Increasing Cerium Content Research Articles

Ce-doped ZnO nanonails synthesized by a simple thermal evaporation method for photocatalytic degradation

One-dimensional (1D) nanomaterials have garnered significant scientific and technological attention due to their potential applications in electronics devices, gas sensing, energy conversion, and photocatalysis. However, the development of a simple and low-cost technique for 1D nanostructure synthesis remains a challenge. The doping of ZnO nanostructures has proven to be an effective way to improve their internal properties. In this work, one-dimensional ZnO and Ce-doped ZnO nanorods and nanonails were synthesized by a simple thermal evaporation method using different weight ratios of ZnS and CeO2 precursor powders in a catalyst-free process. The effects of cerium doping concentration on the structural, morphological, and optical properties of the as-prepared samples were investigated. XRD analysis confirmed that the crystal structure was converted from the cubic ZnS phase to the hexagonal ZnO phase with increasing annealing temperatures. The UV–Vis spectra showed that the optical absorption edge of Ce-doped ZnO samples was slightly red-shifted. Additionally, the band gap energy decreases with increasing cerium concentration. SEM images showed that the morphology of the structures obtained changed from nanorods to nanonails as the Ce content increased. The incorporation of Ce ions into the ZnO matrix has been successfully confirmed by HRTEM, Raman, and EDX analysis. Photocatalytic activity studies showed that Ce-doped ZnO samples exhibited significantly enhanced photocatalytic performance compared to pure ZnO for the degradation of rhodamine B under UV radiation. These results may suggest the use of heterogeneous photocatalysis as an efficient, cheap, and environment-friendly alternative for the removal of pollutants from water and the use of Ce-doped ZnO as a promising candidate.

Order-disorder structural transition and thermal expansion properties in Ce-substituted Y2Zr2O7 system

In the pursuit of advancing inert matrix fuel (IMF) applications, zirconate pyrochlores have emerged as promising candidates for the incorporation of minor actinides and plutonium. This study employs CeO2 as a nonradioactive surrogate for PuO2 and focuses on the synthesis of cerium-substituted Y2Zr2O7 samples (Y2-xCexZr2O7, 0.0 ≤ x ≤ 2.0) through a solid-state route under both reducing and oxidizing conditions to mimic plutonium incorporation. The impact of cerium content and its valence state, which in turn is influenced by synthesis conditions, on crystal structure and phase stability has been investigated through X-ray diffraction and Raman spectroscopic studies. Samples synthesized under reduced conditions undergo a defect fluorite to pyrochlore phase transition through a biphasic mixture consisting of these two phases upon increasing Ce-substitution. Conversely, the high temperature oxidizing synthesis conditions yield a defect fluorite phase field over a wide composition range (0.0 ≤ x ≤ 1.6) and a tetragonal phase at x = 2.0. Intriguingly, pyrochlore-type phases obtained under reducing conditions transform into the metastable kappa-phases upon mild oxidation at a relatively low temperature (1073 K), as confirmed by Raman spectroscopic studies. A combination of thermo-gravimetric and Raman spectroscopic investigations confirms the complete reduction of Ce4+ to Ce3+ under reducing conditions. The lattice thermal expansion behavior has also been investigated for the defect fluorite phases, synthesized under oxidizing conditions, by means of high temperature XRD spanning the temperature range 298–1273 K. Notably, the thermal expansion of compositions exhibits an increasing trend with increasing cerium content.

Investigation on the control of inclusions and tensile strength in Ce-treated P110-grade oil casing steel

This research added rare Earth elements Ce to the P110-grade oil casing steel to reveal their influence on the inclusions and tensile properties. The content of cerium in the steel varied from 0 to 452 ppm. Based on the classical thermodynamic calculation, the predominance diagram of Re-containing inclusions in P110-grade steel was obtained. The evolution route of the inclusions composition with the increasing cerium content in the steel was xCaO⋅yAl2O3 → Al2O3–CeAlO3 → Ce2O3–CeAlO3 → Ce2O3–Ce2O2S → Ce2O2S, which agreed well with the thermodynamic analysis. As the cerium content at 235 ppm, the size of Ce containing inclusions has a minimal size at 2.82 μm. Suitable Ce content can modify the big-size xCaO⋅yAl2O3 inclusions into small-size Re-containing inclusions. The results demonstrate that the tensile performance of this steel can be improved as the cerium content increases from 0 to 235 ppm. However, once the cerium content exceeds 235 ppm, further increases in cerium content led to a decline in performance. The experimental results shows that the presence of large-sized Ce2O2S inclusions and the change of microstructure, will lead to the decrease in tensile performance.

Engineering stoichiometry of high entropy fluorite oxide to obtain optimized thermophysical property and improved corrosion resistance

Engineering stoichiometry of materials is an effective strategy to optimize the comprehensive properties. Here we prepare high-entropy Er2(Y0.2Yb0.2Nb0.2Ta0.2Cex)2Oδ with single-phase fluorite structure by a solid-state reaction. The effects of stoichiometry of cerium on thermophysical properties and corrosion resistance to calcium−magnesium−alumina−silicate (CMAS) of the high-entropy oxides have been investigated. By engineering the cerium stoichiometry, thermal conductivity increases slightly from 1.21 to 1.36 W·m−1·K−1 and thermal expansion coefficients also increases from 10.56 × 10−6 to 11.61 × 10−6 °C−1 at 1000 °C. Furthermore, corrosion resistance of the high-entropy Er2(Nb0.2Ta0.2Y0.2Yb0.2Cex)2Oδ improves with the increase of cerium content. The effects of cerium content on CMAS resistance have been discussed in detail. Our work reveals that engineering stoichiometry of high-entropy oxides is expected to be an effective strategy to broaden the compositional space and optimize the thermophysical properties and CMAS corrosion resistance.

Effects of Cerium Addition on Inclusions and Solidification Structure of a Low‐Nickel Si–Mn‐Killed Stainless Steel

The effect of cerium on inclusions and solidification structure of a low‐nickel Si–Mn‐killed stainless steel is studied using laboratory experiments. When the cerium content in steel increased from 0 to 250 ppm, modification sequence of inclusions is Si–Mn(–Al)–O and MnS → Ce–Si–Mn–O–S → Ce(–Si)–O–S → CeS and CeC2. The number density and area fraction of inclusion first decrease with the increase in the cerium content and then increase due to the formation of CeC2 inclusions when the cerium content is bigger than 150 ppm, which is precipitated in solid steel during solidification. When the cerium content increases from 0 to 250 ppm, the fraction of equiaxed grain zones of steel ingot first increases and reaches a maximum value when the cerium content is 54 ppm; then the fraction of equiaxed grain zones decreases with the increase of the cerium content. 2D lattice misfit calculations are performed and it is found that there are no heterogeneous nucleation cores in the steel without cerium during solidification. For the steel with cerium, Ce4.67Si3O13, Ce2O2S, and CeS inclusions act as heterogeneous nucleation cores, increasing the fraction of the equiaxed grain zone. Bigger effective heterogeneous nucleation cores number density leads to a larger fraction of the equiaxed grain zone.

Effect of cerium on the primary carbides and inclusions in electroslag remelted M35 high speed steel

To restrain the formation of primary carbides in M35 high speed steel, the present work investigated the effect of cerium on the microstructure, primary carbides and inclusions in electroslag remelted M35 high speed steel based on experimental characterizations and thermodynamic calculations. The primary carbides in M35 high speed steel are M2C-type carbides with orthorhombic crystal structure and MC-type carbides with FCC crystal structure. M2C-type carbides are the dominant carbides, whose precipitation is prior to the MC-type carbides. With adding cerium content to 0.0230wt%, the evolutionary process of inclusions is: MgO∙Al2O3→Ce2O3, CeAlO3 and Ce2O2S→Ce2O3, Ce2O2S and Ce2O3 core surrounded by Ce–As–P layer. Adding cerium content from 0 to 0.0230wt% causes the secondary dendrite arm spacing to decrease from 36.8 μm to 29.4 μm, as the heterogeneous nucleation of Ce2O3, Ce2O2S and CeAlO3 inclusions, as well as the effect of dissolved cerium including the increase in the constitutional undercooling and the drag on the migration of liquid–solid interface. Ce2O3, Ce2O2S and CeAlO3 are the less effective heterogeneous nucleation cores for M2C-type and MC-type primary carbides precipitation than MgO∙Al2O3 inclusions, which is conducive to the decrease in the area fraction of primary carbides with adding 0.0067wt% cerium. Further increasing cerium content to 0.0230wt%, the formation of Ce–As–P inclusions surrounding Ce2O3 promotes the precipitation of M2C-type primary carbides, causing the increase in the area fraction of primary carbides.

X-ray photoelectron spectra, conductivity, and oxygen permeation characteristics of (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) perovskites

X-ray photoelectron spectra, conductivity and oxygen permeability of perovskite-type (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) oxides are reported. The concentration of Fe4+ and Ce4+ decreases with ‘x’ via Fe4+(/Ce4+) → Fe3+(/Ce3+) conversions which, in turn, oxygen deficiency (δ) increases. The spectrum of oxygen (O1s) is attributed to stoichiometric, adsorbed and chemically adsorbed species at ∼531.5, 532.8 and 534.4 eV, respectively (say, for x = 0.30). The oxygen permeability (Jo2) of disc membrane lies in the range of ∼1.474–2.204 ml/cm2-min at 950 °C (input feed air ∼400 ml/min, carrier argon gas ∼40 ml/min) for x = 0–1.0. Maximum Jo2 is observed for x = 0 (cubic phase) in comparison to other compositions viz., x = 0.10–0.60 (cubic + orthorhombic phases) and x = 0.80–1.0 (orthorhombic phase). The electrical conductivity increases until a characteristic temperature, then slowly decreases with increasing cerium concentration (x). The structural transformation of (Ba0.5Sr0.5)(Fe1-xCex)O3-δ plays an important role in determining the conductivity (σ) and oxygen permeation. These analyses make material useful for applications dealing with oxygen separations.

Effects of Cerium Doping on the Mechanical Properties and Energy-Releasing Behavior of High-Entropy Alloys.

Energetic structural materials play an important role in improving the damage performance of future weapons. To improve the energy-releasing behavior, Al0.5NbZrTi1.5Ta0.8Cex high-entropy alloys were prepared by vacuum-arc melting. The results showed the presence of BCC and FCC phases in the alloy with dendritic-morphology-element segregation and there were significant dislocations in the alloys. The current study focused on the effects of cerium content on the dynamic compressive mechanical and energetic characteristics. Cerium doping enhanced the energy-releasing characteristics of high-entropy alloys. The severity of the reaction increased with the increase in the cerium content, while the dynamic compressive strength generally decreased with the increase in cerium content. The Al0.5NbZrTi1.5Ta0.8Ce0.25 showed excellent mechanical and energy-releasing characteristics. The ballistic experiments indicated that Al0.5NbZrTi1.5Ta0.8Ce0.25 can penetrate 6-millimeter A3 plates and ignite the cotton behind the target at a velocity of 729 m/s, making it an ideal energetic structural material.

Designing Ceria/Alumina for Efficient Trapping of Platinum Single Atoms

Cerium oxide (ceria) has been shown to be very effective at trapping platinum atoms due to formation of stable surface complexes at step edges, where coordinatively unsaturated cerium cations are present. But ceria loses its effectiveness when heated to high temperatures due to loss of surface area and growth in particle size associated with sintering of the oxide. Being a rare earth, and with limited supplies worldwide, it is important to develop methods to improve the effectiveness of ceria as a catalyst support. Here, we explore the performance for trapping Pt atoms when the ceria is supported on a high surface area alumina carrier. This helps create a more sustainable catalyst formulation, especially if we can retain the high dispersion of Pt seen on ceria supports. For this work, we studied the atom trapping efficacy of ceria/alumina samples with increasing ceria content (8–50 wt %) and contrasted the behavior with pure ceria. Electron microscopy reveals that when dispersed on alumina, ceria is present in the form of crystalline nanoparticles and isolated cerium ions. These two forms of ceria differ markedly in their ability to trap Pt atoms. Atomically dispersed cerium is present in the form of Ce3+ cations on alumina; however, this form of ceria is not effective for trapping Pt atoms. Our results show that the atom-trapped Pt resides primarily on crystalline ceria nanoparticles. CO oxidation was used as a probe reaction to evaluate the performance of these PtAT/ceria-alumina catalysts. We conclude that over the range of ceria loadings we investigated, 50% ceria/alumina represents the optimal catalyst support for achieving high surface area and atom trapping efficiency while helping reduce the total ceria content in this catalyst system.

A hot tearing criterion based on solidification microstructure in cast alloys

A criterion based on solidification microstructure was proposed to precisely predict the hot tearing behavior of cast alloys, which takes into account the effects of both mechanical and nonmechanical factors. This criterion focuses on the events occurring at the grain boundary, which are determined by the thermal contraction, solidification shrinkage, grain growing and liquid feeding. This criterion responds to a series of factors that affect hot tearing, such as alloy composition, mold design, casting process and microstructure. Its credibility has been validated by studying the hot tearing behavior of Mg-Ce alloys. In conformity with the experimental results, this criterion predicted decrease in the number of rods occurring hot tearing with increasing cerium content. A simplified criterion was derived and validated by Mg-Ce (equiaxed grain) and Mg-Al (columnar grain) alloy systems, which is suitable for the case where the eutectic liquid fraction is low and the liquid feeding can be ignored. In addition, a hot tearing index for equiaxed grains was proposed, that is,|dT/d(fs1/3)|near(fs)1/3=1, and its prediction results were consistent with the hot tearing susceptibility calculated from the experimental results.

Direct microalloying of steel with cerium under slags of СаО–SiO 2 – Ce2O3– 15 % Al2O3 –8 % MgO system with additional reducing agents

An assessment of the possibility of steel direct microalloying with cerium was performed using thermodynamic modeling of cerium reduction from slags of CaO– SiO2– Ce2O3 system containing 15 % Al2O3 and 8 % МgO, additional additives of reducing agents (aluminum or ferrosilicoaluminium), at temperatures of 1550 and 1650 °C using the HSC 6.1 Chemistry (Outokumpu) software package. Depending on the additional additives of aluminum or ferroglycoaluminium, metal temperature, slag basicity and content of cerium oxide, 0.228 to 40.5 ppm of cerium transfers into the metal. With an additional additive of aluminum from slag (Y1) containing 1.0 % of cerium oxide, 0.228 ppm of cerium is transferred to the metal at 1550 °C. An increase in the system temperature to 1650 °C is accompanied by a slight increase in cerium content, reaching no more than 0.323 ppm. When added to ferrosilicoaluminium metal, cerium content in the metal is higher and amounts to 0.402 and 0.566 ppm at 1550 and 1650 °C, respectively. When concentration of cerium oxide in the slag (Y2) increases to 7.0 %, more signifcant increase in cerium content in the metal is observed, reaching in temperature range of 1550 – 1650 °C, 1.65 – 2.31 ppm with aluminum additives and 2.90 – 4.05 ppm with ferrosilicoaluminium additives. The most noticeable increase in cerium content in the metal is observed with an increase in slag basicity. During formation of slags with basicity of 2 – 3, containing 1 – 7 % Ce2O3, the equilibrium concentration of cerium in the metal varies from 0.5 to 4 ppm with aluminum additives and 1 – 7 ppm with ferro­silicoaluminium additives at 1550 °C. Slags transfer to the increased (up to 3 – 5) basicity is accompanied by an increase in the equilibrium content of cerium in the metal to 4 – 12 ppm with aluminum additives and 7 – 20 ppm with ferrosilicoaluminium additives at Ce2O3 content of 3 – 7 % and, as a result, an increase in efciency of cerium reduction process.

A Green CeO2−WO3/TiO2 Medium‐Low Temperature de‐NOx Catalyst for Selective Catalytic Reduction of NOx with NH3

AbstractA series of CeO2−WO3/TiO2 catalysts were synthesized by the co‐precipitation method and used for selective catalytic reduction (SCR) of NO with NH3 under medium‐low temperature conditions with metatitanic acid as Ti source. A more reasonable weight ratio of CeO2 and WO3 was explored. The catalytic activity enhanced with the increase of cerium content, but the catalytic activity changed slightly in the temperature range of 240 °C to 400 °C when the cerium content exceeded 15 %. Tungsten could enhance the sulfur resistance by adjusting the degree of crystallization, acidity in the SCR process. When the weight ratio of CeO2 to WO3 was 15: 8, the conversion rate of NO was more than 90 % in the temperature range of 240 °C to 440 °C. For 15 %CeO2‐8 %WO3/TiO2 catalyst, the NO conversion was maintained around 84 % when the mixed gas was introduced SO2. At the same time, we have optimized the selection of carriers, metatitanic acid as a carrier was better than titanium dioxide.

Effect of Cerium on the Behavior of Primary Carbides in Cast H13 Steels

Different amounts of elemental cerium were added into H13 ingots to investigate the effect of cerium content on primary carbides’ behavior. The enrichment of the elemental Cr, Mo, V, and C in the last-to-solidify region was identified by EPMA. The enrichment of alloy elements is the main reason for the precipitation of primary carbides during solidification. As the increase of cerium content, the size of the last-to-solidify region decreases first and then increases. We found a huge difference between the 2D and the 3D observations of primary carbides. The number density of the primary carbides appeared higher, while their size was smaller in the 2D observation. In the 3D observation, as the cerium content increases, the primary carbides’ size also decreases first and then increases, while the morphology of the primary carbides changes from dendritic structure to sheet structure and then to dendritic structure again. The cerium content has little influence on the thermodynamic precipitation process of primary carbides. The enrichment of the elemental cerium in the last-to-solidify region observed by TOF-SIMS accelerates the nucleation of the austenite, further leading to smaller last-to-solidify region size. The smaller last-to-solidify region size provides less space for the further growth of the primary carbide, resulting in the smaller primary carbide size.

Effect of doping level and compensation on thermal conductivity in CexSn1−xSe solid solutions

The paper reports the results of experimental studies of the thermal conductivity and density of CexSn1−xSe solid solutions in the temperature range 80–480 K. Under the assumption of elastic scattering of charge carriers, parabolic band and arbitrary degeneracy, the electronic and lattice components of thermal conductivity have been calculated. The characteristic features of the thermal conductivity of these crystals have been analyzed, it has been shown that with an increase in cerium content and with an increase in temperature, the total (χtot) and lattice (χph) thermal conductivity significantly decrease, while the density increases slightly (at 300 K). The dependence of thermal conductivity on the percentage of cerium in the composition has been established. With prolonged annealing, the total and lattice components of thermal conductivity increase. It has been established that heat transfer in CexSn1−xSe is carried out mainly by phonons.

Effect of the Ce3+ concentration on laser-sintered YAG ceramics for white LEDs applications

This paper describes the laser sintering and luminescence properties of Y3Al5O12 (YAG) phosphors doped with different concentrations of Ce3+ and synthesized using the polymeric precursor method. The ceramics were sintered by a new laser sintering technique in which a CO2 laser is employed as the heating source. The resultant ceramics exhibited a homogeneous microstructure with narrow grain size distribution and high relative density. The introduction of Ce3+ ions led to luminescence quenching at a concentration above 0.5 mol% and a redshift of the emission spectrum band with increasing cerium concentration. The excitation spectrum showed two characteristic bands centered at 340 nm and 460 nm and a relative change in their intensity by change the Ce3+ concentration. The presence of a single valence (Ce3+) of cerium was determined by X-ray absorption near edge structure measurements.

Effect of Cerium Content on Inclusions in an Ultra-Low-Carbon Aluminum-Killed Steel

The effect of cerium on inclusions in an ultra-low-carbon Al-killed steel was studied at 1873 K (1600 °C) using laboratory experiments. The content of cerium in the steel varied from 0 to 0.028 wt pct. The contents of the total oxygen (T.O), total nitrogen (T.N), total sulfur (T.S), total cerium (T.Ce) and dissolved aluminum ([Al]) in the steel samples 1, 5, 10 and 30 minutes after adding cerium were measured, and inclusions were characterized using an automatic scanning electron microscope. It was found that a cerium-concentrated zone formed after the cerium alloy was added to the molten steel. Many inclusions were generated in the cerium-concentrated zone and then disappeared with the decrease of the cerium content. The variation of the inclusion composition was Al2O3 → CeAlO3 → Ce2O2S → Ce2O2S + CeS with the increasing cerium content in the steel, which agreed well with the thermodynamic analysis. The value of T.Ce/T.O was able to evaluate and predict the type of inclusions. A prediction model of the composition of inclusions was established based on thermodynamic calculation and mass balance and was validated by experimental data. When the value of T.Ce/(T.S + T.O) was ≥ 4.4, the average composition of inclusions changed little since most inclusions were fully modified.

Enhanced transport properties in Ce doped cobalt ferrites nanoparticles for resistive RAM applications

Abstracts Polycrystalline Cerium doped Cobalt ferrite with general formula CoFe x − 2 Ce x O 2 (X = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) was synthesized by Co-precipitation method. The effect of Cerium substitution on the structural, dielectric, electrical and switching properties of spinel cobalt ferrite nanoparticles was studied. Formation of the spinel structure was confirmed by X-ray Diffraction (XRD) analysis. With increase in cerium content, secondary phase (CeO2) was also identified. The frequency dependent dielectric constant, AC electrical conductivity, dielectric loss, dielectric loss tangent and impedance was investigated in the frequency range of 20Hz–3MHz. Dielectric constant, AC conductivity and dielectric loss decreased with the addition of Cerium contents. From impedance study, the role of grains and grain boundaries with in prepared spinel ferrite nanoparticles was investigated. The values the activation energies and drift mobility are calculated from the DC electrical resistivity measurements. DC resistivity and hence, activation energy increases with increasing Cerium contents. Resistive switching properties were studied using current–voltage (I–V) measurements. All I–V curves in the current study exhibit a hysteresis loop-type behavior. Hysteresis loop-type trend confirm that resistive switching effect exist in Cerium doped Cobalt ferrites nanoparticles. Our study suggest that Cerium doped Cobalt ferrites have high potential for resistance switching memory devices like Resistive Random-Access Memory (ReRAM). Resistive switching mechanism in Cerium doped cobalt ferrites nanoparticles is also explained by available theoretical model.

Effects of cerium doping on dielectric properties and defect mechanism of barium strontium titanate glass-ceramics

The effect of cerium content on phase evolution, dielectric properties and defect mechanism has been investigated in (Ba,Sr)TiO3 glass-ceramics. Cerium mainly acts as an isovalent dopant in the B-site of ABO3 perovskite structure at low content (1 mol%) and then cerium substitution gradually occurs in the A-site with increasing cerium content. A compensation mechanism related to variation in oxygen vacancy concentration has been identified. When cerium content increased to 2 mol%, the maximum values of dielectric constant and energy storage density were simultaneously achieved. The impedance spectra revealed the highest conductivity. It is due to the increase in the concentration of charge carriers accompanied by the decrease in the activation energy of oxygen vacancy migration. With a further addition of cerium to 3 mol%, the opposite trend was observed. The result is related to the presence of more cation vacancies, which, in turn, limits the diffusion rate of oxygen vacancy.

Magneto-optical properties of cerium-doped phosphate glass

Phosphate glass with a high transmission level in the visible and near-IR spectral regions doped with a high cerium concentration (up to 25 mol%) was synthesized and experimentally investigated in terms of applicability as a material for magneto-optical devices. Glass transition temperature was 590 °C. Glass refractive index varied between 1.5831 and 1.5884 depending on cerium content. The structure of the glass obtained was mostly metaphosphate with admixture of ultraphosphate complexes. It is shown that the maximum values of Verdet constant (11 rad/T/m at 1064 nm) are reached with increasing cerium concentration up to 25 mol%. The analysis proves the viability of the studied glass to create optical elements using the Faraday effect.

Electroless nanoceria films on nickel-based superalloy

ABSTRACT Ceria films were deposited by electroless method on a nickel-based superalloy, Superni 75, to improve its performance at high temperatures. Ceria was produced from cerium acetate using triethanolamine as the reducing agent. The films were produced at three concentrations – 0.1, 0.2 and 0.3 M of cerium acetate, to study the effect of increasing cerium concentration. For comparative study, the coated and bare substrates were oxidized at 1173 K for 100 h in air. The morphology and the chemistry of the oxide scale formed were analysed using FEG-SEM/EDS and XRD. It has been observed that increasing the cerium concentration in the film increases the oxidation resistance of the substrate which is evident from the calculated parabolic rate constant. It was also observed that the morphology of the scale improves with the increase in the concentration of cerium in the film. The scale formed on the ceria-coated substrate at 0.3 M concentration is dense and more uniform.