Nanocrystalline ZrO2 Powders Research Articles

Environmentally friendly production, characterization, and utilization of ZrO2 nanoparticles for the adsorption of amoxicillin in water solutions

Green synthesis is a viable alternative for creating nanoparticles from environmentally friendly sources. Sonchus asper extract was used in this study to prepare ZrO2 nanoparticles that can adsorb amoxicillin from an aqueous solution as a reducing and stabilizing agent. The complex product was synthesized and then annealed for four hours at 500 °C, 600 °C, and 700 °C to produce fine ZrO2 powder. X-ray diffraction, BET, FTIR, and TEM were employed to explore these samples' structural characteristics. Structural analyses showed that a cubic phase with slight size variation at different annealing temperatures is present in nanocrystalline ZrO2 powder. We examined the influence of initial amoxicillin concentration, pH, and temperature on amoxicillin adsorption. Compared with other widely popular materials used to remove amoxicillin, the zirconia produced in this study had a much better adsorption capability. The adsorption processes were spontaneous and endothermic, following thermodynamic characteristics, including standard enthalpy change (H), Gibb's free energy change (G), and standard entropy change (S). The green production method and zirconia nanoparticles are promising to adsorb a developing contaminant.

Influence of annealing temperature on the structural and optical properties of nanocrystalline zirconium oxide

Nanocrystalline zirconium oxide powder was prepared by sol-gel method using zirconyl chloride octahydrate (ZrOCl2·8H2O) and ethylenediaminetetraacitic acid (EDTA) in ammonium hydroxide (NH4OH) solution. The as-synthesized complex product was annealed at 650°C, 750°C and 850°C for 2h to get fine ZrO2 powder. These samples were further analyzed by Scanning electron microscopy (SEM), X- ray diffraction (XRD), Energy-dispersive X- ray spectroscopy (EDX), UV-vis analysis, Fourier transform infrared (FT-IR) spectroscopy, Photoluminescence spectroscopy (PL) and Raman Spectroscopy to study their structural and optical properties. The structural studies revealed that nanocrystalline ZrO2 powder exhibits monoclinic phase with variation in crystallite size with annealing temperature. The UV–vis absorption band edge of ZrO2 decreases from 514nm to 451nm as annealing temperature rises from 650°C to 750°C. It seems that the drastic reduction in band gap energy may be one of the novel unexpected characteristics of ZrO2. The FTIR analyses further confirmed the formation of nanocrystalline monoclinic ZrO2. PL analysis revealed the novel emission peaks at 305 and 565nm. The Raman spectroscopy confirmed the transformation of amorphous zirconium hydroxide to m-ZrO2 with increase in temperature from 650°C to 850°C.

Effect of Grain Size on Phase Transformation and Photoluminescence Property of the Nanocrystalline ZrO2 Powders Prepared by Sol–Gel Method

Nanocrystalline zirconia (ZrO2) powders were prepared by a sol–gel process followed by annealing treatments from 500 to 1200 °C. Phase transformation, microstructural features and photoluminescence properties were characterized by X-ray diffraction, transmission election microscopy and photoluminescence spectra, respectively. The results show that both monoclinic phase and tetragonal phase exist in the nanocrystalline ZrO2 powders at annealing temperature in the range of 500–900 °C, and the concentration of monoclinic phase increases with increasing the annealing temperature. Tetragonal phase is totally transformed to monoclinic phase when annealing temperature is up to 900 °C. The average grain size of the powders also increases when annealing temperature increases. Two emission peaks centered at 390 nm (named as I390) and 470 nm (named as I470) exist in the photoluminescence spectra, and the intensity ratio of I390 to I470 decreases with increasing annealing temperature. The grain size is proposed to be responsible for the phase transformation in the nanocrystalline ZrO2 powders.

Controllable synthesis of zirconia nano-powders using vapor-phase hydrolysis and theoretical analysis

The feasibility of controllable synthesis of nano-crystalline ZrO2 powders using vapor-phase hydrolysis was studied. XRD, SEM, TEM, BET and TG-DTA methods were used to investigate the phase composition, particle size, and agglomeration. The formation process of the nano-particles was also analyzed with the classic Smoluchowski theory, the coupled cluster theory [CCSD(T)]/aT and/or Moller–Plesset perturbation theory (MP2)/aT. The results show that the morphology and size of the ZrO2 nano-particles were very much dependent on the ratio of ZrCl4 : H2O, which played an important part in determining the characteristics of the ZrO2 nano-particles. By increasing the concentration of water to decrease their collision rate and prevent nano-particle agglomeration, the size distribution of the nano-particle product would be decreased and a more monodisperse nano-particle product would be collected. In particular, the best characteristics were obtained using a precursor ratio of 1 : 40 (ZrCl4 : H2O). The nano-powders had a small particle size (15 nm), a high degree of crystallinity and very weak agglomeration, in a continuous instead of batch operation. This route is free of powder drying and calcination processes that are essential for wet chemical preparation, contributing to less agglomeration.

Deformation behavior of zirconia-based porous ceramics

It has been studied a porous ceramics obtained from nanocrystalline ZrO2 powders. Samples were obtained by pressing and sintering of compacts, the porosity of ceramic samples was from 20 to 80%. The average grain size in the studied ceramics increased from 0.4 to 4 microns with increasing sintering temperature and duration of isothermal holding from 1400 to 1600 °C and 1 to 5 hours, respectively. It was shown that the "stress – strain" diagrams on the initial stage of deformation has a nonlinear behavior with high parabolic factor of strain-stress curves. It has been shown that fracture of the materials was observed from the elastic area and has a rod-like and cellular-like parts in its structure.

Facile fabrication and characterisation of MoO3 coated nanocrystalline ZrO2 by polymeric resin route

Surface modification of nanocrystalline ZrO2 powder with an ultrathin MoO3 layer was successfully carried out by a polymeric resin route using polyacrylic acid and ethylene glycol as precursors. Polyacrylic acid plays a vital role in this process, not only as the chelating agent for the molybdate cluster but also to form the uniform layer of molybdate dispersed polymeric resin on the surface of ZrO2. Thermal decomposition of the resin intermediate at 500°C creates the organic free MoO3 layer on the ZrO2 surface. Fourier transform infrared, X-ray diffraction and SEM energy dispersive spectroscopy analysis confirm the uniform formation of crystalline MoO3 on the surface of the ZrO2 powder. Further, the MoO3 layer thickness was identified by TEM characterisation and was found to be ∼3 nm.

Glycothermal synthesis of nanocrystalline ZrO2 powders at low temperature without mineralizers

Zirconia (ZrO2) nanoparticles were synthesized at temperature as low as 200°C through a glycothermal reaction using amorphous zirconium hydrous gel precursors and 1,4-butanediol as solvent, XRD and TEM data support that glycothermal processing method provides a simple low temperature route for producing highly crystallized ZrO2 nanoparticles without mineralizers, which could also be extended to other systems. XRD results also showed that ZrO2 nanoparticles synthesized in glycothermal condition had tetragonal phase with small portion of monoclinic phase, where the tetragonality was confirmed by Raman spectroscopy. The as-prepared ZrO2 nanoparticles have spherical morphology with an average crystal size of 10–15 nm and agglomerated into bigger spheres with a diameter of about 100 nm. The tetragonal phase begins to transform to monoclinic phase at 600°C when the calcinations of the as-synthesized powder was carried out.

Hydrothermal Synthesis of Zirconia Nanoparticles from Commercial Zirconia

Recently, it was observed that nanostructured zirconia (ZrO2) powder exhibits enhanced performance in many applications. In this study, a hydrothermal method was used for the synthesis of nano-crystalline ZrO2 powder from a fully monoclinic commercial zirconia. The products were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of SEM showed that after hydrothermal treatment under alkali condition, a different morphology from the commercial zirconia was obtained and XRD results showed that moreover to monoclinic phase (28%), cubic and tetragonal phases (72%) formed. According to TEM observations and XRD analysis, it was found that the nano-sized zirconia has an average particles size of 15-30 nm.

Synthesizing and Characterizing of ZrO<sub>2</sub> Nanopowders via Ultrasound-Assisted Sol-Gel Method

We have developed an ultrasound-assisted sol-gel approach for the synthesis of ultrafine nanocrystalline ZrO2 powders. The ultrasound-assisted sol-gel synthesis is expected to be able to process continuously, and may lead to energy savings because of rapid heating to the needed temperature and increased kinetics of crystallization. The variation of crystallite size has been investigated using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), TG–DTA analyze and photoluminescence. This method is very simple and can lead to powders with desirable characteristics such as very fine size, narrow size distribution, and good chemical homogeneity.

Stable colloidal suspensions of nanostructured zirconium oxide synthesized by hydrothermal process

Nanocrystalline zirconium oxide was synthesized by hydrothermal treatment of ZrO(NO3)2 and ZrOCl2 aqueous solutions at different temperatures and time in presence of hydrogen peroxide. Hydrothermal treatment of zirconium salts (0.25 and 0.50 mol L−1) produced nanocrystalline monoclinic ZrO2 powders with narrow size distribution, which were formed by the attachment of the smaller particles with crystallites size of 3.5 nm, estimated by means of the Scherrer’s equation and confirmed by transmission electronic microscopy. Typical monoclinic zirconium oxide X-ray powder diffraction patterns and Raman spectra were obtained for all the crystalline powders. It was observed that the crystallization depends strongly on the temperature, resulting in amorphous material when the synthesis was realized at 100 °C, and crystalline with monoclinic phase when synthesized at 110 °C, independently of the salt used. Zirconium oxide colloidal nanoparticles were formed only at hydrothermal treatments longer than 24 h. The stability of the colloids was successfully characterized of zeta potential, showing an initial value of + 59.2 mV in acid media and isoelectric point at pH = 5.2, in good agreement with previous studies.

Phase controlled structure formation of the nanocrystalline zirconia using thermal plasma technique

Nanocrystalline ZrO2 powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO2 is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO2 shows high ionic conductivity. ZrO2 is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO2 powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.

Structure and properties of nanocomposites prepared from ball milled 6061aluminium alloy with ZrO2 nanoparticles

AbstractBall milling of 6061 aluminum alloy and nanocrystalline ZrO2 powder allowed to obtain homogeneous mixture of nanocrystalline aluminum solid solution of grain size near 50 nm and ZrO2 particles. The ZrO2 particles are partially transformed after milling from tetragonal to the monoclinic crystal structure. After hot pressing in vacuum at temperature of 380 °C bulk nanocomposites were obtained of porosity below 1% consisting of aluminum solid solution of the average grain size near 80 nm and nano‐size ZrO2 particles. Partial recrystallization occurred after hot pressing particularly near particles boundaries, where elongated recrystallized grains free from ZrO2 nanoparticles of thickness near 1 μm and length of a few μm were identified. Estimated fraction of recrystallized grains was below 10%. The compression strength approaching 1000 MPa was obtained in composites containing 20% ZrO2 nanoparticles, what is more than reported for ultra and nano‐grain 6XXX aluminum alloys. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural transformations in zirconia under cumulative explosion conditions

We have studied structural transformations in nanocrystalline zirconia (ZrO2) loaded by cumulative jets generated by the explosions of charges with cone-shape linings based on the nanocrystalline ZrO2 powders. It is established that the material under such conditions can occur in a highly nonequilibrium structural state. The phenomenon of relaxation of such a nonequilibrium state upon explosion has been observed, which is terminated at room temperature for a time on the order of 1000 h. Estimation gives an anomalously low value of the apparent activation energy (∼3.5 kcal/mol) of this process

Structural characteristics of nanocrystalline ZrO2 powder sol–gel derived to luminescent applications

Interest in nanocrystalline ceramics is increasing nowadays. Sol–gel is a low temperature method, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than the conventional high-temperature processes. This new preparation method of nanophosphors has been recently strongly developed for producing high-efficiency luminescent devices. When producing ZrO2 it is important to retain a high degree of crystallization of ZrO2 and its possible correlation with the concentration of defects. The X-ray diffraction patterns of ZrO2 showed that the calcined material has a strongly monoclinic structure. The thermoluminescent glow curve of ZrO2 exhibited two peaks. Photoluminescence spectra of ZrO2 also were obtained.

Phase Transformation and Photoluminescence Properties of Nanocrystalline ZrO2Powders Prepared via the Pechini-type Sol−Gel Process

Nanocrystalline ZrO2 fine powders were prepared via the Pechini-type sol−gel process followed by annealing from 500 to 1000 °C. The obtained ZrO2 samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and photoluminescence spectra (PL), respectively. The phase transition process from tetragonal (T) to monoclinic (M) was observed for the nanocrystalline ZrO2 powders in the annealing process, accompanied by the change of their photoluminescence properties. The 500 °C annealed ZrO2 powder with tetragonal structure shows an intense whitish blue emission (λmax = 425 nm) with a wide range of excitation (230−400 nm). This emission decreased in intensity after being annealed at 600 °C (T + M-ZrO2) and disappeared at 700 (T + M-ZrO2), 800 (T + M-ZrO2), and 900 °C (M-ZrO2). After further annealing at 1000 °C (M-ZrO2), a strong blue-green emission appeared again (λmax = 470 nm). Based on spectral analysis and EPR results, the whitish blue emission (425 nm) and blue-green emission (470 nm) can be ascribed to interstitial carbon impurities (Ci) in the tetragonal ZrO2 and oxygen vacancies (VO) in the monoclinic ZrO2, respectively.

Preparation of nanocrystalline ZrO2 by reverse precipitation method

Nanocrystalline ZrO2 particulates with different sizes were prepared by precipitation method using ethanol as dispersive and protective reagent. XRD patterns show that the synthesized ZrO2 is monoclinic in structure with space group P21/a when calcination temperature is in the range of 400–1000°C. It is found that the smaller the particle, the bigger the crystal lattice distortion, the worse the crystal growth, and the lower the diffraction intensity. TEM images reveal that ZrO2 particles are spherical in shape, and the particle size distribution is in, narrow range. The mean sizes of the particles increase with the increase of calcination temperatures. It is first to observe the streaks of different crystallographic planes. Thermogravimetric analysis indicates that the crystallization temperature of ZrO2 is 461.32°C. Measurement of ZrO2 relative density shows that the relative density of nanocrystalline ZrO2 powders increases with the increasing of ZrO2 particle sizes.

Synthesis of nanocrystalline ZrO2 powders by mechanochemical reaction of ZrCl4 with LiOH

Abstract Mechanochemical reaction of anhydrous ZrCl 4 with LiOH has been used to synthesize nanocrystalline powders of ZrO 2 . The mechanism of chemical reaction was found to depend on the presence of LiCl diluent in the initial reactant mixture. In the absence of LiCl diluent, reaction of the precursors occurred in a combustive manner and resulted in the formation of agglomerated nanoparticles of tetragonal ZrO 2 embedded within a matrix of LiCl and LiCl·H 2 O. Continued milling after the combustion event resulted in a progressive loss of specific surface area and transformation of the tetragonal ZrO 2 to the equilibrium monoclinic structure. Dilution of the initial reactant mixture with 4LiCl suppressed combustive reaction. Reaction of the precursors occurred gradually and resulted in the formation of an amorphous ZrO 2 gel that crystallized with the tetragonal structure on calcination at 500 °C for 1 h.

An EXAFS Study of Nanocrystalline Yttrium Stabilized Cubic Zirconia Films and Pure Zirconia Powders

Detailed EXAFS (extended X-ray absorption fine structure spectroscopy) measurements have been collected for two nanocrystalline forms of zirconia, namely, dense films of yttria-stabilized cubic zirconia (YSZ) and tetragonal phase powders of pure ZrO2. Zr and Y K edge EXAFS spectra for the YSZ films with grain sizes of 6, 15, and 240 nm showed no major differences with the corresponding spectra of the bulk counterpart. This is clear proof that these nanocrystalline films exhibit similar levels of disorder to that of large crystals. In particular, there is no support for the view that the intergrain regions are highly disordered, and the present work is consistent with recent EXAFS studies of other nanocrystalline oxides (SnO2 and ZnO) and metals (Cu). The pure nanocrystalline ZrO2 powders were produced by calcining zirconium hydroxide, a widely used method of synthesising ZrO2. The Zr K edge EXAFS of the powders, with grain sizes of 10 and 20 nm, yielded spectra in which the signal was strongly attenuated ...

Oxygen diffusion in ultrafine grained monoclinic ZrO2

The diffusion of oxygen in ultrafine grained, undoped monoclinic ZrO2 was studied using O18 as tracer and secondary ion mass spectroscopy profiling. Samples with a relative mass density of 97%–99% and average crystallite sizes of 80 or 300 nm were prepared from Zr by sputtering, inert-gas-condensation, oxidation, in situ consolidation of nanocrystalline (n-)ZrO2 powder and subsequent pressureless sintering at 950 or 1050 °C in vacuum. Volume and interface diffusivities were directly determined from the O18 diffusion profiles in n-ZrO2 in the type B and type A regime of interface diffusion. The diffusion of O18 in interfaces in undoped n-ZrO2 is 103–104 times faster than in the bulk of the crystallites throughout the temperature range of 450 to 950 °C studied. These diffusivities are independent of the crystallite size in the range of 70–300 nm. The activation energies QV=2.29 eV and QB=1.95 eV for the volume (QV) and interface diffusion (QB) are considerably higher than the diffusion activation energies found in the fast ion conductors Ca- or Y-stabilized ZrO2. Based on the present data on oxygen diffusion in ZrO2, the cation and anion diffusivities of other binary oxides are discussed.

Synthesis and Colloidal Processing of Nanocrystalline (Y2O3-Stabilized) ZrO2 Powders by a Surface Free Energy Controlled Process

AbstractUsing the controlled growth technique, nanocrystalline ZrO2 powders have een prepared from solution. By variation of the Y-content (0-8 mol %), redispersable monoclinic, tetragonal or cubic ZrO2 powders with particle sizes between 5 and 10 mn were obtained after crystallization at elevated temperature and pressure. Nanodisperse suspensions of the powders have been used for colloidal processing techniques such as tape casting, slip casting or extrusion. The resulting green bodies with densities of 55 % and average pore sizes of 5 nm could be sintered at temperatures below 1100 °C leading to monoclinic, tetragonal or cubic ZrO2 ceramics.