Oxygen‐ion conduction in scandia‐stabilized zirconia‐ceria solid electrolyte (xSc2O3–1CeO2–(99−x)ZrO2, 5 ≤ x ≤ 11)

Solid oxide fuel cells (SOFCs) operating at intermediate temperature (500°C‐700°C) provide advantages of better durability, lower cost, and wider target application market. In this work, we have studied Sc₂O₃ (5‐11 mol%) stabilized ZrO₂–CeO₂ as a potential solid electrolyte for application in IT‐SOFCs. Lower Sc₂O₃ doping range than the traditional 11 mol% Sc₂O₃‐stabilized ZrO₂ is an interesting research topic as it could potentially lead to an electrolyte with reduced oxygen vacancy ordering, lower cost, and higher mechanical strength. XRD and Raman spectroscopy was used to study the phase equilibrium in ZrO₂–CeO₂–Sc₂O₃ system and impedance spectroscopy was done to estimate the grain, grain boundary, and total ionic conductivities. Maximum for the grain and grain‐boundary conductivities as well as the tetragonal‐cubic phase boundary was found at 8‐9 Sc₂O₃ mol% in ZrO₂‐1 mol% CeO₂ system. It is suggested that the addition of 1 mol% CeO₂ in the ZrO₂ host lattice has improved the phase stability of high‐conductivity cubic and tetragonal phases at the expense of low‐conductivity t′‐ and β‐phases.     

High catalytic efficiency in liquid‐phase oxidation of 1,4‐dioxane using a Pt/CeO2‐ZrO2‐SnO2/SBA‐16 catalyst

A Pt/CeO₂–ZrO₂–SnO₂/SBA‐16 (SBA‐16: Santa Barbara Amorphous No. 16) catalyst was developed for the efficient removal of 1,4‐dioxane. Because the catalyst showed synergistic action between the high catalytic activity of Pt and the high oxygen release and storage abilities of CeO₂–ZrO₂–SnO₂, high catalytic efficiency in the liquid phase was obtained in an air atmosphere without the supply of any strongly oxidizing additives or photoirradiation. After reaction at 80°C for 4 h, the residual percentage of 1,4‐dioxane reached 31%. Furthermore, the Pt/CeO₂–ZrO₂–SnO₂/SBA‐16 catalyst exhibited high reusability and durability and the rate of net decrease in 1,4‐dioxane reached 44% at 80°C.     

Development of Ce‐PSZ‐/Y‐PSZ‐Toughened Alumina Inserts for High‐Speed Machining Steel

The nanocomposite CeO₂/Y₂O₃ partially stabilized zirconia (Ce‐PSZ/Y‐PSZ)‐toughened alumina was prepared by wet chemical simultaneous coprecipitation process. The thermal stability of phases and morphology of powders were characterized by TG‐DTA, FTIR, and FESEM. The microstructure, stabilization of phases and compositional analysis with different mol% CeO₂/Y₂O₃‐doped zirconia in alumina are characterized by FESEM, XRD, and EDAX spectra. Significant improvement in fracture toughness and flexural strength has been observed in 10 vol% of partially stabilized zirconia (2.5 mol% Y₂O₃ in ZrO₂/9 mol% CeO₂ in ZrO₂)‐toughened alumina, which is suitable for high‐speed machining applications.     

A study on the effect of presence of CeO2 and benzotriazole on activation of self‐healing mechanism in ZrO2 ceramic‐based coating

In this study, the effect of presence of CeO₂ and benzotriazole inhibitor agent on activation of self‐healing reactions and the corrosion behavior of ZrO₂ ceramic‐based coating are evaluated. The ZrO₂ and ZrO₂‐CeO₂‐benzotriazole ceramic‐based coatings were synthesized using sol–gel process and heat treated at 150°C. Afterward, X‐ray diffraction analysis (XRD), and Field Emission Scanning Electron Microscopy (FE‐SEM) were utilized to evaluate the phase analysis and morphology of these coatings. In addition, Energy Dispersive Spectroscopy (EDS) was used for elemental analysis of obtained coatings. Corrosion and self‐healing behavior of the coatings were investigated in 3.5 wt% NaCl solution using Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization tests. The results of XRD analysis revealed the amorphous nature of both coatings. FE‐SEM observations and EDS analysis results showed the presence of benzotriazole inhibitor agent and self‐healing reactions in the cracks and defects of ZrO₂‐CeO₂‐benzotriazole ceramic‐based coating. Moreover, results of electrochemical tests revealed that the presence of CeO₂ and benzotriazole inhibitor agent in the ZrO₂ ceramic‐based coating results in intense increases in the corrosion resistance of this coating by activating the self‐healing mechanism and forming passive layers.     

Cu/Ni‐Loaded CeO2‐ZrO2 Catalyst for the Water‐Gas Shift Reaction: Effects of Loaded Metals and CeO2 Addition

Two different types of metals (Cu and Ni) and the effect of CeO₂ addition to produce a CeO₂‐ZrO₂ co‐supporter were investigated through the water‐gas shift (WGS) reaction. It was found that the WGS activity could be enhanced with CeO₂ addition. At relatively high temperature, Ni‐loaded catalysts exhibited higher CO conversion while Cu‐loaded catalysts demonstrated better performance at low temperatures. The stability and yield of the CO₂ and H₂ products of the Cu catalysts were higher than those of the Ni catalysts. These results may be caused by an irreversible adsorption of CO on Ni and the reverse WGS reaction occurring on the Ni catalysts. In situ diffuse‐reflection infrared Fourier transform spectroscopy data suggests that the WGS mechanism likely proceeded via formate species.     

Effect of High‐Temperature Aging on the Fracture Toughness of 40 mol% Ceria‐Stabilized Zirconia

The 40 mol% CeO₂‐stabilized ZrO₂ ceramic was synthesized by the sol‐spray pyrolysis method and aged at 1400°C–1600°C. The effects of high‐temperature aging on its fracture toughness were investigated after heat treatments at 1500°C for 6–150 h in air. Characterization results indicated that the activation energy for grain growth of 40 mol% CeO₂‐stabilized ZrO₂ was 593 ± 47 kJ/mol. The average grain size of this ceramic varied from 1.4 to 5.6 μm within the aging condition of 1500°C for 6–150 h. The Ce‐lean tetragonal phase has a constant tetragonality (ratio of the c‐axis to a‐axis of the crystal lattice) of 1.0178 during the aging process. It was found that the fracture toughness of 40 mol% CeO₂‐stabilized ZrO₂ was determined to be 2.0 ± 0.1 MPa·m^1/2, which did not vary significantly with prolonging aging time. Since no monoclinic zirconia was detected in the regions around the indentation crack‐middle and crack‐tip, the high fracture toughness maintained after high‐temperature aging can be attributed to the remarkable stability of the tetragonal phase in 40 mol% CeO₂‐stabilized ZrO₂ composition.     

Effect of CeO2 and Al2O3 contents on Ce‐ZrO2/Al2O3 composites

Effect of CeO₂ and Al₂O₃ contents on phase composition, microstructures, and mechanical properties of Ce–ZrO₂/Al₂O₃ composites was studied. The CeO₂ content in CeO₂–ZrO₂ varied from 7 to 16 mol%, and the Al₂O₃ content in Ce‐ZrO₂/Al₂O₃ composites were 7 and 22 wt%. When CeO₂ content was ≤10 mol%, high Al₂O₃ content contributed to hinder the tetragonal‐to‐monoclinic ZrO₂ phase transformation during cooling and decrease the density of microcracks in the composites. Tetragonal ZrO₂ single‐phase was obtained in the composites with ≥12 mol% CeO₂, regardless of the Al₂O₃ content. Hardness, flexural strength, and toughness were dependent on CeO₂ and Al₂O₃ contents which were related to the microcracks, grain size, and phase transformation. The high flexural strength and toughness of the composites with 7wt% Al₂O₃ could be obtained at an optimum CeO₂ content of 12 mol%, whereas those of the composites with 22 wt% Al₂O₃ could be achieved in the wide CeO₂ content range of 8.5‐12 mol%.     

Photoluminescence Enhancement of SiO2‐Coated LaPO4:Eu3+ Inverse Opals by Surface Plasmon Resonance of Ag Nanoparticles

The surface plasmon resonance of Ag nanoparticles (NPs) and SiO₂ coating had been extensively employed to improve the photoluminescence (PL) intensity of nanomaterials. In the article, the LaPO₄:Eu³⁺ inverse opal photonic crystals were fabricated via combining a self‐assembly process with a sol–gel method. The SiO₂ shells were formed on the skeleton surface of LaPO₄:Eu³⁺ inverse opals and the Ag NPs were added into the voids of LaPO₄:Eu³⁺ inverse opals with the SiO₂ shells. The influence of the SiO₂ shells and Ag NPs on the PL of the LaPO₄:Eu³⁺ inverse opals were investigated. About sevenfold luminescence enhancement of LaPO₄:Eu³⁺ inverse opals was obtained by the coordination action of surface plasmon absorption effects of Ag nanoparticle and silica‐coating effects. The luminescence enhancement mechanisms of LaPO₄:Eu³⁺ inverse opals were discussed.     

Phase Transformation Behavior of a Pyrochlore‐Type CeO2–ZrO2 Binary Compound

The phase transformation behavior of the superlattice structure of a CeO₂–ZrO₂ pyrochlore‐type binary compound (CP) was investigated so as to better understand how to improve the thermal stability of such a system. CP was synthesized through high‐temperature reduction of a conventional CeO₂–ZrO₂ solid solution with a 1:1 molar ratio of Ce and Zr. High‐resolution transmission electron microscopy and selected‐area electron diffraction clearly revealed that the pyrochlore structure of CP transformed to the standard disordered cubic fluorite or tetragonal zirconia structure after having been subjected to a high‐temperature durability test; moreover, it was determined that this phase transformation moves inward from the crystallite surface. This discovery suggests a new method by which to improve upon this material for practical applications.     

Electro‐Sintering of Yttria‐Stabilized Cubic Zirconia

Electro‐sintering, i.e., electrically enhanced densification without the assistance of Joule heating, has been observed in 70% dense 8 mol% Y₂O₃‐stabilized ZrO₂ ceramics at temperatures well below those for conventional sintering. Remarkably, full density can be obtained without grain growth under a wide range of conditions, including those standard for solid oxide fuel cell (SOFS) and solid oxide electrolysis cell (SOEC), such as 840°C with 0.15 A/cm². Microstructure evidence and scaling analysis suggest that electro‐sintering is aided by electro‐migration of pores, made possible by surface flow of cations across the pore meeting lattice/grain‐boundary counter flow of O^2?. This allows pore removal from the anode/air interface and densification at unprecedentedly low temperatures. Shrinkage cracking caused by electro‐sintering of residual pores is envisioned as a potential damage mechanism in SOFC/SOEC 8YSZ membranes.     

Fe2O3 on Ce‐, Ca‐, or Mg‐stabilized ZrO2 as oxygen carrier for chemical‐looping combustion using NiO as additive

Oxygen‐carrier particles for chemical‐looping combustion have been manufactured by freeze granulation. The particles consisted of 60 wt % Fe₂O₃ as active phase and 40 wt % stabilized ZrO₂ as support material. Ce, Ca, or Mg was used to stabilize the ZrO₂. The hardness and porosity of the particles were altered by varying the sintering temperature. The oxygen carriers were examined by redox experiments in a batch fluidized‐bed reactor at 800–950°C, using CH₄ as fuel. The experiments showed good reactivity between the particles and CH₄. NiO was used as an additive and was found to reduce the fraction of unconverted CH₄ with up to 80%. The combustion efficiency was 95.9% at best and was achieved using 57 kg oxygen carrier per MW fuel. Most produced oxygen carriers appear to have been decently stable, but using Ca as stabilizer resulting in uneven results. Further, particles sintered at high temperatures had a tendency to defluidize. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Selective Production of H2 from Ethanol at Low Temperatures over Rh/ZrO2–CeO2 Catalysts

A series of Rh catalysts on various supports (Al₂O₃, MgAl₂O₄, ZrO₂, and ZrO₂–CeO₂) have been applied to H₂ production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO₂–CeO₂ > Rh/Al₂O₃ > Rh/MgAl₂O₄ > Rh/ZrO₂. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO₂–CeO₂ catalyst exhibits the highest CO₂ selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO₂–CeO₂ catalyst exhibited the highest H₂ yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO₂–CeO₂ resulting in efficient transfer of mobile oxygen species from the H₂O molecule to the reaction intermediate.     

Ceria‐doped scandia‐stabilized zirconia (10Sc2O3·1CeO2·89ZrO2) as electrolyte for SOFCs: Sintering and ionic conductivity of thin,flat sheets

In this study, thin, flat sheets, about 90 μm thick, were prepared from ceria‐doped scandia‐stabilized zirconia with molecular formula 10Sc₂O₃·1CeO₂·89 ZrO₂ (10Sc1CeSZ) by tape casting and subsequent sintering at different thermal cycles. A sintering thermal cycle was selected that yielded defect‐free flat sheets, with practically negligible porosity (between 0.35% and 0.10%) and average grain diameters ranging from 1.32 to 6.30 μm. Ionic conductivity at 600°C was as high as 21 mS/cm. Ionic conductivity increased with average grain diameters up to 2.7 μm. At higher average grain diameters, conductivity remained practically constant.     

Splitting CO2 with a ceria‐based redox cycle in a solar‐driven thermogravimetric analyzer

Thermochemical splitting of CO₂ via a ceria‐based redox cycle was performed in a solar‐driven thermogravimetric analyzer. Overall reaction rates, including heat and mass transport, were determined under concentrated irradiation mimicking realistic operation of solar reactors. Reticulated porous ceramic (RPC) structures and fibers made of undoped and Zr⁴⁺‐doped CeO₂, were endothermally reduced under radiative fluxes of 1280 suns in the temperature range 1200–1950 K and subsequently re‐oxidized with CO₂ at 950–1400 K. Rapid and uniform heating was observed for 8 ppi ceria RPC with mm‐sized porosity due to its low optical thickness and volumetric radiative absorption, while ceria fibers with μm‐sized porosity performed poorly due to its opacity to incident irradiation. The 10 ppi RPC exhibited higher fuel yield because of its higher sample density. Zr⁴⁺‐doped ceria showed increasing reduction extents with dopant concentration but decreasing specific CO yield due to unfavorable oxidation thermodynamics and slower kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1263–1271, 2017     

Vapor-Phase Dehydration of 1,3-butanediol over CeO2–ZrO2 Catalysts

The dehydration of 1,3-butanediol was investigated over CeO₂–ZrO₂ catalysts prepared by impregnation at temperatures of 325–375 °C. Pure CeO₂ selectively catalyzed the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol, while pure ZrO₂, which was less active than pure CeO₂, catalyzed the dehydration to 3-buten-1-ol. In the CeO₂/ZrO₂ catalyst in which CeO₂ was supported on zirconia, the presence of a small amount of CeO₂ suppressed the formation of 3-buten-1-ol and induced the dehydration of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol and the subsequent dehydrogenation of 3-buten-2-ol to form 3-buten-2-one and butanone. The activity would be related to the redox features of CeO₂. The monoclinic phase of zirconia support decreased while the cubic CeO₂ phase increased as CeO₂ content was increased. In contrast, in the ZrO₂/CeO₂ catalyst in which ZrO₂ was supported on cubic CeO₂, only the cubic CeO₂ phase was observed and ZrO₂ species appeared in the form of a solid solution of CeO₂–ZrO₂ with fluorite structure. Regardless of zirconia loading, ZrO₂ species did not affect the catalytic activity of ZrO₂/CeO₂, which was controlled by CeO₂ species.     

Kinetics of Corrosion of BN–ZrO2–SiC Ceramics in Contact with Si‐Killed Steel

The mechanism and kinetics of corrosion of BN–ZrO₂–SiC (MYCROSINT^®SO43) by molten Si‐killed steel was studied. Isothermal corrosion tests were performed for duration between 2 and 8 h. Refractory and steel composition and morphology changes were investigated. A kinetic model using process simulation software METSIM and thermochemical software FactSage was developed to understand refractory–steel interactions. The corrosion process showed a deviation from parabolic kinetics and was fitted by a combination of linear and parabolic terms. It was determined that corrosion of the BN–ZrO₂–SiC refractory was governed by dissolution of SiC and BN and removal of ZrO₂ as the other phases were eliminated.     

Examination of radio‐opacity enhancing additives in shape memory polyurethane foams

Three microparticle additives, tungsten (W), zirconium oxide (ZrO₂) , and barium sulfate (BaSO₄) were selected to enhance the radio‐opacity in shape memory polymer (SMP) foam biomaterials. The addition of filler causes no significant alterations of glass transition temperatures, density of the materials increases, pore diameter decreases, and total volume recovery decreases from approximately 70 times in unfilled foams to 20 times (4% W and 10% ZrO₂). The addition of W increases time to recovery; ZrO₂ causes little variation in time to shape recovery; BaSO₄ increases the time to recovery. On a 2.00 mean X‐ray density (mean X.D.) scale, a GDC coil standard has a mean X.D. of 0.62 ; 4% W enhances the mean X.D. to 1.89, 10% ZrO₂ to 1.39 and 4% BaSO₄ to 0.74. Radio‐opacity enhancing additives could be used to produce SMP foams with controlled shape memory kinetics, low density , and enhanced X ‐ray opacity for medical materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42054.     

Effects of SDBS and ZrO2 additives on the microstructure and properties of silicon-bonded SiC porous ceramics

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO₂ as sintering additives, the effects of SDBS and ZrO₂ on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO₂ could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na₂O which reacted with ZrO₂ and impurity SiO₂, which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO₂ would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO₂ were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m³/m²·h·kPa and 28.2 MPa, respectively.     

Oxygen diffusion mechanisms during high‐temperature oxidation of ZrB2‐SiC

Oxygen diffusion mechanisms during oxidation of ZrB₂‐30 vol% SiC were explored at temperatures of 1500°C and 1650°C using an ¹⁸O tracer technique. Double oxidation experiments in ¹⁶O₂ and ¹⁸O₂ were performed using a modified resistive heating system. A combination of scanning electron microscopy, energy‐dispersive spectroscopy, and time‐of‐flight secondary ion mass spectrometry was used to characterize the borosilicate and ZrO₂ oxidation products. Oxygen exchange with the borosilicate network was observed to occur quickly at the oxygen‐borosilicate surface at both 1500°C and 1650°C, while evidence of oxygen permeation was only observed at 1650°C for short time (<1 min) exposures. At longer times, >5‐9 min, complete oxygen exchange throughout both the borosilicate glass and ZrO₂ was observed at both temperatures preventing identification of the oxygen transport mechanisms, but demonstrating that oxygen transport is rapid in both oxide phases.     

High‐Speed Preparation of Highly (100)‐Oriented CeO2 Film by Laser Chemical Vapor Deposition

CeO₂ films were prepared at deposition temperature ranged from 947 to 1096 K (corresponding laser power was from 52 to 185 W) on (100) LaAlO₃ single crystal substrate by laser chemical vapor deposition. At deposition temperature of 1027–1096 K (laser power was from 115 to 185 W), highly (100)‐oriented CeO₂ films with wedge‐caped columnar grains were prepared, whose epitaxial growth relationship was CeO₂ [100]//LAO [100] (CeO₂ [010]//LAO [011]). Their full width at half maximum of the ω‐scan on the (200) reflection and that of the ?‐scan on the (220) reflection were 0.8°–1.8° and 0.7°–1.2°, respectively. The highest deposition rate at which CeO₂ film with pure (100) preferred orientation could be obtained was 30 μm h^?1.