Controllable synthesis of metastable tetragonal zirconia nanocrystals using citric acid assisted sol–gel method

Metastable tetragonal ZrO₂ nanoparticles and nanosheets were synthesized with citric acid assisted sol–gel method. In this approach, zirconium acetylacetonato, Zr(acac)₂, citric acid (CA) and ethylene glycol (EG) were used as the source of Zr⁴⁺, the chelating, and solvent agent, respectively. The effects of heat treatment on zirconia phase evolution were investigated. We demonstrate that pure tetragonal nanocrystalline zirconia can be obtained with CA: EG mole ratio=5:1 and calcination temperature 490 °C. The microstructure of the products was characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and Raman scattering. Finally, Photoluminescence (PL) of nanosheets and nanoparticles were also investigated.     

Synthesis and optical properties of pure monoclinic zirconia nanosheets by a new precursor

Pure monoclinic zirconia nanosheets were successfully prepared by the polymeric complex method. In this approach, zirconium acetylacetonato, Zr(acac)₄, citric acid (CA) and ethylene glycol (EG) were used as the source of Zr⁴⁺ and the chelating and polymerization agent, respectively. The effects of heat treatment and EG:CA ratios on the structure, morphology and zirconia particle size were investigated. UV–vis spectra illustrated that ZrO₂ nanosheets did not show any extrinsic states aroused from surface trap states, defect states, or impurities.     

Synthesis and Characterization of Hierarchical Biomorphic Mesoporous TiO2 Nanosheets Using Caltrop-Stem as Biotemplate

Biomorphic TiO₂ nanosheets with hierarchical mesoporous structures were synthesized through facile infiltration and thermal decomposition using caltrop stems as biotemplates. Thermo-gravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscope, atomic force microscopy, N₂ adsorption–desorption equipment and UV–visible diffuse reflectance spectra were applied to characterize the microstructures of the samples. Results indicate that the as-synthesized TiO₂ nanosheets with thickness of about 5 nm are composed of anatase phase. The surfaces of TiO₂ nanosheets were constructed by a large number of mesopores, which pore diameter is in the range of 3.5–9 nm. Compared to TiO₂ powders (P25), the as-synthesized TiO₂ nanosheets exhibit a clear red shift (20 nm) showing an enhanced visible photocatalytic activity. The photocatalytic activity of the TiO₂ nanosheets for the decolorization of methylene blue under sunlight irradiation is superior to P25 powders.     

Synthesis and characterization of nanocrystalline zirconia powder by simple sol–gel method with glucose and fructose as organic additives

The present study has devised the sol–gel method using glucose and fructose as two organic additives so as to synthesize zirconia nanoparticles. The presence of these organic additives has produced some positive effect on the phase transition from tetragonal to monoclinic and played an important role in the morphology and crystallite size of the nanoparticles. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr bond. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles with small size, containing both tetragonal and monoclinic phases with crystallite size between 10 and 30 nm.     

Submicro-zirconia crystal-intergrown zircon opaque glaze

Zircon opaque glaze is widely used in sanitary and building ceramic products due to its high-temperature stability. Massive amounts of zircon are consumed by the ceramic industry yearly. In this work, a method to reduce zircon consumption and enhance opaque effect was proposed by intergrowth of submicro zirconia. Alumina was added to a K–Na–Ca–Al–Si–Zr system glaze to prepare a 5 wt % content highly opaque glaze, where zirconia coexisted with zircon. The crystallization behavior, opacification properties, and Vickers hardness of the glaze were investigated. Back-scattered electron images showed that when Al₂O₃ addition increased into more than 13 wt %, abundant of submicro zirconia crystals would intergrow with zircon crystals. The glaze containing 13 wt % Al₂O₃ had an L* value of 96.76 ± 0.27 after being fired at 1220 ℃.     

Mass spectrometric study of the laser-evaporated Fe–Zr–O system up to 3300 K

Material systems such as U–Zr–O, Fe–Zr–O, and Zr–O have been recognized as fundamental for the analysis of in-vessel nuclear fuel debris behavior during a severe meltdown accident. In the present work, the evaporation behavior of ZrO₂ and Zr–Fe–O systems are investigated using heating with laser pulses of millisecond duration and time-of-flight mass spectrometry. The relative partial pressures of main species of vapor over ZrO₂ and ZrO₂–FeO systems were measured at temperatures above 2750 K. The temperature dependence of O/Zr atomic ratio in vapor over zirconia was analyzed: it turned out that evaporation occurs in a noncongruent mode at temperatures above 3000 K. Evaporation of the Zr–Fe–O system was greatly affected by the fast evaporation of FeO, implying that the atomic Zr/Fe ratio, less than 0.1 below 3000 K, significantly increased with temperature. Moreover, the ratios of main vapor components were defined only by the surface temperature, independent of the zirconia sample origin.     

Palladium Migration Through a Zirconium Carbide Coating in TRISO‐Coated Fuel Particles

Reaction of ZrC with Pd at temperatures up to 1500°C was examined using ZrC/Pd composite, Pd/ZrC‐coated TRISO particles, and Pd/ZrC bulk diffusion couples experiments. Intermetallic phase (Pd₃Zr) and amorphous carbon at the ZrC–Pd interfaces were identified by X‐ray diffraction (XRD), Raman and scanning electron microscope (SEM). Moreover, thicknesses of Pd₃Zr layers were measured by energy‐dispersive X‐ray spectrometry (EDS). The validity of the reaction was proved by thermodynamic calculation. The reaction kinetics parameters, i.e., the activation energy (208.2–266.5 kJ/mol) and the reaction order (3.38–3.78) for Pd attacking through a ZrC coating in TRISO particles were determined based on both the DSC curves and the growth of the Pd₃Zr layer.     

ZrB2–SiC–G Composite Prepared by Spark Plasma Sintering of In‐Situ Synthesized ZrB2–SiC–C Composite Powders

To avoid introduction of milling media during ball‐milling process and ensure uniform distribution of SiC and graphite in ZrB₂ matrix, ultrafine ZrB₂–SiC–C composite powders were in‐situ synthesized using inorganic–organic hybrid precursors of Zr(OPr)₄, Si(OC₂H₅)₄, H₃BO₃, and excessive C₆H₁₄O₆ as source of zirconium, silicon, boron, and carbon, respectively. To inhabit grain growth, the ZrB₂–SiC–C composite powders were densified by spark plasma sintering (SPS) at 1950°C for 10 min with the heating rate of 100°C/min. The precursor powders were investigated by thermogravimetric analysis–differential scanning calorimetry and Fourier transform infrared spectroscopy. The ceramic powders were analyzed by X‐ray diffraction, X‐ray photoelectron spectroscopy, and scanning electron microscopy. The lamellar substance was found and determined as graphite nanosheet by scanning electron microscopy, Raman spectrum, and X‐ray diffraction. The SiC grains and graphite nanosheets distributed in ZrB₂ matrix uniformly and the grain sizes of ZrB₂ and SiC were about 5 μm and 2 μm, respectively. The carbon converted into graphite nanosheets under high temperature during the process of SPS. The presence of graphite nanosheets alters the load‐displacement curves in the fracture process of ZrB₂–SiC–G composite. A novel way was explored to prepare ZrB₂–SiC–G composite by SPS of in‐situ synthesized ZrB₂–SiC–C composite powders.     

Synthesis of non-porous and nanocrystalline lanthana-doped zirconia layers by MOCVD method at low temperatures and pressure

Amorphous and nanocrystalline lathana-doped zirconia layers were synthesized by the MOCVD method using La(tmhd)₃ and Zr(tmhd)₄ as reactants on planar and tubular quartz glass substrates. The synthesis temperature was in the range of 500–700 °C. The gas pressure in the CVD reactor was modified between 3 × 10³ and 6 × 10³ Pa. Argon and air were used as carrier gases. Air was also necessary for oxidation of carbon, which is a solid by-product of reactant pyrolysis. Other synthesis parameters were selected in order to obtain a value of the extended criterion Gr_x/Re_x² below 0.01. Then, laminar gas flow in the CVD reactor will be maintained. The surface, as well as the cross-section of deposited layers were observed using a scanning electron microscope (SEM). Their chemical composition was investigated by means of EDS analysis. XRD investigations on obtained layers were also performed. There was correlation between the chemical composition of reactants and obtained layers when the synthesis process was controlled by reactant diffusion to the substrate. The phenomenon of La³⁺ ion segregation in obtained layers was also observed. The layers exhibited good adhesion to the substrate.     

Hydrothermal synthesis of monoclinic zirconia sol

In this study, we demonstrate a synthetic method of zirconia sol using ZrO(NO₃)₂·xH₂O as Zr⁴⁺ precursor, tetramethylammonium hydroxide as mineralizer, and oxalic acid as a complexing agent. X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and UV–vis adsorption spectroscopy were used to characterize the nanocrystals. The effect of oxalic acid content on the growth of zirconia nanocrystals was investigated. Zirconia sol cannot be synthesized without oxalic acid. The oxalic acid content has no obvious effect on the phase formation of monoclinic zirconia. The transparent and monoclinic zirconia sol with particle size <10 nm was synthesized. This provides a new hydrothermal system for the synthesis of zirconia sol.     

Thermal stability of nanostructured 13 wt% Al2O3–8 wt% Y2O3–ZrO2 thermal barrier coatings

Nanostructured 13 wt% Al₂O₃–8 wt% Y₂O₃–ZrO₂ (13AlYSZ) coatings were developed by atmospheric plasma spraying (APS). The phase structure and the morphology of the 13AlYSZ coatings were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). It was found that the as-sprayed coatings mainly consisted of tetragonal zirconia, with the Al element solid solution in ZrO₂. Heat treatment at 1100 °C increased the average grain size of the ZrO₂ phase from 61 to 120 nm and decreased the porosity from 23.8 to 18%. The addition of the nano-Al₂O₃ can effectively inhibit the grain growth of the zirconia phase. The mechanism on inhibiting the grain growth of nanostructured 8 wt% Y₂O₃–ZrO₂ thermal barrier coatings has been discussed in detail.     

Phase Evolution of SiO2–Al2O3–ZnO–CaO–ZrO2–TiO2‐Based Glass with Added Y‐PSZ Particles

Yttria partially stabilized zirconia Y‐PSZ/glass‐ceramic composites were prepared by reaction sintering using powder mixtures of a SiO₂–Al₂O₃–ZnO–CaO–ZrO₂–TiO₂‐based glass and yttria partially stabilized zirconia (Y‐PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass‐ceramic matrix for high‐temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass‐ceramic material with dispersed zircon particles was prepared in situ. Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid‐like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass‐ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y‐PSZ/glass‐ceramic composites.     

Controllable synthesis of pure monodispersed zirconia nanopowders with tetragonal phase

Nanopowders of pure zirconia have been synthesized using citric acid (CA)-assisted lamellar liquid crystal template method. The microstructure of the zirconia powder prepared at the different mole ratios of CA to zirconium oxynitrate (ZN) was characterized by FT-IR, X-ray diffraction (XRD), laser particle size analyzer, Raman spectroscopy, and scanning electron microscope (SEM) methods. The phase structure of the sodium dodecyl sulfate (SDS)/C₁₀H₂₁OH/H₂O system before and after adding mixing solution CA and ZN was determined by POM (Polarizing Optical Microscope). The results show that lamellar structure of the SDS/C₁₀H₂₁OH/H₂O system after adding mixing solution CA and ZN is stable. The presence of CA inhibits agglomeration and growth of zirconia particle. The crystallite size of zirconia powders decreases and agglomerates lowly with addition of CA. Fourier transform infrared spectrometry (FI-IR) analyses reveal that the structure of chelating organic complex is maintained in zirconia structure at high-temperature calcination to cause oxygen vacancies which stabilizes the tetragonal phase of zirconia. The zirconia powders remained the single metastable tetragonal phase at the molar ratios of CA to ZN ranging from 1:3 to 5:1. The crystallite size of zirconia with spherical morphology varied from 32.2 to 20.1 nm with the increase of the molar ratio of CA to ZN in the range of 1:3 to 5:1.     

CHARACTERIZATION OF ZIRCONIA POWDER SYNTHESIZED VIA REVERSE MICROEMULSION PRECIPITATION

A two-reverse-microemulsion precipitation technique was applied to synthesize nanocrystalline tetragonal zirconia using H₂O solution/CTAB/hexanol as the microemulsion system. Two solutions of reverse microemulsion, one containing Zr⁴⁺ aqueous droplets and the other aqueous ammonia droplets with the same water/surfactant ratio, were prepared separately and mixed together to form a slurry of nanosized ZrO₂ precursors, which filled the matrix of the surfactant, CTAB. The precursors were recovered, calcined to form nanocrystalline zirconia powder, and then characterized by using a transmission electron microscope to determine the particle size, a scanning electron microscope to examine the microstructure of the zirconia powder, and an X-ray diffractometer to determine the crystal phase and crystallite size. It is concluded that the primary particle size of the precursor determines the transformation temperature of the precursor and the crystal structure of the calcined zirconia.     

Effect of ceria and zirconia nanoparticles on corrosion protection and viscoelastic behavior of hybrid coatings

Organic–inorganic hybrid nanocomposite coatings contain inorganic particles that are dispersed in organic phase in nanometric dimensions. Ceria and zirconia colloidal dispersions are uniformly distributed in the epoxy silica-based hybrid nanocomposite by sol–gel method and coated on 1050 aluminum alloy substrate with spin-coating technique. The hybrid sol is prepared by organic–inorganic precursors formed by hydrolysis and condensation of 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate (TEOS) in acidic solution using bisphenol A as networking agent and 1-methylimidazole as initiator in the presence of various ratios of ZrO₂ and CeO₂ colloidal nanoparticles. Particle size distribution, surface morphology and inorganic components distribution were determined by scanning electron microscopy (SEM) and EDXA techniques. SEM and Si, Zr, Ce mapping micrographs proved the uniform distribution of nanoparticles in the coatings. Transmission electron microscopy indicated that the nanoparticles dimension stay at the nanoscale level. The glass transition temperature (T _g) and loss properties (damping) of coatings were evaluated by dynamic mechanical thermal analysis. The corrosion protection of the coatings on the 1050 AA substrate was studied by potentiodynamic measurements. The results indicated that by introducing ceria nanoparticles in 1:1 molar ratio to TEOS in coating composition, corrosion protection was improved. However, the simultaneous presence of two nanoparticles (i.e., ceria and zirconia in 1:1 molar ratio) in the coating compositions increased the corrosion protection efficiency up to 99.8 %. The multiple glass transitions and shifting to higher and wide range of temperatures by adding ceria and zirconia nanoparticles indicated a better network interaction between inorganic nanoparticles and organic molecular chains which also led to better corrosion protection of the coating in this composition.     

Microstructure,optical and magnetic properties of Zr-doped SnO synthesized by the hydrothermal method

Sn_1?xZr_xO was successfully synthesized by the one-step hydrothermal method. X-ray diffraction and Raman patterns reveal that the lattice distortion of SnO occurs with an increase in Zr concentration, and Zr ions are located at the substituted (Zr_Sn) and interstitial (Zr_i) sites successively. Scanning electron microscope and transmission electron microscope images showed that Zr concentration does not affect the well-crystalline nature of Sn_1?xZr_xO. However, the system's morphology changes from three-dimensional flowerlike to two-dimensional sheetlike. Furthermore, X-ray photoelectron spectroscopy and Raman spectra indicate that there are inherent oxygen vacancies (V_O) in pure SnO lattice. UV–Visible absorption spectra show that the optical bandgap first decreases and then increases with Zr doping, which is explained by the sp–d exchange interactions in the case of Zr_Sn and the Burstein–Moss effect in the case of Zr_i. Additionally, Sn_1?xZr_xO samples exhibit room temperature ferromagnetism (RTFM), and the magnetic variation couples with the variation of the relative intensity of the Raman vibration modes. From the experimental results and the first-principles calculations, it can be seen that V_O and the exchange interaction between Zr 4d and O 2p states are accountable for the RTFM of Sn_1?xZr_xO. Meanwhile, the lattice distortion and the Zr–O–Zr super-exchange interaction caused by excessive doping could decrease FM.     

Rapid synthesis and characterization of advanced ceramic-polymeric nanocomposites for efficient photocatalytic decontamination of hazardous organic pollutant under visible light and inhibition of microbial biofilm

Ceramic-polymeric 3C–silicon carbide-graphitic carbon nitride (3C–SiC@g-C₃N₄) nanocomposites were synthesized by decorating cubic phased, ceramic 3C-Silicon carbide (3C–SiC) on the framework of the nanosheets of metal free polymeric graphitic carbon nitride (g-C₃N₄) by single step pulsed laser ablation in liquid (PLAL) method. Morphological, structural, elemental and optical characterizations of the synthesized 3C–SiC@g-C₃N₄ nanocomposites were carried out. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) studies confirm the perfect anchoring of 3C–SiC on g-C₃N₄ nanosheets in 3C–SiC@g-C₃N₄ nanocomposites synthesized by PLAL method. Ultra-violet diffuse reflectance spectra (UV-DRS) of 3C–SiC@g-C₃N₄ indicated the enhancement of visible light absorption and also the narrowing down of band gap energy in 3C–SiC@g-C₃N₄ nanocomposites, as a result of the anchoring of 3C–SiC on g-C₃N₄. Also we noticed the decrease of photoluminescence (PL) emission intensities in the PL spectra of 3C–SiC@g-C₃N₄ with respect to pure g-C₃N₄, which indicates the reduced photo-induced charge recombination by the presence of 3C–SiC content on g-C₃N₄ nanosheets. In the application side, PLAL synthesized 3C–SiC@g-C₃N₄ nanocomposites exhibited enhanced visible light driven photocatalytic degradation of methylene blue dye in water, improved antibacterial activity against Pseudomonas aeruginosa (gram-negative) and Staphylococcus aureus (gram-positive) bacteria, and also served as better inhibiting agent for biofilm formation, compared to pure g-C₃N₄ nanosheets. It is quite obvious from our studies that this ceramic-polymeric nanocomposite, 3C–SiC@g-C₃N₄ has the potential application for antibacterial and anti-biofilm activities in addition to its remarkable photocatalytic performance.     

Microstructure and synthesis mechanism of dysprosia-stabilized zirconia nanocrystals via chemical coprecipitation

In this study, zirconia (ZrO₂) and dysprosia-stabilized zirconia (DySZ) nanocrystals were synthesized using a chemical coprecipitation method. The crystal structure and micromorphology of the as-synthesized powders, as well as the structural evolution from precursors to oxides were investigated, and the synthesis mechanism was also examined. Results show that pure ZrO₂ powders mainly comprise the monoclinic ZrO₂ phase with trace tetragonal ZrO₂, while the DySZ powders exhibit a tetragonal ZrO₂ structure. In addition, the crystal growth rate of DySZ is far slower than that of the pure ZrO₂ under elevated calcination temperature. The addition of Dy could significantly improve the phase stability of DySZ powder and effectively inhibit the crystal growth of DySZ. In the DySZ precursor, the binding energy of chemical bonds is significantly difference than in the ZrO₂ precursor. A composite hydroxide can be formed with -Zr-OH-Dy- and -Zr-OH-Zr- units in the tetramer structure because of the in-situ substitution of Zr by Dy atoms. Both the ZrO₂ and DySZ precursors exhibit analogous dehydration and crystallization behaviours in calcination process. Dy-doping plays a significant role in stabilizing both the intermediate product and the DySZ crystal.     

In situ synthesis of ultrathin 2-D TiO2 with high energy facets on graphene oxide for enhancing photocatalytic activity

Two kinds of TiO₂ with novel structures, interpenetrating anatase TiO₂ tablets (IP-TiO₂), and overlapping anatase TiO₂ nanosheets (OL-TiO₂) with exposed {0 0 1} facets, are synthesized. The graphene oxide (GO) supported ultrathin TiO₂ nanosheets (OL-TiO₂/GO) is also prepared by one-pot hydrothermal method. The microscopic feature, morphology, phase, and nitrogen adsorption–desorption isotherms are characterized. The performance of photocatalytic degradation of methyl blue is also measured. Compared with IP-TiO₂, the OL-TiO₂ with GO possess higher photocatalytic efficiency. The GO can improve the photocatalytic property by increasing specific surface area, accelerating the separation of electron–hole pairs, as well as extending the electron life. The growth process of TiO₂ nanosheets on graphene oxide layers probably follows a step-growth mechanism with F⁻ as morphology controlling agent. The steps on the surface can improve the photocatalytic activity further due to the increase of dangling bonds of 5-coordinated Ti (Ti_5c) which are considered to be the active sites in the photocatalytic reaction.     

Phase Transformation Behavior of a Pyrochlore‐Type CeO2–ZrO2 Binary Compound

The phase transformation behavior of the superlattice structure of a CeO₂–ZrO₂ pyrochlore‐type binary compound (CP) was investigated so as to better understand how to improve the thermal stability of such a system. CP was synthesized through high‐temperature reduction of a conventional CeO₂–ZrO₂ solid solution with a 1:1 molar ratio of Ce and Zr. High‐resolution transmission electron microscopy and selected‐area electron diffraction clearly revealed that the pyrochlore structure of CP transformed to the standard disordered cubic fluorite or tetragonal zirconia structure after having been subjected to a high‐temperature durability test; moreover, it was determined that this phase transformation moves inward from the crystallite surface. This discovery suggests a new method by which to improve upon this material for practical applications.