ZrO2 Doping Research Articles

Controlling low temperature sintering of UO2+x

UO2 nuclear fuel pellets are typically sintered at temperatures of approximately 1700 °C to achieve the high densities and large grain sizes necessary for safe reactor operation. Lowering this sintering temperature is desirable in order to decrease the energy input required for fuel manufacture. Hence, the effect of temperature, time, stoichiometry and ZrO2 doping on sintering efficacy have been investigated. ZrO2 doping, coupled with hyper-stochiometry, acted as a strong sintering aid, enabling higher densities and larger grain sizes when sintering at lower temperatures and for shorter periods compared to the undoped samples. Without ZrO2 doping, at 1500 °C sintering was strongly sensitive to hyper-stoichiometry and only weakly sensitive to sintering duration. Addition of 0.13 mol fraction ZrO2 increased theoretical density up to 10 % and the maximum grain size from 8 µm to 40 µm. Addition of 0.30 mol fraction ZrO2 resulted in even greater densification, reaching 98 % of maximum theoretical density, but also formation of a secondary phase that hindered grain growth.

Unveiling the role of ZrO2 doping in Sr2SmTi2Nb3O15 ceramics: From structural study to dielectric enhancement

Solid-state processing was used to synthesize tungsten bronze type (TTB) solid solutions, specifically Sr2Sm(Ti1-xZrx)2Nb3O15 with x values of 0, 0.2, 0.3, and 0.4. The study examined the crystalline structure, optical properties, morphology, and electrical and dielectric characteristics of these compounds. X-ray diffraction revealed a tetragonal structure (space group P4bm). Scanning electron microscopy showed significant sample densification with grain sizes decreasing from 6.19 μm to 2.78 μm. Dielectric measurements indicated that the dielectric constant varied from 150 for x = 0 to 567.24 for x = 0.2, then decreased to 380.88 for x = 0.4, with the x = 0.3 compound having the lowest dielectric loss. The Curie temperature (Tc) decreased from 332 °C to 248.5 °C with increasing Zr content, corresponding with a reduction in grain size. The energy gap (Eg) narrowed from 2.914 eV to 2.714 eV as Zr content increased. AC conductivity increased with temperature and frequency. Electrical conductivity followed Jonscher's power law, with activation energies decreasing from 1.54 eV to 0.87 eV, explained by the small polaron tunneling (NSPT) model.

Improving the wear resistance of 440C bearing steel balls by adding ZrO2 in mechanical alloying

The wear resistance of 440C bearing steel balls significantly impacts the reliability of bearings. Our method for increasing the wear resistance of steel balls combines mechanical alloying to create nanogradient structures with ZrO2 doping on the surface of the steel balls. The results revealed that ZrO2 formed mechanical alloying on the surface of the steel balls. Under all loads, the processed samples exhibited excellent wear resistance. Compared to untreated samples, the wear of processed samples subjected to 20, 40, and 60 N loads decreased by 28.82 %, 50.25 %, and 50.79 %, respectively. The existing literature indicates that adding ZrO2 powder during mechanical alloying is a promising method for improving the friction performance of bearing steel balls.

Investigation on YSZ- and SiO2-Doped Mn-Fe Oxide Granules Based on Drop Technique for Thermochemical Energy Storage.

The Mn-Fe oxide material possesses the advantages of abundant availability, low cost, and non-toxicity as an energy storage material, particularly addressing the limitation of sluggish reoxidation kinetics observed in pure manganese oxide. However, scaling up the thermal energy storage (TCES) system poses challenges to the stability of the reactivities and mechanical strength of materials over long-term cycles, necessitating their resolution. In this study, Mn-Fe granules were fabricated with a diameter of approximately 2 mm using the feasible and scalable drop technique, and the effects of Y2O3-stabilized ZrO2 (YSZ) and SiO2 doping, at various doping ratios ranging from 1-20 wt%, were investigated on both the anti-sintering behavior and mechanical strength. In a thermal gravimetric analyzer, the redox reaction tests showed that both the dopants led to an enhancement in the reoxidation rates when the doping ratios were in an appropriate range, while they also brought about a decrease in the reduction rate and energy storage density. In a packed-bed reactor, the results of five consecutive redox tests showed a similar pattern to that in a thermal gravimetric analyzer. Additionally, the doping led to the stable reduction/oxidation reaction rates during the cyclic tests. In the subsequent 120 cyclic tests, the Si-doped granules exhibited volume expansion with a decreased crushing strength, whereas the YSZ-doped granules experienced drastic shrinkage with an increase in the crushing strength. The 1 wt% Si and 2 wt% Si presented the best synthetic performance, which resulted from the milder sintering effects during the long-term cyclic tests.

Zirconium Oxide Doped Organosilica Nanodots as Light- and Charge-Management Cathode Interlayer for Highly Efficient and Stable Inverted Organic Solar Cells.

In this work, it is reported that zirconium oxide (ZrO2) doped organosilica nanodots (OSiNDs: ZrO2) with light- and charge-management properties serve as efficient cathode interlayers for high-efficiency inverted organic solar cells (i-OSCs). ZrO2 doping effectively improves the light harvesting of the active layer, the physical contact between the active layer, as well as the electron collection property by habiting charge recombination loss. Consequently, all devices utilizing the OSiNDs: ZrO2 cathode interlayer exhibit enhanced power conversion efficiency (PCE). Specifically, i-OSCs based on PM6:Y6 and PM6:BTP-eC9 achieve remarkable PCEs of 17.16% and 18.43%, respectively. Furthermore, the PCE of device based on PM6:Y6 maintains over 97.2% of its original value following AM 1.5G illumination (including UV light) at 100mWcm-2 for 600min.

Tuning the Interaction between Platinum Single Atoms and Ceria by Zirconia Doping for Efficient Catalytic Ammonia Oxidation.

Aiming at the development of an efficient NH3 oxidation catalyst to eliminate the harmful NH3 slip from the stationary flue gas denitrification system and diesel exhaust aftertreatment system, a facile ZrO2 doping strategy was proposed to construct Pt1/CexZr1-xO2 catalysts with a tunable Pt-CeO2 interaction strength and Pt-O-Ce coordination environment. According to the results of systematic characterizations, Pt species supported on CexZr1-xO2 were mainly in the form of single atoms when x ≥ 0.7, and the strength of the Pt-CeO2 interaction and the coordination number of Pt-O-Ce bond (CNPt-O-Ce) on Pt1/CexZr1-xO2 showed a volcanic change as a function of the ZrO2 doping amount. It was proposed that the balance between the reasonable concentration of oxygen defects and limited surface Zr-Ox species well accounted for the strongest Pt-CeO2 interaction and the highest CNPt-O-Ce on Pt/Ce0.9Zr0.1O2. It was observed that the Pt/Ce0.9Zr0.1O2 catalyst exhibited much higher NH3 oxidation activity than other Pt/CexZr1-xO2 catalysts. The mechanism study revealed that the Pt1 species with the stronger Pt-CeO2 interaction and higher CNPt-O-Ce within Pt/Ce0.9Zr0.1O2 could better activate NH3 adsorbed on Lewis acid sites to react with O2 thus resulting in superior NH3 oxidation activity. This work provides a new approach for designing highly efficient Pt/CeO2 based catalysts for low-temperature NH3 oxidation.

Improving energy storage performance and high-temperature stability in Bi0.5Na0.5TiO3-based lead-free dielectric ceramics by ZrO2 doping

The effects of ZrO2 addition on the microstructure, dielectric properties, and energy storage performance of Bi0.5Na0.5TiO3–Bi0.5K0·5TiO3–BaTiO3–Sr(Mg1/3Nb2/3)O3 (BBNKT-SMN) ceramics were systematically investigated. The XRD results show that ZrO2 dissolved in the perovskite matrix without any detectable secondary phases. ZrO2 doping can improve densification, grain growth, and energy storage performance. The sample doped with 4 mol% ZrO2 exhibited excellent dielectric thermal stability, meeting the Z9R specification and having potential applications in high-temperature capacitors. Finally, an optimal recoverable energy storage density Wrec = 3.0 J/cm3 at 260 kV/cm and a high energy storage efficiency η = 88.2% were achieved. In addition, this ceramic exhibited excellent thermal stability (30–180 °C), frequency insensitivity (1–100 Hz), and high-cycle stability (up to 104). This study further demonstrates that the addition of ZrO2 is a simple and effective way for improving the thermal stability of the dielectric and the energy storage performance.

Zirconia/garnet multiphase ceramics with high immobilization capacity for Nd confers better physical and chemical stability

AbstractMultiphase ceramics have a high application potential in the field of nuclear waste immobilization because of the efficient synergy between the individual phases. In this work, zirconia/garnet multiphase ceramics with high efficient and effective immobilization capacity of trivalent actinides were successfully prepared using conventional solid‐phase sintering. ZrO2 doping increases the lattice site available for nuclide substitution and advance the immobilization capacity of the ceramic substrate for nuclide. At the same time, the phase change of zirconia is used to tougher and improve the physical properties of the ceramic waste form. The feasibility of using multiphase ceramics for the efficient immobilization of trivalent actinides was assessed by studying the phase evolution, microstructure, Vickers hardness, and chemical stability of the multi‐phase ceramics. Zr1‐xNdxO2‐x/2/Ca3‐yNdyZr3‐yFey‐1Fe3O12 multiphase ceramics exhibited superior physical or chemical properties compared to most of the multiphase ceramics as well as the previously prepared single‐phase calcium garnet ceramic waste forms. The Vickers hardness of all the multiphase ceramic samples ranged between 685 and 730 HV0.5. Under the condition of using simulate Bei Shan groundwater as leaching agent, the normalized leaching rates of Nd is approximately 10−6 g·m−2·day−1, showing good chemical stability and achieving efficient and effective immobilization of trivalent actinides. The excellent chemical, as well as physical properties of Zr1‐xNdxO2‐x/2/Ca3‐yNdyZr3‐yFey‐1Fe3O12 multiphase ceramics are expected to make them one of the substrates for more efficient and effective immobilizing of trivalent actinides.

Mechanical properties and corrosion behavior in molten zinc of Mo–ZrO2 alloys

The effect of the ZrO2 doping amounts on the corrosion properties and mechanical properties of the molybdenum alloys in molten zinc was investigated. Among them, the Mo-1.5 wt% ZrO2 alloy has good corrosion resistance (at 460 °C) and excellent mechanical properties. Compared with that of pure molybdenum, the tensile strength of the Mo-1.5 wt%ZrO2 increased by 16.69% in the rotary forged state and 58.26% in the 1200 °C annealed states, and the compressive strength increased by 16.53% and 84.46%, respectively. At a corrosion temperature of 460 °C, a MoZn7 corrosion layer was formed, which isolates the molybdenum matrix from direct contact with the molten zinc. The distribution of ZrO2 particles in the corrosion layer, which changes the diffusion path of zinc and molybdenum atoms, thus slowing down the corrosion process. The thickness of the corrosion layer gradually decreases with increasing doping amount, where the corrosion layer thickness of the Mo-2.0 wt% ZrO2 is 45.21% lower than that of the pure molybdenum. At a corrosion temperature of 560 °C, the molybdenum matrix is exposed to molten zinc and the grains peel off. As the bond between Mo grains is better than the bond between Mo grains and zirconia, the grain spalling of the zirconia-doped molybdenum alloys is severer than that of pure molybdenum.

Atomically Dispersed Pd Sites on ZrO2 Hybridized N-Doped Carbon for Efficient Suzuki–Miyaura Reaction

Researchers studying heterogeneous catalysis are intrigued by single-atom catalysts (SACs) due to their ultrahigh atomic utilization. However, only a few reports on SAC-catalyzed classical organic transformations are available. In this work, atomically dispersed Pd sites are confined to a ZrO2 hybridized N-doped carbon skeleton with a smart design. UiO-66-NH2 is used to anchor Pd atoms by the coordination of the donor atoms including lone pairs of electrons and metal atoms. Subsequently, the in situ introduction of ZrO2 doping is achieved using pyrolysis, which helps improve the catalytic performance by modulating the electronic state. The Pd@ZrO2/N–C catalyst obtained from the unique design exhibits a high yield (99%) in eco-friendly media with an extremely low noble metal dosage (0.03 mol% Pd) for the Suzuki reaction. Moreover, Pd@ZrO2/N–C remains highly active after being reused several times and possesses versatility in a variety of substrates. This strategy offers a feasible alternative to designing SACs with atomically dispersed noble metals for heterogeneous reactions.

Effect of ZrO2 doping on the growth of lead-free piezoelectric 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 single crystals by solid-state single crystal growth

Single crystals of 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 have potential for use in piezoelectric actuators because of their large values of electric field-induced strain. Single crystals of 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 have been prepared by solid-state single crystal growth, but growing large crystals is difficult due to matrix grain growth. Previous experiments with 0.95(Bi1/2Na1/2)TiO3-0.05BaTiO3 showed that doping with ZrO2 reduced matrix grain growth but also reduced single crystal growth. In this work, 0.75(Bi1/2Na1/2)TiO3-0.25SrTiO3 is doped with small amounts of ZrO2 and the effect on both single crystal and matrix grain growth is examined. ZrO2 addition has a minor effect on single crystal and matrix grain growth.

Effect of ZrO2 Content on Microstructure Evolution and Sintering Properties of (Tb0.7Lu0.3)2O3 Magneto-Optic Transparent Ceramics

In this paper, (Tb0.7Lu0.3)2O3 magneto-optical transparent ceramics with different ZrO2 doping levels (0~5 at%) were prepared by hydrogen sintering and sequential HIP technique using ZrO2 as a sintering aid. The effect of ZrO2 doping content on the microstructure and optical properties of (Tb0.7Lu0.3)2O3 ceramics was analyzed. We found that the optimal doping content of ZrO2 was 3 at%. The transmittance of 3 at% ZrO2-doped (Tb0.7Lu0.3)2O3 ceramics at the wavelength of 1064 nm was 74.84 %, and the Verdet constant was approximately 275.28 rad·T−1·m−1 at the wavelength of 650 nm.

Tailoring the performance of Ni-CaO dual function materials for integrated CO2 capture and conversion by doping transition metal oxides

Transition metal oxides (TMOs) doping is proposed as one effective strategy to improve CO2 capture and conversion performance of Ni-CaO dual function materials (DFMs). The effect of single and binary TMOs doping on structure–property-activity relationships of Ni-CaO DFMs for integrated CO2 capture and in-situ reverse water gas shift (RWGS) is investigated. ZrO2 doping enhances the surface basicity and reducibility of Ni-CaO DFMs for improved CO2 uptakes and reinforced catalytic activity. ZrO2 doping also endows Ni-CaO DFMs with improved working stability by forming CaZrO3 solid solution, which acts as physical barrier to retard the agglomeration and sintering of CaO and NiO species. Doping binary metal oxides of ZrO2-CeO2 further boosts the oxygen vacancy concentration in the DFMs for promoted CO2 activation and conversion and stabilized CO yield. The desired Ni-CaO-6ZrO2-6CeO2 DFMs shows a higher CO2 conversion of 72.1% and a lower decay rate of 12.0% for CO yield in consecutive cycles.

Nano-doped PDLC combined with photochromic material for bifunctional optical control films

ABSTRACT Controlling light intensity and colour are the two main functions required to realise smart windows. In this paper, the bifunctional optical control films were prepared by combining a nano-doped polymer-dispersed liquid crystal (PDLC) with the photochromic material. The nano-doped PDLC was prepared by mixing the nematic liquid crystals, UV-curable liquid mixture, and ZrO2 nanoparticles through a polymerization-induced phase separation (PIPS) process. The electro-optical properties of the PDLCs were significantly improved compared to the initial hybrid system; furthermore, the driving voltage reached a minimum of 20.7 V with 0.8 wt% of ZrO2 doping. Spin-coated photochromic powder enabled PDLC films to switch between coloured and colourless under UV or solar irradiation. The bifunctional PDLC films with lower threshold voltage, lower saturation voltage, and better contrast, have shown significant application in areas of smart windows.

In situ measurements of the high-temperature mechanical properties of ZrO2-doped YTaO4 ceramic by three-point bending combined with a digital image correlation method

ZrO2-doped YTaO4 ceramics with different ZrO2 contents (Y1-xTa1-xZr2xO4 ceramics, 2x = 0, 0.1, 0.15, 0.2) are prepared by a solid-state reaction method. The high-temperature mechanical properties are determined by an in situ high-temperature three-point bending combined with the digital image correlation (DIC) method. The results show that when the temperature rises from 25 °C to 800 °C, the temperature dependence of the elastic modulus, fracture toughness and fracture strength with a ZrO2 doping content of 10% mol is relatively small. The elastic modulus, fracture toughness and fracture strength decrease from 105.4 GPa to 96.1 GPa, from 2.6 MPa m1/2 to 2.3 MPa m1/2 and from 73.8 MPa to 64.8 MPa, respectively. Transgranular fracture is the main fracture mode. When the crack propagates through the twin band, a phase transformation and a typical domain change occur. Furthermore, the crack propagating through the twin band at room temperature (25 °C) is more tortuous than that at 800 °C, and more energy needs to be consumed. This illustrates that the fracture toughness and fracture strength at room temperature (25 °C) are higher than those at high temperature.

Transformation of Highly Stable Pt Single Sites on Defect Engineered Ceria into Robust Pt Clusters for Vehicle Emission Control.

Engineering surface defects on metal oxide supports could help promote the dispersion of active sites and catalytic performance of supported catalysts. Herein, a strategy of ZrO2 doping was proposed to create rich surface defects on CeO2 (CZO) and, with these defects, to improve Pt dispersion and enhance its affinity as single sites to the CZO support (Pt/CZO). The strongly anchored Pt single sites on CZO support were initially not efficient for catalytic oxidation of CO/C3H6. However, after a simple activation by H2 reduction, the catalytic oxidation performance over Pt/CZO catalyst was significantly boosted and better than Pt/CeO2. Pt/CZO catalyst also exhibited much higher thermal stability. The structural evolution of Pt active sites by H2 treatment was systematically investigated on aged Pt/CZO and Pt/CeO2 catalysts. With H2 reduction, ionic Pt single sites were transformed into active Pt clusters. Much smaller Pt clusters were created on CZO (ca. 1.2 nm) than on CeO2 (ca. 1.8 nm) due to stronger Pt-CeO2 interaction on aged Pt/CZO. Consequently, more exposed active Pt sites were obtained on the smaller clusters surrounded by more oxygen defects and Ce3+ species, which directly translated to the higher catalytic oxidation performance of activated Pt/CZO catalyst in vehicle emission control applications.

Ultrafast synthesis and densification of ZrO2 doped KNN ceramics by reactive flash sintering

AbstractFabrication of dense KNN‐based lead‐free piezoelectric ceramics at low temperatures in short time through a cost‐effective way remains a challenge. Herein, this challenge could be addressed by using reactive flash sintering. It is demonstrated that the phase transformation of KNbO3‐NaNbO3 into (K,Na)NbO3 and densification occur simultaneously during the flash event. Most importantly, ZrO2 doping can greatly decrease the onset flash temperature, which is ascribed to the increased conductivity of sample. In addition, the current limit has a significant effect on the phase transformation and densification. The flash‐sintered KNN ceramics exhibit the good ferroelectric and piezoelectric properties. Furthermore, the ZrO2 doped and undoped KNN ceramics show a comparable coercive field Ec, which may be related to the residual point defects after the flash. Besides the Joule heating, the avalanche generation of point defects is suggested to be responsible for the ultrafast solid‐state reaction and densification rates.

ZrO2‐doped YTaO4 as potential CMAS‐resistant materials for thermal barrier coatings application

AbstractIn this contribution, the ZrO2‐doped YTaO4 (ZrxY0.5−x/2Ta0.5−x/2O2 (x = 0, 0.1, 0.2, 0.28)) are proposed as potential CMAS‐resistant materials for TBCs. The corrosion behavior of those materials under CMAS attack are investigated from thermodynamics and kinetics. The results show that all compositions have the much better CMAS resistance than the classical Gd2Zr2O7. After 50 h corrosion at 1300℃, the corrosion depth in ZrO2‐doped YTaO4 bulks is about 50–80 µm (for a 20 mg/cm2 CMAS deposition) in contrast with ~140 µm in Gd2Zr2O7 bulk. The CMAS corrosion mechanism of ZrO2‐doped YTaO4 is elucidated, and the excellent CMAS resistance is attributed to the rapid formation and followed thickening of dense reaction product layer. Furthermore, the effects of ZrO2 doping content on CMAS resistance of YTaO4 is discussed. It is elucidated that ZrO2 doping can inhibit the precipitation of apatite, decrease the consumption of CMAS melt, and change the morphology of dense reaction layer. In summary, minor doping of ZrO2 can ensure the excellent short‐ and long‐term CMAS resistance, but heavy doping of ZrO2 will degrade the long‐term CMAS resistance.

A potential ZrO2 doped scandium tantalite ceramics for thermal/environmental barrier coating material

Despite scandium tantalite (ScTaO4) has great potential application for thermal/environmental barrier coating system, it is necessary to reduce the thermal expansion coefficient difference between them to lower the thermal stress in practical applications. In this paper, (ZrO2)x-(ScTaO4)1-x (x = 0.1, 0.2) material was prepared by doping ZrO2 into scandium tantalite ceramics, and its thermal expansion coefficient and calcium–magnesium–alumino-silicate (CMAS) corrosion behavior were studied. After the CMAS corrosion experiments of (ZrO2)x-(ScTaO4)1-x material, the phase composition and microstructures of samples were detected by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. The main results show that the alloying effect of ZrO2 doping can reduce the thermal expansion coefficient of ScTaO4 and then alleviate the thermal expansion coefficient difference in thermal/environmental barrier coating system. Besides, Zr4+ ions are separated from (ZrO2)x-(ScTaO4)1-x lattice by molten CMAS under high-temperature corrosion condition and (ZrO2)x-(ScTaO4)1-x material is decomposed into ScTaO4 and t-ZrO2 finally. In addition, only t-ZrO2 is defected in the corrosion products without other crystal type of ZrO2 in the XRD results of the corrosion products, which indicate that ScTaO4 can increase high-temperature phase stability of t-ZrO2 and prevent phase transformation from t-ZrO2 to m-ZrO2.

The influence of ZrO2 doping on microstructure and electrical properties of ZnO-based conductive ceramics

ZnO-based conductive ceramic materials doping ZrO2 were prepared at 1320 °C by the conventional solid-state sintering method in air, and the influence of comprehensive properties with different ZrO2-doped content were studied carefully. Microstructure and crystals of the samples were investigated by SEM and XRD respectively. As a donor, Zr4+ increases the carrier concentration and decreases the resistivity of grain and grain boundary. As-prepared samples shown excellent linear V–I characteristics and were suitable for high frequency electric field. With the increasing of dopant ZrO2 contents, the dielectric constant and resistivity of ZnO-based conductive ceramics were influenced significantly, moreover, the resistance-temperature characteristics presents the negative temperature coefficient effects. ZnO-based conductive ceramics exhibited excellent comprehensive electrical performance with 0.30 mol% ZrO2-doping, in which the nonlinear coefficient is 1.01, the grain boundary barrier height is 0.014 eV, and the resistance temperature coefficient is −2.6×10−3/°C.