ZrO2 Crystals Research Articles

Petrography, Crystallography, and Geochronology of Baddeleyite With Two Morphologies in a Chang'e‐5 Lunar Basalt

AbstractBaddeleyite (ZrO2) is widespread in lunar basalts and frequently used for U‐Pb geochronology of magmatic and impact events. The formation of baddeleyite involves two primary mechanisms: (a) crystallization from late‐stage magma, and (b) decomposition of zircon under high‐temperature (high‐T) conditions. Baddeleyite with distinct formation mechanisms commonly displays different morphologies. In a Chang'e‐5 lunar basalt, we report baddeleyite with two different morphologies, termed “singular type” and “aggregate type.” Petrographic and crystallographic analyses were conducted on both types of baddeleyite to understand their formation conditions and evolution processes. Despite the similarity in the morphology and mineral assemblages between the aggregate type baddeleyite and zircon decomposition products, the petrographic characteristics and the rarity of zircon in lunar basalts tend to suggest that both types of baddeleyite are derived from magma crystallization. Crystallographic relationships observed in both types indicate a phase transformation from the precursor tetragonal‐ZrO2/cubic‐ZrO2 or orthorhombic‐ZrO2 phase. Two potential scenarios are proposed for the formation of these microstructures: (a) direct crystallization of high symmetry ZrO2 from magma, and (b) crystallization of baddeleyite from magma followed by a high‐pressure (high‐P) event causing its phase transition. However, due to unresolved scientific issues in both scenarios, an accurate evolutionary process cannot currently be determined. Therefore, extensive thermodynamic experiments are necessary to enhance our understanding of baddeleyite microstructures as indicators of P‐T processes, providing insights into magmatism and the impact history of planetary bodies.

Effect of the ZrO2 Crystal Phase on Performance over a CuCeZrO Catalyst for Dehydrogenative Condensation of Ethanol to Ethyl Acetate.

Ethyl acetate is an important chemical, and ethanol dehydrogenative condensation with 95.6% atomic economy is a promising synthetic route. CuZrO-based catalysts are widely applied in this reaction; however, the effect of the ZrO2 crystal phase in the CuCeZrO catalyst upon reaction deserves to be explored further. Herein, the ZrO2 crystal phase in the CuCeZrO catalyst was regulated by controlling the calcination temperature, and a high temperature (≥600 °C) is conducive to the transformation of the tetragonal phase to the monoclinic phase. Additionally, monoclinic ZrO2 (m-ZrO2) with limited density of the strong base is found to be more beneficial to the selective production of ethyl acetate from ethanol, while tetragonal ZrO2 (t-ZrO2) with abundant strongly basic sites is more inclined to the formation of butanol and its downstream esters. This work not only improves our understanding of the crystal phase effect in a CuCeZrO catalytic system but also paves the way for the development of more efficient catalysts for ethyl acetate production.

Unraveling the characteristics of adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals with point defects from molecular dynamic simulations

Unveiling the characteristics of adsorption and diffusion of oxygen atoms on the surface of zirconium alloys at microscale is significant during the initial stages of zirconium oxide layer formation in PWRs or LWRs. In this work, Adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals have been investigated using molecular dynamic simulations. A special focus of this work is on the diffusion coefficient calculation based on our developed unbiased approach. The results show that a weak effect of temperature on the adsorption rate of ZrO2. The greater influence of grain boundary orientation than the concentration of Frenkel defects on the adsorption rate of oxygen atoms. The number of oxygen atoms that diffuse deep into the studied samples after adsorption on the free surface increases with increasing temperature. Moreover, for crystals that have a certain concentration of Frenkel defects in the volume, the diffusion coefficients are greater than for defect-free crystals. The diffusion coefficient of adsorbed oxygen atoms is smaller for crystal system with grain boundary of Zr/Zr. This distinct feature may be solving the experimental puzzle of oxidation rate of zirconium alloys under neutron irradiation.

Enhanced high temperature ablation resistance of dense ZrB2–Al2TiO5 composite coating by very low-pressure plasma spraying

ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.

Effect of melt homogenization on the structure and properties of zirconium-rich basalt fibers

The slow dissolution process of zirconium oxide (ZrO2) limits the efficient and energy-saving production of zirconium-rich basalt fibers with excellent alkali resistance for fiber-reinforced concrete. Therefore, it is necessary to investigate the optimum homogenization conditions to produce high-performance zirconium-rich basalt fibers. In this study, quenched zirconium-rich glasses and zirconium-rich fibers with the addition of 7 wt% ZrO2 at different homogenization temperatures and time were prepared. The quenched melt structure was characterized by XRD and FTIR, and followed information about the melt structure obtained by Gaussian curve fitting of the FTIR spectra. The results indicated that obvious ZrO2 crystals appeared in the melts and fibers with homogenization temperature below 1500 °C and time below 4 h. The degree of polymerization of zirconium-rich basalt melt was found to increase with increasing homogenization temperature and time. Meanwhile, the tensile strength and production stability of zirconium-rich fibers increased with increasing the degree of polymerization. The optimum homogenization temperature and time for zirconium-rich basalt fibers were concluded to be 1580 °C and 10 h, and the corresponding tensile strength is 1799 MPa and 1761 MPa, respectively. By diffusion experiment of ZrO2 in basalt melt with altered major component content, it was found that the Ca, Mg, Na, and Fe significantly facilitated the melting of ZrO2 into basalt melt by XRD and EDS. It was mainly attributed to the charge-compensating effect of metal cations on the [ZrO6] octahedra, which promoted the homogenization of ZrO2 in basalt melt.

Microstructure and thermal shock resistance of ZrO2–Al2O3–A3S2 composites for casting filter materials

ZrO2–Al2O3-A3S2(3Al2O3·2SiO2) composites are ideal Casting filter materials with excellent mechanical properties and thermal shock resistance. In this paper, 3Y–ZrO2 (3 mol% Y2O3-stabilized ZrO2) was added to kaolin and α-Al2O3 to prepare ZrO2–Al2O3-A3S2 composites by pressureless sintering. The results showed that when the addition amount of 3Y–ZrO2 is 15 wt%, the bending strength and fracture toughness of the composites sintered at 1600 °C are 152.51 MPa and 3.52 MPa m1/2, respectively. The bending strength increased to 161.83 MPa after 30 thermal shocks (1100 °C to room temperature), with an increase rate of 6.11 %. The ZrO2 crystals are evenly distributed between corundum and mullite crystals, effectively preventing abnormal growth of corundum and mullite crystals, and a small number of pores exist in the samples, which could act as a “buffer zone” to prevent the expansion of cracks in the thermal shock, resulting in high mechanical strength and excellent thermal shock resistance for composites.

Role of ZrO2 crystal on the hydrodeoxygenation of methyl palmitate over NiMo/ZrO2 catalyst

The hydrodeoxygenation of biomass into high-quality fuels is an effective strategy for solving the shortage of traditional fossil energy sources. In this paper, four NiMo/ZrO2 catalysts with different crystalline ZrO2 supports were synthesized and their catalytic properties for the hydrodeoxygenation of methyl palmitate were further investigated. Different crystalline ZrO2 exhibited different concentrations of oxygen vacancies, which could modulate the Ni valence state of NiMo/ZrO2 catalyst and affect adsorption and activation of CO bands, thus affecting catalyst activity and selectivity. Pure phase ZrO2, especially monoclinic ZrO2, was found to possess a stronger electron transfer capacity, a higher amount of Ni0 and oxygen vacancies on the surface than mixed phase ZrO2, which was conducive to dissociate H2 molecules and activate the CO bond. Thus, NiMo/m-ZrO2 (monoclinic phase) exhibited the highest hydrogenation conversion (99.5%) and liquid alkanes selectivity (96.7%, hexadecane: 68.8%) under relatively mild condition (240 °C, 3 MPa H2). In addition, the NiMo/m-ZrO2 catalyst maintained excellent catalytic stability without significant deactivation after continuous reaction for 86 h.

Interface tuning and electrical property optimization of La-doped ZrO2 gate dielectric based on solution driving

With the development of thin-film optoelectronic components and the increasing requirements for improved integration and performance of ultra-large-scale integrated circuits for devices, finding new high-k gate dielectrics to replace ZrO2 has become a challenge. Elemental doping is an effective method to further improve the dielectric properties of ZrO2. In this work, a novel gate dielectric material was prepared by doping ZrO2 with the rare-earth element La. The results show that the new gate media material has better performance; these include suppressing the crystallization of ZrO2 as well as obtaining a large band gap (∼5.74 eV), a large conduction band shift ΔEC (∼2.96 eV), and a low leakage current (∼6.3 × 10−6 A/cm2). In addition, La doping can significantly suppress the generation of thin-film oxygen vacancies and low-k layers. Furthermore, the leakage current transfer mechanism of the device is systematically investigated. This study provides new insights for selecting a suitable La doping content for the modification of future gate dielectric materials.

Investigations towards incorporation of Eu3+ and Cm3+ during ZrO2 crystallization in aqueous solution

Nuclear energy provides a widely applied carbon-reduced energy source. Following operation, the spent nuclear fuel (SNF), containing a mixture of radiotoxic elements such as transuranics, needs to be safely disposed of. Safe storage of SNF in a deep geological repository (DGR) relies on multiple engineered and natural retention barriers to prevent environmental contamination. In this context, zirconia (ZrO2) formed on the SNF rod cladding, could be employed as an engineered barrier for immobilization of radionuclides via structural incorporation. This study investigates the incorporation of Eu3+ and Cm3+, representatives for trivalent transuranics, into zirconia by co-precipitation and crystallization in aqueous solution at 80 °C. Complementary structural and microstructural characterization has been carried out by powder X-ray diffraction (PXRD), spectrum imaging analysis based on energy-dispersive X-ray spectroscopy in scanning transmission electron microscopy mode (STEM-EDXS), and luminescence spectroscopy. The results reveal the association of the dopants with the zirconia particles and elucidate the presence of distinct bulk and superficially incorporated species. Hydrothermal aging for up to 460 days in alkaline media points to great stability of these incorporated species after initial crystallization, with no indication of phase segregation or release of Eu3+ and Cm3+ over time. These results suggest that zirconia would be a suitable technical retention barrier for mobilized trivalent actinides in a DGR.

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.

Preparation of nanometer zirconia by hydrothermal method: Influence of temperature and mechanism

Monoclinic (m-ZrO2) and tetragonal zirconia (t-ZrO2) nanoparticles with average grain size of 22.8 nm were synthesized by hydrothermal method using zirconium oxychloride octahydrate (ZrOCl2·8H2O), urea (CO(NH2)2) and deionized water as zirconium source, precipitant, and solvent, respectively. The effects of CO(NH2)2 hydrolysis rate, hydrothermal temperature, and time on the crystal structure, morphology, and grain size were studied. The structure, morphology, grain size, and crystal phase of zirconium oxide (ZrO2) were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetry (TG-DTA), and Fourier Transform Infrared spectroscopy (FT-IR). The results show that the formation mechanisms of different crystal forms can be controlled by the average pH value. The hydrolysis rate of CO(NH2)2 was relatively slow at 120 °C, resulting in a slower rate of OH− production. The lower average pH value favors the formation of m-ZrO2 through the dissolution precipitation mechanism. With the increase of crystallization temperature, the hydrolysis rate of CO(NH2)2 is accelerated, and the average pH value of the solution is increased, which is conducive to the structural rearrangement of [Zr(OH)8(H2O)16]8+ precursor to form tetragonal phase. In addition, the number of defect sites is directly proportional to the crystallization temperature. Extension of crystallization time helps the generation of ZrO2 crystals by polycondensation and directional growth.

Local electron-rich structures facilitating the efficient synthesis of dimethyl carbonate from propylene carbonate and methanol over a ZnO/ZrO2 solid solution catalyst

ZnO/ZrO2 solid solution was introduced as the catalyst for synthesizing dimethyl carbonate (DMC) from propylene carbonate (PC) and methanol. Homogeneous catalysts with strong alkaline nature are the current main catalysts for this reaction. Therefore, to supplant the former with a more applicable multiphase one, it is necessary to construct stable and efficient alkaline active centers on the surface of solid catalysts. The ZnO/ZrO2 solid solution created defective structures of coordinative unsaturation in the form of oxygen vacancies (OV) by substituting Zn atoms for Zr atoms in ZrO2 crystals. Characterizations showed that electrons were transferred to the surrounding Zn atoms upon the formation of these OV, leading to a local enrichment of electrons and the formation of basic active centers. The number of oxygen defects and the alkalinity were effectively regulated by changing the ratio of the two metal atoms in the solid solution. Experiments demonstrated that the catalyst had the best DMC selectivity (92.2%) and the highest DMC yield (57.2%) at a 1:1 ratio of Zn to Zr, at 160 °C and 4 h. This superior performance not only establishes the feasibility of solid solution catalysts in synthesizing DMC but also provides a new perspective on the essential understanding of the active centers of such catalysts.

Synthesis of a nanosized homogeneous Al2O3–CeO2–ZrO2 composite as an oxygen-storage material for highly improved thermal durability

Al2O3–CeO2–ZrO2 (ACZ) is widely used in automotive catalysts as an oxygen-storage material. However, ACZ prepared by conventional synthesis methods has poor compositional homogeneity, resulting in thermal degradation of the oxygen storage capacity (OSC) because of the sintering of CeO2–ZrO2 (CZ) crystals. In this study, a nanosized homogeneous ACZ composite is synthesized by an improved co-precipitation method that uses a high-shear agitation reactor and a polyamine dispersant. The sol obtained using the abovementioned method is a monodisperse colloid with an average particle size of 3.2 nm. A quantitative analysis of transmission electron microscopy images reveals that the distribution of Al2O3 and CZ after calcination at 500 °C is 1.6 times more homogeneous in the resulting ACZ than that in the ACZ powder obtained by conventional co-precipitation. Such excellent homogeneity of Al2O3 and CZ distribution results in smaller CZ crystals (11.2 nm) than the conventional one (14.6 nm) obtained after calcination at 1100 °C. The smaller CZ crystals have 1.3 times higher OSC than that of the conventional one. Therefore, the developed method yields homogeneous and thermally stable ACZ that can be used as an efficient automotive catalyst. Furthermore, this method would also be useful for synthesizing homogeneous nano-composites with various elemental combinations.

Zr‐doped SiOC ceramics fibers and the high‐temperature thermal performance

AbstractSilicon‐containing ceramics fibers are ideal candidates for thermal resistance due to their incomparable thermo‐stability and chemical stability. Research into anti‐oxidation behavior of silicon‐containing ceramics through metal elements doping is important for the application in extreme high‐temperature environment. Thus, uniform belts‐like Zr‐doped SiOC ceramics fibers were successfully prepared by electrospinning and polymer‐derived ceramics routine with polycarbosilane (PCS) and zirconium butoxide as precursors. The morphology and dimension of the fibers were conveniently controlled by tuning PCS concentration, types of spinning additives and pyrolysis temperature. The ceramics fibers were composed of SiC, ZrO2 and SiO2 crystals, accompanied with amorphous SimZrnCxOy. The structure and compositions realized the excellent thermal stability above 1300°C and the enhanced flexibility. The obtained fibers maintained ultra‐low thermal conductivity of .038–.053 W/(m·K). Thus, the materials were anticipated to be ideal for the thermal insulation up to 1400°C or higher.

Microstructure of rapidly‐quenched ZrO2‐SiO2 glass‐ceramics fabricated by container‐less aerodynamic levitation technology

AbstractIn this work, an aerodynamic levitation technology (ALT) was utilized to prepare ZrO2‐SiO2 glass‐ceramics with two different ZrO2 contents, that is, 35 mol% and 50 mol%. The glass‐ceramics were partially melted at ∼2000°C or fully melted at ∼3000°C by ALT, followed by rapid quenching to obtain spherical glass‐ceramic beads. The phase compositions and microstructures of the glass‐ceramics were characterized. Crystallization of ZrO2 occurred during the solidification process and ZrO2 content, processing temperature, and the addition of yttrium (3 mol%) affected the crystalline phase of ZrO2. No ZrSiO4 or crystalline SiO2 were formed during the solidification process and the glass‐ceramics were away from thermodynamic equilibrium due to rapid quenching. The glass‐ceramics showed a microstructure of irregular‐shaped ZrO2 micro‐aggregates embedded in an amorphous SiO2 matrix, with lamellar twins and lattice defects formed within ZrO2 crystals. For samples prepared at ∼3000°C, a liquid‐liquid phase separation occurred in the melt, which eventually resulted in the formation of large and irregular‐shaped ZrO2 aggregates. In comparison, for samples prepared at ∼2000°C, pre‐existed ZrO2 crystals formed during heating acted as nucleation sites during the cooling process, followed by grain growth to form large ZrO2 aggregates. Solidification and microstructure formation mechanisms were proposed to elucidate the solidification process during rapid cooling and the microstructure of the glass‐ceramics obtained.

Non-Oxidative Propane Dehydrogenation on CrOx-ZrO2-SiO2 Catalyst Prepared by One-Pot Template-Assisted Method.

A series of CrOx-ZrO2-SiO2 (CrZrSi) catalysts was prepared by a “one-pot” template-assisted evaporation-induced self-assembly process. The chromium content varied from 4 to 9 wt.% assuming Cr2O3 stoichiometry. The catalysts were characterized by XRD, SEM-EDX, temperature-programmed reduction (TPR-H2), Raman spectroscopy, and X-ray photoelectron spectroscopy. The catalysts were tested in non-oxidative propane dehydrogenation at 500–600 °C. The evolution of active sites under the reaction conditions was investigated by reductive treatment of the catalysts with H2. The catalyst with the lowest Cr loading initially contained amorphous Cr3+ and dispersed Cr6+ species. The latter reduced under reaction conditions forming Cr3+ oxide species with low activity in propane dehydrogenation. The catalysts with higher Cr loadings initially contained highly dispersed Cr3+ species stable under the reaction conditions and responsible for high catalyst activity. Silica acted both as a textural promoter that increased the specific surface area of the catalysts and as a stabilizer that inhibited crystallization of Cr2O3 and ZrO2 and provided the formation of coordinatively unsaturated Zr4+ centers. The optimal combination of Cr3+ species and coordinatively unsaturated Zr4+ centers was achieved in the catalyst with the highest Cr loading. This catalyst showed the highest efficiency.

Insights into effects of ZrO2 crystal phase on syngas-to-olefin conversion over ZnO/ZrO2 and SAPO-34 composite catalysts

The utilization of metal oxide-zeolite catalysts in the syngas-to-olefin reaction is a promising strategy for producing C2–C4 olefins from non-petroleum resources. However, the effect of the crystal phase of metal oxides on the catalytic activity of these oxides is still ambiguous. Herein, typical metal oxides (ZnO/ZrO2) with different crystal phases (monoclinic (m-ZrO2) and tetragonal (t-ZrO2)) were employed for syngas conversion. The (ZnO/m-ZrO2+SAPO-34) composite catalyst exhibited 80.5% selectivity for C2–C4 olefins at a CO conversion of 27.9%, where the results are superior to those (CO conversion of 16.4% and C2–C4 olefin selectivity of 76.1%) obtained over (ZnO/t-ZrO2+SAPO-34). The distinct differences are ascribed to the larger number of hydroxyl groups, Lewis acid sites, and oxygen defects in ZnO/m-ZrO2 compared to ZnO/t-ZrO2. These features result in the formation of more formate and methoxy intermediate species on the ZnO/m-ZrO2 oxides during syngas conversion, followed by the formation of more light olefins over SAPO-34. The present findings provide useful information for the design of highly efficient ZrO2-based catalysts for syngas conversion.

Density functional modeling of structural and electronic properties of amorphous high temperature oxides

Ab initio molecular dynamics modeling in the NPT ensemble is used to obtain amorphous states by melting SiO2, ZrO2 and HfO2 crystals. A wide range of melt stabilization temperatures are used. Two types of SiO2 amorphous states are obtained. For melt temperatures below 4500 K, a perfect silica glass is obtained without any point defects. For melt temperatures above 4500 K, silica point defects such as threefold coordinated oxygen atoms, edge-sharing SiO4-tetrahedra, and others together with a wide range of Si-O-Si rings including 3-, and 4-membered rings appear. When the temperature of the melt exceeds the ZrO2 and HfO2 crystal melting point by 100 – 400 K, a sharp drop in the density of amorphous states is observed, accompanied by a decrease in atomic coordination, but this does not lead to the formation of defect states in the depth of the band gap of hafnium and zirconium dioxides.

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Crystals of the concentration series ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3 were grown by the method of directional crystallization of the melt from a cold container. Analysis of the spectral-luminescence characteristics of these crystals after growth and after annealing processing in a vacuum revealed the presence of both Tb3 + and Tb4 + ions in them. In crystals ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3, the presence of a process of non-radiative energy transfer from Tb4 + ions to Tb3 + ions was revealed.

Спектрально-люминесцентные свойства кристаллов ZrO-=SUB=-2-=/SUB=--Sc-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=--Tb-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

Crystals of the concentration series ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3 were grown by the method of directional crystallization of the melt from a cold container. Analysis of the spectral-luminescence characteristics of these crystals after growth and after annealing processing in a vacuum revealed the presence of both Tb3 + and Tb4 + ions in them. In crystals ZrO2- (8-10) mol.% Sc2O3- (1-2) mol.% Tb2O3, the presence of a process of non-radiative energy transfer from Tb4 + ions to Tb3 + ions was revealed.