Oxidation Of NiAl Research Articles

Atomistic Insights into Impact-Induced Energy Release and Deformation of Core-Shell-Structured Ni/Al Nanoparticle in an Oxygen Environment.

In actual atmospheric environments, Ni/Al composites subjected to high-velocity impact will undergo both intermetallic reaction and oxidative combustion simultaneously, and the coupling of mechanical and multiple chemical processes leads to extremely complex characteristics of energy release. This work employs ReaxFF molecular dynamics simulations to investigate the impact-induced deformation and energy release of a core-shell-structured Ni/Al nanoparticle in an oxygen environment. It was found that Al directly undergoes fragmentation, while Ni experiences plastic deformation, melting, and fragmentation in sequence as the impact velocity increased. This results in the final morphology of the nanoparticles being an ellipsoidal-clad nanoparticle, spherical Ni/Al melt, and debris cloud. Furthermore, these deformation characteristics are strongly related to the material property of the shell, manifested as Ni shell-Al core particle, being more prone to breakage. Interestingly, the dissociation phenomenon of Ni-Al-O clusters during deformation is observed, which is driven by Ni dissociation and Al oxidation. In addition, the energy release is strongly related to the deformation behavior. When the nanoparticle is not completely broken (Ni undergoes plastic deformation and melting), the energy release comes from the oxidative combustion of Al fragments and the intermetallic reaction driven by atomic mixing. When the nanoparticle is completely broken, the energy release mainly comes from the oxidative combustion of the debris cloud. At the same time, the promoting effect of oxygen concentration on the energy release efficiency is examined. These findings can provide atomic insights into the regulation of impact-induced energy release for reactive intermetallic materials.

Precipitation of metallic Ni clusters in alumina scale during high-temperature oxidation of NiAl in water vapor

Water vapor is ubiquitously present for energy conversion and combustion systems, yet its effect on the oxidation of crucial structure components of heat-resistant alloys remains elusive. Departure from the well-established phenomenon of exclusive alumina growth from the NiAl oxidation in dry O2, we demonstrate that the NiAl oxidation in H2O results in the precipitation of a significant number of metallic Ni clusters within the Al2O3 scale by adsorbing Ni atoms from the alloy through a vacancy-assisted solute capture solute capture process of the enhanced oxide/alloy interface migration. The Ni clusters initially have a hcp structure at small sized, transitioning into an fcc structure when their size exceeds ∼12.5 nm. Using atomistic modeling, we show that the dissolution of a high concentration of H derived from H2O into the oxide scale is the key to stabilizing the hcp Ni structure. Subsequent coarsening of the hcp Ni clusters lowers the H concentration, leading to the hcp → fcc transformation. These results provide mechanistic insight into the effect of water vapor on the long-term stability of the structure alloys by influencing the oxidation-induced mass transport across the scale/alloy interface and microstructure evolution within the oxide scale.

Atomic-level mechanism of CO2-promoted oxidation of alumina-forming alloys

The high-temperature oxidation of the NiAl alloy in the CO2 and O2 atmospheres is comparatively studied by a combination of electron microscopy characterization and first-principles calculations. It is shown that CO2 accelerates the oxidation of NiAl alloy by the formation of a highly porous γ-Al2O3 scale that is non-protective and follows the linear growth law. By contrast, the NiAl oxidation in O2 results in a double-layered oxide scale consisting of an outer columnar γ-Al2O3 layer and an inner equiaxed α-Al2O3 layer, which is protective and follows parabolic growth law. Our first-principles calculations show that this accelerated NiAl oxidation in the CO2 can be attributed to more ready decomposition of adsorbed CO2 than adsorbed O2 into atomic oxygen on defective γ-Al2O3 surfaces, which leads to the inward γ-Al2O3 growth by the infiltration of gaseous CO2 through the cracked oxide scale toward the exposed NiAl alloy. These results provide new insights into the atomic origin of CO2-promoted alloy oxidation.

One-dimensional γ-Al2O3 growth from the oxidation of NiAl

We report an oxide nanowire growth phenomenon that morphologically resembles the vapor-liquid-solid process but with a fundamentally different mechanism. This is demonstrated with the high-temperature NiAl oxidation that results in the unidirectional γ-Al2O3 growth with a NiO nanoparticle at the nanowire tip. The NiO nanoparticle surface serves as the active site for dissociative O2 adsorption that produces an inward flux of atomic oxygen toward the γ-Al2O3/NiAl interface for γ-Al2O3 growth by reacting with bottom-up diffusing Al3+ cations. The nanowire lengthening follows the parabolic kinetics with the upward lattice diffusion of Al3+ cations in the γ-Al2O3 nanowires as the rate-limiting factor.

Synthesis of Catalytic Precursors Based on Mixed Ni-Al Oxides by Supercritical Antisolvent Co-Precipitation

Mixed Ni-Al oxide catalytic precursors with different elemental ratios (20, 50, and 80 wt.% Ni0) were synthesized using green supercritical antisolvent co-precipitation (SAS). The obtained oxide precursors and metal catalysts were characterized in detail by X-ray diffraction (XRD) analysis, atomic pair distribution function (PDF) analysis, CO adsorption, and high-resolution transmission electron microscopy (HRTEM). It was found that the composition and structure of the Ni-Al precursors are related to the Ni content. The mixed Ni1−xAlxO oxide with NiO-based crystal structure was formed in the Ni-enriched sample, whereas the highly dispersed NiAl2O4 spinel was observed in the Al-enriched sample. The obtained metal catalysts were tested in the process of anisole H2-free hydrogenation. 2-PrOH was used as a hydrogen donor. The catalyst with 50 wt.% Ni0 demonstrated the highest activity in the hydrogenation process.

Template-induced mesoporous Ni–Al oxide catalysts with tuned physico–chemical properties for the oxidative dehydrogenation of ethane

Oxidative dehydrogenation of ethane is a potential industrial process to produce ethylene. In this work, the template-induced mesoporous Ni–Al mixed oxide catalysts synthesized by the template-assisted self-assembly method were investigated for the oxidative dehydrogenation of ethane to ethylene using O2 as an oxidant. The template-induced structure evolution is an effective means to modulate physico-chemical properties of the Ni–Al mixed oxide, thus, it further improves the catalytic performance. All the mesoporous Ni–Al–template catalysts present higher C2H6 conversions and C2H4 selectivities than bulk NiO and non-porous Ni–Al–O catalysts in the temperature range of 350–500 °C. Meanwhile, up to 49.6% C2H6 conversion and 75.3% C2H4 selectivity (37.3% of C2H4 yield) can be obtained over Ni–Al–F127 catalyst at 500 °C. And the mesoporous Ni–Al–F127 catalyst exhibits a superior stability after a long run. The structure–performance correlation indicates that the remarkable catalytic performance is ascribed to the synthesis driven structural effect. The strong interaction between Ni and Al cations caused by the addition of template promotes the formation of small NiO particles and the better dispersion of NiO, which decreases the content of non-selective oxygen species and increases the availability of lattice oxygen.

Синтез и исследование никель-алюминиевых оксидных катализаторов на углеродном носителе

Activated carbons, which have a highly developed specific surface area and large pore sizes, have recently been increasingly considered as economically available carriers of catalytic systems for deep processing of heavy hydrocarbon feedstock. In this work, samples of catalysts obtained by impregnation of active carbon with oxides of NiO and Al2O3 were studied. It is shown that an increase in the ratio of metal cations Ni/Al in the impregnating solution from 2:1 to 3:1 leads to a decrease in the average pore diameter and an increase in the specific surface area of activated carbon by 1.5 times. Activated carbons impregnated with Ni/Al metal oxides with a ratio of metal cations in an impregnating solution of 3:1, calcined in a stream of hydrogen, have the largest pore area with a diameter of 10–200 nm. Heat treatment of Ni-Al oxide catalysts on a carbon carrier at a temperature of 450°С in a hydrogen flow leads to an increase in the pore size and a decrease in the specific surface area. Mechanical activation of oxide catalysts on a carbon carrier by ultrasonic action increases the area of the outer surface of the particles by more than two times.

First-principles study on the NiAl/Al2O3 interfacial segregation of Hf during the oxidation of Hf-modified NiAl

Despite the well-known beneficial effect of reactive element dopants on improving the oxidation resistance of alumina-forming alloys, many open questions remain, including the migration and segregation of reactive elements at the oxide/alloy interface, a key zone in controlling the global oxidation kinetics and interface adhesion. Herein, we elucidate the atomic processes governing the interfacial dynamics of hafnium with γ-Al2O3 and θ-Al2O3, two dominant metastable phases before transforming to stable α-Al2O3 during the oxidation of Ni-Al alloys. Our results show that Al vacancies in the Al2O3 overlayer play a critical role in influencing the interfacial segregation of Hf atoms and HfO2 formation. For the γ-Al2O3 (001)/NiAl (100) interface, the presence of interfacial Al vacancies in γ-Al2O3 drives the interfacial segregation and aggregation of Hf atoms from the NiAl substrate, resulting in interfacial nucleation of HfO2. By contrast, for the θ-Al2O3 (100)/NiAl (100) interface, the presence of interfacial Al vacancies steers the migration of Hf atoms from the NiAl substrate across the oxide/alloy interface deeper into the oxide lattice, promoting the HfO2 formation in the bulk of the θ-Al2O3 layer. These results may find broader applicability for manipulating the interfacial transport process of reactive elements by controlling the phase and stoichiometry of the transient oxide phases.

Reaction mechanism and oxidation resistance at 700–900 °C of high porosity NiAl intermetallic

Porous NiAl intermetallic compound exhibit attractive properties. However, their simple and controllable preparation and understanding of oxidation mechanism are still incipient. Thermal explosion was employed to facilely fabricated highly porosity NiAl. The pore structure of the product has been meticulously characterized using 3D-XRM, and oxidation corrosion test was conducted in a fluid and static air at 700–900 °C for up to 120 h. Dynamic oxidation shows that 800 °C is the turning point of oxidation mechanism. The oxidation of porous NiAl follows the logarithmic oxidation law below 800 °C and the parabolic oxidation law above 800 °C.

Effects of Minor Alloying Elements on Alumina Transformation During the Transient Oxidation of β-NiAl

The transient stage of alumina scale formation on alumina-forming alloys is often accompanied by the formation of metastable Al2O3 phases that may affect oxidation kinetics and scale microstructure. To clarify the role of dopants on the transient stage of NiAl oxidation, we characterized Al2O3 scales on a series of oxidized model β-NiAl samples that were un-doped or doped with additions of Ti, Y, Si, Ti + Y, and Si + Y. Our results confirm that different dopant elements (Ti, Si, and Y) have varied effects on the length of transient oxidation of alumina-forming alloys. Ti and Si accelerated the θ- to α-Al2O3 transformation via two different mechanisms. Ti promoted α-Al2O3 nucleation, while Si delayed nucleation but accelerated the lateral growth of the α-Al2O3 patches. In contrast, Y had little effect on alumina transformation, possibly due to the low Y concentration used in the current study.

Structure and reaction mechanism of binary Ni-Al oxides as materials for lithium-ion battery anodes.

A nanometer sized solid solution of NiO and Al2O3 was synthesized by calcination of Ni-Al layered double hydroxides (LDHs). The crystal structure of the obtained compound was determined by XRD and XAFS analyses: Ni2+ and Al3+ ions are located at the metal ion site of the rock salt structure and a certain amount of cation vacancies are also introduced for charge compensation. The electrochemical properties of the Ni-Al binary metal oxide as an anode material for lithium ion batteries were examined by the constant current charge-discharge test. Ni-Al oxide showed higher charging capacity in comparison with pristine NiO. In particular, the capacity in the lower voltage region (below 1.5 V), the limited capacity in this region is the weak point of the conversion anode, was improved to 540 mA h g-1 that is about twice that of pristine NiO. This improvement in the capacity in the lower voltage region is concluded to be due to the redox activity of Al3+ ions during the charge-discharge on the basis of the results of electrochemical measurements and ex situ XAFS measurements at the Ni and Al edge. The reaction mechanism of this compound is investigated using ex situ XRD and XAFS methods. For the charge (reduction) in the higher voltage region (OCV-1.0 V), lithium ion intercalation into the cation vacancy sites and/or lithium ion adsorption on the surface of particles are proceeding. For the charge in the lower voltage region (1.0-0.03 V), conversion reaction occurs by the reduction of Ni2+ and Al3+ ions to metal particles with surface electrolyte interface (SEI) layer formation. For the discharge in the lower voltage region (0.03-1.5 V), only Al metal particles are oxidized to Al3+ ions and some intermediate complexes are formed. For the discharge in the higher voltage region (1.5-3.0 V), the lattice of the Ni-Al binary oxide solid solution is reconstructed with the oxidation of Ni to Ni2+.

Non-compact oxide-island growth induced by surface phase transition of the intermetallic NiAl during vacuum annealing

Crystal structure and composition are inter-dependent and decoupling their effects on surface reactivity is challenging. Using low-energy electron microscopy to spatially and temporally resolve the oxide film growth during the oxidation of NiAl(100), we differentiate such coupled effects by monitoring oxide growth while simultaneously fine-tuning the surface structure and composition during oxidation. We demonstrate that the oxidation of chemically ordered surfaces results in compact oxide island growth whereas non-compact oxide growth during the surface phase transition. By incorporating the surface phase transition induced chemical disordering into kinetic Monte Carlo simulations, we show that the non-compact oxide growth is induced by the composition effect on the surface diffusion of oxygen, which can be described by the concept of “ant in the labyrinth”.

Effects of Porosity and Ni/Al Molar Ratio in Ni–Al Oxide Precursors on Porous Intermetallic Nickel Aluminide Nanopowders Prepared by Chemical Route

Effects of Porosity and Ni/Al Molar Ratio in Ni–Al Oxide Precursors on Porous Intermetallic Nickel Aluminide Nanopowders Prepared by Chemical Route

Effect of water vapor on high-temperature oxidation of NiAl alloy

The high-temperature oxidation of NiAl is studied with dry oxygen and water vapor. The oxidation in H2O results in a thicker Al2O3 oxide scale than that in O2. The oxide scale formed initially is a single layer of γ-Al2O3 that subsequently transforms into a α-Al2O3/γ-Al2O3 bilayer structure, in which the inner α-Al2O3 layer formed in H2O has a higher porosity than that in O2. Further density functional theory calculations show that H protons derived from H2O molecules penetrate into the oxide lattice and boost the formation of lattice vacancies in both α-Al2O3 and γ-Al2O3, thus enhancing the oxide scale growth.

Prediction of the catalytic activity of Ni-Al mixed oxide in the hydroisomerization of n-alkanes

This article discusses the possibility of using mixed Ni-Al oxides as catalyst systems for the hydroisomerization of n-alkanes. A number of instrumental analysis methods were carried out, on the basis of which elementary lattices of the synthesized mixed oxides were modeled. A preliminary study showed that systems based on mixed Ni-Al oxides have acidic, basic properties. Their structure makes it possible to speak of the presence of molecular sieve properties, which will make it possible to obtain mono- and dimethyl substituted isoalkanes, which will lower the pour point of diesel fuel and at the same time produce high-acetane products. According to preliminary data, the best result is shown by a sample of mixed Ni-Al oxide with a ratio of Ni2+/Al3+ cations equal to two in the synthesis.

Structural Analysis of Defects in Layered Double Hydroxides and Related Mixed Oxides

Results of studying the structural defects in MgAl and NiAl layered double hydroxides and in the products of their thermal decomposition to 1000°C, obtained over the last 10 years at the Laboratory of Analytical and Physicochemical Methods of Research, Institute of Hydrocarbons Processing, Siberian Branch, Russian Academy of Sciences, were reviewed. These studies were performed using the method of simulation of X-ray diffraction patterns for one-dimensionally (1D) disordered crystals. Changes in the type of the structural defects depending on the calcination temperature were revealed, in particular, via in situ X-ray diffraction. A structural mechanism of the formation of the dehydrated phase at T = 200°C was proposed. New models of the MgAl and NiAl oxide structures were presented. The structures of the phases contained in the products of hydration of the oxides were established. The difference in the behavior of the oxides during hydration was explained.

Ni-Fe-Al mixed oxide for combined dry reforming and decomposition of methane with CO2 utilization

The chemical looping dry reforming of methane can be used to convert greenhouse gases into products with much desirable specification. However, developing an oxygen carrier with coke-tolerance and high oxygen exchange rate usually requires the use of rare-earth metals or lanthanides. In this study, by utilizing deposited surface carbon as a reaction intermediate rather than suppressing it, complete methane conversion was possible even with the earth-abundant metal oxide particles. To establish an optimized H2/CO ratio for the hydrocarbon synthesis, the CH4 feedstock was partially replaced with CO2. By itself, Ni-Al oxide exhibited deactivation due to the agglomeration arising from methane decomposition over the redox cycle. Fe-Al oxide had stable performance over cycles, but a sudden performance decline was observed when the amount of CO2 co-feeding exceeded a certain point. Incorporating Ni into the Fe-Al oxide was found to overcome these problems. The formation of a spinel phase with Fe alleviated the agglomeration, and enhanced CH4 activation under high CO2 partial pressure. The introduction of Ni also improved carbon gasification kinetics with CO2.

Effects of iron and platinum on the isothermal oxidation of β-NiAl overlay coatings fabricated by spark plasma sintering

The Fe and Pt modified β-NiAl overlay coatings with controlled concentrations were firstly fabricated on Hastelloy substrates using spark plasma sintering. The effects of Fe, Pt and their concentrations on the isothermal oxidation of the β-NiAl coatings were investigated. The unmodified NiAl coatings showed the worst spallation resistance, both Fe and Pt addition could significantly improve the oxidation performance of β-NiAl coatings. The mechanisms of Fe, Pt and their concentrations on the NiAl oxidation behavior were further discussed in related to the transformation of θ-Al2O3 to α-Al2O3, void formation at scale/coating interface and impurities (S and C) segregations. It is proposed that Fe could be a cheap alternative for Pt, though it was less effective than Pt to improve the oxidation resistance of β-NiAl coatings.

Evaluating the accuracy of common γ-Al2O3 structure models by selected area electron diffraction from high-quality crystalline γ-Al2O3

Single crystal and textured polycrystalline γ-Al2O3 thin films were synthesized by oxidation of NiAl(110) in air at 850 °C for 1 and 2 h, respectively, and used to evaluate the accuracy of two spinel-based and two nonspinel models by comparison of selected-area electron diffraction (SAED). The lattice interplanar distances derived from the polycrystalline SAED pattern most closely matched the cubic spinel γ-Al2O3 model. The single-crystal SAED spot pattern showed symmetry consistent with both the cubic spinel and tetragonal nonspinel models, however, the Al cation distribution better matched the cubic spinel model based on the relative intensities of diffraction spots. Our work indicates that the traditional cubic spinel model is a more accurate model of γ-Al2O3 than the other models considered. The spinel-based monoclinic model is also more accurate than the monoclinic nonspinel model. The understanding of the relative accuracy of the different models is key for simulating γ-Al2O3 containing systems and is of general interest for the metal oxide and ceramic communities.

Conversion of n-alkanes C11-C22 using a catalyst based on Ni-Al mixed oxides

During the work composition and properties of Ni-Al mixed oxides samples were investigated. These oxides were obtained from Ni-Al layered double hydroxide using thermal and hydrothermal methods. Catalytic cracking of a model mixture of alkanes was carried out in the presence of Ni-Al mixed oxides samples. Gas chromatography, chromatography-mass spectrometry, and IR-spectroscopy were used for the analysis of gaseous and liquid products. X-ray structural, X-ray fluorescence, IR-Fourier spectrometry, the specific surface analyzer, particle size analyzer, microphotographic analysis were used for the analysis of the composition and properties of catalytic systems. According to X-ray structural and X-ray fluorescence analyzes, the composition of the supporting structure of the catalyst Ni-Al mixed oxide did not change after catalysis. The content of their low-boiling homologs increases, alkanes of a branched structure is formed in the products of n-alkanes cracking in the presence of the obtained mixed Ni-Al oxide.