Monolithic ZrO2 Research Articles

Zirconia-based nanocomposite toughened by functionalized multi-wall carbon nanotubes

In the present work, we have reported a novel approach to fabricate 3Y-TZP/carbon nanotube (CNTs) nanocomposites with improved fracture toughness using spark plasma sintering technology through the incorporation of functionalized multi-walled carbon nanotubes. For this approach, homogeneous distribution of CNTs in ceramic matrix has been achieved up to 4wt% CNTs content, revealed by SEM observations of both composite powders and fracture surfaces of sintered specimens. In addition, Raman spectroscopic indicates that CNTs can be retained at high sintering temperatures from 1250 to 1400°C. A clear improvement in the fracture toughness was achieved after adding CNTs, and the specimen with 4wt% CNTs sintered at 1300°C exhibited the best indentation toughness of 6.24MPam1/2, increasing 31% over monolithic ZrO2 sintered at the same temperature. Furthermore, the fracture mode transition and the activated toughening mechanisms during crack propagation were taken into account to explain the improvement in fracture toughness.

Sintering of HA/Zirconia Composite for Biomedical and Dental Applications: A Review

Hydroxyapatite is a calcium phosphate product that being widely use in medical application due to its excellence biocompatibility. However its application has being limited due to the inferior mechanical properties, many researcher attempted to improve its mechanical properties. HA-ZrO2 composites have great potential because of their advantages from both constituent materials, such as the excellent biocompatibility of HA and the considerable mechanical strength and toughness of ZrO2. The synergy of the two materials provides a new possibility for developing a composite material with better properties than monolithic ZrO2 and HA. In this work, the stages of development, as well as the different sintering and processing methods of HA and ZrO2 such as conventional sintering, solid-state reaction, microwave sintering and hot isostatic pressing were discussed. It can be concluded that hot isostatic pressing processing yield the most satisfying result amount above method, however the use of nano structured material maybe able to provide alternative processing method and yield better result.

Design and fabrication of laminated–graded zirconia self-lubricating composites

A new design method to achieve the integration of structure and lubricating function in ceramic was proposed by combining the functionally graded material (FGM) concept with the bionic design of ZrO2(3Y) ceramic. ZrO2(3Y)–Al2O3/ZrO2(3Y)/solid lubricant (SL) FGMs were prepared, and gradient exponent p was defined to determine the distribution of SL in the materials. The mechanical and tribological properties of the composites with different p were studied. ZrO2(3Y)–Al2O3/ZrO2(3Y)/SL FGM shows excellent self-lubricating performance over a broad temperature from room temperature to 800°C, and the bending strength of the sample with the p of 2 is four times higher than that of monolithic ZrO2(3Y)/SL composites. The variation of p causes the change in the residual tensile stress generated from the thermal mismatch, and further influences the mechanical property of the materials.

X-ray diffraction and atomic force microscopy study in aged zirconia-toughened alumina composite with dispersion of m-ZrO2 nanoparticles

X-ray diffraction (XRD) and atomic force microscopy (AFM) were utilized to investigate the aging behavior of pressureless sintered monolithic ZrO2 (TZ-3Y) and zirconia-toughened alumina composite with additions of 2wt% m-ZrO2 nanoparticles at 1520°C for 1h. Results show that TZ-3Y exhibited significant aging in water steam at 134°C under pressure 2bar compared to zirconia toughened alumina (ZTA) composite. The maximum fraction of monoclinic polymorph resulted after 10 and 15h of aging for monolithic TZ-3Y (~85%) and ZTA (~2.3%) composite, respectively. The homogeneous dispersion of zirconia into the matrix and its fine grain size as well as the high Young's modulus of the Al2O3 matrix which can provide a constraining effect on the zirconia could partially inhibit the phase transformation. In terms of monoclinic phase content, our ZTA composite fulfil ISO 1336–2008 requirements for implants for surgery, being thus an interesting alternative in this field.

Toughening and reinforcing zirconia ceramics by introducing boron nitride nanotubes

Abstract Boron nitride nanotube (BNNT)-toughened ZrO2 ceramics were fabricated by hot-press sintering. Compared with monolithic ZrO2 ceramic, the addition of 1.0 wt% BNNT could result in an increase of flexural strength from 895.5 MPa to 1143.3 MPa and fracture toughness from 7.94 MPa m1/2 to 13.13 MPa m1/2. The incorporation of BNNTs could not only strengthen grain boundaries but boost BNNT-induced phase transformation. The breakage of BNNTs could also dissipate some fracture energy, giving rise to the enhanced mechanical properties.

Tribological behavior of carbon nanofiber–zirconia composite

The friction and wear behavior of ZrO2 + 1.07 wt.% carbon nanofiber composite and monolithic ZrO2 has been investigated using the ball-on-disk technique with alumina balls as friction partners in an unlubricated condition at room temperature. The coefficient of friction for the composite was found to be significantly lower compared to that for monolithic zirconia with relatively low wear rates for both materials. The main wear mechanism in the nanocomposite was abrasion accompanied with a pull-out of the carbon nanofibers which act in the interface as a sort of lubricating media.

Nano/Micro-Laminated (ZrO2–Y2O3)/(Al2O3–Y2O3) Composite Coatings and Their Oxidation Resistance

Nano/micro-laminated (ZrO2–Y2O3)/(A12O3–Y2O3) composite coatings were deposited onto an Fe–25Cr–7Ni–N alloy substrate by using alternate electrochemical and sintering processes. The thickness of each layer was in the range of 80–500 nm. Experimental results indicated that the multi-laminated coatings were more effective in providing oxidation resistance than monolithic ZrO2–Y2O3 or A12O3–Y2O3 coatings, with the oxidation resistance of the former increasing with increasing number of laminated layers. The microstructural studies suggest that the laminated coatings possess the advantages of these two types of coatings and avoid the weakness of single ZrO2–Y2O3 or A12O3–Y2O3 coatings. Reactive elements Y and Zr also played a role in this nano-layered setting in improving the oxidation resistance of the coatings.

Strengthening Zirconia by Adding Both Nickel and Alumina Particles

In the present study, the processing-properties relationships of the ZrO2/(Ni+Al2O3) composites are examined. Dense composites were prepared either by pulse electrical current sintering (PECS) at 1350C for 5 minutes or by pressureless sintering (PLS) at 1600C for 1 h. The size of Ni particles is as small as 30 nm to 50 nm. Though the size of ZrO2 grains in the matrix increases as alumina and nickel particles are added, the strength of the ZrO2/(Ni+Al2O3) composites is significantly higher than that of monolithic ZrO2.

Direct Synthesis of Zirconia Aerogel Nanoarchitecture in Supercritical CO2

The objective of the present study was to synthesize porous ZrO2 aerogels with a nanostructure via a direct sol-gel route in the green solvent supercritical carbon dioxide (scCO2). The synthesis involved the coordination and polycondensation of a zirconium alkoxide using acetic acid in CO2, followed by scCO2 drying and calcination. Either a translucent or opaque monolith was obtained, which was subsequently characterized by electron microscopy, X-ray diffraction, thermal analysis, N2 physisorption, and infrared spectroscopy analysis. The electron microscopy results showed that the translucent monolithic ZrO2 exhibited a well-defined mesoporous structure, while the opaque monolith, formed using added alcohol as a cosolvent, was composed of loosely compacted nanospherical particles with a diameter of ca. 20 nm. After calcination at 400 and 500 degrees C, X-ray diffraction results indicated that the ZrO2 exhibited tetragonal and/or monoclinic phases. In situ infrared spectroscopy results showed the formation of a Zr-acetate coordinate complex at the initial stage of the polycondensation, followed by further condensation of the complex into macromolecules.

Biaxial Strength of a ZrO2/(Ni+Al2O3) Nanocomposite

Previous studies demonstrated that the strength of zirconia (ZrO2) could be enhanced or reduced by respectively adding micrometer‐sized alumina (Al2O3) or nickel (Ni) particles. In the present study, 5 vol% micrometer‐sized Al2O3 particles and 1 vol% nanometer‐sized Ni particles are incorporated into the ZrO2 matrix, which is subsequently densified by pressureless sintering. The biaxial strength of the ZrO2/(Ni+Al2O3) nanocomposite is nearly double that of the monolithic ZrO2. The increase in strength correlated with a reduction in the critical flaw size and not with any change in toughness, which may be a result of grain boundary strengthening.

Effects Of Fine Alumina Dispersion On Ionic Conductivity And Mechanical Properties Of Ytterbia Stabilized Cubic Zirconia

Nanocomposites of Yb2O3 stabilized ZrO2 (YbSZ) containing fine Al2O3 dispersions were fabricated by conventional powder mixing and a pressureless sintering technique. A fine homogeneous microstructure was obtained for the composites. This microstructural refinement decreased the size of defects in the composites, which significantly increased the fracture strength of the composites compared to that of monolithic ZrO2. The composites had the same ionic conductivity values as those of the monolithic ceramics at high temperatures (in the range of 800–1000 °C). Furthermore, the activation energy at high temperatures was independent of the Al2O3 content, whereas in the lower temperature regime (300–800 °C), it varied with the Al2O3 fraction. This indicated that different O2- conduction-based activation processes were operating in the two temperature regimes. The O2- ion transfer could easily occur at high temperatures due to the presence of the Al2O3 particulate dispersion in the composite system. From these results, it was concluded that the dispersion of fine grained Al2O3 into YbSZ is advantageous for achieving high-strength ion-conductive cubic zirconia.

Synthesis of Monolithic ZrO2 in a New Polymorph of Orthorhombic Crystal Structure with a Mesoporous Precursor

A high energy amorphous ZrO(OH)2.xH2O precursor (porous) is obtained by a controlled hydrolysis of dispersed Zr4+ cations in an aqueous solution in reaction with NH4OH at 5°C followed by aging and drying of the recovered gel at room temperature. At 20° to 40°C in air, the excess H20 evaporates leaving behind a porous ZrO(OH)2.xH2O powder with φ ∼ 37% porosity. On heating, a reconstructive ZrO2 phase transformation occurs from a refined amorphous state at 500°C to form a new orthorhombic structure in a mesoporous structure. Average crystallite size is D ∼ 15 nm. X-ray diffractogram determines the lattice parameters of a = 0.3340, b = 0.5535 and c = 0.6364 nm, with V0 = 0.1177 nm3 lattice volume or ρ = 6.96 g.cm−3. A high-pressure phase of Pnma o-ZrO2 is known of a similar value of ρ = 6.78 g.cm−3. Other known c-, t- or m-ZrO2 polymorphs of the cubic, tetragonal, or mono-clinic structures have somewhat lower ρ-values of 6.21 g.cm−3or still smaller. The o-ZrO2 irreversibly transforms to m-ZrO2, D = 23 nm, at as early a temperature as 800°C.

Microstructure and thermal shock resistance of Al2O3 fiber/ZrO2 and SiC fiber/ZrO2 composites fabricated by hot pressing

Al2O3 chopped fiber/ZrO2 and SiC continuous fiber/ZrO2 composites were fabricated by hot pressing at 1550°C and 15 MPa in vacuum. The mechanical properties of thermally shocked composites were measured at room temperature by four-point bending. The addition of Al2O3 fibers into ZrO2 matrix degraded the fracture strength, but improved significantly the thermal shock resistance. In addition, the mechanical properties of SiC fiber/ZrO2 composites were much lower than those of monolithic ZrO2 because of the presence of microcracks on the surface. The SiC fiber/ZrO2 composites showed an excellent thermal shock resistance.

Correlation between High Temperature-High Pressure Water Corrosion Behaviors and Microstructural Changes and Residual Strength Characteristics of ZrO2-Particle-Dispersed Al2O3.

High temperature and high pressure water corrosion behaviors of ZrO2-particle-dispersed Al2O3 composites were investigated in terms of with the microstructural changes and residual strength characteristics. Sintered Al2O3 bodies with 5, 15, and 30 wt.% 3 mol% Y2O3-doped tetragonal ZrO2 were made using a pressureless sintering method at 1 550. 1 600 and 1 650°C, respectively. These Al2O3/ZrO2 ceramic composites were corroded in high temperature and high pressure deionized water at 200°C∼300°C. Corrosion damage of the Al2O3/ZrO2 ceramic composites occurred preferentially on ZrO2 particles after long-term immersion in deionized water. The tetragonal to monoclinic phase transformation occurred in yittria-doped tetragonal ZrO2 polycrystals due to high temperature and high pressure deionized water corrosion. For improvement of the corrosion characteristics of the composites, are important increasing the ZrO2 content within a range in which no remarkable residual strength degradation is recognized and lowering of the sintering temperature. Al2O3/ZrO2 ceramic composites also have superior residual strength characteristics compared to monolithic ZrO2 ceramics. The residual strength characteristics are improved by increasing the ZrO2 particle concentration. and loweringthe sintering temperature. The fracture surface morphology change from transgranular to intergranular was brought about by increasing the ZrO2 content. Improvement in residual strength characteristics of Al2O3/ZrO2 composites was realized. due to intergranular crack propagation, crack pinning caused by remarkable grain bridging by Al2O3 and stress-induced transformation from tetragonal ZrO2 to stable monoclinic in the vicinity of the crack tip. Then, the necessary manufacturing conditions for sustaining the improved strength characteristics after high pressure and high temperature water immersion were clarified. In addition design concepts used to obtain water-corrosion-resistant high strength and high toughness particle dispersed ceramic composites were proposed.

Microstructure and Thermal Conductivity of Thermal Barrier Coatings Processed by Plasma Spray and Physical Vapor Deposition Techniques

AbstractThe temperature dependence of the thermal conductivity of multilayer coatings made by a plasma spray technique as well as some coatings made by physical vapor deposition (PVD) was investigated. The multilayer coatings consisted of a varying number of layers of Al2O3 and ZrO2 stabilized by 8%Y2O3. Plasma sprayed coatings exhibited a large reduction in thermal conductivity at all temperatures when compared to the bulk monolithic materials. This reduction was found to be due to porosity as well as thermal resistance brought about by interfaces in the coatings. A comparable reduction in thermal conductivity was achieved in monolithic ZrO2 as well as in a composite coating deposited by the PVD technique. Microstructural factors that may be responsible for this reduction are discussed.

Dynamic Grain Growth in Superplastic Y-TZP and Al2O3/YTZ

ABSTRACTBoth static and dynamic grain growth have been studied during superplastic deformation of fine-grained yttria-stabilized tetragonal zirconia (Y-TZP) and alumina reinforced yttria-stabilized tetragonal zirconia (Al2O3/YTZ). Grain growth was observed in both materials at temperatures above 1350° C. In the case of Y-TZP, both static and dynamic grain growth were found to obey a similar equation of the form: where D is the instantaneous grain size, Do is the initial grain size, t is the time, and k is a kinetic constant which depends primarily on temperature and grain boundary energy. The activation energies for Y-TZP were approximately 580 and 520 kJ/mol, for static and dynamic grain growth, respectively. In the case of Al2O3/YTZ, it was found that the grain growth rate for the Al2O3 phase was slower than that for the ZrO2 phase. The growth rate of the ZrO2 phase in Al2O3/YTZ is, however, similar to that in monolithic ZrO2, i.e., Y-TZP.