Phase Transition Of Zirconia Research Articles

Investigation of the hot corrosion effects on the lifetime of TBCs with and without TC

This paper investigates the influence of hot corrosion on the lifetime of TBCs with and without top coat under cyclic thermal loading. The tests were performed on two types of samples: Type A coating consisting solely of a bond coat (BC) fabricated by the HVOF method, and type B coating comprising a BC fabricated by the HVOF method and a TC fabricated by the APS method. The lifetime and degradation mechanism of these two types of coatings under hot corrosion in the presence of sulfate and vanadate molten salts were compared. The lifetime of type A and B coatings under the hot corrosion test is 31 and 24 cycles, respectively. Results indicate that the TGO acts as a barrier against the penetration of corrosive salts and delays the degradation of the type A coating. XRD patterns reveal that the reaction products of BC with molten salts are (Co,Ni)3(VO4)2 and (Cr,Al)VO4. In the type B coating, YVO4 is formed as a hot corrosion product due to the reaction of molten salts with yttria. With the depletion of yttria, the phase transition of zirconia from tetragonal to monoclinic causes volumetric expansion and coating degradation.

In-situ synchrotron X-ray diffraction of hydroxyapatite-zirconia composite during conventional and flash sintering

We conducted in-situ X-ray diffraction to study the crystalline phase evolution in hydroxyapatite-zirconia composites during both conventional and flash sintering processes. Additionally, we examined the thermal history and microstructure of the composite under these sintering conditions. Despite both sintering methods reaching similar average temperatures, they yielded distinct results in terms of crystalline phase composition and microstructure. In the flash sintered samples, we observed a complete transformation of hydroxyapatite into α- tricalcium phosphate and a complete tetragonal to cubic phase transition in zirconia. Conversely, the conventionally sintered samples remained practically stable. Notably, the flash sintered samples exhibited needle-like microstructures, which were absent in their conventionally sintered counterparts. This divergence suggests that the application of an electric field plays a role in generating athermal effects during the sintering of hydroxyapatite-zirconia composites.

La/Nd-doped zirconium oxide: Impact of zirconia phase transition on gamma-ray shielding properties

We investigate the effect of neodymium and lanthanum on zirconia radiation shielding and structural properties. To achieve this, new La/Nd-doped ZrO2 nanomaterials were synthesized and analyzed via various experimental techniques, including energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, to determine the fabricated materials' structure, chemical composition, and morphology. Additionally, to enable the estimation of the effect of the ZrO2 phase transition on the synthesized La/Nd-doped ZrO2 nanomaterials' γ-ray shielding properties, Monte Carlo simulation was used. The simulated data revealed that the fabricated materials' linear attenuation coefficient decreased slightly from 17.584 cm−1–17.442 cm−1 at 0.059 MeV, from 0.382 cm−1 to 0.375 cm−1 at 0.662 MeV, from 0.253 cm−1 to 0.248 cm−1 at 1.408 MeV, and from 0.180 cm−1 to 0.176 cm−1 at 15 MeV with decrease of the fraction of the tetragonal phase from 84 % to 57 %. The reduction in the linear attenuation coefficient is associated with increased thickness in terms of the fabricated materials' Pb equivalent and half values.

Machine learning potential for Ab Initio phase transitions of zirconia

Zirconia has been extensively used in aerospace, military, biomedical and industrial fields due to its unusual combination of high mechanical, electrical and thermal properties. However, the fundamental and critical phase transition process of zirconia has not been well studied because of its difficult first-order phase transition with formidable energy barrier. Here, we generated a machine learning interatomic potential with ab initio accuracy to discover the mechanism behind all kinds of phase transition of zirconia at ambient pressure. The machine learning potential precisely characterized atomic interactions among all zirconia allotropes and liquid zirconia in a wide temperature range. We realized the challenging reversible first-order monoclinic-tetragonal and cubic-liquid phase transition processes with enhanced sampling techniques. From the thermodynamic information, we gave a better understanding of the thermal hysteresis phenomenon in martensitic monoclinic-tetragonal transition. The phase diagram of zirconia from our machine learning potential based molecular dynamics simulations corresponded well with experimental results.

Influence of Cu doping on the biocompatibility of zirconia-toughened alumina ceramics for artificial joints

Zirconia-toughened alumina (ZTA) is considered the gold standard material for total hip arthroplasty (THA). However, it still lacks sufficient lubrication and fracture toughness, and it has the risk of wearing, squeaking, and fracturing. Cu doping is considered to address these issues. To further promote the application of Cu doping, its effect on biocompatibility needs to be studied. In this study, Cu-doped ZTA (Cu-ZTA) ceramics with different Cu contents were prepared using a fast hot pressed sintering (FHPS) equipment and their biocompatibility was systematically studied. The results demonstrate that, depending on the Cu content, Cu doping reduces the stability of the tetragonal zirconia, resulting in a tetragonal-to-monoclinic phase transition of zirconia, thereby creating pores on the surface of the ZTA. The biocompatibility of the Cu-ZTA with different Cu contents was analyzed based on osteoblasts and macrophages. The results suggested that Cu doping increased the adhesion of osteoblasts and slightly improved their viability. In contrast, Cu doping influenced the morphology of macrophages, causing the shrinkage and extension of their pseudopodia. Cu doping also induced the pro-inflammatory polarization of macrophages and stimulated the secretion of pro-inflammatory cytokines (TNF-α and IL-6). Therefore, Cu doping can improve the cytocompatibility of osteoblasts with ZTA ceramic surfaces, however, the enhanced effect of Cu-doped ZTA ceramics on the early inflammatory response requires special attention and further study.

Enhancement of thermal shock and slag corrosion resistance of MgO–ZrO2 ceramics by doping CeO2

The purpose of this paper was to develop ceramics materials with high thermal shock resistance and corrosion resistance for preparing gas blowing components. In this paper, MgO-rich MgO–ZrO2 ceramics were obtained by using MgO powder and ZrO2 powder as starting materials and CeO2 as an additive. Changes in the properties in terms of thermal shock resistance, mechanical properties, and slag corrosion-resistance with chemical compositions were examined correlated to microstructure and phase changes. Especially, the effect of doping CeO2 on phase transition of zirconia in MgO-rich system was discussed. The results showed that doping amount of CeO2 significantly improved properties of MgO–ZrO2 ceramics. Especially when doping amount of CeO2 was 2 wt%, residual strength ratio was enhanced over 100% after thermal shock testing. In samples doped with CeO2, ZrO2 was stable in cubic or tetragonal form due to complete solution of CeO2, which was important reason for the improvement of various properties of MgO–ZrO2 ceramics.

Changes in high-temperature thermal properties of modified YSZ with various rare earth doping elements

To protect the high-temperature components of gas turbines, 6–8 wt.% yttria stabilised zirconia (YSZ) has been extensively used as a thermal barrier coating (TBC) material. However, its application is severely limited at high temperatures because of zirconia phase transition and sintering densification above 1200 °C. This study developed modified YSZ with enhanced high-temperature thermal properties owing to the addition of various rare-earth doping elements. Among the various rare earth-doped compositions, all the thermal properties were significantly improved in compositions containing scandium, gadolinium, and dysprosium. Furthermore, in the selected compositions, the high-temperature thermal properties were analysed under heat treatment conditions of 1300 °C, with a target turbine inlet temperature (TIT) of 1500 °C. The high-temperature phase stability of the tetragonal phase was significantly improved in the newly developed compositions, and they exhibited glass-like low thermal conductivity (∼0.984 W/mK) due to the influence of lattice distortion caused by the differences in the substituent-ion mass and size, and the oxygen vacancies. Moreover, there was notable improvement in the thermal expansion coefficient (∼11 × 10−6/K) and resistance to high-temperature densification.

Phase transition and interface evolution of Al2O3/ZrO2 particles in plasma-sprayed coatings

Alumina and zirconia ceramic particles exhibit high hardness and excellent wear resistance at high temperature, and hence are used as ceramic reinforcement phases in some plasma sprayed coatings. In this study, the interface evolution of a zirconia/alumina eutectic ceramic and the phase transition of zirconia in a plasma-sprayed coating were investigated. Scanning electron microscopy and transmission electron microscopy combined with focused-ion beam and energy dispersive X-ray were used to analyze the microstructure and composition of the ceramic interface. The results showed that the eutectic ceramic particles consisted of alumina (outer) and columnar zirconia (inner) before and after the plasma spraying process. The inner zirconia part showed the martensitic transformation of t-type zirconia to stripe-like m-type zirconia. After the plasma spraying, the interface between alumina and zirconia changed significantly, which formed a new oxide layer. The phase transition mechanism in the ceramic particle and oxide layer formation mechanism at the alumina/zirconia interface were investigated.

High-temperature corrosion mechanism of YSZ coatings subject to calcium–magnesium–aluminosilicate (CMAS) deposits: First-principles calculations

To study the degradation mechanism of yttria-stabilized zirconia (YSZ) coatings by CMAS glass attack at high temperature, density functional theory is used to calculate the energy of CMAS/YSZ(111) system. Over 1513K, the diffusion coefficients of atoms in CMAS are larger than those in YSZ (111) and the diffusion process of (Ca↔Y) and (Si↔Y) occurs, which induced to the formation of a sandwich structure and YSZ depleting in yttrium, allowing tetragonal to monoclinic phase transition of zirconia. The cracking and peeling off of the coating is attributed to the change of YSZ volume and the thermal stress.

<i>In Situ</i> XRD Study of Zirconia Phase Transformation Produced from Chemical and Mineral Processes

The high temperature phase transition of zirconia produced from commercial zirconyl chloride chemical was compared with that produced from a Malaysian zircon mineral. Zirconyl chloride was produced from zircon by using the hydrothermal fusion method. Initial XRD diffractogram of these samples at room temperature show that they are of amorphous structure. High temperature XRD studies was then performed on these samples; heated up to 1500°C. The XRD diffractograms shows that the crystalline structure of tetragonal zirconia was first observed and the monoclinic zirconia becomes more visible at higher heating temperature.

Theoretical and experimental evidence for the post-cotunnite phase transition in zirconia at high pressure

A post-cotunnite phase transition in zirconia (ZrO2) at high pressure was investigated by synchrotron X-ray diffraction measurements and ab initio calculations based on density functional theory. This study successfully demonstrated a cotunnite- to Fe2P-type phase transition. Static enthalpy difference (ΔH) calculations predicted the appearance of the Fe2P phase at 124 GPa (LDA) and 143 GPa (GGA), and experimental trials demonstrated the coexistence of the Fe2P and cotunnite phases at 175 GPa after heating to 3,000 K. Both phases were quenchable to ambient conditions. The volume of the Fe2P phase was slightly less (~Δ 0.6 %) than that of the cotunnite phase over the experimental pressure range, indicating that the Fe2P phase is the higher pressure phase. The coexistence of both phases in this study may be attributed to the slow kinetics of the phase transition resulting from the close structural relationship of the two phases. An Fe2P-type structural model can be derived by applying a simple operation to the cotunnite-type structure, consisting of a 1/2 shift of several zirconium arrangements parallel to the b-axis of the cotunnite-type unit cell. It is concluded that the high-pressure cotunnite-to-Fe2P phase transition may be a common trend in many dioxides.

Evaluation of leaching components and color stability for colored dental zirconia with various coloring liquids

The objective of this study was to evaluate the leaching components from the zirconia colored with various coloring liquids and color stability of the colored zirconia after accelerating aging. Commercially avaliable six coloring agents (AQU, BRU, DMA, LAV, RAI and INC) were tested. 3Y-TZP powder were used to prepare the disk-typed pre-sintered zirconia block. After application of coloring agents to pre-sintered zirconia block according to manufacturer’s instruction, final sintering was performed. XRD analysis was done to detect formation of secondary phases and phase transition of zirconia due to the addition of coloring agents. For the chemical stability test, ISO 6872:2008 was adopted and analytical equipments were used. ISO 7491:2000 was adopted for the color stability test. After accelerated aging treatments, color coordinates (CIE L<SUP>*</SUP>a<SUP>*</SUP>b<SUP>*</SUP>) were measured using spectrophotometer.BR Effects of coloring liquid on the microstructure of zirconia were not observed using XRD analysis, however, small peak of yittrium (Y) was observed in INC. In CTL and all experimental groups, Fe, Y, Mn and Ni ions were leached. Small amounts of Er, Co, and Cr ions were released from some experimental groups. The test of chemical stability in acetic acid solution did not affect the color stability of the colored zirconia (ΔE=0.06-0.69). After the accelerated aging treatment for 24 hrs, lightness (L<SUP>*</SUP>) and a<SUP>*</SUP> values showed the increasing behavior, but b<SUP>*</SUP> values did not show consistent changes. Color difference (ΔE) of CTL was 0.56, 1.61 for BRU, 1.26 for RAI, 1.16 for INC, 1.01 for DMA, 0.60 for AQU and 0.52 for LAV.

Crystallite size and phase transition demeanor of ceramic steel

Zirconia is an important oxide of zirconium used in variety of field ranging from dentistry, fuel cells, and thermal barrier coatings. Phase transition of zirconia is an important phenomenon controlling its fracture strength, low temperature degradability and ion conductivity. In the present study, effect of molar concentration of precursor and calcination temperature on phase transition and crystallite size of zirconia was investigated. All the samples were characterized by X-ray diffractometry (XRD), Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). In sample having lowest precursor concentration crystallite size of monoclinic zirconia was found to be lower than that of tetragonal zirconia, simultaneously with the higher proportion of tetragonal zirconia (67.62%) as compared to all other samples (42.75%–58.04%). In all cases, monoclinic to tetragonal phase transition occurs with raise of temperature but in the sample with lowest precursor concentration, tetragonal to monoclinic phase transition occurred on raising the temperature.

Effect of high intensity ultrasound on the mesostructure of hydrated zirconia

We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic treatment studied by means of small-angle neutron scattering (SANS) and X-ray diffraction (XRD). It was established that sonication affects the mesostructure of ZrO2×xH2O gels (i.e. decreases their homogeneity, increases surface fractal dimension and the size of monomer particles). Ultrasound induced structural changes in hydrated zirconia governs its thermal behaviour, namely decreases the rate of tetragonal to monoclinic zirconia phase transition.

Effect of sandblasting on the mechanical properties of Y-TZP zirconia

Surface modification techniques affect phase transformation which in turn influences strength of zirconia biomaterial. The study aimed at evaluating the tetragonal to monoclinic (t-m) phase transition of zirconia occurring after sandblasting three different ceramic abrasive materials and its subsequent effect on the strength. Zirconia bars (n=24) were sandblasted using silicon carbide (SiC), alumina (Al2O3) and zirconia (ZrO2) particles. After surface characterization by a scanning electron microscope (SEM) and a laser profilometer, the relative amount of transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD) and its corresponding effect on the flexural strength and fatigue strength were determined. Data were analyzed using one-way analysis of variance ANOVA (p<0.05). Furthermore, Weibull statistics was used to analyze the variability of flexural strength. The highest amount of monoclinic content was found after sandblasting with SiC consequently resulting in an increased flexural strength and fracture resistance under cyclic load conditions. Weibull modulus was reduced in all the groups with SiC blasting showing the least degradation of m values. The strengthening mechanism that is attributed to sandblasting procedure is influenced by the abrasive material used.

Study of ZrO2 phase structure and electronic properties

The phase structure and electronic properties of c-ZrO2, t-ZrO2 and m-ZrO2 are calculated and compared using density functional theory. By calculating the energies for different lattice constants, the crystal structures of the three zirconia polymorphs are optimised. The calculation results are in good agreement with related experimental data and the cohesive energies do reflect the relative phase stability of the three zirconia polymorphs. The valence electronic density of states and the charge distributions on some typical planes are presented and discussed to investigate the valence electronic structure, the special electronic properties, and the Zr–O bond strength. The calculation results in this paper would be helpful to further predict the zirconia phase transition and some basic physical properties.

Role of metal additives in mechanochemical phase transformation of zirconia

Reasons for a phase transition in zirconia subjected to intensive mechanical treatment in planetary mill have been considered. If steel balls and vials are used for milling the comminution is accompanied by oxidation of wear metal particles and successive mechanochemical reaction with ZrO2. Aluminum has been shown to behave similarly and, being deliberately added to zirconia powder, to form solid solutions. Foreign metal cations introduced into the lattice stabilize a modification with higher crystal symmetry thus increasing the threshold size above which the monoclinic modification is stable. An increase of surface energy contribution to the Gibbs’ energy of zirconia plays an important role in phase transformation at the initial stages of mechanical treatment, while henceforth thermodynamic stability is more and more determined by the stabilizing effect of the impurity cations. Under the conditions that rule out contamination of ZrO2 with wear material or other metal additives, dynamic equilibrium sets in between the direct transition to the tetragonal phase and the reverse transition to the monoclinic form.

Phase Stability in Nanocrystalline Zirconia

Zirconia can be considered to be one of the most important ceramic materials because of its large range of industrial applications (catalysis, coatings, spacecraft shielding, paint additives, oxygen sensors, fuel cells, nuclear fuel matrices, an alternative high permittivity material to replace silicon oxide as a gate dielectric in MOS devices). Many of these applications require the use of zirconia in a nanocrystalline form. It is now well established that a monoclinc to tetragonal phase transition is trigged by the grain size of zirconia. The mechanism of this phase transition in zirconia is not yet clearly understood. Several experiments point out that the thermodynamic properties of nanocrystalline solids are particle-size dependent. Size-related effects like the reduction of the melting temperature and displacement of the phase boundaries can be predicted. Zirconia can be considered a textbook example for describing these effects. In this ceramic several polymorphic transformations occur with the change of external parameters (Temperature, pressure, …). In this paper, the behaviour of the tetragonal to monoclinic martensitic phase transition within Landau theory framework in particular will be discussed, pointing out the peculiar effects related the small grain size of the nanoparticles. Neutron diffraction experiments will illustrate the of these arguments and provide some insight to the understanding of the behaviour of nanocrystals in severe environments, such as in nuclear reactors or in space applications.

Territory, Proximity, and Spatiality: The Geography of International Conflict

High-temperature differential thermal analysis provided data on phase transitions in zirconia and yttria. The tetragonal form of ZrO2 transforms to the cubic fluorite structure at 2311°±15°C with an enthalpy of 3.4±3.1 kJ/mol. Cubic C-type Y2O3 transforms, probably to the fluorite structure, at 2308°±15°C with ΔH=47.7±3.0 kJ/mol. This high-temperature polymorph melts at 2382°±15°C with an enthalpy of fusion of 35.6±3.0 kJ/mol.

Swift heavy ion induced crystalline-to-crystalline phase transition in zirconia and hafnia: a comparative study

Zirconia and hafnia are well-known isomorphic materials which share many physical and chemical properties but have also some differences. Regarding ion-beam induced effects, these features offer the interesting possibility to fix a lot of experimental parameters and to vary only a few ones. In this context, both oxides were irradiated with swift heavy ions and their structural evolution was monitored in situ by the X-ray diffraction technique. The results indicate – for both oxides – the occurrence of an ion-beam induced transition from the monoclinic to the tetragonal phase which is driven by a double ion impact mechanism. Moreover, this transition is related to an effective threshold in the electronic energy loss which is higher in hafnia than in zirconia. Finally, it is found that these threshold values scale reasonably well with the corresponding transition temperatures at thermodynamic equilibrium.