Advanced Materials Research Vols. 11-12

Abstract: High concentrated hydrochloric/nitric/sulfuric acid were used to dissolve Ti(OH)4 produced with TiOSO4. It was found that, titania, from pure rutile phase to anatase-rutile mixed phase to pure anatase phase have been synthesized at low temperature in liquid media through controlling the hydrolyzation conditions. The phase composition and the special surface area of nanometer titania powder were characterized by means of XRD and BET. The K-edge fine structure of Ti atom sites of rutile TiO2 was investigated with grazing incidence reflection mode XAFS (EXAFS and XANES) spectroscopy. The well-crystal rutile TiO2 with fine particle size and high specific surface (above200m2/g) was formed at low temperature below 80°C, while the anatase TiO2 was formed at higher temperature in hydrochloric or nitric acid solution. But in sulfuric acid solution the crystal phase was always anatase at any temperatures. The EXAFS and XANES result showed that the order of the lattice, the coordination numbers of the Ti atom for the first shell, the second shell and the third shell as well as the relative intensity of K-preedge three peaks increased with the increase of the rutile TiO2 nanoparticle size.

Abstract: We have prepared titania aerogel (=AG) embedded by NiB nano-clusters by sol-gel method, immersion of the prepared wet gel into the NiB dispersed solution, and the subsequent super critical drying (=SCD). The AG was characterized by X-ray diffraction (XRD), a transmission electron microscopy (TEM), and a fourier transform infrared spectrophotometer (FT-IR). XRD and selected area electron diffraction (SAED) patterns assured the formation of TiO2 anatase phase. TEM observation reveled the composition of TiO2 crystallites with about 4 nm in size. Catalyst performance for the ground sample was confirmed by chemical reaction of oxidation of benzene at low temperature, and the difference in catalyst performance between TiO2 AGs with and without the embedded NiB nano-clusters has been examined.

Abstract: YAG precursors were co–precipitated from a mixed solution of aluminum and yttrium nitrates using urea as precipitant. After being washed by ethanol several times, the gel–like precursor was dispersed in absolute ethanol to form suspended liquid. The mixture was placed into a high–pressure autoclave, which followed by heating ethanol to supercritical state (Tc > 243°C and Pc > 6.3Mpa). The precursor dried via supercritical ethanol fluid technique was sintered at different temperature according to requirement. The phase transformation, composition and micro–structural features of the products were characterized by XRD, TG/DSC, BET and TEM techniques. It was found that after supercritical ethanol fluid drying the precursor was well dispersed, uniform and caused better sinterability of the resultant YAG powder. XRD results indicated that the precursor was partial crystalline and the pure phase YAG can be obtained at 1200°C calcinated for 2h. TG/DSC revealed the formation process of YAG phase. The averaged size of YAG nanocrystalline powder was 30–40nm and well dispersed according to TEM.

Abstract: The photocatalytic effects of 4 samples, which TiO2 layer uniformly coated on Al fiber, are evaluated by NOx removal. An anatase TiO2 coating with good crystal quality and high Ti content exhibits the best photocatalytic effect on NOx removal. It is coincidence with the results of XRD, XPS results for 4 samples. The photocatalytic ability is enhanced by the introduction of H2O2 due to the formation of large amount OH radicals.

Abstract: RF (Resorcinol-Formaldehyde) aerogels and carbon aerogels were prepared through the sol-gel method following the routes of polymerization, gelation, supercritical drying and pyrolysis processes. The influence of fabrication parameters on the textural structure of the samples, e.g., specific surface area, pore size, and pore size distribution, etc., were systematically investigated. With a decrease in the R/F molar ratio, or an increase in the catalyst content within a limited range, the porosity of the nanostructure materials increases. The optimal temperature of pyrolysis for RF aerogel was investigated by TGA (Thermogravimetric Analysis).

Abstract: Nano-sized barium titanate powders were prepared by the high-gravity reactive precipitation (HGRP)-hydrothermal method. The properties and defects of hydrothermal barium titanate crystallites were investigated by TEM, XRD and FTIR. The mean particle size of the hydrothermal barium titanate was about 70 nm with narrow particle size distribution. The crystallite phases and OH defects were focused. The results show that the powders without heat treatment were crystallized as cubic-BaTiO3 and the absence of tetragonal with increasing calcined temperature to 1100°C. The IR results exhibited the OH defect content in the crystallites was to increase the heat treatment temperature and reduced the probability of forming barium vacancies.

Abstract: Sintering behavior and mechanism of barium titanate powders prepared by high-gravity reactive precipitation (HGRP) process has been investigated by a dilatometer. The mean particle size of barium titanate powders prepared by HGRP was about 80 nm. Pure BaTiO3 pellets were sintered at a constant heating rate of 2.0 K/min and the temperature of shrinkage-onset for pellet was 1060°C. The maximal shrinkage was 165um and the maximum of shrinkage rate was 8.0 x 10-3 / min at 1170°C. The sintering mechanism for the initial stages of sintering was determined by isothermal dilatometric measurements and was found to be viscous flow.

Abstract: Thermal shock resistances of commercially available aluminum nitride and alumina ceramics as used for the circuit substrate were evaluated by infrared radiation heating (IRH) technique. Thermal shock fracture toughness, R2c of these materials was estimated experimentally and theoretically using IRH technique at various ambient temperatures. Temperature dependence of thermal properties of the materials was taken into account for the temperature and the thermal stress analysis. Experimental values of thermal shock fracture toughness were in good agreement with the calculated values. Thermal shock fracture toughness decreased with elevated ambient temperature in both ceramics.

Abstract: Thermal shock test for porous SiC ceramics heated up to testing temperature was performed by a water flow cooling method. In order to find the influence of the penetration for the porous material under the thermal shock, transient temperature distribution was simulated with taking account of the infiltration of the cooling media into the specimen. Thermal stress distributions in the specimens were also calculated from the estimated temperature distributions. In this study, it was evident that the temperature variation of the porous ceramics was more rapid than that of the ceramics without taking account of the penetration.

Abstract: A membrane support provides mechanical strength to a membrane top layer to withstand the stress induced by the pressure difference applied over the entire membrane and must simultaneously have a low resistance to the filtrate flow. Due to their low thermal-expansion coefficient and good thermal-shock resistance as well as excellent mechanical and chemical stability at elevated temperatures, porous SiC ceramics have been widely used as catalyst supports and hot-gas or molten-metal filters. In this work, the influence of the particle size, sintering time and sintering temperature on the porosity and permeability of supports made by dry-pressing of micron-sized SiC powders is investigated. The present work presents a comparison of properties and performance data for samples made with different particle size. The effects of sintering time and temperature were analyzed in view of overall porosity and permeability. From calculations it becomes clear that optimum values exist for the material properties of the support.