ZrO2 Y2O3 Research Articles

Effects of thermal treatment conditions on redox properties of ceria-zirconia materials

The nanostructures and redox properties of CeO2–ZrO2 materials can be tuned via optimized thermal treatments. In this study, the CeO2–ZrO2–Y2O3–La2O3 (CZ) materials were prepared by co-precipitation method and submitted to different thermal treatment conditions (atmosphere: nitrogen (N) and air (A); temperature (x): 700, 800 and 900 °C). Due to the protective effects of the “in-situ-formed” carbon powder, treating the surfactants assisted-CZ precursors under N2 atmosphere can keep the pore structures and then the CZ-N700 and CZ-N800 can achieve larger surface area than CZ-A700 and CZ-A800, respectively. In comparison, with high treatment temperature (900 °C), the effects of thermal atmosphere on surface area can be ignored. However, the redox properties of CZ materials correlate closely with thermal treatment atmosphere and temperature simultaneously. As demonstrated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterizations, the N2 atmosphere facilitates the formation of Ce3+ without disturbing the mixing degree of Ce and Zr. Thereby the CZ-Nx materials exhibit superior reducibility than corresponding CZ-Ax materials. In addition, the XRD and XPS results also demonstrate the formation of a more homogeneous CZ solid solution by Zr atoms rearrangement with temperature ignoring the atmosphere. As a result, the reducibility of CZ materials increases with the treatment temperature increasing and is not affected by the worsening of the textural properties. Specially, due to the synergistic effects of N2 atmosphere and high treatment temperature, the CZ-N900 shows the best reducibility. This improvement also emphasizes the important role of structural properties of CZ in explaining the temperature-dependent reducibility.

Effect of Pt Addition on the Formation of Ni–Pt Porous Layer

A Ni–Pt alloy porous layer was formed by electrodepositing Pt using Ni as the substrate sample, followed by Al-depositing and Al-dissolving. The Pt was electrolyzed using an aqueous solution as the medium, and the Al-depositing and Al-dissolving were treated using a molten salt as the medium. The molten salt used was NaCl–KCl with 3.5 mol% AlF3 added. It was found that Pt electrodeposition formed on the surface had a finer structure. Furthermore, it was clarified that the lower the electrodeposition potential, the thicker the Ni-Pt alloy porous layer. The cathode polarization curve was measured in KOH solution, and the hydrogen gas was determined when a constant voltage electrolysis was performed with a hydrogen detection gas sensor using a tubular yttria-stabilized zirconia (8 mol% Y2O3–ZrO2).

Mechanical behavior of ion-irradiated ODS RAF steels strengthened with different types of refractory oxides

One of the most promising candidates for constructing IV generation nuclear reactors is Oxide Dispersed Strengthening (ODS) Reduced Activation Ferritic (RAF) steel. It is known that introducing refractory oxides to the ferritic matrix makes it possible to obtain a brand-new kind of materials with an excellent set of properties. In the present work, the authors focused on verifying materials' structural and mechanical properties strengthened by three different types of refractory oxides submitted to ion-irradiation. Three materials with an elemental chemical composition of 12 %Cr, 2 %W, 0.3 %Ti, and strengthened with 0.3% Y2O3 or Al2O3 or ZrO2 were produced by mechanical alloying and subsequently consolidated by Spark Plasma Sintering technique. Manufactured materials have been submitted to high energy (500 keV) Ar-ion irradiation at room temperature with three fluences (up to 5x1015 ions/cm2). This procedure allowed to generate a thin, strongly damaged zone with approximate thickness of 230 nm. SEM/EBSD and TEM bservations, Grazing Incidence X-ray Diffraction analysis, and nanoindentation tests have been included in examination of modified layers. Implementation of these techniques allowed to reveal alteration of structural and mechanical features between unmodified material and radiation-affected layer. Obtained results showed a strong correlation between the strengthening oxide and materials' microstructural and mechanical behavior under radiation damage. It has been proved that below 1x1015 ions/cm2 mechanical properties in the modified layer of all materials are very similar. Reported behavior may be related to the efficient annealing of the radiation defect process. Above this limit, significant differences between the materials are visible. It is believed that described phenomenon is directly related to the presence of the structural features and their capacity to act as defect sinks. Consequently, type of dominant mechanisms occurring in modified layer is proposed.

Thermophysical and mechanical properties of Sm3TaO7/7 wt.% Y2O3–ZrO2 ceramics

In this current study, Sm3TaO7 was used as the second phase to fabricate a composite ceramic with 7 wt.% Y2O3–ZrO2 (7YSZ). Effective phonon scattering was achieved by controlling the content of the second phase Sm3TaO7, which significantly reduced the thermal conductivity. The results show that Sm3TaO7/7YSZ ceramics have a minimum thermal conductivity of 0.81 W m−1 K−1 at 900 °C. The minimum thermal conductivity of the composite was 50% lower than that of 7YSZ. The maximum thermal expansion coefficient was obtained for 5 wt.% Sm3TaO7/7YSZ ceramics (12.1 × 10−6 K−1, 1200 °C), which was much higher than that for 7YSZ (∼10.0 × 10−6 K−1). The hardness and Young's modulus of 5 wt.% Sm3TaO7/7YSZ ceramics were much lower than those of 7YSZ, which is clearly attributable to the low modulus and hardness of Sm3TaO7. Our experimental results showed that the 5 wt.% Sm3TaO7/7YSZ ceramics are excellent thermal barrier coating materials.

Investigation of the Applicability of Y2O3–ZrO2 Spherical Nanoparticles as Tribological Lubricant Additives

Long-term environmental goals will motivate the automotive industry, component suppliers, and lubricating oil developers to reduce the friction of their tribosystems to improve overall efficiency and wear for increased component lifetime. Nanoscale ceramic particles have been shown to form a protective layer on components’ surface that reduces wear rate with its high hardness and chemical resistance. One such ceramic is yttria (Y2O3), which has an excellent anti-wear effect, but due to its rarity it would be extremely expensive to produce engine lubricant made from it. Therefore, part of the yttria is replaced by zirconia (ZrO2) with similar physical properties. The study presents the result of the experimental tribological investigation of nanosized yttria–zirconia ceramic mixture as an engine lubricant additive. Yttria-stabilized zirconia (YSZ) nanoparticle was used as the basis for the ratio of the ceramic mixture, so that the weight ratio of yttria–zirconia in the resulting mixture was determined to be 11:69. After the evaluation of the ball-on-disc tribological measurements, it can be stated that the optimal concentration was 0.4 wt%, which reduced the wear diameter by 30% and the wear volume by 90% at the same coefficient of friction. High-resolution SEM analysis showed a significant amount of zirconia on the surface, but no yttria was found.

Variation of photoluminescence intensity depending on the timing of electric field application during isothermal flash sintering for 3mol%Y2O3–ZrO2 polycrystal

The shrinkage process and the change in photoluminescence (PL) intensity during isothermal flash sintering were investigated for 3 mol% Y2O3–ZrO2 (3YSZ) polycrystals doped with 300 ppm Bi2O3 as a PL impurity centre. The PL intensity of 3YSZ is enhanced by isothermal flash sintering. However, the enhancement of the PL intensity was revealed to become smaller when flash-treatment was applied for thermally pre-sintered 3YSZ polycrystal. To maximize the efficiency of electric field on the enhancement of the PL intensity, the electric field needs to be applied throughout the sintering from the initial stage to the final densification. The necessity for continuing to apply the electric field until the densification is completed is due to the fact that the recovery of oxygen vacancies, the origin of the F+ band, must be suppressed.

Structure of Nanocomposites in the ZrO2–Y2O3–Al2O3 System and Their Formation under Hydrothermal Conditions

Structure of Nanocomposites in the ZrO2–Y2O3–Al2O3 System and Their Formation under Hydrothermal Conditions

Direct power generation from methanol by solid oxide fuel cells with a Cu-ceria based catalyst layer

In this work, Cu–CeO2 co-impregnated 8 mol.% Y2O3–ZrO2 (YSZ) has been synthesized and characterized as an integrated catalyst layer for methanol-fueled Ni-YSZ anode-supported solid oxide fuel cells (SOFCs). With the addition of the integrated catalyst layer, single cell fueled by methanol demonstrates 55.2% reduction of polarization resistance (from 0.67 to 0.30 Ω·cm2) and 42.32% incensement of peak power density (from 501 to 713 mW·cm−2) at 800 °C. Moreover, under constant current output mode, the cell with an integrated catalyst layer exhibits good stability for more than 45 h. The enhanced electrochemical performance proves that the integrated catalyst layer is helpful to catalytic the methanol fuel for Ni-YSZ anode-supported SOFCs. The reforming ability of the integrated catalyst layer for methanol is studied by analyzing the microstructural and composition of the anode and catalyst layer after the stability test. This work proves that the adding of an integrated catalyst layer is a promising strategy to directly utilize methanol for Ni-YSZ anode-supported SOFCs.

High-surface-area mesoporous silica-yttria-zirconia ceramic materials prepared by coprecipitation method ― the role of silicon

A high surface area is one of desired properties for yttria-zirconia (Y2O3–ZrO2) ceramic materials given their catalytic applications. The objective of this study is to develop high-surface-area Y2O3–ZrO2 materials by silicon (Si) modification and investigate the role of Si. Si-modified yttrium-zirconium hydroxides were prepared via a one-step precipitation process and calcined at 800 or 950 °C to form Si-modified Y2O3–ZrO2 (denoted as SiO2–Y2O3–ZrO2) materials containing 0-20 wt% Si as SiO2. These hydroxides or materials were characterized by 29Si NMR, XPS, TG-DSC, XRD, UV Raman, TEM, and N2 physisorption measurements. Si species uniformly distributed in the hydroxides tended to be enriched on the material surface at high temperatures. These Si species dominated by the silicates blocked the migration of Y and Zr atoms, which resisted the crystallite growth of Y2O3–ZrO2 components and reduced their crystallite size. Therefore, the SiO2–Y2O3–ZrO2 possessed a surface area of 59-112 m2/g after calcination at 950 °C for 9 h, which was significantly higher than that of the Y2O3–ZrO2 (23 m2/g). This study may stimulate ideas for developing high-surface-area crystalline ceramic materials calcined at high temperatures.

Tetragonal reconstruction and monoclinic variants rearrangement during heat treatment in zirconia

AbstractAn in situ monoclinic variants selection and rearrangement study on Y2O3–ZrO2 coatings was conducted using electron backscattered diffraction. The sequence growth of variants with the correspondence of (100)m ∼// (010)t, [010]m ∼// [001]t, and [001]m ∼// [100]t (CAB‐OR2) was found initially and converted to the 90°‐rotated sequence growth with (100)m ∼// (100)t, [001]m ∼// [001]t, and [010]m ∼// [010]t (ABC‐OR2) after heat treatment. In another coating, most of the variants first exhibited interleaving growth and changed to typically fourfold growth. This in situ evolution of both variants orientation relationship and arrangement revealed the effects of stress and stress relief on the martensitic transformation. Moreover, the variants selection might be diversified during the cyclic transformation, and the classical phenomenological theory could mainly be proved by the transformation triggered by temperature, instead of external stress. Furthermore, the variants orientation relationship was exactly confirmed by the tetragonal grain reconstructions. In particular, the orientation variation of reconstructed tetragonal grains was also found and could mainly be explained by the behavior of stress relief and dynamic recrystallization.

Near-infrared emission in Er- and Pr-doped YSZ crystalline superlattices

Broadband on-chip light amplifier is one of the key building blocks for the development of integrated circuits for datacom and telecom applications. In this context, the article reports on the near-IR emission properties of rare-earth doped crystalline thin layers of Y2O3–ZrO2 (YSZ): Er-doped YSZ, Pr-doped YSZ and a superlattice of Er- and Pr-doped YSZ. Absorption studies proved differences in wavelengths in superlattice sample with Pr3+ and Er3+ in comparison with Er-doped YSZ and Pr-doped YSZ monolayers. Power efficiency was determined for all samples, revealing larger emission and higher optical efficiency for Er3+ ions at 1530 nm (C-band) than Pr3+ emission at 1350 nm (O-band) in the superlattice sample. Simultaneous emission from Er3+ and Pr3+ ions was observed by exciting the Er- and Pr-doped YSZ superlattice in a range from 980 to 1000 nm wavelengths. Besides, energy transfer from Pr3+ to Er3+ was demonstrated in the superlattice sample containing Pr3+ and Er3+ ions.

Effect of isothermal heat treatment on nanoindentation hardness and Young’s modulus of 4 mol% Y2O3-ZrO2 EB-PVD TBCs

4 mol% Y2O3–ZrO2 (4YSZ) is commonly used in thermal barrier coatings (TBCs) for high-temperature applications such as gas turbine engines. This study was investigated the effects of heat treatment at 1400 °C for 0, 2, 20, and 100 h on the hardness and Young’s modulus of 4YSZ coatings prepared by electron-beam physical vapor deposition. Nanoindentation measurements were performed on the top and side surfaces of the coating. The as-coated and the heat-treated coatings exhibited strong anisotropy in the mechanical properties; the hardness and Young’s modulus of the side surface of the coatings were lower than those of the top surface. Increasing the heat treatment time was found to increase the hardness and Young’s modulus in both the directions. This is correlated with the decrease in porosity with increase in the heat-treatment time and closure of gaps between the columns and arms of their (as-coated) featherlike microstructures, which are known to deleteriously affect both the toughness and thermal insulating properties of TBCs.

Structure and Transport Characteristics of Single-Crystal and Ceramic ZrO2–Y2O3 Solid Electrolytes

Structure and Transport Characteristics of Single-Crystal and Ceramic ZrO2–Y2O3 Solid Electrolytes

Comparative study of zirconia based powders prepared by co-precipitation and in a microreactor with impinging swirled flows

Mesoporous nanosized xerogels and powders in the system ZrO2–Y2O3 are obtained by two techniques, including co-precipitation of hydroxides and micromixing in a microreactor with impinging swirled flows (MRISF). The phase composition, surface characteristics, microstructure and textural features of the prepared xerogels and powders are studied. Compared with the conventional co-precipitation procedure, MRISF technique provides xerogels with improved performances, including significantly lower hydrodynamic diameter, ζ-potential and agglomeration of the particles, probably due to a reduced content of active centers on their surface and high level of shear stresses in the course of the synthesis. Furthermore, the developed MRISF is shown to provide a continuous high-throughput process advantageous in respect of easy numbering-up instead of the conventional scaling-up. Particularly, the lab-scale MRISF device used in this study affords a daily output of the slurry up to 8.5 m3 yielding 200–300 kg/day of the target nanosized particles.

An interesting application-oriented design of high-strength anode support for protonic ceramic fuel cells by a non-proton-conducting cermet

One key problem of protonic ceramic fuel cells (PCFCs) is insufficient mechanical strength of anode support. Herein, an interesting application-oriented design is to enhance the mechanical strength of PCFCs by using a non-proton-conducting cermet NiO-3mol%Y2O3–ZrO2 (3YSZ) based on the assumption that anode reactive thickness is relative limited. The flexural strength of NiO-3YSZ anode support can reach 210 MPa while that of NiO–BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) is only 58.5 MPa. Novel half-cells of NiO-3YSZ anode support, NiO-3YSZ-BZCYYb anode transition layer, NiO-BZCYYb anode functional layer and BZCYYb electrolyte layer are sequentially fabricated by tape-casting combined with the hot-pressing lamination. Fully integrated single cells can obtain a peak power density of 676 mW cm−2 at 700 °C and exhibit an acceptable long-term stability with the operation voltage of 0.75 V at 650 °C for 120 h with humid H2 as fuel and air as oxidation. Electrode polarization processes before and after the long-term stability test are further investigated by the relaxation time distribution method. The performance degradation is mainly related to the oxygen reduction reaction and oxygen ion transport processes on the cathode side, and there is little effect of the side reaction involved by Ni-3YSZ anode support.

Changes in the Properties of Ultrafine Al2O3–ZrO2–Y2O3–CeO2 Powders After Heat Treatment in the Range 400–1450°C

Changes in the Properties of Ultrafine Al2O3–ZrO2–Y2O3–CeO2 Powders After Heat Treatment in the Range 400–1450°C

Влияние высокопористого керамического материала-имплантата на основе системы ZrO2 – Y2O3 – Al2O3 на жизненные показатели экспериментальных животных

Nanodispersed xerogels and powders (average size 9 nm) were obtained by co-precipitation of hydroxides in the ZrO2–Y2O3–Al2O3. Solid-state sintering of samples from the initial [(ZrO2)0,97(Y2O3)0,03]0,8(Al2O3)0,2 powder with pore-forming additives using a patented technology strong highly porous ceramics was produced. Dopplerography was used to assess the volume of blood flow in arterioles and capillaries on 150 and 250 days after implantation of the plates. Thus, microcirculatory Doppler sonography seems to be a promising intravital method for assessing blood flow in the plate location area and, possibly, inside the plate. It was found that ceramic plates based on zirconium dioxide, placed in the body of experimental animals, do not cause a negative reaction of the animal’s body. The results of studies under in vivo conditions suggest that the obtained bioceramic based on zirconium dioxide is promising for use as a material for endo-prosthetics.

Morphology and Properties of the Nanometer-Sized Rare-Earth Oxide Doped W–La2o3–Y2o3–Zro2 Cathode Tip

Morphology and Properties of the Nanometer-Sized Rare-Earth Oxide Doped W–La2o3–Y2o3–Zro2 Cathode Tip

Влияние технологии спекания нанопорошков на трещиностойкость тетрагонального диоксида циркония

The effect of various technological conditions of the preparation of samples from ZrO2 ceramics stabilized by various additives of yttrium oxide Y2O3 on the fracture toughness of the material has been investigated. Various modes of sintering of samples obtained by the method of co-deposition of nanopowders of zirconium dioxide ZrO2 and yttrium oxide Y2O3 were performed. An original technique for calculating the critical stress intensity factor from the test data of double cantilever beam specimens with a chevron notch by the wedging method is described. A characteristic feature of the loading diagrams for ceramics based on zirconium dioxide stabilized by additives of yttrium oxide is the presence of a stage of inelastic deformation, which develops without cracking. The mechanism of inelastic deformation is based on the phase transition of the tetragonal modification to the monoclinic modification of the crystal structure. For each mode, the values of fracture toughness characteristics are determined. Ceramics with the composition ZrO2 + 3 mol% Y2O3 (KIc = 6.86 MPa ∙ m1/2) exhibit the maximum crack resistance at a sintering temperature Tsint =1500°C for an hour. Deviation from the composition of 3 mol% Y2O3 reduces the fracture toughness. The increase in fracture toughness is favored by the grinding of the powder in a planetary mill. It is generally accepted that mechanical stresses arising at the top of a growing microcrack cause all round compression stresses, since the phase transformation is accompanied by an increase in the unit cell volume by 4%. This stabilizes the microcrack, slowing down its growth. This point of view was confirmed due to the well-known fact that when zirconium dioxide is cooled from 950°C to room temperature during the t → m transition, microcracks are intensively formed in the bulk of the material. However, when wedging a two-cantilever specimen with a chevron notch, the probability of the formation of compression stresses is small. This is also evidenced by the absence of cracking throughout the inelastic stage of material deformation. In the fine-crystalline structure of zirconium ceramics under loading, favorable conditions arise for the relaxation of shear stresses through the t → m transition.

Relationship among the composition, synthesis conditions, and surface acid-basic properties of xerogel particles based on zirconium dioxide

ZrO2–Y2O3–CeO2, ZrO2–Y2O3 and ZrO2–CeO2 xerogels were prepared by coprecipitation of the corresponding hydroxides followed by the precipitate processing using different procedures involving maturation in the mother liquor within 24 h, freezing and ultrasonic treatment. The surface acid-base properties of the prepared xerogel particles were studied by measuring pH changes upon their suspension in water. The obtained results allow the analysis of relationships among the xerogel synthesis conditions, behavior of xerogel particles in the aqueous medium and their agglomeration, thus providing the adjustment and prediction of the properties of ceramic materials prepared from the studied powders.