Influence of hafnium oxide on the structure and properties of powders and ceramics of the YSZ–HfO2 composition

Using the X-ray diffraction, internal friction, 4-point bending, and electron microscopy methods we have studied the structural compatibility and influence of Y₂O₃ and HfO₂ dopants addition on the structure and phase composition of ZrO₂ powders and ceramics based on them. The mechanical properties of ZrO₂–Y₂O₃-HfO₂ (YSZ) system have been investigated.It was determined that the similarity of the structure and properties of yttrium and hafnium oxides is not complete. The individual structural features of ZrO₂, Y₂O₃, and HfO₂ oxides reviled themselves during the formation of ternary systems of the YSZ-Hf type. Studies of the nY₂O₃–ZrO₂ - mHf₂O₃ system in the range of hafnium amount from 1 to 15 wt% and yttrium oxide concentration from 0 to 12 mol% showed the possibility of increase in the values of physical and mechanical properties of common two-component zirconium ceramics by the forming ternary systems of the YSZ-Hf type.     

Coating Y2O3 nano-particles with ZrO2-additive via precipitation method for colloidal processing of highly transparent Y2O3 ceramics

In the present work, transparent Y₂O₃ ceramics were prepared via colloidal processing method using ZrO₂-coated nano-sized Y₂O₃ powders. The chemical precipitation method was adopted for the coating of Y₂O₃ raw powder. The evolution of the coated-ZrO₂ layer upon calcination was studied. The rheological behaviors of the slurries of Y₂O₃ powders coated with different content of ZrO₂-additive were investigated. The pH_IEP of ZrO₂-coated Y₂O₃ powders shows intermediate values between that of raw Y₂O₃ and ZrO₂ powders. As the ZrO₂-coating concentration increased from 0 to 5.0 at%, the magnitude of the negative zeta potential at pH > pH_IEP shows a general trend of increment, whereas it decreased at pH < pH_IEP. The viscosity decreases pronouncedly with the increase of ZrO₂ content from 0.5 at% to 3.0 at%. The suspensions with low viscosity and high stability was achieved for a solid loading of 35.0 vol% using Y₂O₃ powders coated with 5.0 at% ZrO₂. The dispersed suspensions were consolidated by centrifugal casting method and the green bodies shown improved homogeneity. Transparent Y₂O₃ ceramics were fabricated by vacuum sintering at 1800 ℃ for 5 h. Transmittance at wavelength 800 nm (1.0 mm thick) reached 80.8%, close to the theoretical value of Y₂O₃.     

Synthesis and study of mesoporous xerogels and nanopowders of a metastable solid solution 97ZrO<Subscript>2</Subscript>–3Y<Subscript>2</Subscript>O<Subscript>3</Subscript> for the fabrication of catalyst substrates

The—technology of the liquid-phase synthesis of metastable phases in the ZrO₂–Y₂O₃ system has been developed. Mesoporous xerogels with the specific surface area of ~350 m²/g and monophase nanopowders (5–10 nm) of the tetragonal solid solution (ZrO₂)_0.97(Y₂O₃)_0.03 have been obtained and their structural peculiarities have been revealed. The efficiency of the suggested technology and good prospects of the synthesized ZrO₂-based precursors in creating catalysts’ substrates have been demonstrated.     

Porous network ZrO2/ZnFe2O4 nanocomposite with heterojunction towards industrial water purification under sunlight: Enhanced charge separation and elucidation of photo-mechanism

This work majorly aims to synthesize and also investigate the structural, optical, magnetic and optical features of ZrO₂/ZnFe₂O₄ nanocomposite. Here, different ratios of novel hetero-junction ZrO₂/ZnFe₂O₄ were synthesized by simple and fast solution combustion route. The X-ray diffraction results showed the formation of ZrO₂ and ZnFe₂O₄ nanoparticles and ZrO₂/ZnFe₂O₄ nanocomposites without any impurity. The formation of hetero-junction effectively inhibits the photo-generated charge carrier recombination. The degradation of Indigo Carmine dye by ZrO₂/ZnFe₂O₄ photocatalyst was achieved through synergistic effects with 98% degradation and removal of 77% COD from the industrial dye waste water under Sunlight irradiation. Mixing of ferrites with zirconia greatly improves the photocatalytic activity that has been clearly proposed with the help of mechanism. ZZFO 12 NC exhibits better photocatalytic activity due to the combined facets of photo and Fenton activity. The exposure and enhancement of fingerprints in various surfaces are achieved by a modest, extremely sensitive and eco-friendly method. ZZFO12 NC offer great potential as an active photocatalyst for degradation of 54% of organic pollutant present in industrial waste water under natural Sunlight.     

Structure and conductivity of yttria and scandia‐doped zirconia crystals grown by skull melting

In this paper a detailed study of the (ZrO₂)_1‐x(Y₂O₃)_x (x=0.025–0.15), (ZrO₂)_1‐x(Sc₂O₃)_x (x = 0.06 – 0.11) and (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y (x=0.07 – 0.11; y=0.01 – 0.04) solid solution crystals grown by skull melting technique is presented. The structure, phase composition, and ion conductivity of the obtained crystals were investigated by X‐ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, and impedance spectroscopy. Maximum conductivity as (ZrO₂)_1‐x(Y₂O₃)_x and (ZrO₂)_1‐x(Sc₂O₃)_x solid solution crystals is observed for the compositions containing 10 mol% stabilizing oxide, and the conductivity of 10ScSZ is ~3 times higher than for 10YSZ. Experiments on crystal growth (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y solid solutions showed that uniform, transparent crystals 7Sc3YSZ, 7Sc4YSZ, 8Sc2YSZ, 8Sc3YSZ, 9Sc2YSZ, 9Sc3YSZ, 10Sc1YSZ, and 10Sc2YSZ are single phase crystal containing t″ phase. It is established that a necessary condition of melt growth of (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y single‐phase crystals is the total concentration of the stabilizing oxides from 10 to 12 mol%. The addition of Y₂O₃ affects the (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y solid solution conductivity different ways and depends on the Sc₂O₃ content in the starting composition. The effects of structure, phase composition, concentration, and type of stabilizing oxides on the electrical characteristics of obtained crystals are discussed.     

A highly refractory material based on zirconia stabilized with yttrium and aluminum oxides

Conclusions With combined additives (Y₂O₃ + Al₂O₃), zirconium dioxide forms solid solutions which resist thermal decomposition.A material was synthesized containing from 90–93 mol. % ZrO₂, from 3.5 to 5 mol.% Y₂O₃, and from 3.5 to 5% mol Al₂O₃, possessing an average coefficient of thermal expansion which is lower, and a thermalshock resistance which is higher, than the double solid solutions in the system ZrO₂-Y₂O₃ and ZrO₂-CaO.Translated from Ogneupory, No. 4, pp. 42–45, April, 1973.     

Effect of the support on the mechanism of partial oxidation of methane on platinum catalysts

The partial oxidation of methane was studio on Pt/Al₂O₃, Pt/ZrO₂, Pt/CeO₂ and Pt/Y₂O₃ catalysts. For Pt/Al₂O₃, Pt/ZrO₂ and Pt/CeO₂, temperature programmed surface reaction (TPSR) studies showed partial oxidation of methane comprehends two steps: combustion of methane followed by CO₂ and steam reforming of unreacted methane, while for Pt/Y₂O₃ a direct mechanism was observed. Oxygen Storage Capacity (OSC) evaluated the reducibility and oxygen transfer capacity of the catalysts. Pt/CeO₂ catalyst showed the highest stability on partial oxidation. The results were explained by the higher reducibility and oxygen storage/release capacity which allowed a continuous removal of carbonaceous deposits from the active sites, favoring the stability of the catalyst. For Pt/Al₂O₃ and Pt/ZrO₂ catalysts the increase of carbon deposits around or near the metal particle inhibits the CO₂ dissociation on CO₂ reforming of methane. Pt/Y₂O₃ was active and stable for partial oxidation of methane and its behaviour was explained by a change in the reaction mechanism.     

Effect of the support on the mechanism of partial oxidation of methane on platinum catalysts

The partial oxidation of methane was studied on Pt/Al₂O₃, Pt/ZrO₂, Pt/CeO₂ and Pt/Y₂O₃ catalysts. For Pt/Al₂O₃, Pt/ZrO₂ and Pt/CeO₂, temperature programmed surface reaction (TPSR) studies showed partial oxidation of methane comprehends two steps: combustion of methane followed by CO₂, and steam reforming of unreacted methane, while for Pt/Y₂O₃ a direct mechanism was observed. Oxygen Storage Capacity (OSC) evaluated the reducibility and oxygen transfer capacity of the catalysts. Pt/CeO₂ catalyst showed the highest stability on partial oxidation. The results were explained by the higher reducibility and oxygen storage/release capacity which allowed a continuous removal of carbonaceous deposits from the active sites, favoring the stability of the catalyst, For Pt/Al₂O₃ and Pt/ZrO₂ catalysts the increase of carbon deposits around or near the metal particle inhibits the CO₂ dissociation on CO₂ reforming of methane. Pt/Y₂O₃ was active and stable for partial oxidation of methane, and its behavior was explained by a change in the reaction mechanism.     

Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts

A partial oxidation of methane was carried out using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H₂O and CO₂, followed by the reforming of methane from CO₂ and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity for the reforming of methane from CO₂ was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO₂ with iridium catalysts was as follows: TiO₂≧ZrO₂≧Y₂O₃>La₂O₃>MgO≧Al₂O₃>SiO₂. The same order was observed in the synthesis gas production from the partial oxidation of methane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanical characteristics of porous hydroxyapatite/oxide composites produced by post-sintering hot isostatic pressing

Porous hydroxyapatite and hydroxyapatite/oxide composites, with 10 wt% addition of Y₂O₃, ZrO₂ or TiO₂ have been prepared by hot isostatic pressing after pressureless sintering, and their phase composition, mechanical properties and microstructure investigated. The quantitative X-ray diffraction analyses reveal that the addition of Y₂O₃ inhibits the hydroxyapatite decomposition completely during the consolidation processes as a result of the Y ion dissolution into the hydroxyapatite lattice. On the contrary, it is found that the addition of ZrO₂ or TiO₂ enhances the decomposition of hydroxyapatite into Ca₃(PO₄)₂, which causes the transformation of the starting oxides. The mechanical characterization of the materials has been accomplished by three-point flexure tests, and nanoindentation and microhardness measurements. Post-sintering hot isostatic pressed pure hydroxyapatite, which resulted in a porous biphasic material with 13.2 wt% β-Ca₃(PO₄)₂, exhibited the best mechanical properties. The failure of hydroxyapatite-10Y₂O₃ during the flexure tests was no catastrophic in contrast to the catastrophic behaviour found in the other materials.     

Formation and properties of solid solutions of zirconium dioxide with oxides of rare earth elements

Conclusions Interaction of zirconium dioxide with oxides of cerium, yttrium and lanthanum in solid phases occurs at 1400°C with the formation of solid solutions with the cubic structure.Sintering of the specimens may result at 1700–1750°C with a 3-h soak. At 1400°C and a 6-h soak the porosity of the specimens was 30–40%.Complete stabilization of the zirconia is attained by heating to 1700–1750°C with additions of 20 mol.% CeO₂, 15% Y₂O₃ or 25% La₂O₃. An addition of ceria and yttria displaces the effects of polymorphic inversion of the zirconia to the lower temperature region.New highly refractory materials may be obtained from solid solutions of ZrO₂-20% CeO₂, ZrO₂-80% CeO₂, ZrO₂-15% Y₂O₃, ZrO₂-80% Y₂O₃ and ZrO₂-25% La₂O₃ and firing to 1750°C. Some of them have a low coefficient of thermal expansion compared with ZrO₂, stabilized with calcium oxide and magnesium oxide, and apparently better thermal-shock resistance. The advantage in regard to resistance during prolonged heating at 1200°C is possessed by the solution ZrO₂-Y₂O₃. The region of the most effective use of goods made from solid solutions of ZrO₂ with CeO₂, Y₂O₃ and La₂O₃ as highly refractory materials should be determined by extra studies.The possibility of reducing CeO₂ (fusing temperature about 2700°C) to Ce₂O₃ (fusing temperature about 1700°C) limits the use of cerium-containing materials as refractories in chiefly oxidizing conditions.     

Quantification of Yttria in Stabilized Zirconia by Raman Spectroscopy

The relationship between Y₂O₃ content in tetragonal and cubic ZrO₂ phases and the shift of the Raman band at ～645/cm was investigated. With increasing Y₂O₃ content, the 645/cm Raman band position decreases to lower Raman shift values. A fit of x = Y₂O₃ content in wt% and y = Raman band position in per cm, was found to be valid for low Y₂O₃‐stabilized t‐ZrO₂, t′′‐ZrO₂ transition, and fully stabilized c‐ZrO₂. Modeling the change in lattice parameters due to the incorporation of Y₂O₃ in ZrO₂ as obtained from Rietveld‐refined XRD data confirms that the peculiar sigmoidal form of the band shift with Y₂O₃ content is mainly due to a variation of the amount of oxygen vacancies. The resultant method is highly attractive in fields of Y₂O₃ determination in ZrO₂ materials where a fast, spatially resolved, and nondestructive analysis is required.     

High-strength ceramic based on zirconium dioxide: preparation and properties

Strength properties are considered for ZrO₂ hot-pressed ceramic materials stabilized with 4 – 6 wt.% Y₂O₃ in relation to original powder preparation method: solid phase synthesis, high-temperature salt thermolysis, combined hydroxide precipitation followed by freezing, drying and calcining, and the sol-gel method. Ceramic material with the highest strength in bending (up to 1350 MPa) are prepared from ZrO₂ – 5 wt.% Y₂O₃ powders, synthesized by coprecipitation of hydroxides followed by freezing.     

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

Mineral-like Y₂(Ti_1–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(Ti_1–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.     

Reactivity between rare‐earth oxides based thermal barrier coatings and a silicate melt

The reactivity between rare‐earth (RE‐) oxide stabilized ZrO₂ or HfO₂ thermal barrier coatings (TBCs) and a calcium‐magnesium‐aluminum‐silicate (CMAS) melt was studied at 1310°C. These reactions are representative of the ingestion of siliceous materials by the intake air of gas turbines (e.g., in aircraft engines) at high temperatures (>1200°C). These materials can melt and react with coated components in the hot section, resulting in premature failure. The goal of this work was to probe the effect of various RE (RE = Y, Yb, Dy, Gd, Nd, and Sm) oxides in the melt phase equilibrium and stability of the top‐coating system. Thermodynamic calculations of the phase assemblage of the (1?x) ZrO₂‐xY₂O₃ coating materials and CMAS melt are compared with the experimental findings. CMAS was found to penetrate the samples at the grain boundaries and dissolve the coating materials to form silicate phases containing the RE elements. Furthermore, apatite and garnet crystalline phases formed in the samples with total RE‐oxide content higher than 16 mol% in the reaction zone for the ZrO₂ system. In general, samples with nominal compositions ZrO₂‐9Dy₂O₃, HfO₂‐7Dy₂O₃, ZrO₂‐8Y₂O₃, HfO₂‐6Er₂O₃, ZrO₂‐9.5Y₂O₃‐2.25Gd₂O₃‐2.25Yb₂O₃, and ZrO₂‐30Y₂O₃ exhibited lower reactivity, or more resistance, to CMAS than the other coating compositions.     

Effect of TiO2 and Ta2O5 co-doping on phase stability,fracture toughness,and sintering behavior of ZrO2 stabilized by 10mol%(Y0.4Gd0.3Yb0.3)2O3

The effect of TiO₂ and Ta₂O₅ co-doping on the phase structure, fracture toughness, and sintering behavior of 10mol%(Y_0.4Gd_0.3Yb_0.3)₂O₃-stabilized zirconia was investigated using X-ray diffraction, scanning electron microscopy, microindentation, and pressureless sintering. The results showed that 10mol%(Y_0.4Gd_0.3Yb_0.3)₂O₃–ZrO₂ had a single cubic phase structure, and an increase in the Ta₂O₅ (≥6 mol%) and TiO₂ doping concentrations resulted in a simultaneous increase in the content and stability of the tetragonal phase. The fracture toughness of TiO₂ and Ta₂O₅ co-doping 10mol%(Y_0.4Gd_0.3Yb_0.3)₂O₃–ZrO₂ decreased with an increase in the Ta₂O₅ content. On the other hand, the TiO₂ content had no significant effect on the fracture toughness of 10mol%(Y_0.4Gd_0.3Yb_0.3)₂O₃–ZrO₂. The sintering resistance of the specimens increased with an increasing in the Ta₂O₅ content; however, an increase in the TiO₂ content accelerated the densification of the specimens. When the Ta₂O₅ content was 10 mol% and the TiO₂ content was in the range of 4–8 mol%, a single non-transformable tetragonal phase structure with fracture toughness similar to that of 6–8 wt% Y₂O₃ stabilized ZrO₂ and excellent anti-sintering properties could be obtained. This structure can be explored as a thermal barrier coating material for high-temperature applications.     

Study on the effect and mechanism of zirconia on the sinterability of yttria transparent ceramic

Transparent Y₂O₃ ceramics were fabricated by solid-state reaction using high purity Y₂O₃ and ZrO₂ powder as starting material. The results indicated that ZrO₂ additive can improve the transparency of Y₂O₃ ceramic greatly. The best transmittance appears with 3 at.% ZrO₂ doped Y₂O₃ transparent ceramic with transmittance at 1100 nm of 83.1%, which is up to 98.6% of the theoretical value. The microstructure is uniform and no secondary phase is observed in the ceramic with the average grain size of 15 μm. The mechanism of ZrO₂ improving the transparency of Y₂O₃ ceramic is analyzed in detail. On this basis, Yb³⁺ doped Y₂O₃ transparent ceramic was also fabricated and spectroscopic properties were investigated.     

Calculating the electric parameters of heaters based on highly refractory oxides

Conclusions A method was developed for computerized calculation of the resistance of heating elements based on the highly refractory oxides, zirconia, thorium oxide, and hafnia. We made an evaluative calculation of the electrical resistance of heaters containing 90% ZrO₂ + 10% Y₂O₃ of known shape and with the most useful sizes.Translated from Ogneupory, No. 5, pp. 48–50, May, 1973.     

Phase formation and lattice distortion of Lu2O3-doped ZrO2 in comparison with Y2O3-doped ZrO2

Lu₂O₃ and Y₂O₃ doping of 8, 11, and 18 mol% in ZrO₂ were prepared by solid solution reaction, aiming to study the phase stabilization of Lu₂O₃-doped ZrO₂ and Y₂O₃-doped ZrO₂ in terms of phase formation and lattice distortion. The Rietveld refinement results indicated that Lu₂O₃-doped ZrO₂ and Y₂O₃-doped ZrO₂ followed the same trend in terms of cubic phase fraction, increasing from 25%–30% (8 mol%) to 95%–100% (11 and 18 mol%). This phase formation was confirmed by observing the same diffraction ring pattern observed for the Lu₂O₃-doped ZrO₂ and Y₂O₃-doped ZrO₂. The Vickers hardness of the Lu₂O₃-doped ZrO₂ was 4.3% higher than that of Y₂O₃-doped ZrO₂ at 8 mol%, but 9.7% and 14.8% lower at 11 and 18 mol%, respectively. This was likely caused by the lattice distortion effect of Y₂O₃ doping overpowering the field strength difference between Lu³⁺ and Y³⁺.     

Carbon dioxide reforming of ethanol over Ni/Y2O3–ZrO2 catalysts

Supported nickel catalysts of composition Ni/Y₂O₃–ZrO₂ were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y₂O₃–ZrO₂ in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO₂ conversion of 61% on the 5NiYZ catalyst at 800 °C, representing a better response than for the catalyst of the same composition prepared by wet impregnation.