFCs

In this study, anode supported micro-tubular solid oxide fuel cells (SOFCs) are fabricated by extrusion method and the effects of powder size, thickness and sintering temperature of the anode functional layer (AFL) on the electrochemical performance is experimentally investigated. For this purpose, four different commercial NiO powders are tested as initial powder for the fabrication of the anode functional layer. The thickness of AFL is also considered by varying the number of coatings. After deciding the optimum initial NiO powder size used in AFL and AFL thickness, the effect of pre-sintering temperature is examined. The performance tests are performed at an operating temperature of 800 °C under hydrogen and air. The microstructures of the samples are also investigated by a scanning electron microscope. The best peak power density is obtained as ∼0.5 W/cm2 from the cell having a single layer anode functional layer pre-sintered at 1250 °C prepared by NiO powders with 4 m2/g surface area.

Boosted microwave dissipation performance via integration of magneto/dielectric particles with hierarchical 3D morphology in bilayer absorber

In this study, X-band bilayer absorber was designed based on integration of magneto/dielectric phases particles with hierarchical 3D morphology. Pure CoFe2O4, SrFe12O19 and NiO as magnetic and dielectric components with unique 3D morphology were developed via facile chemical method. Morphological evaluations confirmed the formation of hierarchical structure of CoFe2O4 (Co), SrFe12O19 (Sr) and NiO (NiO) with crochet ball, brain-coral and rose-flower-like particles morphology, respectively. In the first step, the synthesized Co and Sr particles were physically blended with 1:1 wt ratio (SC). In a second step, the as-prepared SC composite mixed with NiO powder with 1:1 wt ratio (SCN). The reflection loss simulations of bilayer absorbers with total thickness of 2 mm were performed via CST Studio software based on the electromagnetic characteristics of as-prepared resin base SC and SCN composite monolayer absorbers. The optimized bilayer absorber in which SCN composite placed as matching layer with 1.5 mm thickness and SC composite placed as absorbing layer with 0.5 mm thickness exhibited a minimum reflection loss value of −21.43 dB at 10.8 GHz matching frequency, with 3.2 effective absorption bandwidth and a loading percentage as low as 20 w%. The aforementioned results indicated that tailoring the configuration of particle morphology along with tuning optimal layers thickness could be a rational way to reach considerable absorption bandwidth in double layer absorber. The improvement in microwave dissipation performance is linked to various parameters such as defect induced dipole polarization, multiple scatterings and reflections between particles and pores, coupling interactions between layers, promotion of interfacial polarization, etc.

Unsupervised Generative Adversarial Network for 3-D Microstructure Synthesis from 2-D Image

Three-dimensional microstructure reconstruction is indispensable for understanding the performance and reliability of SOFC electrodes. Not only the microstructure parameters, but also SOFC electrochemical characteristics such as overpotentials can be calculated when combined with numerical simulations. The most common method to analyze 3-D structures with a feature size of 0.01 – 10 μm is a focused ion beam - scanning electron microscope (FIB-SEM). However, there’s a tradeoff between reconstruction volume size and resolution. Besides, in order to obtain high quality reconstruction, accumulation of know-hows for pre and post-processing is required. Therefore, fast screening of the microstructures is not easy for FIB-SEM due to the difficulty of measurement. On the other hand, a single SEM image can be obtained very easily. An arising question is if it is possible to extract properties of microstructures and numerically synthesize 3-D model directly from a single 2-D SEM image.In recent years, machine learning techniques have become a powerful tool for image processing. Nevertheless, applications of machine learning in the field of porous materials, in particular fuel cells and batteries are still limited. The previous works concentrated on relatively simple artificial neural networks (ANN), but the class of neural networks that can effectively analyze visual images is the convolutional neural network (CNN). Gayon-Lombardo et al. (1) demonstrated a successful application of generative adversarial network (GAN) based on CNN layers to fabricate synthetic 3-D SOFC microstructures. It is indicated that the GAN-based approach can be very effective, but the algorithm requires 3-D teaching data (GAN3Dto3D).In the scope of this research, a novel method for fabrication of synthetic 3-D microstructure directly from a 2-D SEM image is proposed (Fig. 1A). The GAN2Dto3D network consists of a 3-D microstructure generator and a discriminator which operate on 2-D data. Each microstructure fabricated by the generator is treated as a set of individual cross-sectional 2-D images. The discriminator checks the validity of each 2-D slice in the generated microstructure in all spatial directions (height, width and thickness). Patches extracted from a real 2-D cross-section image are used as training data. In each training iteration, new random patches are extracted to increase the number of available training data. Additionally, the training images are augmented by random horizontal and vertical flipping. As all of the cross-section of the newly generated microstructure has to be statistically equivalent to the real 2-D cross-section, the generated 3-D microstructure is smooth in all spatial directions.The GAN2Dto3D approach is tested on the dataset of real SOFC microstructures. For the real microstructure, a set of nickel (Ni) – gadolinium doped ceria (GDC) microstructures was fabricated. All composite anode samples were prepared with NiO (AGC Seimi, Japan) and GDC (Gd0.1Ce0.9O ShinEtsu, Japan) powders mixed in a designated proportion and sintered at 1350 oC. Differences in the structure are due to the initial anode slurry composition and packing density. The solid phase fractions were controlled by GDC share in the composite in the range of 30 – 70 vol.%, and their porosity was controlled by isostatic pressing (2). 3-D microstructures were reconstructed by FIB-SEM and used as the ground truth data for the validation of GAN2Dto3D model. The results of the GAN2Dto3D algorithm applied to generate two synthetic microstructures with different GDC share and the porosity are shown in Fig. 1B and 1C. The size of the generated microstructures is 64 × 64 × 64 voxels, which is equivalent to 6.4 × 6.4 × 6.4 µm. The real microstructures reconstructed with FIB-SEM are shown for comparison. The proposed GAN algorithm produces realistic microstructures, which indicates that GAN has a great potential to enable fast evaluation of various samples without carrying out complex FIB-SEM measurements.1. Gayon-Lombardo, L. Mosser, N. P. Brandon, and S. J. Cooper, npj Comput. Mater., 6, 1–11 (2020).2. Komatsu, A. Sciazko, and N. Shikazono, J. Power Sources, 485, 229317 (2021). Figure 1

Effect of pH Value on the Synthesis of NiO Nanoparticles and Microstructure of NiO Based Composite Anode

NiO nanoparticle was synthesized by a sol-gel method with three different pH values namely pH=1, 7 and 11, and then calcined at temperature of 450 ᵒC. The influence of different pH values on the physical properties of NiO nanoparticles were investigated by a particle size analyzer (PSA), field emission scanning electron microscope (FESEM) and X-ray diffractometer (XRD). Structural analysis confirmed that a cubic structure of NiO nanoparticle was obtained without any secondary phase for NiO powders prepared with pH=1, while the peak of secondary phase (Ni) appeared for NiO powders prepared with pH= 7 and 11. Morphological observation showed that the NiO nanoparticles prepared with pH=7 and 11 tend to form more agglomerates compared to one prepared with pH=1. The average diameter of NiO nanoparticles with pH 1, 7 and 11 were approximately in the range of 19-26 nm, 21-28 nm, and 24-30 nm, respectively. NiO powder that was synthesized with pH=1 was further used to prepare composite anode of NiO Nps-BaCe0.54Zr0.36Y0.1O2.95 (BCZY) powder. Unfortunately a composite of NiO Nps-BaCeO3-BaZrO3 was obtained instead of BCZY and governed by agglomerates with size in the range of 70-300 nm.

Band Structure and Thermoelectric Properties of Ni<sub>(x)</sub>Zn<sub>(1-x)</sub>Fe<sub>2</sub>O<sub>4</sub>

Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity. The band structure and thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 have been investigated. The bulk pellets were prepared from analytical grade ZnO, NiO and Fe2O3 powder using solid-state method. It was possible to obtain high thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 by controlling the ratios of dopants and the sintering temperature. XRD analysis showed that the fabricated samples have a single phase formation of cubic spinel structure. The thermoelectric properties of Ni(x)Zn(1-x)Fe2O4 pellets improved with increasing Ni. The electrical conductivity of Ni(x)Zn(1-x)Fe2O4 pellets decreased with increasing Ni content. The electrical conductivity of Ni(x)Zn(1-x)Fe2O4 (x = 0.0) is (0.515 x10-3 Scm-1). The band structure shows that ZnxCu1-xFe2O4 is an indirect band gap material with the valence band maximum (VBM) at M and conduction band minimum (CBM) at A. The band gap of Ni(x)Zn(1-x)Fe2O4 increased with increasing Ni content. The increasing band gap correlated with the lower electrical conductivity. The thermal conductivity of Ni(x)Zn(1-x)Fe2O4 pellets decreased with increasing Ni content. The presence of Ni served to decrease thermal conductivity by 8 Wm-1K-1 over pure samples. The magnitude of the Seebeck coefficient for Ni(x)Zn(1-x)Fe2O4 pellets increased with increasing amounts of Ni. The figure of merit for Ni(x)Zn(1-x)Fe2O4 pellets and thin films was improved by increasing Ni due to its high Seebeck coefficient and low thermal conductivity.

Single layered hollow NiO–NiS catalyst with large specific surface area and highly efficient visible-light-driven carbon dioxide conversion

A sea urchin-shaped, single-layer, and hollow NiO–NiS photocatalyst with a large surface area was designed for carbon dioxide (CO2) conversion in this study. A d-glucose polymeric hollow frame was fabricated using a d-glucose monomer, and NiO particles were stably grown on it using the hydrothermal method to form a hollow NiO surface. The d-glucose frame was removed by heat treatment to create hollowed NiO; hollowed NiO–NiS (h-NiO–NiS) was subsequently obtained through ion exchange between the O ions in NiO and S ions in the sulfur powder. Additionally, we attempted to determine the correlation among the surface area of the h-NiO–NiS catalyst, CO2 gas adsorption capacity, and catalyst performance. The surface area of the h-NiO–NiS catalyst was ten times larger than that of the nanometer-sized NiO–NiS (n-NiO–NiS, 21.2 m2 g−1) catalyst. The CO2 photocatalytic conversion performance of the hollowed catalyst was approximately seven times larger than that of the nanosized catalyst. As the amount of ion-exchanged S increased, methane selectivity increased, and optimal methane production was obtained when the weight ratio of NiO and sulfur powder was 1 : 4. Using temperature-programmed desorption (TPD) analyses of CO2 and H2O, the adsorption of water molecules on the Ni–S surface and that of CO2 gas on the Ni–O surface during CO2 conversion reaction were confirmed. The h-NiO–NiS catalyst facilitated an effective charge separation through a well-developed interfacial transition between the linked NiS and NiO, and resulted in increased CO2 photoreduction performance under sunlight.

Extraction of Selenium and Tellurium from CaCl2–LiCl-Based Molten Chlorides Containing Na2Se, Na2Te, and CaO

This study was conducted considering the separation of long-lived fission products of 79Se from vitrified high-level radioactive wastes. The redox behavior of Se on various electrodes was investigated in CaCl2 melts containing Na2Se and CaO at 1093 K. Se2− ions were anodically oxidized to form selenide compounds on Cu and Ni electrodes, which were not affected by presence of O2− ions. Potentiostatic electrolysis using a Ni anode yielded liquid Ni–Se alloy and Ni was thus evaluated as a suitable anode material for extracting Se. A chemical reaction using NiO and Ni metal was investigated for the extraction of Se as an alternative to electrodeposition. In addition, anodic deposition behaviors of Te and Se on Ni in an equimolar CaCl2–LiCl melt containing Na2Se, Na2Te, CaO, BaCl2, SrCl2, CsCl, KCl, and EuCl2 were investigated. The potential difference between the Ni telluride and selenide formations was about 0.20 V, indicating that Te can be extracted prior to Se. The NiO/Ni apparatus consisting of a Ni rod immersed in NiO powder placed in a MgO crucible was used to extract Te and Se in two steps. Most of Te was first extracted. Then, the remaining Te and Se were almost completely extracted.

Microstructure and compressive properties of 3D-extrusion-printed, aluminized cobalt-based superalloy microlattices

Cobalt-based superalloy microlattices with γ/γ′ microstructure are manufactured by combining two additive methods: ink-extrusion 3D-printing and pack-cementation surface alloying. First, a microlattice green structure is 3D-printed at ambient temperature from inks comprised of Co3O4, NiO, and WO3 powders, an elastomeric binder and solvents. Organic removal followed by oxide reduction under Ar-5% H2, sintering and homogenization at 1250 °C lead to a metallic microlattice with dense struts with uniform γ (fcc)-Co–22Ni–8W (at.%) composition. Second, aluminum is deposited on the strut surfaces via pack-cementation at 1000 °C, diffused at 1300 °C through the strut volume to achieve a uniform composition (Co–20Ni–6W–10Al or Co–18Ni–5W–13Al, at.%), and precipitated during aging at 900 °C as γ′ precipitates within the γ matrix. The compressive strength, ductility and energy absorption of these γ/γ′ Co-based precipitation-strengthened microlattices is measured at ambient temperatures for two aging time (16 and 65 h) and found to be much superior to those of an unalloyed Co microlattice.

Microwave Performance, Microstructure, and Crystallization of (Mg0.6Zn0.4)1−yNiyTiO3 Ilmenite Ceramics

The sintering behavior, microstructure analysis, crystallization, and microwave performance of (Mg0.6Zn0.4)1−yNiyTiO3 (y = 0.01–0.2) ceramics, processed with raw powders of MgO, NiO, ZnO, and TiO2 via the conventional solid-state method, are investigated. The main phases of (Mg0.6Zn0.4)1−yNiyTiO3 ceramics were obtained. With partial replacement by Ni2+, the (Mg0.6Zn0.4)0.95Ni0.05TiO3 could be well sintered at 1200 °C, and the microwave performance was shown to be positively correlated with sintering temperature. The permittivity (εr) saturated at 18.7–19.3, and the quality factor (Qf) values approached 72,000–165,000 (GHz) as the sintering temperatures increase from 1125 to 1250 °C. The temperature coefficient of resonance frequency (τf) falls in a stable range of −62.9 to −66 ppm/°C as sintering temperature rising. A permittivity (εr) of 19.3, a maximum Qf value of 165,000 (GHz), and a temperature coefficient (τf) of −65.4 ppm/°C were measured for the samples at 1200 °C/4 h. (Mg0.6Zn0.4)0.95Ni0.05TiO3 material system shows high potential for applications of high frequency-selection components in satellite communication and 5G wireless telecommunication systems.

The effect of nickel doped Bismuth Vanadium Oxide on microstructures and electric properties towards BiVO4-NiO composite

The preparation of BiVO4-NiO of microstructures and electric properties has been done using water solution and coated with indium tin oxide (ITO). BiVO4-NiO material was prepared using BiVO4, NiO powders and ITO. Mixing and coating processes were held using water and the resulting paste was coated by screen printing using a small glass stick on an ITO. The heat temperature process was done at 260 °C for 2 h. Samples were characterized using XRD, SEM-EDS and FTIR. The effect of ion Nickel addition did not change the monoclinic structure of bismuth vanadium. The Ni ions have been substituted Bi ion in the bismuth vanadium system which is indicated by the change of lattice parameters and compositions. Then, the additions decrease peak intensity increases due to the bigger microstructures observed. The addition Ni does not affect BiVO4 but decreased the peak band BiVO4 as increases Ni. The linear voltammograms observed an increase BiVO4 with increases Ni because the enhancement of current could improve the oxygen kinetics properties and surface passivation of the electrode in BiVO4-NiO. Therefore, the addition of NiO is reflected in an increase in electrical conductivity.

Room temperature ferromagnetism in Zn-doped NiO nanoparticles: An experimental and DFT+U approach

Abstract We report the room temperature ferromagnetism in Zn-doped NiO nanoparticles of Ni1−x ZnxO (x = 0.00, 0.01, 0.03, 0.05 and 0.1) prepared by the sol-gel method. Zn dopant has significant influence on structural, optical, and magnetic properties of NiO crystal when there is a size reduction and lattice distortions. The crystalline nature of the samples were characterized by the room temperature X-ray Diffraction and we found that the range of crystallite size is about 7 ± 0.01 to 9 ± 0.01 nm for 3–10% of Zn doping concentration. The lattice parameter and the effective strain increases with the increase of doping concentration. Local structure and defects are probed through Raman characterization which reveals that there are no secondary or impurity peaks on the Zn-doped NiO samples. Photoluminescence spectra at room temperature shows two major emission peaks at wavelength 357 nm and 393 nm for both pure and Zn-doped NiO powder respectively. There also exists a blue shift for wavelength 357 nm emission band with the increase of Zn doping concentration. The band gap energy calculated from the PL spectra is ≈3.46 eV for pure NiO and it increases with the doping upto 3% then it decreases with further doping. To understand the effect of doping on magnetic properties, we measured the temperature dependent M-H loops and M-T curve for zero field cooled (ZFC) and field cooled (FC) condition in the temperature range 25–350 K using Vibrating Sample Magnetometer. We observed that the Ni1−x ZnxO nanoparticles are ferromagnetic in nature at room temperature with highest magnetic moment of ≈1.9 emu/g when the doping of Zn is 3% and it decreases with further increase of doping concentration. M-T data bifurcation peak was observed around 300 K and a broad peak in ZFC curve below the bifurcation. This broad peak is attributed to the thermal relaxation of uncompensated spins. We have also investigated the first-principle DFT+U calculation to study the electronic properties of the materials. The results show that the Zn-doped NiO with oxygen vacancies are ferromagnetic in nature whereas without defects the compound is non-magnetic, which agrees quite well with the experimental results. The nanoparticle with ferro-magnetic properties have potential application in the field of nanomagnetism and also its optical properties could be useful for optical device applications.

The Mechanical Alloying Behavior of Fe2O3 into NiO in the High‐Energy Ball‐Milling Process

The NiO and Fe2O3 powders were mixed by the high‐energy ball‐milling, followed by a sintering of the mixture at 1340°C for 0.5 h. XRD, SEM, DSC, and size measurements were preformed to study the microstructure evolution in the high‐energy ball‐milled mixture and the sintered ones, as well. It showed that the high‐energy ball‐milling processes resulted in a severe lattice distortion in the powder of Fe2O3, but only a slight lattice distortion in NiO. Meanwhile, a solid solution of iron atoms into the NiO lattice was also detected in the milling process. It was also found that the solubility of the iron atoms into the NiO lattice delayed the synthesizing reaction in the following sintering process.

KINETICS OF SYNTHESIZING PROCESS OF MICRON NICKEL POWDER BY HYDROGEN REDUCTION FROM OXIDE COMPOUND UNDER NON-ISOTHERMAL CONDITIONS

In this work the kinetics of the process of obtaining micron nickel powder by hydrogen reduction of the oxide compound under non-isothermal conditions were studied. The hydrogen reduction process of micron NiO powder with hydrogen under non-isothermal conditions was carried out in the linear heating mode at a rate of 10°C/ min in the temperature range of 20-450°C. The study of crystal structure and composition of the powder samples was performed by XRD phase analysis. The specific surface area S of the powders was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powder samples was determined via the measured S value. The size and shape of the particles were investigated by scanning electron microscopic method. The calculation of kinetic parameters of the reduction process of nickel oxide in nonisothermal conditions was carried out by the differential-difference method using the data of thermogravimetric analysis and the equation for non-isothermal kinetics. It was revealed that the hydrogen reduction process of micron NiO powder in non-isothermia occurs in the temperature range of 270-335°C with a maximum specific rate of 9.667·10-8 kg/s recorded at 316°C. The dependence of the degree of conversion during reduction process was determined by mathematical statistics method and can be well described by the expression y=0.0001e0.0168·x with the coefficient of determination R2=0.9739. The activation energy of hydrogen reduction processes of the micron NiO powder under non-isothermal conditions was found to be ~43 kJ/mol, which indicates a mixed reaction mode. In this mode, a rational way to accelerate the process is both increasing the temperature and eliminating the diffusion layer of the reduction product by intensive mixing. It is shown that an increase in temperature to 316ºС can effectively increase the rate of the overall process of hydrogen reduction of micron NiO powder while guaranteeing the quality of the reduction product. The obtained micron Ni particles are highly porous material, while the Ni particles are collected in large porous aggregates up to 10 μm in size.

Synthesis and Characterization of (Co,Ni)O Solid Solutions As Protective Coatings for Inert Anodes in Aluminum Electrolysis

The industrial production of primary aluminum from alumina ore (Al2O3) is still carried out by the Hall-Héroult process. The process relies on dissolving alumina in an electrolyte consisting mainly of liquid Na3AlF6 at 950-1000 °C. While the reduction of dissolved Al3+ ions in aluminum occurs at the cathode, the complementary reaction occurs at a carbon anode that is consumed to form carbon dioxide, which necessitates its regular replacement (every 25 days). The overall reaction is the following:Canadian aluminum smelters produce annually about 6 Mt of CO2 eq(reported in 2017), which is equivalent to the CO2 amount generated annually by about 2 million cars.The substitution of consumable carbon anodes with inert (O2-evolving) anodes in the electrochemical cells to produce aluminium would have significant environmental benefits because it would eliminate the emissions of carbon dioxide and perfluorocarbons associated with the consumption of the carbon anode. However, the design of inert anodes is a major challenge because of the severe Al electrolysis conditions (cryolithic medium at 960 °C), which requires materials with excellent resistance to corrosion and thermal shock as well as adequate electrochemical properties [1].Single phase Cu65Ni20Fe15 alloy is a promising inert anode for Al production due to its ability to form a protective NiFe2O4 layer upon Al electrolysis. However, its corrosion resistance is still insufficient and a protective layer is required to prevent the penetration of electrolyte into the nickel ferrite layer and the formation of fluorides during Al electrolysis [2-4].In this context, the use of (Co,Ni)O-based protective coatings for metallic anode appears promising [5]. However, it is challenging to prepare a single phase, coherent and crack-free oxide layer as required for industrial Al production. A potentially relevant method to produce (Co,Ni)O coated inert anodes is by direct deposition of (Co,Ni)O oxide compounds by spray deposition techniques such as suspension plasma spray (SPS) and high velocity oxygen fuel (HVOF). These additive manufacturing deposition are well-established technologies for producing protective oxide coatings for various industrial applications (e.g. gas turbines).As a first step toward this goal, pure CoxNi1−xO solid solutions have been prepared over the whole composition range by a two-step procedure that consisted of high-energy ball milling followed by a heat treatment of Co3O4 and NiO powders [6]. Then, the thermal stability and electrical conductivity of (Co,Ni)O solid solutions were determined at temperatures ranging between 700 and 1000 °C. Also, their dissolution rate was measured in K-based cryolite at 700 °C and in Na-based cryolite at 1000 °C.In a second step, (Co,Ni)O powders have been used as raw materials for the thermal spraying (HVOF and SPS) of protective coatings onto Cu-Ni-Fe inert anodes [7]. The morphological and microstructural characteristics of the coating depending on the thermal spray conditions will be presented. The oxidation behaviour of the coated inert anodes under air and argon is presented. Preliminary investigation of the electrochemical behaviour under Al electrolysis conditions of the (Co,Ni)O/Cu-Ni-Fe anodes will be also presented and discussed.

Study of the Redox Behavior of SOFC’s Anode Functional Layers

The cermet Ni-YSZ is the most common fuel electrode used for solid oxide fuel cells[i]. Under polarization, the Nickel phase remains metallic because of the reducing atmosphere. However, troubleshooting like system emergency shutdown may cause the Ni phase to be completely/partially oxidized, resulting in a large bulk volume change (volume expansion >65%)[ii]. Microstructure failures can then occur in the Ni-YSZ matrix. Redox cycles of the Nickel could also degrade the microstructure of the Ni-YSZ anode (for instance, coarsening of the Ni phase yielding loss of Ni percolation), and thus the performance of the cell[iii]. All these phenomena lead to an increase of the polarization resistance of the anode.The target of the OxiGEN project is to develop the next-generation all ceramic Solid Oxide Fuel Cell stack and hot box solution for small stationary applications[iv]. One of the objectives of the project is the improvement of the redox tolerance of the anode functional layer, in order to prevent nickel coarsening. A large experimental matrix with various combinations of parameters (NiO / YSZ ratio, porosity and electrolyte particle size) was established to investigate innovative anode functional layers with better redox resistance and improved electrochemical performance compared to a reference anode prepared with the same NiO powder and a proprietary YSZ based composition. Thin ceramic-polymer tapes (<100µm) have been manufactured by a tape-casting process developed by EIfER following the industrial requirements provided by Saint-Gobain. The microstructural characterization performed after sintering show homogeneous anode functional layers with a thickness below 30 µm and a good repartition between the ceramic phases and the porosity for all samples prepared in this study (see Figure 1). The influence of the modification of the microstructure resulting from the variation of the electrolyte particle size properties was investigated by SINTEF on the electrical properties of the reduced anodes using Van der Paw method. An increase of the total electrical conductivity from 100 to 900 S.cm-1 was observed between the reference and innovative layers, respectively.Specific redox cycle protocols were defined to observe the modification of the microstructure of single layers and complete cells after redox cycles simulating specific emergency shutdown (see figure 2). They are composed of two main steps. The first one corresponds to an oxidation phase where the temperature is decreased while the supply of hydrogen is stopped (controlled emergency shutdown). An air leakage was also simulated by introducing a small quantity of air into the fuel chamber. The second phase represents the restart of the system with an increase of the temperature and the reintroduction of hydrogen to the fuel side. The intermediate stage was also optimized in order to emphasize the effect of the oxidation phase on the fuel electrode. The influence of the integration of advanced layers on the microstructure and redox behavior of layers and complete cells will be discussed. “This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 779537 . This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme and Hydrogen Europe and Hydrogen Europe Research”. [i] S.P.S. Shaikh, A. Muchtar, M.R. Somalu, Ren. Sus. Energy Reviews 51 (2015) 1-8. [ii] S. Toros, Ceram. Int. 42 (2016) 8915-8924. [iii] T. Shimura, Z. Jiao, S. Hara, N. Shikazono, J. Power Sources 267 (2014) 58-68. [iv] http://oxigen-fch-project.eu/ Figure 1

Relationship between reaction and diffusion during ultrafine NiO reduction toward agglomeration fluidization

AbstractThe relationship between reaction and diffusion during ultrafine NiO reduction by H2 in a fluidized bed reactor were investigated. The result illuminates that the reduction reaction proceeding in the unreduced NiO powders is according to the nucleation model. A modified force balance model between cohesive and collision forces incorporating grain‐boundary diffusion and reaction is proposed to predict the agglomeration behavior of ultrafine Ni during the reduction of NiO in a fluidized bed. The modified force balance model shows more precise predictions than the model without consideration of grain‐boundary diffusion. Based on the model, it is found that the core of the two‐step reduction is to decouple grain growth from reduction for achieving full conversion while retaining nanosized grain sizes.

Endodontide Kullanılan Nikel-Titanyum Atık Eğelerin Sülfürik Asit Liçi İşlemleri ile Geri Kazanımı

Nickel - titanium based alloys are widely used as a root canal files in dental canal treatment in endodontics. According to the Turkish Ministry of Health, approximately, two million root canal treatments were applied yearly in Turkey. Ni-Ti rotary files have been used for 80 % of these endodontic root canal treatments. Rotary files contain 55-60 wt.% nickel and 40-45 wt.% titanium. Ni-Ti endodontic files can be recovered by hydrometallurgy, which is an economical way, instead of treating them as medical waste. The aim of this study is to provide economical hydrometallurgical recycling of metallic wastes that cannot be recovered by direct melting. Nickel and titanium based endodontic rotary files were recovered via using different leaching techniques in high corrosive environments such as dissolution in concentrated acid, baking in sulfuric acid and hydrothermal treatment in concentrated sulfuric acid. The acid concentration, temperature and time parameters were optimized for concentrated sulfuric acid leaching in autoclave. The acid baking method is a simple system more efficient than the pure dissolution in acid. At the end of the hydroxide structures dehydration, TiO2 (anatase) and NiO powders were obtained. Moreover, under pressure within non-stirring autoclave the rotary file is completely dissolved with a cost-effective two-step process. Thus, an efficient recycling process has been created for waste Ni-Ti alloy tooth files.

Ag3PO4/NiO Composites with Enhanced Photocatalytic Activity under Visible Light.

Black NiO powders were prepared by a hydrothermal method. Moreover, the visible light-driven Ag3PO4/NiO photocatalyst composites were successfully synthesized by in situ precipitation method. These samples were structurally characterized by X-ray diffraction and Rietveld refinement. The strong interaction between the phases and the defects in the samples was affected by the formation of the composites, as identified by Fourier transform infrared spectroscopy and Raman spectroscopy. UV–vis diffuse reflectance spectroscopy exhibited enhanced light absorption for all Ag3PO4/NiO composites, suggesting the effective interaction between the phases. Moreover, field-emission scanning electron microscopy images revealed the presence of NiO microflowers composed of nanoflakes in contact with Ag3PO4 microparticles. The composite with 5% NiO presented enhanced photocatalytic efficiency in comparison with pure Ag3PO4, degrading 96% of rhodamine B (RhB) dye in just 15 min under visible light; however, the recycling experiments confirmed that the composite with 75% NiO showed superior stability. The recombination of the electron–hole pairs was considered for the measurement of the photoluminescence of the samples. These measurements were performed to evaluate the possible causes for the difference in the photocatalytic responses of the composites. From these experimental results, possible photocatalytic mechanisms for RhB degradation over Ag3PO4/NiO composites under visible-light irradiation were proposed.