Tetragonal ZrO2 Phase Research Articles

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.

The role of crystalline phase of zirconia in catalytic conversion of ethanol to propylene

Zirconia catalysts can selectively convert ethanol to propylene and exhibit excellent catalytic stability. However, the effects of crystalline phase of ZrO2 on the catalyst active sites and catalytic performance have not been fully recognized. In this work, when Y or La was doped into ZrO2, the monoclinic to tetragonal phase transition occurred, and the propylene yields were improved to 44.0% and 42.3%, respectively. The effects of different crystalline phases of ZrO2 on the ethanol to propylene reaction were analyzed by density functional theory. Comparing the monoclinic, tetragonal and cubic phases of ZrO2, the tetragonal phase ZrO2 has the lowest oxygen vacancy formation energy and is likely to form oxygen vacancies to convert ethanol to propylene. Moreover, the adsorption energy of ethanol on tetragonal ZrO2 is moderate, which is not only beneficial to ethanol conversion, but also reduces catalyst deactivation caused by excessive adsorption. Therefore, tetragonal ZrO2 shows practical significance for catalyzing ethanol to propylene.

Selectivity of Ethanol Conversion on Al/Zr/Ce Mixed Oxides: Dehydration and Dehydrogenation Pathways Based on Surface Acidity Properties

AbstractZirconia‐alumina mixed oxides (Zr+Ce)O2−Al2O3 with various mol. ratios (5, 10, 20, 50, and 75 % alumina) were prepared using the sol‐gel method. The catalysts were characterised via XRD, SEM, DTA/TG, BET, and FT‐IR spectroscopy. The acidities of the catalysts were measured through the absorption of anthraquinone and pyridine probe molecules using EPR and IR spectroscopy, respectively. Catalytic activity and selectivity were investigated for ethanol conversion to acetaldehyde, ethylene, and diethyl ether, which were used as model reactions to identify surface‐active sites. The relationship between the surface structure and the dehydration/dehydrogenation activity was evaluated. Diethyl ether formation is promoted by the presence of the ZrO2 tetragonal phase at a low ZrO2/Al2O3 ratio in the sample composition, at which the Lewis acid site has an aluminum‐oxygen environment. The reaction mechanism was also discussed. In the low‐temperature reaction region, dehydrogenation competes with dehydration; ethylene and acetaldehyde share a common reactive intermediate.

Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres

The paper is concerned with (i) the hydrothermal synthesis of hydrous zirconium dioxide (HZD) bearing analcime (HZD-ANA, zirconia-analcime) and (ii) its sorption properties with respect to Cs+ and Sr2+. The HZD-ANA particles were synthesized from coal fly ash cenospheres composed of aluminosilicate glass with (SiO2/Al2O3)wt.=3.1 and characterized by PXRD, SEM-EDS, STA, and low-temperature N2 adsorption. The non-radioactive simulant solutions of different acidity (pH=2–10) and Cs+/Sr2+ content (0.5–50.0 mg/L) were used in the work. The effect of synthesis conditions on the HZD-ANA particle size, zirconia content and localization as well as the sorption behavior with respect to Cs+ and Sr2+ (capacity, KD) were clarified. It was found that the small-sized HZD-ANA composites surpasses the Zr free analcime and large-sized HZD-ANA material in the Cs+ and Sr2+ sorption parameters (KD ~104–106 mL/g). The conditions to synthesize the zirconia-analcime composite of the highly enhanced sorption ability with respect to Sr2+ (KD ~106 mL/g) were determined. The high-temperature solid-phase re-crystallization of Cs+/Sr2+-exchanged HZD-ANA composites was shown to occur at 1000 °C resulting in a polyphase system based on nepheline, tetragonal ZrO2, and glass phase.

(Digital Presentation) Effect of Iron Doping on Oxygen Reduction Activity of Zirconium Oxides Containing Carbon and Nitrogen Using Pyrazine Carboxylic Acid As Platinum Alternative Cathodes for PEFC

The use of carbon-supported platinum catalysts as cathode of present polymer electrolyte fuel cells (PEFCs) have some problems such as high cost and low amount of resources of platinum. Therefore, we have attempted to develop substitute of platinum based on group 4 transition metal oxides. We found that stable oxygen vacancies on the surface and lattice distortion by doping foreign elements of these metal oxides could act as active sites of oxygen reduction reaction (ORR) [1]. However, although zirconium oxides show some ORR activity, the onset potential of the ORR still remains low. Then, we focused on the improvement of the ORR activity by an addition of iron ions to zirconium oxides according to the research of P. Madkikar et. al. [2]. In this study, we used pyrazine carboxylic acid as ligand of metal ions to prepare zirconium-iron complexes including carbon and nitrogen as precursors. The precursors were heat-treated under low oxygen pressure to obtain the iron-added zirconium oxide-based catalysts, which are designated as ZrOx-Fe. We investigated the correlation between the ORR activity and physical characteristics such as crystalline phase.ZrOx-Fe catalysts were synthesized according to the previous patent [3]. We prepared zirconium complexes solutions by mixing zirconium butoxide and acetic acid in acetylacetone as a solvent. On the other hand, we also prepared iron complexes solutions by mixing iron acetic acid and pyrazine carboxylic acid in mixed solvents of water, ethanol and acetic acid. The amount of the iron addition was changed in atomic ratios of 0, 0.004, 0.01, 0.1, and 0.2 against Zr atoms. The iron atomic ratio of 0.004 was selected according to P. Madkikar’s results, because Fe atomic ratio of 0.0036 caused the highest ORR activity in the report [2]. After mixing of two solutions, the solutions were stirring several days, and the precursors were obtained by evaporation and vacuum drying. These precursors were heat-treated under argon including 2 % hydrogen and 0.05 % oxygen for low oxygen pressure oxidation, and finally ZrOx-Fe catalysts were obtained. To investigate the effect of Fe addition to zirconium oxides, we also synthesized iron-based catalyst without Zr in the same way. Electrochemical measurements were conducted in the solution of 0.5 M H2SO4 at 30 oC. In this study, we used the ORR onset potential as the parameter of the ORR activity, which was defined as the potential when the ORR current (i ORR) was 0.01 ampere per a mass of the whole catalysts.Among the ZrOx-Fe catalysts prepared in this study, ZrOx-Fe with the Fe atomic ratio of 0.1 showed the highest E ORR, which was designated as ZrOx-Fe(0.1). Therefore, we compared with ZrOx and FeOx prepared by the same way as well as conventional catalysts. Fig. 1 shows the ORR polarization curves of the ZrOx, ZrOx / CNT [1], ZrOx-Fe / KB [2], FeOx and ZrOx-Fe(0.1) catalysts. As shown in Fig.1, the ZrOx-Fe(0.1) catalyst had highest ORR onset potential among these catalysts. Comparing with ZrOx, FeOx and ZrOx-Fe(0.1), the Fe addition into zirconium oxide was essential to increase the ORR onset potential. In addition, the onset potential of the ZrOx-Fe(0.1) was higher than that of the ZrOx-Fe / KB [2] and our previous ZrOx / CNT [1]. The onset potential of the ZrOx-Fe(0.1) was exceeded 0.9 V that we have never been able to reach with zirconium oxides. Therefore, the addition of iron to zirconium oxides improved drastically the quality of the active sites of the ORR.Next, we examined crystalline phase of all ZrOx-Fe catalysts with XRD. All ZrOx-Fe catalysts were consisted of ZrO2 monoclinic or tetragonal phase. We calculated monoclinic rate in each catalyst using the equation in the literature [4]. The change of atomic ratio of Fe caused the different monoclinic rate. A positive correlation between the ORR onset potentials and the monoclinic rates of the ZrOx-Fe was obtained. Thus, the ORR onset potential increased with increasing the monoclinic rate in the catalysts, suggesting that the monoclinic phase formed the active sites of the ORR.AcknowledgementThe authors thank the financial support of the New Energy and Industrial Technology Development Organization (NEDO), JSPS grants-in-aid for scientific research, and ENEOS Tonen General Sekiyu Research / Development Encouragement & Scholarship Foundation.References(1) A. Ishihara et. al., Int. J. Hydro. Energy, 45, 5438 (2019).(2) P. Madkikar et. al., J. Electrochem. Soc., 166, F3032 (2019).(3) Showa Denko Corp., R. Monden et. al., Oxygen reduction catalysts, the methods of these, and polymer electrolyte fuel cells, JP 2013-240785, 2013-12-05.(4) H. Toraya et. al., J. Am. Ceram. Soc., 67, C119 (1984). Figure 1

Microwave-synthesized ZrO2/ZnO heterostructures: fast and high charge separation solar catalysts for dyes-waste degradation

In 60 min, microwave-synthesized ZrO2/ZnO heterostructures exhibited high and fast sunlight photodegradation efficiencies for 50 ppm Congo red (CR) and 50 ppm methylene blue (MB) pollutants. ZrO2/ZnO heterostructures were characterized by XRD, SEM, EDX, FTIR, and diffuse reflectance (DR) techniques. The XRD analysis showed that these heterostructures have combined components of tetragonal ZrO2 and hexagonal ZnO phases. The SEM micrographs of all ZrO2/ZnO nanocomposites demonstrate the formation of nanospherical particles (major) and rod-like (minor) structures. The EDX spectra verified the presence of Zr, Zn and O elements with percentage ratios equivalent or close to that used during the experimental preparation. The FT-IR spectra showed the vibrational characteristic absorption modes of ZrO2 and ZnO bonds around 400–600 cm−1. Two band gap energies were estimated corresponding to ZrO2 (5.05–5.16 eV) and ZnO (3.1–3.16 eV) components. Remarkably, in presence of ZrO2/ZnO (30/70 at%) heterostructure, the free solar energy initiated photodegradation efficiencies of 87% and 98% for 50 ppm CR and 50 ppm MB dyes after 60 min, respectively, which indicates the fast and superior photocatalytic activity of microwave-synthesized ZrO2/ZnO heterostructure. As well, this composition reveals good reusability and stability for three photocatalytic cycles. This uppermost photodegradation performance can be assigned to the high separation of charge carriers, especially for the ZrO2/ZnO (30/70 at%) nanocomposite.Graphical abstract

High capacity synergistic immobilization of simulated trivalent actinides by zirconia/zircon multiphase ceramics

Zircon (ZrSiO4) ceramics are candidate waste form for immobilizing actinides. However, ZrSiO4 with single phase suffers from the low actinides solubility. Herein, 0.2Zr1-aNdaO2-a/2/Zr1-bNdbSiO4-b/2 (0≤a+b ≤ 0.3) multiphase ceramics were fabricated and their actinides immobilization ability and aqueous stability were evaluated. The evolutions of phase and microstructure affected by Nd doping were investigated. 0.2Zr1-aNdaO2-a/2/Zr1-bNdbSiO4-b/2 ceramics with 0≤a+b˂0.1 exhibited monoclinic ZrO2, tetragonal ZrO2 and ZrSiO4 mixed phases, while monoclinic ZrO2, tetragonal ZrO2, ZrSiO4 and Nd2Si2O7 phases with 0.1≤a+b ≤ 0.3. The increase of lattice volume revealed the successful lattice immobilization of Nd by ZrO2/ZrSiO4. Due to synergistic immobilization effect, the Nd immobilization capacity of ZrO2/ZrSiO4 is up to 10 at%, which is higher than that of single-phase ZrSiO4 (4 at%). Furthermore, the obtained ceramics waste form exhibited good compactness and excellent aqueous stability. The results indicated that zirconia/zircon multiphase ceramics can be a potential candidate waste form for actinides.

Effect of Dy2O3 doping on phase compositions, microstructures, thermophysical properties and fracture toughness of YSZ coatings

Yttria-stabilized zirconia (YSZ) coatings with different Dy2O3 doping contents were prepared via plasma spraying. The effects of phase compositions, microstructures and lattice defects on the thermal conductivity, fracture toughness and thermal shock resistance were analyzed. The result indicates that the Dy2O3 doping significantly affects thermophysical properties of YSZ coatings. The Dy2O3 doping can improve the insulation performance of the YSZ coating and the minimum thermal conductivity of the coating has reached 0.89 W/K·m. A decrease in thermal conductivity with increasing Dy2O3 doping content can be attributed to the lattice distortion, ions substitution, oxygen vacancies and reducing grain size. Meanwhile, the Dy2O3 doping causes the fracture toughness of YSZ coatings to decrease. Consequently, the Dy2O3-doped YSZ coatings exhibit weaker thermal shock resistance because the Dy2O3 doping promotes the formation of the cubic YSZ phase. The tetragonal phase in plasma-sprayed coatings is beneficial for service lifetime owing to its phase transformation and ferroelasticity-induced toughening under stress. Although the Dy2O3-doped YSZ coatings undergo more severe sintering owing to a decrease in the activation energy of grain growth caused by lattice distortion, they exhibit better phase stability than the YSZ coating under high temperatures because the Dy2O3 doping inhibits the diffusion of Y. Finally, a Dy2O3-doped ZrO2 coating composed mainly of the tetragonal ZrO2 phase was designed, which exhibited a better thermal shock resistance.

Synthesis of NiO/MgO/ZrO2 catalyst for syngas production from partial oxidation and dry reforming of biogas

This work focuses on a facile NiO/MgO/ZrO2 synthesis protocol for syngas production via partial oxidation and dry reforming of biogas. Herein, performance of the developed catalysts with different amounts of MgO (0–40 %wt. of support) and NiO (10–50 %wt.) on %CH4 conversion, %CO2 conversion, H2/CO ratio, and carbon formation are studied. The results reveal the presence of monoclinic ZrO2 and tetragonal ZrO2 phases with 50%NiO/ZrO2 catalyst synthesized by surface modification technique using carbon derived from urea. Addition of MgO in the catalyst shows ability to stabilize tetragonal ZrO2 phase as well as enhance basic surface of the catalyst. These properties render the adsorption of CO2 molecules on the surface, which subsequently are reduced by carbon, leading to CO production. Appropriated amount of NiO and MgO, which is 30 %wt. NiO and 20 %wt. MgO (relative to ZrO2) can produce syngas having quality (H2/CO molar ratio) of ca. 2.

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia.

It is known that the yttria-stabilized zirconia (YSZ) material has superior thermal, mechanical, and electrical properties. This material is used for manufacturing products and components of air heaters, hydrogen reformers, cracking furnaces, fired heaters, etc. This work is aimed at searching for the optimal sintering mode of YSZ ceramics that provides a high crack growth resistance. Beam specimens of ZrO2 ceramics doped with 6, 7, and 8 mol% Y2O3 (hereinafter: 6YSZ, 7YSZ, and 8YSZ) were prepared using a conventional sintering technique. Four sintering temperatures (1450 °C, 1500 °C, 1550 °C, and 1600 °C) were used for the 6YSZ series and two sintering temperatures (1550 °C and 1600 °C) were used for the 7YSZ and 8YSZ series. The series of sintered specimens were ground and polished to reach a good surface quality. Several mechanical tests of the materials were performed, namely, the microhardness test, fracture toughness test by the indentation method, and single-edge notch beam (SENB) test under three-point bending. Based on XRD analysis, the phase balance (percentages of tetragonal, cubic, and monoclinic ZrO2 phases) of each composition was substantiated. The morphology of the fracture surfaces of specimens after both the fracture toughness tests was studied in relation to the mechanical behavior of the specimens and the microstructure of corresponding materials. SEM-EDX analysis was used for microstructural characterization. It was found that both the yttria percentage and sintering temperature affect the mechanical behavior of the ceramics. Optimal chemical composition and sintering temperature were determined for the studied series of ceramics. The maximum transformation toughening effect was revealed for ZrO2-6 mol% Y2O3 ceramics during indentation. However, in the case of a SENB test, the maximum transformation toughening effect in the crack tip vicinity was found in ZrO2-7 mol% Y2O3 ceramics. The conditions for obtaining YSZ ceramics with high fracture toughness are discussed.

High intensity orange-red emission of chemically deposited Sm3+-doped ZrO2 thin films - Beneficial effects of host and dopant

Samarium doped (0.5–5 at.%) ZrO2 films with high surface and optical quality were obtained by sol–gel method using inorganic zirconium precursor. The morphology and roughness of the samples were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A phase transition following the doping with Sm3+ ions was registered by the X-ray diffraction (XRD) method, leading to stabilization of the tetragonal ZrO2 phase. Optical parameters such as refractive index and extinction coefficient were determined for each sample. X-ray photoelectron spectroscopy (XPS) revealed the presence of carbon impurities as well as a shift of the valence band (VB) edge to lower binding energies with the increase of the dopant level. The electron paramagnetic resonance (EPR) proved the presence of oxygen vacancies and other defects (Zr3+, T-centers) in the structure of the films which prompted photoluminescence (PL) in the material. The emission spectra of the pure ZrO2 and Sm-doped samples revealed the beneficial effect of the host matrix, capable of boosting the characteristic orange-red emission of the Sm3+ ions. The obtained films have very high ratio of acceptor/donor emission intensity (Ia/Id = 25) making them promising candidates for applications in the field of photonics, including in the development of white LEDs.

Microstructure and corrosion performance of Zr–1Nb alloy laser welded joints treated by micro-arc oxidation

The protective coatings on laser-welded joints of Zr–1Nb alloy were prepared by the micro-arc oxidation (MAO) process. The morphology, microstructure and phase composition of MAO coatings at different regions of Zr–1Nb alloy laser-welded joints were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behaviors of the coatings. The MAO coatings at the fusion zone (FZ) and heat-affected zone (HAZ) were smooth with some small holes, while MAO coatings at base metal (BM) were relatively rough with large holes. The cross-sectional topography at FZ coatings was quite dense with less distribution of pores and cracks, which can effectively improve the protective properties of the coatings. HAZ coatings were divided into outer loose layer and inner dense layer. The BM coating layer possessing many holes was a typical sparse layer structure. The phase compositions of welded joints treated by MAO were diverse at different zones of the joints, but all of them consisted of the monoclinic ZrO2 and tetragonal ZrO2 phases. The coatings of FZ had the best corrosion resistance, compared with HAZ and BM. The results of EIS indicated that the thickness and defects of the inner compact layer played a key role in improving the corrosion resistance of the MAO coatings on the surface of the Zr–1Nb alloy laser-welded joints.

Stabilization of tetragonal phase of nanostructured Fex/ZrO2 system (0 ≤ x ≤ 25) prepared by modified sol-gel method

In the present study, Fex/ZrO2 (0 ≤ x ≤ 25) nanoparticles were synthesized by a facile modified Sol-Gel method. Stabilization of the tetragonal phase of ZrO2 is studied as a function of both the Fe incorporation ratios and thermal treatment. The Fe incorporation ratios are tested up to the extreme just before FeO and Fe2O3 phases are formed separately. The prepared Fex/ZrO2 nanoparticles XRD analysis depicts the formation of zirconium oxide at different Fe ratios in the nanoscale with an excellent degree of crystallinity in the tetragonal phase. The effect of thermal treatment on stabilizing the tetragonal phase of Fex/ZrO2 nanoparticles is extensively studied. The phase transition to the monoclinic phase is determined as function of Fe incorporation ratios and annealing temperatures. The optical absorbance spectra showed that the optical band gap decreased with increasing Fe ratios without the formation of doping bands which confirms the formation of Fex/ZrO2 single matrix.

Deformation and fracture behaviour of alumina-zirconia multi-material nanocomposites reinforced with graphene and carbon nanotubes

An effort to improve the low fracture toughness of monolithic alumina (Al2O3) ceramic demands microstructural manipulation with nanostructured materials such as zirconia (ZrO2), Graphene (GN) and Carbon Nanotubes (CNTs). Despite these attempts, the fundamental understanding of the mechanical properties and deformation behaviour of multiple combinations of these second-phase additives within the advanced Al2O3 structure are still being explored. In this respect, Al2O3-based nanocomposites reinforced with optimum amounts of ZrO2(10 wt%), GN(0.5 wt%) and CNTs(2 wt%) were evaluated via hot-pressing at 1600 °C, preceding colloidal mixing of the Al2O3 matrix and nanostructured additives. Mechanical properties such as fracture toughness (KIC) and bending strength (σf) measured using three-point bending techniques including single edge notched beam (SENB) test, and direct crack measurement (DCM) methods were calculated from the near-dense fabricated multi-material nanocomposites and benchmarked against the monolithic Al2O3 material under similar experimental conditions. From the conventional SENB test, the fracture toughness values increased by up to 60% on the addition of only 10 wt%ZrO2 to the monolithic Al2O3, whilst a drastic increase by up to 159% was achieved with the incorporation of both GN and CNTs within the Al2O3–ZrO2 structure, as compared to the monolithic Al2O3. The KIC values obtained from SENB tests were typically lower than the DCM method, but similar trend in the toughness behaviour were realized regardless. Bending strength of the prepared monolithic Al2O3 was also increased by up to 46% with the combined additions of ZrO2, GN and CNTs. Toughening and strengthening mechanisms including pull-outs by GN and CNTs, crack arrest and cack bridging were identified as the main source of enhancement in the mechanical properties of the multi-material nanocomposites. The addition of carbon additives also influenced monoclinic and tetragonal ZrO2 phase transformations, which also contributed to the overall mechanical behaviour of the Al2O3-10 wt%ZrO2 nanocomposites.

Influência do Percentual de Ítrio nas Propriedades da Zircônia Monolítica: Revisão de Literatura

The main disadvantage of conventional zirconia is its high opacity. Depending on different conditions, especially the content of the yttrium stabilizer, it is possible to circumvent this issue, in view of this, several generations of yttrium stabilized zirconia were developed seeking to combine the robustness of zirconia with the aesthetics of porcelain veneers. The present work aimed to carry out an analysis on how the increase or decrease in the percentage of yttrium in the composition of monolithic zirconia can influence their properties, especially with regard to translucency. This study was carried out through a review in the Scielo, PubMed and Google Scholar databases with articles published between 2008 and 2021. In this way, it was concluded that the higher content of Y2O3 tended to increase the amount of isotropic cubic phase present and reduce the amount of birefringent tetragonal phase in ZrO2 together with a minimization of light scattering by secondary phases, leading to increased translucency and aging resistance. As yttrium oxide increases, zirconia grain sizes tend to increase as well, and translucency may improve with increasing grain size. Toughness and fracture toughness can be sacrificed considerably

Laser innovation of YSZ electrophoretic deposition overlay on plasma sprayed thermal barrier coating system

In this study, laser surface treatment was used on electrophoretically deposited YSZ overlay coatings on APS YSZ to enhance and improve the TBCs system. First, preliminary preparation of TBC YSZ samples were produced by APS over superalloy substrates and the co-deposition to protecting of TBCs by applying overlay EPD coating followed by sintering was characterized. An electrophoretic deposition process was carried out on the TBC YSZ samples at the optimum coating parameters 40 V in 5 min with a solid concentration of 10 g/L of YSZ. After deposition the samples were dried at room temperature for 24 h and Subsequently, the electrophoretic deposition was followed by sintering in a vacuum furnace at 1200 °C for 2 h. coating samples after sintering were further treated by using Pulsed Nd: YAG laser beam. The surface morphology and microstructure of the samples were studied by a field emission scanning electron microscope (FESEM), Optical microscope, microroughness, and phase purity of the coating material were investigated by XRD. Results indicated that the YSZ oxide overlay produced by electrophoretic deposition (EPD) was successfully performed as an environmental barrier overlay in protecting the APS YSZ TBCs against environmental degradation. The analysis of the XRD pattern of the sintered coating showed the presence of only equilibrium tetragonal phase (t) while in laser state the phase was only nontransformable tetragonal ZrO2 phase (t -ZrO2). Which is regarded to be a desirable ZrO2 phase to beneficial for TBC. It is found from microroughness inspection, decreasing surface roughness after laser treatment. Which indicated improvement in coating surface properties.

Oxidation Behavior and Microstructural Evolution of ZrB2–35MoSi2–10Al Composite Coating

The problem of creating and implementing high-temperature coatings for the protection of carbon–carbon (C/C) composites remains relevant due to the extremely low or insufficient heat resistance of C/C composites in an oxygen-containing environment. In the present work, detonation spraying was used for preparing new ZrB2–35MoSi2–10Al coatings on the surface of C/C composites without a sublayer. As a stabilizer of high-temperature modification of zirconia, and to increase the wettability of the surface of C/C composites, 5 wt.% Y2O3 and 10 wt.% Al were added to the initial powder mixture, respectively. The structure of the as-sprayed coating presents many lamellae piled up one upon another, and is composed of hexagonal ZrB2 (h- ZrB2), tetragonal MoSi2 (t-MoSi2), monoclinic ZrO2 (m-ZrO2), tetragonal ZrO2 (t-ZrO2), monoclinic SiO2 (m-SiO2), and cubic Al phases. The oxidation behavior and microstructural evolution of the ZrB2–35MoSi2–10Al composite coating were characterized from RT to 1400 °C in open air. During oxidation at 1400 °C, a continuous layer of silicate glass was formed on the coating surface. This layer contained cubic ZrO2 (c-ZrO2), m-ZrO2, and small amounts of mullite and zircon. The results indicated that a new ZrB2–35MoSi2–10Al composite coating could be used on the surface of C/C composites as a protective layer from oxidation at elevated temperatures.

Sorption Properties of ZrO2-Analcime Composites in Relation to Cs(I) and Sr(II)

Composite zeolite sorbents based on analcime with inclusions of hydrated zirconium dioxide (ZrO2-analcime) have been obtained by hydrothermal treatment of coal fly ash cenospheres with a high glass phase content in the presence of a zirconium compound and an alkaline activating agent at 150 °C and different stirring modes of the reaction mixture. The synthesis products were characterized by XRD, SEM-EDS, STA and low-temperature nitrogen adsorption; their sorption properties with respect to Cs+ and Sr2+ were studied in the pH range of 2–10. It was found that the ZrO2-analcime compositions surpass unmodified analcime by 2–5 times in terms of sorption of Cs+ and Sr2+ and by two orders of magnitude in terms of the distribution coefficient value (KD ~106 ml/g). The process of high-temperature solid-phase transformation of Cs+/Sr2+-exchanged forms of the compositions was studied, which simulates the process of conversion of water-soluble forms of Cs‑137 and Sr‑90 radionuclides into a mineral-like form. It was shown that at 1000 °C the ZrO2-analcime compositions with sorbed Cs+ and Sr2+ undergo the phase transformation resulting in polyphase systems of similar composition based on nepheline, tetragonal ZrO2, and glass phase

Plasma electrolytic oxidation of zircaloy-4 in a mixed alkaline electrolyte

Characteristics of coating resulted from plasma electrolytic oxidation (PEO) of zircaloy-4 in an electrolyte containing phosphate, silicate, and hydroxide were investigated. The mixed electrolyte is proposed to reduce power consumption. PEO was conducted in a DC mode at a current density of 30, 50, and 70 mA/cm2. Plasma was generated at a relatively low breakdown voltage of 150 V, independent of the current density. The resulting coating was composed of amorphous SiO2 and crystalline monoclinic (m) and tetragonal (t) ZrO2 phases. XRD analysis revealed that the porous outer layer developed at 30 mA/cm2 was dominated by the m phase. The percentage of the m phase decreased while the t phase increased with increasing current density. Therefore, the coating formed at 70 mA/cm2 showed the highest abrasive wear resistance, three times higher than the substrate. Similarly, the polarization curve and electrochemical impedance spectroscopy showed that the highest corrosion resistance, more than two orders of magnitude higher than the substrate, was obtained in the coated-70 mA/cm2 specimen. The use of low power and a mixed electrolyte is beneficial in producing PEO coating with high wear resistance and excellent anti-corrosion characteristic.