Preparation and properties of cross-linked zirconia nanoparticle films on polycarbonate

Highly-crystalline zirconia (ZrO₂) nanoparticle was functionalized with 3-(N-aminoethyl) aminopropyltrimethoxysilane (AAPTMS) and dispersed in water at primary particle size level under basic condition (pH 13-14). The aqueous ZrO₂ nanoparticle dispersion was cast on a polycarbonate substrate with 1,4-butanediol digylcidyl ether as a cross-linker. Nanoparticle films with as high as 81 wt.% of ZrO₂ were obtained through heating the cast dispersion at 120 °C, which are highly transparent. The refractive index ranges from 1.70 to 1.77 at wavelength of 632 nm with the decrease of the amount of AAPTMS attached to ZrO₂ nanoparticles. Nanoindentation tests show that the hardness of the film reaches 1.7 GPa. In addition, both punched tape abrasion and nanoscratch tests reveal that the films exhibit prominent scratch resistant performance.     

Microstructure and optical properties of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

The aluminium oxide/zirconium oxide (Al₂O₃/ZrO₂) nanolaminate thin films (5/20 nm with 4 bilayers, 5/15 nm with 5 bilayers and 5/10 nm with 7 bilayers) were deposited on Si (100) and quartz substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar at room temperature using pulsed laser deposition. The multilayer films were characterized using X-ray diffraction, X-ray reflectivity, Atomic force microscopy and UV–Visible spectroscopy. The X-ray diffraction studies showed amorphous nature for 5/20 nm film, whereas 5/15 nm and 5/10 nm multilayers showed only tetragonal zirconia at room temperature. X-ray reflectivity studies showed the Kiessig fringes and Bragg peaks, indicating the well defined formation of individual layers and bilayer periodicity in the multilayer films. The AFM studies showed the RMS roughness values of 0.7 nm, 0.9 nm and 1.1 nm for 5/10 nm, 5/15 nm and 5/20 nm multilayers respectively. The optical performance of the combined Al₂O₃/ZrO₂ nanolaminates showed that the refractive indices of the films increased from 1.75 to 1.99 with the decrease of ZrO₂ layer thickness from 20 to 10 nm.     

Characterization of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Microstructural characterization of pulsed laser deposited Al₂O₃/ZrO₂ multilayers on Si (1 0 0) substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar and at room temperature (298 K) has been carried out. A nanolaminate structure consisting of alternate layers of ZrO₂ and Al₂O₃ with 40 bi-layers was fabricated at different zirconia layer thicknesses (20, 15 and 10 nm). The objective of the work is to study the effect of ZrO₂ layer thickness on the stabilization of tetragonal ZrO₂ phase for a constant Al₂O₃ layer thickness of 5 nm. The Al₂O₃/ZrO₂ multilayer films were characterized using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1473 K. The studies showed that the thickness of the zirconia layer has a profound influence on the crystallization temperature for the formation of tetragonal zirconia phase. The tetragonal phase content increased with the decrease of ZrO₂ layer thickness. The cross-sectional transmission electron microscope (XTEM) investigations were carried out on a multilayer thin films deposited at room temperature. The XTEM studies showed the formation of uniform thickness layers with higher fraction of monoclinic and small fraction of tetragonal phases of zirconia and amorphous alumina.     

Preparation of porous ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> macrobeads from ion-exchange resin templates

In this work, we will report a method to prepare porous ZrO₂ and ZrO₂/Al₂O₃ macrobeads using cation-exchange resins with sulfonate groups as templates. The preparation process involves metal ion-loading, ammonia-precipitation, and calcination at an appropriate temperature. Several characterization methods, such as TGA, XRD, SEM with EDX, TEM and N₂ adsorption and desorption, were used to characterize the ZrO₂ and ZrO₂/Al₂O₃ macrobeads. The results showed that the porous structures of the resin templates were negatively duplicated in the two kinds of macrobeads. We found the following interesting results: (1) The ZrO₂/Al₂O₃ macrobeads are composed of tetragonal zirconia nanocrystals that are more technologically important, while the pure ZrO₂ macrobeads consist of a mixture of tetragonal and monoclinic zirconia. (2) In the ZrO₂/Al₂O₃ macrobeads, the size of ZrO₂ nanocrystals is about 5 nm smaller than that (about 19 nm) found in the pure ZrO₂ macrobeads. (3) The ZrO₂/Al₂O₃ macrobeads have more mesopores and, therefore, have a larger surface area than the pure ZrO₂ macrobeads. These oxide macrobeads will have potential applications in catalysis by taking advantage of their macrobeads shape and pores structure.     

Preparation and characterization of zirconia and mixed zirconia/titania in ionic liquids

Zirconia and mixed zirconia/titania were synthesized in two different ionic liquids, namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP]TFSA) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide ([EMIm]TFSA) using sol–gel methods. The synthesized oxides were characterized by means of X-ray diffraction, scanning electron microscopy with energy dispersive X-ray (SEM-EDX)), thermogravimetric and differential thermal analyses (TGA–DTA). The results show that the as-synthesized ZrO₂ powders obtained either in [BMP]TFSA or in [EMIm]TFSA show amorphous behaviour, and calcination at 500 °C yields t-ZrO₂ which is subject to further phase transformation to m-ZrO₂ at 1000 °C. The type of the ionic liquid influences the morphology of the synthesized zirconia as the sample obtained from [BMP]TFSA showed a porous morphology with very fine particles in the nanometer regime, whereas micro-rods were obtained from [EMIm]TFSA. ZrO₂-TiO₂ nanorods with an average diameter of about 100 nm were synthesized in [EMIm]TFSA. The presence of zirconia in the mixed oxides stabilizes the anatase phase and elevates the temperature at which the phase transformation to rutile occurs.     

Fabrication of high aspect ratio zirconia nanotube arrays by anodization of zirconium foils

The zirconia nanotube arrays with diameter of about 130 nm, a length of up to 190 μm and aspect ratios of more than 1400 were prepared by anodizing a zirconium foil in mixture of formamide and glycerol (volume ratio = 1:1) containing 1 wt.% NH₄F and 3 wt.% H₂O. The as-prepared nanotube arrays were amorphous zirconia. Monoclinic and tetragonal zirconia coexisted when annealed at 400 °C and 600 °C, while monoclinic zirconia was obtained at 800 °C. The ZrO₂ nanotubes retained their shape after heating up to 800 °C. The lower dissolving rate of zirconia in organic electrolytes might be the main reason for fabrication of zirconia nanotube arrays with high aspect ratio.     

Innovative fabrication of ZrO2-HAp-TiO2 nano/micro-structured composites through MAO/EPD combined method

ZrO₂-HAp-TiO₂ porous layers were fabricated by micro arc oxidation/electrophoretic deposition hybrid processes in the electrolytes consisted of β-glycerophosphate, calcium acetate, sodium phosphate, and yttria-stabilized zirconia within short times and only in one step. The layers had a porous structure with a pores size of 50-750 nm. They contained anatase, hydroxyapatite, monoclinic ZrO₂, tetragonal ZrO₂, and some minor phases with a varying fraction depending on time. Increasing the time, the tetragonal ZrO₂ transformed to monoclinic ZrO₂. Moreover, hydroxyapatite relative content decreased with time. The nanosized zirconia particles (d = 20-40 nm) were dispersed on the surface and in the layers depth.     

Ambient temperature stabilization of crystalline zirconia thin films deposited by direct current magnetron sputtering

Nanocrystalline zirconia thin films have been deposited on borosilicate glass substrates at ambient temperature by direct current (dc) magnetron sputtering. The present study demonstrates the possibility of growing zirconium oxide films in 100% pure oxygen dc plasma. Films of thickness of the order of 500 nm have been grown using a metallic Zr target in pure oxygen plasma. Interestingly, the presence of high temperature polymorphs of ZrO₂ is observed in films deposited with 40, 60 and 80% oxygen in the sputtering gas, while only the monoclinic phase is observed at lower and higher oxygen percentages. The refractive index in this range of oxygen percentages peaks at 1.85 in the dispersion free region. The crystallite size in the films varies between 11-25 nm, as calculated from X-ray diffraction patterns and is dependent on oxygen percentage in the sputtering gas. The grain sizes observed in atomic force microscope images are in the range 38 to 45 nm. The dielectric constants of the films, measured at microwave frequencies [8-12 GHz] ranged between 13-19.2.     

Thermal treatment effect on the optical properties of ZrO2 thin films deposited by thermionic vacuum arc

This paper shows the ex situ thermal treatment effects of the ZrO₂ thin films obtained by TVA (thermionic vacuum arc) technique on the optical properties (e.g., transmittance, refractive index and band-gap energy) of ZrO₂ thin films. The crystal structure, surface and optical properties were investigated for ZrO₂ thin films deposited on glass substrates by thermionic vacuum arc (TVA) method. The thermal treatment effect on the optical properties of the thin films was determined. The XRD analysis showed that the deposited ZrO₂ thin films have baddeleyite (monoclinic) and zirconium (hexagonal) structures. The thicknesses and refractive index were determined by interferometric measurements. The thin films were thermal treated at different temperatures (350 °C, 450 °C and 550 °C), and the analysis showed that the optical properties of ZrO₂ deposited thin films were improved by thermal treatment at 450 °C.     

Layer-by-layer deposition of zirconia thin films from aqueous solutions

Thin films of ZrO₂ and Y₂O₃-doped ZrO₂ were deposited using a novel yet simple layer-by-layer technique by means of electrostatic assembling and surface precipitation via dipping substrates alternately in cationic and anionic precursor solutions. Uniform films have been made. A constant growth rate of 5.4 ± 0.3 nm per deposition cycle for the dehydrated nanocrystalline films was achieved. This generic technique can be adapted to make other oxide films and novel multilayers or functionally-graded coatings.     

Characterization of nano-crystalline ZrO2 synthesized via reactive plasma processing

Nano-crystalline ZrO₂ powder has been synthesized via reactive plasma processing. The synthesized ZrO₂ powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and FTIR spectroscopy. The synthesized powder consists of a mixture of tetragonal and monoclinic phases of zirconia. Average crystallite size calculated from the XRD pattern shows that particles with crystallite size 20 nm or less than 20 nm are in tetragonal phase, whereas particles greater than 20 nm are in the monoclinic phase. TEM results show that particles have spherical morphology with maximum percentage of particles distributed in a narrow size from about 15 nm to 30 nm.     

Preparation and characterization of unique zirconia crystals within pores via a sol–gel-hydrothermal method

Unique ZrO₂ crystals within pores were prepared by a sol–gel-hydrothermal method and characterized by XRD, TG/DTA, TEM, SEM, and N₂ adsorption–desorption isotherms. Results show that the dried sol–gel was converted into monoclinic zirconia crystals after calcined above 550 °C. The crystal sizes of the zirconia single crystal were in the range of 20–70 nm. A number of irregular pores were embedded within the zirconia crystals. This unique structure was obtained due to the combination of sol–gel and hydrothermal treatments.     

Effect of highly dispersible zirconia nanoparticles on the properties of UV-curable poly(urethane-acrylate) coatings

Highly crystalline and dispersible zirconia nanoparticles, ex situ synthesized from a solvothermal reaction of zirconium(IV) isopropoxide isopropanol complex in benzyl alcohol, were functionalized with 3-(trimethoxysilyl)propyl methacrylate and blended with UV-curable urethane-acrylate formulations to fabricate poly(urethane-acrylate)/zirconia (PUA/ZrO₂) nanocomposite coatings. A critical ZrO₂ concentration of 20 wt% was observed for the evolutions of both the structure and properties of the nanocomposites as a function of ZrO₂ content. Below the critical concentration, completely transparent nanocomposite film was obtained and the nanocomposites exhibited increasing final carbon–carbon double bond conversion, refractive index, hardness, elastic modulus, and thermal stability as ZrO₂ content increased. However, serious agglomeration of ZrO₂ nanoparticles occurred at 25 wt% of ZrO₂, which decreased final conversion, transparency and hardness, and thermal stability of the nanocomposite film. These results clearly reveal that the performance of UV-curable nanocomposites is strongly dependent on the dispersion of nanoparticles.     

Effect of NaF content on the preparation of zirconia whiskers by molten salt method

Zirconia whiskers were successfully fabricated by molten salt method, using NaVO₃/NaF as composite molten salt. The effect of NaF content on the growth of zirconia whiskers were systematically investigated by XRD, FE-SEM, TEM, SAED, HR-TEM, Raman and XPS. When optimized NaF content is 10%, the obtained zirconia whiskers with monoclinic crystal structure show an length of 1–3 μm and diameters of 100–300 nm. The as-prepared whiskers preferentially grow along [0 0 1] direction and exhibit a smooth surface without distinct defects. Fluoride is proved to play an important role in the growth of zirconia whiskers. On the one hand, fluoride can be served as mass transfer agent, promoting the dissolution and precipitation of ZrO₂ through the mass transfer process of fluorozirconate species. On the other hand, fluoride can act as morphology controlling agent, enhancing the anisotropic growth of ZrO₂ crystals by the formation of fluorine-terminated surface.     

Dye-sensitized solar cells using TiO<Subscript>2</Subscript> nanoparticles transformed from nanotube arrays

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ mesoporous layers obtained by very simple method—transformation of TiO₂ nanotube (NT) films grown by electrochemical oxidation to nanoparticle (NP) films. This transformation is based on thermal annealing of TiO₂ NT arrays formed by anodization of titanium foil in fluorine ambient. Performance of DSSCs fabricated with different size NPs was studied in the range from 35 to 350 nm. Highest nominal efficiency (9.05%) was achieved for DSSC with NP size 65 nm while the lowest nominal efficiency (1.48%) was observed for DSSCs with NP size 350 nm. The dependence of the solar cell parameters with NP size is discussed.     

Destabilization of cubic-stabilized zirconia electrolyte induced by boron oxide under reducing atmosphere

The stability of yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) electrolytes against boron oxide was examined. Boron oxide was painted on the polished surface of YSZ and ScSZ and annealed at 1273 K for 100 h under wet hydrogen flowing condition. The X-ray diffractometry, scanning electron microscopy/energy dispersive X-ray analysis, and Raman studies revealed that formation of Y₂O₃ and Sc₂O₃ occurred on YSZ and ScSZ surfaces contacting the boron oxide, but rare earth borates were not observed. The surface of electrolytes around precipitated particles became rough and phase transformation was confirmed from the cubic to the tetragonal or the monoclinic phases due to stabilizer removal from cubic zirconia. It has been also verified that small amounts of zirconium and yttrium were transported from the electrolyte to the gas phase via boron component. This destabilization effect induced by boron oxide was more serious for ScSZ than for YSZ. A destabilization mechanism under wet hydrogen atmosphere is proposed based on pseudo ternary phase diagrams for the YO_1.5–BO_1.5–ZrO₂ system and the ScO_1.5–BO_1.5–ZrO₂ system and thermodynamic considerations.     

Fabrication of transparent polymer-matrix nanocomposites with enhanced mechanical properties from chemically modified ZrO<Subscript>2</Subscript> nanoparticles

Optically transparent nanocomposites with enhanced mechanical properties were fabricated using stable dispersions of sub 10 nm ZrO₂ nanoparticles. The ZrO₂ dispersions were mixed with a commercially available bisphenol-A-based epoxy resin (RIMR 135i) and cured with a mixture of two amine-based curing agents (RIMH 134 and RIMH 137) after complete solvent removal. The colloidal dispersions of ZrO₂ nanoparticles, synthesized through a non-aqueous approach, were obtained through a chemical modification of the ZrO₂ nanoparticle surface, employing different organic ligands through simple mixing at room temperature. Successful binding of the ligands to the surface was studied utilizing ATR–FT-IR and thermogravimetric analysis. The homogeneous distribution of the nanoparticles within the matrix was proven by SAXS and the observed high optical transmittance for ZrO₂ contents of up to 8 wt%. Nanocomposites with a ZrO₂ content of only 2 wt% showed a significant enhancement of the mechanical properties, e.g., an increase of the tensile strength and Young’s modulus by up to 11.9 and 12.5%, respectively. Also the effect of different surface bound ligands on the mechanical properties is discussed.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

Preparation of graded zirconia–CaP composite and studies of its effects on rat osteoblast cells in vitro

Hydroxyapatite (HAP) has excellent biocompatibility and bone bonding ability, but it is mechanically weak and brittle. To overcome this problem, we prepared a graded composite with calcium phosphide (CaP, decomposed from HAP during sintering) coating on the surface of zirconia (ZrO₂) ceramics. The mechanical properties and microstructure characteristics were studied with various techniques. The biocompatibility of graded ZrO₂–CaP composite was examined with rat osteoblast cells (OB cells) in vitro. Its effects on the production of alkaline phosphatase (ALP), Interleukin-6 (IL-6) and Growth-transforming Factor-β (TGF-β) by the OB cells were measured. The results showed that the mean tensile strength of the graded ZrO₂–CaP composites was 17.8 MPa, the maximum bending strength was 1112.24 MPa, and K_IC was 7.3–11.4 MPa·m^1/2, indicating that the composite was physically strong for use as an implant material. The ALP activity, IL-6 and TGF-β concentrations of the graded composite treated OB cells were much higher than that of the pure ZrO₂ treated group. There was no significant difference in ALP activity, the IL-6 and TGF-β concentrations between the graded ZrO₂–CaP composite group and HAP. The cytotoxicity of the composite material to rat fibroblast cells was insignificant. The graded zirconia–CaP composite greatly facilitated the proliferation and differentiation of rat OB cells in vitro, demonstrating excellent biocompatibility.     

Silicone rubber ablative composites improved with zirconium carbide or zirconia

Silicone rubber ablative composites with zirconium carbide (ZrC) or zirconia (ZrO₂) were prepared and tested for thermal protection systems. The incorporation of ZrC or ZrO₂ powders increased the tensile strength but reduced the elongation at break of the composites. The thermal stabilities of the composites were enhanced by adding ZrC or ZrO₂. The ceramic layers containing ZrO₂, SiO₂ and SiC were formed on the ablated surface of the composites with ZrO₂ or ZrC, and acted as effective oxygen and heat barriers. The ablated surface of the composite with ZrO₂ was more uniform than that of the composite with ZrC in the experiment. The linear ablation rates of the composites were reduced by 40% and 72% by the incorporation of 40 phr ZrC and ZrO₂, respectively.