Ni Diffusion Research Articles

Outstanding Oxygen Reduction Reaction Catalytic Performance of In–PtNi Octahedral Nanoparticles Designed via Computational Dopant Screening

PtNi octahedral nanoparticles are considered as one of the best-performing catalysts for the oxygen reduction reaction (ORR). However, Ni dissolution deteriorates their catalytic activity and stability during the ORR. Here, we report a strategy that improves the ORR activity and stability of the PtNi octahedral nanoparticle catalyst through the incorporation of a novel dopant. Computational screening with seven different elements (Bi, In, Ru, Sn, Te, Zn, and Zr) suggests In as the most promising candidate based on the metal doping energy and the OH* adsorption energy. Consideration of the OH* coverage and Ni diffusion energy demonstrates the superior ORR activity and stability of the In-doped PtNi(111) structure. The calculation results were validated by synthesizing In-doped PtNi octahedral nanoparticles on a carbon support (In–PtNi/C). In–PtNi/C demonstrated excellent ORR performance outcomes (1.36 A mgPt–1 and 2.64 mA cm–2@0.9 VRHE), which were 2.1 and 7.9 times higher in terms of the mass activity and 2.4 and 13.4 times higher in terms of the specific activity compared to PtNi/C and Pt/C, respectively. After 12k potential cycles, In–PtNi/C showed excellent stability with high Ni retention; 2.4 and 43% of Ni were lost from In–PtNi/C and PtNi/C, respectively. Computational and experimental investigation demonstrates that surface-doped In creates a new active site toward the ORR and blocks Ni diffusion to the surface by making Pt less oxophilic.

Proximity-induced magnetism and the enhancement of damping in ferromagnetic/heavy metal systems

The relationship between proximity-induced magnetism (PIM) at the heavy metal/ferromagnet interface and spin-transport across such interfaces has generated significant debate. To investigate the link between the two, element specific x-ray magnetic circular dichroism and ferromagnetic resonance measurements were made on the same CoFe/Au/Pt and NiFe/Au/Pt thin film samples with varying Au thickness, with complementary SIMS analysis, which shows evidence of Ni diffusion from NiFe into the Pt. An approximately linear relationship is observed between the magnitude of Pt PIM and magnitude of damping enhancement in both systems. The results demonstrate that electronic hybridization of the heavy metal and ferromagnet is required for a full understanding of damping enhancement and interfacial spin-transport for spintronic devices.

Development of corrosion-resistant Ni–Mo coatings from low-concentration bath: effect of magnetoconvection

The phenomenon of magnetoconvection has been used effectively to improve the corrosion protection efficacy of Ni–Mo coatings from a low-concentration bath. Experimental studies demonstrated that magnetoelectrodeposited (MED) coatings developed under parallel (||) and perpendicular (⊥) magnetic field (B) are, respectively, about 4 and 7 times more corrosion resistant than electrodeposited (ED) alloy coatings, developed from the same bath. Properties of MED alloy coatings have been analysed by FESEM-EDS and XRD studies. An attempt has been made to understand changed properties of MED⊥(Ni–Mo) coatings considering B controlled diffusion of Ni2+ ions, and magnetic field-controlled limiting current density (i L) of metal ions in the bath. Ni–Mo coating of high corrosion resistance were developed from a low-concentration bath by proper manipulation of i L using induced B.

Uncovering the Structure and Stability of Thermoelectric La3–xTe4–Ni Composites Using High-Resolution and In Situ TEM

Lanthanum telluride (La3–xTe4) is a high-performance, next-generation thermoelectric material with a thermoelectric dimensionless figure of merit (zT) of 1.1 at 1273 K (x = 0.23) and has potential applications in radioisotope thermoelectric generators (RTGs) to power the space missions conducted by National Aeronautics and Space Administration (NASA). It has been shown that the zT can be increased by 30% when nickel (Ni) nanoparticle inclusions are introduced to the La3–xTe4 matrix. The coherent interfaces between La3–xTe4 and Ni are likely a key factor determining the stability and performance of the La3–xTe4–Ni composites, but their role and nature are not well understood. It is important to determine the stability of the La3–xTe4/Ni interface in deep-space conditions, in addition to the effect of heat and oxygen on the mechanisms and kinetics of interface degradation. Here, we show the high-resolution structural characterization and the epitaxial crystallographic relationship of La3–xTe4–Ni thermoelectric composites and their interfaces at high-vacuum and ambient-temperature conditions using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). We further demonstrate the La3–xTe4/Ni interface degradation and Ni diffusion over its operating temperature range (25–1000 °C), in the presence and absence of oxygen, in real time, using in situ TEM.

Ni diffusion in ceria lattice: A combined experimental and theoretical study

Cation diffusion in ceria is of significant importance in many fundamental processes, but the mechanism by which 3d-transition metals migrate in ceria has not yet been elucidated. Here, we select Ni as a representative transition metal and combine experimental and theoretical analyses to determine where Ni is located in ceria and how it migrates. Bulk Ce0.995Sm0.005O1.9975-δ pellets are prepared with a sputtered NiO source on top, and the diffusion coefficient of the Ni impurity is measured at temperatures from 1250 to 1350 °C by analyzing the depth profiles of Ni via time-of-flight secondary ion mass spectrometry. In addition, corresponding activation enthalpy values for Ni diffusion when Ni is present in substitutional and interstitial sites are calculated by density functional theory and compared with the measured values. We reveal that the diffusion of Ni impurity mainly occurs via the interstitial mechanism in ceria and propose an atomic-scale interpretation of Ni migration.

Post-Operational Characterization of a Long-Term Operated Solid Oxide Fuel Cell Stack

A two layer solid oxide cell stack based on anode-supported cells was operated galvanostatically at 0.5 A / cm² and 700°C for nearly 100,000 h in fuel cell mode. The overall degradation rate during the operation was approx. 0.5 %1000 h but the stack shows different degradation rates over different time periods. In contrast to our typical stack material choice this stack was mainly assembled with another type of metal: ITM from Plansee SE, Austria instead of Crofer22APU. Crofer 22 APU was merely used for a 200 µm thick foils inserted in the manifold areas at the gas in- and outlet of the cells. After controlled shut-down, the stack was post-test analyzed. After leakage test by pressure drop method, part of the stack was embedded as a whole and part was dissected plane-by-plane. All stack components, the cell, the metallic interconnects, frames and the glass-ceramic sealing were afterwards characterized by means of SEM, TEM and wet chemical analysis. Some analysis were made on whole stack parts including the top and bottom plates and some were performed on dissected individual parts.In summary, most of the components look optically quite good despite the 11 years operation. The measured gas-tightness at room temperature was below the threshold of 1 % gas loss on the fuel side but in an acceptable range regarding the air side. The microstructure of the glass-ceramic sealant showed a high crystallization state of the material with moderate porosity. The triple phase boundary to the furnace atmosphere had a thin layer of barium chromate indicating an early crystallization equilibrium achieved after short terms not being effected by the long-term exposition afterwards. An antiquated application method was used for the sealant resulting in an infiltration of the protective layer up to 100µm depth by the excess glass-ceramic squeezing out of the joining gap. Regarding the interfacial reactions to the YSZ electrolyte, zirconium containing silicate needles are formed as a thin layer. The reaction zone to the steel ITM is very similar to the phenomena observed for Crofer22APU: a chromium manganese spinel layer is dissolved by the glass during joining process resulting in an interfacial layer of 1-2 µm thickness.The interconnect steel ITM formed a thin protective chromia surface scale. The relatively high contents of chromium (ca. 25%) and molybdenum (ca. 3%) in the steel resulted in extensive s-phase formation in the large areas of the interconnect. Gas distributing steel foils of 200 µm thickness made from Crofer 22 APU showed only in some locations nodules of Fe-rich oxide. Substantial parts of these foils formed a protective surface oxide scale consisting of an outer Mn, Cr- spinel layer on top of an inner chromia scale. Interdiffusion phenomena were observed at the spot-welded joints between nickel contact wires and steel components. Ni diffusion from the wire into the ITM interconnect and Crofer 22 APU foils resulted in local transformation of ferritic into austenite structure. On the other hand diffusion of Cr from the interconnect into the Ni-wires resulted in minor Cr-oxide formation on the surfaces of the Ni wires.The cell itself and the air-side contacting reveal no obvious macroscopic changes like delamination, cracking etc. A closer look into the cell shows the formation of an interface zone between the LSCF cathode and the GDC barrier layer. This zone looks fragmented and being composed of various tiny crystals which in turn can be traced back to LSCF and GDC. But in many areas additionally Cr as foreign element could be detected. This Cr is also present in the first micrometers of the GDC barrier layer forming also tiny crystals on the inner surface of pores within the GDC. In the fuel electrode, composed of Ni and 8YSZ, also very small foreign phases containing Mn and Al were found. The amount is very low as the ITM contains only traces of Mn. But an enrichment in Ni in the fuel electrode could be detected. This is opposite to the effect in electrolysis mode were a Ni depletion takes place.To sum up the cell-related findings: i) an enrichment in Nickel in the fuel electrode has been observed in this stack for the first time; ii) a foreign phase composed of Mn-Al-(O) is present in the fuel electrode; iii) the LSCF cathode is, closed to the barrier layer, fragmented and chemically disintegrated; iv) the GDC barrier is also fragmented at the border towards the cathode and lastly v) an interaction between Cr and GDC has been observed also for the first time.

Enhanced output power of thermoelectric modules with reduced contact resistance by adopting the optimized Ni diffusion barrier layer

The diffusion barrier layers in thermoelectric generators (TEGs) are widely used to improve their mechanical/thermal stabilities and energy generation performance; however, thickness dependence of diffusion barrier was rarely reported. In this study, we prepared Bi2Te3-based thermoelectric (TE) modules and Ni diffusion barrier with a thickness of 0–30 µm to investigate the correlation between the thickness of Ni layers and TE output performance. A TE module with 1 μm-thick Ni layer harvests a maximum output power of 2.79 mW under a temperature difference (ΔT) of 200 K, which is a higher value than that of a module without a diffusion barrier. Regarding the dependence of TE output performance on the diffusion barrier’s thickness, TEGs based on the thicker Ni layers showed lower output performance for all ΔT ranges compared with a 1 µm-Ni layer TEG. The degradation of TE conversion efficiency was related to the increment of contact resistance (Rc) with the thickness of the diffusion barrier. This Ni thickness-dependent Rc was explored using the transmission line method. The results from this study prove that the thickness of optimized diffusion barriers would maximize the output performance of TEGs, which could be used as a guide for improving the performance of TEGs.

Densification mechanism and microstructure development of Fe-Ni alloys consolidated by field assisted sintering

Fe-xNi alloys (x = 0–5.0 in wt%) were consolidated by conventional sintering (CS), hot pressing (HP), and field assisted (activated) sintering technique (FAS or FAST), and their densification, microstructure, mechanical properties were comparatively investigated, particularly focusing on the field or current effects of FAS technique. The Ni addition promoted the densification and suppressed the grain growth in Fe-Ni alloys consolidated by both CS and FAS, and the FAS produced the Fe-Ni alloys with higher apparent density and smaller grain size. Consequently, the Fe-Ni alloys fabricated by FAS exhibited a significant improvement in the bulk hardness compared to those consolidated by CS and HP. The element distribution mapping by energy dispersive spectroscopy (EDS) indicated that Ni was mainly present along the grain boundaries in the FAS specimen. Furthermore, the diffusion couple experiment showed that the FAS enhanced the Ni diffusion along the grain boundaries. The obtained results indicated that the electric current together with mechanical pressure in FAS promoted the Ni diffusion along the grain boundaries, which resulted in the enhanced densification with suppressed grain growth.

High performance NiO/Ag/NiO transparent conducting electrodes for p-Si/n-ZnO heterojunction photodiodes

A NiO/Ag/NiO (NAN) transparent conducting electrode (TCE) was fabricated using a magnetron-sputtering system, and the NAN TCE was applied to p-Si/n-ZnO heterojunction photodiodes (HPDs). The NAN TCE exhibits a 50% higher transmittance than the Al electrode (less than 1%). However, a very low sheet resistance of 0.27 Ω/sq is obtained in Al electrode than in NAN TCE (6.5 Ω/sq). The NAN TCE could effectively enhance the photo response of p-Si/n-ZnO HPDs for both ultraviolet (UV) and visible bands as compared to the p-Si/n-ZnO HPDs with the traditional Al electrode. Compared to the traditional p-Si/n-ZnO HPDs using the Al electrode, for the p-Si/n-ZnO HPDs using NAN TCE, the 500 nm photo response is increased by approximately 10 times and the 280 nm photo response is significantly enhanced by approximately 100 times at a reverse-bias voltage of 1 V. The dark current of p-Si/n-ZnO HPDs with NAN TCE is two orders of magnitude lower than that of p-Si/n-ZnO HPDs with an Al electrode. The improved performance enhances the photo (500 nm) to dark current ratio from 2 for the p-Si/n-ZnO HPDs with Al electrode to 1.4 × 103 for the one with NAN TCE. The photo (280 nm) to dark current ratio is enhanced from 8.5 × 102 to 6.8 × 105. The mechanism results from the high transmittance in the NAN TCE and Ni diffusion in ZnO. The Ni diffusion in ZnO suppresses its defects and hence decreases electron scattering from crystallites/grains, thereby increasing carrier mobility.

Fabrication and mechanical properties of homogeneous and gradient nanocomposites by two-step sintering

Homogeneous and functional gradient nanocomposites were prepared using a two-step sintering process at a pressure of 30 MPa. The effects of macro –micro fracture morphologies and element distributions on the mechanical properties of the composites were studied. The results showed that the fracture toughness of the inner layers of the gradient material was almost the same as that of the corresponding homogeneous material. The composition content difference between the gradient layers had a significant influence on the bending strength and hardness. There was little Ni and Mo diffusion in the gradient nanocomposites because of the relatively low contents and suitable processing parameters. A gradient distribution of the metals was ensured. The surface layer thickness had little influence on the flexural strength of the gradient nanocomposite, but it had an obvious influence on the hardness and fracture toughness of the surface. The five-layered gradient composite with a surface layer thickness of 85 μm exhibited the best mechanical properties, including a flexural strength of 1021 ± 35 MPa, fracture toughness of 7.60 ± 0.21 MPa m1/2 and surface hardness of 19.26 ± 0.62 GPa.

Phase Formation during Reduction-Oxidation of Ni-Substituted Sr(Ti,Fe)O3-δ Solid Oxide Fuel Electrodes

High performance solid oxide fuel cell anodes have recently been achieved via the exsolution of bimetallic (Ni,Fe) particles from a parent Sr(Ti,Fe,Ni)O3-δ (STFN) matrix. However, a number of unknowns remain regarding the detailed nature of the exsolution process, the role of initial A-site deficiency, and the effect of the change in perovskite stoichiometry during exsolution. In this study, the dynamics of exsolution are explored via thermogravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM), both during exsolution and redox cycling. The diffraction results show that the (Ni,Fe) phase starts Ni-rich during the initial exsolution, gradually shifting to more Fe-rich with time; this result indicates that Ni diffusion towards the surface is occurring faster than for Fe. The TGA results suggest that holding STFN under too-reducing conditions can lead to continued Fe exsolution instead of reaching a stable equilibrium. TEM images display regions where SrO formed after Fe-Ni exsolution, likely as a consequence of increased A-site excess in the perovskite. In-situ re-oxidation and subsequent re-incorporation of exsolved species into the parent oxide have been suggested as a means to “reset” exsolution electrodes after degradation by, e.g., particle coarsening. The present TGA results taken during redox cycling suggest that a shorter oxidation step results in faster exsolution, a hint that, in this case, the exsolved surface species do not have sufficient time to fully re-incorporate into the oxide. The effects of new phase formation, changes in exsolved particle composition, and redox cycling on electrochemical characteristics will also be reported.Figure 1. Ex-situ X-ray diffraction scans from Sr(Ti,Fe,Ni)O3-δ after reduction in 30% H2 – 3% H2O – 67% Ar, showing peaks from the perovskite matrix along with a peak associated with exsolved (Ni,Fe) metal alloy; the latter shifts with increasing reduction time indicating that the alloy becomes increasingly Fe-rich. Figure 1

Microstructural evolution, mechanical properties, and oxidation performance of highly Ni-rich NiTi alloys with added V using vacuum arc melting

Highly Ni-rich NiTi alloys have attracted increasing attention as new candidates for bearing materials owing to their high hardness, low density, good corrosion resistance, and good dimensional stability. The main phases of the Ni55Ti45 (at%) (60NiTi) alloy consist of B2-NiTi matrix, equilibrium Ni3Ti, metastable Ni4Ti3 and Ni3Ti2, and a small amount of Ti2Ni phase. The ultra-high hardness of 60NiTi was attributed to the high volume fraction of nanoscale Ni4Ti3 phase and significant internal strain resulted from its coherence with the NiTi matrix. In this study, a series of 60NiTi-V alloys were prepared to study the effect of V addition on the microstructure, mechanical properties and oxidation performance of 60NiTi. The additional V enhanced the transformation from Ni4Ti3 phase to Ni3Ti2 and Ni3Ti phases. When the V content exceeded 3 at%, a grid-like Ni3Ti2 phase was formed in the alloy, and when the V content reached 10 at%, the formation of Ni3Ti phase was promoted. Moreover, the morphology and distribution of Ni3Ti2 phase changed with changing V content. The hardness of the alloy increased with increasing V content, whereas the fracture toughness and tensile strength increased at first and then decreased, owing to the solid solution strengthening effect of V and strengthening effect of Ni3Ti2 phase. At 500 °C, the oxidation resistance of 60NiTi-V alloys with V contents of less than 3 at% V was higher than that of binary 60NiTi. Conversely, the oxidation of the 60NiTi-V alloy with a V content of 3 at% was more severe than that of binary 60NiTi at a high oxidation temperature of 800 °C, because V promoted outward Ni diffusion. Therefore, a V content of less than 3 at% was effective for improving the microstructure and properties of highly Ni-rich NiTi alloys; moreover, in this study, we provided a new idea for strengthening highly Ni-rich NiTi alloys and expanding their applications.

Ab initio molecular dynamics study on local structure and dynamic properties of liquid Ni62Nb38 alloy

In the temperature range between 1873 K and 1233 K, structural evolution and dynamic properties of liquid Ni62Nb38 alloy have been studied by ab initio molecular dynamics. The evolution of local structure was characterized by pair distribution functions, structure factors, bond angle distributions, coordination numbers and chemical short-range order parameters, and electronic structure is mainly reflected by the density of states. Self-diffusion coefficients were calculated out to represent dynamic properties. It is found that with the decrease of temperature, short-range order tends to increase and medium-range order can be discovered in the under-cooling system. Meanwhile, a series of complex local structure like tetrahedron and icosahedron gradually forms in the liquid. Moreover, the whole system is hetero-coordinating. During the whole process, both Ni and Nb diffusion coefficients show a decreasing trend, effectively prohibiting nucleation and crystal growth, and it is beneficial to the amorphous transformation of liquid Ni62Nb38 alloy. The formation of chemical bonds between Ni and Nb atoms is mainly because of the hybridization interaction between Ni and Nb d-states.

Platinum redistribution in the Ni0.9Pt0.1/InP system: Impact on solid-state reaction and layer morphology

In the scope of integrating III–V device contacts on a 300 mm platform, Ni-based contacts are envisioned. In this regard, the Pt redistribution in the Ni0.9Pt0.1/InP system, and the impact of Pt-alloying of Ni thin films on InP over solid-state reaction and layer morphology have been investigated. Results have shown that at low temperature (T < 300 °C), the presence of Pt partially slows down the diffusion of Ni towards the InP substrate, which as a result delays the growth of an intermixing amorphous Ni–In–P layer. In addition, the presence of Pt in the system has delayed the consumption of the Ni0.9Pt0.1 layer. At higher temperatures (T ≥ 300 °C), the thermal energy brought to the system overcomes the Pt-induced partially slowed down Ni diffusion, and the observed phase formation sequence indicates that the Ni-based crystallized phases (Ni2P, Ni3P and Ni2InP) are identified regardless of the presence of Pt, which is not incorporated into the formed Ni-based phases (Ni2P, Ni3P and Ni2InP). Instead, the latter is rejected from the forming interface, which allows it to participate to the formation of the stable Pt3In7 crystallized phase.

Sorption enhancement of nickel(II) from wastewater by ZIF-8 modified with poly (sodium 4-styrenesulfonate): Mechanism and kinetic study

Effective removal of toxic metal Ni(II) from wastewater is essential to water safety and human health. Although zeolitic imidazolate framework-8 (ZIF-8) has demonstrated outstanding selective removal of Ni(II) in high-salinity wastewater, the practical applications of ZIF-8 are mainly limited by low active sites utilization, slow adsorption kinetics and poor reusability. In this study, we prepared a novel negatively charged poly (sodium 4-styrenesulfonate) (PSS)-modified ZIF-8 adsorbent, ZIF-8@PSS (12 h), which increased the adsorption rate of Ni(II) (kinetic constant k = 0.0299 g mg−1 min−1) by nearly 10 times and the adsorption capacity (329.58 mg/g) by 1.6 times compared to pristine ZIF-8 (k = 0.0021 g mg−1 min−1). ZIF-8@PSS (12 h) (0.5 g/L) could quickly decrease Ni(II) (C0 = 1.0 mg/L) to 0.1 mg/L (discharged standard) in 25 min, while 600 min for ZIF-8. Batch experiments and characterization analyses revealed PSS can improve particle dispersion, increase active sites utilization, and strengthen Ni(II) diffusion kinetics, thereby enhancing the adsorption of Ni(II). Among them, the increase in active sites utilization of ZIF-8 contributes 83.3% to capacity improvement, while the –SO3− on PSS is 16.7%. Furthermore, the enhancements of adsorption kinetics and capacity were also applicable to other heavy metals (e.g., Cu2+, Pb2+, Cr3+, Cd2+). Column experiments using real nickel plating effluent shown that 1 g ZIF-8@PSS (12 h) could produce ~3675 mL of clean water before breakthrough (Ni2+ < 0.1 mg/L). Moreover, a specific nickel chelator, dimethylglyoxime was used to regenerate the exhausted adsorbent and showed an insignificant capacity loss after four cycles. This study indicates the potential of ZIF-8@PSS (12 h) to remove Ni(II) from nickel plating effluent.

Modeling a Ni/β-Ga2O3 Schottky barrier diode deposited by confined magnetic-field-based sputtering

In this work, a detailed numerical simulation is carried out to model the current–voltage characteristics of a nickel/β-Ga2O3 Schottky barrier diode at different temperatures. These SBDs are produced using confined magnetic-field-based sputtering to deposit the nickel (Ni) Schottky contact of the diode. This method reduces the thickness of the defect area created by plasma and argon bombardment, and consequently, the electrical characteristics are less affected by temperature changes or annealing (i.e. the device is more stable). During annealing, Ni diffuses into β-Ga2O3. A model for this diffusion is proposed in this work, in which Ni diffusion reduces the defects produced by plasma and argon bombardment by filling the Ga vacancy. Furthermore, Ni diffusion produces a new interfacial compound, namely at the interface between the Ni and the β-Ga2O3. This new compound layer has different properties than those of β-Ga2O3, in particular, those of the bandgap and the affinity. Finally, the temperature-dependent current-density–voltage (J–V) characteristics are simulated, taking the proposed model into account. A good agreement with measured values is achieved, especially at low forward voltages, which demonstrates the soundness of the proposed model.

Ni diffusion in vertical growth of MoS2 nanosheets on carbon nanotubes towards highly efficient hydrogen evolution

The effect of transition metal particle size and distribution on the catalytic performances of carbon nanotubes (CNTs)-based catalysts has been attracting considerable attention in recent years. In this paper, Ni nanoparticles with a Ni3C shell structure were embedded in N-doped CNTs by thermal condensation of dicyandiamide with Ni salts followed by MoS2 nanosheets deposition. Most interesting, dissolution, redistribution and diffusion of the embedded Ni/Ni3C nanoparticles take place during the stage of deposition of MoS2 nanosheets on the CNTs with the help of excess S precursors. The dissolution, redistribution and diffusion result in the disappearance of Ni nanoparticles and formation of much finer Ni nanoclusters, which significantly facilitates the deposition and formation of vertical MoS2 nanosheets on CNTs. The homogeneous distribution of Ni nanocluster leads to improved intrinsic conductivity and increased active sites. N-doped CNTs with optimized Ni and MoS2 loading revealed high activity and stability for electrocatalytic hydrogen evolution reaction (HER). The as-prepared MoNiCNTs electrocatalysts exhibit superior HER activity with low onset potential and small Tafel slope value in both acidic and alkaline electrolyte conditions. The result provides a new platform for rational design and fabrication of high-performance non-precious transition metal based HER electrocatalysts.

The Effects of Nb Addition on the Oxidation Behavior of Ni–Fe–Cr Alloys at 800 °C

High temperature oxidation of Ni–18Fe–19Cr alloys with different Nb contents (based on the chemical composition of Alloy718) was investigated to elucidate the effect of Nb on oxidation kinetics and scale formation after exposure at 800 °C in air. The experimental results indicated that the oxidation kinetics decreased with increasing niobium content. Rapid establishment of an external Cr2O3 scale was interpreted by the formation of a continuous CrNbO4 layer at the metal-oxide interface, which acts as a diffusion barrier for inward oxygen and outward Fe and Ni diffusion and is of benefit for the establishment of an external Cr2O3 scale. The early establishment of this diffusion barrier prevented internal oxidation of chromium and reduced the growth of the outer Ni2FeO4 oxide scale. The beneficial effect of Nb could be attributed to effectively increasing the volume fraction of internal oxide precipitates, which are favorable for rapid establishment of an external Cr2O3 scale.

Evolution and formation mechanism of the interfacial microstructure on diffusion bonded joints of single crystal Ni-based superalloys to Ti3AlC2 ceramic with Ni interlayer

Abstract Single crystal Ni-based superalloys DD3 and nanolaminated ternary ceramics Ti3AlC2 were the critical high-temperature structural materials, so the bonding of them is of great significance in promoting their potential applications at elevated temperatures. A strong DD3/Ti3AlC2 joint with the average shear strength of 86.4 MPa was obtained by vacuum diffusion bonding using the Ni interlayer at 900 °C for 60 min. The joint microstructure and its formation mechanism were investigated in detail. Especially, the role of Ni diffusion in the process of forming a mixed phase zone at the Ti3AlC2 interface was clarified. The diffusion zone adjacent to the DD3 was mainly composed of (Ni)ss, where Al and Ti existed mainly in the form of solid solution. In contrast, a more complex diffusion process occurred at the Ti3AlC2 interface. A Ni3Al single layer and a mixed phases zone, containing Ni3Al, AlNi2Ti and TiC, were formed from the Ni interlayer to the Ti3AlC2 substrate. Ni had a strong tendency to diffuse along grain boundaries of the Ti3AlC2 substrate, leading to the decomposition of its nanolaminated structure. Along with inward-diffusion of Ni, the Ni3Al phase was mainly formed, and a small amount of AlNi2Ti and TiC were also formed.

Non-destructive elemental depth profiling of Ni/Ti multilayers by GIXRF technique

In thin film multilayer along with total interface widths, study of individual interface widths of the constituent elements of the multilayer is important for the knowledge of diffusion mechanism and diffusion kinetics. Element specific Grazing Incidence X-ray Fluorescence (GIXRF) technique has been used to study the individual interface diffusion of Ni and Ti in the Ni/Ti multilayer. The above measurements yield similar results on the interface qualities of the multilayer as obtained from more widely used Grazing Incidence X-ray reflectivity (GIXRR) technique and give additional information regarding Ni and Ti diffusion separately which cannot be obtained from GIXRR. Ni-fluorescence and Ti-fluorescence GIXRF spectra of 10-bilayer Ni/Ti multilayer films are fitted simultaneously to find the interface widths of Ni and Ti at the Ni-on-Ti and Ti-on-Ni interfaces. The Error function distribution has been used to describe the concentration of elements at the interfaces. Further, the variation of these individual diffusion and individual concentration profile of elements has been studied with annealing of the multilayer. It has been shown that non-destructive and relatively simpler GIXRF technique can be used for elemental depth profiling of a multilayer very precisely, which otherwise can be obtained by using complicated destructive technique like atom probe tomography.