Mixture Of CeO2 Research Articles

Atomistic insights from DFT calculations into the catalytic properties on ceria-lanthanum clusters for methane activation.

Improving the catalytic performance of materials based on cerium oxide (CeO2) for the activation of methane (CH4) can be achieved through the following strategies: mixture of CeO2 with different oxides (e.g., CeO2-La2O3) and the use of particles with different sizes. In this study, we present a theoretical investigation of the initial CH4 dehydrogenation on (La2Ce2O7)n clusters, where n = 2, 4, and 6. Our framework relies on density functional theory calculations combined with the unity bond index-quadratic exponential potential approximation. Our results indicate that chemical species arising from the first dehydrogenation of CH4, that is, CH3 and H, bind through the formation of C-O and H-O bonds with the clusters, respectively. The coordination of the adsorption site and the chemical environment plays a crucial role in the magnitude of the adsorption energy; for example, species adsorb more strongly in the low-coordinated topO sites located close to the La atoms. Thus, it affects the activation energy barrier, which tends to be lower in configurations where the adsorption of the chemical species is stronger. During CH4 dehydrogenation, the CH3 radical can be present in a planar or tetrahedral configuration. Its conformation changes as a function of the charge transference between the molecule and the cluster, which depends on the CH3-cluster distance. Finally, we analyze the effects of the Hubbard effective parameter (Ueff) on adsorption properties, as the magnitude of localization of Ce f-states affects the hybridization of the interaction between the molecule and the clusters and hence the magnitude of the adsorption energies. We obtained a linear decrease in the adsorption energies by increasing the Ueff parameter; however, the activation energy is only slightly affected.

Resolving a structural issue in cerium-nickel-based oxide: a single compound or a two-phase system?

CeNiO3 has been reported in the literature in the last few years as a novel LnNiO3 compound with promising applications in different catalytic fields, but its structure has not been correctly reported so far. In this research, CeNiO3 (RB1), CeO2 and NiO have been synthesized in a nanocrystalline form using a modified citrate aqueous sol-gel route. A direct comparison between the equimolar physical mixture (n(CeO2) : n(NiO) = 1 : 1) and compound RB1 was made. Their structural differences were investigated by laboratory powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS) detector, and Raman spectroscopy. The surface of the compounds was analyzed by X-ray photoelectron spectroscopy (XPS), while the thermal behaviour was explored by thermogravimetric analysis (TGA). Their magnetic properties were also investigated with the aim of exploring the differences between these two compounds. There were clear differences between the physical mixture of CeO2 + NiO and RB1 presented by all of these employed methods. Synchrotron methods, such as atomic pair distribution function analysis (PDF), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), were used to explore the structure of RB1 in more detail. Three different models for the structural solution of RB1 were proposed. One structural solution proposes that RB1 is a single-phase pyrochlore compound (Ce2Ni2O7) while the other two solutions suggest that RB1 is a two-phase system of either CeO2 + NiO or Ce1-xNixO2 and NiO.

Effect of phosphate post-treatment on corrosion behavior of cerium-based conversion coated Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca (wt.%) alloys

The present study aims to investigate the effect of cerium-based conversion coating and phosphate post-treatment on the corrosion behavior of Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca (wt.%) alloy (WZ44) in chlorinated solution. In this regard, as-cast and forged WZ44 alloy was subjected to cerium salt bath treatment at ambient followed by NaH2PO4 solution at 85 °C. The morphological evolution and chemical composition of the composite coating were examined using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), two and three-dimensional surface topography, and X-ray photoelectron spectroscopy (XPS) reveal the formation of complex phase mixture of CeO2, Ce2O3, CePO4, Mg(OH)2, and unknown hydrated compounds. The as-prepared cerium conversion coating possesses nodular CeO2 precipitates with abundant mud-cracks features originating due to hydrogen evolution and film dehydration-induced tensile stress. However, phosphate treatment develops a relatively smoother and compact coating with minimum surface roughness and conversion of nodular CeO2 precipitates into CePO4, albeit with few fine cracks. The tape adhesion and scratch test disclose that coating delamination predominant in cerium conversion coated specimens was reduced drastically by phosphate treatment with ∼16–23 % improvement in scratch hardness. Corrosion in terms of mass loss and potentiodynamic polarization (PDP) highlights that phosphate treatment improves the corrosion rate by ∼25–65 % compared to blank. Electrochemical impedance spectroscopy (EIS) demonstrates that coating (Rcoat) and polarization resistance (RP) at the film-metal interface was substantially increased to ∼953 Ω cm2 and ∼729 Ω cm2 for phosphate-treated specimens with a progressive increase in semicircular capacitive loop diameter indicating surface passivation. Overall, a duplex coating strategy with cerium salt bath followed by phosphate treatment can essentially develop a compact double-layer that effectively minimizes severe corrosion of WZ44 alloy in a 0.1 M NaCl electrolyte.

Control over crystal, local atomic and electronic structures of cerium chromates/chromites via the synthesis conditions

The influence exerted by specific synthesis protocol conditions on the crystal, local atomic and electronic structures of various types of Ce chromates/chromites prepared by the coprecipitation is studied using synchrotron X-ray diffraction, X-ray absorption fine structure (XAFS), Raman and Fourier transform infrared (FT-IR) spectroscopies, and simultaneous thermal analysis. Cerium chromate heptahydrate [Ce2+3(Cr+6O4)3(H2O)5]⋅2H2O with the monoclinic structure (sp. gr. P21/c) has been synthesized and characterized structurally for the first time.It has been established that calcination of all types of precursors in air at a temperature ≥ 450 °C leads to the formation of a mixture of CeO2 and Cr2O3 phases. The calcination in vacuum at 1200 °C affords CeCrO3 (with the orthorhombic structure, sp. gr. Pnma(62)), which upon repeated heating to above 650–700 °C in air tends to decompose into CeO2 and Cr2O3 phases. Long-range XRD data correlate well with the results of techniques sensitive to the local structure parameters, such as XAFS, Raman and FT-IR. XANES spectra measured at the Cr K- and Ce L3- edges strongly imply that the synthesis procedures are accompanied by concerted redox transformations Cr6+→ Cr3＋ and Ce3+⟷ Ce4+.

Inclusion Characteristics in Steel with CeO2 Nanoparticle Addition

The application of Ce oxides in oxide metallurgy has received extensive attention, but until now, the direct adding of CeO2 into molten steel to generate Ce oxides has not occurred. In this paper, a mixture of CeO2 and Si nanoparticles were added into molten steel. The resultant formation of micrometer scale Ce-bearing oxides confirmed its adding validity. This behavior may be interpreted as the reactivity between CeO2 and [Al], and the improved wettability between CeO2 and molten steel with the assistance of Si powder. Thus, when the quantity of CeO2 is kept constant, its added yield should increase when increasing the added quantity of Si. This was verified by the larger percentage of Ce-bearing oxides of the total oxides and the greater average content of Ce in Ce-bearing oxides after normalization. Moreover, compared with the blank sample, statistical results indicated that the oxides in CeO2-modified samples were refined, and their dispersion homogeneity was enhanced. This comparison indicates the effectiveness of the external adding method in oxide metallurgy.

Photocatalytic Easy Recovery of Orthophosphates Contaminants in Water Using Amberlite‐732 Cationic‐Resin Exchanged by Ce3+and Ce3+‐Au3+ Species

AbstractThis report discusses the efficiency of photo‐recovery of orthophosphate anions in water under visible irradiation using materials containing amorphous carbon, ceria and gold‐ceria species. Catalysts were obtained by the exchange of Amberlite‐732 polymeric‐resin with isolated Ce(III) and co‐mixing of Ce(III)‐Au(III) cations. Syntheses were developed for molar ratios Ce(III)/3H+=100 and Au(III)‐Ce(III)/3H+=0.01. Solids were treated at 800 °C under Air or Ar atmosphere then characterized by: X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy coupled to energy‐dispersive X‐ray spectroscopy (EDS), X‐ray photoemission spectroscopy (XPS) and UV‐visible spectroscopy. By XRD, non‐stoichiometric Ce2.658S4 sulfide and particles of metallic gold are identified in Ce‐Au‐Amb‐Ar and in the case of Ce‐Au‐Amb‐Air, mixture of CeO2 and Au0 is clearly observed. Moreover, XPS study of Ce3d emission spectra showed well resolved electronic states of the spin‐orbit Ce3d5/2 and Ce3d3/2 levels in the Ce4+ and Ce3+ oxidation states confirming coexistence of Ce(IV)/Ce(III). On the surfaces of both Ce‐Au‐Amb‐Air and Ce‐Au‐Amb‐Ar, XPS revealed metallic Au species. A certain amount of carbon, identified by EDS and XPS, corresponds to poorly ordered carbon formed by the resin decomposition during thermal treatments under Air and Ar. The UV‐vis spectroscopy was valuable to quantify the remaining PO43− anions in solution (at each moment of reaction) using “Molybdenum Blue” method. Photo‐recovery of orthophosphates under visible irradiation yields optimal trapping of ∼75 % of PO43− on Ce‐Au‐Amb‐Ar, attributed to a catalyst surface enrichment with Ce3+ species, which promoted structural oxygen vacancies.

Fabrication and Characterization of Mullite Reinforced CeO2 Added ZrO2 Ceramics

In this study, mullite (3Al2O3.2SiO2) and 10 mol % ceria added zirconia (10 mol % CeO2 - 90 mol % ZrO2) ceramic powders were synthesized by conventional ceramic production processing route. The mixtures were prepared by mechanical alloying method in acetone environment with zirconia ball mill. Mullite and ceria added zirconia ceramic powders were synthesized in air at 1600 oC for 3 h and 1300 oC for 2 h, respectively. Then, the ceramic phases formed were made ready to form ceramic - ceramic composites by crushing, grinding and sieving processes. Then 0 and 10% by weight mullite added ceria doped zirconia mixtures were prepared by powder metallurgy method. The prepared mixtures were wet milled with zirconia ball mill for 24 h and sieved. After drying, the powders were compacted by uniaxial pressing at 200 MPa. The green compacts were sintered at 1500-1600 oC for 1-5 h in air conditions using a heating rate of 5 oC min-1 in a high temperature furnace. Then, microstructure (SEM), phase analysis (XRD), mechanical (hardness, 3-point bending and wear) and physical properties (% shrinkage, water absorption, porosity and density) tests were performed on the ceramic composites. In this study, whether there is a phase change in the ZrO2 - CeO2 mixture at high sintering temperatures and the effect of mullite additive on the properties of this mixture was investigated.

Electrochemical characteristics of grain boundaries in gadolinium and aluminum co-doped ceria and ceria-alumina composites

The influence of 1, 2, 4 and 10 cat.% Al2O3 addition on the electrochemical characteristics of commercially available 10 cat.% Gd-doped ceria and a 1:1 cat.% mixture of CeO2:Al2O3 were evaluated in our study. Analysis of the electronic conductivity and polarization-relaxation behavior of the samples showed that an Ohmic contribution to the total electronic resistance cannot only be attributed to the electrode contact resistance but is a combined contribution from the electrode interface and decreased pO2 dependence of the grain boundary resistivity of the material. The average electrical potential barrier at the grain boundaries was calculated from impedance spectroscopy data at 50–300 °C. Kelvin probe force microscopy (KPFM) measurements were used to analyze the local Volta potential distribution at the grain boundaries of pure Ce0.9Gd0.1O1.95 and of samples with 4 and 10 cat.% Al addition at room temperature. KPFM measurements showed clear evidence for an increased Volta potential difference between bulk and grain boundary cores and for a considerable broadening of the Volta potential gradient at the grain boundaries with increasing Al concentration.

Super fine cerium hydroxide abrasives for SiO2 film chemical mechanical planarization performing scratch free

Face-centered-cubic crystallized super-fine (~ 2 nm in size) wet-ceria-abrasives are synthesized using a novel wet precipitation process that comprises a Ce4+ precursor, C3H4N2 catalyst, and NaOH titrant for a synthesized termination process at temperature of at temperature of 25 °C. This process overcomes the limitations of chemical–mechanical-planarization (CMP)-induced scratches from conventional dry ceria abrasives with irregular surfaces or wet ceria abrasives with crystalline facets in nanoscale semiconductor devices. The chemical composition of super-fine wet ceria abrasives depends on the synthesis termination pH, that is, Ce(OH)4 abrasives at a pH of 4.0–5.0 and a mixture of CeO2 and Ce(OH)4 abrasives at a pH of 5.5–6.5. The Ce(OH)4 abrasives demonstrate better abrasive stability in the SiO2-film CMP slurry than the CeO2 abrasives and produce a minimum abrasive zeta potential (~ 12 mV) and a minimum secondary abrasive size (~ 130 nm) at the synthesis termination pH of 5.0. Additionally, the abrasive stability of the SiO2-film CMP slurry that includes super-fine wet ceria abrasives is notably sensitive to the CMP slurry pH; the best abrasive stability (i.e., a minimum secondary abrasive size of ~ 130 nm) is observed at a specific pH (6.0). As a result, a maximum SiO2-film polishing rate (~ 524 nm/min) is achieved at pH 6.0, and the surface is free of stick-and-slip type scratches.

Green and Short Preparation of CeO2 Nanoparticles with Large Specific Surface Area by Spray Pyrolysis.

Green and short preparation of CeO2 nanoparticles with large specific surface area from rare earth extraction (CeCl3) was successfully achieved by spray pyrolysis (SP). In this method, a precursor solution is first prepared by mixing CeCl3, C6H8O, and H2O in the requisite quantities. Subsequently, the precursor consisting of a mixture of CeO2 and C was obtained by SP method by using the precursor solution. Finally, the calcination at 500 °C~800 °C in air for two hours to transform the precursor to CeO2 nanoparticles. Thermodynamic analysis and experimental studies were performed to determine the optimal SP temperature and citric acid amount. The results indicated that the maximum specific surface area (59.72 m2/g) of CeO2 nanoparticles were obtained when the SP temperature was 650 °C and the molar ratio of citric acid to CeCl3 was 1.5.

Superior catalytic activity of Pd-based catalysts upon tuning the structure of the ceria-zirconia support for methane combustion

Pd-based catalysts supported on CeO2-ZrO2 (CZ) mixed oxides have been universally applied toward the oxidation of methane, a strong greenhouse gas. Herein, CZ supports of different structures were prepared using hydrothermal (ST-CZ), co-precipitation (CP-CZ), and physical mixing (Mix-CZ) methods. Subsequently, the effects of the CZ support structure on the catalytic activity of the resulting Pd/CZ catalysts toward methane combustion were evaluated. ST-CZ shows the presence of cubic and tetragonal phases of CZ solid solutions, while CP-CZ is a pure tetragonal-phase solid solution and Mix-CZ is a mixture of CeO2 and ZrO2. The CZ solid solution improved the Pd dispersion and Pd2+/Pd ratio on the catalyst surface. Furthermore, CZ oxides with a two-phase composite structure resulted in higher oxygen storage capacity and oxygen mobility in the Pd/CZ catalysts than in the pure solid solution phase. Therefore, the Pd/ST-CZ catalyst shows superior catalytic activity for methane combustion than the other two catalysts.

On the existence of the compound “Ce3NbO7+δ” prepared under air atmosphere

The solid state synthesis of the phase “Ce3NbO7+δ”, from stoichiometric quantities of CeO2 and Nb2O5, was investigated under air atmosphere, as previously described by Zhang et al. (Journal of Rare Earths, 2007, 25, 730–733). A combination of powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and laboratory Ce L3 X-ray absorption spectroscopy, demonstrates the product of the reaction to be a mixture of CeO2 and CeNbO4. These data, and reexamination of the published X-ray diffraction data of “Ce3NbO7+δ”, are consistent with this phase in fact being CeO2. No evidence for the formation of a phase of composition “Ce3NbO7+δ” is found, by solid state synthesis under air atmosphere.

Pt@g-C3N4/CeO2 photocatalyst for the remediation of low concentration NOx at room temperature

Pt@g-C3N4/CeO2 photocatalyst was prepared by calcination of g-C3N4/CeO2 mixture followed by impregnating Pt. Under the irradiation of visible light with the presence of water vapor at room temperature, Pt@g-C3N4/CeO2 showed significant performance for remediation of NOx. The deNOx mechanism was studied by modified in-situ FTIR. The results proved that NO was prone to adsorb on the surface of Pt@CeO2 and oxidized to nitrite for storage. Then, the photoinduced hydrogen on Pt@g-C3N4 component could diffuse into the vicinity of nitrite through the spillover effect of Pt and reacted with nitride to produce N2 and H2O.

High selectivity epoxidation of ethylene in chemical looping setup

We describe the remarkable performance of a new catalyst for the chemical looping (CL-) epoxidation of ethylene, performed at atmospheric pressure and without any promoters added to either the catalyst or the feed gas. To undertake the CL-epoxidation of ethylene, silver was used as the catalyst, supported on either the perovskite SrFeO3 or Ce-modified SrFeO3. Here, the oxygen for the reaction is supplied to the silver catalyst from the active solid support, not from the gas stream. When the support has been reduced and depleted of oxygen, it is regenerated in a separate step with air, which makes the process cyclic and closes a chemical loop. Thus, there is no need to co-feed gaseous oxygen along with the ethylene feed, an important improvement in safety. Two methods were used to synthesise Ce-modified materials, employing either (i) the mechanical mixing of powdered CeO2 and the solid precursors of the perovskite, or (ii) the impregnation of a solution of cerium nitrate into solid particles of SrFeO3. In both cases, the materials were calcined to produce a mixture of CeO2 and SrFeO3. Both CeO2-SrFeO3 materials surpassed the unmodified SrFeO3 for CL-epoxidation. For the CeO2-SrFeO3 prepared by mechanical mixing, the production of ethylene oxide was stable over 15 cycles, giving 60% selectivity at 10% conversion of C2H4. In contrast, the material prepared by impregnation gave up to 85% selectivity but only in the first cycle of reduction, with the performance degrading over subsequent cycles. The reported results are better than the 50% selectivity achieved for the classical epoxidation using pure silver as the catalyst and feeds of gaseous ethylene and oxygen, without reaction promoters.

Heteroaggregation of CeO2 nanoparticles in presence of alginate and iron (III) oxide

When manufactured nanoparticles are released to natural waters, heteroaggregation between nanoparticles and water compounds is expected to occur and play a key role in nanoparticle fate, transport and transformation. In this work, the heteroaggregation between CeO2 nanoparticles and Fe2O3 inorganic colloids, which represent the main inorganic fraction from Lake Geneva water, is studied. The heteroaggregation processes between CeO2, Fe2O3 and alginate in multiple water samples are investigated using zeta potential and z-average diameter measurements. The kinetics of heteroaggregation of individual components as well as mixtures of CeO2 nanoparticles and Fe2O3 colloids and alginate are studied using time resolved dynamic light scattering. The global attachment efficiency (αglobal) is calculated using data from kinetic experiments. αglobal for pristine CeO2 nanoparticles varied from 0.5 to 0.7 in lake and synthetic waters and is found around 1 for pristine Fe2O3 and mixture CeO2 and Fe2O3. Our findings demonstrate that heteroaggregation is highly dependent on environmental conditions and resulting electrostatic scenarios. No heteroaggregation at pH 8 between CeO2, Fe2O3 and alginate is observed in ultrapure water, because of electrostatic repulsions between negatively charged compounds. In synthetic and lake waters, the situation is opposite. Indeed, specific adsorption of divalent cations and presence of salt are found to promote heteroaggregation via cation bridging and screening effects. The kinetic experiments indicate that aggregation rate of pristine Fe2O3 is higher (89 nm/min in lake water) compared to pristine CeO2 nanoparticles (50 nm/min) and on the same level as mixture of CeO2 and Fe2O3 (96 nm/min). Low alginate concentration, 0.25 mg/L, has no effect on heteroaggregation in mixture of CeO2 and Fe2O3 in lake and synthetic waters. On the other hand, in natural water, the presence of higher alginate concentration, 2 mg/L, is found to reduce the heteroaggregation rate.

Investigating the effect of MgO and CeO2 metal nanoparticle on the gasoline fuel properties: empirical modeling and process optimization by surface methodology.

The main purpose of this paper is to investigate how to optimize gasoline in order to reduce the emitted pollutants caused by combustion, while the torque and power of the engine reach the maximum capabilities. To optimize gasoline formulation, an ethanol and magnesium oxide (MgO) or cerium oxide (CeO2) mixture was added to gasoline. This study explores the role of main variables such as type of metal nanoparticle additive, engine speed, and throttle on engine performance and exhaust gas emissions through the modeling and optimization methods. Experimental design conducted through the implementation of D-optimal design, taking into account the three main parameters. To review the efficiency of this novel fuel, it was tested by a four-stroke engine connected to a dynamometer and an analyzer, under different controlled environments: speeds of 1500, 2000, 2500, and 3000rpm at both half and full throttle conditions. The analyzed data are the power and torque of the engine, the amount of emitted CO, CO2, HC, and NOx, the octane index, and the viscosity. The analyzed data were calculated and turned into models. Applying the models to data (the optimization process), close correlation between predicted and actual outcomes was found, highlighting the validity of the work. A secondary finding is that the CeO2 mixture used at higher speeds and throttles produces less emissions, while lower speeds and throttles using the MgO mixture produce less emissions.

A five-component entropy-stabilized fluorite oxide

In this paper, we report a new entropy-stabilized fluorite oxide, formed by solid-state reacting the equimolar mixture of CeO2, ZrO2, HfO2, TiO2 and SnO2 at 1500 °C. We demonstrated that the oxide is truly entropy-stabilized by showing that the oxide was transferred to a multiphase state when annealed at lower temperatures, and the transition between the low-temperature multiphase and high-temperature single-phase states is reversible. Room-temperature thermal conductivity of the fluorite oxide was measured to be 1.28 Wm−1 K−1. The value is only half of that for 7 wt% yttria-stabilized zirconia, suggesting the material could be useful for thermal-insulation applications.

Mechanochemical Activation of Cu–CeO2 Mixture as a Promising Technique for the Solid-State Synthesis of Catalysts for the Selective Oxidation of CO in the Presence of H2

A new ecologically clean method for the solid-phase synthesis of oxide copper–ceria catalysts with the use of the mechanochemical activation of a mixture of Cu powder (8 wt %) with CeO2 was developed. It was established that metallic copper was oxidized by oxygen from CeO2 in the course of mechanochemical activation. The intensity of a signal due to metallic Cu in the X-ray diffraction analysis spectra decreased with the duration of mechanochemical activation. The Cu1+, Cu2+, and Ce3+ ions were detected on the sample surface by X-ray photoelectron spectroscopy. The application of temperature-programmed reduction (TPR) made it possible to detect two active oxygen species in the reaction of CO oxidation in the regions of 190 and 210–220°C by a TPR-H2 method and in the regions of 150 and 180–190°C by a TPR-CO method. It is likely that the former species occurred in the catalytically active nanocomposite surface structures containing Cu–O–Ce bonds, whereas the latter occurred in the finely dispersed particles of CuO on the surface of CeO2. The maximum conversion of CO (98%, 165°C) reached by the mechanochemical activation of the sample for 60 min was almost the same as conversion on a supported CuO/CeO2 catalyst.

Structural Characterization and Electrical Conductivity of Mechanically Alloyed 10mol% In2O3–Doped CeO2 Nanoparticles

Method: Nanocrystalline powder of 10 mol% indium oxide doped ceria is synthesized by mechanically alloying the stiochiometric powder mixture of CeO2 and In2O3 within 5 h of milling in open air. Further milling up to 8 h confirms the stable cubic structure of the compound with increase in milling time. Objective: Detailed structure and microstructure of the compound have been characterized by Rietveld powder structure and microstructure refinement method using XRD data and analyzing HRTEM images. Effect of In2O3 doping on electrical conductivity of nanocrystalline CeO2 is studied by measuring the electrical conductivity of the compound in the temperature range 300°C-600°C. The DC conductivity of doped ceria (σdc ~ 3x10-4 S/cm at 540°C for doped ceria) has been enhanced to ~100 times in comparison to that of the undoped ceria (σdc ~ 4x10-6 S/cm at 540°C) nanoparticles has been found. Conclusion: This significant increment in electrical conductivity has been interpreted through the microstructure characterization of the doped compound. Keywords: Oxides, milling, defects, x-ray diffraction, microstructure, electrical conductivity.

SHS of pyrochlore-type ceramic matrices for immobilization of actinide-containing nuclear wastes

Mineral-like Y2(Ti1–x Zr x )2O7 ceramic matrices for immobilization of actinide–Zr–RE-containing high-level nuclear wastes (HLW) were prepared by SHS method. In experiments, HLW were modeled by a mixture of CeO2, La2O3, ZrO2, MnO2, and Fe2O3 powders. An increase in the HLW content of green mixture decreased the amount of Y2(Ti1–x Zr x )2O7 in combustion product and increased that of ZrO2, LaTiO3, and CaTiO3; decreased the fractional substitutionality of Zr for Ti; and increased the product porosity. An increase in combustion temperature and suppression of heat sink during SHS reaction did not diminish markedly the porosity of synthesized ceramics.