c-ZrO2 Phase Research Articles

Exploration into the microstructural, mechanical, and biological characteristics of the functionally graded 3Y-TZP/Ti6Al4V system as a potential material for dental implants

This study investigated the mechanical, microstructural, and biological properties of 3Y-TZP/Ti6Al4V functionally graded material (FGM) fabricated by the spark plasma sintering (SPS) method. For this purpose, 11 layers of 100-x vol% Ti6Al4V/x vol% Yttria stabilized zirconia (YSZ) (x = 0 to 100) were sintered at 1450 °C and a pressure of 30 MPa for 8 min. To investigate the properties of each layer in more detail, 11 batches of 100-x vol% (Ti6Al4V)/x vol% YSZ (x = 0 to 100) composites were sintered separately with the same sintering conditions mentioned for the FGM sample. Phase identification of the FGM sample showed the formation of Ti3O, c-ZrO2, and Zr3O phases as by-products. A schematic model was proposed for the formation of the mentioned phases with the aid of thermodynamic calculations. The formation of these phases was confirmed by microstructural and elemental tests. The results of the relative density of the samples showed that these values were obtained for each layer above 99%. The microhardness of 590 ± 18 Vickers was obtained for Ti6Al4V; by increasing the amount of 3Y-TZP, this value reached 1510 ± 24 Vickers for the YSZ sample. The fracture toughness value for Ti6Al4V was 39.2 ± 2 MPa m0.5, which was significantly reduced to 4.84 ± 1 MPa m0.5 by adding 10 vol% YSZ. After that, with the further increase of YSZ, this value increased slowly. A similar trend was observed for the bending strength of the samples. By increasing 3Y-TZP from 0 to 30 vol%, the bending strength was decreased from 1556 ± 32 to 272 ± 62 MPa. By further increasing the amount of 3Y-TZP from 30 to 100 vol%, an increase in the bending strength was observed in the samples, which reached 1180 ± 71 MPa for the YSZ sample. The FGM sample showed a brittle fracture despite a metal layer, but a higher bending strength (982 ± 44 MPa) was obtained for this structure than the composite samples. The biological results show that increasing YSZ content leads to a decrease in antimicrobial activity. Additionally, all samples demonstrated high biocompatibility based on MTT cytotoxicity tests after 1 and 7 days of culture.

High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites

A study of porous YSZ abradable sealing coating (ASC) plasma-sprayed onto SiCf/SiC ceramic matrix composites (CMC) through the compatibility of intermediate layers is reported. The multilayer Si/Yb2Si2O7/LaMgAl11O19 thermal-environmental barrier coating (T-EBC) is served as intermediate layers in consideration of its ability to protect the CMC from recession and ease the misfit of the thermal expansivity. Isothermal exposure and thermal shock tests were conducted at 1200°C and led to the decomposition of t'-ZrO2 phase to t-ZrO2 and c-ZrO2 phases in YSZ topcoat, the formation of mud-cracks throughout the entire coating structure and thermally grown oxide (SiO2), with following an Yb2Si2O7 reaction layer. The measured bond strength of the coated samples was 5.47 ± 0.85 MPa, and the fracture position mainly happened inside the CMC substrate. The Superficial Rockwell Hardness (HR15Y) considered to be an important factor in abradability increased by only 1.34% after 1200°C isothermal exposure for 100 h, showing excellent high temperature hardness stability. The abradability of the ASC was investigated by a sliding wear test, the fatigue wear mainly occurred in worn scar when encountering Si3N4 ceramic ball with high hardness and low thermal conductivity, while adhesive wear occurred when GCr15 steel ball with low hardness and high thermal conductivity are encountered.

Structure and energetics of ZrC(100)||c-ZrO2(001) interface: A combination of experiments, finite temperature molecular dynamics, periodic DFT and atomistic thermodynamic modeling

The oxidation process of ZrC is very important as it affects its initial excellent mechanical and physical properties. ZrC is an ultra-high temperature ceramic, but forms low refractory oxides at lower temperatures of 500–600 °C. To develop core/shell materials by coating the ZrC surface with another material that forms protective layers on ZrC and prevents it from oxidation (such as SiC), there is the need to study and characterize the oxidized layer surrounding ZrC particles. XPS, ToF-SIMS, TEM-ED and EDX analyses were used to investigate the covering oxidized layer, and polycrystalline ZrO2(mainly cubic phase) was identified. Some traces of the tetragonal phase are observed to be present as shells around the ZrC particles with a thickness of about 4 nm on the average. Periodic DFT was subsequently used to characterize the interface formed between ZrC(100) and c-ZrO2(001) phases. A strong interface was noticed mainly with charge transfer from Zr (c-ZrO2 side) at the interface to O and C (ZrC side) atoms at the interface. The interfacial properties are local to only the first and second layers of ZrO2, and not on the third and fourth layers of ZrO2, as Bader charge analysis revealed substantial charge transfer at the interface region with no charge redistribution in the second ZrO2 layer and subsequent bulk layers. The main physical quantity, ideal work of adhesion (Wad), used to characterize the interface, remains quite constant for all ZrO2 layers, and converges at three layers of ZrO2. The interfacial bonds formed are observed to be stronger than the free surfaces in the corresponding ZrC and c-ZrO2 used to generate the interface.

Study of the mechanisms of the t-ZrO2 → c-ZrO2 type polymorphic transformations in ceramics as a result of irradiation with heavy Xe22+ ions

In this work, we present the results of a study of the t-ZrO2 → c-ZrO2 type polymorphic transformations in ZrO2 ceramics resulting from irradiation with heavy ions with different energies and fluences. The relevance of this work lies in obtaining new data on the radiation resistance of oxide ceramics to irradiation, as well as the effect of defect formation processes on the change in structural and strength properties. During the studies carried out, it was found that an increase in the energy of incident ions leads to an acceleration of the polymorphic transformation processes, and in the case of an ion energy of 230 MeV, the complete polymorphic transformation occurs at an irradiation dose of 5 × 1013 ion/cm2. It was found that polymorphic transformations caused by irradiation lead to crystal lattice swelling and deformation. At the same time, depending on the degree of polymorphic transformations, the crystal structure deformation rate changes. An analysis of the strength properties showed that the formation of a more stable cubic phase at high radiation doses slows down the processes of hardness and swelling reduction. The dependences obtained indicate that in the case of incident ion energies of more than 200 MeV, the formed cubic c-ZrO2 phase leads to an increase in resistance to radiation damage and a slowdown in degradation processes.

Study of the Effect of Doping ZrO2 Ceramics with MgO to Increase the Resistance to Polymorphic Transformations under the Action of Irradiation.

The purpose of this study is to assess the effect of doping ZrO2 ceramics with MgO on radiation swelling and polymorphic transformations, as a result of irradiation with heavy ions. Interest in these types of materials is due to the great prospects for their use as structural materials for new-generation reactors. The study established the dependences of the phase composition formation and changes in the structural parameters following a change in the concentration of MgO. It has been established that the main mechanism for changing the structural properties of ceramics is the displacement of the cubic c-ZrO2 phase by the Zr0.9Mg0.1O2 substitution phase, which leads to an increase in the stability of ceramic properties to irradiation. It has been determined that an increase in MgO concentration leads to the formation of an impurity phase Zr0.9Mg0.1O2 due to the type of substitution, resulting in changes to the structural parameters of ceramics. During studies of changes in the strength properties of irradiated ceramics, it was found that the formation of a phase in the Zr0.9Mg0.1O2 structure leads to an increase in the resistance to cracking and embrittlement of the surface layers of ceramics.

Silicate ash-resistant novel thermal barrier coatings in gas turbines

Gas turbines, used to propel aircraft or generate electricity, are vulnerable to attack by environmental silicate debris. When silicate ash is ingested into gas turbines, it melts and may adhere to the hot-section components of gas turbines (typically operating at > 1250 °C), infiltrating into their thermal barrier coatings (TBCs). These ash-related TBC issues pose a critical hazard for aircraft aviation. Here, we have developed here a novel NdYbZr2O7 coating substrate which addresses these challenges. We have quantitatively analyzed the in-situ wetting process of three representative silicate ash compositions—CMAS, volcanic ash and fly ash, and compare their infiltration behavior in the newly-developed NdYbZr2O7 coating substrate. The widely differing chemical compositions of the three ash samples yield differences in their high temperature viscosities which in turn impact their respective propensities for wetting and infiltration. CMAS exhibits the greatest dynamic wettability due to its lower viscosity over the entire range of temperature. Volcanic ash exhibits the largest infiltration depth, probably related to the relatively high solubility of rare-earth oxides (RE2O3) in volcanic ash melt. Nevertheless, compared with a traditional YSZ coating, the NdYbZr2O7 coating exhibits a better corrosion resistance in the presence of all three silicate ash samples due to the rapid precipitation of (Nd, Yb)-apatite and c-ZrO2 phases, which build a dense reaction layer, inhibiting further melt infiltration.

Low-temperature degradation resistance and plastic deformation of ATZ ceramics stabilized by CaO

In this work, the phase composition (relative fractions of monoclinic m-ZrO2, tetragonal t-ZrO2, and cubic c-ZrO2 phases) and mechanical properties (hardness, fracture toughness, compressive strength) of alumina toughened zirconia (ATZ) ceramics, with an addition of silica were investigated. Calcium oxide was used as a stabilizer for the zirconia tetragonal phase. It was shown that CaO-ATZ+SiO2 ceramics demonstrate increased resistance to low-temperature degradation. The plasticity signs at room temperature were found due to the SiO2 addition to CaO-ATZ ceramics. A yield plateau appears in the uniaxial compression diagram at 5 mol. % SiO2 concentration. It is hypothesized that discovered plasticity is due to the increased t→m transformability.

Phase Relations in the ZrO2-MgO-FeOx System: Experimental Data and Assessment of Thermodynamic Parameters

Thermodynamic parameters were assessed for the MgO–FeOx system and combined with already available descriptions of ZrO2-FeOx and ZrO2-MgO systems to calculate preliminary phase diagrams for planning experimental investigations. Samples of selected compositions were heat treated at 1523, 1673 and 1873 K and characterized using x-ray and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Experiments indicated extension of cubic ZrO2 solid solution into the ternary system at 1873 K (75 mol.% ZrO2, 10 mol.% FeOx and 15 mol.% MgO) and limited solubility of 4 mol.% ZrO2 in spinel phase. Based on the obtained results thermodynamic parameters of C-ZrO2 and spinel phase were optimized.

Fracture toughness enhancement of yttria-stabilized tetragonal zirconia polycrystalline ceramics through magnesia-partially stabilized zirconia addition

Abstract In this work, for the first time, we report a novel method on the fracture toughness enhancement of 3 mol % yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramics through the incorporation of 8 mol % magnesia-partially stabilized zirconia (8 Mg-PSZ) powders having high fracture toughness. Highly densified composites (x3Y-TZP/y8Mg-PSZ; where x and y vary between 0.25 and 0.75 wt. %) were obtained with a relative density over 99% by pressureless sintering. Relative density, Vickers hardness (HV) and indentation fracture toughness (KIc) were significantly improved by sintering temperature and dwell-time increment. Specifically, HV and KIc values of 0.5(3Y-TZP)/0.5(8 Mg-PSZ) composite sintered at 1500oC-2h were increased by 7% and 30%, respectively, compared to that of 3Y-TZP. Sintered bodies consisted of c-ZrO2, t-ZrO2 and m-ZrO2 phases without any new phase formation. m-ZrO2/c-ZrO2+t-ZrO2 volumetric phase ratios changed with the increase of sintering temperature and time. Stress-induced t-ZrO2→m-ZrO2 phase transformation within c-ZrO2 grains in 8 Mg-PSZ was the main mechanism for toughness enhancement. Energy absorbing mechanisms, e.g., crack-bridging, crack-deflection and crack branching were also found to contribute the blunting of cracks. It is thought that our approach presented herein can be considered not only fracture toughness enhancement but also other properties in various materials for functional and structural purposes.

Insights into CO2 methanation mechanism on cubic ZrO2 supported Ni catalyst via a combination of experiments and DFT calculations

The CO2 methanation mechanism was studied via combined in-situ FTIR and DFT calculations on the cubic ZrO2 supported Ni catalyst. The formation and evolution of CO2 initial adsorbed species were addressed. The bicarbonates produced from CO2 reacting with surface OH sites are transformed to the CO2* adsorbed state on the Ni/ZrO2 interface (CO2*-interface) that are hydrogenated to CH4. The CO2 adsorbed states (CO2*-Ni) generated from CO2 reacting with surface Ni sites are hydrogenated to CO* as a byproduct rather than an intermediate for methanation. The formate pathway is dominated for methanation on Ni/ZrO2, in which bidentate formates hydrogenation to H2COO* is the rate-determining step with the activation energy of 1.01 eV. The presence of ZrO2 support improves the electron mobility and reducibility of Ni, and induces H-spillover effect to promote H2O* formation. Y3+ doping into the support of Ni/ZrO2 stabilizes the c-ZrO2 phase and promote methanation activity of the catalyst.

The Effect of the ZrO2 Loading in SiO2@ZrO2-CaO Catalysts for Transesterification Reaction.

The effect of the ZrO2 loading was studied on spherical SiO2@ZrO2-CaO structures synthetized by a simple route that combines the Stöber and sol-gel methods. The texture of these materials was determined using SBET by N2 adsorption, where the increment in SiO2 spheres’ surface areas was reached with the incorporation of ZrO2. Combined the characterization techniques of using different alcoholic dissolutions of zirconium (VI) butoxide 0.04 M, 0.06 M, and 0.08 M, we obtained SiO2@ZrO2 materials with 5.7, 20.2, and 25.2 wt % of Zr. Transmission electron microscopy (TEM) analysis also uncovered the shape and reproducibility of the SiO2 spheres. The presence of Zr and Ca in the core–shell was also determined by TEM. X-ray diffraction (XRD) profiles showed that the c-ZrO2 phase changed in to m-ZrO2 by incorporating calcium, which was confirmed by Raman spectroscopy. The purity of the SiO2 spheres, as well as the presence of Zr and Ca in the core–shell, was assessed by the Fourier transform infrared (FTIR) method. CO2 temperature programmed desorption (TPD-CO2) measurements confirmed the increment in the amount of the basic sites and strength of these basic sites due to calcium incorporation. The catalyst reuse in FAME production from canola oil transesterification allowed confirmation that these calcium core@shell catalysts turn out to be actives and stables for this reaction.

Fabrication and characterizations of 8.7 mol% Y2O3-ZrO2 transparent ceramics using co-precipitated nanopowders

8.7 mol% Y2O3-ZrO2 (Y0.16Zr0.84O1.92) precursor was synthesized by the co-precipitation method using ammonia as the precipitant. The Y0.16Zr0.84O1.92 powders calcined at 800 °C show a pure c-ZrO2 phase. The average crystallite size of the powders is 12.4 nm and weakly agglomerated to an average particle size of 15.5 nm. Y0.16Zr0.84O1.92 transparent ceramics were then successfully fabricated by pre-sintering at 1350 °C for 2 h and HIP post-treatment at 1750 °C for 1 h under 200 MPa without sintering additives. The in-line transmittance of Y0.16Zr0.84O1.92 ceramics (1 mm thick) exceeds 50.3% in the region of 400–850 nm, reaching about 65.3% at 800 nm.

Structural, Mechanical, Imaging and in Vitro Evaluation of the Combined Effect of Gd3+ and Dy3+ in the ZrO2-SiO2 Binary System.

Mechanical strength and biocompatibility are considered the main prerequisites for materials in total hip replacement or joint prosthesis. Noninvasive surgical procedures are necessary to monitor the performance of a medical device in vivo after implantation. To this aim, simultaneous Gd3+ and Dy3+ additions to the ZrO2-SiO2 binary system were investigated. The results demonstrate the effective role of Gd3+ and Dy3+ to maintain the structural and mechanical stability of cubic zirconia ( c-ZrO2) up to 1400 °C, through their occupancy of ZrO2 lattice sites. A gradual tetragonal to cubic zirconia ( t-ZrO2 → c-ZrO2) phase transition is also observed that is dependent on the Gd3+ and Dy3+ content in the ZrO2-SiO2. The crystallization of either ZrSiO4 or SiO2 at elevated temperatures is delayed by the enhanced thermal energy consumed by the excess inclusion of Gd3+ and Dy3+ at c-ZrO2 lattice. The addition of Gd3+ and Dy3+ leads to an increase in the density, elastic modulus, hardness, and toughness above that of unmodified ZrO2-SiO2. The multimodal imaging contrast enhancement of the Gd3+ and Dy3+ combinations were revealed through magnetic resonance imaging and computed tomography contrast imaging tests. Biocompatibility of the Gd3+ and Dy3+ dual-doped ZrO2-SiO2 systems was verified through in vitro biological studies.

Spraying power influence on microstructure and bonding strength of ZrSi2 coating for SiC coated carbon/carbon composites

The objective of this current paper was to characterize the ZrSi2 coating deposited on the SiC coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying (SAPS) at different spraying power. The microstructure, phase composition and bonding strength were investigated. In the process of spraying, a few of ZrSi2 powders were quickly oxidized to produce ZrO2, SiO2 and ZrSiO4 ceramic phases. These phases were randomly embedded in the ZrSi2 coating to enhance the mechanical performances of the coating to some extent. In addition, t-ZrO2 and c-ZrO2 phases formed above 1473K might be converted into m-ZrO2 accompanied with 8% volume expansion, which can heal part of microcracks of the ZrSi2 coating. Therefore, only a few microcracks and pores at the spraying power of 40kW were found at the surface of ZrSi2 coating and no penetrative cracks existed in the cross section. Meanwhile, the bonding strength of the interface between the ZrSi2 and the SiC coating reached up to 11N at 40kW. In short, the SAPS technology was deemed to be a useful method to deposit the ZrSi2 coating on SiC coated C/C composites with high performance.

Crystallographic and morphological analysis of sandblasted highly translucent dental zirconia

ObjectiveTo assess the influence of alumina sandblasting on four highly translucent dental zirconia grades. MethodsFully sintered zirconia disk-shaped specimens (15-mm diameter; 0.5-mm thickness) of four highly translucent yttria partially stabilized zirconia (Y-PSZ) grades (KATANA HT, KATANA STML, KATANA UTML, Kuraray Noritake; Zpex Smile, Tosoh) were sandblasted with 50-μm alumina (Al2O3) sand (Kulzer) or left ‘as-sintered’ (control) (n=5). For each zirconia grade, the translucency was measured using a colorimeter. Surface roughness was assessed using 3D confocal laser microscopy, upon which the zirconia grades were statistically compared for surface roughness using a Kruskal–Wallis test (n=10). X-ray diffraction (XRD) with Rietveld analysis was used to assess the zirconia-phase composition. Micro-Raman spectroscopy was used to assess the potentially induced residual stress. ResultsThe translucency of KATANA UTML was the highest (36.7±1.8), whereas that of KATANA HT was the lowest (29.5±0.9). The ‘Al2O3-sandblasted’ and ‘as-sintered’ zirconia revealed comparable surface-roughness Sa values. Regarding zirconia-phase composition, XRD with Rietveld analysis revealed that the ‘as-sintered’ KATANA UTML contained the highest amount of cubic zirconia (c-ZrO2) phase (71wt%), while KATANA HT had the lowest amount of c-ZrO2 phase (41wt%). KATANA STML and Zpex Smile had a comparable zirconia-phase composition (60wt% c-ZrO2 phase). After Al2O3-sandblasting, a significant amount (over 25wt%) of rhombohedral zirconia (r-ZrO2) phase was detected for all highly translucent zirconia grades. SignificanceAl2O3-sandblasting did not affect the surface roughness of the three highly translucent Y-PSZ zirconia grades, but it changed its phase composition.

Structural investigations on the tetragonal to cubic phase transformations in zirconia induced by progressive yttrium additions

Yttria stabilized zirconia (YSZ) is inevitable in many industrial applications. Yttrium additions in ZrO2 system induces either tetragonal (t-ZrO2) or cubic (c-ZrO2) phase stabilization that predominantly depends on the yttrium content. Here, the structural changes in ZrO2 system upon a wide range of yttrium additions are investigated. Powder synthesis is carried out through citrate-nitrate assisted sol-gel technique and analytical techniques involving XRD, Raman spectra and structural analysis through Rietveld refinement were utilized to investigate the structural changes in ZrO2 upon progressive yttrium additions. The critical limit of yttrium content to retain unique t-ZrO2, mixtures of t-ZrO2 and c-ZrO2 and discrete c-ZrO2 is determined.

Study of phase transformation induced by electronic excitation in pure and yttrium doped ZrO2 thin films

The study of polymorphic ZrO2 and its structural stability of high temperature phases, such as tetragonal (t-ZrO2) and cubic (c-ZrO2) phases has been a pivotal issue for technological applications. In this work, nanocrystalline ZrO2 thin film was fabricated using the sol-gel route and comparative investigations were carried out for structural phases, surface morphology and optical band-gap for pure and yttrium doping. The changes in structural and optical studies were studied before and after irradiation with Ag9+, 120 MeV ion beam. The structural findings have shown complete transformation of phase with doping and irradiation. Two direct bands electronic structures have also evolved for doped samples under irradiation. These multiple band transitions in optical measurement could be attributed to the presence of oxygen point defects state in forbidden band gap. Presence of point defects is believed to be responsible for phase transformation/stabilization in pure zirconium oxide under irradiation.

Gadolinium Doping in Zirconia-Toughened Alumina Systems and Their Structural, Mechanical, and Aging Behavior Repercussions.

A series of Gd3+ dopings in zirconia-toughened alumina (ZTA) systems were undertaken to explore the resultant structural, morphological, hydrothermal aging, and mechanical behavior and imaging contrast abilities. The results from the characterization techniques demonstrate the significance of Gd3+ in preserving the structural stability of ZTA systems. ZTA undergoes phase degradation with 10 wt % Gd3+ at 1400 °C, while the 100 wt % Gd3+ yields GdAlO3 even at 1200 °C. Gd3+ doping at the intermediate level preserves the structural stability of ZTA systems until 1400 °C. Gd3+ occupies the ZrO2 lattice, and its gradual accumulation induces tetragonal ZrO2 (t-ZrO2) to cubic ZrO2 (c-ZrO2) phase transition. α-Al2O3 crystallizes at 1200 °C and remains unperturbed except for its reaction with the free Gd3+ ions to yield GdAlO3. Aging studies and mechanical tests signify the impeccable role of Gd3+ in ZTA systems to resist phase degradation. Further, the imaging contrast ability of ZTA systems due to Gd3+ doping is verified from the in vitro magnetic resonance imaging (MRI) tests.

Dy3+ Occupancy in Zirconia Lattice Affects Tetragonal to Cubic Phase Transitions in Zirconia Toughened Alumina Systems

Current research on zirconia toughened alumina (ZTA) systems employed in total hip joint replacement applications is focused on the usage of alternative stabilizers to improve their properties. Herein, a wide range of dysprosium (Dy3+) additions to ZTA systems have been formed through an in situ method. Dy3+ induced significant structural changes in ZrO2 rather than the α-Al2O3 component of the composite. Dy3+ tends to occupy along the a = b-axis of the ZrO2 lattice to stabilize tetragonal zirconia (t-ZrO2), whereas its enhanced accumulation directed the formation of cubic zirconia (c-ZrO2). As a consequence of phase transition, a different behavior in the emission characteristics was also noticed. However, t- → c-ZrO2 phase transition was not found to affect the paramagnetic behavior of Dy3+ added ZTA systems. The structural stability of the Dy3+ added ZTA systems was preserved until 1500 °C, and moreover it was also determined that optimum Dy3+ content is essential for enhanced mechanical stability of t...

Structure and properties of a bioactive coating on zirconium produced by microarc oxidation

Zirconium (Zr) is a potential orthopaedic and dental implant material because of excellent mechanical properties and biocompatibility. However, it is difficult to integrate Zr with biomaterials because it is bioinert. In this study, a rough and porous zirconium oxide (ZrO2) coating containing calcium phosphate was prepared on pure Zr by plasma electrolytic oxidation. The microstructure, surface topography, and elemental and phase composition of the coating were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction crystallography. The thickness of the coating was measured using an eddy current thickness gauge. The results indicate that the coating mainly comprised c-ZrO2 and m-ZrO2 crystal phases, and calcium phosphate was successfully incorporated into the ZrO2 coating. In conclusion, the formation of a rough and porous ZrO2 coating made Zr bioactive, and thus a promising coating was obtained for orthopaedic implants.