Zirconia Phase Research Articles

Characterization of hot‐pressed ZrC–TiC composites

AbstractSynthesis and consolidation of (Zr,Ti)C were investigated in the present work. ZrC–TiC powder mixture was synthesized at 1650°C for 90 min by the carbothermal method. The prepared powder mixture was hot‐pressed at 1800 C for 60 min under a pressure of 40Mpa and then heat‐treated at 2100 C for 60 min. There were ZrC‐rich and TiC‐rich phases together with zirconium oxide phases in powder mixture and hot‐pressed samples, while there were no oxide phases in the heat‐treated sample and only ZrC‐rich and TiC‐rich phases were present in the sample. The FESEM image of the fracture surface of the samples shows that the porosity of the samples decreases with increasing temperature. Relative density, microhardness, and flexural strength increased from 93.8% to 98.6%, from 15.26 to 21.41 GPa, and from 185.02 to 220.69 MPa, respectively, with increasing temperatures from 1800 C to 2100 C. In contrast to these properties, the fracture toughness of the samples was reduced from 3.71 to 3.47 MPa·m1/2. The investigation of oxidation behavior also showed that oxidation is influenced by oxygen diffusion and exhibits nonlinear behavior as a function of time. With increasing oxidation temperature of hot‐pressed and heat‐treated samples from 600 to 1000°C, parabolic oxidation rate constants (kp) increased from .267 to 11.793 and from .367 to 10.993, respectively.

Effect of Ceramic Veneering on the Microstructure of Pre-sintered Cobalt-Chromium, Compared to Pre-sintered Zirconia and Conventional Cast Alloys.

Objectives: We aimed to evaluate ceramic-alloy interface and emphasize the alteration of alloy microstructure after ceramic layering. Materials and Methods: Thirty-two discs made from a ceramic-alloy combination of pre-sintered cobalt-chromium (CoCr), cast CoCr, cast nickel-chromium (NiCr), or pre-sintered zirconia were prepared with eight discs in each group. Four specimens were examined as manufactured and four were ceramic-layered. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-Ray diffractometer (XRD), and an atomic force microscope were used for analysis. Non-layered specimens received ceramic fire-heating without adding any ceramic. Alloy microstructure was compared before and after ceramic veneering or heating within the same group. Mean differences in grain size and surface roughness were compared among groups. P<0.05 was considered significant. Results: SEM showed a close bonding interface between alloys and ceramics. EDX demonstrated differences compared to the manufacturer's composition. Ceramic-layering reduced grain size for both milled alloys (P<0.05), whereas grain size increased in cast groups (P=0.011). Heat treatment did the same for the CoCr groups (P=0.013). Ceramic veneering increased the surface roughness of the cast CoCr (Gi) (P=0.029) and NiCr (Wi) (P=0.005) groups, whereas zirconia roughness average (Ra) showed a slight decrease (P=0.282). XRD showed no differences among zirconia, NiCr, and milled CoCr groups before and after veneering. Crystallite size differed between monoclinic and tetragonal phases in zirconia. Conclusion: The study highlights that ceramic-layering induces significant microstructural changes in alloys, enhancing bonding potential and mechanical stability. Pre-sintered materials show a fine homogeneous surface, optimizing ceramic adherence and potentially improving clinical outcomes.

Exploring enhanced syngas production via the catalytic performance of metal‐doped X‐Ni/CeO2 (X = Zr, La, Sr) in the dry reforming of methane

AbstractBackgroundThe quest to manufacture large amounts of syngas to bridge fossil fuels and the renewable energy ecosystem stimulates the creation of efficient and stable heterogeneous catalysts. The NiCeO2 catalysts, synthesized via ultrasonic‐assisted citric acid complexation, are highly efficient for the dry reforming of methane (DRM) reaction. Different promoter metals (Zr, La and Sr) were tested for catalytic performance and syngas production. A range of analyses, including X‐ray diffraction (XRD), N2 physisorption, H2 temperature‐programmed reduction, CO2 temperature‐programmed desorption, field emission scanning electron microscopy (FESEM), transmission electron microscopy and X‐ray photoelectron spectroscopy, were employed to characterize the physicochemical properties of the catalysts.ResultsXRD results indicated the formation of NiO, CeO2, solid solution ceria–zirconia, perovskite LaNiO3 and SrNiO3 crystalline phases. FESEM results showed the promoted catalysts (Zr, La, Sr) produce large pores to facilitate reactant diffusion, with zirconia specifically creating a spiderweb morphology. At 800 °C, the CH4 and CO2 conversions follow the sequence of NiCeO2 catalyst (CH4 = 54%, CO2 = 45%) &lt; Sr/NiCeO2 (CH4 = 60%, CO2 = 67%) &lt; La/NiCeO2 (CH4 = 85%, CO2 = 84%) &lt; Zr/NiCeO2 (CH4 = 95%, CO2 = 87%). The integration of promoters in DRM catalysts has notably improved carbon formation resistance, as evidenced by the following ranking: Zr/NiCeO2 (5.1 wt%) &lt; commercial catalyst (6.0 wt%) &lt; La/NiCeO2 (7.85 wt%) &lt; Sr/NiCeO2 (10.9 wt%) &lt; NiCeO2 (11.3 wt%).ConclusionThis study demonstrates that incorporating promoters, particularly Zr, in NiCeO2 significantly enhances resistance to carbon formation. It offers valuable insights into selecting metal catalyst promoters for excellent catalytic performance in DRM. © 2024 Society of Chemical Industry (SCI).

Encoding CO2 Adsorption in Sodium Zirconate by Neutron Diffraction.

Recent research into sodium zirconate as a high-temperature CO2 sorbent has been extensive, but detailed knowledge of the material's crystal structure during synthesis and carbon dioxide uptake remains limited. This study employs neutron diffraction (ND), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) to explore these aspects. An improved synthesis method, involving the pre-drying and ball milling of raw materials, produced pure samples with average crystal sizes of 37-48 nm in the monoclinic phase. However, using a slower heating rate (1 °C/min) decreased the purity. Despite this, the 1 °C/min rate resulted in the highest CO2 uptake capacity (4.32 mmol CO2/g Na2ZrO3) and CO2 sorption rate (0.0017 mmol CO2/g) after 5 min at 700 °C. This was attributed to a larger presence of microstructure defects that facilitate Na diffusion from the core to the shell of the particles. An ND analysis showed that the conversion of Na2ZrO3 was complete under the studied conditions and that CO2 concentration significantly impacts the rate of CO2 absorption. The TGA results indicated that the reaction rate during CO2 sorption remained steady until full conversion due to the absorptive nature of the chemisorption process. During the sorbent reforming step, ND revealed the disappearance of Na2O and ZrO2 as the zirconate phase reformed. However, trace amounts of Na2CO3 and ZrO2 remained after the cycles.

Uranium oxidation states in zircon and other accessory phases

Zircon and other U-bearing accessory phases are important time-capsules for studying the evolution of Earth and other planetary bodies as these minerals can record both temporal and compositional information regarding their host rocks. In silicate melts, uranium can occur in either the UIV, UV, or UVI valence state and its redox sensitive nature could, in principle, allow for information on magma oxygen fugacity (ƒO2) to be gleaned from U-bearing phases provided they can incorporate multivalent U during crystallization. Currently, however, little is known regarding the details of how U is speciated in these minerals.In this study, we conducted conventional X-ray absorption near-edge structure (XANES) spectroscopy at the U M4-edge on a set of natural zircon (n = 140), titanite (n = 9), apatite (n = 7), baddeleyite (n = 7), and garnet (n = 2) samples to determine the oxidation state of U in these crystals. We also collected U L3-edge spectra for select zircon samples to investigate the bonding environment of U using extended X-ray absorption fine structure (EXAFS) analysis. The effects of crystallographic orientation and radiation damage on zircon U M4-edge spectra are found to be minimal compared to the magnitude of the peak shifts associated with U oxidation state. We find that titanite and garnet contain only tetravalent U, while zircon, apatite, and baddeleyite can contain U of variable valence. Of these phases, zircon shows the greatest variability, with white-line energy, Ewl (i.e., peak absorbance) covering a range of >2.0 eV between grains: i.e., the entire energy range expected between pure UIV and pure UVI species. Moreover, a correlation is observed between the Ewl of zircon U M4-edge spectra (i.e., relative proportions of UIV, UV, UVI) and the ƒO2 of their host rocks. Our results thus establish U oxidation states in zircon as a powerful new tracer of magma redox. Since XANES is non-destructive and can be performed in situ, this technique can be utilized alongside other microanalytical methods (e.g., LA-ICPMS, SIMS) to further expand the breadth of information that can be extracted from single mineral grains.

Spray-Flame Synthesis of NASICON-Type Rhombohedral (α) Li1+xYxZr2-x(PO4)3 [x = 0-0.2] Solid Electrolytes.

Since solid electrolytes have a broad electrochemical stability window, are exceptionally electrochemically stable against Li metal, and function as a physical separator to prevent dendrite growth, they are at the forefront of alternate possibilities, further increasing the stability and energy density of Li-ion batteries. NASICON-type electrolytes are a promising candidate due to their negligible moisture sensitivity, which results in outstanding stability and a lower probability of Li2CO3 passivity under the ambient atmosphere. However, one of the most promising representatives, Li1+xYxZr2-x(PO4)3 (LYZP), has multiple stable phases with significant variation in their corresponding Li-ion conductivity. In this paper, we have successfully synthesized the highly ionically conductive rhombohedral phase of LYZP via spray-flame synthesis. Two different solvent mixtures (e.g., 2-ethyl hexanoic acid/ethanol, propanol/propanoic acid) were chosen to explore the effect of precursor composition and combustion enthalpy on the phase composition of the nanoparticle. The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline tetragonal zirconia (t-ZrO2) phase, while lithium, yttrium, and phosphate were present on the nanoparticles' surface as amorphous phases. However, a short annealing step (1 h) was sufficient to obtain the NASICON phase. Moreover, we have shown the gradual phase conversion from orthorhombic β phase to rhombohedral α phase as the annealing temperature increased from 700 °C to 1300 °C (complete removal of β phase). In this context, Y3+ doping was also crucial, along with the appropriate solvent mixture and annealing temperature, for obtaining the much-desired rhombohedral α phase. Further, 0.2 at% Y3+ doping was added to the solvent mixture of 2-ethyl hexanoic acid/ethanol, and annealing at 1300 °C for 1 h resulted in a high ionic conductivity of 1.14∙10-5 S cm-1.

Iron-rich Ca[sbnd]Mg skarns from the SW East European Craton (Lithuania): Microstructural study, mineral reactions and direct age constraints of ore-forming events using LA-ICPMS

The Varena Iron Ore deposit in the SW East European Craton is a significant ore body that occurs within metamorphosed and hydrothermally reworked Paleoproterozoic dolostones. We have performed microstructural investigations supplemented with mineral chemistry and geochronological investigations (LA-ICP-MS) to obtain age constraints on the ore-forming event(s) and improve the understanding of the conditions during mineralization process. Mineral chemistry and textures suggest a drop in pressure after the event of peak metamorphic skarn formation. Influx of oxidized, iron-rich H2O fluids resulted in (1) Mg mobility that caused secondary dolomitization of calcite, (2) dissolution of metamorphic magnetite and formation of a new, inclusion-rich (Mag-1) and inclusion-poor (Mag-2) magnetite, and (3) replacement of the peak skarn assemblages. During these fluid-related processes, accessory phases of monazite, baddeleyite, and zircon were formed. Their UPb dating yield individually robust ages of 1721 ± 9 Ma (monazite, 23 spots), 1703 ± 10 Ma (baddeleyite, 18 spots) and 1706 ± 54 Ma (zircon, 14 spots), respectively. The weighted mean age of 1713 ± 7 Ma (2σ internal) is considered to represent the best age estimate of the iron-ore mineralization in the Varena Iron Ore deposit, and possibly also dates influx of P, REEs etc. into the system. This mineralization event is contemporaneous with ca. 1.73–1.70 Ga metamorphic reworking of the host rocks in the region and may be linked to regional continental-margin type Transscandinavian Igneous Belt (TIB) magmatism in south-central Sweden.

Sensitization and mineralization synergistically enhanced the coloration of V to Cr-doping ZrSiO4 based jewel green pigment and its near-infrared reflection performance

Sensitization and mineralization synergistically effects of V to Cr-doping ZrSiO4 based jewel green pigment were studied in this work. The sensitization and mineralization effects of pigment were characterized via several analysis techniques, such as XRD, SEM, EDS, TEM, XPS, UV–Vis–NIR spectrophotometer and CIE L*a*b*. Experimental results show that V can serve as a mineralizer to promote the formation of zircon phase and can also serve as a sensitizer to promote the coloration of Cr. The energy can be transferred from 2E level of V4+ to nearby Cr3+, promoting the 4T1 (4F) energy level transition of Cr3+. There is no loss of silicon and zirconium throughout the process, and the pigment presents a series of pure green gradient by changing the amount of V. When the amount of V addition is 0.08, a single zircon phase shows in the pigment with a jewel green color (L* = 56.89, a* = -16.36, b* = -4.42), and the test results show that the pigment possesses a good near-infrared reflection effect. The prepared pigment has some promising application values.

ZrO2 reinforced porous Si3N4-based ceramics with improved mechanical properties fabricated via vat photopolymerization (VPP)

Porous Si3N4 ceramics are widely applied in many fields owing to their excellent properties such as high electromagnetic wave permeability, oxidation resistance, and wear resistance. Besides, the vat photopolymerization (VPP) technique can fabricate porous Si3N4-based ceramics with complex shapes and high precision. Nevertheless, The high absorptivity and refractive index of Si3N4 to ultraviolet light make it difficult to form porous Si3N4-based ceramics with the VPP technique. In this work, the addition of ZrO2 simultaneously improved the printability of Si3N4 slurries and the performance of Si3N4 ceramics via VPP technology. Rheological behavior and curing properties of the slurries were investigated, and the influence of ZrO2 content on the mechanical properties of printed Si3N4-based ceramics was investigated systematically. The addition of ZrO2 decreased the UV absorptivity of composite powder, thus improving the curing depth from 25.2 ± 2.6 μm to 64.8 ± 3.7 μm. XRD analysis revealed that ZrO2 in the composite ceramics mainly exists as the phase of yttria-stabilized tetragonal zirconia (Zr0.92Y0.08O1.96), which could ensure the effect of phase transformation toughening. With the increase of ZrO2 content, flexural strength and fracture toughness of porous Si3N4-based ceramics exhibited a trend of increase first and then decrease. As ZrO2 content increased to 10 wt%, the flexural strength and fracture toughness of porous Si3N4-based ceramics were improved from 214.7 MPa and 4.23 MPa·m1/2 to 345.0 MPa and 5.69 MPa·m1/2, respectively. Therefore, this work provided an important reference for the fabrication of high-performance porous Si3N4-based ceramic components with complex structures.

Effect of TiC addition on microstructure and properties of network structured TiC–ZrO2 composite conductive ceramics

Zirconia (ZrO2) ceramics have excellent mechanical properties and high-temperature conductivities. However, ZrO2 ceramics do not possess room-temperature conductivity, which significantly limits their application as functional components in smart communication devices and wearable smart products. To achieve room-temperature conductivity in ZrO2 ceramics, this study prepared a network-structured TiC–ZrO2 composite conductive ceramic with a low titanium carbide (TiC) addition using pressureless sintering. The influence of the TiC addition on the microstructure, mechanical properties, and electrical properties of the TiC–ZrO2 composite material was investigated. The results showed that the composite material consists of cubic zirconia (c-ZrO2), tetragonal zirconia (t-ZrO2), and titanium carbide (TiC) phases. When the TiC content was 11 vol %, the relative density, open porosity, flexural strength, and fracture toughness of the sample were 98.6 ± 0.1 %, 0.16 ± 0.06 %, 383 ± 38 MPa, and 4.66 ± 0.26 MPa m1/2, respectively. The electrical percolation threshold of the TiC–ZrO2 composite was between 8.0 and 11.0 vol %. When the TiC content is 18.8 vol %, the sample exhibited the lowest room-temperature resistivity of 3.00 × 10−5 Ω m. The electrical resistance of the TiC–ZrO2 composite material is mainly attributed to the grain boundary effect. With increasing TiC content, the resistivity of the composite material decreased, exhibiting linear conductivity and achieving conductive percolation characteristics.

Correlation between phase composition and physicochemical properties in Cu-, Mo-, and W- doped bismuth vanadate

We report a detailed study about the correlation between the physicochemical properties of solvothermally synthesized pristine and 1 %, 2.5 %, and 5 % Cu, Mo, and W-doped bismuth vanadate (BiVO4, BVO) with its phase composition. The effect of the dopant and the duration of synthesis (8 h and 20 h) on the physicochemical properties of BVO allowed us to tune the ratio of monoclinic scheelite to tetragonal zircon phase in BVO powders. This approach helped us to establish the relationship between the presence of monoclinic scheelite or tetragonal zircon phase with structural, morphological and optical properties of BVO powders, obtained by different physicochemical methods (e.g. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Spectroscopy (DRS) and Photoluminescence spectroscopy (PL)). The results indicated that, in addition to XRD, Raman, and DRS, several other methods could distinguish between the two phases. For example, SEM analysis revealed that monoclinic scheelite BVO exhibits either elongated assemblies of cube-like particles or prismatic particles with sizes ∼500 nm. In contrast, tetragonal zircon BVO exclusively exhibited porous spherical particles with diameter ∼2 μm. DRS and Raman spectroscopy indicated that there is a possibility of distinguishing between the two phases if their shares are large enough. For instance, monoclinic BVO showed band gap values in the range of 2.35–2.52 eV, while tetragonal zircon BVO exhibited values in the range of 2.80–3.00 eV. XPS showed a correlation between phase composition and surface chemistry of BVO only for Cu-doped samples, revealing the presence of Cu+ in monoclinic BVO and the presence of both Cu+ and Cu2+ in tetragonal zircon BVO. PL showed that monoclinic scheelite BVO displayed decreased charge recombination compared to tetragonal zircon BVO. Deeper insight into the correlation between the physicochemical properties and phase composition of Cu, Mo, and W-doped bismuth vanadate (BiVO4, BVO) was based on water/pentanol medium (2:1 vol%) as a novel synthesis pathway. This may open new avenues for the broader methodological exploration of surface chemistry, particle size, and morphology of BVO particles through the use of diverse functionalization agents. Finally, the established links between phase composition and structural, morphological, and other physicochemical properties provide new and more predictable opportunities for further improvement of BVO properties for various applications.

Exploring Rare Earth Elements in complex microscopic mineral phases: Inputs from μLIBS imaging

Understanding the distribution and concentration of Rare Earth Elements (REE) within various minerals and ores is crucial in mineralogy and geology for comprehending the micro-scale processes that contribute to the formation of REE-bearing minerals. Laser Induced Breakdown Spectroscopy elemental imaging emerges as a valuable tool due to its spatial resolution (15 μm) and ability for blind and rapid identification of elements within thin rock sections. Geological samples from the metamorphic core of the Zagros orogen (Iran) prepared as thin rock sections have been analyzed by LIBS imaging. Mineralogical phases have been determined from LIBS images of major elements. We first found that the distribution of Yttrium and REEs varies depending on the metamorphic stage. Then, while garnets may exhibit zoning in Mn, we observed that not all of them incorporate Yttrium. Finally, we demonstrated that REEs carriers include bastnaesite (Y Ce La F) and xenotime-like minerals primarily composed of Y with varying amounts of Yb, Gd, and Nd. We also demonstrated that the REEs minerals can exhibit either millimetric size when embedded within andalusite phases, or micrometric size when randomly scattered throughout the matrix. And we have also observed that some samples feature abundant Y-enriched Zircon phases. This study demonstrates that μLIBS imaging enables drawing a comprehensive picture of geological samples down to the micrometric scale. It has become a key technique in this field, providing access to the mineralogy of REE minerals, which is paramount for optimizing the final exploitation process compared to other analytical techniques.

A comprehensive study on crystal structure, phase compositions of the BiVO4-LaVO4 binary dielectric ceramic system and a typical design of dielectric resonator antenna for C-band applications

Novel multi-component (Bi1-xLax)VO4 (BLVOx) (0.05 ≤ x ≤ 0.9) solid-solution/composite ceramics crystal structures, phase compositions as well as its applications in the C-band dielectric resonator antenna have been designed and investigated. With the increased substitution of La3+, phase transitions among the monoclinic scheelite (mBiVO4), tetragonal zircon (zt(La,Bi)VO4) and monoclinic monazite (mLaVO4), driven by the compositional changes, were detected. La3+ played an essential role in the optimization of the dielectric properties of BLVOx. The measured Q × f values at the microwave band are considerably larger around the range of compositions forming the zircon phase and reached the maximum value (12,800 GHz) at pure zircon phase (x = 0.5), demonstrating that the impact of zircon structure on the intrinsic loss should not be disregarded and is beneficial for low dielectric loss. Meanwhile, the εr and TCF values could be tuned by regulating the concentration ratio of Bi3+/La3+ to obtain composites or solid-solutions with appropriate εr and near-zero TCF values. Additionally, a cylindrical dielectric resonator antenna (CDRA) of BVLO0.5 ceramic was designed with high simulated radiation efficiency (99.8%) and gain (4.58 dBi) at the center frequency (6.73 GHz), indicating its potential application in C-band because of its tunable permittivity and low-loss.

A thermogravimetric comparative study of the high temperature steam oxidation of bare and pre-oxidized Zircaloy-4, M5Framatome and Optimized ZIRLO™

For Loss of Coolant Accident (LOCA) analysis, high-temperature oxidation kinetics in steam of Zircaloy-4 and the two Nb-bearing alloys used in French Pressurized Water Reactors (PWRs), M5Framatome11M5 and M5Framatome are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries. and Optimized ZIRLO™22Optimized ZIRLO is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners., have been studied using Thermo-Gravimetric Analysis (TGA) technique in the temperature range of 900–1200 °C. A specific test procedure allowing the use of a high steam flow rate and good steam supply to the whole specimen surface, as well as fast heating of the specimen, has been developed. Clean kinetic data, not affected by steam starvation, were obtained on the bare, as-received alloys. For as-received claddings, oxidation kinetics are comparable and close to parabolic for the three alloys at 1100 °C and above. Below 1100 °C, a significant deviation from the parabolic kinetic regime was observed, and M5 Framatome oxidizes slower than Zircaloy-4 and Optimized ZIRLO. Thanks to the fast-heating protocol, the influence of pre-oxidation, simulating corrosion in normal reactor operation, could be investigated, avoiding evolution of the pre-oxidation scale during a slow, long heating phase. Pre-oxidized Zircaloy-4 and M5 Framatome were investigated. A strong protective effect is observed below 1200 °C, while at 1200 °C, the pre-oxidation layer appears to be much less protective, possibly due to the monoclinic to tetragonal zirconia phase transformation.

Zirconium phase diagram from ab initio molecular dynamics

The paper presents analysis of precision of a phonon-based free energy calculation technique (Temperature Dependent Effective Potential method) in comparison with the thermodynamic integration method within classical molecular dynamics. It is shown that the use of the second order force constants is insufficient for accurate calculations of free energies at elevated temperatures due to noticeable anharmonic contributions to lattice vibrations. On the other hand, reliable calculations of the crystal phase equilibrium lines requires free energy accuracy better than 1–3 meV per atom. Based upon the obtained results the Temperature Dependent Effective Potential technique is applied to the detailed study of the solid-state Zr phase diagram from ab initio molecular dynamics that may be achieved if force constants up to the fourth order are used. The calculated zirconium phase diagram is in good agreement with experiment. The α−β−ω triple point was determined at P≈6.74 GPa, T≈837 K.

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

The potential of bi2–xZrxO3+x/2@ZrO2 (BZO) as a heavyweight radiation shielding material: Fabrication and characterization using a hydrothermal technique directly from zircon mineral

The hydrothermal technique was utilized to produce a new zirconia doped Bi ions to be suitable for gamma ray shielding applications. The monoclinic phase of zirconia in the manufactured samples is revealed by X-ray diffraction, and each sample's variation in the intensity and position of the diffraction peaks prominently represented the different percentage of BiZrO. Furthermore, the scanning electron microscope and energy dispersive X-ray analysis show the morphology and chemical composition of the fabricated composites. Additionally, utilizing the Monte Carlo simulation, the radiation shielding properties of the fabricated composites were estimated. Regarding the fabricated composites, the highest linear attenuation coefficient of the fabricated composites varied from 21.796 cm−1 to 0.333 cm−1, raising the applied γ-photon energy between 0.059 and 1.332 MeV. Moreover, Addition of Bi2 to zirconia by concentration varied between 14 and 27 wt% slightly enhances the linear attenuation coefficient from 0.503 cm−1 to 0.539 cm−1, respectively, at γ-photon energy of 0.662 MeV. The slight enhancement in the linear attenuation coefficient increases the radiation protection efficiency and decreases the half value thickness from 1.379 cm to 1.285 cm.

Nanocrystalline Cubic Phase Scandium-Stabilized Zirconia Thin Films.

The cubic zirconia (ZrO2) is attractive for a broad range of applications. However, at room temperature, the cubic phase needs to be stabilized. The most studied stabilization method is the addition of the oxides of trivalent metals, such as Sc2O3. Another method is the stabilization of the cubic phase in nanostructures-nanopowders or nanocrystallites of pure zirconia. We studied the relationship between the size factor and the dopant concentration range for the formation and stabilization of the cubic phase in scandium-stabilized zirconia (ScSZ) films. The thin films of (ZrO2)1-x(Sc2O3)x, with x from 0 to 0.2, were deposited on room-temperature substrates by reactive direct current magnetron co-sputtering. The crystal structure of films with an average crystallite size of 85 Å was cubic at Sc2O3 content from 6.5 to 17.5 mol%, which is much broader than the range of 8-12 mol.% of the conventional deposition methods. The sputtering of ScSZ films on hot substrates resulted in a doubling of crystallite size and a decrease in the cubic phase range to 7.4-11 mol% of Sc2O3 content. This confirmed that the size of crystallites is one of the determining factors for expanding the concentration range for forming and stabilizing the cubic phase of ScSZ films.

Assembling bifunctional ceria-zirconia electrocatalyst for efficient electrochemical conversion of methane at room temperature

The electrochemical conversion of methane to C2 compounds at room temperature is reported using CeO2-ZrO2 electrocatalysts. The mixed oxide electrocatalysts produced methanol, ethanol, and acetone, along with traces of acetaldehyde and isopropanol, under a polarization of 1.2 V with ∼ 50 % Faradaic efficiency. Detailed characterization of the CeO2-ZrO2 revealed the formation of nanoparticles (7–9 nm mean size) composed of ceria-zirconia solid solution or a mixture of ceria with both tetragonal and monoclinic zirconia polymorphs depending on the assembling configuration of the electrocatalyst. Samples with separated phases and limited solid solution formation showed the highest electrochemical activity, indicating that an optimal assembly of ceria and zirconia was crucial to achieving efficient conversion with high Faradaic efficiency and selectivity. Such high electrochemical activity observed for the phase separated CeO2-ZrO2 electrocatalyst suggests that a synergic effect between ceria and zirconia is required for the critical reaction steps, such as the activation and partial oxidation of methane. The experimental results point to credible routes to efficiently convert methane into valuable chemicals in mild conditions.

Combined experimental and first principles look into (Ce, Mo) doped BiVO4

Here we investigated the effects of Ce and Mo doping on hydrothermally synthesized bismuth vanadate BiVO4 nanoparticles (NPs). The existence of monoclinic scheelite and tetragonal zircon phases of NPs was validated from Rietveld refinement of the powdered X-ray diffraction, room temperature Raman, and Fourier-transform infrared spectroscopy. The co-doping of Bi and V sites with respective Ce and Mo dopants in a mixed tetragonal zircon and monoclinic scheelite phases of BiVO4 lattice was corroborated from high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The photoluminescence measurements revealed enhancement of photo-generated carrier recombination in (Ce, Mo) co-doped BiVO4 NPs which may have hampered its photocatalytic efficiency in degrading the methylene blue dye. The simulations based on Hubbard U corrected density functional theory (DFT+U) suggest that Mo and Ce co-doping introduced deep impurity states which may have facilitated the photo-generated carrier recombination detrimental to photocatalytic performance. The UV-vis diffuse reflectance measurements provided evidence for the presence of these defect states. In summary, this work may have presented a comprehensive experimental analysis of (Ce, Mo) doped BiVO4 supported by DFT simulations.