Papers by Keyword: Titania (TiO₂)

Abstract: The large negative temperature coefficient of resonant frequency ( τ f ) of Al2O3 is a problem for applicable microwave/millimeter wave dielectrics. A Previous study reported that the τ f was improved by sintering with TiO2 and then annealing, where the annealing decompose the secondary phase of Al2TiO5. This study investigated the hold time of annealing. The Quality factor (Qf ) value decreased when the sample was annealed at 1100°C for 2hrs. While Al2TiO5 was not detected by X-ray powder diffraction, it was located around TiO2 by scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. It should be considered that the degradation of the Qf was caused by the existence of noncrystalline Al2TiO5 and new boundaries between noncrystalline Al2TiO5 and TiO2.

Abstract: The purpose of this study is to prepare high-quality TiO2 thin films suitable for dye-sensitized solar cells using electrophoresis method. A high-quality TiO2 thin film without crack could be deposited using highly dispersed colloidal solution of TiO2 fine particles. Highly dispersed colloidal solution was prepared using mechanical milling (MM). The two electrodes of electrophoresis were set parallel to liquid level. Optimum preparing condition to disperse TiO2 fine particles using MM could be found. Under this condition, homogeneous TiO2 thin film was deposited on ITO glass. The open-electromotive force and short-circuit current of dye-sensitized solar cell showed excellent reproducibility.

Abstract: TiO2 was crystallized to form particles in aqueous solutions containing ammonium hexafluorotitanate and boric acid. XRD diffraction patterns indicated they were in a single phase of anatase TiO2. TiO2 particles prepared at 90 °C exhibited N2 adsorption-desorption isotherms of type IV. BET specific surface area of the particles was estimated to 13 m2/g. On the other hand, TiO2 particles prepared at 50 °C exhibited N2 adsorption-desorption isotherms of type I. BET specific surface area of the particles was estimated to 168 m2/g. Crystal growth of TiO2 was strongly affected by synthesis temperature. Nano-sized pores or surface structure of TiO2 particles prepared at 50 °C would increase N2 adsorption volume to realize high BET specific surface area. Additionally, aqueous solution process described here had an advantage that TiO2 crystallized at ambient temperature. Anatase TiO2 was prepared without annealing at high temperature which caused aggregation of particles and disappearance of surface nanostructures. The particles with large surface area can be thus utilized for catalyst, cosmetic, photocatalyst, dye-sensitized solar cell or sensors.

Abstract: For the growth of Electroluminescent (EL) device market, the attention of many researchers is centered on improving the properties such as brightness, power consumption, device reliability, etc. The powder EL device is one of solutions for the easy mass production, the simplification of structure, and low cost. Although the powder process is the solution, that has the problem with the poor brightness than the film process. So, we focused on increasing the brightness of powder EL device. The emissive layer was made up the composites adding metal oxide nanopowder such as TiO2 and ZnO to powder phosphors. As the data of previous researcher, the TiO2 and ZnO had the different dominating traps by photovoltage measure, that is, TiO2 show hole traps, ZnO show electron traps [1]. The brightness of powder EL device proportions to the high electricfield formation. The TiO2 or ZnO in the powder phosphor composite can help the emission that may be advantageous to form high electricfield at low voltage. The EL devices with green ZnS phosphor were fabricated using spin coating method. The effect of TiO2 and ZnO on the luminescent property of EL device was investigated. The brightness was obtained as applied driving voltage at 400 Hz and frequency variation at 50 V.

Abstract: In past years scientists have interest in new specific TiO2 properties, which result from oxygen and titanium ratio in ceramic. Recently such TiO2 applications as implantable biomaterials in medicine and photocatalysts in purification of waste water become very significant. High temperature vacuum treated titanium oxide ceramics become biologically active and decrease microbiological water pollution when used as electrodes in electrochemical water treatment. In most of these cases highly dense ceramics are requested. TiO2 low-temperature modification anatase and TiO2 high-temperature modification rutile was used during the investigation. Different additives were used to improve particle packing and increase green density of pressed pellets as well as following sinter density. During the investigation it was found that green density of the samples depends not only on powder characteristics such as particle size distribution, grain size, mineralogical composition of raw material, quantity and nature of additives used in mass preparation procedure but also on kind and magnitude of compaction and sintering conditions.

Abstract: In this work, we present the effect of DC power from 100 W to 500 W on the structural and hydrophilic activity of TiO2 films. The TiO2 films were prepared by DC magnetron sputtering on the glass substrate without any external heating. The structure of TiO2 films were analyzed by atomic force microscope and X-ray diffraction. XRD patterns indicated the films were amorphous. The surface roughness and grain size were enlarged by the increasing of the DC power while the substrate temperature was climbed up with the increasing of the DC power. From the point of energetic ion bombardment, it was related with DC power between sputtering processes. The hydrophilic activity of TiO2 films were analyzed by the contact angle meter. The water contact angle decrease with increasing of the DC power.

Abstract: The photocatalytic decolorization of aqueous solutions of Direct Red 27 in the presence of various amounts of semiconductor powder suspensions has been investigated in a batch reactor with the use of artificial light sources. ZnO and TiO2 have been found the most active photocatalysts; the effect of catalyst loading and type on the reaction rate was optimized for maximum degradation. The results imply that 1:1 ratio is proper for the photocatalytic removal of Direct Red 27. In addition, the effects of particle size and surface area were examined in this photocatalytic process. The results showed that the decolorization efficiency increases with increase in surface area, and decrease in powder size. The efficiency is related to mechanism of reactions on the active sites of the catalyst surface and broad adsorption of compounds with different band gaps

Abstract: TiO2 films were prepared using radio frequency (RF) magnetron sputtering and were deposited on glass and Si substrates. We varied deposition time at room temperature with RF density of 3.7 W/cm2 and argon flow rate of 4 sccm. The morphological, structural, optical and electrical properties were studied by Atomic Force Microscope (AFM), X ray Diffractometer (XRD) and UV-VIS-NIR spectrophotometer. The transmittance is maintained in the range of 70- 90% in the visible and near-infrared range, high refractive index of 2.4 and large direct band gap of about 3.5 eV are obtained. These films are annealed at 300°C during 2 hours. The annealing effect is investigated in this work. The results of this study suggest that the variation of the deposition time allow the control of the structural, optical and electrical properties of the films.

Abstract: The combustion process of Mg-TiO2 system was preliminarily investigated from three aspects of thermodynamics, reaction kinetics and the technological parameters. The result indicates that the adiabatic temperature of Mg-TiO2 system is between 2060K and 2140K because the major existent modalities of TiO2 is the rutile and anatase, this meets the empirical criterion that the SHS reaction will be self-sustaining; The solid-solid reaction occurs at about 767K; Ti powders can be produced only when the ratio between Mg and TiO2 arrives at 2.9:1; The higher the vacuum, the more complete the reaction; The combustion temperature arrives at its peak when the pressure of green compact arrives at 250MPa; the velocity of the combustion wave increases with the augmentation of the pressure of green compact. So the proper control of the technological parameters can change the reaction temperature, reaction rate and the components of reaction products.

Abstract: After reviewing most of the recent developments performed on hybrid processes, basic physical phenomena of PVD-PECVD processes are detailed with the help of a model showing the different influences of main process parameters. Ti-Si-O and Zn-Si-O thin films are synthesized as possible examples of composite thin films. Limitations of the model developed are also discussed with respect to the composition and structure of deposited thin films.