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This work explores the incorporation of graphene-based two-dimensional nanostructures as moisture barriers to delay hydrothermal ageing of yttria-stabilized zirconia and strengthen its use in biomedical applications. Two sets of highly dense zirconia composites incorporating multilayered graphene with very different lateral dimensions, few layer graphene and exfoliated graphene nanoplatelets, were prepared. The effect of the addition of graphene nanostructures on zirconia ageing was investigated by conducting accelerated hydrothermal degradation experiments in an autoclave. An improved resistance to low-temperature degradation and a high tolerance to damage were achieved in the composites compared to those of monolithic zirconia. The incorporation of 1 vol% multilayered graphene was very effective in restricting the hydrothermal degradation. In particular, the composite incorporating exfoliated graphene nanosheets exhibited outstanding resistance to ageing because of their fine dispersion throughout the matrix, which effectively seemed to restrict grain growth and slow the propagation of the transformation front to the ceramic bulk.

The chemical and structural stability of two commercial multicomponent silicate glasses (SCN and G6) in contact with yttria-stabilized zirconia (YSZ) was investigated after exposure times of up to 40,000 hours in air at 800 °C. With exposure time, interfacial layers develop at the SCN-YSZ and G6-YSZ interfaces, which were characterized in detail using both quantitative chemical analysis and atomic-resolution imaging. At the SCN-YSZ interface, a Ca-Ba-Si-O reaction phase was found to grow by diffusion control. In G6-YSZ, Raman spectroscopy and electron microscopy revealed a disorganized interfacial reaction later between G6 and YSZ, and the occurrence of cubic to tetragonal to monoclinic phase transformations in YSZ. This microstructural evolution is discussed in terms of devitrification resistance of glass and diffusion processes at interfaces.

Zirconia ceramics have excellent physical and chemical properties and have several applications. However, owing to their hardness and brittleness, it is difficult to realise the non-destructive high-efficiency machining of zirconia ceramics. Herein, we propose an efficient non-Newtonian fluid polishing method for zirconia ceramics based on the weak magnetorheological strengthening thickening effect. The nanoscale material removal and evolution mechanisms of the zirconia ceramic surface were investigated. Based on the results obtained through scanning electron microscopy and a derivation of the fluid shear stress model in the polishing zone, we clarify the microscopic material removal mechanism during the machining process, and establish the prediction model of material removal rate. The detection results of the surface quality were in good agreement with the established material removal mechanism. The model of material removal rate could predict the processing effectively, and the average relative error was 4.45%. The experimental results demonstrate that the proposed weak magnetorheological shear thickening polishing (WMRSTP) method can realise lossless, self-adaptive, ultra-precision machining of a hemispherical zirconia ceramic workpiece. Compared to the traditional non-Newtonian fluid polishing method, the polishing quality and polishing efficiency of this method are significantly improved. The surface roughness Sa, the surface accuracy PV, and the material removal rate MRR of the zirconia hemispherical workpiece after 1 h of WMRSTP were 13.2 nm, 0.104 μm, and 5.96 μm/h, respectively.

The effect of copper oxide doping (0.05–1 wt%) on the densification, microstructure evolution and mechanical characteristics of alumina toughened zirconia (ATZ: 80 wt% Y-TZP + 20 wt% Al2O3) ceramic composites was investigated. Green samples were pressureless sintered using a short hold time of 12 min at temperatures varying from 1250 °C to 1500 °C. The incorporation of up to 0.2 wt% copper oxide was beneficial in promoting densification at low sintering temperature and improving the mechanical properties of ATZ without affecting the tetragonal phase stability. It was found that 0.2 wt% copper oxide addition was most efficacious, and the samples could attain a relative density of approximately 92% at 1250 °C, approximately 97% dense at 1350 °C and above 99% dense at 1450–1500 °C. This approach was also accompanied by an improvement in the Vickers hardness (12.7 GPa) and fracture toughness (6.94 MPam1/2) when consolidated at 1450 °C/12 min. In comparison, the undoped composite exhibited relative densities of approximately 80% at 1250 °C, 87% at 1350 °C and approximately 97%–98% at 1450 °C-1500 °C. However, the study also found that higher dopant levels (0.5 wt% and 1 wt%) was not beneficial because the tetragonal zirconia phase was disrupted upon cooling from sintering, resulting in the monoclinic phase formation. In addition, low densification and poor mechanical properties were obtained.

The additive composition of an AlN ceramic substrate material was optimized to achieve high strength and thermal conductivity. MgO-CaO-Al2O3-SiO2 (MCAS) glass and Y2O3 were used as basic additives for improved sintering properties and thermal conductivity, thereby allowing for AlN to be sintered at a relatively low temperature of 1600 °C without pressurization. Yttria-stabilized zirconia (YSZ) was added (0–3 wt%) to further improve the strength of the AlN ceramic. YSZ and Y2O3 reacted with AlN to produce ZrN, Y4Al2O9, and Y3Al5O12 secondary phases. The formation of these yttrium aluminate phases improved the thermal conductivity by removing oxygen impurities, while ZrN formed at the AlN grain boundaries provided resistance to grain boundary fractures for improved strength. Overall, the AlN ceramic with 1 wt% MCAS, 3 wt% Y2O3, and 1 wt% YSZ exhibited excellent thermal and mechanical properties, including a thermal conductivity of 109 W/mK and flexural strength of 608 MPa.

Zirconia ceramic is a significant structural material, but its use under some extreme circumstances is limited by its mechanical properties. In this work, SiC particles (SiCp) were added into alumina toughened zirconia ceramics to prepare ZrO2–Al2O3-SiCp ceramics with high performance by using oscillatory pressure sintering (OPS). Results showed that the best OPS temperature of 1600 °C was obtained, and the optimal SiCp particle size and content were 200 nm and 10 vol% respectively. Under these conditions, the specimen exhibited higher mechanical properties including Vickers hardness of 15.43 GPa, bending strength of 1162 MPa and fracture toughness of 6.36 MPa m1/2. Moreover, it was found that the atomic matching between ZrO2/SiCp, Al2O3/SiCp, and ZrO2/Al2O3 was much higher, showing the coherent interface relationship. Therefore, it was favorable for enhanced mechanical properties of as-prepared ZrO2–Al2O3-SiCp ceramics.

In this study, a La0.8Ba0.2TiO3−δ (LBT) upper layer was deposited on an yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC) through atmospheric plasma spraying. The thermal cycling behaviors of the YSZ single-ceramic-layer and LBT–YSZ double-ceramic-layer coatings at 1000 °C were investigated through a water quenching method. Moreover, phases, microstructural evolution, and elemental distributions were studied through by X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that the thermal cycling lifetime of the LBT–YSZ coating was 27% higher than that of conventional YSZ coating. The conventional YSZ coating failed after 251 cycles because of the joining of the continuous horizontal and vertical cracks caused by the formation of thermal growth oxides and the bending effect of the single-ceramic-layer structure. The thermal cycling behavior of the LBT–YSZ coating was different from that of the YSZ coating at the edge and center. Although the former was similar to the failure behavior of the YSZ coating, the cracks in the vertical direction were deflected as a result of the bending effect of the double-ceramic-layer structure during quenching. This deflection led to the formation of slope cracks with longer propagation paths and slope spallation zones. The latter showed small-debris spallation on top of the LBT upper layer due to the lower fracture toughness of the LBT, which protected the central coating from the structural damage of the ceramic coating. These two behaviors would either release the thermal stress or increase the crack-propagation energy requirement in the ceramic coating, consequently improving the thermal cycling lifetime of the LBT–YSZ coating. In summary, depositing an LBT upper layer could potentially improve the thermal cycling lifetimes of TBCs.

Made available in DSpace on 2022-04-28T19:48:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-03-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The objective of this study was to assess the wear behavior and its effects on the flexural strength of silica-infiltrated zirconia compared to glaze and polishing finishing treatments. To do so, disc-shaped samples of a second-generation zirconia were prepared and divided into three groups: silica infiltration, glazing, or polishing. Half of the samples of each finishing were subjected to sliding wear testing using a steatite antagonist. The discs and antagonists had their volume loss measured. The wear-tested and the other half of samples were subjected to biaxial flexural strength testing and the following characterization analyses were also performed: roughness, hardness, X-ray diffraction, profilometry, and scanning electron microscopy (SEM). Data were evaluated with ANOVA and Weibull analyses. Glazing caused greater antagonist volume loss, followed by silica infiltration, and polishing. Silica-infiltrated zirconia surface was similarly worn to polished, which was lower than that for glazed zirconia. Polished zirconia presented the highest flexural strength. However,the strength decreased and became similar in all worn groups. Silica infiltration showed slightly lower characteristic strength after sliding wear. The highest roughness and hardness values were observed on glazed zirconia. These values decreased after wear testing and became similar to the other groups. SEM evidenced an irregular surface for glazing. No phase transformation occurred after sliding wear. Despite producing some volume loss on zirconia and antagonist surfaces, silica infiltration is a promising alternative for finishing monolithic restorations. Moreover, the damage caused by sliding wear leads to decreasing the strength of zirconia regardless of the surface finishing. Department of Dental Materials and Prosthodontics São Paulo State University (Unesp) Institute of Science and Technology, Av. Eng. Francisco José Longo, 777, Jardim São Dimas, SP Department of Physics Aeronautics Technological Institute (ITA), Praça Marechal Eduardo Gomes, 50, SP Department of Dental Materials and Prosthodontics São Paulo State University (Unesp) Institute of Science and Technology, Av. Eng. Francisco José Longo, 777, Jardim São Dimas, SP FAPESP: 2015/11405-7 FAPESP: 2016/07920-6 FAPESP: 2017/20633-9 FAPESP: 2018/22627-9 CNPq: 408932/2016-3

Adsorption is a simple and efficient phosphorus removal method used to control the eutrophication of water bodies. A simple and gentle atmospheric pressure hydrothermal method by adjusting the dosage of ammonium chloride and sodium hydroxide was used to synthesize amorphous, monoclinic, and tetragonal zirconia nano-powders with high specific surface areas (383.91 m2/g, 330.01 m2/g, and 234.36 m2/g) and particle size of about 40 nm for phosphate adsorption. When pH = 6.3, the phosphate adsorption capacity of the amorphous monoclinic phase and the tetragonal phase respectively reached 102.58 mg P/g, 68.11 mg P/g, and 37.25 mg P/g and the adsorption process of the three crystal forms of zirconia powders conformed to the Langmuir adsorption model. In the first 2 min of rapid adsorption, amorphous zirconia completed 76.23% of the adsorption process and the monoclinic phase also completed more than 60%. The adsorption process of the three crystal forms of zirconia was completed within 240 min and conformed to the pseudo-second-order kinetic model. Their adsorption characteristics of the three crystal forms of zirconia decreased with the increase in pH. While the pH was above than the isoelectric point of the solution, the adsorption capacity was significantly reduced. The large specific surface area and high hydroxyl content of the zirconia nano-powder made a great contribution to the adsorption process.

Inorganic fibers and opacifiers are indispensable for improving the strength and high temperature insulation performance of the fumed silica-based thermal insulation material. However, zirconia fiber enhances the strength of the fumed silica-based thermal insulation material and reduces the radiative heat transfer to replace the opacifier. The sample of fumed SiO2/Al2O3 doped with 7% zirconia fiber (FZ7) has a lower density of 0.70 g/cm3 and a high porosity of 75.0%. In addition, the thermal conductivity of FZ7 at 800 °C is 0.077 W/(m·K), which is lower than the sample of fumed SiO2/Al2O3 doped with 7% glass fiber (FG7) and 0.089 W/(m·K) at 800 °C. The effective extinction coefficient of the thermal insulation material containing zirconia fiber is larger than that of the glass fiber by Fourier transform infrared spectroscopy analysis and calculation, indicating that the zirconia fiber has a distinct absorption and scattering effect on infrared radiation to reduce the radiative heat transfer. Therefore, zirconia fiber enhances the strength and decreases the high temperature thermal conductivity of the composites with the dual effect on the insulation and mechanical performance of the fumed silica-based thermal insulation material.

For dental materials, a certain defect tolerance would be beneficial. Some Ceria-stabilized zirconia (Ce-TZP) composites are promising dental repair materials, as they have been shown to exhibit an obvious amount of transformation-induced plasticity with almost no dispersion in strength data. The purpose of this study was to design a novel tricalcium silicate (C3S)-based dental repair material by adding 10 mol.% Ce-TZP to improve fracture toughness and dipotassium hydrogen phosphate (K2HPO4) as the setting accelerator. The study evaluated the physicochemical properties, in vitro cell activity, and antibacterial activity of Ce-TZP/C3S composite cement, and the results revealed that Ce-TZP/C3S cement showed a fast-setting ability and good washout resistance when the setting time was controlled within 26–43 min. With increasing Ce-TZP content, the mechanical properties, especially the flexural strength and fracture toughness, were gradually enhanced. Additionally, the 30% Ce-TZP/C3S composite showed good antibacterial activity and in vitro cytocompatibility. The study concluded that 30% Ce-TZP/C3S composites could be regarded as ideal candidates in the field of dental materials due to their excellent physical and chemical properties, antimicrobial activity, in vitro cytocompatibility, outstanding fracture toughness and fast-setting ability.

The wettability of 3 mol% yttria-stabilized zirconia (3YSZ) by molten Cu was noticeably improved by applying a direct current (DC). Furthermore, robust brazing of 3YSZ to a GH3128 superalloy using a Cu filler was achieved within seconds at 1100 °C with the assistance of a DC. When the DC flowed from 3YSZ to GH3128, the shear strength of the joints reached 225 ± 20 MPa at 1 s of energization and increased to 330 ± 30 MPa at 5 s of energization. The formation of Cu51Zr14 at the 3YSZ/Cu interface, the dissolution of Ni into the Cu filler, the dispersive distribution of fine granular (Mo, Cr, W)(Ni, Cu) in the brazing seam and the relief of residual stress by ductile (Cu, Ni) solid solution were crucial for achieving the high-strength joints. This work provides a novel and economical method for ultrafast brazing of zirconia to metals.

Understanding the microstructural transformation of plasma sprayed (APS) yttria-stabilized zirconia (YSZ) after experiencing the thermal shocking cycles is practically important for the coating optimization in terms of structure and performance. In this study, thermal shocking tests were conducted on the YSZ coated piston crown. The microscopic morphology and structure alteration across the YSZ coating interface over the piston crown was characterized by the ex-situ techniques. The results revealed that the YSZ coating primarily consisted of a stable tetragonal phase, without the monoclinic phase even after 800 cycles of thermal shocking. As the thermal shocking test continued, the pore number within the YSZ coating gradually decreased due to their spontaneous closure and the grain size correspondingly increased. Some visible cracks parallel to the interface consisting of YSZ and bonding layer happened at the localized regions of the YSZ coating. The stress state of YSZ coating was from originally tensile to compressive after thermal exposure, which helped prolonging the service lifetime of YSZ coating. In particular, the thermal shock resistance of plasma sprayed YSZ coated piston crown in association with the varying microstructure was also discussed.

Thermal barrier coating (TBC) materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine. In this study, a novel high entropy hafnate (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 was synthesized by solution combustion method and investigated as a potential TBC layer. The as-synthesized (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 possesses a pure single disordered fluorite phase with a highly homogeneous distribution of rare earth (RE) cations, exhibiting prominent phase stability and excellent chemical compatibility with Al2O3 even at 1300 °C. Moreover, (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 demonstrates a more sluggish grain growth rate than Y2Hf2O7. The thermal conductivity of (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 (0.73-0.93 W m−1 K−1) is smaller than those of components RE2Hf2O7 and many high entropy TBC materials. Beside, the calculated thermal expansion coefficient (TEC) of (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 (10.68 × 10−6/K, 1100 °C) is smaller than that of yttria-stabilized zirconia (YSZ). Based on the results of this work, (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 is suitable for the next generation TBC materials with outstanding properties.

In this study, composite ceramic slurries based on submicron-micron-sized cordierite-zirconia were prepared with varied zirconia content. Standard bending strength and fracture toughness testing samples were directly designed and fabricated using stereolithography 3D printing followed by different sintering schemes to study the mechanical reinforcement effect. The physical compositions and microstructures of the samples were characterized. The additively manufactured cordierite-zirconia composites exhibit excellent mechanical properties. Maximum measured bending strength (136 MPa) and fracture toughness (1.8 MPa m1/2) were reached by adding 2 wt% and 6 wt% zirconia, namely an increase of 44% and 66% relative to pure cordierite, respectively. The strengthening and toughening mechanisms of the composites were further explained mainly by microstructural analysis. This study provides an alternative and direct design and manufacturing method for the mechanical measurement and reinforcement of ceramic composite parts based on the use of 3D printing technology.

A bstract The purpose of this study was to fully realize the clinical plausibility of a newly introduced yttria gradient monolithic multilayer dental zirconia and the current indication range for dental zirconia; hence, an investigation leading to a comprehensive understanding of the effect of yttria content on the properties of zirconia was undertaken. Each layer from a yttria gradient monolithic multilayer zirconia system with two types (esthetic and functional types, Meiying Zirconia, UPCERA, China) was selected for investigation of its chemical composition by X-ray fluorescence. Layers with yttria content interval of about 0.4 mol%-0.5 mol% were chosen for subsequent testing. Their phase fractions, grain sizes, low-temperature degradation (LTD) resistance, coefficient of thermal expansion (CTE), and mechanical properties were characterized. The yttria content from the occlusal to the gingival region was from 5 mol% to 4.1 mol% and 4.7 mol% to 3.2 mol% for esthetic type and functional type, respectively. Ultimately, we investigated the selected five yttria content layers, 5Y, 4.5Y, 4Y, 3.6Y, and 3.2Y. With increased yttria content, increasing cubic phase fractions (from 25.86 wt% to 58.53 wt%) and mean grain sizes (from 0.31 μm to 0.72 μm) were detected; monoclinic content after LTD decreased; and there was a decreasing tendency for CTE, although no statistically significant difference was found (F = 2.43, p = 0.117). In addition, yttria dopant showed no effect on elastic modulus (F = 2.43, p = 0.464) but slightly increased hardness (F = 4.10, p = 0.014). However, there were notable decreases in fracture toughness (F = 227.58, p

Nano-zirconia has been widely applied due to its excellent physical and chemical properties (e.g., high strength, corrosion resistance, oxygen ion conductivity). Existing preparation methods of nano-zirconia tend to require long reaction time, and the sizes of final particles are large with uneven distributions. Sub-/supercritical hydrothermal synthesis of nanoparticles is favored by researchers owing to controllable reaction process, uniform particle size distribution, good reproducibility, short reaction time, high conversion rate and harmlessness to environment. In this paper, the characteristics and mechanisms of dissolution, crystallization and growth of nano-zirconia during sub-/supercritical hydrothermal synthesis are systematically reviewed. The influences of process and material parameters on the size and purity of particles are analyzed. Then, the reaction mechanism and product phase transition mechanism during hydrothermal synthesis of zirconia are summarized to provide a theoretical reference for the oriented preparation. Finally, the improvement and commercialization of sub-/supercritical hydrothermal synthesis technology are evaluated, and the future research topics are proposed.

Zirconia toughened alumina (ZTA) materials are applied for cutting tools, wear parts and in biomedical applications. Due to the constraint of the rigid alumina matrix, ZTA materials with up to 10 vol% zirconia addition (AZ10) do not require addition of stabilizer oxides. AZ10 materials based on submicron sized alumina and four different submicron to nanoscale zirconia powders were manufactured by hot pressing at temperatures between 1475−1600 °C. Results show that the powder choice has a strong influence on mechanical properties, evolution of microstructure and phase composition. Best results with strength up to 850 MPa, fracture toughness values of 8.5 MPa√m and invulnerability to overfiring were obtained with zirconia powders showing the coarsest yet most homogeneous primary particle size and a low degree of agglomeration. Ultrafine but hard agglomerated powders lead to materials with extremely inhomogeneous microstructure and inferior properties.

The wettability of 3 mol% Y2O3-stabilized ZrO2 (3YSZ) by molten Cu can be greatly improved by applying pulsed currents at 1373 K. The improvement was closely related to current polarity and influenced by duty cycle and frequency. When the Cu/3YSZ interface was under cathodic condition, the wettability was mainly improved by the formation of substoichiometric ZrO2-δ and metallic Zr at the interface. Increasing duty cycle caused the interface to change from forming protrusions to creating depression. Decreasing frequency further deepened the depression. In the opposite polarity, the adsorption and enrichment of oxygen reduced the solid-liquid and liquid-vacuum interfacial energies, thus improving the wettability. Only bubbles formed at the interface. The larger the duty cycle, the more rapidly bubbles formed and escaped. The effect of frequency at this polarity was weak. Overall, this work provides a novel and effective strategy for tailoring the wettability and interfacial chemistry between zirconia and metals.

Leucite and zirconia are commonly used in the production of prosthetic dental materials. Leucite presents attractive optical properties but low toughness and wear resistance, which limits its use. Zirconia has much higher toughness, but due to aesthetic reasons and ageing issues, needs to be glass veneered. Chipping of such veneer is usually responsible for the abnormal wear induced on the antagonist teeth. Leucite reinforced with 25% of nano-zirconia is a promising alternative to overcome these issues, allowing the production of dental restorations without veneer. This study aims to investigate if leucite-zirconia composites have suitable optical, mechanical and tribological properties to be used in dental restoration. Samples with different compositions of leucite and/or nano-zirconia were produced by unidirectional compression and characterized concerning density, surface morphology, roughness, hardness, toughness, and translucency. Wear tests were performed in a chewing simulator using human cusps as counterbodies. Tests were also performed in glazed zirconia for comparison. 25% ZrO2 leads to the lowest wear of the tribological pair among the studied systems, except 100% ZrO2. This can be attributed to the toughening effect of zirconia and reduced size of third body particles. Abrasion was the main wear mechanism observed in this pair. In addition, this was the composite that presented the highest translucency.

Understanding and optimization the rheological properties characterization of zirconia (ZrO2) based ceramics inks is critical for optimizing the production of Direct Ink Writing (DIW) components to achieve complex structures with similar properties as those obtained by using the traditional processing routes. In this work, ZrO2 based ceramic materials with different yttrium contents (3 and 8 mol %) were designed and produced by DIW to determine the most suitable ceramic ink composition in terms of the rheological properties (e.g. flow curves, viscosity, loss modulus G', storage modulus G¿, etc.) to design new components. Different ceramic inks with charges up to 75 wt % were prepared and characterized. A systematic study of the feedstock, as well as the different ceramic inks, was performed to determine the optimal ceramic charge. This characterization evidences that rheological properties of zirconia based ceramic inks are influenced by the particle size and amount of ceramic content. Furthermore, the rheological study highlights that the ZrO2 inks present a Non-Newtonian behavior depending on the ceramic content. Results revealed that the yttrium content affects the flow properties of ZrO2 suspensions in such a way that, higher shear rate was required to make the suspensions flow at increasing the amount of powder. It was also found that the best rheological properties corresponded to 73 and 70% for the 3Y- and 8Y–ZrO2 of ceramic charge, respectively.

Solid solutions based on BaAl12-xMxO19 (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 BaAl12-xCoxO19 or BaAl12-xNixO19 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.

In this work, a commercial 3 mol% yttrium oxide partially stabilized zirconia spray-dried granules were used as such, and after intensive milling, for the production of dense samples by robocasting technique. The aim was to evaluate the suitability of using spray-dried granules instead of submicron particles in robocasting of ceramic parts. To this aim, robocasting pastes were produced from the as-received granules as well as from nanometric particles obtained from an effective ball milling of the granules. The formulation of the pastes was optimized in order to achieve optimal printability. The drying conditions were optimized as well, and the control of temperature and humidity either in the printing and drying chambers allowed to eliminate any warping issue. After sintering at 1450 °C, the monolithic dense parts were characterized by ultra-fine and highly sintered microstructures, with the highest density achieved by the sample produced from granules. This material not only did not show the typical defects of granules-derived ceramics but was also characterized by fewer and smaller defects than the sample produced by the fine particles. It seemed that the presence of large granules, and thus large intergranular space, favored the debinding process and limited the formation of the typical processing flaws. The ball-on-three balls test was used for the evaluation of the mechanical properties of the dense samples. Biaxial flexural strength values in the range from ∼100 to 500 MPa (with an average value of 255 ± 93 MPa) were determined for the samples made from granules while these values ranged from ∼100 to 300 MPa (with an average strength of 198 ± 52 MPa) for the samples prepared from the milled particles. In spite of low, these values are in line with literature data, obtained on 3 mol% Y2O3–ZrO2 samples fabricated by the robocasting technique, and suitable to demonstrate the feasibility to use as-received granules as feeding material for robocasting parts.

One of the strategies for improving alumina ceramics' strength and optical properties is to eliminate grain growth during sintering. In this work, a casting process from water suspension was applied to prepare bulk alumina specimens doped with zirconia inclusions in the amount up to 0.5 wt.%. The effect of pure monoclinic (m-ZrO2) or cubic zirconia (ZrO2 stabilised with 8 mol.% Y2O3) on the sintering and alumina grain growth up to 1600 °C was studied. The results demonstrate that even a negligible addition of zirconia particles (0.2 wt.%) reduces grain growth after sintering up to 1400 °C. At the sintering temperature of 1600 °C, significant grain growth was observed for both pure and doped alumina ceramics. However, the careful analysis of the grain size distribution revealed narrower distribution for zirconia-doped alumina compared to pure alumina ceramic. The Vickers hardness decreases with the increasing sintering temperature due to grains' growth independently on the load applied. The indentation fracture toughness of samples sintered at 1400 °C does not significantly depend on the presence of inclusions added in amounts up to 0.5 wt.%.

Preparation and growth mechanism of anodization of Ti and Al has been widely concerned for two decades, but the research on anodic ZrO2 is relatively lacking. In this paper, anodic TiO2 and ZrO2 nanotubes were prepared in glycerol electrolyte containing 0.35 M NH4F and 4 vol% H2O under different anodizing voltages. We had successfully prepared the anodic ZrO2 nanotubes (AZNTs) with a complete top and a “bulb” at the bottom under 60 V, and with the increase of the applied anodizing voltage, the “bulb” cavity also increased. However, under the same anodizing conditions, the surface of anodic TiO2 nanotubes (ATNTs) is a cluster of nano-tip morphology, and the bottom of the ATNTs is a conventional hemisphere shape. In addition, both AZNTs and porous anodic zirconia (PAZ) were found to coexist in the anodic ZrO2 layer prepared at 60 V. Here, we used the oxygen bubble model and ionic current and electronic current theories to analyze the reason of the special morphology. It is confirmed that the porous anodic oxides are actually evolved from nanotubes. In other words, the structure is essentially the same.

Solid oxide fuel cells are promising renewable energy devices due to their high efficiency and fuel flexibility. As they operate at a higher temperature than other fuel cells, ceramic materials, such as perovskite-based La0.6Sr0.4CoO3 and La0.6Sr0.4Co0.2Fe0.8O3, can be used as electrodes to replace expensive noble metals. However, when the corresponding electrode and yttria-stabilized zirconia electrolyte are sintered together, SrZrO3 produced from a side reaction acts as an insulator and deteriorates the performance of the fuel cell. Thus, the dense functional layer of a ceria-based material should be introduced between the electrode and the electrolyte to suppress the formation of secondary phases. However, in the conventional cell manufacturing process, it is challenging to manufacture a dense functional layer under constrained sintering conditions. In this study, we develop a method for fabricating a dense gadolinia-doped ceria (GDC) functional layer, even under constrained sintering conditions, by using a sacrificial bismuth oxide, Bi2O3, sintering aid layer above the GDC layer. As thermal sintering progresses at 1000–1200 °C, the Bi2O3 sintering aid layer is sublimated, leaving only the pure GDC functional layer. The fabricated dense GDC functional layer characterized by various analysis methods shows improved solid oxide fuel cell performance.

Nanocrystals (NCs) of refractory oxides are widely used in both industry and fundamental research, despite their strong covalent bonding posing a serious obstacle to crystallisation under moderate liquid-phase environments. Here, we demonstrate a facile high-liquid-phase synthetic route for the fabrication of a refractory oxide, ZrO2, by employing molten metal chloride salt as the liquid reaction medium. The molten-salt-derived ZrO2 NCs exhibit an average size of approximately 120 nm with a limited size distribution. We also show that the molten-salt process allows for the direct doping of ZrO2 NCs with rare earth (RE) ions using soluble salt precursors, which results in the strong photoluminescence of the products. These luminescent refractory oxides based on RE-doped ZrO2 could be promising candidates for high-temperature sensing applications in industry. Furthermore, the molten-salt process could be generalised for the production of refractory metal oxide NCs that are otherwise not easily produced by ordinary wet-chemistry processes.

The wetting of 3% yttria-stabilized zirconia (YSZ) by Sn–8Zr, Sn–4Zr–4Ti, and Sn–8Ti alloys was studied at 800–900 °C. Both Zr and Ti improve the wettability via the formation of reaction products and adsorption. In the systems containing Zr additives in the alloys, ZrO2-x precipitates preferentially, and the wettability is dominated by interface adsorption. An anomalous temperature dependence was found in the final wettability of these systems owing to the decrease in adsorption with an increase in the temperature. The spreading dynamics are controlled by the dissolution of Zr, followed by the formation of a wetting ridge. The wettability of the Sn–8Ti/YSZ system is dominated by the precipitation of reaction products (Ti2O3 and Ti11.31Sn3O10). The reaction kinetics is the limiting factor for spreading in Sn–8Ti/YSZ, and the adsorption at the interface significantly decreased the energy barrier for wetting.

Pore structure is one of the major factors influencing the failure mechanisms of thermal barrier coatings (TBCs) during high-temperature service. Powders exhibiting different pore structures have been produced using the plasma spheroidization technique. To improve the strain tolerance of an aircraft engine's hot sections, the preparation method of the TBCs material—8-wt% yttria-stabilized zirconia powders—has been continuously optimized. In this paper, the constrained effects of pores on the ceramic top coating of plasma-sprayed lamellar TBCs were investigated. Furthermore, the crystal phase structures, thermophysical properties, porosity, microstructures, and synthesis mechanism of powders and coatings were analyzed. Results revealed that the top ceramic coating, which was made from powders cooled by air and distilled water, can influence the coating porosity. Moreover, thermal insulation was substantiated by the finite element analysis method. Consequently, dense powders cooled by water can be used on the top surface in direct contact with high temperature flame flow to resist the diffusion of oxides, and the porous powder cooled by air can be applied in the middle coating to decrease the thermal conductivity. Hence, TBCs with various layers of different porosities can prolong the service life of thermal barrier coatings.

International audience; Flash sintering is a very promising method with a great potential for the ultra-rapid production of objects with firing processes of mere seconds. However, the transition from few millimeters samples to larger scales is a key issue. In this study, we explore the spark plasma sintering approach allowing a stable hybrid heating in flash condition and producing near net shape sintered specimens. Two electric current configurations are employed for diameters of 15 and 30 mm to determine the effect of scale change and of electric current concentration. These experiments coupled with a Multiphysics simulation indicate that stable flash conditions can be reached for 30 mm specimens. However, even if the electrical current concentration is very effective at small sizes, it generates peripheral hot spots for large specimen dimensions. The blackening effect on zirconia flash specimens acts then as an indicator of the specimen thermal history.

Bubble formation and removal within the molten glass is an important issue in glass industry. Various sources of bubbles have been identified in glass manufacturing: decomposition of the glass components, air trapping, oxidation/reduction reactions, precipitation resulting from insufficient refining, etc. It has been demonstrated in a previous paper that the blistering phenomenon at the interface between a molten glass and a zirconia-based refractory can be ascribed to the oxygen semipermeability through the zirconia phase. The objective of this study is to clarify the role of temperature on the blistering process, and especially, below and above the phase transition temperature of zirconia (monoclinic/tetragonal transformation) and to evaluate the role of zirconia doping on the blistering level. The influence of the kinetics of the surface processes at the glass/refractory interface is emphasized. Quantitative measurement of the slight blistering ascribed to the so-called “redox shock” is also given.

In this study, the corrosion resistance and thermal shock resistance of ScxTa0.5−xYSZ (x = 0, 0.05, 0.25, 0.45, and 0.5 mol%) coatings prepared via the solid-state reaction method were compared and evaluated. The corrosion resistance and thermal shock resistance of different materials were analyzed using X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive spectrometry, and stereomicroscopy. Results show that Sc0.25Ta0.25YSZ has the best corrosion resistance and thermal shock resistance among all tested materials and the number of thermal cycles exceeds 679 at 1150 °C. The excellent properties can be attributed to the small ionic radius of Sc3+ in the Sc0.25Ta0.25YSZ composite, which gives the material good thermal stability at high temperatures. In the corrosion process, Sc0.25Ta0.25YSZ forms highly stable zirconia tantalum, affording good corrosion resistance.

The present work aims to address the effects of the sintering temperature (800–1500 °C) on the mechanical properties and material removal mechanisms of 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) based on a series of nanoindentation and nanoscratch experiments. The impacts of the sintering temperature on the mechanical properties, including plasticity, deformation behavior, indentation energies, and cracking resistance were rigorously studied. The acquired results indicate that 1100 °C signifies the transition threshold for the ceramic microstructure, leading to the entirely different mechanical properties and indentation responses for materials sintered at temperatures lower or higher than the threshold value. Moreover, 1100 °C is also a transition threshold of the material removal mechanism, before which the material removal mechanism is dominated by the plastic regime, and beyond which, the material removal mechanism tends to show ductile-brittle characteristics.

Two 3Gd-TZP materials were manufactured from powders produced by intense mixing and milling of unstabilized zirconia starting powders and gadolinia as stabilizer oxide by hot pressing at 1250 °C – 1400 °C. The materials show a combination of high toughness and moderate strength. In detail depending on starting powder the two TZP showed distinct differences concerning transformation characteristics, sintering temperature dependence of mechanical properties and the tendency to develop R-curve related deformation features such as non-linear stress strain curves and formation of transformation bands prior to fracture.

Herein, we propose a new multidisciplinary approach for investigating the corrosion behavior of thermal barrier coatings, combining the thermal-gradient mechanical fatigue method with hot corrosion tests. Corrosive salts (Na2SO4; V2O5) of varying concentrations (10−20 mg/cm2) were deposited on the surface of yttria-stabilized zirconia (YSZ) coatings to evaluate the microstructural changes occurring during the reaction, via thermal graded mechanical fatigue tests. The tests were conducted at a surface temperature of 1150 °C in 10 min cycles and underwent applied uniaxial tensile loads. The corrosion tests show that the ZrV2O7 plays an important role as an intermediate in the collapse of the lamellar structures during the reaction, which results from the repetitive precipitation of V2O5 and m-ZrO2 from the ZrV2O7. The microstructure of corroded YSZ coatings exhibited a different degradation mechanism under a thermomechanical environment, compared with the testing under isothermal atmospheric conditions.

Zirconia composites with few-layer graphene (FLG) were prepared by two powder processing routines -ultrasonic agitation or planetary ball milling- and spark plasma sintered at 1250 and 1300 °C. An in-depth study of the crystallinity of FLG, in terms of presence and nature of defects, was performed by Raman spectroscopy, revealing enhanced FLG crystallinity after sintering. This enhancement was more noticeable in the composites sintered at the highest temperature, with lower amount of structural defects and amorphous carbon. However, remaining amorphous carbon was detected in the composites prepared by planetary ball milling even after sintering at the highest temperature, resulting in lower electrical conductivities. Optimum results in terms of electrical conductivity were achieved for the composites prepared by ultrasonic agitation and sintered at 1300 °C, with electrical percolation limit below 2.5 vol% FLG and high electrical conductivity (678 S/m for 5 vol% FLG), as result of the enhanced FLG crystallinity after sintering.

In the present work, four oxides (SiO2, TiO2, LaO1.5, or CeO2) were selected as additives to increase the surface areas and the pore wall stability of mesoporous zirconia (ZrO2) fibers in virtue of enhancing the skeleton stability and hindering the grain growth. The preparation, characterization, and thermal evolution of mesoporous ZrO2 fibers incorporated with different amounts of oxide additive and simultaneously combined with heat treatment via water vapour are presented. The effects of different oxide additives on the crystallization and phase transformation of mesoporous ZrO2 fibers were investigated by X-ray diffraction. N2 adsorption-desorption studies were conducted to investigate the changes in the porous structure of the ZrO2 fibers heat-treated at different temperatures. Scanning electron microscopy confirmed the mesoporous structure of the ZrO2 fibers. The oxide-added ZrO2 fibers heat-treated in the presence of water vapour exhibited a mesoporous structure with increased surface areas and thermal stability. The related reinforcing mechanisms were proposed. It was deduced that water vapour promoted the removal of the soft template, leading to the formation of a mesoporous structure with a high surface area. Meanwhile, the increase in the surface areas of mesoporous ZrO2 fibers with the incorporation of the oxide additive was mainly due to the enhanced thermal stability of the porous walls. The relationship between the mesoporous structure stability and the zirconia phase stability was fully discussed. This work provides a new route for enhancing the surface areas and structure thermal stability of mesoporous ZrO2 fibers.

One approach to the improvement of implant-tissue interface is the creation of a bioactive surface. Here, bioactive glass-zirconia core-shell spherical nanoparticles were synthesized using a combination of sol-gel and sonochemical methods. The results revealed that the nanoparticles possess a ∼ 16 ± 4 nm rough tetragonal zirconia shell that surrounded the bioactive glass core. The optimized structure was coated on Ti6Al4V substrate through electrophoretic deposition technique. In order to obtain a stable suspension of nanoparticles in ethanol, dopamine was used as a surface treatment agent and cathodic electrophoretic deposition was successfully achieved on Ti6Al4V substrate. Also, the utilization of polyethyleneimine improved the adhesion between the coating and substrate. Due to the differences in surface charge of zirconia and bioactive glass nanoparticles, a high voltage and surfactant concentration are necessary for the simultaneous deposition of the particles. However, in the presence of core-shell nanoparticles, this issue was overcome. Microscopic examination of the coatings confirmed the elimination of cracks in core-shell constituted coatings. The adhesion between the coating and substrate increased significantly due to the rough surface of the core-shell nanoparticles. The Ca–P deposit formation on the surface of the bioactive glass and core-shell coatings were confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy.

Thulium oxide (Tm2O3) transparent ceramics with outstanding optical transparency were successfully prepared with various contents (0–4 at%) of zirconia (ZrO2) added as sintering additive using pressureless vacuum sintering at 1850 °C for 8 h. The effect of ZrO2 content on the changes of microstructure, transparency, Vickers hardness, fracture toughness, and thermal conductivity of Tm2O3 transparent ceramics were systematically investigated in this research. The experimental measurements showed that the in-line transmittance of 3 at% ZrO2-doped Tm2O3 transparent ceramics with the grain size of 6.7 μm was 76.3% at the wavelength of 880 nm and approximately 85% in the range of 2100–2500 nm. In addition, the Vickers hardness and fracture toughness were significantly improved from 7.8 ± 0.4 to 10.2 ± 0.2 GPa and 0.97 ± 0.06 to 1.32 ± 0.10 MPa m1/2, respectively, with content of ZrO2 increasing from 0 to 4 at%, while on the contrary the thermal performance was observed to decrease. This study showed that the in-line transmittance of Tm2O3 ceramics with favorably combined optical and mechanical properties could be achieved by the proper tailoring of ZrO2 content.

The mechanical properties and phase transformation behavior of carbon nanotube (CNT) reinforced 3 mol% yttria-stabilized zirconia (3YSZ) composites prepared by spark plasma sintering are reported for CNT contents between 0 and 7 wt%. CNTs are shown to improve the fracture toughness of the material by a combination of fiber pull-out and crack-bridging toughening mechanisms. Stress release by these mechanisms results in a smaller proportion of the YSZ matrix transforming from the tetragonal to monoclinic phase, reducing the microcracking that would otherwise result from cumulative volume expansion associated with this well-known phase transformation process. This produces a material with high fracture toughness without compromising hardness, thereby providing superior mechanical reliability. The high fracture toughness (7.0 MPa∗m1/2) of the 7 wt% CNT/3YSZ composite makes it an attractive material for high-impact, high-temperature applications such as environmental barrier coatings.

Surface modification of Zirconium (Zr) with Zirconia (ZrO2) nanotubes (NTs) was performed using a two-step electrochemical anodization to investigate the role of such a modified surface in apatite formation and the inhibition of bacterial growth on Zr implants. Pore size at the surface of the NT arrays was controlled, along with the NT length, by varying the 2nd-step anodizing time duration. Nearly four-fold changes in the pore size were achieved by varying the anodization at the second anodizing step. The apatite formation on the implant surfaces plays an important role in the osteointegration process, which can be greatly influenced by the morphology and crystalline structure of the surface. XRD analysis of the anodized surfaces identified a mixed phase of monoclinic and tetragonal ZrO2 NTs with the crystallite size decreasing with increased 2nd anodizing time duration. Surface roughness of the ZrO2 NTs decreased with an increase in anodizing time duration. The ZrO2 NTs with the largest pore sizes, and the smallest crystallite sizes (ZrO2-15 m) favoured the deposition of a Ca-rich compound on their surfaces following 24 days of soaking in SBF, and showed the highest apatite-forming ability among all studied samples. Antibacterial tests showed that the ZrO2-15 m sample exhibited antibacterial properties with 1log10 CFU/mL reduction of S. aureus and E. coli incubated in a buffer solution for 4 h. Loading the NT layer with antibacterial drug led to a complete inhibition of both bacterial species. The rate of drug release was slowed down by dip coating the drug loaded NTs in a PLGA solution. A higher number of dip-coating steps not only slowed down the release of the drug, it also led to a higher suppression of growth in both bacteria. Longer antibiotic exposure and optimized dosage of the drug released from ZrO2 NTs can therefore be managed by modifying the NT morphology and the number of PLGA dip-coating steps.

A type of strontium and amorphous calcium phosphate dipped premixed injectable tricalcium silicate-based dental root canal sealer was developed as the following protocols. A powder mixture containing tricalcium silicate, strontium carbonate (6, 8, 10, and 12 wt%), zirconia (20 wt%), calcium chloride (6 wt%), and amorphous calcium phosphate (ACP) (5 wt%) was mixed with liquid polyethylene glycol 400 (PEG 400) at a liquid-to-powder ratio of 0.5 mL/g and mechanically ground using a planetary ball to obtain the premixed injectable calcium silicate-based sealer. The sealer’s physicochemical property and cytocompatibility were evaluated in vitro. Quantitative data were expressed as mean ± standard deviation, and Student's t-test or a one-way analysis of variance (ANOVA) test were carried out at significant differences with P

Benefiting from the mature technology of ceramic injection molding, Fused deposition modeling based on highly-filled ceramic-polymer granular feedstocks has been showing great potential and advantage for fabricating 3D ceramics. Herein, 3D zirconia ceramics using granular feedstock were fabricated, and typical morphology, surface quality, and effect of the thermal accumulation on 3D structure were clarified. Typical morphology of printing steps on the surface were quantitatively characterized, and determined by the surface curvature and layer height of the printed structure. Aligned triangular pores were confirmed at the junction of the deposited filaments with elliptical cross-section morphology. Simple square plates with different size were used to illustrate the influence of thermal accumulation on the morphology of 3D structure. Small printing size increased the thermal accumulation during deposition, resulting in decreased printing quality caused by the secondary over-melting of former deposited layers. Except for the pores at the junctions, dense zirconia ceramics with uniform structure and smooth surface could be achieved. A low-cost and high-quality route for the preparation of 3D ceramics was demonstrated via FDM of highly-filled granular feedstocks.

Three-phase alumina/YAG/yttria-stabilized cubic zirconia (YSZ) composites were fabricated by a solid-state reaction route starting from commercial powders of Al2O3, Y2O3 and monoclinic ZrO2. The final phases Al2O3, YAG and YSZ were obtained after calcination of the powder mixtures at 1400 °C. Dense bulk composites were obtained after sintering, with a homogeneous microstructure of fine and equiaxed grains with sizes of 1 μm. Compressive mechanical tests were performed at 1300–1450 °C in air at constant load and at constant initial strain rate. A brittle-to-ductile transition was found with increasing temperature. Grain boundary sliding is the main deformation mechanism in the ductile regime, characterized by a stress exponent of 2 and by the absence of dislocation activity and changes in grain morphology. Alumina seems to be the rate-controlling phase owing to the improvement in creep resistance by the presence of yttrium and zirconium of the other two phases.

Flash event caused by a DC electric field/current was applied to the crack healing in 8 mol % Y2O3 stabilized cubic ZrO2 polycrystals (8Y-CSZ). The flash event, which occurred by applying the DC power higher than a critical value of 100 mW/mm3, successfully healed the microcrack within several minutes without any healing agents at a furnace temperature of 800 °C. As compared to the healing treatment under static annealing, the healing phenomena were accelerated about 2 times under the flash treatment even at the same temperatures, suggesting that the enhanced healing phenomena cannot be explained only by the temperature effect. Since the rate of grain growth was accelerated under the flash treatment, the flash healing would be accelerated through the current-enhanced diffusional processes. This study shows for the first time that the flash event has a potential to apply to the crack healing process in the ceramic materials and composites.

The shortcomings of high-temperature solid oxide fuel cells necessitate research on SOFCs designs that are capable of operation at intermediate temperatures (600–800 °C), the so-called intermediate-temperature SOFCs. One of the limitations for the efficient operation of these fuel cells lies in insufficient ionic conductivity of the electrolyte material. This review briefly covers the types of ceramic electrolytes used in intermediate-temperature SOFCs and focuses on scandia-stabilized zirconia (ScSZ) electrolytes. It explores possibilities of control of phase stability and ionic conductivity of ScSZ by co-doping by various oxides, such as ceria, bismuth oxide, yttria, ytterbia, and several other co-dopants. It also covers a range of novel techniques applied to preparation of ScSZ electrolytes, which can be used to influence microstructure and phase composition of the electrolytes. The recommendations on the optimal ScSZ co-doping scheme are developed in the course of the present work.

Three different alumina sources (boehmite, aluminium nitrate and α-alumina particles) and 12Ce-TZP powder containing 1 wt% lanthanum oxide were used to prepare 12Ce-TZP-based alumina-toughened-zirconia (ATZ) composites. The obtained ATZs had similar density and phase composition, whereas the microstructures were significantly different. Alumina-particle addition gave rise to a typical ATZ microstructure consisting of equiaxial sub-micrometer zirconia and alumina phases, while the lanthanum hexa-aluminate phase was formed in large and non-homogenously distributed precipitates (∼3.5 μm in length). The boehmite and aluminium nitrate-based composites contained not only sub-micrometer equiaxial alumina and zirconia grains but also small-sized lanthanum hexa-aluminate precipitates (∼1.2 μm in length) that were inter- and transgranularly positioned in the zirconia matrix and effectively promoted crack deflection and toughening. In combination with a higher t-ZrO2 transformability, the boehmite-based composites had a higher indentation fracture resistance, strength and reliability compared to the aluminium-nitrate and alumina-particle based equivalents.

The relationship between fracture toughness and Yttria content in modern zirconia ceramics was revised. For that purpose, we evaluated here 10 modern Y2O3-stabilized zirconia (YSZ) materials currently used in biomedical applications, namely prosthetic and implant dentistry. The most relevant range between 2-5 mol% Y2O3 was addressed by selecting from conventional opaque 3 mol% YSZ up to more translucent compositions (4−5 mol% YSZs). A technical 2YSZ was used to extend the range of our evaluation. The bulk mol% Y2O3 concentration was measured by X-Ray Fluorescence Spectroscopy. Phase quantification by Rietveld refinement considered two tetragonal phases or an additional cubic phase. A first-account of the fracture toughness (KIc) of the pre-sintered blocks is given, which amounted to 0.4 – 0.7 MPa√m. In the fully-densified state, an inverse power-law behavior was obtained between KIc and bulk mol% Y2O3 content, whether using only our measurements or including literature data, challenging some established relationships. A linear relationship between KIc and the fraction of the transformable t-phase was established within the range of 30–70 vol%.