ZrO2 System Research Articles

Phase equilibria investigations and thermodynamic modeling of the Eu2O3 - La2O3 and Eu2O3 - La2O3 - ZrO2 systems

The phase relationships of the ternary system Eu2O3 - La2O3 - ZrO2 and binary Eu2O3 - La2O3 subsystem were experimentally and thermodynamically studied. Six three-phase fields and nine two-phase ones in the Eu2O3 - La2O3 - ZrO2 system were investigated by X-ray diffraction, scanning electron microscopy and electron probe microanalysis with wavelength dispersive spectrometer at 1873 K and 1673 K. Nevertheless, there only existed a two-phase region in the Eu2O3 - La2O3 system in the temperature range from 1873 K to 1673 K. After that, the ternary mixing parameters for the system Eu2O3 - La2O3 - ZrO2 including the binary interaction parameters in the Eu2O3 - La2O3 subsystem are optimized with the CALPHAD (CALculation of PHAse Diagrams) method, based on obtained experimental results. The high-temperature phase relationships and the special type of continuous solid solutions (La2-xEuxZr2O7) investigated in present work will contribute to exploring new materials with specific properties such as optical transparency.

Structure Formation of a Ceramic Composite of the Al2O3–ZrO2 System During Strontium Hexaaluminate Synthesis During Firing

Structure Formation of a Ceramic Composite of the Al2O3–ZrO2 System During Strontium Hexaaluminate Synthesis During Firing

Ceramic Dielectrics in the Oxide System ZrO2–SnO2–TiO2 for Microwave Technology

Ceramic Dielectrics in the Oxide System ZrO2–SnO2–TiO2 for Microwave Technology

Propane dehydrogenation over zinc-on-zirconia catalyst via atom trapping

Propylene is an important resource for large petrochemicals production. Propane dehydrogenation (PDH), which directly produces propylene while producing hydrogen as a by-product, has attracted extensive attention in recent years. Among various PDH catalysts, Zn-based catalyst has great potentials in industrial implementation because of its low cost and eco-friendly. Herein, we synthesized Zn–O–Zr active center via atom trapping strategy for effectively catalyzing PDH reaction. The ability of phase transition upon Zn deposition is supposed to be a possible indicator to assess active degree of ZrO2, which is directly related to the proportion of surface absorbed oxygen species (SAOS) on ZrO2. We demonstrate that SAOS concentration can be promoted through stabilizing tetragonal-phase and doping Hf, results in more Zn–O–Zr species, lower active energy, and easier phase transition. This study reveals the electronic effect on atom trapping process used in Zn–ZrO2 system and provides guidance to design and prepare high-performance Zn-based PDH catalysts.

Experimental phase diagram study of the Eu2O3–Gd2O3–ZrO2 system at 1673 K and 1873 K and thermodynamic modeling of the ternary system

The phase relationships of Eu2O3 - Gd2O3 – ZrO2 system at 1873 K and 1673 K were investigated. To experimentally determine the phase relationships, the scanning electron microscopy, X-ray diffraction, and electron probe microanalyzer with wavelength dispersive spectrometer were employed. Our findings indicated that there were no ternary compounds. However, the binary pyrochlore phases (Eu2Zr2O7 and Gd2Zr2O7) formed a continuous solid solution, denotated as (Eu2-xGdx)Zr2O7 at 1673 K. Moreover, the solubility of Gd2O3 was observed to reach at least 28.0 mol.% along Eu2Zr2O7 - Gd2O3 composition line at 1873 K. Additionally, a continuous cubic solid solution was formed between C–Gd2O3 and C–Eu2O3 at 1673 K. The obtained experimental data were utilized to optimize the thermodynamic parameters for the Eu2O3 - Gd2O3 – ZrO2 system. Thermodynamic modeling was carried out to reproduce the present phase diagram experimental results and isothermal phase diagrams of this ternary system at 1673 and 1873 K were calculated.

Investigation on the activity of Ni doped Ce0.8Zr0.2O2 for solar thermochemical water splitting combined with partial oxidation of methane

The incredible potential of metal oxide-based two-step solar-driven thermochemical water splitting technology lies in its ability to harness limitless solar energy to produce clean and renewable hydrogen fuel. However, achieving high redox kinetics and lowering the reaction temperature remain the primary challenges in hydrogen production. The CeO2–ZrO2 system is a well-known oxygen carrier for thermochemical water splitting on account of its high temperature stability, quick kinetics, and redox cyclability. While recent studies have explored the combination of methane partial oxidation with metal oxide reduction, the reduction effect of cerium-zirconium oxide is relatively low, and reactivity still needs improvement. The nickel-doped system exhibits good redox performance and is regenerative. In this study, different mass percentages nickel-loaded oxygen carriers mNi/Ce0.8Zr0.2O2 (m = 0, 1, 3, 5, 7, 9) were prepared using the impregnation method. Redox properties of oxygen carriers were investigated in a fixed bed reactor and various characterizations were performed. To assess the durability of mNi/Ce0.8Zr0.2O2, 60 long-cycle experiments were also conducted. The results indicate that the lattice oxygen in mNi/Ce0.8Zr0.2O2 exhibits remarkable selectivity for the partial oxidation of CH4 at temperatures ranging from 880 to 925 °C. The best reactivity performance was achieved with a nickel loading ratio of 5 wt%, and after 60 consecutive redox cycles, 5Ni/Ce0.8Zr0.2O2 demonstrates remarkable robustness, maintaining its redox activity.

Characterization of Zr-bearing crystalline phases from Rb-bearing model matrix materials

As part of the synthesis of new matrix materials for vitrifcation of highly active radioactive wastes, the crystalline phases formed during rapid cooling from melts of the Na2O–Rb2O–SrO(Ba)–B2O3– SiO2–Al2O3–ZrO2 system with a high Rb and Zr content (up to 10 mol. %) are found and studied. The presence of numerous Zr and Rb-bearing crystals in samples is established by electron microscopy, X-ray diffraction and Raman spectroscopy; their morphology, chemical composition and spectral characteristics are studied. It is concluded that these crystalline phases form due to the excessive content of individual components of the melt and their formation is responsible for the undesirable fnal local heterogeneity and crystallization of matrix materials.

Vaporization Processes and Thermodynamic Properties of the SrO–ZrO2 System at High Temperatures

Vaporization Processes and Thermodynamic Properties of the SrO–ZrO2 System at High Temperatures

Formation of the structure of a ceramic composite of the Al<sub>2</sub> O<sub>3</sub> ‒ZrO<sub>2</sub> system during the synthesis of strontium hexaaluminate during firing

Experimental results of the formation of the structure of a ceramic composite of the Al2O3‒ZrO2 system with the formation of strontium hexaaluminate, a reinforcing element of the material, during firing, are presented. It is shown that a uniform distribution of lamellar crystals of strontium hexaaluminate over the volume of the structure and a 30 % increase in strength is achieved during its synthesis during the firing of ceramics with the introduction of pre-synthesized strontium zirconate (precursor) into the charge. The introduction of pre-synthesized strontium hexaaluminate into the composition of the composite charge, followed by mixing and grinding, does not provide the effect of hardening the composite.

Spreading and reaction behavior of CMAS-type silicate melts with multiphase Y and Gd aluminate-zirconate T/EBC materials

Thermal and environmental barrier coatings must be robust against attack by calcium magnesium aluminosilicate (CMAS, or CMFAS with iron) deposits, and coatings that produce thin, uniform reaction layers are desirable. The reactions of four multiphase coating compositions in the AlO1.5–REO1.5–ZrO2 systems (RE = Gd or Y) with three model CMFAS deposits were studied. Following CMFAS exposure for 1 h at 1400 ºC, some samples exhibited thin, uniform CMFAS reaction product layers, while others were less uniform with pockets of deep reactions. Coating materials with higher AlO1.5 content produced uniform reaction layers, while the most SiO2-rich CMFAS was most likely to produce a non-uniform response. Apatite was formed in all cases, while the Y was more likely than Gd to form aluminosilicate garnet and cuspidine reaction products. The results are discussed in terms of implications for CMFAS-resistant T/EBC design.

Wetting and interfacial reactions in liquid Au-Ti alloys / ZrO2 system

This study investigates wetting of zirconia by Au-Ti alloys containing 0.6 to 4 wt% Ti in view of brazing zirconia to titanium with pure gold for biomedical applications. Experiments were carried out using sessile and dispensed drop methods under high vacuum at 1040-1250 °C. Bulk drops and Au-Ti / ZrO2 interfaces were characterized by SEM and FEG-SEM with EDXS analysis. While Au does not wet zirconia, the contact angle θ being ∼ 120°, the addition of Ti in Au leads to a significant improvement of wetting due to the formation of a wettable oxide layer at Au-Ti / ZrO2 interface. The nature of this oxide was determined by X-ray diffraction of the reaction layer after the detachment of the droplet from the substrate or after the dissolution of the droplet. The mechanism of formation and growth of the oxide layer and its growth kinetics were determined based on fine analysis of the Au-Ti / oxide layer / ZrO2 interfacial system.

Lu2O3–Y2O3–ZrO2: A Lu3+ co-doped YSZ system—Oxygen-ion conductor with high electrical conductivity and improved mechanical properties

This study investigates the electrical and mechanical properties of a Lu2O3–Y2O3–ZrO2 system (ZrO2 co-doped with Lu2O3 and Y2O3) and evaluates its possibility for use as a high-performance oxygen-ion conducting ceramic suitable for intermediate/high-temperature solid electrolytes. The use of electrochemical impedance spectroscopy (EIS) in the analysis and fitting of AC impedance spectra arcs on 8 mol% (Lu2O3–Y2O3)– ZrO2 has allowed to compare with the Y2O3-doped ZrO2 (YSZ) and Sc2O3-doped ZrO2 (ScSZ). (ZrO2)0.92(Y2O3)0.07(Lu2O3)0.01, with 1 mol% Lu2O3 co-doped with Y2O3, shows a bulk conductivity of 9.60 × 10−1 S/cm at 1000 °C and 3.47 × 10−2 S/cm at 800 °C, which are least several times higher than the corresponding values of any other sample in the experimental group, including Sc2O3-doped ZrO2, over the entire measured temperature range. (ZrO2)0.92(Y2O3)0.075(Lu2O3)0.005 also shows an outstanding conductivity; over two times higher than that of ScSZ. Thus, Lu2O3 co-doping can enhance mechanical properties such as flexural strength (19.5 % (1 mol% Lu2O3) and 21.5 % (2 mol% Lu2O3) higher than that of YSZ), as confirmed by the flexural strength and Vickers hardness tests. After 8 mol% sesquioxide doping of YSZ, the maximum improvement in the electrical and mechanical properties occurs at approximately 1 mol% (for electrical properties) and 2 mol% (for mechanical properties) Lu2O3 co-doping, respectively. The results of this work suggest that a small amount of Lu doping, performed during the development of materials for use in electrochemical devices (including high-efficiency energy conversion apparatus), could be a considerable approach to overcome the limitations of conventional solid oxide electrolytes.

Phase diagram study and thermodynamic modeling of the Na2O–Al2O3–ZrO2 system

AbstractThe phase diagram of the Na2O–Al2O3–ZrO2 system was experimentally studied at 1500°C–1650°C by a classical equilibration/quenching method and differential thermal analysis followed by X‐ray diffraction phase analysis and electron probe micro‐analysis. A sealed Pt crucible was utilized to prevent the volatile loss of Na2O during high‐temperature phase equilibrium experiments and the hydration upon quenching. The phase diagram of the Na2O–Al2O3–ZrO2 system was revealed for the first time. Based on the present experimental data and available binary modeling results in literature, the thermodynamic modeling of the ternary system was performed using the Calculation of Phase Diagram method and the phase diagram of the entire the Na2O–Al2O3–ZrO2 system was constructed and the optimized thermodynamic properties for all solids and liquid phase within the ternary system were obtained.

Effect of Acid‐Base Properties of Oxide Catalysts on Glycerol Transformation into Diglycerides

AbstractGlycerol oligomerization in a liquid phase was studied over the acid‐base bifunctional catalysts for the following oxides: TiO2, ZrO2, CeO2, binary CeO2−ZrO2 systems, and purely basic oxide MgO. The phase composition and surface area have been estimated by XRD and BET. The acid and basic properties of catalysts have been characterized using the quasi‐equilibrium thermal desorption (QE‐TD) of NH3 (acidity) and CO2 (basicity). Attenuated total reflectance FTIR (ATR‐FTIR) spectroscopy provided qualitative insights into the interactions in the oxide‐glycerol systems. A comparison of catalytic and acid‐base properties of the oxide systems showed that the reaction requires the presence of both acid and base sites in the catalyst. Moreover, the strength of base sites should exceed the strength of acid sites.

Reaction-Induced Metal-Metal Oxide Interactions in Pd-In2 O3 /ZrO2 Catalysts Drive Selective and Stable CO2 Hydrogenation to Methanol.

Ternary Pd-In2 O3 /ZrO2 catalysts exhibit technological potential for CO2 -based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd-In2 O3 /ZrO2 systems prepared by wet impregnation evolves under CO2 hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal-metal oxide interaction energetics. The proximity of InPdx alloy particles decorated by InOx layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction-induced restructuring in complex CO2 hydrogenation catalysts and offer insights into the optimal integration of acid-base and redox functions for practical implementation.

MgO-Al2O3-SiO2- ZrO2 system ceramic glass as sintering aids to fabricate Al2O3 ceramic membrane with high acid corrosion resistance

The shortcoming of ceramic membranes is the high cost caused by high sintering temperatures. Sintering aids can be chosen to reduce the sintering temperature. However, it results in the low corrosion resistance, especially in corrosive wastewater treatment and membranes’ chemical cleaning processes. Glass phase generated in the sintering is the main factor. In the present work, MgO-Al2O3-SiO2-ZrO2 system ceramic glass is chosen as sintering aids with a crystallinity of 89.63 %. The bending strength of the alumina membrane can be increased from 46.79 MPa of pure alumina to 111.02 MPa with 4.8 wt% ceramic glass addition. The sintering temperature of pure Al2O3 membrane is much higher than 1600 °C when the equal bending strength is obtained. The bending strength loss rate of the tubular ceramic membrane is only 5.13 % and 3.85 % after the static stage and dynamic separation for 36 h acid corrosion. MgAl2O4, Mg2SiO4, and ZrO2 crystals locate on alumina particles’ necks and provide the membrane with excellent mechanical properties and outstanding corrosion resistance. The Al2O3 membrane has a porosity of 34.06 % and a mean pore size of 1.42 μm, besides, acid corrosion can promote the permeability of membranes.

Theoretical study on the electronic properties and quantum capacitance ofZr2CO2MXenewith atomic swap

AbstractMXenes have the excellent electrochemical properties as electrode of supercapacitors. Using density functional theory, we investigated the electronic properties and quantum capacitance of Zr2CO2with atomic swap. The atomic swap results in the appearance of Frenkel‐type defect and Schottky defect. The negative binding energy confirms the stability of the studied systems. The atomic swap makes ZrC1, ZrC2, ZrO1, ZrO2, CO2 systems maintain the indirect semiconductor character, and CO2 system has the direct semiconductor character. The thermionic emission performance of Zr2CO2MXene is greatly improved by atomic swap. ZrO1 and ZrO2 systems in aqueous system are appropriate anode materials. The wide voltage has little effect on the electrode type for perfect Zr2CO2, ZrO1, ZrO2, CO1, and CO2 systems, but changes ZrC1 and ZrC2 systems from cathode material in aqueous system to anode material in ionic/organic system. The work function and effective mass are also explored.

Rare earth (Sm/Eu/Tm) doped ZrO2 driven electro-catalysis, energy storage, and scaffolding in high-performance perovskite solar cells

Current work presents the first report on the modification of zirconia (ZrO2) by doping it with the lanthanides oxides i.e. [samarium, europium, and thulium] forming a [Sm/Eu/Tm] co-doped ZrO2 system. Lanthanide doping tailored the structure of host material by causing considerable bandgap energy shrinkage from 4.04 to 3.57 eV and reduction in the crystallite size from 67.92 to 45.23 nm. Profound electro-catalytic potential was reflected analyzed via linear sweep voltammetry showing the excellent of developed catalytic towards H2 evolution with lower overpotential i.e. 133 mV and Tafel slope of 119.3 mV dec−1. While for O2 evolution, the electro-catalyst succeeded in gaining overpotential and Tafel slope values of 310 mV and 294.8 mV dec−1, respectively. With such values, this material has surpassed the conventional electro-catalysts and is proved to be an excellent hydrogen producing electro-catalyst. The electrical charge storage potential was analyzed for [Sm/Eu/Tm] co-doped ZrO2 decorated nickel foam electrode for development into a super-capacitor. This electrode was impressively stable for 10 cycles after 20 days checked through cyclic voltammetry. Furthermore, an augmented specific capacitance of 447 F g−1 was achieved by the doped electrode when compared with the pristine one approaching 83.69 F g−1. The electrical energy storage capacity of [Sm/Eu/Tm] co-doped ZrO2 is even higher than the conventionally used metal oxides. In terms of the interfacial electrode-electrolyte, electrochemical impedance spectroscopy was done expressing the excellent ionic diffusion and electrochemically active sites for [Sm/Eu/Tm] co-doped ZrO2 electrode with minimal resistance. The developed doped system was used a spacer layer in a cesium lead halide perovskite solar cells having planar architecture. The spacer layer containing solar cell device succeeded in gaining a power conversion efficiency of 16.31% and a fill factor of 78% evaluated via photo-current measurements carried out under artificial solar irradiance. The impressively higher fill factor shows the effective passivation and scaffolding by the [Sm/Eu/Tm] co-doped ZrO2. The associated device was also marked by negligible hysteresis. Chrono-potentiometry and chrono-amperometry expressed commendable accelerated service lives for 100 min inside an electrolyte. The lanthanide co-doped ZrO2 is an effective material for the utilization in energy systems associated with the electro-catalysis of water, charge storage electrode for super-capacitors, and photovoltaic solar to electrical energy conversion.

First principles investigations of structural and electronic properties of Ga-doped ZnZrOx solid solutions for catalytic reduction of CO2

ZnZrOx and gallium-doped ZnZrOx solid solutions exhibit excellent catalytic properties for the hydronation of CO2 to methanol. However, the details of the structures and catalytic properties are not fully understood. Herein, density functional theory has been used to explore the structural, electronic and catalytic properties of ZnZrOx and gallium-doped ZnZrOx catalysts. We used zinc-doped Zr sites of tetragonal ZrO2 with different Zn concentrations as a model to simulate the ZnZrOx solid solution. For the Ga-doped ZnZrOx catalysts, Zr atoms were substituted by Ga atoms. The doping of Zn atoms in ZrO2 reduce the coordination numbers of Zr atoms. Heavily Zn-doped ZrO2 systems do not maintain the tetragonal structure and, hence, deviate from the perfect tetragonal phase. At ∼29.16% Zn concentration, the bandgap of ZnZrOx has been reduced from 4.45 to 2.45 eV. The insertion of Ga in ZnZrOx solid solutions shifts the conduction band edges back, increasing the bandgap of the solid solutions. The Ga doping improves the CO2 adsorption ability of ZnZrOx solid solutions and efficiently dissociates the H2 molecules. On the surface of Ga-Zn doped ZrO2(101), the hydrogenation of CO2 to methanol via the formate pathway is more favorable than the CO pathway.

High-temperature mass spectrometric study and modeling of ceramics based on the Al2 O3 -SiO2 -ZrO2 system.

Materials based on the Al2 O3 -SiO2 -ZrO2 system are promising for a wide range of high-temperature technological applications, such as thermal barrier coatings in the aviation and space industry or advanced materials in nuclear power reactors. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric (KEMS) method are of significant interest in designing technological processes for the synthesis and exploitation of the Al2 O3 -SiO2 -ZrO2 materials. Samples of ceramics in the Al2 O3 -SiO2 -ZrO2 system, including the Al2 O3 -ZrO2 and SiO2 -ZrO2 binaries, were prepared by solid-state synthesis. Analysis of the samples was performed by X-ray fluorescence and diffraction techniques. The vapor composition and thermodynamic properties of the components in this system were determined by KEMS. The derived thermodynamic functions were optimized within the generalized lattice theory of associated solutions (GLTAS). In the temperature range 1900-2600 K, the SiO, Al,AlO, Al2 O, ZrO, ZrO2 , and O vapor species were identified over the samples in the systems under study. For the thermodynamic properties to be determined correctly, the samples of the Al2 O3 -SiO2 -ZrO2 system had to be vaporized at temperatures less than 2000 K, where data could be obtained only for the SiO species. The SiO2 activities obtained were taken as the experimental basis for the modeling within the GLTAS approach. This allowed evaluation of the component activities and excess Gibbs energy, and assessment of the relative number of bonds of different types. At 1920 K, the Al2 O3 -SiO2 -ZrO2 system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. The consistency of the obtained modeling results was illustrated by comparison of the values derived from the data for the ternary and the boundary binary systems and thereby indicates the reasonable uniformity of the energy parameters of the lattice model derived in the calculations, which may be used in further modeling of multicomponent systems.