NiAl2O4 Spinel Research Articles

Effect of NiO and/or TiO2 mullite formation and microstructure from gels

Polymeric and colloidal gels with a constant molar ratio of (Al+Ni and/or Ti)/Si=3/1 and various (Al/Ni and/or Ti) ratios (up to 21.42 mol% NiO+TiO2) were prepared and used to study the effect of the precursor chemical homogeneity on mullite formation processes and the resulting microstructure. Both kinds of gel precursors were preheated at 750°C for 3 h in order to obtain appropriate gel-derived glasses for further thermal processing. After annealing for several time periods at temperatures between 750 and 1500°C, differences in crystallization pathways were observed. Polymeric gels crystallized Al–Si and NiAl2O4 spinels from the amorphous form at temperatures in the range between 900 and 1000°C, depending on the amount of aluminium substitution. Mullite formation was initiated at temperatures between 1100 and 1200°C, except for the higher substituted 3:2 mullite in which it was produced at 1000°C. In constrast, γ-Al2O3 and NiAl2O4 spinel were the first crystalline phases identified at 750°C in specimens from colloidal gels, whereas mullite was formed at temperatures higher than 1200°C. In specimens with high substitution, mullite was observed at lower temperatures. Although the sequences of reaction from either kind of gel were rather different, mainly at low temperatures (as could be inferred from the chemical homogeneity attained in both gel-derived glasses), the final set of crystalline phases after long annealing at 1400°C was quite similar. Differences in the microstructure of specimens from either type of gel precursor after annealing at 1400°C concerned the size of mullite particles and the presence of secondary phases in specimens derived from colloidal precursors. © 1998 Kluwer Academic Publishers

Cation ordering in NiAl2O4 spinel by systematic row CBED

Cation ordering in NiAl2O4 spinel by systematic row CBED

Ceramic coating on ceramic with metallic bond coating

The change in structure and adhesion strength of the interface by heating in air has been investigated for a plasma- sprayed alumina coating on a ceramic substrate with a 50Ni- 50Cr alloy bond coating. A veined structure composed of NiO, NiCr 2O4, and NiAl2O4 oxides grew from the bond coating into cracks or pores in the top coating and the alumina substrate after heating at 1273 K for 20 h in air. The NiAl2O4 spinel may have formed by the oxidization of nickel, which subsequently reacted with the alumina coating or the substrate. The mechanism of the penetration of the spinel oxides into the cracks or pores is not clear. The adhesion strength of the coating is increased to about 15 MPa after heating at 1273 K for 20 h in air, compared to an as- sprayed coating strength of only 1.5 MPa.

An X‐ray diffraction study on the kinetics of the cation redistribution in the spinel NiAl2O4

AbstractA study of the relaxation kinetics in the partially inverse NiAl2O4 spinel after temperature jumps T1 T2 is reported. The change of the lattice parameter was measured by high temperature X‐ray diffraction at T2 (695–760°C) using NiAl2O4 powder samples equilibrated with NiO in air. For the temperature range of T1 under study (1100–1450°C), the kinetics can be well described by an equation which is formally equivalent to a third‐order rate law. Changes of the diffraction line widths occur during the relaxation which are due to elastic stresses, strongly dependent on the initial temperature T1. Comparison with recent results from optical spectroscopy indicates that the process observed by lattice parameter measurements is not the homogeneous exchange reaction between the two cation sublattices. The nature of the various relaxation phenomena occurring on different time scales is discussed taking concentration inhomogeneities of structure elements and elastic stress fields on different length scales into account.

Reaction Sequence in the Preparation of NiAl2O4 Spinel—Mullite Composites by Sol—Gel

NiAl2O4 spinel—mullite composites were prepared by simultaneous replacement of Al by Ti and/or Ni in 3:2 stoichiometric mullite. Specimens having nominal compositions 3(Al2‐2xNixTixO3) · 2SiO2 (x= 0, 0.025, 0.05, 0.2) and 3(Al2‐xMxO3) · 2SiO2 (M = Ni2+ or Ti4+ and x= 0.05) were synthesized by sol—gel techniques, which provide homogeneous gels in the SiO2‐Al2O3 system. Gel structures investigated by infrared (IR) spectroscopy revealed the formation of Al‐O‐Si bonds in dried gels. The reaction sequence of gel‐derived glasses, previously obtained by preheating gels at 750°3C for 3 h, was evaluated by X‐ray powder diffraction (XRD) and ultraviolet—visible (UV—vis) spectroscopy. All samples crystallized at around 1000°3C from an amorphous state, but unexpectedly the first crystalline phase was Al‐Si spinel in all aluminum‐substituted specimens; i.e., a change in the sequence of reaction with respect to the 3:2 stoichiometric mullite was produced. NiAl2O4 spinel was almost simultaneously detected. Two processes of mullite crystallization were observed. The temperature of formation of mullite was the lowest for the higher substituted sample. The microstructure of the final NiAl2O4 spinel—mullite composites found in all Ni‐containing samples after annealing for 96 h was examined by scanning electron microscopy with energy dispersive X‐ray analysis (SEM/EDX), which revealed the presence of small particles of NiAl2O4 spinel dispersed in a mullite matrix. For annealed compositions with the larger Al replacement, i.e., when x= 0.2, a small amount of very small Al2TiO5 particles was also detected by XRD and transmission electron microscopy (TEM).

Structure and composition of oxidized aluminum on NiO(100)

Aluminum was deposited on stoichiometric NiO(100) in 5×10−6 Torr O2 at substrate temperatures of 250 and 800 °C, and the resulting film interfaces were studied by photoemission [x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] and electron diffraction [reflection high-energy electron diffraction (RHEED)]. At 800 °C, RHEED patterns indicate that the growing overlayer interacts with the NiO(100) substrate forming a NiAl2O4 spinel phase. This observation is further supported by XPS and UPS results where peak shapes and relative peak positions correspond to values reported for thick NiAl2O4 films. During film growth at 250 °C, the underlying NiO RHEED pattern becomes diffuse due to formation of an amorphous overlayer. XPS and UPS results indicate that the amorphous film is Al2O3 and that little interaction with the NiO substrate occurs. Postdeposition annealing of the amorphous Al2O3 film to 800 °C in O2 results in a strong reaction at the interface and film crystallization to the NiAl2O4 spinel phase. These results demonstrate that kinetic factors are significant in determining interactions in this system.

Determination of Cation Distribution in ZnFe2O4, NiFe2O4 and NiAl2O4 Spinels by An In-house Anomalous X-ray Scattering Method.

An in-house anomalous X-ray scatterig (AXS) method has been done for determiningcation distribution in ZnFe2O4, NiFe2O4 and NiAl2O4 spinels using the anomalous dispersion effect near the K absorption edges of Zn and Ni. When introduced the ratio (x) of the number of divalent cations of M element, MA, residing in the tetrahedral A-site to the total number of M element, x=MA/Mtotal, the measured intensity ratios of three reflection peaks with two energies close to the K edge of Zn or Ni can be quantitatively explained only by assigning the case where ZnFe2O4 is the normal type (x=1.0) and NiFe2O4 is the inverse type (x=0.0) spinel structure. On the other hand, the results for NiAl2O4 suggests that 15% of Ni2+ cations occupy the tetrahedral A-site (x=0.15) and the rest are octahedrally coordinated. The usefulness of the in-house AXS method is rather surprisingly well-recognized, particularly for obtaining the cation distribution in crystalline materials containing two elements of nearly the same atomic number.

An ion microprobe study of the microchemistry of Ni‐base superalloy‐Al2O3 metal‐matrix composites

SUMMARYThe chemical microstructure of Ni‐base superalloy/Al2O3 metal‐matrix composites (MMCs) has been studied by scanning ion microprobe microanalysis, using the secondary ion mass spectrometry (SIMS) technique. The MMCs were fabricated using the transient‐liquid‐phase bonding (TLP) process, with B‐doped superalloy powder as an interlayer. Boron was found to diffuse rapidly throughout the matrix to form boride phases, mostly at the grain boundaries in the matrix. These borides contain excess Cr (also Mo, Si, W) in comparison with the Ni alloy‐matrix, but are depleted in Ni (also in Al and Co). Carbides form at the grain boundaries as thin platelets and inside the grains as fine particles. Chemical reaction occurs between the sapphire fibre and the matrix; formation of NiAl2O4 spinel at the interface is suggested. This interface reaction layer is friable and parts of it peel off during consolidation to become inclusions in the matrix near the fibre/matrix interface.

Effects of Cr+ ion implantation on the oxidation of Ni3Al

Ni3Al samples were implanted with different doses of 150 keV Cr+ ions to modify the surface region. The high temperature oxidation behavior was tested. The surface layer structure was investigated by AES, TEM, XRD, and optical microscope before and after the test. The experimental results show that chromium ions turn a small amount of ordered superlattice Ni3Al phase into a disordered Ni–Al–Cr phase. Also there is a bcc chromium phase in the implanted sample. Implanted Ni3Al alloy has better oxidation resistance than the unimplanted one at 900 °C. The oxide layer is of a multilayer structure after 50 h oxidation, composed of a NiO inner layer, Cr2O3, spinel NiAl2O4 intermediate layers, and an α–Al2O3 external layer at the oxide/air interface. The α-Al2O3 and Cr2O3 are independent scale-like layers. The two protective layers improve the oxidation resistance significantly. The effects of implanted elements and possible reaction mechanisms are discussed.

Catalytic behaviour of NiAl2O4 spinel upon hydrogen treatment

The effect of reduction on the catalytic activity and selectivity of nickel aluminate spinel has been reported using the 2-propanol decomposition reaction. The unreduced catalyst showed only dehydration activity. When reduced in hydrogen at different temperatures starting from 200 °C, dehydrogenation activity was observed. After reduction at 450 °C, the activity completely transformed into dehydrogenation, while the spinel structure remained unchanged. The unreduced and reduced catalysts were characterized by X-ray diffraction, temperature-programmed reduction, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The mechanism for the decomposition is discussed in terms of the coordination of aluminium ion and reducibility of nickel.

Oxidation of a zirconia-toughened Alumina Fiber-Reinforced Ni3Al Composite

A Ni3Al composite reinforced with zirconia-toughened alumina fiber, PRD-166 fiber, was produced by pressure casting. The thermochemical stability of the composite at 1100 °C in vacuum and air was investigated by optical and transmission electron microscopy and energy- dispersive spectroscopy (EDS). Vacuum annealing resulted in precipitation of needle-shaped ZrB and cuboid-shaped Cr-rich, tentatively identified as Cr7C3, particles. Annealing in air led to the precipitation of large ZrO2 particles at the fiber/matrix interface and fine ZrO2 platelets in the matrix. A thin layer of A12O3 was observed to cover the fiber/matrix interface and to envelop the ZrO2 platelets. Diffusion of Ni through the A12O3 layer and its oxidation and sub- sequent reaction with A12O3 resulted in the formation of NiAl2O4 spinel around the ZrO2 particles at the fiber/matrix interface. Further annealing resulted in the formation of a thin layer of Cr2O3 on the A12O3 layer and precipitation of A12O3 and Cr2O3 particles within the matrix. These particles subsequently reacted with NiO to form Ni(AlxCr1-x)2O4grains. Diffusion of oxygen through the fiber is believed to be responsible for the rapid oxidation of the composite.

Characterization of dispersion and surface states of NiO/γ-alumina and NiO/La2O3–γ-alumina catalysts

A series of NiO/γ-alumina and NiO/La2O3–γ-alumina catalysts prepared by impregnation have been investigated by X-ray diffraction, diffuse reflectance spectroscopy and temperature-programmed reduction. For the NiO/γ-alumina catalysts with low nickel oxide content, a strong interaction between NiO and γ-alumina leads to the diffusion of Ni2+ ions into vacant surface sites of the support to form surface spinel NiAl2O4 and thus the reducibility of NiO was decreased. At high nickel oxide contents, NiO crystal appears after the surface vacancies have been filled. In this case, the counter-diffusion of Ni2+ and Al3+ ions at the interface was observed during calcination.

Metal-Oxide Interfacial Structures Produced By Internal Oxidation

ABSTRACTInterfaces in Cu/MgO, Pd/MgO, Pd/Al2O3, Ni/NiAl2O4 and Ni/Al2O3 systems produced by internal oxidation have been studied by transmission electron microscopy. For the Cu/MgO system, the MgO particles, with a cube-on-cube orientation with respect to Cu matrix, are faceted with principal faces parallel to {111} lattice planes of Cu and MgO. For the Pd/MgO system, the MgO particles, with a cube-on-cube orientation with Pd matrix, are faceted with interfaces parallel to the {100} and {111} lattice planes of MgO and Pd. Additional plate-like MgO particles with main facets parallel to {111} lattice planes possess a twin orientation relationship with the Pd matrix. Interfaces in Cu/MgO and Pd/MgO systems are all partially coherent with interfacial misfit dislocations. For the Pd/Al2O3 system, various transition oxide phases such as η, δ, and θ-Al2O3 and stable α-Al2O3 phase have been observed. The [1100] direction of α-Al2O3 is parallel to the [110] direction of Pd and the (0001) plane of α-Al2O3 is parallel or nearly parallel to the (110) plane of Pd. The NiAl2O4 spinel phase and Al2O3 phases are formed in Ni-Al alloys under two different oxidation conditions. The NiAl2O4 particles have a plate-like morphology with a cube-on-cube orientation relationship with the Ni matrix, while Al2O3 particles are randomly oriented.

Effect of the reduction temperature on the formation and activity of bimetallic Ni-Tc catalysts

The effect of the temperature on the formation, surface state, and catalytic activity in the reactions of dehydrogenation of cyclohexane and dehydrocyclization of n-hexane by Ni-Tc/γ-Al2O3 mono- and bimetallic catalysts was investigated. TcO2, NiCl2, and metal phases, and at a high temperature (500–700‡C), NiAl2O4 spinel and Ni-Tc clusters, were found on the surface of all of the catalysts. It was shown that the maximum activity is observed in reduction of monometallic catalysts at 500‡C and bimetallic catalysts at 700–800‡C. Synergism appeared in the bimetallic catalysts due to the formation of Ni-Tc clusters.

Reaction couples of ceramic thin films prepared by CVD

Solid-state reactions have traditionally been studied in the form of diffusion couples. This ‘bulk’ approach has been modified, for the specific case of the reaction between NiO and Al2O3, by growing NiAl2O4 (spinel) from electron-transparent Al2O3 TEM foils which had been exposed to NiO vapor at 1415°C. This latter ‘thin-film’ approach has been used to characterize the initial stage of spinel formation and to produce clean phase boundaries since further TEM preparation is not required after the reaction is completed. The present study demonstrates that chemical-vapor deposition (CVD) can be used to deposit NiO particles, with controlled size and spatial distributions, onto Al2O3 TEM specimens. Chemical reactions do not occur during the deposition process, since CVD is a relatively low-temperature technique, and thus the NiO-Al2O3 interface can be characterized. Moreover, a series of annealing treatments can be performed on the same sample which allows both Ni0-NiAl2O4 and NiAl2O4-Al2O3 interfaces to be characterized and which therefore makes this technique amenable to kinetics studies of thin-film reactions.

High temperature ligand field spectra in spinels: Cation disorder and cation kinetics in NiAl2O4

AbstractResults are reported of optical transmission experiments on the spinel NiAl2O4 that have been made at temperatures up to 1400°C. The spectra are discussed, and analyzed in relation to the temperature dependence of the distribution of cations on the two cation sublattices. The kinetics of cation sublattice exchange is studied by means of temperature jump experiments performed under in‐situ conditions in the temperature range between 600°C and 700°C.

Calorimetric study of the stability of spinelloids in the system NiAl2O4-Ni2SiO4

Enthalpies of solution in molten 2 PbO · B2O3 at 974 K were measured for four spinelloids, phases I (0.75 NiAl2O4 · 0.25 Ni2SiO4), II (0.60 NiAl2O4 · 0.40 Ni2SiO4), III and IV (0.50 NiAl2O4 · 0.50 Ni2SiO4) in the system NiAl2O4 · Ni2SiO4. The enthalpies (in cal per 4-oxygen mol) of formation from NiAl2O4 and Ni2SiO4 spinels are: phase I, 945±366; phase II, 1072±360; phase III, 2253±390; phase IV, 3565±544. Using these enthalpy data in combination with phase relations at high pressure at 1373 K, positive entropies of formation of the spinelloids from NiAl2O4 and Ni2SiO4 spinels were estimated (in cal mol−1 K−1): phase I, 1.2; phase II, 1.5; phase III, 2.0–2.3; phase IV, 3.0–3.1. The thermochemical data obtained above suggest that the spinelloids are “entropy-stabilized” phases with partially disordered cation distributions. The configurational entropies of the spinelloids were calculated based on the observed cation distribution in each spinelloid phase. The positive entropies of formation of the spinelloids from the spinel endmembers are due primarily to the configurational entropies although small positive vibrational entropy changes may also exist.

New orthorhombic phases on the join NiAl2O4 (spinel analog)-Ni2SiO4 (olivine analog): Stability and implications to mantle mineralogy

Three new crystalline phases differing in Si/Al ratio have been synthesized from compositions along the join NiAl2O4-Ni2SiO4. Four reversible univariant equilibria involving these new phases plus Ni2SiO4 (olivine) have been located within the P-T region studied (1 atm–40 kb, 1000–1700° C); an invariant point occurs near 22 kb, 1150°C.

Discussion of “Equilibrium Cation Distribution in NiAl2O4, CuAl2O4, and ZnAl2O4 Spinels”

Journal of the American Ceramic SocietyVolume 56, Issue 2 p. 106-107 Discussion of “Equilibrium Cation Distribution in NiAl2O4, CuAl2O4, and ZnAl2O4 Spinels” A. NAVROTSKY, A. NAVROTSKYSearch for more papers by this author A. NAVROTSKY, A. NAVROTSKYSearch for more papers by this author First published: February 1973 https://doi.org/10.1111/j.1151-2916.1973.tb12372.x-i1Citations: 5 The writer is with the Department of Chemistry, Arizona State University, Tempe, AZ 85281. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume56, Issue2February 1973Pages 106-107 RelatedInformation

Solid Reactions of Egyptian Kaolin towards Ni(II). II

AbstractThe solid reactions between Kaolin of particle size 37 and 74μ and NiO in different mole ratios were performed at two temperatures, viz., 900 and 1100°C. The effect of the three parameters: concentration, particle size and temperature was studied spectrophotometrically and by x‐ray diffractometry. The identified resulting phases are mainly the green spinel NiAl2O4, together with free SiO2 and mullite Al6Si2O13.