Volume Fraction Of Zirconia Research Articles

Microstructure and fracture behaviour of biomimetic Al2O3-ZrO2 composite with 2-levels of structural hierarchy

We report new class of natural nacre-like alumina toughened by zirconia fabricated by the simple two-step approach of unidirectional freeze-casting and spark plasma sintering. The biomimetic alumina-zirconia with a relative density of more than 98 % was achieved by consolidating at temperature of 1300–1425 °C with 50 MPa pressure. The resultant microstructure consists of two levels of structural hierarchy, i.e. level-1: bulk lamellar brick phase (alumina platelets) and level-2: mortar phase (yttria stabilized tetragonal zirconia polycrystals). The increase in volume fraction of zirconia (in tetragonal form) from 0 to 15 vol% was effective in progressively reducing the size of alumina platelets from 12 to 9 μm, and significantly improved the flexural strength of the composite by 60 % (from 172 to 270 MPa). By optimizing the hierarchical architecture from micro to macroscopic level, the structural performance of our synthetic nacre, where strength and toughness of 270 MPa and 13.5 MPa√m respectively are superior to that of natural nacre and many other engineering materials (illustrated in the form of Ashby map). The exceptional damage resistance is rationalized by both intrinsic (stress induced tetragonal to monoclinic phase transformation of zirconia) and extrinsic (crack deflection, crack branching and bridging, multiple cracking, platelets interlocking) toughening mechanisms. For 15 vol% ZrO2 composition, the contribution of intrinsic and extrinsic toughness was quantitatively evaluated as 0.9 ± 0.03 and 4.3 ± 0.07 MPa√m respectively (with experimentally measured toughness at crack initiation as 5.2 ± 0.2 MPa√m).

Effect of hydroxyapatite:zirconia volume fraction ratio on mechanical and corrosive properties of Ti-matrix composite scaffolds

Ti-based scaffolds reinforced with zirconia and hydroxyapatite were produced successfully by a hybrid method with an eco-friendliness and low cost to obtain low elastic modulus (E) with sufficient physical, electrochemical and biological properties. The effect of simultaneous modification of the volume fraction of hydroxyapatite (HA) and zirconia (ZrO2) on scaffolds was investigated in terms of mechanical, corrosive, and antibacterial properties. Scanning electron microscopy with attached electron dispersive spectroscopy and X-ray diffraction were used for the characterization of scaffolds. Compression and electrochemical tests were performed to determine mechanical properties with detailed fracture mechanism and in-vitro corrosion susceptibility to simulated body fluid at 37 °C, respectively. Antibacterial tests were carried out by comparing the inhibition areas of E.coli and S.aureus bacteria. It was observed that the mechanical strength of the scaffolds decreased with increasing HA:ZrO2 volume fraction ratio. The lowest E was achieved (6.61 GPa) in 6:4 HA:ZrO2 composite scaffolds. Corrosion current density (Jcorr) values were calculated to be 21, 337, and 504 µA/cm2 for unreinforced Ti, 3:2 and 6:4 HA:ZrO2 reinforced scaffolds, respectively. The inhibition capacity of the 6:4 reinforced composite scaffold was found to be more effective against S.aureus bacteria than other scaffolds.

Evaluation of Physical Properties of Zirconia Suspension with Added Silane Coupling Agent for Additive Manufacturing Processes.

In this study, we have analysed the effects of a silane coupling agent on the volume fraction of zirconia for digital light processing (DLP)-based additive manufacturing processes. Zirconia suspension was prepared by the incorporation of silane-modified zirconia particles (experimental group) or untreated zirconia particles (control group). Furthermore, the control and experimental group were subdivided into three groups based on the volume fraction (52, 54, and 56 vol%) of zirconia particles. The disk-shaped zirconia samples were 3D (three-dimensional) printed using the DLP technique and their physical and mechanical properties were evaluated. The addition of a silane coupling agent to the zirconia samples was found to have influence of about 6% on the hardness and biaxial flexural strength. Moreover, the decrease in minute air gaps inside the zirconia layers significantly increased the material density (visualized from the microstructure analysis). Thus, from this study, it was established that the silane-modified zirconia particles had a positive effect on the physical properties of the zirconia parts.

Stress distribution in the composite electrodes of sulfide all-solid-state lithium-ion batteries

Pressurization of all-solid-state lithium-ion batteries is expected to increase the efficiency of ion transport between solid electrolyte particles. Here, we show the practicality of considering internal stress distribution to explain the ion transport behavior inside a composite electrode containing a sulfide solid electrolyte. Considering internal stress distribution allows for an accurate evaluation in microscale, and phenomenon stemming from nanoscale features is explained. To independently analyze the effect of ohmic overpotential on ion transport, undesired electrochemical reactions are eliminated by replacing active materials in a composite electrode by zirconia. The ionic conductivity of the zirconia composite at different pressures is measured and its three-dimensional structure is visualized by X-ray computed tomography. Graphics processing unit-based large-scale voxel finite element method stress analysis and an electric field numerical calculation are conducted to analyze the effect of stress distribution on the ion transport characteristics of the composite electrode. Experimentally, the ionic conductivity of the zirconia composite decreases drastically as the volume fraction of zirconia increases. The degree to which the ionic conductivity decreases exceeds that expected when considering the volume fraction and tortuosity of zirconia. When stress distribution is also considered, the discrepancy between experimental and numerical results decreases greatly.

Evaluation of Cure Depth and Geometrical Overgrowth Depending on Zirconia Volume Fraction Using Digital Light Processing.

The optical properties of zirconia photopolymer suspension for DLP (Digital Light Processing) were evaluated. The light source and intensity were set to 395 nm and 30 mW/cm². Experimental groups were divided into 48, 50, 52, 54, 56 and 58 vol% according to the zirconia volume fraction. The cure depth of all groups was at least 47.35 um when cured for 1 sec, which was higher than layer parameter values of the 3D printer. The geometrical overgrowth showed 28.55% at 48 vol% and 36.94% at 58 vol%. As the volume fraction of zirconia increased, the geometrical overgrowth increased and the cure depth reduced.

Effect of the volume fraction of zirconia suspensions on the microstructure and physical properties of products produced by additive manufacturing

ObjectiveThe objectives of the present study were: (1) to analyze the dispersion and optical properties of suspensions with various volume fractions of zirconia, and (2) to assess the influence of zirconia volume fraction on the microstructure and physical properties of products produced by the additive manufacturing and sintering process. MethodsZirconia specimens were fabricated by an additive manufacturing technique using a DLP (digital light processing) system. The zirconia suspensions were divided into six groups based on zirconia volume fraction within the range of 48–58vol%. ResultsThe maximum volume fraction of zirconia in suspensions possible for printing was 58vol%. The cure depth of the zirconia suspensions decreased as the volume fraction increased. The cure depth was greater than 100μm after 15s photocuring in all groups. Geometrical overgrowth tended to increase gradually as the volume fraction of zirconia increased within the range of 28.55–36.94%. The 3-point bending strength of the specimens increased as the volume fraction of zirconia in the suspension increased, reaching a maximum value of 674.74±32.35MPa for a volume fraction of 58vol%. Cracks were observed on the surfaces of zirconia specimens and these cracks increased in number as zirconia volume fraction decreased. SignificanceIn this experiment, the viscosity of zirconia suspensions sharply increased from a volume fraction of 54vol%. Because of the very high viscosity, 58vol% was the maximum volume fraction possible for additive manufacturing. After polymerization, all specimens showed some distortion due to geometrical overgrowth. The maximum 3-point bending strength was 674.74±32.35MPa for a volume fraction of 58vol%. But the maximum strength of sintered zirconia prepared by additive manufacturing is inferior to that of conventionally sintered zirconia.

Effect of color shading procedures and cyclic loading on the biaxial flexural strength of zirconia.

Zirconia is the most preferred ceramic restoration in posterior areas because of its flexural strength. The aim of the study is the evaluation of biaxial flexural strength of different colored zirconium oxide core materials after cyclic loading. Zirconia discs (12 mm diameter and 1.2 mm thickness) were divided into 6 groups of 12 discs each. Groups were colored according to the Vita Classic shade guide: A3 and D4. One group was not colored and left as control. Each group was randomly divided into subgroups and subjected to mechanical cycling prior to biaxial flexural strength test. Cyclic loading was applied as 50 N loads for 20,000 times for the loaded groups. Samples were subjected to biaxial flexural strength test in a universal testing machine with a crosshead speed of 1 mm/min. Two-way analysis of variance (ANOVA) and Tukey's HSD tests were used for comparisons of the groups. Biaxial flexural strength values did not vary significantly depending on coloring procedure or loading process tested (p>.05). XRD analysis displayed that the monoclinic volume fraction of zirconia was highest in cyclic loaded D4 and was lowest in non-loaded control group. The SEM image revealed that A3 color solution created metallic coloring pigments at grain boundaries. Coloring procedures and cyclic loading did not affect the biaxial flexural strength of zirconia core material; however, microstructural analysis displays changes, which may weaken the zirconia structure on the long term.

Residual stress and diffraction line-broadening analysis of Al2O3/Y-TZP ceramic composites by neutron diffraction measurement

Time-of-flight neutron diffraction and Rietveld analysis have been used to investigate the residual stresses, crystallite structure and microstructural features in Al2O3/Y-TZP ceramic composites fabricated by two different green processing techniques (a novel tape casting and conventional slip casting) and with different zirconia content (5 and 40vol.% Y-TZP). The change in lattice parameters, individual peak shifts and peak-broadening were analyzed, in order to calculate the uniform residual stress field (mean phase stresses and peak-specific stresses) and the non-uniform microstrains. Peak-specific residual stresses were calculated for different hkl reflections both for the Al2O3 matrix and the Y-TZP particulates. The sign and the magnitude of the peak-specific residual stress are highly dependent on the individual hkl reflection studied and on the volume fraction of zirconia. Peak broadening was observed in the Y-TZP reflections, due to non-uniform microstrains. Both the mean phase stress field and the non-uniform microstrains were mainly influenced by the Y-TZP content in the studied Al2O3/Y-TZP composites, irrespective of the measured direction and the fabrication process.

Sliding Wear Behavior of ZTA with Different Yttria Stabilizer Content

In this study, tribological investigations were carried out on ZTA ceramics with 17 vol% Y‐TZP and different stabilizer contents (1, 1.5, and 2 mol% yttria) to analyze the influence of zirconia transformation on wear properties. Samples were tested in a linearly reciprocating ball on flat setup with different applied loads. Raising the fracture toughness by transformation toughening, microcracking, and residual stresses improves the wear resistance only at transition load but increases the wear at high loads. Higher yttria content of 2 mol% and lower zirconia grain size and thus low transformability, decreases fracture toughness but increases the wear resistance at high loads. Therefore the adjustment of stabilizer content on zirconia volume fraction in ZTA plays a decisive role in tribological applications.

Joining of Zirconia Reinforced Metal–Matrix Composites by a Ceramics‐Derived Technology

Metal–matrix composites composed of an austenitic stainless steel and magnesia partially stabilized zirconia were prepared via a powder metallurgical processing route with the ceramics‐derived extrusion at room temperature. Various combinations of the base materials with zirconia volume fractions of 0, 5, and 10% were joined by applying an aqueous paste which forms the joint during thermal processing. The materials were tested under tensile loading at room temperature. The addition of zirconia particles led to a considerable decrease of the plasticity and ultimate tensile strength of the basic compositions. However, the strength of joint specimens was not limited by the bonding strength of the joining zone. Among all material combinations tested, failure occurred in the joining partner with the higher zirconia volume fraction and not at the joint interface. Thus, the strength of sinter‐joined materials based on MMC with 0–10 vol% was limited by the strength of the base materials. The advance of the present sinter‐joining method is the single thermal operation of the composite materials. The formation of a homogeneous bonding zone and the absence of a heat‐affected zone lead to negligible interference with the microstructure and the mechanical properties of the base materials.

MoO<sub>x</sub>-ZrO<sub>2</sub> System: Preparation, Characterization and Catalytic Activity for Selective Oxidation of Diphenylsulfide

MoOx-ZrO2 based catalysts were prepared by equilibrium adsorption in basic (pH 8) or in acid (pH 2) conditions with molybdenum content up to 3 wt.% (pH 8) and up to 8 wt.% (pH 2) using hydrous zirconium oxide, designated as ZrO2(383), as support. The samples were characterized by textural analysis (BET), X-ray diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopies. The catalytic behavior was analyzed for the selective oxidation of diphenylsulfide (DPS) to diphenylsulfone (DPSO2) or diphenylsulfoxide (DPSO) using H2O2 as oxidizing agent. The results show that the pH of the contacting solution affects the uptake of the Mo species and the molecular state of the adsorbed species. Raman spectroscopy identified polymolybdate structures at pH 2 and molybdate aggregates at pH 8. XRD analysis revealed that at increasing molybdenum concentration the interaction between the supported species and the zirconia surface favored the tetragonal volume fraction of zirconia at the expense of the thermodynamically stable monoclinic phase in all series of samples. High conversion of DPS (88%) and selectivity to diphenylsulfone (DPSO2) (60%) was obtained for the pH 2 series of catalysts. These results suggest that the acid environment was the most efficient synthesis parameter leading to the formation of polymolybdates species which are considered the active phases in this reaction. Keywords: MoOx/ZrO2, Zirconia, Selective diphenylsulfide oxidation, Raman spectroscopy.

Toughening enhanced at elevated temperatures in an alumina/zirconia dual-phase matrix composite reinforced with silicon carbide whiskers

Abstract A unique temperature dependence of toughening is observed in an alumina/zirconia dual-phase matrix composite reinforced with silicon carbide whiskers. The work of fracture (WOF) of the composite is maximized at 400 °C to 130 J/m 2 , which is about 6.5 times larger than that of monolithic alumina at room temperature. The WOF decreases sharply with an increase in temperature above 400 °C. The enhanced toughening at elevated temperatures is described by the stress-induced transformation toughening of tetragonal zirconia, which is affected by the internal thermal stress owing to thermoelastic mismatch between the matrix and the whiskers. The maximum WOF is not given only by the stress-induced transformation but also by the crack-face bridging of the whiskers. The WOF was optimized at a specific zirconia volume fraction of 0.7 in the matrix, which was essentially due to the maximized tensile internal stress on zirconia in the dual-phase matrix.

412 SiCウィスカー強化Al_2O_3/ZrO_22相マトリックス複合材料の高温下での高靱性化

A unique temperature dependence of toughening is observed in an alumina/zirconia dual-phase matrix composite reinforced with silicon carbide whiskers. The work-of-fracture (WOF) of the composite is maximized at 400℃ to be 130J/m^2 which is about 6.5 times larger than that of monolithic alumina at room temperature. The WOF decreases steeply with an increase in temperature above 400℃. The toughening enhanced at elevated temperatures is described by the stress-induced transformation toughening of tetragonal zirconia, which is affected by the internal thermal stress owing to thermoelastic mismatch between the matrix and the whiskers. The maximum WOF is not given only by the stress-induced transformation but also by the crack-face bridging of the whiskers. The WOF was optimized at a specific zirconia volume fraction in the matrix of 0.7, which was basically due to the maximized tensile internal stress on zirconia in the dual-phase matrix.

Phase evolution in zirconia thin films prepared by pulsed laser deposition

Zirconia thin films were deposited on silicon (100) and quartz substrates using pulsed laser deposition. Phase formation in zirconia films was monitored as a function of substrate temperature (473–973K) and oxygen partial pressure (0.001–1Pa). Volume fraction of tetragonal zirconia is determined from X-ray diffraction and Raman analysis. Tetragonal volume fraction of zirconia films varies from 10 to 76% for different substrate temperature and oxygen partial pressure. Zirconia films show a good transparency in the visible region, except for the films deposited at 473K and at 0.002Pa. The band gap values and refractive index of the films are discussed in relation with the microstructure and phase composition of the zirconia films as well as with 8mol% yttria stabilised zirconia films.

Surface characterization of zirconia dental implants

Objectives The aim of the study was to characterize the chemical composition, microstructure and roughness of two commercially available zirconia dental implants (WhiteSky and Zit-Z). Methods The chemical composition of the cervical collar and threaded root parts of the implants ( n = 2) were studied by XPS and HV-EDX. LV-SEM was used for morphological assessment, Raman microanalysis for microstructural characterization and optical profilometry for surface roughness measurements. XRD, HV-EDX and Raman microanalysis of bulk regions (longitudinal sections) were used as reference. Results XPS showed the presence of C, O, Zr and Y (collar) plus Al (root) at implant surfaces. More C (10–26 at%) and a lower Al/Zr ratio were found in WhiteSky (1.05 vs 1.26 in Zit-Z). Zr, Y and Al were detected in single, fully oxidized states. The same elements, plus Hf, were identified by HV-EDX at bulk and surface regions, with a Al/Zr ratio higher in WhiteSky (0.17 vs 0.09 in Zit-Z). Na, K and Cl contaminants were traced at implant root parts by both methods. XRD analysis of cross-sectioned specimens revealed the presence of monoclinic and tetragonal zirconia along with cubic yttria phases. Raman microanalysis showed that the monoclinic zirconia volume fraction was higher at root surfaces than the collar. No monoclinic phase was found at bulk regions. Significantly higher Sa and Sq values were recorded in WhiteSky than Zit-Z, whereas Zit-Z showed higher Rt value. Significance The differences found between the implants in the extent of carbon contamination, residual alumina content, tetragonal to monoclinic ZrO 2 phase transformation and 3D-roughness parameters may contribute to a substantial differentiation in the cellular and tissue response.

Residual stresses in Al<sub>2</sub>O<sub>3</sub>/Y-TZP Ceramic Laminates Fabricated by Tape and Slip Casting

Residual stress profiles were measured by neutron diffraction in Al2O3/Y-TZP ceramic composites containing 5 and 40 vol.% Y-TZP fabricated by conventional slip casting and by a novel tape casting route. Residual stresses in the zirconia are tensile and increase as its volume fraction decreases. For the alumina matrix, residual stress is compressive and increases with the zirconia volume fraction. In the composite with 5 vol.% zirconia, the processing route does not have an influence on residual stresses. However, in the composite with 40 vol.% zirconia, residual stresses are different in the samples obtained by both processing routes.

Development of Intermixed Zones of Alumina/Zirconia in Thermal Barrier Coating Systems

The mechanisms whereby intermixed zones of alumina and zirconia are formed at the interface between the metallic bond coat and the ceramic top coat (yttria-stabilized zirconia) in thermal barrier coating systems have been investigated. The results lead to the following mechanism for the formation of the zones. The predominant mechanism for intermixed zone formation involves formation of a metastable alumina polymorph (θ or γ) during TBC deposition, with a significant amount of zirconia dissolved in it. The outward growth also begins to incorporate zirconia particles, which initiates the formation of the intermixed zone. Upon thermal exposure, the metastable TGO continues to grow outward, extending the intermixed zone, and eventually transforms to the equilibrium α-Al2O3. The transformation to α-Al2O3 results in an increase in the volume fraction of zirconia in the intermixed zone as it is rejected from solution. Once the α-Al2O3 appears, subsequent TGO growth produces a columnar zone of the TGO without a second phase. When α-alumina was preformed on the bond coat, prior to TBC deposition, no intermixed zone was formed for Pt-modified aluminide bond coats.

Transmission electron microtomography without the “missing wedge” for quantitative structural analysis

A three-dimensional (3D) visualization and structural analysis of a rod-shaped specimen of a zirconia/polymer nanocomposite material were carried out by transmission electron microtomography (TEMT) with particular emphasis on complete rotation of the specimen (tilt angular range: ±90°). In order to achieve such an ideal experimental condition for the TEMT, improvements in the specimen as well as the sample holder were made. A rod-shaped specimen was necessary in order to obtain a high transmission of the specimen upon tilting to large angles. The image resolution of the reconstructed tomogram was isotropic, in sharp contrast to the anisotropic image resolution of the conventional TEMT with a limited angular range (the “missing wedge” problem). A volume fraction of zirconia, φ, evaluated from the 3D reconstruction was in quantitative agreement with the known composition of the nanocomposite. A series of 3D reconstructions was made from the tilt series with complete rotation by limiting the maximum tilt angle, α, from which a couple of structural parameters, the volume fraction and surface area per unit volume, Σ, of the zirconia, were evaluated as a function of α. It was confirmed from actual experimental data that both φ and Σ slightly decreased with the increasing α and reached constant values at around α = 80 ° , suggesting that the specimen may have to be tilted to ±80° for truly quantitative measurements.

Simulation Design for the Composition of Zirconia Composite Ceramic Tool

The relationship between the fracture toughness increment (ΔK IC) resulting from toughening mechanisms, such as phase transition, residual stress, geometry effect, and grain bridging, and the volume fraction of zirconia was established to simulate and design the composition of a zirconia-matrix composite tool, thereby avoiding “trial-and-error” experiments. The composition of the ZrO2/Al2O3 ceramic tool was simulated in accordance with the requirement for fracture toughness. It was shown that the simulated result was in agreement with experiment and that the established simulation model was to some extent valid in predicting the composition of the zirconia-matrix composite ceramic tool with dispersed α-Al2O3. Thus, a new type of ceramic tool material, a ZrO2/Al2O3 composite, was developed by adding α-Al2O3 to ZrO2 on the basis of the results of the computer simulation.

Electrical properties of zirconia–alumina composites

Sintered zirconia–alumina composites, prepared in a wide range of compositions, are studied in terms of their electrical response. Both grain conductivity and dielectric constant show the typical characteristics expected from the percolation theory, with v c=0.14±0.2 as the critical zirconia volume fraction for the onset of conduction. When the conducting zirconia phase is calcined prior to forming the composite, the whole system still shows a strongly reduced conduction response even for zirconia volume fractions ( v) in the range of 0.4–0.5, after which it is considerably enhanced for v=0.7. These results are discussed in terms of (i) the influence of the material's microstructure and (ii) the effect of stress resulting from the alumina sintering on the calcined zirconia grains on the overall electrical response of the composite.