Toughened glass-ceramics in the ZrO2-Al2O3-SiO2 system prepared by the sol-gel process

Monolithic glass-ceramics containing Al₂O₃ or TiO₂ were prepared in the ZrO₂-SiO₂ system by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 900–1200 °C and its crystal growth was increased by adding TiO₂ or Al₂O₃. Further heating at higher temperature resulted in the precipitation of zircon and monoclinic ZrO₂ which was transformed from tetragonal ZrO₂. The addition of Al₂O₃ had less effect on both the tetragonal-to-monoclinic ZrO₂ transformation and the precipitation of zircon. The fracture toughness increased as the size of tetragonal ZrO₂ particles increased and then decreased with the appearance of monoclinic ZrO₂ or zircon. The fracture toughness of the glass-ceramics was measured in the glass-forming regions of the ZrO₂-Al₂O₃-SiO₂ system. The fracture toughness was sensitively dependent on both Al₂O₃ and ZrO₂ content, of which the highest value achieved was 9 MPa m^1/2 for the 50ZrO₂·10Al₂O₃·40SiO₂ composition.     

The role of P2O5, TiO2 and ZrO2 as nucleating agents on microstructure and crystallization behaviour of lithium disilicate-based glass

The aim of this study was to investigate the effects of different nucleating agents (P₂O₅, TiO₂ and ZrO₂) on the crystallization behaviour and the properties of a parent glass with composition 23.7 Li₂O–2.63 K₂O–2.63 Al₂O₃–71.78 SiO₂ (mol%) and SiO₂/Li₂O molar ratio far beyond that of stoichiometric lithium disilicate (LD, Li₂Si₂O₅). The scanning electron microscopy examination of the as-cast non-annealed glasses revealed the occurrence of liquid–liquid phase separation for all the compositions. P₂O₅ revealed to be effective in promoting bulk crystallization of LD, while TiO₂ and ZrO₂ led to surface crystallization. Moreover, ZrO₂ enhances the glass polymerization and shifts T _p to higher temperatures, hindering crystallization. At 900 °C, TiO₂-containing glasses feature LD and lithium metasilicate (LMS, Li₂SiO₃), while P₂O₅- and ZrO₂-containing ones present monophasic LD and LMS glass–ceramics, respectively.     

Effects of light scattering TiO2 surface-modified by dual oxide coating in dye-sensitized solar cells

The surface of light scattering TiO₂ particles in the dye-sensitized solar cell (DSSC) was dual-coated with Al₂O₃ and SiO₂ nanoparticles. The surface modification of the light scattering TiO₂ particles was performed by a modified sol–gel method using the colloidal alumina and the colloidal silica as surface coating precursors. It was revealed that the dual-coated light scattering TiO₂ particles leads to an increase in short-circuit photocurrent of DSSC device, resulting in an increase in energy conversion efficiency. This seems to be due to the increase of the light scattering by a combination of the light scattering TiO₂ particles and the oxide nanoparticles such as Al₂O₃ and SiO₂.     

Growth mode transition of atomic layer deposited Al2O3 on porous TiO2 electrodes of dye-sensitized solar cells

This study investigates the growth behavior of atomic-layer-deposited (ALD) Al₂O₃ overlayers on porous TiO₂ electrodes, which comprise an anatase nanoparticle layer and a rutile particle layer, for optimizing dye-sensitized solar cells. The growth mode of the ALD Al₂O₃ overlayers changes from island growth to layer-by-layer growth during the first few ALD reaction cycles, and the growth mode transition is much more pronounced for the anatase electrode layer. The transition is likely a result of the reduction in the contractive lattice strain of the TiO₂ nanoparticles. The lattice strain in the hydroxylated TiO₂ nanoparticles is progressively reduced during the ALD Al₂O₃ deposition, resulting in the growth mode transition.     

Temperature-dependent emissivity of coatings produced from mixtures of BaCO3 and TiO2 powders and ZrO2 micro- or nanoparticles

We have determined temperature-dependent emissivity of coatings produced from annealed mixtures of BaCO₃ and TiO₂ powders and ZrO₂ micro- or nanoparticles. The results demonstrate that the best coatings have been obtained using ZrO₂ microparticles.     

A new method for surface modification of TiO2/Al2O3 nanocomposites with enhanced anti-friction properties

In this paper, the TiO₂/Al₂O₃ composite nanoparticles were prepared by a hydrothermal method and in situ modified with acrylic acid. It was found that the mean particle size of modified TiO₂/Al₂O₃ composite nanoparticles was about 80 nm with a uniform distribution by the particle size analysis. The modified TiO₂/Al₂O₃ composite nanoparticles can disperse in lubricating oil homogenously for several weeks. The dispersion stabilization of modified TiO₂/Al₂O₃ composite nanoparticles in lubricating oil was significantly improved in comparison with the as-prepared nanoparticles, which was due to the introduction of grafted polymers by surface modification. The formation of covalent bands was identified by Fourier transform infrared spectrum. Under an optimized concentration of 0.1 wt%, the averaged friction coefficient was reduced by 14.75%, when the modified TiO₂/Al₂O₃ composite nanoparticles were used as lubricating oil additivities.     

Evolution of microstructures and mechanical properties of AZ31B magnesium alloy weldment with active oxide fluxes and GTAW process

In this study, the effect of active oxide fluxes with gas tungsten arc welding on the microstructure and mechanical properties of AZ31B magnesium alloy weldment was investigated. The gas tungsten arc welding process through a flux spray layer was applied to an AZ31B magnesium alloy sheet to produce a bead-on-plate specimen. Oxide (TiO₂, SiO₂, Fe₂O₃, Al₂O_3, and ZrO₂) powders were used as the activating fluxes. The macrographs and micrographs of the weld beads were examined using an optical microscope and a scanning electron microscope. The specimens with SiO₂ and Fe₂O₃ fluxes had high depth-to-width ratio welds, followed by those with TiO₂ and ZrO₂ fluxes and while that with Al₂O₃ flux had the low ratio weld. The use of 70?A welding current for the specimens with different fluxes produced complete penetration, whereas the specimen without any flux required a 90 A welding current to produce complete penetration. The weld bead microstructure was affected by the activating fluxes, which created different thermal effects that changed the convection direction and promoted the formation of various precipitates in the fusion zone during solidification. Three types of precipitates were found in the fusion zones, that is, a long layer-shaped TiAlMg precipitate with TiO₂ flux, a spherical AlMgZn precipitate with Al₂O₃ flux, and an oval-shaped MgAlMn precipitate with all types of fluxes. The mechanical properties of AZ31B magnesium alloy were measured by tensile testing in the rolling direction. Fractures occurred in the fusion zone near the heat-affected zone interface of specimens welded with TiO₂ flux, revealing a brittle fracture with trans-granular cleavage facets and a large number of small, bright dimples at the center. Such brittle fractures also occurred in the fusion zone of specimens welded with Al₂O_3, ZrO₂, SiO₂, and Fe₂O₃ fluxes. Similarly, the specimens welded with Al₂O₃ exhibited a brittle fracture with trans-granular facets, whereas the other specimens revealed a brittle fracture with inter-granular cleavage facets.     

Effect of substituting Al2O3 and ZrO2 on thermal and optical properties of high refractive index La2O3–TiO2 glass system prepared by containerless processing

La₄Ti₉O₂₄ glass and La₂O₃–TiO₂–Al₂O₃ and La₂O₃–TiO₂–ZrO₂ glass systems were prepared by containerless processing. The thermal stability and refractive indices of these glasses were investigated. It was found that these glasses had high refractive indices over 2.29 and high glass transition temperatures. The effects of substituting Al₂O₃ or ZrO₂ for La₂O₃ or TiO₂ in La₄Ti₉O₂₄ glass on the refractive index is discussed by analyzing the optical parameters of the glasses. The high refractive index of these glasses was due to their large oxygen packing densities and significant electronic polarizabilities of oxygen ions. The substitution of Al₂O₃ and ZrO₂ was effective for the refractive indices and wavelength dispersions.     

Structural and morphological properties of Fe2O3/TiO2 nanocrystals in silica matrix

We report on structural, morphological and ordering properties of Fe₂O₃/TiO₂ nanoparticles embedded in SiO₂-based multilayers. We investigated the structure of these systems by X-ray diffraction and grazing incidence small angle X-ray scattering after post-growth annealing. We found that the presence of TiO₂ promotes the growth and crystallization of the nanocrystals of Fe₂O₃. In multilayers containing both Fe₂O₃ and TiO₂, crystalline nanoparticles create partially ordered three-dimensional arrays.     

Large Faraday rotation in magnetophotonic crystals containing SiO2/ZrO2 matrix doped with CoFe2O4 magnetic nanoparticles

This paper has focused on the potential of the SiO₂/ZrO₂ matrix doped with CoFe₂O₄ magnetic nanoparticles in order to achieve the high performance one-dimensional magnetophotonic crystals (MPCs) and to overcome the problem of integration of the magneto-optical devices. Because of importance of magneto-optical Faraday effect in most non-reciprocal optical components, we have investigated the capability of such silicon-based materials for providing large Faraday rotations. We have introduced some MPC structures containing SiO₂/ZrO₂ matrix doped with CoFe₂O₄ magnetic nanoparticles and by varying the concentration of magnetic nanoparticles, influence of volume fraction VF% on the Faraday rotation and transmittance of the structures has studied.     

Glasses and glass-ceramics in the SrO–TiO2–Al2O3–SiO2–B2O3 system and the effect of P2O5 additions

The glass formation abilities of various compositions in SrO–TiO₂–Al₂O₃–SiO₂, SrO–TiO₂–B₂O₃–SiO₂, SrO–TiO₂–Al₂O₃–B₂O₃, and SrO–TiO₂–Al₂O₃–SiO₂–B₂O₃ systems were studied. Many new compositions were found to be suitable for the casting of crack-free, optically clear glasses of different color and with glass transition temperatures ranging from 595 to 775 °C. The crystallization behavior, structure, and thermal expansion behavior of selected glasses were analyzed by DTA, XRD, dilatometry, and heat treatment. The effect of P₂O₅ on the glass structure and crystallization behavior was also studied. P₂O₅ played a dual role depending on composition. In some glasses it acted as a nucleating agent while in others it suppressed crystallization. Heat treatment of borate and borosilicate glasses transformed them into glass-ceramics while comparable SrO–TiO₂–Al₂O₃–SiO₂ glasses showed a lower tendency to crystallize and form glass-ceramics under the same conditions.     

A complex investigation of the nanofluids R600а-mineral oil-AL2O3 and R600а-mineral oil-TiO2. Thermophysical properties

This paper presents experimental data for the density, solubility, viscosity and capillary constant for solutions of the natural refrigerant isobutane (R600a) with mineral compressor oil and nanoparticles Al₂O₃ and TiO₂ over a wide range of temperatures and concentrations. Based on obtained information for the capillary constant, the surface tension of the solutions isobutane/mineral oil/Al₂O₃ nanoparticles and isobutane/mineral oil/TiO₂ nanoparticles is determined. SP-QSPR (Scaling Principles–Quantitative Structure Property Relationship) model has been successfully applied for fitting the experimental data obtained for solutions of isobutane with mineral compressor oil and nanoparticles Al₂O₃ and TiO₂. It was shown that the nanoparticle additives lead to increase of the viscosity and reduce surface tension of the refrigerant/oil solutions.     

Experimental Study on the Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids

This paper reports measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al₂O₃ thin film. Using distilled water and toluene as standard liquids of known thermal conductivity and thermal diffusivity, the length and radius of the hot wire and the thickness of the Al₂O₃ film are calibrated before and after application of the coating. The electrical leakage of the short-hot-wire probes is frequently checked, and only those probes that are coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Al₂O₃/water, ZrO₂/water, TiO₂/water, and CuO/water nanofluids are measured and the effects of the volume fractions and thermal conductivities of nanoparticles and temperature are clarified. The average diameters of Al₂O₃, ZrO₂, TiO₂, and CuO particles are 20, 20, 40, and 33 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancement and can be predicted accurately by the model equation of Hamilton and Crosser, when the spherical nanoparticles are dispersed into fluids.     

ArF-line high transmittance attenuated phase shift mask blanks using amorphous Al2O3-ZrO2-SiO2 composite thin films for the 65-, 45- and 32-nm technology nodes

Amorphous (ZrO₂)_x-(SiO₂)_1−x and (Al₂O₃)_x-(ZrO₂)_y-(SiO₂)_1−x−y composite films were prepared using r.f. unbalanced magnetron sputtering in an atmosphere of argon and oxygen at room temperature. The (ZrO₂)_x-(SiO₂)_1−x and (Al₂O₃)_x-(ZrO₂)_y-(SiO₂)_1−x−y composite films were completely oxidized when an O₂/Ar flow rate ratio of 2.0 was used. The optical constants of these thin films depend linearly on the mole fraction of corresponding films. By tuning the (x, y) mole fractions of (Al₂O₃, ZrO₂) in the (Al₂O₃)_x-(ZrO₂)_y-(SiO₂)_1−x−y composite films, the optical constants can meet the optical requirements for a high transmittance attenuated phase shift mask (HT-AttPSM) blank. The n-k values in the quadrangular area in the (x, y) plane, where x and y represent the mole fractions of Al₂O₃ and ZrO₂, respectively, meet the optical requirements for an HT-AttPSM blank with an optimized transmittance of 20 ± 5% in ArF lithography. It is noted that the quadrangular area is bounded by (0, 0.31), (0, 0.62), (0.26, 0) and (0.57, 0). All the films also met the chemical and adhesion requirements for an HT-AttPSM application. One (Al₂O₃)_0.1-(ZrO₂)_0.52-(SiO₂)_0.38 composite film was fabricated with optical properties that meet the optimized optical requirements of ArF-line HT-AttPSM blanks. Combined with these HT-AttPSMs, ArF-line (immersion) lithography may have the potential of reaching 65-, 45-nm and possibly the 32-nm technology nodes for the next three generations.     

Pressureless-sintering behavior of nanocrystalline ZrO2–Y2O3–Al2O3 system

ZrO₂–Y₂O₃–Al₂O₃ nanocrystalline powders have been synthesized using chemical coprecipitation method. Nano-powders were compacted uniaxially and densified in a muffle furnace. Densification studies showed that a fully dense pellet of ZrO₂(3Y) and a 99% relative density for 5 mol% Al₂O₃ doped ZrO₂(3Y) were obtained after sintering at 1200 °C. The presence of Al₂O₃ inhibits grain growth and suppresses the densification process. Full densification and the maximum microhardness of 17.8 GPa were achieved for the ZrO₂(3Y)/5 mol% Al₂O₃ composites sintered at 1250 °C.     

Oriented eutectic microstructures in the system Al2O3/ZrO2

Oriented eutectic microstructures have been produced in the system Al₂O₃/ZrO₂ using a Bridgman-type crystal-growing furnace. Ingots consisted of elongated columnar grains or colonies. Inside the colonies a rod-type eutectic microstructure consisting of rods of ZrO₂ surrounded by an Al₂O₃ matrix was observed. The eutectic point was re-established at 63 mol % Al₂O₃/37.0 mol % ZrO₂ and 1870±5° C. Al₂O₃ is the first phase to nucleate when eutectic growth occurs.     

Microstructure and mechanical properties of Al2O3-Cr2O3-ZrO2 composites

Al₂O₃ is a popular ceramic and has been used widely in many applications and studied in many aspects. On the other hand, zirconia-toughened alumina (ZTA) is a desirable material for engineering ceramics because of its high hardness, high wear resistance and high toughness. In the present research, Al₂O₃-Cr₂O₃-ZrO₂ composites were produced by hot-pressing in order to harden the Al₂O₃ matrix in ZTA. Its microstructure and mechanical properties were studied by SEM, ESCA, XRD, Vickers hardness and bending strength test. It was found that addition of ZrO₂ inhibited the grain growth of Al₂O₃-Cr₂O₃ and the grain growth of ZrO₂ proceeded with increasing amounts of ZrO₂ in the Al₂O₃-Cr₂O₃-Zr₂ composite. The formation of solid solution Al₂O₃-Cr₂O₃ was also confirmed by XRD, and monoclinic ZrO₂ increased on addition of Cr₂O₃. Maximum hardness was at Al₂O₃-10wt% Cr₂O₃ with 10 vol% ZrO₂ and a stress-induced transformation was confirmed on the fracture surface of the specimen after the bending test.     

Evaluation of antibacterial property of hydroxyapatite and zirconium oxide‐modificated magnetic nanoparticles against Staphylococcus aureus and Escherichia coli

In the first section of this research, superparamagnetic nanoparticles (NPs) (Fe₃ O₄) modified with hydroxyapatite (HAP) and zirconium oxide (ZrO₂) and thereby Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs were synthesised through co‐precipitation method. Then Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs characterised with various techniques such as X‐ray photoelectron spectroscopy, X‐ray diffraction, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer–Emmett–Teller, Fourier transform infrared, and vibrating sample magnetometer. Observed results confirmed the successful synthesis of desired NPs. In the second section, the antibacterial activity of synthesised magnetic NPs (MNPs) was investigated. This investigation performed with multiple microbial cultivations on the two bacteria; Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Obtained results proved that although both MNPs have good antibacterial properties, however, Fe₃ O₄ /HAP NP has greater antibacterial performance than the other. Based on minimum inhibitory concentration and minimum bactericidal concentration evaluations, S. aureus bacteria are more sensitive to both NPs. These nanocomposites combine the advantages of MNP and antibacterial effects, with distinctive merits including easy preparation, high inactivation capacity, and easy isolation from sample solutions by the application of an external magnetic field.Inspec keywords: nanocomposites, X‐ray chemical analysis, microorganisms, magnetic particles, scanning electron microscopy, precipitation (physical chemistry), nanomagnetics, X‐ray diffraction, X‐ray photoelectron spectra, nanoparticles, superparamagnetism, iron compounds, antibacterial activity, biomedical materials, nanomedicine, calcium compounds, nanofabrication, Fourier transform infrared spectra, magnetometers, zirconium compoundsOther keywords: antibacterial effects, antibacterial property, superparamagnetic nanoparticles, X‐ray photoelectron spectroscopy, X‐ray diffraction, X‐ray analysis, antibacterial activity, bactericidal concentration, S. aureus bacteria, Staphylococcus aureus, Escherichia coli, hydroxyapatite, coprecipitation method, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer‐Emmett‐Teller method, Fourier transform infrared spectroscopy, vibrating sample magnetometer, microbial cultivations, nanocomposites     

Solid state reactions in the ZrO2 · SiO2 - αAl2O3 system

Solid state reactions between ZrO₂· SiO₂ and Al₂O₃ in mixed powders were studied by quantitative X-ray diffraction, density measurements and qualitative EDAX. Data were obtained at temperatures ranging from 1400 to 1600° C for 5 h; the initial molar ratios of the reactants (Al₂O₃/ZrO₂ · SiO₂) varying from 0 to 5. The results indicate that: (1) ZrO₂· SiO₂ and Al₂O₃ react and form ZrO₂, crystalline 3Al₂O₃ · 2SiO₂ and a noncrystalline mullite phase; (2) the non-crystalline mullite phase is an important transitional phase towards equilibrium under subsolidus conditions. In the experimental conditions used the amount of the non-crystalline phase varies by as much as about 15%. This phase is of great importance in the mechanisms of reaction sintering between ZrO₂ · SiO₂ and Al₂O₃.     

Ion-based methods for optical thin film deposition

The optical properties of the dielectric oxide films SiO₂, Al₂O₃, TiO₂, ZrO₂, CeO₂ and Ta₂O₅ produced by ion-based techniques have been reviewed. The influence of ion bombardment during deposition is discussed in some detail and the various production techniques are described. Recent results on the deposition and properties of diamond-like carbon films are also reviewed. Finally, some examples of the practical applications of high quality dielectric oxide films are given.