Papers by Keyword: Nanoporous

Abstract: Research on preparation of nanoporous silica aerogels that using cheap silica sol as silica source, undering atmospheric drying. Using orthogonal test method study the different components how to influence the gel time and the aerogel density and obtaining the best ratio. Also study the different PH value how to influence the gel time, aerogel density and the micro-structure. The results showed that: in Silica Sol, ethanol and water system, the ratio of silica sol and alcohol has significantly affected on gel time and aerogel density, the best volume ratio is 1:3, PH from 2 to 5 aerogel density is about 0.32g/cm³, but the gel time decreases rapidly, PH from 5 to 7 aerogel density increases to 0.4g/cm³ quickly, and gel time changes a little, SEM showed that the micro-structure of aerogel is the best when the PH is 5. The non-critical drying method of cheap preparation comes true.

Abstract: This study provides a simple and low cost method to deposit TiO2 nanoporous thin films onto the titanium mesh substrate. The flexible titanium mesh is adopted as electrodes where a novel structure of dye-sensitized solar cell (DSSC) is fabricated. The titanium mesh owns many advantages such as low resistance, cheap and high temperature tolerance. The photoanode is fabricated while the Ti mesh immersed into the alcohol solution of nanopowder of TiO2 (P25). For a better adhesion, several treatments against the titanium mesh are carried out. The photovoltaic parameters of various DSSC are discussed through the observations of TiO2 nanoporous thin films. The alcohol solution of N719 dye is used to sensitized the photovoltaic and the electrolyte is a mixture of 0.5 M LiI, 0.05 M I2 and 0.5 M 4-tert-butyl-pyridine in 3-methoxypropionitrile. With a Xenon illuminating, a flexible cell with Jsc=2.9 mA, Voc=0.5 V and F.F =0.68, η=1.02 % is obtained.

Abstract: Formation behavior of nanovoids during the annealing of amorphous Al₂O₃ and WO₃ was studied by transmission electron microscopy. The density and size of the voids in Al₂O₃ and WO₃ increase with increasing annealing temperature from 973 to 1123 K and from 573 to 673 K, respectively. It is suggested that the formation of nanovoids during annealing is attributed to the large difference in density between as-deposited amorphous and crystalline oxides.

Abstract: We reported our detailed investigation of the microstructure and surface chemistry of nanoporous black Si layers using transmission electron microscopy techniques such as HRTEM, EDS, and EELS. We found that a one-step nanoparticle-catalyzed liquid etch creates deep conical nanovoids. The cones provide the density-graded surface that suppresses reflection. The surface of the as-etched nanoporous black Si is an amorphous Si suboxide (SiOx) produced by the strongly oxidizing nanocatalyzed etch. The c-Si/suboxide interface is rough at the nanometer scale and contains a high density of point defects.

Abstract: Ordered nanoporous carbon (ONC) was synthesized by adopting sucrose as precursor and SBA-15 as template. The thermal stability of sucrose and its SBA-15 composite were detected by thermogravimertic analysis. Transmission Electron Microscope, X-ray diffraction and nitrogen adsorption technology were used to characterize the morphology, microstructure and specific surface area of resultant ONC. The effects of carbonization temperature and pre-carbonization on the microstructure of ONC were investigated. The results have shown that SBA-15 is a kind of ideal template for preparing ONC, from which ONC with the diameter around 8 nm was obtained. When carbonized at 700 °C, the specific surface area of ONC derived is 2884.05 m²/g.

Abstract: . In intermetallic compounds, random vacancy motion is not possible as it would disrupt the equilibrium ordered arrangement of atoms on lattice sites. In view of this limitation, various atomistic models have been proposed, which allow atom-vacancy exchanges to take place without concomitant long range disordering. For a L12 -type A3B structure, the major element A diffuses faster than the minor element B. The trend is attributed to the different diffusing paths; A atoms can diffuse through site exchanges with a neighbouring vacancy on its own sublattice, while the jump of a B atom to a neighbouring site always creates wrong bonds. For L10-type structures such as γ-TiAl, significant diffusion anisotropy is observed; Ti atoms diffuse on the Ti sublattice, while Al atoms also diffuse on the Ti sublattice. The formation of hollow metal oxide nanoparticles through the oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni. The hollow structure is obtained as a result of vacancy aggregation, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process. This suggests the occurrence of two different diffusion processes in the formation of hollow oxides.

Abstract: Eco-debinding process using supercritical extraction of low molecular organic binders in nano-porous ceramic bodies was examined. The debinding properties related to structural changes during supercritical extraction and conventional solvent extraction were also compared. The debinding rate of supercritical extraction was significantly enhanced compared to the debinding rate of solvent extraction because of the high diffusivity of the supercritical carbon dioxide for the low molecular weight wax binder in the molded bodies with nano-sized pore structure, although both debinding rates showed same a square root of time dependence. The extraction rates with morphological changes varied depending on the degree of saturation at the end of debinding stages. Both the debinding methods experienced morphological changes with a debinding front separating the pendular state region from the undebinded region with fluid state in low molecular paraffin wax based powder compacts during extraction. The capillary structural changes in the green bodies caused severe defects during extraction and degraded the physical properties. In spite of the abrupt changes of the capillary structure, the debinding defect was significantly alleviated for the supercritical debinded ceramic bodies, compared to the solvent extracted bodies.

Abstract: Refractories are used in a variety of processing industries including the ceramic, steel, aluminum, metal casting and heat treatment industries. Refractories provide thermal insulation, and do so by providing stagnant or "dead" gas space, namely, they contain a large volume fraction of voids. The prime criterion for material selection is refractoriness (i.e. use temperature) and the dimensional stability. One key property required for insulating refractory qualification is the service temperature limit (STL), which is related to composition, sinterability at use temperature, sintering temperature, and void volume. During the past ten years nano-pore and nano-scale fractal refractories have become available which are possibly significantly less toxic when compared to fibrous refractories. The materials used in fractal refractories are discussed in this article. Apart from use as high temperature thermal insulators the new class of materials are also finding use in a variety of products and applications of structural components such as nano-pore high performance coatings, sensors, filters and membranes used in the electronics, aeronautics, space, energy, and biomedical engineering fields.

Abstract: Nanoporous hydroxyapatite ceramic was simply fabricated from nano hydroxyapatite powder and polyvinyl alcohol (as a pore former). The vibro-milling method was used to produce the nano hydroxyapatite composite powder. The powder was then sintered at 1200°C for 3 h. It was found that average porosity of the final product of 64.6±1.4% could be achieved. Open and interconnected pores were obtained with average pore size of less than 100 nm, indicating a nanostructure occurring in the ceramic. In addition, the bending strength of the nanoporous ceramic was measured to be 14.7±3.2 MPa which is practically high for bone repairing applications.

Abstract: Surface modification is a process in which Si-CH3 groups of trimethylchlorosilane (TMCS) replace -OH groups on the inner surface of SiO2 aerogels, so the surface property of aerogels has shown hydrophobic performance which could be changed back to hydrophilic by 450 heat treatment. This aerogels with surface property controlled are prepared via sol-gel process with polyethoxydisiloxanes (E-40) used as precursor, and have typical porous structures dried at ambient pressure: high porosity (above 90 %), super specific surface area (about 1000 m2/g), low bulk density (down to 3.03 kg/m3) and average pore size is about 20 nm. This paper presents adsorption mechanisms in aerogels and illustrates that the adsorption capacity of aerogels is three or four times as much as that of activated carbon fiber (ACF) and granule of activated carbon (GAC). So SiO2 aerogels are potentially important to be used as absorbents being quite efficient to adsorb toxic substances.