Yttria-stabilized Zirconia Ceramics Research Articles

Experimental and computational model approach to assess the photothermal effects in transparent nanocrystalline yttria stabilized zirconia cranial implant

Background and objectiveIn the last few years, we have been exploring the use of transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) ceramics as a biomedical transparent cranial implant, referred as the “Window to the Brain” (WttB). The WttB aims at providing chronical optical access to the brain for diagnostics and therapeutic procedures and it has shown to provide an effective means to obtain enhanced results from optical imaging techniques. The objective of this work is to explore the photothermal effects of the Wttb produced when it is irradiated by a laser source. MethodsWe make experimental and computer models. The thermal effects of laser irradiation on the nc-YSZ samples were evaluated upon registering the induced temperature changes by means of thermal imaging. The computer models try to mimic the experimental models using a similar geometry, reproducing the physical situation by a couple thermal-optical problem and adjusting the main parameters from the experimental results. ResultsExperimental and computational coincides in results: Temperatures at the bottom surface of the implant does not exceed those which produce thermal damage. The quantitative comparison between experimental and computational models show that differences in results are under a reasonable value of 5% and qualitatively we observe a similar behavior. The results provide optimum values for the thermal-optical nc-YSZ parameters considering a linear and exponential relationship with temperature for the absorption coefficient: The thermal conductivity is k = 2.13 W/m·K and the absorption coefficient α varies from 426 to 526 m−1 with the linear relationship, and k = 2.04 W/m·K and α ∈ [433,502] m−1 with the exponential. The reflection coefficient is R = 19% in both cases. ConclusionsThe temperatures achieved in the nc-YSZ during the laser irradiation are suitable for biomedical applications. The combination of experimental and computational models contributes to build a clinically oriented model with the thermal-optical parameters values stablished and to determine their influence in results. Specifically, the absorption coefficient of the nc-YSZ samples is the most influent parameter in the obtained temperatures. Moreover, this combination provides a method to evaluate the relevant thermal-optical parameters of nc-YSZ samples obtained with different manufacturing processes.

Influence of forming methods on the microstructure of 3YSZ flash-sintered ceramics

We evaluated the influence of three different forming methods (uniaxial and isostatic pressings and slip casting) on the densification and microstructure of cylindrical flash sintered 3mol% yttria-stabilized zirconia (3YSZ) ceramics. Conventional sintering was also analyzed as a comparison. Irrespective of the forming method applied, all the conventionally and the flash sintered specimens presented high final densities. Regarding the grain size distribution, while conventionally sintered specimens presented homogeneity over the entire ceramics, flash sintering yielded specimens with grain size heterogeneity depending on the forming method used. The microstructure of the specimens prepared with slip casting was homogeneous. On the other hand, uniaxial pressure induced bigger grains at the core of the ceramics. This heterogeneity is attributed to the presence of green density gradients in the samples prepared by uniaxial pressing, which affects the current flow and, consequently, the heat distribution within the specimens.

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia.

It is known that the yttria-stabilized zirconia (YSZ) material has superior thermal, mechanical, and electrical properties. This material is used for manufacturing products and components of air heaters, hydrogen reformers, cracking furnaces, fired heaters, etc. This work is aimed at searching for the optimal sintering mode of YSZ ceramics that provides a high crack growth resistance. Beam specimens of ZrO2 ceramics doped with 6, 7, and 8 mol% Y2O3 (hereinafter: 6YSZ, 7YSZ, and 8YSZ) were prepared using a conventional sintering technique. Four sintering temperatures (1450 °C, 1500 °C, 1550 °C, and 1600 °C) were used for the 6YSZ series and two sintering temperatures (1550 °C and 1600 °C) were used for the 7YSZ and 8YSZ series. The series of sintered specimens were ground and polished to reach a good surface quality. Several mechanical tests of the materials were performed, namely, the microhardness test, fracture toughness test by the indentation method, and single-edge notch beam (SENB) test under three-point bending. Based on XRD analysis, the phase balance (percentages of tetragonal, cubic, and monoclinic ZrO2 phases) of each composition was substantiated. The morphology of the fracture surfaces of specimens after both the fracture toughness tests was studied in relation to the mechanical behavior of the specimens and the microstructure of corresponding materials. SEM-EDX analysis was used for microstructural characterization. It was found that both the yttria percentage and sintering temperature affect the mechanical behavior of the ceramics. Optimal chemical composition and sintering temperature were determined for the studied series of ceramics. The maximum transformation toughening effect was revealed for ZrO2-6 mol% Y2O3 ceramics during indentation. However, in the case of a SENB test, the maximum transformation toughening effect in the crack tip vicinity was found in ZrO2-7 mol% Y2O3 ceramics. The conditions for obtaining YSZ ceramics with high fracture toughness are discussed.

Gas-discharge induced flash sintering of YSZ ceramics at room temperature

This is the first study to conduct the flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) ceramics at room temperature (25 °C) under a strong electric field, larger than 1 kV/cm. At the standard atmospheric pressure (101 kPa), the probability of successful sintering is approximately half of that at low atmospheric pressure, lower than 80 kPa. The success of the proposed flash sintering process was determined based on the high electric arc performance at different atmospheric pressures ranging from 20 to 100 kPa. The 3YSZ samples achieved a maximum relative density of 99.5% with a grain size of ∼200 nm. The results showed that as the atmospheric pressure decreases, the onset electric field of flash sintering decreases, corresponding to the empirical formula of the flashover voltage. Moreover, flash sintering was found to be triggered by the surface flashover of ceramic samples, and the electric arc on the sample surfaces floated upward before complete flash sintering at overly high pressures, resulting in the failure of flash sintering. This study reveals a new method for the facile preparation of flash-sintered ceramics at room temperature, which will promote the application of flash sintering in the ceramic industry.

Room temperature plasticity of zirconia-yttria-titania ceramics: Experimental indications and structural modelling

Yttria-stabilized tetragonal zirconia (Y-TZP) ceramics have excellent mechanical properties. However, such materials cannot undergo plastic deformation at room temperature due to their high hardness and brittleness values, hindering machinability. To overcome these limitations, we propose a zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria and up to 15mol% titania. The zirconia-yttria-titania powders were synthesized by co-precipitation method, uniaxially pressed and sintered at 1400?C/5 h. Sample characterizations were carried out by X-ray diffraction, scanning electron microscopy and mechanical properties through Vickers hardness and toughness measurements. Compared to the Y-TZP ceramics, the yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed noticeable increase of tetragonality parameter, higher toughness and lower hardness values, indicating plasticity at room temperature. Furthermore, the atomistic simulation by Density Functional Theory methodology suggests the occurrence of spatial arrangement of the atoms, explaining the proposed plasticity.

Correction to: Porous yttria-stabilized zirconia ceramics with low thermal conductivity via a novel foam-gelcasting method

Correction to: Porous yttria-stabilized zirconia ceramics with low thermal conductivity via a novel foam-gelcasting method

Influence of incongruent dissolution-precipitation on 8YSZ ceramics during cold sintering process

The incongruent dissolution-precipitation behaviors of 8YSZ (8 mol% yttria-stabilized zirconia) ceramics during cold sintering process is studied in this paper by changing the pH of liquid media. The different solubility of Y3+ and Zr4+ at the same lattice position causes the disparate dissolution behaviors, and results in incongruent precipitation. Compared with acidic or alkaline solution, neutral solution is more conducive to the incongruent dissolution-precipitation process, and the concentration ratio of dissolved Y3+ and Zr4+ can reach ∼6385. The incongruent dissolution-precipitation process facilitates the formation of neck structure and promotes the ionic migration and diffusion at the subsequent high-temperature sintering process, which improves the mechanical properties and electrochemical properties of 8YSZ ceramics. This work reveals the principle of incongruent dissolution-precipitation process of zirconia-based ceramics, and it is of significance for selecting suitable liquid media to control the incongruent dissolution-precipitation behaviors in cold sintering process to prepare high-performance zirconia-based ceramics.

Grain boundary energies in yttria‐stabilized zirconia

AbstractThe three‐dimensional microstructure of 8% yttria‐stabilized zirconia (YSZ) was measured by electron backscatter diffraction and focused ion beam serial sectioning. The relative grain boundary energies as a function of all five crystallographic grain boundary parameters were determined based on the assumption of thermodynamic equilibrium at the internal triple junctions. Grain boundaries with (100) orientations have low energies compared to boundaries of other orientations, and all [100] twist boundaries have relatively low energies. Other classes of boundaries with lower than average energies include [100] symmetric tilt boundaries with disorientations less than 40° and [111] twist boundaries with disorientations greater than 20°. At fixed misorientations, the relative areas of boundaries are inversely correlated to the relative grain boundary energy. The results suggest that texturing microstructures to increase the relative areas of [100] twist boundaries might increase the oxygen ion conductivity of YSZ ceramics.

In vitro evaluation of tooth-colored yttria stabilized zirconia ceramics

ABSTRACT Effects of MoCl3 and NiCl2, originally incorporated as coloring agent, on the cellular response of 3 mol% yttria stabilized zirconia (3Y-TZP) ceramics was investigated. MoCl3 and NiCl2-MoCl3 incorporated, tooth-colored 3Y-TZP ceramics were produced through cold isostatic pressing at 100 MPa followed by pressureless sintering at 1450°C for 2 h. Aging was performed on the sintered ceramics using distilled water in a reactor at 134°C at 2.3 bar pressure for 2 h. The phases developed during different stages of processing were identified by X-ray diffraction (XRD) analysis. In vitro cell culture studies were carried out using L929 fibroblast cell line. The cell viability and proliferation studies revealed that none of the specimens showed cytotoxicity with respect to coloring. Confocal laser scanning microscope (CLSM) analyses suggested that all of the specimens exhibited good in vitro cytocompatibility. Enhancement in cell attachment, adhesion, and proliferation was observed in all specimens via scanning electron microscope (SEM) analysis. Although the coloring process did not improve the proliferation performance of the aged specimens, the incorporation of transition metals enhanced the in vitro performance of 3Y-TZP ceramics.

A novel Ag–CuAlO2 sealant for reactive air brazing of 3YSZ and AISI 310S

Based on reactive air brazing (RAB), we designed a new type of sealant (Ag–xCuAlO2) for joining 3 mol.% yttria-stabilized zirconia (YSZ) ceramics and AISI 310S stainless steel. The CuAlO2 content affected the wettability of the sealant on the YSZ surface, and the joints had a high shear strength when Ag–2 wt.%CuAlO2, which had a small contact angle on the YSZ substrate, was used as the sealant. In addition, the thickness of the oxide layer was reduced compared to that for the Ag–CuO sealant. The effects of the processing parameters on the microstructure and shear strength of the joints were investigated, and the as-brazed joints reached their highest shear strength (93.7 MPa) when brazed at 1040 °C for 30 min. After high-temperature oxidation at 800 °C for 200 h, the shear strength of the joints remained at 50 MPa, and no apparent change in the microstructure was observed, proving that the joints possessed excellent oxidation resistance.

On the Arrhenius-like behavior of conductivity during flash sintering of 3 mol% yttria stabilized zirconia ceramics

We discuss the Arrhenius behavior of electrical conductivity σ during flash sintering of 3 mol% yttria stabilized zirconia (3YSZ). In situ x-ray diffraction is used to determine sample temperature. Sintering contribution to σ is excluded by investigating the flash event on a dense ceramic. We show that total conductivity follows an Arrhenius-like equation in both dense and green samples, even during Stage II of flash. The non-linearity often verified during flash sintering of 3YSZ is therefore related to the furnace temperature instead of the sample temperature when building the ln(σ) vs. 1/T plots. Furthermore, we verified a change in the activation energy for conduction prior to the ignition of the flash event and discussed the possible mechanisms. For instance, the decrease in activation energy from Stage I to II in the dense sample is attributed to a contribution from electronic carriers.

Thin high-strength zirconia tapes with extreme flexibility

ABSTRACT The yttria stabilized zirconia ceramics (Y-TZP) are known for their high fracture toughness and high strength. Due to their excellent mechanical properties, the thin zirconia tapes can possess extraordinary behavior – extreme flexibility. In the present work, we introduce an adaptation of gel-tape casting method for the preparation of thin, high-strength zirconia tapes from water-based suspensions. Fine ceramic powder with a particle size of around 100 nm was used. The negative effect of sodium ions on the strength and toughness of sintered ceramic samples was revealed and explained. Ceramic tapes with a thickness of 190 µm with as-sintered surfaces reached a characteristic biaxial strength of 1805 MPa. The huge elastic deformation of ceramic tapes was demonstrated in a 3- point bend test, and a bending radius of 25 mm for a 75 µm thick tape was reached.

Effects of pyrolytic carbon on carburization strengthening and corrosion of 3YSZ hollow fiber membranes

Carbon species incorporation and carbon deposits are common in the manufacture process and application of yttria-stabilized zirconia (YSZ) ceramics, while the potential corrosion induced by the resultant carburization is unclear. The 3YSZ hollow fiber membranes were prepared by wet spinning method. A sintering procedure at 1300–1450 °C under 0.02 MPa oxygen partial pressure, and thereafter an oxidation treatment at 800 °C were applied to investigate the carbothermal reaction and carburization corrosion mechanism. It was found that the trace carbon species of 1.0–2.2 mol% derived from polymeric precursors triggered the carburizing strengthening of porous YSZ membranes without sacrificing porosity and deformability. However, the carburization corrosion also occurred at the mild oxidation treatment, resulting in deterioration in bending strength and integrated structure converting into fine grains. Raman spectra, XPS bands and HR-TEM images confirmed that the in-situ synthesized ZrCxOy oxidized into monoclinic ZrO2, and micro-cracking formed along grain boundaries, which led to substantial mechanical strength loss.

Manufacturing Optically Transparent Thick Zirconia Ceramics by Spark Plasma Sintering with the Use of Collector Pressing

The efficiency of using the collector pressing scheme in the Spark Plasma Sintering (SPS) process has been confirmed in improving the optical, physical, and mechanical properties of yttria-stabilized zirconia (YSZ) ceramics with an increased shape factor. An approach for developing a seal surface and determining the optimal method of increasing pressure and temperature during SPS on this surface was used to optimize the consolidation modes of the materials. It has been shown that transparent/translucent YSZ ceramics with an increased shape factor (14 mm in diameter and up to 5 mm in height, h/d = 0.36) can be successfully fabricated by the SPS technique combined with the collector pressing scheme. The optical properties and microhardness of ceramics obtained using the collector scheme are better to the optical properties of ceramics obtained using the conventional uniaxial pressing scheme.

Flash Spark Plasma Sintering of 3YSZ: Modified Sintering Pathway and Impact on Grain Boundary Formation

We demonstrate the possibility to prepare porous 3 mol.% yttria stabilized zirconia ceramics thanks to a recently developed method called Flash-SPS, allowing extremely fast densification in just a few seconds. This method allows to reach heating rates up to 200 °C/s, which has a strong impact on sintering mechanisms, both in terms of densification and grain growth. We demonstrate the possible preparation of specimens with 5 to 15% porosity, limited grain growth (< 350 nm) and mechanical properties similar to fully dense ceramic. Through the use of sintering trajectories, but also based on microscopy, mechanical and electrical analyses, we highlight a new sintering mechanism. It appears that densification is largely advanced at grain boundary interfaces, while inter-grain porosity remains present. This phenomenon is particularly supported by the mechanical hardness and impedance spectroscopy measurements, the latter showing a very low impedance contribution from the grain boundaries despite the low density. This opens up opportunities for the fabrication of porous lightweight materials with high mechanical properties, but also presents interests in alternative sintering pathways for refractory ceramics.

Increasing fracture toughness of zirconia-based composites as a synergistic effect of the introducing different inclusions

The effect of multi-walled carbon nanotubes (MWCNTs) and hexagonal boron nitride (h-BN) inclusions on the fracture toughness of yttria-stabilized zirconia (YSZ) ceramics has been studied. It is shown that an increase in the MWCNTs and h-BN content has a positive effect on the K1C of zirconia ceramics. The greatest increase in the fracture toughness of YSZ ceramics was observed with the introduction of hexagonal boron nitride particles. For YSZ ceramics, the K1C value was ≈6.1 MPa m1/2, for ceramics with a 5 wt % of h-BN K1C ≈ 9.2 MPa m1/2. It was shown that an increase of the YSZ ceramics fracture toughness with the introduction of MWCNTs and h-BN, both and separately was provided by the combined action of several mechanisms of increasing the work of crack propagation. In addition, in all composites obtained in this work, the transformation of tetragonal ZrO2 into monoclinic was observed.

Long-term stability of SOFC glass sealant under oxidising and reducing atmospheres

The behaviour of the 59.6SiO2–11.0Al2O3–6.6ZrO2–3.4CaO–15.4Na2O–4Y2O3 (wt. %) non-crystallising glass sealant was studied while in contact with NiO–YSZ (yttria-stabilized zirconia) ceramics and an Fe–Ni alloy after exposure to reducing and oxidising atmospheres at 850 °C and while on a Pt substrate. The sealant was completely amorphous after exposure on a Pt substrate for 1000 h in an air atmosphere. After exposure on a NiO–YSZ substrate in both oxidising and reducing atmospheres, no interaction on the NiO(Ni)–YSZ|sealant interface was observed. For the Fe–Ni alloy substrate, the formation of an Fe2SiO4 layer was observed after exposure in an oxidising atmosphere. In the reducing atmosphere, the Fe–Ni alloy substrate intensified sealant crystallisation, leading to the formation of numerous crystalline phases, but no interaction on the Fe–Ni alloy|sealant interface was observed.

Preparation of epitaxial yttria-stabilized zirconia with non-quilibrium t' phase and ferroelastic domain by pulsed laser deposition

The non-equilibrium tetragonal t' phase of yttria-stabilizedzirconia (YSZ) plays a key role in improving the toughness of YSZ ceramics owing to its own ferroelastic domain toughening mechanism. Due to the disadvantages of traditional processes for preparing the YSZ t' phase, which requires high heating temperature, difficult to control defects and inability to regulate microstructure, it is not conducive to the preparation of YSZ by these methods. We report the use of substrate clamping and non-equilibrium growth process of PLD to render stable t' epitaxial YSZ films with multiple domain structure on (0001) Al2O3 substrates. Thin film structure and epitaxial relationship with substrate were subsequently analyzed by XRD, RSM, and HRTEM. It was found that the crystal orientation of the YSZ film changes as a function of oxygen pressure during deposition. When oxygenpressure is larger than 100 mtorr, YSZ films with highly oriented ferroelastic domains are obtained. Based on the symmetry relationship, we know that the film has three in-plane domain structures. The epitaxial relationship between the film and the substrate is (002) [110] YSZ // (0001) [112¯0] Al2O3.

Retraction

AbstractRetraction: AKM Asif Iqbal, Muhamad Zami Bin Abdul Hamid, A. K. M. Parvez Iqbal (2020) Effect of porosity on the microstructure and mechanical properties of YSZ thermal barrier coating densified by spark plasma sintering (SPS). International Journal of Applied Ceramic Technology: https://doi.org/10.1111/ijac.13599The above article, published online on 9 August 2020 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the outgoing Editor‐in‐Chief, Monica Ferraris, the incoming Editor‐in‐Chief, Young‐Wook Kim, and Wiley Periodicals, LLC. The retraction has been agreed due to unattributed overlap between images presented as original data in this article and the following article published in Ceramics International, “Relationship between mechanical properties and microstructure of yttria stabilized zirconia ceramics densified by spark plasma sintering” by Arnaud Fregeac, Florence Ansart, Serge Selezneff, Claude Estournès, Volume 45, 2019, pages 23740‐23749.

Porous yttria-stabilized zirconia ceramics with low thermal conductivity via a novel foam-gelcasting method

In this work, the preparation of foam-gelcasting was simplified with a copolymer of isobutylene and maleic anhydride (Isobam), avoiding the traditional gelling system including many additives such as monomer, cross-linking agent, initiator and catalyst. Highly porous yttria-stabilized zirconia (YSZ) ceramics with 76.2–84.9% porosity were prepared via foam-gelcasting method using YSZ powder as the raw material, Isobam as the dispersant and gelling agent, triethanolamine lauryl sulfate as the foaming agent and sodium carboxymethyl cellulose as the foam stabilizing agent. The effects of solid loading, the content of foaming agent as well as sintering temperature were investigated. With the increase in solid loading of slurries, lower porosity was obtained, and the compressive strength and thermal conductivity showed a tendency of increase. Porous YSZ ceramics with compressive strength of 0.69–3.66 MPa showed low thermal conductivity in the range of 0.137–0.254 W/(m·K) at room temperature. The as-prepared sample showed good thermal insulating performance at high temperature. The km in GM model was during 0.4–0.7, which indicated the pore structure containing the internal and external porosities. This work provides a facile method for the fabrication of porous YSZ ceramics which can be potentially applied as thermal insulation materials at high temperature.