Tetragonal ZrO2 Phase Research Articles

Structural and optical properties of Ce-stabilized tetragonal phase and intense blue emission of monoclinic phase in ZrO2 nanoparticles

Structural and optical properties of Ce-stabilized tetragonal zirconium dioxide (ZrO2) and intense blue emission of monoclinic ZrO2 are presented in this paper. Nanoparticles of ZrO2 in the stabilized tetragonal and monoclinic phases have been prepared by the solution combustion method. X-ray diffraction studies and Rietveld refinement of the diffraction pattern show the stabilization of ZrO2 in the tetragonal phase (t-ZrO2) with Ce doping. It is the host-dopant ionic size mismatch that leads to lattice distortion and hence the t-ZrO2 stabilized phase. Raman modes confirm the phase transformation from the monoclinic to a tetragonal phase of ZrO2. The presence of oxygen vacancies and surface states in the samples play a role in altering the optical band gap. The dopant Ce-ions create defects/oxygen vacancies, which act as the trapping sites for electrons and holes/the donor and vacancy-related impurity levels. It is transition between these levels or between delocalized conduction bands that lead to band gap reduction. Photoluminescence studies reveal the presence of structural phase transformation dependent emission bands. The monoclinic phase (m-ZrO2) exhibits an intense blue emission originating from the asymmetric and unusual oxygen coordination of Zr in the m-ZrO2. The chromaticity coordinates indicate that the prepared material and adopted strategies are suitable in the field of optoelectronic application.

Coloring Multilayer Zirconia May Affect Its Optical and Mechanical Properties

The coloring process of monolithic dental zirconia caused considerable debate on the possible effects of different coloring methods. The main objective of this study was to investigate the influence of pigments in 3 multilayer 5-mol% yttria partially stabilized zirconia (5Y-PSZ) disks (Lava Esthetic A2 [Zr-AGG_A2] and Bleach [Zr-AGG_BL], both 3M Oral Care, and Katana STML A2 [Zr-NoAGG], Kuraray Noritake). The influence of pigment addition on the translucency parameter (TP00), fracture toughness, Vickers hardness, biaxial strength, and hydrothermal stability was assessed and correlated with the microstructure and phase composition. The pigment composition and distribution were evaluated by light and fluorescence microscopy, electron probe microanalysis, and nano–scanning electron microscopy. The chemical and phase composition and aging behavior were assessed using X-ray fluorescence and X-ray diffraction, respectively, while the aging sensitivity of the pigments was evaluated using micro-Raman spectroscopy. In contrast to Zr-NoAGG, possessing a typical 5Y-PSZ microstructure, the pigment additions in both Zr-AGG_A2/BL zirconia resulted in large yellow and blue fluorescent Er-, Hf-, and Al-containing agglomerates composed of small grains (0.57 µm and 0.38 µm, respectively, vs. 0.92 µm for the surrounding grains) with lower Y2O3 content. Zr-AGG_A2 had the lowest aging resistance, with transformation degradation occurring exclusively within the pigment agglomerates. All zirconia grades had a high Y2O3 content (4.2%–5.7 mol%) tetragonal ZrO2 phase and a high (42%–55 wt%) cubic ZrO2 phase content. Although no statistical differences were measured for hardness and toughness, Zr-NoAGG had a significantly higher TP00, higher flexural strength, and lower mechanical reliability compared to both Zr-AGG_A2/BL zirconia. The rare-earth oxide-containing zirconia agglomerates that were added as pigments to the multilayered monolithic Zr-AGG_A2/BL zirconia are the cause for their lower optical and mechanical properties and reduced aging resistance.

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ∼4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO2 phases, tetragonal and monoclinic HfO2 phases, Nb2O5 and Ta2O5 phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf4+, Nb5+, Ta5+, Zr4+ and O2− besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ∼70 nm wide were mainly composed of the monoclinic ZrO2 and monoclinic HfO2 phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.

Introducing Y2O3 passivation layer for utilizing TiSiN electrode on ZrO2-based metal-insulator-metal capacitor applications

This study investigates the degradation and improvement of the dielectric properties of ZrO2-based metal-insulator-metal (MIM) capacitors using TiSiN electrodes. As dynamic random-access memory (DRAM) design rules scale down, the mechanical properties of TiSiN electrodes provide advantages over conventional TiN, but also introduce challenges due to Si diffusion into ZrO2 films, forming low-dielectric constant (k) Zr-silicate and defect-related dielectric degradation. We evaluate the dielectric properties of ZrO2 films on TiSiN electrodes and identify significant reductions in the dielectric constant and an increase in DC and AC non-linearity due to Zr-silicate formation. To mitigate these problems, a Y2O3 passivation layer is introduced between the TiSiN electrode and ZrO2 dielectric film. Physical and chemical analyses, including X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), confirm that Y2O3 passivation effectively suppresses Si diffusion, preventing formation of Zr silicate, and preserving the high-k tetragonal phase of ZrO2. Electrical measurements show that the Y2O3 layer significantly improves the dielectric constant and reduces non-linearity effects. Notably, even at a reduced ZrO2 thickness of 4 nm, a relatively high k value is maintained with Y2O3 passivation. This study concludes that the Y2O3 passivation layer is indispensable for maintaining high dielectric performance in ZrO2-based MIM capacitors with TiSiN electrodes, ensuring stability and efficiency in advanced DRAM applications.

Optimizing additive Y2O3 concentration for improving corrosion resistance of ceramic coatings formed by plasma electrolytic oxidation on Zr-4 alloy

Abstract The corrosion resistance of ceramic coatings developed by plasma electrolytic oxidation (PEO) can be improved by embedding particles. Optimizing the concentration of particles in the electrolyte is essential to obtain the best coating performance. This work aims to optimize the concentration of Y2O3 embedded in the PEO coatings on Zr-4 alloy to obtain the best corrosion resistance. Nanoparticles Y2O3 was suspended in the PEO electrolyte at a concentration of 2, 3 and 4 g l−1. The particles were successfully embedded in the PEO coating composed of ZrO2–SiO2. The electrochemical test in an aqueous solution and oxidation test at 600 °C revealed a consistent result that the best corrosion resistance was obtained in the coating formed in the 3 g l−1 Y2O3-containing electrolyte. At the corresponding optimum concentration, the coating contained high SiO2 and tetragonal (t) ZrO2 phase, which potentially formed a stable solid solution ZrO2–SiO2. The improved coating stability enhanced the corrosion resistance during both aqueous solution and high temperature exposure.

Hydrodeoxygenation of C15 furanic precursor over mesoporous NiMo-ZrO2 composite catalysts for the production of sustainable aviation fuel

Sustainable aviation fuel (SAF) is essential for achieving carbon neutrality in the transportation sector. This study elucidates the production of SAF range C9-C15 branched alkanes by hydrodeoxygenation (HDO) of C15 furanic precursor derived from 2-methylfuran and furfural via hydroxyalkylation-alkylation reaction. HDO reaction was performed using high surface area mesoporous NiMo-ZrO2 composite catalysts that exhibited high selectivity to central SAF alkanes (C13-C14). Deoxygenation follows a complex reaction network involving furanic double bond saturation and furan-ring opening reactions in series, followed by the cascade of HDO, dehydroformylation, and C-C bond cleavage. The present investigation enlightens the impact of calcination temperatures and metal (Mo and Ni) contents on structural stability, physicochemical properties, and catalytic performance of NiMo-ZrO2. Both Ni and Mo stabilized the tetragonal ZrO2 phases with improved surface area. The catalytic activity proliferated with rising calcination temperature till 873 K due to the enrichment of Mo-O-Zr acidic species and deteriorated beyond this temperature owing to the generation of crystalline MoO3/Zr(MoO4)2 species. NiMo alloy formation was enhanced, and concurrently, acidity was reduced with increasing Mo content. 30 wt% MoO3-containing catalyst showed the best catalytic activity due to the proper balance between acidity and NiMo alloy. Oxygenate conversion was boosted by increasing NiO addition up to 15 wt% due to the enhanced Ni and NiMo alloy formation and decreased at 20 wt% owing to the evolution of catalytically inactive bulk metal oxide species. Catalytic cracking was prominent at elevated reaction temperatures, with significant amounts of C13 alkane.

Effect of dopant loading and calcination conditions on structural and optical properties of ZrO2 nanopowders doped with copper and yttrium

Undoped, Cu and/or Y doped ZrO2 nanopowders were synthesized with Zr, Y, and Cu nitrates using a co-precipitation approach. Their structural and optical properties were examined regarding dopant content (0.1–8.0 mol.% of CuO and 3–15 mol.% of Y2O3) and calcination conditions (400 °C–1000 °C and, 1,2 or 5 h) through Raman scattering, XRD, TEM, EDS, AES, EPR, UV–vis and FTIR diffused reflectance methods. The results showed that both Cu and Y dopants promoted the appearance of additional oxygen vacancies in ZrO2 host, while the formation of tetragonal and cubic ZrO2 phases was primarily influenced by the Y content, regardless of Cu loading. The bandgap of most of the powders was observed within the 5.45–5.65 eV spectral range, while for those with high Y content it exceeded 5.8 eV. The (Cu,Y)-ZrO2 powders with 0.2 mol.% CuO and 3 mol.% Y2O3 calcined at 600 °C for 2 h demonstrated nanoscaled tetragonal grains (8–12 nm) and a significant surface area covered with dispersed CuxO species. For higher calcination temperatures, the formation of CuZr 2+ EPR centers, accompanied by tetragonal-to-monoclinic phase transformation, was found. For fitting of experimental FTIR reflection spectra, theoretical models with one, five, and seven oscillators were constructed for cubic, tetragonal, and monoclinic ZrO2 phases, respectively. Comparing experimental and theoretical spectra, the parameters of various phonons were determined. It was found that the distinct position of the high-frequency FTIR reflection minimum is a unique feature for each crystalline phase. It was centered at 700–720 cm−1, 790–800 cm−1, and 820–840 cm−1 for cubic, tetragonal, and monoclinic phases, respectively, showing minimal dependence on phonon damping coefficients. Based on the complementary nature of results obtained from structural and optical methods, an approach for monitoring powder properties and predicting catalytic activity can be proposed for ZrO2–based nanopowders.

Effect of water-based electrolyte on surface, mechanical and tribological properties of ZrO2 nanotube arrays produced on zirconium

In this work, highly ordered ZrO2 nanotube arrays were fabricated on commercial pure Zr substrates through anodic oxidation in the water-based electrolyte at various voltages (30 V, 40 V and 50 V) for 1 h. The monoclinic- and tetragonal-ZrO2 phases were obtained on ZrO2 nanotubes through anodic oxidation. 13 vibration modes have been observed for the samples grown at low voltages (30 V and 40 V), which are assigned to monoclinic symmetry (7Ag + 6Bg), while—with the increasing growth voltage, the dominant phonon peak intensities associated with the monoclinic symmetry 6 times are decreased, and Eg (268 and 645 cm − 1) mode corresponding to tetragonal symmetry is observed. The nanotube array surfaces exhibited hydrophilic and super-hydrophilic behavior compared to the bare Zr surface. The elastic modulus values of ZrO2 nanotube surfaces (14.41 GPa) were highly similar to those of bone structure (10–30 GPa) compared to bare Zr substrate (120.5 GPa). Moreover, hardness values of ZrO2 nanotube surfaces were measured between ∼76.1 MPa and ∼ 283.0 MPa. The critical load values required to separate the nanotubes from the metal surface were measured between ∼1.6 N and ∼26.3 N. The wear resistance of the ZrO2 nanotube arrays was improved compared to that of plain Zr substrate.

Effects of the ZrO2 Crystalline Phase and Morphology on the Thermocatalytic Decomposition of Dimethyl Methylphosphonate.

Thermocatalytic decomposition is an efficient purification technology that is potentially applicable to degrading chemical warfare agents and industrial toxic gases. In particular, ZrO2 has attracted attention as a catalyst for the thermocatalytic decomposition of dimethyl methylphosphonate (DMMP), which is a simulant of the nerve gas sarin. However, the influence of the crystal phase and morphology on the catalytic performance of ZrO2 requires further exploration. In this study, monoclinic- and tetragonal-phase ZrO2 (m- and t-ZrO2, respectively) with nanoparticle, flower-like shape and hollow microsphere morphologies were prepared via hydrothermal and solvothermal methods, and their thermocatalytic decomposition of DMMP was systematically investigated. For a given morphology, m-ZrO2 performed better than t-ZrO2. For a given crystalline phase, the morphology of hollow microspheres resulted in the longest protection time. The exhaust gases generated by the thermocatalytic decomposition of DMMP mainly comprised H2, CO2, H2O and CH3OH, and the by-products were phosphorus oxide species. Thus, the deactivation of ZrO2 was attributed to the deposition of these phosphorous oxide species on the catalyst surface. These results are expected to help guide the development of catalysts for the safe disposal of chemical warfare agents.

THE EFFECT OF THE CHOICE OF THE STARTING MATERIAL ON THE PHASE COMPOSITION AND PHASE STABILITY OF ZRO<sub>2</sub> PARTICLES SYNTHESIZED BY THE HYDROTHERMAL METHOD

In this work, the phase composition, microstructure and phase stability of zirconium dioxide samples obtained by hydrothermal synthesis from various starting materials were investigated. It was found that when using ZrOCl2·8H2O as a starting material, zirconium dioxide particles containing monoclinic and tetragonal (cubic) phases are formed, at the same time, when using ZrO(NO3)2·2H2O as a starting material, only the monoclinic phase was identified in the samples. The CSR dimensions calculated using the Scherrer equation are in the range from 9 to 40 nm. Analysis of SEM images of experimental samples showed that nanoparticles form conglomerates with sizes of several microns. A study of the phase stability of the t, c – ZrO2 phase from temperature exposure showed that t, c – ZrO2 is a metastable phase with CSR sizes up to annealing of 10 nm. With an increase in the annealing temperature, the metastable tetragonal (cubic) phase of ZrO2 gradually transforms into a monoclinic one, due to the processes of minimizing surface energy and particle proliferation, as well as sintering conglomerates into larger monolithic particles.

Unraveling the effect of Cu doping on the structural and morphological properties and photocatalytic activity of ZrO2

Pristine ZrO2 and doped with different concentrations of Copper (0–7 %) were synthesized using a sol-gel combustion route. Several advanced techniques like XRD, EDX, TEM, XPS, P.L., and UV–vis spectrophotometer have characterized the compositions. The XRD proved that all peaks matched with a tetragonal phase of ZrO2 without any impurities of other phases. An average crystallite size rises from 20 to 55 nm by increasing the concentrations of Copper. The elemental analysis was examined by EDX and confirmed the presence of Cooper, Zirconium, and Oxygen. The red shift was observed due to a decrease in the bandgap (5.5–4.01 eV) with increasing the Cu concentrations. From the analysis of photocatalysis of pure ZrO2 and different concentrations of Cu-doped ZrO2 for M.B., RHB, and mix of them. The increase in doping of Cu led to enhancing the performance of the removing MB from 35 to 80 %, however, the RHB degradation was from 42 to 81 % while the mix of M.B. and RHB reached 85 % with 7 % Cu-doping ZrO2.

Highly efficient ZrO2 photocatalysts in the presence of UV radiation synthesized in a very short time by plasma electrolytic oxidation of zirconium

We demonstrated in this paper that plasma electrolytic oxidation of zirconium in an alkaline electrolyte (10 g/L trisodium phosphate decahydrate) with the addition of NaAlO2 is a highly efficient method for obtaining ZrO2 coatings that are effective photocatalysts for the decomposition of organic pollutants under UV irradiation. ZrO2 coatings were formed by varying the PEO time from 60 s to 600 s, the NaAlO2 concentration up to 4 g/L, and characterized by SEM/EDS, XRD, XPS, DRS, and photoluminescence spectroscopy. Methyl orange decomposition was used to examine the photocatalytic activity (PA) of ZrO2 coatings. The PA of the formed PEO coatings is determined by the ratio of monoclinic and tetragonal ZrO2 phases, as well as the content of incorporated Al3+ in the crystal structure of ZrO2. Al3+ incorporated into ZrO2 coatings improves tetragonal phase stability by causing the formation of oxygen vacancies, which is crucial for enhancing their PA. Furthermore, the Al3+ dopant serves as a capture site for photo-induced electrons, inhibiting electron/hole recombination. The best PA was demonstrated by the ZrO2 coating formed after 60 s in an alkaline electrolyte with 4 g/L NaAlO2 addition, which contains the most tetragonal ZrO2 phases (around 51.3 %) and Al (around 3.14 at. %) of all formed ZrO2 coatings. After 8 h of irradiation, the PA of this coating was approximately 95 %.

AC Conduction Mechanism and Impedance Analysis of Conventional and Plasma‐Sintered Yttria‐Stabilized ZrO2@Mullite Composite

AbstractThe addition of 8 mol% of Y2O3 to the ZrO2@mullite composites stabilizes the metastable tetragonal phase of ZrO2 in conventional and plasma‐sintered Y2O3‐stabilized ZrO2@mullite composites. A fused, highly dense, and interconnected microstructure is formed in the case of plasma‐sintered Y2O3 stabilized ZrO2@mullite composite. At 1 MHz frequency, the room temperature and tanδ of (10.37 and 2.06) is obtained for the conventional Y2O3 stabilized ZrO2@mullite composite and that of (38.8 and 4.02) is observed for the plasma sintered Y2O3 stabilized ZrO2@mullite composite. The substitution of Y3+ in place of Zr4+ creates sufficiently large oxygen vacancies at the grain boundary regions of these composites endowed mostly with the ZrO2 phase. In conventional Y2O3‐ ZrO2@mullite composites, both dielectric relaxation as well as conductivity relaxation are observed due to the dynamic motion of dipoles and relaxation due to the presence of defect states and porous structures. This leads to higher grain boundary conductivity than the grain conductivity of these composites. Thermally activated conduction mechanisms exhibited in these composite materials are projected from the complex impedance and modulus analysis. The conventional and plasma sintered Y2O3‐ ZrO2@mullite composite has an optical bandgap of 3.26 and 3.58 eV, respectively.

A comprehensive study on ZrO2-ZnO nanocomposites synthesized by the plant-mediated green method

Zirconia—zinc oxide (ZrO2-ZnO) nanocomposites with three different amounts of zirconia (ZrO2) contents (5%, 10%, and 15%) were successfully synthesized using the leaf extract of Azadirachta indica (also known as Neem). The prepared nanocomposites were examined from the microstructural and optical point of view. The existence of the mixed phase of hexagonal ZnO together with the tetragonal ZrO2 in each sample was confirmed by the X-ray diffraction data. Rietveld refinement was performed to determine the microstructural parameters. A significant morphological as well as microstructural change was also noticed from SEM and HRTEM images with the admixture of increasing quantities of zirconia. A characteristic metal oxide band within 1000 cm−1, was confirmed by the Fourier transform infrared spectroscopy. UV–visible spectra confirm the decrease in optical band gap energy values from 3.30 eV to 3.15 eV for the ZnO phase and from 3.93 eV to 3.73 eV for the tetragonal ZrO2 phase with the increasing amount of ZrO2 admixture into the ZnO host material. All of these findings would likely be useful not only in the manufacture of electronic and optical devices, but would also be useful for water purification through photocatalytic activities.

Temperature-mediated phase evolution of perovskite-type CuZrO3 nanoparticles

ABSTRACT Herein, we report the phase evolution of perovskite-type copper zirconate nanoparticles synthesized via the coprecipitation method. The XRD investigations confirm the dominant orthorhombic CuZrO3 phase formation at 700 °C along with frail tetragonal ZrO2 and monoclinic CuO phases. XRD analysis confirms the presence of orthorhombic perovskite type CuZrO3 in the sample annealed at 700 °C with cell parameters: a = 6.4552 Å, b = 7.4008 Å, and c = 8.4013 Å whose crystallite sizes is 54 nm. Higher calcination temperatures (above 700 °C) induce the crystallinity deterioration in the CuZrO3 phase. The XPS studies substantiate the chemical state of constituent elements present in the sample annealed at 700 °C. The chemical bonding and optical features of the samples were probed using FTIR and UV-Vis-NIR spectroscopy, respectively. The optical bandgap energies for the synthesized samples that were annealed at various temperatures ranged from 3.36–3.08 eV.

First-principles investigations of the crystal and electronic structures, dynamical and mechanical stabilities, Born effective charges and dielectric permittivities of a novel tetragonal zirconia

In this paper, a novel tetragonal ZrO2 phase has been predicted from first-principles calculations. The detailed crystal structural analysis shows that the tetragonal ZrO2 has a space group I41/amd (D4h19, No. 141) with 4 formula units per unit cell and 16 symmetry operations as well as six-fold cation coordination. The Zr atoms occupy 4a Wyckoff positions (0, 1/2, 1/4) and (1/2, 1/2, 1/2) and the O atoms occupy 8e Wyckoff positions (0, 0, z+1/8), (0, 1/2, z+3/8), (1/2, 0, -z+5/8) and (1/2, 1/2, -z+3/8) with z = 0.0761. The electronic structures, dynamical and mechanical stabilities investigations show the tetragonal ZrO2 is dynamical and mechanical stable as well as with a large direct band gap of 3.9015eV at Γ point. The phonon dispersion is divided into two regions: the low frequency part (0–8.6240 THz) and the high frequency part (10.3453–18.4034 THz) with a separation gap of 1.7213 THz. The magnitudes of Born effective charges are greater than the nominal chemical valences of +4 and −2 for Zr and O ions, respectively, reflecting a strong dynamic charge transfer from Zr to O atoms and thus a p-d hybridized Zr–O ionic bond. A diagonal and anisotropic static dielectric permittivity εij0 is obtained between ab-plane ε110=ε220=17.80 and along c axis ε330=14.77.

Phase stability and thermophysical properties of CeO2-Re2O3 (Re[dbnd]Eu, Gd, Dy, Y, Er, Yb) co-stabilised zirconia

A series of 16 mol% CeO2-2 mol% Re2O3 co-stabilised zirconia (ZrO2) (16Ce4ReSZ, ReEu, Gd, Dy, Y, Er, Yb) ceramic materials were synthesised using a chemical coprecipitation– high-temperature roasting method. Their phase structure, high-temperature phase stability, mechanical properties, thermal conductivity and coefficient of thermal expansion (CTE) were investigated. The results show that the ZrO2 tetragonal phase co-stabilised by CeO2 and Re3+ with a smaller radius has better stability. The 16Ce4ReSZ (ReDy, Y, Er, Yb) materials have high fracture toughnesses, low thermal conductivities, and high CTE values. As the radius of the Re3+ ions decreases, the lattice energy increased, while the lattice distortion decreases, the CTE decreases slightly and the thermal conductivity of the material increases slightly. Owing to the high phase stability of 16Ce4YbSZ, its mechanical properties are best after 100 h of sintering at 1400 °C.

Consolidation of alumina toughened zirconia by two-step sintering

Sol-gel-synthesized ZrO2-based nanoparticles, containing 1.5mol% Y2O3 used as dopant and 25mol% Al2O3 (abbreviated as ZrO2(1.5Y)-25Al2O3), were densified by pulsed electric current sintering (PECS) accompanied with a two-step heating profile. Particularly, sintering was carried out in the temperature range from 1050 to 1200?C for 10min, followed by dwell at 1325?C for 10min. The ZrO2-based ceramics achieved by the two-step sintering was fully dense, containing 98 vol.% of tetragonal ZrO2 phase. Morphology of the sintered samples showed the submicron grains with uniform size distribution. Although the second-step sintering temperature was fixed at 1325?C, the mean grain size was increased along with the increase in the first-step sintering temperature. In addition, the material characterization of the samples after the first-step heating was tested to investigate the influence of the first-step sintering on the consolidation of ceramics achieved via the two-step sintering.

Oxide formation mechanism of a corrosion-resistant CZ1 zirconium alloy

Tailoring microstructure and microchemistry by altering elemental compositions and thermomechanical treatment parameters enables superior corrosion performance in zirconium alloys for nuclear applications. However, our understanding of the relationship between various defects and the corrosion process remains limited in the newly developed zirconium alloys. Here we report the oxide formation mechanism of a CZ1 zirconium alloy with corrosion resistance surpassing many other zirconium alloy systems, such as Zircaloy-4 and Zr-1Nb-1Sn alloys. Autoclave experiments of CZ1 alloy and Zr-1Nb-1Sn model alloy were performed in 360 °C water for up to 820 d. We quantitively determined oxide phases by transmission Kikuchi diffraction (TKD) and examined lateral cracks, nano-porosity, and second-phase particles in oxide scales by transmission electron microscopy (TEM). Compared to the Zr-1Nb-1Sn model alloy, CZ1 alloy with lower Nb and Sn concentrations has shown smaller and lower-density lateral cracks but slightly larger oxide grains, reducing the diffusion route for oxidating species. Using analytical scanning and transmission electron microscopy, we demonstrate that due to the lower content of Sn (∼0.9 wt.%), there is less tetragonal ZrO2 phase formed in the oxide, and the level of tetragonal to the monoclinic phase transition is reduced. Although the Nb content (0.1 wt.%–0.3 wt.%) is lower than the solid solution limit of Nb in Zr, by introducing minor elements such as Fe, Cr, and Cu, there are still a reasonable number of second-phase particles to relieve the high stress associated with the metal-to-oxide transformation. These mechanisms have substantially changed the density and distribution of lateral cracks in the oxide, thus reducing the corrosion rate of zirconium alloys.

Aerosol-assisted CVD method for the synthesis of solid particles of t-YSZ-Fe3O4

This work details the production of solid composite particles by the aerosol-assisted chemical vapor deposition method. With this method it is feasible to produce at low temperature (450 °C) the tetragonal phase of zirconium oxide stabilizing it with yttrium oxide (YSZ) and cubic iron oxide (Fe3O4) at the same time. The particles have a solid morphology in which both metal oxides coexist without mixing. The average size of the obtained particles is 329 ± 81 nm, moreover, each particle is formed by thousands of crystallites of size 2 ± 0.5 nm. The formation of solid structures is due to the amount of Zr and Y found in each particle. These particles can be applied as reinforcements of metallic structures.•A simple and low-cost method for producing composite particles to be applied as reinforcing agents for metal structures.•The particles are formed by two phases of tetragonal yttria-stabilized zirconia (t-YSZ) and cubic Fe3O4, which was synthesized following a one-step process via the aerosol-assisted chemical vapor deposition method (AACVD).•The tetragonal phase of ZrO2 is obtained at 450 °C stabilizing it with ∼3.8% of yttrium oxide.