Nickel Chromite Research Articles

Ceramic Black Pigments Based on Chromium-Nickel Spinel NiCr2O4

The possibility of obtaining black pigment based on nickel chromite (NiCr2O4) is examined. The morphological, granulometric, x-ray structural, and optical characteristics of synthesized crystalline powders of chromium nickel spinel are investigated. Upon spontaneous crystallization at temperature 950°C nickel chromite crystallizes in the spinel structure Fd3m with crystals ranging in size from 1.29 to 84 μm (predominantly in the form of an octahedron). The diffuse reflection spectra showed high emissivity of NiCr2O4: the diffuse reflection coefficient ranges from 2.65 to 4.81% in the range 320 – 1080 nm. Black glazes based on nickel chromite were obtained; the optimal weight content of the pigment is 6 – 8%.

Effect of cobalt substitution on the magnetic properties of nickel chromite

It is of interest to study the magneto-structural coupling in geometrically frustrated antiferromagnets, where structural distortion elevates the ground state degeneracy, leading to a long-range magnetic order. In this regard a cubic spinel compound of the form AB2O4 is currently drawing much attention, where A refers to tetrahedral and B to octahedral sites. In the particular case of NiCr2O4 the material undergoes several structural phase transitions associated with the magnetic ordering. It is therefore necessary to study the magnetic behaviour of NiCr2O4 by substituting either A or B sites, or both systematically with suitable cations. The current work therefore aims at the modification of magnetic properties of NiCr2O4 by doping with Co2+ at A sites. In order to achieve the afore mentioned, (Ni1−xCox)Cr2O4 (0 ≤ x ≤ 1) were prepared using chemical co-precipitation techniques. X–ray diffraction (XRD) results indicate that the samples are in the expected phase without any trace of Cr2O3 impurities after calcination. Transmission electron microcopy (TEM) analyses of these samples show that the particles are mostly bi-pyramidal in shape, with sizes ranging from 50 nm to 100 nm. In the present study the ferrimagnetic transition temperatures (TC) of the various samples were determined utilizing magnetization as function of temperature measurements. TC for NiCr2O4 and CoCr2O4 was determined to be 82.4 ± 0.8 K and 99.5 ± 0.5 K, respectively. These values are higher than those previously reported in the literature for both these compounds. Substitution of Ni by Co, results in an increase in the TC, giving values of 89.2 ± 0.7 K and 90.6 ± 0.9 K for (Ni0.5Co0.5)Cr2O4 and (Ni0.25Co0.75)Cr2O4, respectively. The (Ni0.5Co0.5)Cr2O4 sample demonstrated a high coercivity of 3.6 ± 0.1 T and a shift in the hysteresis loop observed under field cooled measurement, not previously reported in literature. X–ray photoelectron spectroscopy (XPS) of (Ni0.5Co0.5)Cr2O4 suggests that the oxidation states of Ni and Co are 2+, while that of Cr is 3+. In order to investigate the local structure around the cations, low temperature extended x–ray absorption fine structure (EXAFS) measurements were performed. From EXAFS it is confirmed that no redistribution of A and B site cations occur at low temperatures. Present findings demonstrate that the magnetic properties of NiCr2O4 can easily and dramatically be modified by doping Co2+ at A sites.

Development of Chemical Decontamination Process Based on Ozone for System Surfaces with Chromium Containing Oxides

Chromite or chromium containing oxides are formed as a protective oxide film on the stainless steel surface of heat transport systems. The chemical dissolution of these passive oxide films forms an important step in decontamination formulation development for water-cooled nuclear reactor systems. Dissolved ozone as a reagent was tested for effective chemical dissolution of Fe3+ substituted in nickel chromite and individual component oxides. The study showed the importance of the solution pH and temperature on the dissolution kinetics of Cr2O3, NiO, and NiFexCr2-xO4. Neutral water pH or 0.04 mM OH− were better for achieving a high dissolution rate for chromium containing oxides compared to acidic (2.5 mM H+) or alkaline conditions. In an acidic condition, the release of nickel from NiO or nickel chromite was more in the ozone medium compared to a high pH condition. Substitution of Fe3+ in nickel chromite affected the dissolution behavior in the ozone medium. The dissolution of Fe3+ substituted in nickel chromite showed a small increase in the dissolution rate constant with up to composition x = 0.4, and further increase in the Fe3+ composition in the oxide lattice decreased the dissolution rate constant.

Facile mechanical milling synthesis of NiCr2O4 using novel organometallic precursors and investigation of its photocatalytic activity

Herein, NiCr2O4 nanostructures were successfully prepared via a facile and solvent-less ball milling method using new set of organometallic starting reagents including Ni(Sal)2 as nickel source and [Cr(en)3]Cl3.3H2O as chrome source. Effect of ball mill time, speed of ball mill, mass ratio of ball to powder and process control agent on morphology of as-prepared NiCr2O4 nanostructures was well studied. The morphology and microstructure of as-synthesized products were characterized by XRD, SEM, FTIR and EDX. Finally, the photocatalytic activity of nickel chromite nanostructures were studied by performing the photocatalytic degradation of an azo dye (Acid Red 88) at different irradiation time. The effect of irradiation time on the degradation of the azo dye was evaluated and the results showed that more than 99% of the dye was degraded in 150 min of irradiation. The pseudo-first-order kinetic models were used and the rate constants were evaluated with pseudo first order rate constants of 2.47 × 10− 2 min− 1. Also, the effect of particle size and morphology on the photocatalytic activity was evaluated.

Simple morphology-controlled fabrication of nickel chromite nanostructures via a novel route

Pure nickel chromite (NiCr2O4) nanostructures were prepared via a new coprecipitation–calcination route by using [Ni(en)2(H2O)2](NO3)2 and [Cr(en)3]Cl3·3H2O as novel precursors. The as-prepared nickel chromite nanostructures were characterized by energy dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). Results of this study demonstrate that particle size and morphology of the nickel chromite can be controlled by setting main preparation parameters such as the precipitator, the speed of the reaction stirrer, reaction time, surfactant, reaction temperature and calcination temperature. Nickel chromite nanostructures with different particle size and morphology were successfully synthesized. The magnetic properties of as-prepared nickel chromite nanostructures were also investigated with vibrating sample magnetometer (VSM).

FACILE SYNTHESIS OF NICKEL CHROMITE NANOSTRUCTURES BY HYDROTHERMAL ROUTE FOR PHOTOCATALYTIC DEGRADATION OF ACID BLACK 1 UNDER VISIBLE LIGHT

NiCr2O4 normal spinel nanostructures were prepared via hydrothermal treatment at 180 °C for 12 h in the presence of cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and poly vinylpyrrolidone-25000 (PVP-25000) as capping agents and subsequent calcination process at 500 °C for 3 h . In this method, [Ni(en)2(H2O)2](NO3)2 and [Cr(en)3]Cl3.3H2O used as precursors and not utilized any alkaline or precipitating agent. Detailed characterization of the as-prepared nanostructures were carried out by Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS). XRD revealed the formation of pure nickel chromite spinel phase and SEM showed the formation of uniform sphere-like nanoparticles. Furthermore, the photocatalytic degradation of acid black 1 as diazo dye used in textile and dyeing water pollutants was Investigated.

Temperature-dependent vibrational spectroscopic and X-ray diffraction investigation of nanosized nickel chromite

The nanocrystalline nickel chromite (NiCr2O4) with particle size of ∼20nm was prepared by auto-combustion method. The nanocrystals were characterized by powder X-ray diffraction, vibrational spectroscopy and magnetic measurements. The expected structural phase transitions (cubic–tetragonal–orthorhombic) were studied by methods of temperature-dependent X-ray powder diffraction and vibrational spectroscopy. The evolution of the Raman spectra and X-ray diffraction patterns collected from 350K down to 4K confirmed the cubic-to-tetragonal distortion at ∼250K, whereas the tetragonal-to-orthorhombic transition was not confirmed in the nanocrystalline sample.

Structural and paramagnetic behavior of spinel NiCr2O4 nanoparticles synthesized by thermal treatment method: Effect of calcination temperature

Spinel nickel chromite nanoparticles were synthesized using a simple thermal treatment method. The effect of calcination temperatures on the final properties of obtained materials was carefully examined using various characterization techniques.The infrared spectra of nickel chromite (NiCr2O4) revealed the characteristic bonds of metal–oxygen for NiO and CrO bands around 600 and 470cm−1, respectively. The powder X-ray diffraction patterns exhibited the formation of normal spinel phase of NiCr2O4 in the calcination process at temperature between 550 and 850°C. From transmission electron micrographs, nanosized particles with average size of ~7–64nm were observed at calcination temperatures of 550–850°C, respectively. The calcined samples at 750 and 850°C exhibited paramagnetic behavior with g-factor values of 1.92 and 2.15, peak-to-peak line width of 25.59 and 117.02Oe and resonance magnetic field of 342.04 and 306.49Oe, respectively. Variation in the value of g-factor, peak-to-peak line width and resonance magnetic field can be attributed to the dipole–dipole and super exchange interactions.

Ceramic nanocomposites based on oxides of transition metals for ionistors

Low-temperature synthesis methods are used to produce nanoceramic materials for electrodes of the following ionistors: (ZrO2)0.6(In2O3)0.4, praseodymium cobaltite, as well as neodymium, lanthanum, and nickel chromites; they operate in the presence of an ion-conducting phosphorosilicate separator membrane and phosphate impregnation. Film electrodes of ionistors are fabricated that consist of nanocrystalline oxide materials deposited as a thin film on a porous electroconductive metal substrate, i.e., foamed nickel. The MnO2-foamed nickel electrode has a specific capacity of 45.0 F g−1, which is compared with that of industrial supercapacitors.

Evaluation of cation influence on the formation of M(II)Cr2O4 during the thermal decomposition of mixed carboxylate type precursors

This paper reports an investigation regarding the influence of the cation M(II) (M = Zn, Ni, Mg) on the formation of MCr2O4 by thermal decomposition of the corresponding M(II),Cr(III)-carboxylates (precursors) obtained by redox reaction between the corresponding metal nitrates and 1,3-propanediol. The decomposition products at different temperatures have been characterized by FT-IR spectroscopy and thermal analysis. Thus, we have evidenced that by thermal decomposition of the studied precursors in the range 250–300 °C, different amorphous oxidic phases mixtures form depending on the nature of metalic cation: (Cr2O3+x + ZnO) (Cr2O3+x + Ni/NiO) and (Cr2O3+x+MgO). In case of M = Zn, around 400 °C when the transition Cr2O3+x to Cr2O3 takes place, zinc chromite nuclei form by the interaction ZnO with Cr2O3. In case of M = Ni, due to the partial reduction of Ni(II) at Ni(0) during the thermal decomposition of the precursor the formation of nickel chromite by the reaction NiO + Cr2O3 is shifted toward 500 °C, when Ni is oxidized at NiO. The thermal evolution of the mixture (MgO + CrO3) is different due to the formation as intermediary phase of MgCrO4, which decomposes to MgCr2O4 around 560 °C. In order to investigate the chromites formation mechanism, we have studied the mechanical mixtures of single oxides obtained from the corresponding carboxylates. These mixtures (MO + Cr2O3) have been annealed at 400, 500, and 600 °C to study the evolution of the crystalline phases. It results in the prepared mixture behaving different from the mixtures obtained by thermal decomposition of the binary M(II),Cr(III)-carboxylates, recommending our synthesis method for obtaining binary oxides.

Studies regarding the formation from metal nitrates and diol of NiM 2 III O4 spinels, inside a silica matrix

The present study deals with preparation and characterization of spinel mixed oxide systems NiM2IIIO4, where MIII = FeIII, CrIII. In order to obtain 50% NiFe2O4/50% SiO2 and 50% NiCr2O4/50% SiO2 nanocomposite, we have used a versatile route based on the thermal decomposition inside the SiO2 matrix, of some particular precursors, coordination compounds of the involved MII and MIII cations with dicarboxylate ligands. The ligands form in the redox reaction between metal nitrates mixture and 1,3-propanediol at the heating around 140 °C of the gels (tetraethylorthosilicate–metal nitrates–1,3-propanediol–water). The as-obtained precursors, embedded in silica gels, have been characterized by FT-IR spectrometry and thermal analysis. Both precursors thermally decompose up to 350 °C leading to the formation of the corresponding metal oxides inside the silica matrix. X-ray diffraction of the annealed powders have evidenced the formation of NiFe2O4 starting with 600 °C, and NiCr2O4 starting with 400 °C. This behavior can be explained by the fact that, by thermal decomposition of the Fe(III) carboxylate at 300 °C, the spinelic phase γ-Fe2O3 is formed, which interacts with the NiO, forming the ferrite nuclei. By thermal decomposition of chromium carboxylate, a nonstoichiometric chromium oxide (Cr2O3+x) is formed. In the range 380–400 °C, Cr2O3+x turns into Cr2O3 which immediately interacts with NiO leading to the formation of nickel chromites nuclei inside the pores of silica matrix. Both spinels have been obtained as nanocrystalites homogenously dispersed as resulted from XRD and TEM data.

Study on the Magnetic Behavior of In-doped Nickel Chromite by Using M?ssbauer Spectroscopy

NiCr1.9−x Fe0.1InxO4 (x = 0.0, 0.1, 0.3, and 0.5) was prepared by using a sol-gel method. The crystal structure at room temperature was determined to be a normal cubic spinel with space group Fd3m. An analysis of the x-ray diffraction patterns was performed using a Rietveld refinement method while the Bragg RB and RF factors were below 5%. The magnetic Neel temperature decreased from 150 K to 77 K with increasing In concentration, which was confirmed by zero-fieldcooled (ZFC) magnetization at applied fields under 100 Oe and by Mossbauer spectra measured at various temperatures. Magnetic hysteresis loops of the samples at 77 K showed drastically increasing magnetization and decreasing coercivity with increasing In concentration. The Mossbauer spectra of the samples were measured at various temperatures ranging from 4.2 to 295 K. The isomer shift value showed that the charge states of the iron ions are ferric. The Mossbauer spectra showed two magnetic phases with two different magnetic spin direction sites for the Cr ion state. Mossbauer spectra below 77 K showed 6 sharp absorption lines and the linewidth became broader with increasing temperature, which indicates a Jahn-Teller distortion and relaxation.

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni2+/Cr3+ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni2+/Cr3+ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ∼400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 A. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 A). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 A is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni0 crystallites with a size of ∼5.5 nm and a specific surface area of ∼7.0 m2 g−1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO2. The catalysts with the ratio Ni2+/Cr3+ = 1/(2−3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.

A detailed TEM and SEM study of Ni-base alloys oxide scales formed in primary conditions of pressurized water reactor

Abstract The oxide film formed on nickel-based alloys in pressurized water reactors (PWR) primary coolant conditions (325 °C, aqueous media) is very thin, in the range of 1–100 nm thick, depending on the surface state and on the corrosion test duration. The nature and the structure of this scale have been investigated by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). TEM observations revealed an oxide layer divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni (1− x ) Fe x Cr 2 O 4 ). Moreover, nodules of Cr 2 O 3 , with a size about 5 nm, were present at the interface between this spinel and the alloy. No chromium depletion was observed in the alloy, at the alloy/oxide interface. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni (1− z ) Fe (2+ z ) O 4 ) resulting from precipitation phenomena. SEM and TEM observations showed a link between the nucleation and/or the growth of crystallites of nickel ferrite and the crystallographic orientation of the substrate. A link between the presence of surface defects and the nucleation of the crystallites was also underlined by SEM observations. Partially hydrated nickel hydroxide, was also observed by TEM in the external scale. Based on these results, some considerations about the mechanism of formation of this oxide layer are discussed.

Magnetic Properties and Crystalline Transition for the NiCr1.7Fe0.3O4

We have studied the temperature dependent magnetic properties and crystalline phase transitionn in small amount Fe doped nickel chromite. The Crystalline structure of NiCr 1.7 Fe 0.3 O₄ is spinel cubic (Fd-3m) structure with a lattice constant ^a0 = 8.317 A at room temperature. The magnetic Neel temperature (T N ) of the Fe doped nickel chromite sample is determined to be 250 K. The Mossbauer spectra exhibit that there are two magnetic phases with the two different sites for the Cr 3+ ions. The spectrum at 4.2 K is fitted to two magnetic components of the magnetic hyperfine fields Hhf = 496 and 485 kOe. From the spectrum at 295 K, the electric quadrupole splittings are observed with large values of 0.49 and 0.50 ㎜/s, respectively. The values of the isomer shifts at all temperature ranges show that the Fe ions are ferric states. We are suggested that the dynamic Jahn-Teller distortion and anisotropic magnetic relaxation effects due to the crystalline phase transition.

Corrosion study of heat exchanger tubes in pressurized water cooled nuclear reactors by conversion electron Mössbauer spectroscopy

57Fe-conversion electron Mossbauer spectroscopy (CEMS) — a sensitive tool to analyze the phase composition of corrosion products on the surface of stainless steel — was applied to study real specimens from the Paks Nuclear Power Plant, Hungary. The primary circuit side of the heat exchanger tubes was studied on selected samples cut out from the steam generators during regular maintenance. Mostly Cr-and Ni-substituted magnetite, amorphous Fe-oxides/oxyhydroxides as well as the signal of bulk austenitic steel of the tubes were detected. The level of Cr-and Ni-substitution in the magnetite phase could be estimated from the Mossbauer spectra. It is suggested that Cr-Ni substitution occurs simultaneously so that the inverse spinel structure of magnetite is preserved up to a certain limit which appears to be roughly at [Fe3+]tet[Fe2+ 1/4Ni2+ 3/4Fe3+ 1/4Cr3+ 3/4]octO4. Further decrease of the iron content of this phase results in the formation of nickel chromite of regular spinel structure, with very low Fe content. This transformation may be responsible for the hybrid structure of the protective oxide layer, being substantially accelerated by previously performed, factory developed and proposed AP-CITROX decontamination cycles.

Thermal Decomposition of Crystalline NiII−CrIII Layered Double Hydroxide: A Structural Study of the Segregation Process

A structural study of the thermal evolution of Ni(0.69)Cr(0.31)(OH)(2)(CO(3))(0.155) x nH(2)O into NiO and tetragonal NiCr(2)O(4) is reported. The characteristic structural parameters of the two coexisting crystalline phases, as well as their relative abundance, were determined by Rietveld refinement of powder x-ray diffraction (PXRD) patterns. The results of the simulations allowed us to elucidate the mechanism of the demixing process of the oxides. It is demonstrated that nucleation of a metastable nickel chromite within the common oxygen framework of the parent Cr(III)-doped bunsenite is the initial step of the cationic redistribution. The role that trivalent cations play in the segregation of crystalline spinels is also discussed.

Thermodynamic properties of nickel chromite (NiCr 2 O 4 ) based on adiabatic calorimetry at low temperatures

The hitherto unknown low-temperature heat capacity of nickel chromite (NiCr2O4) was measured between 8 and 381 K using adiabatic calorimetry, and some thermochemical functions [CP(T), S(T), S°298, H(T)−H(0)] were derived from the results. The standard entropy (S°298=140.0 ± 0.3 J mol−1 K−1) for nickel chromite was calculated from the results. Our calorimetric measurements indicate three major anomalies in the heat-capacity curve at temperatures between 8 and 381 K. A short literature review indicates that two of these anomalies can be accounted for, whereas an anomaly peaking at 29 K has not been reported previously.

Formation of graded structures under high-temperature oxidation conditions with surface light-heat treatment

Complex alloying of low-carbon steel with treatment by artificial concentrated solar radiation (CSR) in air using a LaB6-based composite is studied. The distribution of elements through the thickness of the alloyed layer along the axis of CSR entry and at the periphery of the working zone is established. On the basis of electron-probe microanalysis, x-radiographic, and metallographic data it is established that as a result of high-temperature oxidation of the composite, formation of new phases, and convective mass transfer under CSR conditions, a graded structure forms at the steel surface in the form of a dense three-layer oxide film. Its outer layer contains lanthanum and nickel chromites that provide high resistance to marine corrosion.

The low-temperature tetragonal phase of NiCr2O4

The title compound, normal spinel nickel chromite, NiCr 2 O 4 , undergoes a cubic to tetragonal phase transition at low temperature. The crystal structure of the tetragonal phase at 200K was determined by single-crystal X-ray diffraction data. Details of the crystal information, including anisotropic displacement parameters, are reported.