The effect of SiO 2 addition on the anatase-to-rutile phase transition was investigated by DTA, XRD, FTIR, and XPS. TiO 2 xerogels containing SiO 2 up to 20 mol% were prepared by mixing and hydrolyzing titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) with HNO 3 as a catalyst. With increased amounts of SiO 2 in the xerogels, the following results were obtained: (1) the crystallization temperature of anatase increased from 415°C in pure TiO 2 to 609°C in 20-mol%-SiO 2 -containing xerogel in the DTA curves; (2) the formation temperature of rutile, according to quantitative XRD analysis, increased with increased SiO 2 content up to 5 mol% SiO 2 but became constant at higher SiO 2 contents; (3) the crystallinity of anatase became lower; and (4) the lattice parameter a of the anatase decreased slightly, but the parameter c decreased greatly up to 20 mol% SiO 2 . Although the added silicon atoms were considered from these results to be incorporated into the amorphous TiO 2 and anatase structures, the 29 Si MAS NMR spectra of the xerogels containing 10 mol% SiO 2 showed only tetrahedral silicon, with no indication of silicon in octahedral coordination. When calcined at higher temperatures, the xerogel showed polymerization of the SiO 4 tetrahedra in the NMR spectra and the Si-O-Si vibration in the FTIR spectra. The chemical composition of the xerogel surfaces, measured using XPS, showed increased SiO 2 content with increased calcining temperature, indicating the expulsion of silicon from inside the particles to form an amorphous SiO 2 surface layer. The formation of this amorphous SiO 2 surface layer was considered to be important in retarding the anataseto-rutile phase transition by suppressing diffusion between anatase particles in direct contact and limiting their ability to act as surface nucleation sites for rutile. These effects of silicon additions were similar to those observed in the ␥-Al 2 O 3 -to-␣-Al 2 O 3 transition.

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Adsorption properties of activated carbons prepared from waste newspaper by chemical and physical activation were investigated using water vapor, ammonia, methane, and methylene blue (MB) as adsorbents. The water vapor adsorption isotherms show type V behavior and the maximum vapor adsorption of the chemically and physically activated products is about 1050 and 450 ml/g, respectively. The higher water vapor adsorption of the chemically activated products is attributed to the higher specific surface area (S(BET)) and greater hydrophilic activity (arising from the surface oxygen-containing functional groups) than in the physically activated products. The adsorption of ammonia and methane was measured by temperature-programmed desorption (TPD). NH(3) adsorption is found to be higher in the chemically activated product than in the physically activated product while methane adsorption is slightly higher in the physically activated products even though these have lower S(BET) values. In the MB adsorption, the chemically activated products show higher adsorption (390 mg/g) than the physically activated product. These results are suggested to be related to the surface characteristics.

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ZnO flower‐like nanostructures were grown on Ge (100) substrate, by a modified chemical vapor condensation technique of zinc acetate dihydrate at 300 °C, without using any catalyst. These self‐organized three‐dimensional nanostructures were composed of hierarchical arrangement of ZnO nanorods of diameter ∼50 nm around a common nucleus and were distributed uniformly over the entire substrate surface. Evolution study of these structures indicates that the growth begins with a two‐dimensional planar arrangement of 〈0001〉‐oriented ZnO nanorods. With increasing growth time, the expanding adjacent two‐dimensional growth fronts approach each other, followed by which, the formation of three‐dimensional flower‐like structures evolve. Surface diffusion mechanism seems to play an important role in forming these nanostructures, which has been discussed in detail. Elaborate electron microscopic (SEM, TEM) techniques have been used to investigate the growth characteristics of the flower structures. The photoluminescence measurements showed pure free excitonic transition centered at about 3.249 eV with full width at half‐maximum of about 141 meV at 300 K, which blue shifted to 3.361 eV at 10 K with corresponding half width of 7 meV with no defect‐related bandgap peak due to relatively low growth temperature. The optical emission area was imaged through a cathodoluminescence technique. Scanning electron micrograph of a typical ZnO nanorod flower structure grown at 300 °C on Ge (100).

Humidity sensors based on QCM (quartz crystal microbalance) have been developed using an anodized alumina thin‐film as a sensing material. An aluminum thin‐film is deposited on a silver‐coated quartz crystal by electron beam deposition and is anodized in an acid solution. The resultant alumina film is porous. The resonant frequency gradually decreases from 5% to 94% relative humidity (RH) and steeply changes near 100% RH. This result shows that the sensor can be used as a dew‐point sensor as well as a humidity sensor. The response times to the humidity changes from 27% to 59% RH and from 59% to 27% RH are less than 5 s. The sensor shows reversible response to some gases such as ethanol, toluene, and acetone vapors in addition to airborne particles such as pollen.

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Heat transfer from a micro heater is investigated experimentally and numerically. The micro heaters made of Indium Tin Oxide (ITO) are set on a glass substrate immersed in FX3250 coolant. Two different sizes (50μm, 100μm) of heaters are used in the experiments to analyze the size effect. The effect of the surface deposited layer by Al2O3 is also investigated with changing the thickness of the layer. All the experiments are performed in both subcooled and saturated boiling. The boiling curves of different conditions are obtained and compared. The results show that there exists an optimum thickness of deposited layer for heat transfer enhancement. They also show that the present heat transfer process is quite different from that of usual boiling. The phenomena are dominated by heat conduction in the substrate and large portion of the generated heat is transferred to the liquid and then vapor bubble through the substrate around a heater. Further, a photograph of a liquid microlayer under a vapor bubble is taken and the relation between an unsteady bubble behavior and local temperature fluctuations is analyzed.