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.     

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.     

Heat-treatment effect on the properties of a zirconia ceramic with a grainy structure

Conclusions The heat treatment at 2000°C of zirconia ceramic with a grainy structure causes the destabilization of the ZrO₂-CaO solid solutions but this is not complete after a 200-h dwell; the electrosmelted ZrO₂ ceramic stabilized with CaO is more stable under these conditions. The ZrO₂-Y₂O₃ solid solutions have greater stability on heating.When the grainy-structure zirconia ceramic is subjected to an isothermal dwell at 2000°C there is a consequent reduction in the strength properties caused either by the decomposition if the solid solutions (CaO-stabilized ceramic) or by the growth of crystals (Y₂O₃-stabilized ceramic).Deceased.Translated from Ogneupory, No, 7, pp. 51–55, July, 1979.     

Low Thermal Conductivity of SnO2‐Doped Y2O3‐Stabilized ZrO2: Effect of the Lattice Tetragonal Distortion

Considering the phonon scattering effect and the stability of t′ zirconia, Sn⁴⁺ ion is recognized as an appropriate dopant to achieve the best combination of thermal insulating capability and durability of yttria‐stabilized zirconia thermal barrier coatings (TBCs). In this research, unusual lattice expansion and strong structural disordering were observed in a series of SnO₂‐doped Y₂O₃‐stabilized ZrO₂ compounds, which are caused by the tetragonal distortion of oxygen coordination. Phonon scattering due to the structural disordering rather than point defects of Sn⁴⁺ substitutions predominates in reducing the thermal conductivity. However, deterioration of the thermal properties was observed at high doping content, which may be attributed to the t‐m phase transformation during the measurements. Considering the structure stability and thermal properties, SnO₂‐doped Y₂O₃‐stabilized ZrO₂ compounds can be promising candidates for TBCs.     

Evaluation of hot corrosion behavior of plasma sprayed ceria and yttria stabilized zirconia thermal barrier coatings in the presence of Na2SO4+V2O5 molten salt

In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ; ZrO₂−25 wt%CeO₂−2.5 wt%Y₂O₃) topcoat by air plasma spraying (APS). Hot corrosion studies of plasma sprayed thermal barrier coatings (TBCs) were conducted in 45 wt%Na₂SO₄+55 wt%V₂O₅ molten salt at 1000 °C for 30 h. The results showed that the coating defects, such as pores and microcracks play important roles as effective paths for the salt penetration in hot corrosion. Based on the results, the reaction between molten salt and stabilizers of zirconia (Y₂O₃ and CeO₂), the formation of YVO₄, CeVO₄ and CeO₂ crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to the depletion of stabilizers and finally, the creation of stresses were recognized to be in the degradation mechanism of CYSZ ceramic coatings in the presence of molten sulfate–vanadate salt.     

Low–thermal–conductivity and high–toughness CeO2–Gd2O3 co–stabilized zirconia ceramic for potential thermal barrier coating applications

Yttria partially stabilized zirconia (～4.0?mol% Y₂O₃–ZrO₂, 4YSZ) has been widely employed as thermal barrier coatings (TBCs) to protect the high–temperature components of gas–turbine engines. The phase stability problem existing in the conventional 4YSZ has limited it to application below 1200?°C. Here we report an excellent zirconia system co–doped with 16?mol% CeO₂ and 4?mol% Gd₂O₃ (16Ce–4Gd) presenting nontransformable feature up to 1500?°C, in which no detrimental monoclinic (m) ZrO₂ phase formed on partitioning. It also exhibits a high fracture toughness of ～46?J m^?2 and shows high sintering resistance. Besides, the thermal conductivity and thermal expansion coefficient of 16Ce–4Gd are more competent for TBCs applications as compared to the 4YSZ. The combination of properties suggests that the 16Ce–4Gd system could be of potential use as a thermal barrier coating at 1500?°C.     

Ball milling assisted preparation of nano La–Y/ZrO2 powder ternary oxide system: Influence of doping amounts

Zirconia powder with good dispersion, fine particle size, and stability is used as high-quality raw material in many fields, such as ceramic materials and refractories. In this paper, the influence of lanthanum oxide (La₂O₃) and yttrium oxide (Y₂O₃) co-doped zirconia (ZrO₂) on its phase transformation behavior, phase stability, and microstructure were investigated. The ball milling method is applied to fabricate different amounts of La₂O₃-doped yttrium oxide stabilized zirconia oxide. Then, the powder obtained from ball milling was roasted using the microwave sintering method. The samples were characterized using XRD, FT-IR, Raman, SEM and BET to determine the optimal conditions for La₂O₃–Y₂O₃ co-doped ZrO₂ powder. The results showed that replacing part of Y₂O₃ with La₂O₃ increases zirconia powder's tetragonal and cubic phase, enhancing the fracture strength of the subsequent synthesized materials. At the same time, the stability of zirconia stabilized with La₂O₃ doping is significantly improved compared to that of Y₂O₃ alone. According to all analysis methods, when the doping amount is 2.8Y0.2La, the powder's phase composition, stability, particle size distribution, and dispersion degree are the best compared with other doping amounts in our study. The obtained powder has a smaller specific surface area, a lower surface energy, a smaller porosity, and a higher density. The samples under this condition can be better used in subsequent materials. The enhancement of various properties of zirconia can significantly prolong the service life of materials in practical applications.     

Preparation and characterization of ZTA bioceramics with and without gradient in composition

Properties and proof of suitability of homogeneously and graded ZTA bioceramics with various Y₂O₃ stabilized zirconia contents were investigated. Therefore porous alumina was infiltrated with different amounts of Y₂O₃ doped ZrO₂ precursors. At homogeneously infiltrated samples biaxial flexural strength and wear behavior were investigated (ISO 6474). Subsequently, at hip joint heads the static fracture strength was determined (ISO 7206-10). Materials ranging from approx. 4 to 20 wt% Y₂O₃ stabilized zirconia were characterized relative to the sinter density, the microstructure, the phase composition and the dispersion of the stabilized zirconia phase. Bioceramics showed high sinter density, fine microstructures, excellent wear property and significantly increased biaxial flexural strength. A 41% increase in strength through the formation of Y₂O₃ stabilized zirconia gradient in the conical bore of the heads was reached. Low compressive stresses in cone of this heads were found.ZTA bioceramics are potentially suitable for use as hip replacement components.     

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.     

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.     

Slag-resistant products made from stabilized ZrO2

Conclusions The resistance of zirconia refractories to the action of acid slags is determined by the interaction between the added stabilizer and the silica component of the slag and by the rate of formation of the corresponding silicates. Of those materials studied, the most resistant of the action of the more acid slags is ZrO₂ stabilized by Y₂O₃.The rate of wear of the articles made from stabilized zirconia under the action of the more basic of the melts we studied is determined by the diffusion of Ca²⁺ into the structure of ZrO₂ forming CaZrO₃ which leads to the articles becoming less dense. The interaction between the stabilized ZrO₂ and the basic industrial slag, moreover, is accompanied by the intense dissolution of the refractory in the slag as a result of the formation of low-melting melts at the slag-refractory interface.Thus, zirconia refractories have an excellent resistance to the action of an acid multicomponent slag and are intensively damaged by basic slags.Translated from Ogneupory, No. 3, pp. 54–57, March, 1979.     

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.     

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⁺.     

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.     

Al2O3–Y3Al5O12(YAG)–ZrO2 ternary composite rapidly solidified from the eutectic melt

In situ fabrication of new ceramic eutectic composites by rapid solidification of eutectic drops is a cheap and quick method compared to fabrication of directional solidification or multi-step fabrication methods of fiber reinforced/layered composites for high temperature use. This study reports the fabrication of ceramic composites during rapid solification of eutectics melts in the ternary oxide alumina–yttria–zirconia system. Layered ternary eutectics are obtained in the alumina–YAG–zirconia subsystem. The microstructure of Al₂O₃–Y₃Al₅O₁₂–ZrO₂ composites rapidly solidified from melts is presented.     

Synthesis and properties of novel blue zirconia ceramic based on Co/Ni-doped BaAl12O19 blue chromophore

Solid solutions based on BaAl_12-xM_xO₁₉ (M = Co²⁺, Ni²⁺) showing intense blue shades were successfully synthesized by conventional solid state reaction. Then, novel zirconia ceramic materials with intense blue hues were then prepared upon addition of 5 wt% of the synthesized chromophore to a ZrO₂ white matrix containing 5 wt% Y₂O₃ and sintered at 1400 °C for 6 h. The colors of the BaAl_12-xCo_xO₁₉ or BaAl_12-xNi_xO₁₉ are due to the d-d transitions of Co²⁺ or Ni²⁺ in tetrahedral coordination, respectively. The colored zirconia ceramics were all indexed with tetragonal phase. The coexistence of the chromophore and ZrO₂ were observed by scanning electron microscopy and energy dispersive spectrometer. The hardness of the as-synthesized blue zirconia ceramic was slightly higher as compared to the pure undoped sample.     

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.     

Development of stabilized zirconia–alkali salts dual membranes for carbon dioxide capture

Molten Na₂CO₃–K₂CO₃ (NKC, 56–44 mol%) eutectic compositions were vacuum-impregnated, at the eutectic temperature, into two porous ZrO₂:8.6 mol% MgO (magnesium-partially stabilized zirconia, MgPSZ) and ZrO₂:8 mol% Y₂O₂ (yttria-fully stabilized zirconia, 8YSZ) ceramics. Thermogravimetric analyses were performed in mixtures of that composition with MgPSZ and 8YSZ ceramic powders. Before impregnation, porosity was achieved in the two compounds by addition and thermal removal of 30 vol.% NKC. To ascertain the carbonates had filled up through the ceramic body, both sides of the parallel and fracture surfaces of the disk-shaped impregnated compositions were observed in a scanning electron microscope and analyzed by energy-dispersive X-ray spectroscopy. The electrical conductivity of the two ceramics, before and after impregnation, was evaluated by electrochemical impedance spectroscopy in the 5 Hz–13 MHz frequency range from approximately 530 to 740°C. The permeation of the carbonate ions through the membranes via the eutectic composition was assessed by the threshold temperatures of the onset of the carbonate ion percolation. The objectives were to prepare dual-phase membranes for the separation of carbon dioxide and for the development of carbon dioxide sensors.     

Ceramics Based on Cubic ZrO2 (Y2O3) with Addition of a Fused Al2O3 – ZrO2 (Y2O3) Eutectic

Ceramics based on cubic zirconia with addition of crushed granules of fused or rapidly cooled Al₂O₃ – ZrO₂ (Y₂O₃) eutectic are developed and their properties (shrinkage, open porosity, apparent density, bending strength, and grain size) determined. The ceramic composites can find use in the preparation of electrolyte material for high-temperature fuel cells.     

Effect of waste-derived MA spinel on sintering and stabilization behavior of partially stabilized double phase zirconia

Cubic-stabilized zirconia ceramic composites have been synthesized by conventional sintering, starting from commercial m-ZrO₂, Y₂O₃, and waste-derived magnesium aluminate spinel (MA) powders. In this work, the effect of sintering temperature and MA content on stabilization and densification properties of YSZ have been duly considered. MA-free YSZ0 composite sintered at 1600°C-1700°C revealed m- and t-ZrO₂ dual-phase structure where its m-ZrO₂ was partially stabilized upon temperature rising into tetragonal phase by Y³⁺ diffusion inside zirconia structure. YSZ10-50 composites containing 10-50 wt% MA demonstrated dissimilar behavior where their m-ZrO₂ was transformed and stabilized into a cubic form by diffusion of Y³⁺, Mg⁺², and Al⁺³ inside zirconia lattice. Furthermore, densification of YSZ10-50 powder mixtures by conventional sintering at 1600°C for 2 hours resulted in fully dense compacts with micrometer-sized grains. The outcomes indicate that MA has a significant effect on m-ZrO₂ stabilization into the cubic phase structure at room temperature. In this respect, this study offers huge potentials for developing fully stabilized c-ZrO₂ ceramics that could be possibly used as industrial ceramics for structural applications of harsh chemical and thermal environmental conditions.