Stabilized Zirconia Materials Research Articles

Properties of a Pressureless Sintered 2Y-TZP Material Combining High Strength and Toughness

Yttria stabilized zirconia materials are frequently used in mechanical engineering and biomedical applications. Demanding loading conditions require materials combining a high level of strength and fracture toughness. A ready-to-press alumina doped 2 mol% yttria-stabilized zirconia powder was shaped by axial pressing and sintering in air at 1250–1500 °C for 2 h. At 1350 °C the best combination of strength (1450 MPa) and toughness (7.8 MPa√m) was achieved. Materials sintered in the middle of the chosen temperature range combine full density, high transformability and small grain size. Toughness measurements by direct crack length measurements delivered unrealistically high fracture toughness values.

Effect of TiO2 doping on the fracture toughness and thermal conductivity of HfO2 ceramic

AbstractHafnia‐based ceramic coating is considered one of the candidates to substitute yttria partially stabilized zirconia material as thermal barrier coating working above 1200°C. In this work, a series of TiO2‐doped HfO2 ceramics (Hf1–xTixO2, x = 0%, 5%, 10%, 15%, 20%, and 40%) were fabricated by solid‐state reaction. The microstructure, fracture toughness, and thermal conductivity were systematically investigated. The results show that Hf1–xTixO2 ceramics are comprised of monoclinic HfO2 and orthorhombic HfTiO4 phases when Ti4+ doping amount is between 5% and 20%, and the weight fraction of HfTiO4 phase linearly increases with the Ti4+ content and finally reaches 100% for Hf0.6Ti0.4O2. The fracture toughness of TiO2‐doped HfO2 ceramic is higher than 1.75 MPa m.5 when TiO2 content is no more than 15% and decreases below 1.5 MPa m0.5 if TiO2 content further increases. The thermal conductivity is significantly decreased by TiO2 doping attributed to the precipitated HfTiO4 phase. Considering the mechanical properties and thermal insulation capacity, the doping of 15% TiO2 would be beneficial for the HfO2‐based ceramics.

1Yb-2Sm-TZP, a new co-stabilized zirconia material with high toughness and low temperature degradation resistance

Partially stabilized zirconia materials are well known for their combination of high strength and toughness. In this study a new ytterbia samaria co-stabilized zirconia is manufactured by intensive co-milling of zirconia and stabilizer oxides with subsequent consolidation by hot-pressing. Evolution of microstructure, mechanical properties and phase composition are studied with respect to sintering temperature. The material exhibits a transformation dominated fracture behavior and a combination of high strength of up to 1050 MPa, a fracture toughness exceeding 12 MPa√m and an excellent resistance to low temperature degradation.

Effects of Thermal Barrier Coated Piston on Performance and Combustion Characteristics in Dual-Fuel Common-Rail Diesel Engine

In this study, performance and combustion characteristics of biogas and biogas+hydrogen mixtures were experimentally analysed and compared with baseline diesel fuel in a common-rail diesel engine with and without thermal barrier coated piston. Tests were conducted at three different loads (50 Nm, 75 Nm, and 100 Nm) and a constant speed of 1750 min-1. Engine pistons were coated with Yttria Stabilized Zirconia by atmospheric plasma spray method. Results showed that by replacing the standard pistons with the coated pistons, an increase for diesel, biogas, and hydrogen enriched biogas was respectively defined by 8.1%, 6%, and 23% in cylinder pressure, and 19.8%, 12.6%, and 25% in HRR at medium load. Similarly, there was an increase in range of 1.05-12.8% in gas temperature and 20.5-117.2% in knock intensity by the piston coating. CA10-90 was prolonged between 1-15 oCA with gaseous fuel modes and increased with the engine load. Volumetric efficiency was reduced by 0.1-4% with the gaseous fuel operations, while it was increased by using the coated piston for all fuels. Exhaust gas temperature increased with the gaseous fuels whereas showed discrepancies with the coated piston engine. Dual-fuel mode and coated pis-ton application caused brake specific energy consumption to increase significantly.

CMAS corrosion behavior of a LaPO4 ceramic prepared by spark plasma sintering

AbstractAt high temperatures in gas turbines, traditional yttria stabilized zirconia materials fail prematurely owing to CMAS (calcium–magnesium–alumina–silicate) corrosion. Thus, new materials need to be developed urgently. In this study, LaPO4 powder was synthesized by chemical coprecipitation and heat treatment using lanthanum nitrate (La(NO3)3∙6H2O) and ammonium dihydrogen phosphate (NH4H2PO4) as starting materials, and LaPO4 bulk was prepared by spark plasma sintering. The surface of the LaPO4 bulk was coated with CMAS (CaO–MgO–Al2O3–SiO2) powder, and the CMAS interaction with the LaPO4 bulk at different temperatures was investigated. The phase and microstructure of the LaPO4 powder and bulk, as well as the CMAS corrosion products, were characterized using X‐ray diffraction and scanning electron microscope. The superior CMAS resistance of the LaPO4 bulk was attributed to the low wettability of LaPO4 by the CMAS melt and the development of dense layers of new corrosion products, which effectively protected the LaPO4 bulk from CMAS infiltration.

Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La, Gd, Nd, Sm): Crystalline Structure, Thermal and Dielectric Properties.

Zirconium dioxide (ZrO2) is one of the ceramic materials with high potential in many areas of modern technologies. ZrO2 doped with 8 wt.% (~4.5 mol%) Y2O3 is a commercial powder used for obtaining stabilized zirconia materials (8 wt.% YSZ) with high temperature resistance and good ionic conductivity. During recent years it was reported the co-doping with multiple rare earth elements has a significant influence on the thermal, mechanical and ionic conductivity of zirconia, due complex grain size segregation and enhanced oxygen vacancies mobility. Different methods have been proposed to synthesize these materials. Here, we present the hydrothermal synthesis of 8 wt.% (~4.5 mol%) YSZ co-doped with 4, 6 and 8 wt.% La2O3, Nd2O3, Sm2O3 and Gd2O3 respectively. The crystalline phases formed during their thermal treatment in a large temperature range were analyzed by X-ray diffraction. The evolution of phase composition vs. thermal treatment temperatures shows as a major trend the formation at temperatures >1000 °C of a cubic solid solutions enriched in the rare earth oxide used for co-doping as major phase. The first results on the thermal conductivities and impedance measurements on sintered pellets obtained from powders co-doped with 8 wt.% Y and 6% Ln (Ln = La, Nd, Sm and Gd) and the corresponding activation energies are presented and discussed. The lowest thermal conductivity was obtained for La co-doped 8 wt.% YSZ while the lowest activation energy for ionic conduction for Gd co-doped 8 wt.% YSZ materials.

Interaction between Yb2O3-Y2O3 co-stabilized ZrO2 ceramic powder and molten silicate deposition, and its implication on thermal barrier coating application

Currently molten silicate deposition in thermal barrier coatings application is an ongoing challenge for material scientists. To some extent, it has already been the greatest weakness of traditional yttria partially stabilized zirconia material. Thus new material candidates and strategies that can mitigate calcium‑magnesium-alumina-silicate corrosion are urgently needed. To this end, a ‘model’ experiment involving high-temperature interactions between Yb 2 O 3 -Y 2 O 3 co-stabilized ZrO 2 ceramic powders and CMAS glass was conducted in this study. This study proposes a simple but effective methodology for comparing the transport behavior of Yb 3+ and Y 3+ during the interaction which provides further understanding of the anti-corrosion mechanism. After exposure at 1300 °C for various durations, less degradation was observed in YbYSZ samples. Further analyses ascribed the enhancement of CMAS-mitigating capability to the low diffusion rate of Yb 3+ , which was highly beneficial for maintaining the microstructure and phase stability. Additionally, the potential of YbYSZ as a CMAS-resistant material for TBCs was supported by the dramatically improved thermo-physical and mechanical properties of YbYSZ compared to those of conventional YSZ. • A simple but effective method for comparing the transport behavior was proposed. • The Yb 2 O 3 and Y 2 O 3 co-stabilized ZrO 2 shows enhanced CMAS resistance. • YbYSZ shows better thermo-physical properties as compared with traditional YSZ.

Surface treatments and its effects on the fatigue behavior of a 5% mol yttria partially stabilized zirconia material

This study evaluated the effect of distinct surface treatments on the fatigue behavior (biaxial flexural fatigue testing) and surface characteristics (topography and roughness) of a 5% mol yttria partially stabilized zirconia ceramic (5Y-PSZ). Disc-shaped specimens of 5Y-PSZ (IPS e.max ZirCAD MT Multi) were manufactured (ISO 6872–2015) and allocated into six groups (n = 15) considering the following surface treatments: Ctrl – no-treatment; GLZ – low-fusing porcelain glaze application; SNF – 5 nm SiO2 nanofilm; AlOx – aluminum oxide particle air-abrasion; SiC – silica-coated aluminum oxide particles (silica-coating); and 7%Si – 7% silica-coated aluminum oxide particles (silica-coating). The biaxial flexural fatigue tests were performed by the step-stress method (20Hz for 10,000 cycles) with a step increment of 50N starting at 100N and proceeding until failure detection. The samples were tested with the treated surface facing down (tensile stress side). Topography, fractography, roughness, and phase content assessments of treated specimens were performed. GLZ group presented the highest fatigue behavior, while AlOx presented the lowest performance, and was only similar to SiC and 7%Si. Ctrl and SNF presented intermediary fatigue behavior, and were also similar to SiC and 7%Si. GLZ promoted a rougher surface, Ctrl and SNF had the lowest roughness, while the air-abrasion groups presented intermediary roughness. No m-phase content was detected (only t and c phases were detected). In conclusion, the application of a thin-layer of low-fusing porcelain glaze, the deposition of silica nanofilms and the air-abrasion with silica-coated alumina particles had no detrimental effect on the fatigue behavior of the 5Y-PSZ, while the air-abrasion with alumina particles damaged the fatigue outcomes.

Analysis of Performance characteristics of an Internal Combustion Engine with Thermal barrier coated piston

Investigation of the thermal analysis of a conventional (uncoated) diesel piston made up of Aluminum silicon alloy was carried out in this present study. Secondly, thermal analysis was performed on piston crown, coated with 20% Al2O3 & 80% Yttria Stabilized Zirconia material. TBC comes with two layers; the first layer is a bond coating with NiCoCrAlY compound. The second layer with TBC material (20% Aluminum oxide & 80% Yttria Stabilized Zirconia). The method of multilayer coating was achieved through the Air Plasma spraying technique. Using the coated piston the required temperature in the combustion chamber will be maintained. This will reduce the heat loss to the piston. This reduction in the heat loss will be used to burn the un-burnt gases thereby reducing the polluted exhaust gases. Result will be shown as the thermal efficiency of the coated piston at full load will be increased than uncoated piston and the oxides of nitrogen will be increased.

Corrosion Resistance of Partially Stabilized Zirconia Materials to Alkaline Steel Slag

Partially stabilized zirconia (PSZ) materials were fabricated using 4 wt% CaO, 3 wt% MgO, and 5.4 wt% Y2O3 as stabilizing agents together with monoclinic zirconia powder. The physical properties, phase compositions, and microstructures of the Ca-PSZ, Mg-PSZ, and Y-PSZ samples were investigated by X-ray diffraction, scanning electron microscopy, and energy spectrum analysis. A crucible method was used to explore the relationship between the stabilizing agent and erosion resistance to alkaline steel slag. The results revealed that the zirconia materials stabilized by different stabilizing agents showed obvious differences in their bulk densities, apparent porosities, microstructures, and erosion resistances to alkaline steel slag. The structure of Y-PSZ showed highest density, containing a small number of uniformly distributed pores. In terms of Mg-PSZ, the intergranular bonding in its structure was observed to not be close, and the sample contained some cracks, but no pores. A large number of intragranular pores and a small number of overall pores was observed in Ca-PSZ, resulting in this material having the lowest bulk density. The pores and cracks provide the path to penetrate and diffuse for alkaline steel slag, which weakens the corrosion resistance of PSZ materials. The phase composition of the affected layers in all of the samples after corrosion was almost completely transformed from monoclinic phase to cubic phase, and the phase transition of both the original and transition layers was not obvious due to the formation of a slag film. Y-PSZ did not react with components of the steel slag such as SiO2 and Al2O3, showing the best corrosion resistance to alkaline steel slag.

Silica infiltration in partially stabilized zirconia: Effect of hydrothermal aging on mechanical properties

It aimed to evaluate if silica infiltration might influence the hydrothermal degradation of zirconia by determining: the phases formed, hardness, microstructure, and flexural strength of a 3Y-TZP. Yttria partially stabilized zirconia discs (1.2 mm thickness x 13 mm diameter) (InCeram YZ, Vita Zanhfabrik) were produced and assigned into 6 groups, considering 2 factors: silica infiltration in 2 levels (as-sintered or infiltration) and hydrothermal aging (LTD-Low Temperature Degradation) in 3 levels (baseline, aging at 132 °C for 35 h or 140 h). All the groups were subjected to the biaxial flexural test (n = 30), and Vickers hardness (n = 42). Weibull analysis was performed to determine the Weibull moduli (m) and characteristic strenghts (σ0). The specimens were characterized by scanning electron microscopy (SEM) to evaluate microstructure and X-ray diffraction (XRD) for phases percentages determination. For as-sintered condition: there was saturation of the amount of monoclinic zirconia after 35 h of hydrothermal aging, with 66% of monoclinic zirconia formed on the surface. LTD generated a progressive reduction in hardness over time; flexural strength was increased by the 35-h treatment (baseline: 974 MPa; 35 h: 1161.5 MPa), but, the 140 °C treatment was deleterious (698.5 MPa). On the other hand, the infiltrated specimens had an increase in the amount of cubic zirconia on the surface and showed 26% (35h) and 31% (140h) of monoclinic zirconia after the hydrothermal aging ; the strength was kept unaltered after LTD–35 h (935.9 MPa) and an increase was observed after LTD–140 h (1033.6 MPa); the hardness values had no statistically significant changes during the process. Thus, one can concludes that the silica infiltration can prevent the decrease in the mechanical properties due to the LTD on partially stabilized zirconia materials.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia

Statement of problemRecent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. PurposeThe purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. Material and methodsEach partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). ResultsThe control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P<.05) flexural strength than FSZ (582 MPa). Airborne-particle abrasion significantly (P<.05) enhanced the strength of the control and PSZ (1413 and 1227 MPa) but significantly (P<.05) reduced the flexural strength of the FSZ (442 MPa). Staining, artificial aging, and vacuum sintering had no significant effects on any of the groups. ConclusionsFully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.

In vitro and in vivo biocompatibility evaluation of dental zirconia ceramic

Recently, zirconia ceramics have been extensively used as the artificial tooth in modern dentistry on account of their excellent mechanical properties and good esthetics. The purpose of this study was to evaluate biocompatibility of zirconia ceramics using agar diffusion test, acute systemic toxicity, intracutaneous test and local lymph node assay(LLNA). For in vitro test, the agar diffusion assay was used sintered zirconia specimens (In-ceram YZ-55, VITA Co., Bad sackingen, Germany) were performed according to ISO 7405. For in vivo test, three different tests were carried out and samples were prepared according to ISO 10993-12 for all of the test. Acute systemic toxicity test and Intracutaneous test, were performed according to ISO 10993-11 and ISO 10993-10. The murine local lymph node assay test was performed according to OECD guide line 442 B. The overall criterion for the cytotoxicity of zirconia sample was "0". For the acute systemic toxicity test, no symptoms were observed during the visual observation of the animal. For the intracutaneous irritation test, there was no redness and swellings on the reaction sites. The result of LLNA test, the samples extractions in polar solvents showed average OD value of 1.078 and those in non-polar solvents showed average OD value of 1.059. The partially stabilized zirconia materials were proved to be biocompatible. The results of both in vitro and in vivo test concluded that the zirconia materials were biocompatible.

In vivo wear performance of highly cross-linked polyethylene vs. yttria stabilized zirconia and alumina stabilized zirconia at a mean seven-year follow-up

BackgroundZirconia was introduced as an alternative to alumina for use in the femoral head. The yttria stabilized zirconia material was improved by adding alumina. We evaluated highly cross-linked polyethylene wear performance of zirconia in total hip arthroplasty. The hypothesis was that alumina stabilized zirconia could decrease highly cross-linked polyethylene wear.MethodsHighly cross-linked polyethylene wear was measured with a computerized method (PolyWare) in 91 hips. The steady-state wear rates were measured based on the radiographs from the first year postoperatively to the final follow-up and were compared between hips with yttria stabilized zirconia and alumina stabilized zirconia.ResultsThe steady-state wear rate of highly cross-linked polyethylene against zirconia was 0.02 mm/year at a mean follow-up of 7 years. No significant difference was observed between groups with yttria stabilized zirconia and alumina stabilized zirconia.ConclusionsAddition of alumina to the zirconia material failed to show further reduction of highly cross-linked polyethylene wear and our hypothesis was not verified.

Low thermal conductivity without oxygen vacancies in equimolar YO 1.5 + TaO 2.5- and YbO 1.5 + TaO 2.5-stabilized tetragonal zirconia ceramics

A narrow range of composition exists along both the ZrO 2–YTaO 4 and ZrO 2–YbTaO 4 quasi-binaries over which the tetragonal zirconia phase can be retained on cooling. Unlike other stabilized zirconia materials which have low thermal conductivity as a result of phonon scattering by oxygen vacancies, these compositions do not contain oxygen vacancies and yet an equimolar YO 1.5 + TaO 2.5 composition has been reported to also exhibit low thermal conductivity [1]. We find that zirconia compositions along the quasi-binaries have low and temperature-independent thermal conductivities, and that the thermal conductivities and their temperature dependence are consistent with a defect scattering model that takes into account a minimum phonon mean free path due to the inter-atomic spacing. Furthermore, the conductivities of the Yb and Y trivalent-doped compositions scale in a predictable manner with atomic site disorder effects on the cation sub-lattice associated with the lighter Y 3+ ions and the heavier Yb 3+ and Ta 5+ ions. The lowest thermal conductivity measured was ∼1.4 W mK –1 at 900 °C. The low thermal conductivity and phase stability makes these systems promising candidates for low conductivity applications, such as thermal barrier coatings.

Behavior of High Temperature SOFC Materials Subjected to Thermal Cycles

In order to evaluate the thermal stress of high temperature SOFC materials, four different square bars of materials were examined under four different thermal cycles. Materials composed of a Ni-YSZ anode in H2 and 5%H2-N2, a YSZ electrolyte, and a (La,Sr)(Cr,Co)O3 interconnect were unaffected by the thermal cycles. However, a Ni-YSZ anode in N2 purge gas and a (La,Sr)MnO3+d cathode in air were affected by the thermal cycles strongly. Thus, by using 5%H2-N2, the anode can evade thermal cycle damage. The shrinkage characteristic of two cathode materials in air and N2 atmospheres were also evaluated. A reduction of thermal cycle induced shrinkage is made possible by a mixture of La0.6Sr0.4MnO3 and stabilized zirconia materials, and when the atmosphere of the temperature decrease phase of the thermal cycle is nitrogen, the behavior becomes independent of the atmosphere for the temperature increase portion of the cycle.

Effect of Thermal Aging on Microstructure and Functional Properties of Zirconia-Base Thermal Barrier Coatings

Thermal barrier coating (TBCs) systems made of plasma sprayed zirconia are commonly used in gas turbine engines to lower metal components surface temperature and allow higher combustion temperature that results in higher fuel efficiency and environmentally cleaner emissions. Low thermal conductivity and long service life are the most important properties of these coatings. The objective of this work was to study the influence of a long-term heat treatment (i.e., 1200 °C/2000 h) on different characteristics of atmospheric plasma sprayed TBCs. Two zirconia feedstock materials were evaluated, namely, yttria partially stabilized zirconia and dysprosia partially stabilized zirconia. Several spray conditions were designed and employed to achieve different coating morphologies. Microstructure analyses revealed that the coating microstructure was significantly dependent on both operating conditions and heat treatment conditions. Significant changes in coatings porosity occurred during heat treatment. The lowest thermal conductivity was reached with the dysprosia partially stabilized zirconia material. Heat treatment affected TBCs adhesion strength as well.

On the basic properties of an iron-based simulated cermet inert matrix fuel, synthesized by a dry route in oxidizing conditions

Simulated stabilized zirconia inert matrix fuels are synthesized by sintering in air at 1573 K. Iron cermet materials are obtained using the latter ceramic phase, with the chemical compositions of 70 and 90 vol.% (Zr 0.73Y 0.14Er 0.05Ce 0.08)O 2-Fe. The cerium is used as a minor actinide surrogate. The stabilized zirconia phase is taken as a reference material. The cermet 90 vol.% (Zr 0.73Y 0.14Er 0.05Ce 0.08)O 2-Fe has the best density. It was selected to measure the material properties. The dilatometric study showed that the speed of sintering of the iron cermet is 10 times slower than that of the stabilized zirconia inert matrix. However, good values of microhardness and specific heat are reached for the cermet. A static leach test gives weak cerium amounts in the water leachates. They are three times weaker for the cermet compared with the zirconia matrix and the speed of cerium diffusion is higher for the cermet. For these simulated materials, one can conclude that the iron cermet is chemically much stable than the stabilized zirconia material.

Comparative study of simulated zirconia inert matrix fuel stabilized with yttrium, lanthanum or praseodymium: Synthesis and leaching tests

Stabilized zirconia inert matrix fuels were synthesized with different lanthanides: yttrium, lanthanum and praseodymium. The materials were sintered in air at 1723 K. Cerium, an analog element of plutonium and americium, was employed to simulate a minor actinide in the process development, owing to the high activity of minor actinides. For each matrix, several properties, such as crystalline structure, density, microhardness, specific area, microstructure and corrosion behaviour were measured. The best materials were those crystallized in a face centred cubic system, with the compositions: (Zr 0.73Y 0.14Er 0.05Ce 0.08)O 2, (Zr 0.73La 0.14Er 0.05Ce 0.08)O 2 and (Zr 0.73Pr 0.05Er 0.07Ce 0.15)O 2. Lanthanum stabilized zirconia materials were the best. The corrosion tests showed that the whole of materials has a satisfactory chemical stability.

A comparative study on ionic conductivity of Sr and Mg stabilized zirconia by impedance spectroscopy

The high ionic conductivity of stabilized zirconia materials by substitutional doping of lower valent metal oxides (MgO, SrO, CaO, Y 2O 3, Sc 2O 3, etc.) are materials of outstanding technological importance. The Mg and Sr stabilized zirconia have been synthesized by co-precipitation method. The formation of the compound has been confirmed from XRD analysis. The particle size has been calculated from the XRD analysis and are found to be in the order of nm. The electrical characterization is carried out using the impedance spectroscopy method in the frequency range of 50 Hz–5 MHz. The conductance spectra show the dc plateau and dispersive region. The dispersive region suggests the correlated hopping motion of ions. The charge carrier concentration is found to be higher for Sr stabilized zirconia rather than for Mg stabilized zirconia. The bulk resistance for Sr and Mg stabilized zirconia have been found to be in the order of 3.47 × 10 7 Ω cm −1 and 5.05 × 10 5 Ω cm −1.