Effect of silver and palladium on dye-removal characteristics of anatase-titania nanotubes

Anatase-titania nanotubes have been synthesized via hydrothermal and surface-modified by depositing silver and palladium via ultraviolet-reduction method. The pure and surface-modified anatase-titania nanotubes have been characterized using the transmission electron microscope, selected-area electron diffraction, X-ray diffraction, diffuse reflectance, photoluminescence, and Fourier transform infrared spectroscope to reveal their average size, structure, and surface-chemistry. The nanotubes have been utilized for the dye-removal application involving the surface-adsorption mechanism under the dark-condition and photocatalytic degradation mechanism under the ultraviolet-radiation exposure. The variation in the dye-concentration during the dye-adsorption and photocatalysis processes has been determined using the ultraviolet-visible absorption spectrophotometer with methylene blue as a model catalytic dye-agent. It has been shown that silver-deposited anatase-titania nanotubes are more effective in enhancing the kinetics of the dye-removal via surface-adsorption and photocatalytic degradation mechanisms relative to the palladium-deposited anatase-titania nanotubes, which has been attributed to the differences in the surface-chemistry of anatase-titania nanotubes induced by the respective metal-deposition.     

Microwave drying of boehmite sol intercalated smectites

Monohydroxy aluminium oxide (boehmite) intercalated (cross-linked) smectites (SCLS) have been prepared from an aqueous suspension containing sodium mono-ion-exchanged bentonite (2 wt%) and boehmite (AlOOH) sol at pH 3.5 and at 32 °C. The SCLS has been separated by centrifugation and repeated washing. The intercalated smectite was dried in an oven at 60 °C over a period of 24 h and also in a microwave oven of 2.45 GHz frequency and 600 W power over a range of 3–15 min. Both samples have identical thermal and electrical properties. However, the microwave-dried samples have a distinctly higher surface area of 120 m² g^–1, stable up to 650 °C with a marginal reduction to 116 m² g^–1 compared with 94 m²g^–1 for the oven-dried sample. Similarly there was clear difference in the morphological features of the two samples, the air-dried sample having a close packed structure while the microwave one is delaminated and porous.     

Characteristics of Alumina Powders Prepared by Spray-Drying of Boehmite Sol

Boehmite sol prepared from aluminum nitrate has been spray-dried to obtain micrometer-size spherical particles consisting of submicrometer crystallites. The spray-dried powder was further washed with solvents of varying polarities such as acetone, 2-propano1, and 2-methyl-2-propanol. Particle-size distribution, morphology, density, compaction, and sintering characteristics of powders washed with different solvents are reported. The effect of posttreatments on the boehmite-sol-derived powders toward reducing agglomeration and obtaining high-density bodies is discussed.     

Processing and Properties of Sol–Gel-Derived Alumina/Silicon Carbide Nanocomposites

Dense alumina/5 vol% SiC nanocomposites were prepared by sol–gel processing using nanosized (180 nm) precoated SiC powders and a commercial boehmite sol. The SiC powder was precoated with boehmite by a controlled heterogeneous precipitation from an aluminum nitrate solution. The coated SiC powder was then dispersed in a boehmite sol, gelled, calcined, and densified by gas pressure sintering under argon atmosphere at 7–8 MPa pressure. The dependence of the calcination conditions on densification, the effect of seeding on the microstructural development, as well as the mechanical behavior of the sintered specimens, are presented and discussed.     

A hierarchical multi-scale method to simulate reactive–diffusive transport in porous media

A time-dependent, hierarchical multi-scale model to simulate reactive–diffusive transport in a 3-dimensional, porous structure, using a combination of molecular dynamics (MD), kinetic Monte-Carlo (KMC) and Monte-Carlo diffusion (MCD) methods has been developed. The parameters that are passed from the models at the lower spatial and temporal scales (MD, KMC) to those at the higher scales (KMC, MCD respectively) are identified. The advantages and disadvantages of the different methods are discussed with respect to reactive–diffusive transport simulations of atoms in porous 3D structures. The model is illustrated by simulating hydrogen transport, reactions, inventory and re-emission from a porous hydrocarbon layer.     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Fatigue crack growth in Ti-matrix composites with spatially varied interfaces

Spatially varied interfaces (SVIs) is a design concept for composite materials where the interface mechanical properties are varied along the length and circumference of the fiber/matrix interface. These engineered interfaces can be used to modify critical titanium matrix composite properties such as transverse tensile strength and fatigue crack growth resistance in ways that produce a balanced set of properties. The SVI approach may also be used to probe interface failure mechanisms for the purpose of understanding complex mechanical phenomena. Single lamina Ti-6Al-4V matrix composites containing strongly bonded SiC fibers were fabricated both in the as-received condition and with a weak longitudinal stripe along the sides of the fibers. The striped SVI composites exhibited an increase in the overall fatigue crack growth life of the specimens compared to the unmodified specimens. This improvement was caused by an increased extent of debonding and crack bridging in SVI composites. This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee.