NiCr2O4 Spinel Research Articles

Investigation on the high-temperature oxidation behavior and mechanism of laser-cladded Inconel625 coating at various temperatures

This study examines the high-temperature oxidation behavior of laser-clad Inconel 625 coatings under different temperature and time conditions. The coating's microstructure, compositional elements, and oxidation products have been characterized through various analytical methods, including Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and Laser Confocal Microscopy. The experimental results showed that as the temperature increased in the isothermal oxidation process, the mass of the coatings increased, and the mass gain followed a parabolic relationship with oxidation time. The rate constant exhibited an exponential relationship with temperature. Both oxidation time and temperature had significant effects on the composition and formation of the oxide layer. At lower temperatures, the oxidation process is slow, with an oxidation weight gain of approximately 0.00053 mg/cm2. However, above 600 °C, the oxidation films began to form rapidly, increasing by 0.0169 mg/cm2. Moreover, as the temperature rose, different types of oxides formed at various temperature regimes. At 800 °C, the oxidation film had a thickness of approximately 3.75 μm and a weight gain of 1.19921 mg/cm2. At this point, oxides such as Cr2O3, Nb2O5, NiO, and spinel NiCr2O4 appeared. When the temperature reached 1000 °C, the oxidation film expanded to approximately 63.88 μm in thickness, with a weight gain of 3.5326 mg/cm2. The oxidation products at this temperature were Cr3O4 and spinels NiCr2O4, CrNbO4, NiNb2O6. These findings contribute valuable insights for understanding the dynamic behavior and assessing the service life of laser-clad nickel-based alloy coatings subjected to high-temperature oxidation corrosion.

Effect of WC-Co and 86WC-10Co-4Cr coatings on type-II hot corrosion behaviour & microstructure characteristics at 650 degree celsius

In this study, WC-Co and 86WC-10Co-4Cr coatings were applied on the AISI316 stainless steel by HVOF with Fe2 (SO4)3‐12%Na2SO4 corrosive environment at 650 °C. Measurements of the weight change were taken after every cycle for a total of fifty cycles to provide an approximation of the kinetics of the corrosion. This coating increases the corrosion resistance of surfaces. The surface morphology and phases produced during hot corrosion were investigated using EDS, XRD, and field emission SEM. The oxides of the surface coatings were high in Cr and W. These oxides contributed to hot corrosion resistance in corrosive environments by acting as barriers to corrosive element penetration/diffusion employing coatings. The greater tungsten the coating's content improved corrosion resistance at high temperatures. The coating's chromium (Cr) induced the growth of spinel NiCr2O4 and Cr2O3, which also contributes to maintaining corrosion resistance. Some oxides, including FeSCr2S3, Na2FeO2, and FeS, were discovered. The examination of the data confirmed that HVOF 86WC-10Co-4Cr sprayed on AISI316L stainless steel had shown high type-II hot corrosion resistance compared to WC-Co, although both coatings provide improved resistance to corrosion for sprayed base metal versus the bare base metal.

Microstructure, mechanical properties and high temperature corrosion of [AlTiCrNiTa/(AlTiCrNiTa)N]20 high entropy alloy multilayer coatings for nuclear fuel cladding

[AlTiCrNiTa/(AlTiCrNiTa)N]20 multilayer coatings were prepared by magnetron sputtering on Zr-4 substrate. The mechanical properties, microstructure and wettability of multilayer coatings were systematically studied by SEM, nano indentation instrument, scratch instrument and contact Angle instrument. In addition, after high temperature oxidation corrosion for 45 days, the coating was characterized by SEM and XRD. Al in the coating was wrapped in dense spinel NiCr2O4, which inhibits layer by layer dissolution of the coating, thus improving the corrosion resistance of the coating. The corrosion mechanism of [AlTiCrNiTa/(AlTiCrNiTa)N]20 multilayer coatings was evaluated in detail.

Study of Ce-doping effects on optical, morphological, magnetic, structural, and antibacterial properties of NiCr2O4 ceramics

We present a comprehensive study on optimization of microwave method routes for producing well-crystalline spinel chromite, nicr2o4 and Ce-doped nicr2o4. All samples were characterized by powder X-ray diffraction (XRD) and vibrational spectroscopy in order to evaluate their phase composition, particle size and micro-strain. Selected samples were investigated by adopting transmission electron microscopy (TEM) and optical spectra (absorption spectroscopy & photoluminescence, PL). The presence of large concentration of anion deficiency and its related defects, are reflected in the intense emission of PL spectra and in lowering the band gap value with respect to the bulk counterpart. As the Ce concentration increases, the size of the nanoparticles reduced from ∼33 to 22 nm. The effects of the cation distributions on geometrical variations of electronic and magnetic properties of nicr2o4 can be interpreted as dominated by the local behavior of Ni2+ at octahedral and Cr3+ tetrahedral sites. In the present work, the results indicate that the substitution of Ce ion into nickel chromite particles, enhances effects of the magnetic, optical properties, and also enhances the antibacterial properties.

EFFECT OF SILVER ADDITION TO HIGH-ENTROPY ALLOYS AL0.5COCRCU0.5FENI AND AL0.5COCRCUFENI ON THEIR MICROSTRUCTURE, PHASE COMPOSITION, MICROHARDNESS AND SURFACE OXIDE LAYER FORMATION

High-entropy alloys (HEAs) consisting of five or more components in an equimolar ratio are attracting increasing attention due to a unique combination of various properties. Alloying HEAs with small amounts of certain elements (most often rare earth, trace or noble metals) is a promising way to improve the characteristics of such alloys and control their properties. This paper reports the results on the microstructure, phase composition, and microhardness of cast AgxAl0.5CoCrCuyFeNi HEAs (x = 0, 0.1; y = 0.5, 1.0). The effect of silver addition on the oxidation behavior of the studied HEAs at 700°C was determined. The morphology, phase and chemical composition of the resulting oxide film were studied. It was shown that the introduction of silver improves the mechanical characteristics of the alloys, but deteriorates the oxidation resistance due to the formation of copper-silver eutectic in the alloy microstructure, leading to a change in the morphology and phase composition of the formed oxide layer. Along with the solid solution of (Al, Cr)2O3 oxides and CuCr2O4, NiCr2O4 spinels, the addition of silver leads to the formation of copper oxide CuO and a small amount of silver oxide Ag2O in the surface film.

Interrelation between the Solid-State Synthesis Conditions and Magnetic Properties of the NiCr2O4 Spinel

The synthesis of the NiCr2O4 compound with the spinel structure via the high-temperature solid-state reaction leads to different deviations of the cationic composition from the nominal depending on the atmosphere in the furnace chamber. The samples prepared from the same starting NiO and Cr2O3 compounds but in different atmospheres differ in phase composition and orbital and spin ordering temperatures. We find that a common route of synthesis in the air and a possible presence of the Ni2O3 in initial NiO lead to the incorporation of the Ni3+ ions into the octahedral sites regularly occupied by the Cr3+ ions. This results in a decrease in the orbital ordering and an increase in the Nèel temperatures. We propose that the Nèel temperature value serves as a measure of a departure of a composition from the nominal NiCr2O4. The lowest Nèel temperature among our series was TN = 63 K which we consider the closest to the intrinsic quantity of the NiCr2O4 compound.

Effect of Al Addition on Microstructure and Properties of CoCrNi Medium-Entropy Alloy Prepared by Powder Metallurgy.

Powder metallurgy possesses the advantages of low energy consumption, less material consumption, uniform composition, and near-final forming. In order to improve the mechanical properties and high-temperature oxidation resistance of CoCrNi medium-entropy alloy (MEA), CoCrNiAlX (X = 0, 0.1, 0.3, 0.5, 0.7) MEAs were prepared using mechanical alloying (MA) and spark-plasma sintering (SPS). The effect of aluminum content on the microstructure and properties of the MEAs was investigated. The results show that the CoCrNi MEA is composed of face center cubic (fcc) phase and some carbides (Cr23C6). With the increase in Al content, there exists Al2O3 precipitation. When the Al content is increased to Al0.5 and Al0.7, the body center cubic (bcc) phase begins to precipitate. The addition of aluminum significantly enhances the properties of the alloys, especially those containing fcc+bcc dual-phase solid solutions. The yield strength, compressive strength, and hardness of CoCrNiAl0.7 alloy are as high as 2083 MPa, 2498 MPa, and 646 HV, respectively. The high-temperature resistance also reaches the oxidation resistance level. Different oxides include Cr2O3, Al2O3, and (Co, Ni) Cr2O4 and NiCrO3 spinel oxides formed on the surface of alloys. The formation of an Al2O3 oxidation film prevents the further erosion of the matrix by oxygen elements.

Boosting catalyst activity with high valency metal species through Fe doping on normal spinel NiCr2O4 for superior water oxidation

Designing and tailoring valence states of transition metal has been highlighted as a potential technology to develop efficient electrocatalysts for water splitting because high valence metal sites enable to accelerate reaction kinetics for oxygen evolution reaction (OER). In this study, we designed and engineered spinel nickel–chromium oxide (NiFexCr2-xO4, 0 ≤ x ≤ 0.6) with high-valence metal sites and porous structure consisting of interconnected small nanoparticles using an in-situ Fe heteroatom doping synthesis route. The Fe-doped NiFexCr2-xO4 series (x = 0.2, 0.4, 0.6) catalysts exhibit superior OER activities compared to the pristine NiCr2O4 and benchmark IrO2 catalysts. Moreover, it is observed that for x = 0.2, the NiFexCr2-xO4 catalyst exhibited the best OER performance with a low overpotential of 187 mV at 10 mA cm−2, a high current density of 172 mA cm−2 at 0.28 V, and electrochemical long-term stability (decreasing only by ∼3 %) after a 200 h test. We further demonstrate that the remarkably improved catalytic performance of NiFexCr2-xO4 is attributed to the increased high-valence metal species (Ni3+ and Cr6+) and the highly oxidative oxygen species (O22−/O−), which are highly active to accelerate catalytic reactions, as well as the improved charge transfer kinetics and the porous structural feature by rationally doped Fe. Thus, it is believed that this research provides a novel strategy for developing efficient, robust, and low-cost OER electrocatalysts.

Anchoring spinel NiCr2O4 nanoparticles on tubular g-C3N4: Efficacious p-n heterojunction photocatalysts for removal of tetracycline hydrochloride under visible light

This study reports anchoring spinel NiCr2O4 nanoparticles over tubular g-C3N4 (TGC) through a facile process. The features of resultant photocatalysts were characterized via various analyses to perusal phase, optical, elemental, morphological, and electrochemical properties. Among the binary photocatalysts, the TGC/NiCr2O4 (20%) composite exhibited superior performance in the removal of tetracycline, which was 29.7 and 2.22-folds as much as the pristine g-C3N4 (abbreviated as GC) and TGC materials, respectively. Interestingly, the binary photocatalyst displayed tremendous activity in the visible-light degradation of cationic and anionic dye pollutants. The Mott-Schottky, EIS, photocurrent density, and PL analyses, along with scavenger tests confirmed the formation of a type II heterojunction between p-NiCr2O4 and n-TGC semiconductors, which resulted in effectual transfer and segregation of the photoinduced charges reinforced by the constructed electric field. The trapping results disclosed that the holes and superoxide anion radicals play major role in the photocatalytic degradation reaction. Considering the superior activity in visible-light-triggered degradation of different pollutants, high stability, and facile synthesis method, this binary photocatalyst is recommended as a sustainable photocatalyst for environmental applications.

Creep and Oxidation Behaviors of 25 wt.% Cr–Containing Nickel-Based Alloys Reinforced by ZrC Carbides

Three alloys based on nickel, rich in chromium due to their oxidation resistance at high temperature and containing ZrC carbides for their mechanical reinforcing against creep, were elaborated by foundry. After control of their as-cast microstructures, these alloys were subjected at 1100 °C to flexural creep and to oxidation in air. Script-like ZrC carbides were obtained in the interdendritic spaces, forming a eutectic compound with a part of the matrix. One of the alloys additionally contained Cr7C3 eutectic carbides. By comparison with a Ni–Cr–C reference alloy with similar contents in Cr and C, the three alloys demonstrated a much better creep resistance for the same conditions of stress and temperature. However, their oxidation rates were much greater than for the reference alloy. In contrast with the chromia-forming reference alloy, several kinds of oxides formed in the case of the three alloys, as NiCr2O4 spinel and oxides involving zirconium. A significant inward interdendritic oxidation progression was noticed for the three studied alloys. To benefit from the interesting creep resistance of these alloys for long sustainability in service, it appears necessary to significantly improve their oxidation behavior.

Ball milling transformed electroplating sludges with different components to spinels for stable electrocatalytic ammonia production under ambient conditions

Electroplating sludge is classified as hazardous waste, but it is also a potential raw resource since it contains plenty of transition metals. However, the component of electroplating sludge is unstable, which hinders recycling. This work investigates the possibility to synthesize spinels with stable catalytic performances by different electroplating sludges. The obtained catalysts are used in electrocatalytic N2 reduction to produce ammonia. As a result, CuCr2O4, ZnCr2O4, and NiCr2O4 spinels are successfully synthesized by a ball-milling and calcination method. These spinels result in ammonia yields of 7.30–8.86 μg h−1 mg−1cat. Among the three spinels, CuCr2O4 shows the highest yield of 8.86 μg h−1 mg−1cat at −0.9 V. Its faradaic efficiency reaches 0.57%. In addition, no by-product N2H4 is detected, indicating a high selectivity. The catalytic process is carried out by both distal and alternating pathways, in which metal doping and oxygen vacancy function as binding sites for N2 adsorption and reduction. Above results indicate that electroplating sludges with unstable components are feasible to produce spinels for stable electrocatalytic ammonia production under ambient temperature. This is in favor of high-value-added utilization of hazardous waste, and devotes to circular economy.

Boosting Catalyst Activity with High Valency Metal Species Through Fe Doping on Normal Spinel Nicr2o4 for Superior Water Oxidation

Boosting Catalyst Activity with High Valency Metal Species Through Fe Doping on Normal Spinel Nicr2o4 for Superior Water Oxidation

Solution Combustion Synthesis of Nanostructured NiCr2O4 Spinel and Its Catalytic Activity in CO Oxidation

Solution Combustion Synthesis of Nanostructured NiCr2O4 Spinel and Its Catalytic Activity in CO Oxidation

Dielectric relaxation and small polaron hopping transport in sol-gel-derived NiCr2O4 spinel chromite

Herein, we have synthesized NiCr2O4 chromite by the sol-gel auto-combustion route. The refined X-ray powder diffraction pattern confirmed the single-phase formation of the material, which crystallized in a cubic normal spinel structure with space group Fd3m. The complex impedance study indicated the existence of relaxation phenomenon and predicted the semiconducting nature of the material. The frequency-dependent Nyquist plot modeled by (RGBCGB) (RGQG) equivalent circuit exhibited the effects of grain and grain boundary to the electrical response of the compound over the measured temperature range of 263-393 K. The experimental AC conductivity data followed Jonscher’s double power-law behavior, and the frequency exponent profile suggested small polaron hopping as the most probable transport mechanism for the sample. The complex modulus analysis showed the non-Debye type behavior of the material. In contrast, the dielectric constant exhibited dispersion in the low-frequency regime with a large tangent loss directly related to temperature.

Designing spinel NiCr2O4 loaded Bi2O3 semiconductor hybrid for mitigating the charge recombination and tuned band gap for enhanced white light photocatalysis and antibacterial applications

This study investigates the enhancement of Bi2O3 activity as photocatalyst by loading NiCr2O4 as an effective catalyst. High-resolution transmission electron microscopy (HRTEM) analysis revealed the attachment of NiCr2O4 nanospheres on surface of sheet-like Bi2O3 nanoparticle (NPs). X-ray powder diffraction (XRD) revealed the successful fabrication of crystalline nanocomposites (NCs) with coexistence of NiCr2O4 and Bi2O3. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDAX) confirmed the elemental composition (Ni, Cr, Bi and O) with no trace of impurity. Peaks related to tetrahedral and octahedral oxygen-metal bonds were observed in fourier-transform infrared spectroscopy (FTIR). BET analyzer indicates presence of more reactive sites in NCs than individual NPs. UV–vis diffuse reflectance spectroscopy (DRS) showed shift in band gap of NiCr2O4 (2.1 eV) and Bi2O3 (2.8 eV) to 2.3 eV for NiCr2O4-Bi2O3 NCs with visible light sensitization. The life time of charge carriers in NCs was greatly improved and it was revealed by photoluminescence (PL) study. The photocatalytic performance of NiCr2O4-Bi2O3 NCs was higher with apparent kinetic constant (kapp) of 0.012 min−1 which was 4–6 times boosted than its pure individual parts (Bi2O3 = 0.003 min−1; NiCr2O4 = 0.002 min−1). The study identified that ·OH play major role in dye degradation. The NiCr2O4-Bi2O3 NCs exhibited a stable photocatalysis performance with good photostability after six cycles. In addition, NCs exhibited excellent antimicrobial activity against Escherichia coli and Bacillus subtilis. The potential usage of visible-light energy and operation simplicity prompted NiCr2O4-Bi2O3 NCs as a promising magnetically removable candidate for photodegradation of toxic organic contaminants in the aqueous solutions and for antimicrobial applications.

Structural State of High-Entropy Fe40–xNiCoCrAlx Alloys in High-Temperature Oxidation

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe40–xNiCoCrAlx (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000°C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = = 7.75 e/a). Thin continuous oxide scales containing Cr2O3 and NiCr2O4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al2O3 in the scale on the Fe30Ni25Co15Cr20Al10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe35Ni25Co15Cr20Al5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe30Ni25Co15Cr20Al10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. The hardness (HIT) and elastic modulus (E) of the cast Fe35Ni25Co15Cr20Al5 alloy are equal to 2 and 147 GPa, respectively, and decrease to 1.8 and 106 GPa after a series of long-term annealing operations. The Fe30Ni25Co15Cr20Al10 alloy shows the opposite dependence: HIT increases from 2.5 in the initial state to 3.1 GPa after annealing and E decreases from 152 to 134 GPa. This indicates that the Fe30Ni25Co15Cr20Al10 alloy is promising as a high-temperature oxidation-resistant and creep-resistant material.

A new insight into rapid oxidation of alloy 925 contaminated by oxide powder

Rapid oxidation takes place both in the laboratory and in industrial conditions when alloy 925 is contaminated by oxide powder, and the oxidation rate is much higher than normal. Herein, the rapid oxidation behavior and mechanism of alloy 925 were investigated by a series of comparison tests at 1160 °C. It is found that the oxide powder produced during the oxidation process is mainly composed of NiCr2O4 spinel, accompanied by NiO and NiMoO4. The oxide powder plays a triggering role in the rapid oxidation of alloy 925, as NiO has a strong affinity with O. A composition adjustment experiment of alloy 925 shows that rapid oxidation is the synergetic effect of Mo and Cu in the alloy. Mo and Cu easily combine to form low melting point eutectics. The formation and volatilization of MoO3 oxide can destroy the completeness of the protective oxide layer. The MoO3 flux can dissolve protective Cr2O3 and prevent the repair of the oxide layer and also promote the formation of nonprotective and easy-spall NiCr2O4 spinel. The synergetic effect of Cu and Mo in accelerating oxidation should be considered in any nickel-based alloy with a high content of Cu and Mo.

The degradation behaviour of nickel-based superalloys in the medical waste incineration plant

The present work was aimed at analysing the oxidation behaviour of three nickel-based superalloys-Superni 718, Superni 75 and Superni 750, by conducting in-situ study in the secondary chamber of a medical waste incinerator at 800–850°C for 1000 h. It was observed that among the three superalloys, Superni 75 is best suited for such an environment. This was concluded by comparing the weight change after 100 h for total 1000 h, constituting 10 thermal cycles. The morphology of the oxide scale formed on the substrate was analysed using FE-SEM. The elemental composition was obtained by EDS. The depth profiling of the scale was done using the XPS technique. The chemical composition was also examined by the XRD analysis. The superior oxidation property of Superni 75 is due to the higher Ni-Cr content. The oxidation resistance of the nickel-based superalloys in the aggressive environment of medical waste incinerator is attributed to the presence of chromia oxide-Cr2O3 and spinel NiCr2O4.

Microstructural Evolution and Oxidation Behavior of Alloy Ni-13Mo-13Cr-9W-3Fe-3Ti-2Al During Isothermal Exposure at 900 °C

The microstructure evolution and oxidation behavior of alloy Ni-13Mo-13Cr-9W-3Fe-3Ti-2Al (alloy K4208), a newly developed Ni-Cr-W-Mo-based wear-resistant superalloy, were investigated by isothermal aging at 900 °C in air. Thermodynamic calculations, microstructure observations, electron probe microanalysis (EPMA), and precise microchemical analysis were used to study the microstructure evolution and oxidation mechanism of alloy K4208. The results showed that alloy K4208 was mainly composed of a P-like phase, M6C (and M12C) carbide, γ′ phase, μ phase, and γ matrix. During the 900 °C aging, the γ′ phase coarsened into irregular shapes, the M6C (and M12C) carbide decomposed, and the μ phase dissolved into the matrix, providing abundant Cr, Mo, and W for the growth of the P-like phase. Hence, the relationship between the different phases was established by element redistribution. In addition, the oxidation of alloy K4208 was a diffusion-controlled process, leading to the formation of a stable oxide layer composed of three parts: a thin layer of NiCr2O4 spinel located on the outermost side, a continuous Cr2O3 layer decorated with TiO2 in the middle, and an internal Al2O3 layer.

Room and elevated temperature sliding wear behavior and mechanisms of additively manufactured novel precipitation strengthened metallic composites

Laser Engineered Net Shaping (LENS™) is an additive manufacturing technique used to fabricate complex 3-D components directly from a CAD model. LENS™ permits the processing of novel, tailored hybrid materials with unique microstructures spanning across multiple length scales that are not possible to achieve via conventional melt or solid-state powder processing techniques. Such novel microstructures include solid solution/precipitation strengthened metallic matrices with a refined uniform distribution of reinforcing in situ formed hard ceramic and solid lubricant phases. In this work, two such novel composites composed of Ni-18Al-11Cr-9C and Ni-14Al-8Cr-29C (at%) were processed via LENS™. The tribological properties of the composites were assessed at room temperature (RT) and 500 °C to determine the chemical and microstructural evolution during wear. Due to the variation in graphite (C) content in the composites, different microstructures of nickel aluminide and chromium carbide phases were formed during solidification that affect the dry sliding wear behavior. It was determined with SEM/EDS and Raman spectroscopy that NiO and Cr2O3 are the predominate phases on the room temperature wear surfaces, while at 500 °C, NiCr2O4 (spinel structure) becomes the main tribochemical phase, forming an oxide glaze layer at the sliding interface that further mitigates friction and wear. Overall, the increase from 9 at% to 29 at% C in the composite did not lower the dry sliding friction coefficient; however, there was a reduction in the 500 °C sliding wear rate to 7.1 × 10−6 mm3/N·m and increase in the micro- and macro-hardness of the composite to HV0.3 = 539 and HRC = 48, respectively.