Redox stability of SOFC: Thermal analysis of Ni–YSZ composites

A re-oxidation of a Ni-based SOFC can seriously damage the cells. Important aspects of this thermomechanical instability are reduction–oxidation kinetics and the dimensional behaviour of the Ni–YSZ composites. These were investigated in the temperature range of 600–1000 °C and different combinations of reduction and oxidation temperatures. Automated temperature and gas change programmes were implemented in thermogravimetry and identically repeated using a high precision dilatometer to show the dimensional behaviour of the cermets simultaneously with the Degree of Oxidation (DoO) as a function of time during redox cycling. The activation energy for reduction was 84.4 kJ/mol and the kinetics was largely linear. Different kinetic models were fitted to the reduction data; the best agreement was found using the Avrami equation. On the re-oxidation, initially linear kinetics was observed, followed by a period of parabolic kinetics slowing down to logarithmic towards full DoO. The shifts in the kinetic shape with time depended on the temperature and DoO. The rate constants for oxidation were fitted to the data. The BET surface area of the cermets after different reduction and oxidation treatments was measured and show decrease of surface area with increasing reduction temperature and no significant differences in the surface area depending on the re-oxidation temperature in the range of 600–1000 °C.     

Tensile behavior of post-irradiation annealed Cu–Ni alloy

The present paper investigates the tensile properties of post-irradiation annealed Cu–Ni alloy. The specimens were irradiated with a 15 MeV electron beam at room temperature and the post-irradiation annealing (PIA) of the specimens was carried out under vacuum at 450 °C for 15–120 min. The yield stress (YS), ultimate tensile stress (UTS), percentage elongation, stress relaxation rate and activation volume of both as-irradiated and post-irradiation annealed specimens were examined at room temperature using a universal testing machine. The results show that PIA of the specimen at 450 °C for 15 min decreases its YS and UTS, whereas the percentage elongation is increased. The changes in the tensile parameters become more pronounced with increases in annealing time. Effects of PIA on the stress relaxation rate and activation volume indicate that the relaxation rate of post-irradiation annealed specimens increases, and the activation volume decreases, with an increase in annealing time.     

Anomalous behavior of curves of pseudo-elastic deformation of Ni–Fe–Ga–Co alloy crystals as a result of interphase stresses

The compression diagram of Ni₄₉Fe₁₈Ga₂₇Co₆ alloy crystals in the [011] direction was studied until full shape memory strain at various temperatures in the range of 259–340 K. It is found that all load curves are anomalously shaped and contain portions of sharp and gradual decreases in deformation stresses. Simulation of pseudo-elastic stress–strain curves within the theory of diffuse martensitic transitions, describing not only equilibrium of phases, but also the kinetics of the transition between them, shows that elastic interphase stresses during martensitic reactions Ll ₂ → 14M and 14M → Ll ₀ characteristic of this alloy can be responsible for the extraordinary shape of compression diagrams.     

Abnormal resistivity behavior of Cu–Ni and Cu–Co alloys in undercooled liquid state

The resistivity behavior of undercooled liquid Cu–Ni and Cu–Co alloys had been studied in the contactless method, to probe the structure transition in undercooled melts during the cooling process. Over the entire concentration range, linear behavior of resistivity with temperature was obtained in liquid and undercooled liquid Cu–Ni system. It implied that the formation of icosahedral order might not influence the electron scattering in undercooled liquid Cu–Ni alloys. Similar results were obtained in Cu–Co system in the vicinity of liquidus temperature. A turning point was obvious in temperature coefficient of resistivity for undercooled liquid Cu–Co alloys around the bimodal line, which was interpreted to be responsible for metastable liquid–liquid phase separation. During liquid phase separation process, resistivity decreased and the temperature coefficient of resistivity was larger than that of homogeneous melts. In combination with transmission electron microscopy and scanning electron microscope studies on the as-solidified microstructure, this was interpreted as the formation of egg-type structure and concentration change in Cu-rich and Co-rich phases. The mechanism controlling the separation and droplets motion was also discussed in undercooled liquid Cu–Co system.     

Strain behavior of Fe—Ni—C martensite

This article examines the effect of carbon on the structure of slip traces and characteristics of the deformation resistance of quenched iron-nickel-carbon alloys deformed at 77°K. It is established that an increase in the carbon concentration in the martensite within the range 0.03–0.30 wt. % is accompanied by the formation of channels of easy slip during low-temperature deformation, which explains the simultaneously observed increase in the plastic strain of the alloys. Localization of slip in these channels leads to a reduction in the nonconservative component of resistance to deformation.Translated from Izvestiya Vysshikh Uchehnykh Zavedenii, Fizika, No. 6, pp, 33–38, June, 1985.     

Electrochemical corrosion behavior,Vickers microhardness,and microstructure of Co–Cr and Ni–Cr dental alloys

Electrochemical corrosion behaviors, Vickers microhardness, microstructure, and electrical properties of Magnum H50 (Co=64.5%, Cr=29%, Mo=6.5% ) and Nikkeli–Kromi–Polttosekoitus (Ni=65.2%, Cr=22.5%, Mo=9.5%, X=2.8% Nb, Si, Fe, and Mn) dental alloys have been investigated. The corrosion potential for the Co_64.5Cr₂₉Mo_6.5 alloy in HCl was higher than that of the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy. The corrosion rate with 0.5 M HCl for the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy was measured as being high and the corrosion resistance as being small as compared with the values for the Co_64.5Cr₂₉Mo_6.5 alloy. Vickers hardness of the Co_64.5Cr₂₉Mo_6.5 alloy was higher than that of the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy. Also Vickers hardness values of the used alloys were decreased by increasing indentation load. The thermal conductivity and minimum shear stress values of the used alloys are calculated.     

Microstructural studies on degradation of interface between LSM–YSZ cathode and YSZ electrolyte in SOFCs

The changes in the cathode/electrolyte interface microstructure have been studied on anode-supported technological solid oxide fuel cells (SOFCs) that were subjected to long-term (1500 h) testing at 750 °C under high electrical loading (a current density of 0.75 A/cm²). These cells exhibit different cathode degradation rates depending on, among others, the composition of the cathode gas, being significantly smaller in oxygen than in air. FE-SEM and high resolution analytical TEM were applied for characterization of the interface on a submicron- and nano-scale. The interface degradation has been identified as the loss of LSM coverage and the loss of three-phase-boundary (TPB) length. Firstly, the degradation is caused by the size reduction of the individual LSM/YSZ electrolyte contact points (areas) that are initially of 100–200 nm in diameter. Quantitative microstructure evaluation shows that in the cell tested in air this mechanism contributes to an estimated overall reduction in the LSM coverage and the TPB length by 50 and 30%, respectively. For the cell tested in oxygen the corresponding values are 10 and 4%. Secondly, in the cell tested in air the LSM coverage and the TPB length appear to decrease further due to the more pronounced formation of insulating zirconate phases that are present locally and preferably in LSM/YSZ electrolyte contact areas. The effects of the cathode gas on the interface degradation are discussed considering the change of oxygen activity at the interface, possible changes in the Mn diffusion pattern as well as the LSM/YSZ reactivity. Finally, based on thermodynamic calculations a T–p(O₂) diagram predicting the safe and risky operation conditions in terms of the zirconate formation is presented and compared with the experimental observations.     

Influence of gamma radiation on morphology structure,electrochemical corrosion behavior and hardness of Ni–Cr based alloys

This study evaluates the effects of gamma radiation on structure, electrochemical corrosion behavior and Vickers hardness of commercial dental Nikkeli–Kromi–Polttosekoitus [Ni_65.2Cr_22.5Mo_9.5X_2.8 (X=Nb, Si, Fe and Mn)] alloy. The corrosion rate of Ni_65.2Cr_22.5Mo_9.5X_2.8 (X=Nb, Si, Fe and Mn) alloy with 0.5 M HCl is increased with increasing the exposure rate of gamma radiation. The corrosion resistance of Ni_65.2Cr_22.5Mo_9.5X_2.8 (X=Nb, Si, Fe and Mn) is varied and reaches a minimum value at 30 KGy. The corrosion potential value also is varied and reaches its highest value at 30 KGy. The Vickers hardness value of Ni_65.2Cr_22.5Mo_9.5X_2.8 (X=Nb, Si, Fe and Mn) alloy is decreased by increasing the gamma radiation dose. Also it is obvious from our results that the effects of gamma radiation at the surface are much higher as compared with deeper parts and the structure of the alloy is changed due to its exposure to gamma radiation.     

Towards a Deeper Understanding of the Einstein–Podolsky–Rosen Problem

Most of the nearly innumerable attempts to provide for a sound understanding of the gedanken experiment of Einstein, Podolsky, and Rosen (EPR) contain additional ideas, notions or features imposed on pioneer or traditional quantum mechanics (TQM). In the present paper the problem is analyzed without employing any new or philosophically contested concept. We do even without referring to the probability calculus, and we especially avoid any admixture of realistic ideas. Neither entanglement nor special features of states are used. Instead, formulating strictly within the framework of TQM and using an ensemble approach, the crucial point is boiled down to the decision between separability and non-separability. The corresponding second-order correlation functions _s and _n–s, resp., which predict the experimental outcome, may differ by a factor of 2 if certain operator pairs are maximally non-commuting. Even in the case of commuting pairs, an experimentally relevant difference between the -functions might exist. Taking into account the experimental evidence, it is unavoidable to accept that the sub-ensembles involved in EPR-type experiments are in fact non-separable. This result has been obtained without resort to Bell's inequality.     

Resistive switching behavior in a Ni–Ag<Subscript>2</Subscript>Se–Ni nanowire

Hysteretic resistive switching behavior in a silver selenide (Ag₂Se) nanowire, which had a diameter of about 200 nm and a length of about 10 μm, was studied using scanning probe microscopy. Electrical current measurements were carried out in a range from 0 to −10 V and in temperatures below and above the phase transition of Ag₂Se. ON/OFF switching times were measured with pulsed voltages. They displayed different characteristics at low and high temperatures. The results confirm that Ag₂Se nanowires have applications in nanoscale switching devices.     

Dielectric behavior of BaTiO<Subscript>3</Subscript>–Ni composite ferroic films

Composite ferroic BaTiO₃–Ni films with different Ni content were fabricated by radio frequency (RF) cosputtering method. Complex impedance analysis indicates that the addition of Ni has greatly reduced the resistivity of the Ni-enriched boundaries. All the composite films exhibit room temperature ferromagnetism, while the ferroelectricity of the films is degrading with increasing Ni content. Dielectric measurements reveal that below the Ni content of 22.7 at.%, the dielectric response follows the general percolation theory and the increase of dielectric constant and loss tangent with Ni addition is mainly associated with the microstructure induced nanocapacitor effect and Maxwell–Wagner interface polarization which also induces significant dielectric anomaly at low frequency range.     

Characterization of Ni–Cu mixed spinel ferrite

Crystal structure, X-ray density, porosity, compressive strength of Ni_1−xCu_xFe₂O₄ have been investigated along with scanning electron microscopy (SEM) to study the effect of composition and microstructure on the magnetic and electrical properties. The formation of single-phase ferrite is confirmed by the X-ray diffraction. Tetragonal deformation is observed for the sample of composition x=1, i.e. for pure CuFe₂O₄ Crystal structure for samples of other compositions are face centered cubic (FCC). SEM micrographs exhibit increase in grain size with the increase of copper content. Compressive strength decreases with the increase of Cu. Initial magnetic permeability and saturation magnetization is maximum for the composition of x=0.2, i.e. for Ni_0.8Cu_0.2Fe₂O₄, which can be attributed to the maximum sintered density obtained for this composition. Resistivity decreases with the increase of Cu content.     

High-temperature abnormal behavior of resistivities for Bi–In melts

The patterns of electrical resistivities versus temperature in large temperature range have been studied, using the D.C. four-probe method, for liquid Bi–In alloys (Bi–In(33 wt%), Bi–In(38 wt%), Bi–In(50.5 wt%), Bi–In(66 wt%)). The clear turning point of each resistivity–temperature curves of the liquid Bi–In alloys is observed at the temperature much above the melting point, in which temperature range the resistivity–temperature coefficient increases rapidly. Except for the turning temperature range, the resistivities of Bi–In alloys increase linearly with temperature. Because resistivity is sensitive to the structure, this experiment shows the structural transition in Bi–In melts at the temperature much higher than the liquidus. And it is suggested that there are different Bi–In short-range orderings in different Bi–In melts, so the resistivity–temperature curves have the turns at different temperatures and the resistivity–temperature coefficients are also different.     

Synthesis and performance of Zn–Ni–P thin films

The electroplating of Zn–Ni–P thin film alloys from a sulfate bath containing phosphoric and phosphorous acid was investigated. The bath composition and the deposition parameters were optimized through Hull cell experiments, and the optimum experimental conditions were determined(p H = 2, temperature = 298–313 K, zinc sulfate concentration =30 g·L-1, EDTA concentration = 15 g·L-1, and current density = 1.0–2.0 A·dm-2). The SEM analysis of the coating deposited from the optimum bath revealed fine-grained deposits of the alloy in the presence of EDTA. Optical microscopy analysis indicated an electrodeposited thin film with uniform thickness and good adhesion to the steel substrate. The good adherence of the coatings was also demonstrated by the scratch tests that were performed, with a maximum determined value of 25 N for the critical load. Corrosion resistance tests revealed good protection of the steel substrate by the obtained Zn–Ni–P coatings, with values up to 85.89% for samples with Ni contents higher than 76%. The surface analysis of the thin film samples before and after corrosion was performed by X-ray photoelectron spectroscopy(XPS).     

Electronic structure of bimetallic Ni–Rh nanowires

The electronic structure of a bare Rh(553) surface and of a Ni-decorated Rh(553) surface has been investigated by angle-resolved UV photoelectron spectroscopy and density functional theory calculations. The self-assembly of Ni adatoms leads to the decoration of the steps of the Rh(553) surface with monoatomic Ni rows under suitable kinetic conditions, thus forming a regular array of pseudomorphic bimetallic Ni–Rh nanowires. The electronic structure of the clean Rh(553) surface has been compared to the one of the flat Rh(111) surface, and additional surface states localized at the step edges due to the lower coordination of the step atoms have been detected. The Ni wires are weakly hybridized with the Rh substrate states and are characterized by only weakly dispersing states. This leads to a strong narrowing of the d-band, which is argued to be the origin of the observed high chemical reactivity of the Ni–Rh nanowires.     

Microwave behavior of ferrites prepared via sol–gel method

Ni-ferrites were prepared at different temperatures via sol–gel method. The electromagnetic properties of these materials, namely permittivity and permeability were measured in the 0.1–13 GHz frequency range. Following a mathematical procedure, microwave absorption diagrams were constructed including the dependence of the microwave absorption of ferrite layer on microwave frequency and layer thickness. The permeability spectra broaden and the microwave absorption improves at 9–10 GHz with increase of annealing temperature.     

Modeling of Radiation-Induced Segregation in Fe–Cr–Ni Alloys

Physics of the Solid State - In the model of radiation-induced segregation based on the first and second Fick laws and taking into account the inverse Kirkendall effect, concentration profiles of...     

Macroscopic inhomogeneous deformation behavior arising in single crystal Ni–Mn–Ga foils under tensile loading

This study investigated macroscopic inhomogeneous deformation occurring in single-crystal Ni–Mn–Ga foils under uniaxial tensile loading. Two types of single-crystal Ni–Mn–Ga foil samples were examined as-received and after thermo-mechanical training. Local strain and the strain field were measured under tensile loading using laser speckle and digital image correlation. The as-received sample showed a strongly inhomogeneous strain field with intermittence under progressive deformation, but the trained sample result showed strain field homogeneity throughout the specimen surface. The as-received sample is a mainly polycrystalline-like state composed of the domain structure. The sample contains many domain boundaries and large domain structures in the body. Its structure would cause large local strain band nucleation with intermittence. However, the trained one is an ideal single-crystalline state with a transformation preferential orientation of variants after almost all domain boundary and large domain structures vanish during thermo-mechanical training. As a result, macroscopic homogeneous deformation occurs on the trained sample surface during deformation.