Papers by Keyword: TiO2-ZrO2

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Authors: M.A. Ribeiro, Laédna Souto Neiva, Ruth Herta Goldsmith Aliaga Kiminami, J.B.L. de Oliveira, L. Gama
Abstract: Because of the unique properties that the system TiO2-ZrO2 has, this system has attracted great interest in catalytic circles. In general, the TiO2-ZrO2 oxides composites have a greater surface area and a stronger acidity when compared to the single oxide and they are used as catalysts supports for many catalytic reactions. This work is to evaluate the effect of calcined temperature in structural and morphological characteristics of Ti1-xZrxO2 nanopowders obtained by Pechini method. For this study, the doping value was 0.25 moles of Zr. The powders were calcined at temperature of 500 to 900°C for one hour. The powders were characterized by XRD, SEM and BET. The X-ray diffraction showed that the powders present a TiO2 anatase phase and another of ZrO2 tetragonal. The crystallite size ranged from 4.8 to 14.6 nm for the temperature of 500 to 900°C, respectively. The analysis of scanning electron microscopy showed soft homogeneous agglomerates with particles around 100 nm. The main particles sizes by BET were ranged from 10 to 20 nm, showing that the synthesis is effective to obtain nanometric powders.
1393
Authors: José Vitor C. Souza, Pedro José Castro, Maria do Carmo de Andrade Nono, Sergio Luiz Mineiro
Abstract: For microwave applications, including mobile and satellite communications, ceramic resonators should have a high dielectric constant, low dielectric losses, and high frequency stability. In this sense, TiO2-ZrO2 ceramics have been investigated as a function of sintering behavior, phase composition, and microstructure. The ceramics were densified reaching a value of about 86% of theoretical density at 1400°C sintering temperature. The ceramics are prepared by mixing raw materials with the following TiO2-ZrO2 weight % ratio: 100 to 0, 90 to 10, and 80 to 20, respectively. The measured dielectric constants are between 79 and 88 values, while the quality factor due to dielectric losses are between 2820 and 5170. These results point out the influence of Ti/Zr ratio on controlling the dielectric properties.
641
Authors: Jae-Kil Han, Sung Min Choi, Ik Hyun Oh, Fumio Saito, Byung Teak Lee
Abstract: TiO2(1-.ZrO2. (.=- 0.2, 0.4, 0.6 and 0.8) composite powders having a homogeneous distribution and nanocrystalline were successfully synthesized by sol-gel process using titanium iso-propoxide as precursor. The particle sizes of TiO2-ZrO2 powders calcined at 600°C were measured ranging from 10nm to 19nm by XRD and TEM. For the comparison of photocatalytic activity, TiO2-ZrO2 composite powders were tested in the degradation of phenol and the photoreduction of inorganic pollutants. The degradation of phenol increased with increase the content of anatase TiO2 phase.
289
Authors: José Vitor C. Souza, Pedro José Castro, Maria do Carmo de Andrade Nono, Sergio Luiz Mineiro
Abstract: Dielectric ceramics have been widely investigated and used for microwave applications such as resonators and filters. The present study deals with the influence of sintering temperature on microwave dielectric properties of TiO2 ceramics with 10, 20, and 30 wt% ZrO2. Three compositions have been developed through mixing procedures and then tested for each sintering temperature: 1500 and 1400 °C. X-ray diffraction and scanning electron microscopy are carried out aiming to explain the ceramic behavior of each sample. The dielectric constants of different ceramics for both temperatures varied from 85.4 to 62.6, while their quality factor due to dielectric losses varied from 3110 to 1630. The Q decrease is attributed to the non uniform grain growth and to the obtained crystalline phases. The best microwave parameters were obtained for the ceramics sintered at 1400 °C, which can be applied in microwave circuits as dielectric resonators.
646
Authors: Xi Ning Lu, Cun Yi Song
Abstract: TiO2, 50%TiO2-ZrO2 and 80%TiO2-ZrO2 were prepared by sol-gel method. The manganese oxides were impregnated on the carrier and the catalysts were used for low-temperature selective catalytic reduction of NOx with ammonia (NH3-SCR) in the presence of excess O2. The samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results showed that the particle size of 80%TiO2-ZrO2 is the smallest among the three kind of carrier and the particles are highly dispersed. By adding the ZrO2, the Zr4+ ions replaced the lattice Ti4+ ions, and thus caused lattice distortion in the TiO2 and an increase of the active point amount on the carrier. Furthermore, the Zr also promoted the dispersion of the active ingredients carried on the carrier, increased the surface concentration of Mn. The most active catalyst was obtained with a mass MnOx/80%TiO2-ZrO2 ratio of 0.1.The best MnOx/80%TiO2-ZrO2 catalyst yielded nearly 92.6% NO conversion at 130°C at a high space velocity of 67,000 h-1.
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