ZrO2 Nanopowders Research Articles

The Effect of Reinforcement Weight Ratios on the Mechanical Properties of ZrO2/ Unsaturated Polyester Nanocomposites

This work aims to prepare ZrO2/ unsaturated polyester nanocomposites with reinforcement weight percentage ratios (1, 2, 3, 4, 5, and 6) wt.% and study the effect of this reinforcement weight ratio on some mechanical properties such as hardness, impact strength, and tensile strength. The used powder has a monoclinic structure, P2/m space group, and unit cell parameters a, b, and c = 5.313Å, 5.210 Å, and 5.145 Å, receptively, and angels α, γ = 90º and β= 99.233º according to XRD data and using Dicvol 91 indexing program. The grain size of the used powder was estimated using Scherrer’s equation to be 43.2 nm. The SEM micrograph of ZrO2 nanopowder showed the particle morphology having homogenous irregular grains and appears to be similar to a coral shape. The results of the hardness test showed that increasing the reinforcement weight ratio led to an increase in the hardness values. Impact, tensile, and flexural strength values increase with the reinforcement weight ratio and peaked at 6 wt. %, and decreased at a higher ratio.

Effects of ZrO2 Nano-Particles' Incorporation into SnAgCu Solder Alloys: An Experimental and Theoretical Study.

This study investigates the mechanism and effects of incorporating different ZrO2 nano-particles into SAC0307 solder alloys. ZrO2 nano-powder and nano-fibers in 0.25-0.5 wt% were added to the SAC0307 alloy to prepare composite solder joints by surface mount technology. The solder joints were shear tested before and after a 4000 h long 85 °C/85% RH corrosive reliability test. The incorporation of ZrO2 nano-particles enhanced the initial shear force of the solder joint, but they decreased the corrosion resistance in the case of 0.5 wt%. SEM, EDS, and FIB analysis revealed intensive growth of SnO2 on the solder joint surfaces, leading to the formation of Sn whiskers. Density functional theory (DFT) simulations showed that, despite Sn being able to bond to the surface of ZrO2, the binding energy was weak, and the whole system was therefore unstable. It was also found that ZrO2 nano-particles refined the microstructure of the solder joints. Decreased β-Sn grain size and more dispersed intermetallic compounds were observed. The microstructural refinement caused mechanical improvement of the ZrO2 composite solder joints by dispersion strengthening but could also decrease their corrosion resistance. While ZrO2 nano-particles improved the solder joint mechanical properties, their use is recommended only in non-corrosive environments, such as microelectronics for space applications.

Laser synthesis of oxide nanoparticles with controlled gas condensation

In this work, the oxide nanopowders of Al2O3, ZrO2, Y2O3, Gd2O3, CeO2, and SiO2 were synthesized by CW CO2 laser vaporization technique with controlled gas condensation in an inert atmosphere. Methods for controlling the size of the resulting nanoparticles by adjusting the gas composition and pressure during the vaporization process have been demonstrated. The potential for producing ultrasmall oxide nanoparticles with dimensions less than 5 nm has been shown. The size distribution of nanoparticles taken from different parts of the evaporation-condensation tract was studied using scanning (SEM) and transmission (TEM) electron microscopy methods. The effect of synthesis conditions (pressure and composition of the inert gas) on characteristics of the nanoparticles is discussed. Using a wide class of simple oxides as the example, it is shown that the powders synthesized by the laser method consist of three types of particles: target spherical particles with a diameter of 3–20 nm (more than 98%), larger spherical particles with a diameter of 50–200 nm, and shapeless large particles with sizes more than 200 nm. The possibility of separating large particles from the main particles using the original labyrinth system for gas pumping is shown. The obtained particles with controlled sizes can be effectively used in various applications, in particular, for the preparation of catalysts and adsorbents.

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.

The phase-stabilized behavior of Sc2O3–Y2O3 co-doped ZrO2 nanopowders by co-precipitation synthesis

Single stabilizer-doped ZrO2 has drawbacks such as inferior mechanical properties and thermal stability, making it difficult to obtain ZrO2 ceramics with good density and high crystallinity. Thus, it is expected that ZrO2 is doped and modified by two or more stabilizers. In this paper, the Sc2O3–Y2O3–ZrO2 nanocomposite ceramic powders were prepared using ZrOCl2⋅8H2O, ScCl3⋅6H2O, and YCl3⋅6H2O as raw materials and polyvinylpyrrolidone as dispersant. They calcined at diverse temperaturesby the pressureless sintering-assisted co-precipitation method after being pressed into disc shape. Sc2O3 and Y2O3 were added as ZrO2 stabilizers to ameliorate the lack of insufficient mechanical properties and high-temperature stability of ZrO2 ceramics caused by single doping. To study the stability of the phases at high temperatures, the specimens were characterized by TG-DTG, XRD, Raman, SEM, FT-IR, etc. The effects of different pH valuesand different calcination temperatures on the Sc2O3–Y2O3–ZrO2 nanocomposite ceramics were investigated. It was demonstrated that ternary doping has very excellent phase stability. After calcination no monoclinic phase appeared, and the precursor samples were transformed from amorphous to a large amount of tetragonal phases and a few cubic phases. The samples at pH = 10 and calcination temperature of 1000 °C showed the best stabilization, the most uniform grain development, the best crystallinity, the most regular morphology, the highest tetragonal phase content of 89.2 %, the stabilization rate of 94.58 %, and the highest relative density of 98.75 %. The results show that this nanocrystalline powder can be used to prepare high-density nanoceramics. Furthermore, the activation energy for grain growth of Sc2O3–Y2O3–ZrO2 nanocomposite ceramics was calculated as 13.87 kJ/mol. This paper provides a theoretical and experimental research basis for the controlled synthesis of Sc2O3–Y2O3–ZrO2 nanocomposite ceramics using a pressureless sintering-assisted co-precipitation method.

Influence of microwave heating on grain growth behavior and phase stability of nano Y2O3/La2O3 co-doped ZrO2 ceramics

Y2O3-doped ZrO2 (YSZ) is a significant structural material and excellent functional material, it has been widely used in fields such as ceramics, thermal barrier coatings, and medical, etc. The disadvantage of YSZ is that it undergoes phase transition occurs during high-temperature cooling, leading to cracks in zirconia. It is worth mentioning that the failure phase transition of YSZ can be suppressed by the addition of rare earth oxide such as lanthanum oxide. In this paper, ZrO2 nano-powders with 0.2 mol% La2O3-2.8 mol% Y2O3 were prepared by a high-energy ball milling method. The comparison of microwave sintering and conventional sintering temperatures (800 °C–1300 °C) on the phase transition transformation of La2O3-doped Y2O3-stabilized zirconia powders was investigated by the control variable method. Meanwhile, the effects of microwave sintering technology on the microstructure and grain growth behavior of the sintered powders were further analyzed. The results show that microwave sintering is superior to conventional sintering technology. Microwave sintering promotes the rate of conversion of zirconia from monoclinic to tetragonal phase. Furthermore, the average grain size of the samples increased linearly with increasing temperature, and the grain growth further contributed to the presence of stable phases. Adding La3+ and Y3+ can reduce the grain growth activation energy and increase the contents of both the t-ZrO2 and c-ZrO2 in the sample. In this experiment, we find that the samples sintered best at 1200 °C with stable phase composition, well-defined morphology and uniform particle distribution. It is well known that the synthesis of high-quality zirconia materials is essential for good zirconia raw materials in practical production. This study provides an experimental and theoretical basis for the synthesis of zirconia powder with excellent performance.

Structural and optical analyses of hydrothermally synthesized ZrO2 nanopowder

In the present work, the hydrothermal method was used to synthesize mixed phase zirconium oxide (ZrO2) nanopowder. X-ray diffraction and scanning electron microscopy were employed for structural and morphological study, respectively. Fourier transform infrared spectroscopy confirms the presence of the Zirconium-Oxygen bond. To study the optical properties of ZrO2 nanopowder, Raman and Ultra-Violet visible spectroscopies were used at room temperature. The Tauc’s plot reveals that the average value of the optical bandgap is ∼ 3.4 eV. These studies of dual-phase ZrO2 nanopowder suggest that ZrO2 nanopowder can be a suitable candidate for many potential applications including optoelectronic devices and optical sensors.

In situ self-assembly preparation and characterization of CaO–ZrO2 nanopowders under vacuum

CaO–ZrO2 nanocomposite powders were prepared by in situ self-assembly method under vacuum. The effects of calcium oxide content on the physical phase composition and microscopic morphology of the as-prepared nanopowders were investigated. The results showed that the content of the tetragonal phase in the powders gradually increased with increasing calcium oxide content. When the calcium oxide content reached 10 wt%, the prepared CaO–ZrO2 nanopowders were a pure tetragonal phase with good dispersion and average particle size about 57 nm. In comparison to the situation in air, the amorphous carbon particles formed by the pyrolysis of organic matter under vacuum were evenly distributed on the surface of the nanocomposite particles or between them. In this way, direct contact of the nanoparticles was avoided, thus inhibiting their rapid growth at high temperatures and facilitating the formation of fine grains with high surface energy. The preliminary results indicated that the smaller average particle size and narrower particle size distribution of the nanocomposite powders prepared in vacuum were significantly beneficial for improving the bending strength of the nanoceramic products compared to that in air. It is expected to provide valuable information for further optimization of the controllable preparation of high-quality nanoceramic powders.

Sintering Properties of Tetragonal Zirconia Nanopowder Preparation of the NaCl + KCl Binary System by the Sol–Gel–Flux Method

Tetragonal zirconia nanopowders (3Y-TZP NPs) stabilized by 3 mol % Y2O3 were synthesized by a novel sol–gel–flux method. The effects of calcination temperature, Y2O3 content, and molten salt system (NaCl + KCl binary system and NaCl unary system) on the phase composition and morphology of nanopowders (NPs) were investigated. Meanwhile, the sintering properties of the prepared 3Y-TZP NPs were studied. The 3Y-TZP NPs and sintered ceramics were characterized by thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, and X-ray fluorescence (XRF) spectroscopy. The results show that the optimum calcination temperature for obtaining dispersed ZrO2 NPs is reduced from 800 to 660 °C when the NaCl unary system is substituted by the NaCl + KCl binary system. 3Y-TZP NPs with a single tetragonal phase are obtained in the NaCl + KCl binary system when Y2O3 content in the raw material is 5 mol %. The average particle size of the obtained ZrO2 NPs is reduced from 47.25 nm in the unary system to 26.18 nm in the binary system because of the lower calcining temperature. Furthermore, the 3Y-TZP NPs obtained in the binary system have narrower particle size distribution and better sintering performance than ZrO2 NPs obtained in the unary system. After sintering for 4 h at 1200 °C, the former generated 3Y-TZP ceramics with higher density and finer grain size. This work produced narrow-distributed well-dispersed 3Y-TZP NPs with quasi-spherical morphology, which are good candidates for the applications, including oxygen sensors and thermal barrier coatings.

A Comparison between Solution-Based Synthesis Methods of ZrO2 Nanomaterials for Energy Storage Applications

The present study is focused on the synthesis of zirconium dioxide (ZrO2) nanomaterials using the hydrothermal method assisted by microwave irradiation and solution combustion synthesis. Both synthesis techniques resulted in ZrO2 powders with a mixture of tetragonal and monoclinic phases. For microwave synthesis, a further calcination treatment at 800 °C for 15 min was carried out to produce nanopowders with a dominant monoclinic ZrO2 phase, as attested by X-ray diffraction (XRD) and Raman spectroscopy. The thermal behavior of the ZrO2 nanopowder was investigated by in situ XRD measurements. From the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, the presence of near spherical nanoparticles was clear, and TEM confirmed the ZrO2 phases that comprised the calcinated nanopowders, which include a residual tetragonal phase. The optical properties of these ZrO2 nanopowders were assessed through photoluminescence (PL) and PL excitation (PLE) at room temperature (RT), revealing the presence of a broad emission band peaked in the visible spectral region, which suffers a redshift in its peak position, as well as intensity enhancement, after the calcination treatment. The powder resultant from the solution combustion synthesis was composed of plate-like structures with a micrometer size; however, ZrO2 nanoparticles with different shapes were also observed. Thin films were also produced by solution combustion synthesis and deposited on silicon substrates to produce energy storage devices, i.e., ZrO2 capacitors. The capacitors that were prepared from a 0.2 M zirconium nitrate-based precursor solution in 2-methoxyethanol and annealed at 350 °C exhibited an average dielectric constant (κ) of 11 ± 0.5 and low leakage current density of 3.9 ± 1.1 × 10−7 A/cm2 at 1 MV/cm. This study demonstrates the simple and cost-effective aspects of both synthesis routes to produce ZrO2 nanomaterials that can be applied to energy storage devices, such as capacitors.

Modified room temperature solid-state synthesis of yttria-stabilized zirconia (YSZ) nano-powders for solid oxide fuel cells

High-performance solid oxide fuel cell (SOFC) is in urgent need of high-quality electrolyte powders with high reactivity and chemical uniformity. Here, 8 mol% Y2O3 doped ZrO2 (YSZ) nano-powders were synthesized by an improved solid-state reaction method at ambient temperature, and were applied to the fabrication of SOFC electrolytes. YSZ nano-powders show average grain sizes of ∼20 nm and high dispersibility, which is comparable with or even better than some other chemical methods. Benefitting from their high reactivity, dense YSZ electrolytes (relative density of 97.9%) can be obtained at a relatively low sintering temperature of 1400 °C. The optimized electrical conductivity reaches up to a high value of 0.034 S/cm at 800 °C in air. The anode supported single cell with the construction of Ni-YSZ/YSZ/Sm0.2Ce0.8O2–δ (SDC)/La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) exhibits the peak power density of 0.827 W/cm2 at 800 °C while taking wet H2 as fuels and ambient air as oxidants.

Co-precipitation of nano Mg–Y/ZrO2 ternary oxide eutectic system: Effects of calcination temperature

In the family of inorganic nanomaterials, zirconia is a highly promising functional ceramic with a high refractive index, hardness, and dielectric constant, as well as excellent chemical inertness and thermal stability. These properties are enhanced in nano-zirconia ceramics, because nanopowders have a small particle size, good morphology, and uniform and dispersive distribution. In this study, a co-precipitation process was proposed to synthesise highly dispersed MgO–Y2O3 co-stabilized ZrO2 nanopowders. The effects of different calcination temperatures on the crystallisation degree and particle dispersion of zirconia nanopowders were characterised by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption using the Brunauer–Emmett–Teller (BET) theory, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The optimum synthesis conditions were obtained as follows: 6 h of high-energy planetary grinding and calcination at 800 °C in an electric furnace. Under these optimum conditions, the average particle size of the prepared powder was 28.7 nm. This process enriches the literature on the controllable preparation of Mg–Y/ZrO2 nanopowders obtained by the co-precipitation method.

Properties of ZrO2 and Ag–ZrO2 nanopowders prepared by pulsed electron beam evaporation

ZrO2 and Ag doped ZrO2 powders were prepared from mixtures of ZrO2 and AgNO3 commercial powders (99:1 and 95:5 wt %) by pulsed electron beam evaporation (PEBE) in vacuum. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), textural and magnetic analysis, photocatalytic test, photoluminescence spectroscopy (PL) and cell cytology (Vero and Hela). XRD analysis confirmed the presence of monoclinic ZrO2 phase and cubic Ag phase in the final product. НRTEM pictures showed a large range of particle sizes approximately from 10 to 500 nm; the spherical silver nanoparticles (NPles) (10 nm) were observed on the ZrO2 particle surfaces. Ferromagnetic contribution in pure ZrO2 powder was 0,002 emu/g, and in Ag doped ZrO2 powders it reached 0,016 emu/g. It was found that Ag doped ZrO2 powders showed increased photocatalytic activity in methyl orange (MO) compared with pure ZrO2 NPles. The produced powders can be used to kill Hela cancer cells, as low (<0.1 wt) Ag photocatalysts and in other applications.

Reversible Martensitic Phase Transition in Yttrium-Stabilized ZrO2 Nanopowders by Adsorption of Water

The present study was aimed at revealing the influence of the mechanical stress induced by water molecule adsorption on the composition of crystalline phases in the ZrO2 + 3 mol% Y2O3-nanoparticles. Three basic methods were used to determine the phase transition: neutron diffraction, Raman microspectroscopic scanning, and X-ray diffraction. The fact of reversible phase-structural β → α transformation and the simultaneous presence of two polymorphic structural modifications (β is the phase of the tetragonal syngony and α of monoclinic syngony in nanosized particles (9 nm)) under normal physical conditions was established by these methods. An assumption was made regarding the connection of the physical mechanism of transformation of the extremely nonequilibrium surface of nanoparticles with electronic exchange of the material of the near-surface layer of nanoparticles with the adsorption layer through donor–acceptor interaction. The principal possibility of creating direct-acting hydroelectric converters based on nanoscale YSZ (Yttria-Stabilized Zirconia) systems due to the reversible character of the considered effect was shown.

Армированные одностенными углеродными нанотрубками композиты на основе ZrO2, полученные свободным вакуумным спеканием

The results of a study of sintered composites based on yttria-stabilized zirconia (ZrO2) reinforced with single-walled carbon nanotubes (SWCNTs) are presented in this paper. Mixing of ZrO2 nanopowder with SWCNTs was carried out in ethanol using an ultrasonic bath and a magnetic stirrer. Composite powders with 0.1, 0.5 and 1 wt.% SWCNTs and ZrO2 nanopowder were pressed into compacts at a pressure of 100 MPa, and then they were sintered in a high temperature vacuum furnace for 2 h at a temperature of 1500°C with a heating rate of 300°C / h. Changes in the microstructure, phase composition, and mechanical properties were investigated depending on the SWCNT content in the samples. It was found that in the selected sintering mode, high density samples (99.2 – 97.5 %) were obtained. It was found by scanning electron microscopy that undivided, entangled SWCNT bundles / aggregates and individual nanotubes, which together formed a continuous reinforcing structure, were observed in the microstructure of the composites. Moreover, SWCNTs led to the refinement of the microstructure of composites; the average grain size of composites was 16 % lower than that of ZrO2 ceramics. It was found by X-Ray diffraction that only high temperature modifications of zirconia (cubic and tetragonal) were present in ZrO2 ceramics and composites, and SWCNTs led to a slight decrease in the size of coherent scattering domain. It was found by the Vickers indentation method that the composite based on ZrO2 with 0.5 wt.% SWCNT was optimal in terms of mechanical properties, since it had the highest microhardness (13.6 GPa, which was 6 % higher than that of ZrO2 ceramics) and had a 12 % higher fracture toughness.

Влияние технологии спекания нанопорошков на трещиностойкость тетрагонального диоксида циркония

The effect of various technological conditions of the preparation of samples from ZrO2 ceramics stabilized by various additives of yttrium oxide Y2O3 on the fracture toughness of the material has been investigated. Various modes of sintering of samples obtained by the method of co-deposition of nanopowders of zirconium dioxide ZrO2 and yttrium oxide Y2O3 were performed. An original technique for calculating the critical stress intensity factor from the test data of double cantilever beam specimens with a chevron notch by the wedging method is described. A characteristic feature of the loading diagrams for ceramics based on zirconium dioxide stabilized by additives of yttrium oxide is the presence of a stage of inelastic deformation, which develops without cracking. The mechanism of inelastic deformation is based on the phase transition of the tetragonal modification to the monoclinic modification of the crystal structure. For each mode, the values of fracture toughness characteristics are determined. Ceramics with the composition ZrO2 + 3 mol% Y2O3 (KIc = 6.86 MPa ∙ m1/2) exhibit the maximum crack resistance at a sintering temperature Tsint =1500°C for an hour. Deviation from the composition of 3 mol% Y2O3 reduces the fracture toughness. The increase in fracture toughness is favored by the grinding of the powder in a planetary mill. It is generally accepted that mechanical stresses arising at the top of a growing microcrack cause all round compression stresses, since the phase transformation is accompanied by an increase in the unit cell volume by 4%. This stabilizes the microcrack, slowing down its growth. This point of view was confirmed due to the well-known fact that when zirconium dioxide is cooled from 950°C to room temperature during the t → m transition, microcracks are intensively formed in the bulk of the material. However, when wedging a two-cantilever specimen with a chevron notch, the probability of the formation of compression stresses is small. This is also evidenced by the absence of cracking throughout the inelastic stage of material deformation. In the fine-crystalline structure of zirconium ceramics under loading, favorable conditions arise for the relaxation of shear stresses through the t → m transition.

Sol-Gel Synthesis and Characterization of YSZ Nanofillers for Dental Cements at Different Temperatures.

Background: Yttria-stabilized zirconia nanoparticles can be applied as fillers to improve the mechanical and antibacterial properties of luting cement. The aim of this study was to synthesize yttria-stabilized zirconia nanoparticles by the sol–gel method and to investigate their composition, structure, morphology and biological properties. Methods: Nanopowders of ZrO2 7 wt% Y2O3 (nY-ZrO) were synthesized by the sol–gel method and were sintered at three different temperatures: 800, 1000 and 1200 °C, and their composition, size and morphology were investigated. The biocompatibility was investigated with human gingival fibroblasts (hGFs), while reactive oxygen species (ROS) production was evaluated through fluorescence analysis. Results: All synthesized materials were composed of tetragonal zirconia, while nanopowders sintered at 800 °C and 1000 °C additionally contained 5 and 20 wt% of the cubic phase. By increasing the calcination temperature, the crystalline size of the nanoparticles increased from 12.1 nm for nY-ZrO800 to 47.2 nm for nY-ZrO1200. Nano-sized particles with good dispersion and low agglomeration were received. Cell culture studies with human gingival fibroblasts verified the nanopowders’ biocompatibility and their ROS scavenging activity. Conclusions: the obtained sol–gel derived nanopowders showed suitable properties to be potentially used as nanofillers for dental luting cement.

Phase and photoluminescence analysis of dual-color emissive Eu3+-doped ZrO2 nanoparticles for advanced security features in anti-counterfeiting

In the present work, lower concentration-based dual-color emissive Eu3+-doped ZrO2 loose nanosized particles have been developed via precipitation method with sodium borohydride for the potential use of advanced security in anti-counterfeiting application. Stabilization of tetragonal zirconia up to moderate temperature has been explored considering lower Eu3+-concentration, particle size, and strain. Different phases of Eu3+-doped zirconia phosphors induce variation in photoluminescence characteristics such as photoluminescence emission, asymmetric ratio i.e. intensity of red to orange emission ratio, Commission International de I'Eclairage i.e. CIE chromaticity coordinates, and color emission. Also, phases of Eu3+-doped zirconia may produce multi-color emission, including white light depending on Eu3+-concentration, calcination temperature, and excitation wavelength. Photoluminescence emission spectra have been investigated at the excitation wavelengths of 254 nm, 365 nm, 393 nm, and 463 nm. Change in the peak position of the transition 5D0→7F2 and 5D0→7F1 in emission spectra indicates the presence of either mixed-phase or tetragonal zirconia polycrystals in Eu3+-doped zirconia samples. It was mainly due to the unlike site symmetry position of Eu3+-ions in different phases of Eu3+-doped zirconia. The intensity variation of the transitions in different phases of Eu3+-doped zirconia affects the asymmetric ratio, and thus produces shades of dual color emission, including near-white. In addition, the dual-color emissive sample, i.e., 0.5 mol% Eu3+-doped ZrO2 nanopowders, has been explored for anti-counterfeiting applications using a standard screen-printing technique.

Phase and luminescence behaviour of Ce-doped zirconia nanopowders for latent fingerprint visualisation

Present work focuses on the phase evolution, emission behaviour of Ce-doped zirconia nanopowders, calcined under air and argon atmosphere and its application in latent fingerprint visualisation. The different concentration of Ce-doped ZrO2 nanoparticles were prepared via precipitation method using sodium borohydride and calcined at 600 °C under air and argon atmosphere. The tetragonal phase of zirconia was detected for all samples under air atmosphere. However, the crystalline phase of tetragonal zirconia was observed for above 1 mol% Ce-doped ZrO2 samples, calcined under argon atmosphere. A broad photoluminescence emission was observed in the UV and visible range for all samples due to 5D3/2 →7FJ transitions (J = 7/2 and 5/2) of Ce3+ ions. The increase of Ce-concentration causes more distortion in the tetragonal structure of zirconia, and provides an enhanced emission intensity under air atmosphere. However, the emission intensity was found to be similar under argon atmospheric condition due to lower crystallinity of t-zirconia. Further, all the samples lie in the violet-bluish region of the CIE-diagram. The latent fingerprint visualisation was explored using Ce-doped ZrO2 nanopowders on both non-porous and porous surface, and the obtained results validate its use in the forensic applications.

Fabrication of Al2O3–ZrO2 ceramics with high porosity and strength

This study describes the synthesis of ceramics, in which a micrometre-sized Al2O3–ZrO2 nanopowder was used as an oxide base for the hardening of the materials. To a suspension of this mixed metal oxide, the pore-forming crystallisation additives camphor and carbamide were added to produce ceramics with thin permeable pores. Camphor crystallised in the oxide suspension in the form of single pentagonal stars and сarbamide crystallised in the form of thin elongated needles. The use of the different crystallisation additives allowed the formation of ceramics after sintering that have both permeable and complex pore morphologies, where anisotropic properties were observed using carbamide as an additive but not when camphor was used. The total porosity of the resulting ceramics was 51.3%, with a compressive strength in the range of 17.3–92.3 MPa.