Alumina Surface (alumina + surface)

Distribution by Scientific Domains

Selected Abstracts

Electric Field Singularity Assisted Nanopatterning,

N. Ravishankar
Ordered arrays of Pt nanoparticles (see Figure) have been produced on a reconstructed alumina surface that serves as a template for nanopatterning. The Pt particles condense from an undersaturated vapor phase only along the crest regions on the reconstructed plane. It is shown that the presence of an electric field singularity leads at the crest regions to the highly site-specific formation of nanoparticles. [source]

Influence of Impurities on Dispersion Properties of Bayer Alumina

J. Kiennemann
Among the different impurities contained in Bayer alumina (Ca, Fe, Na, Si, Mg), calcium was found to greatly influence the dispersion of alumina particles in water. Up to 90% of calcium is dissolved at acidic pH, whereas calcium remains on the alumina surface in the basic pH range and screens the negative Al,O, charges. The presence of calcium, through reducing repulsive interactions between particles, has a negative effect on the dispersion of alumina. The adsorption of the Na+ salt of poly(acrylic acid) (PAA-Na) is strongly influenced by Ca2+/PAA-Na interactions in suspension with an increase of the maximum adsorbed amount of PAA-Na in the presence of calcium. The amount of PAA-Na needed to reach a high electrostatic repulsion and a minimum of viscosity is 2 times higher in the presence of 400 pm calcium than for a low calcium content (,80 ppm). Finally, with an appropriate amount of PAA-Na, a similar state of dispersion can be reached with or without the presence of calcium. [source]

Critical Factors Affecting the Wettability of ,-Alumina by Molten Aluminum

Ping Shen
The wetting behaviors of ,-Al2O3 single crystals with three different faces,R(0112), A(01120), and C(0001),and polycrystals (PC) by molten aluminum were studied over a wide temperature range using both a conventional and an improved sessile-drop method. The critical factors affecting the wettability, such as temperature, atmosphere, substrate surface roughness, and crystallographic orientation, and the influence from the experimental technique, were thoroughly investigated. The results show that the aluminum surface oxidation and the thickness of the oxide film have a pronounced effect on the wettability, especially at low temperatures. To eliminate this effect, the experimental temperature must be over a critical value. Vacuum favors lowering this value compared with atmosphere, and the improved sessile-drop method, particularly using an impingement-dropping mode (I-mode), helps to weaken this effect by mechanical disruption and removal of the oxide film. However, the dropping distance and the dropping force must be controlled to prevent an overspreading of the drop. The effects of the substrate surface roughness and temperature are not significant in the case of a clean aluminum surface and a fine-prepared alumina surface. On the other hand, the effect of the alumina surface crystallographic orientation is noticeable and the wettability is in the order of R > A > PC > C. The intrinsic contact angles of the Al/,-Al2O3 system in the temperature range of 1000,1500C were estimated to be 76,85 for the R and A faces, 88,100 for the C face, and 77,90 for the polycrystal, depending on the temperature. [source]

Antibacterial and Abrasion-Resistant Alumina Micropatterns,

Laura Treccani
In this work, a novel processing route to fabricate alumina surfaces that feature remarkable antibacterial and abrasion-resistant properties is reported. By combining micropatterning with antibacterial enzymes and alumina nanoparticles, we fabricated surfaces that present a feasible and highly interesting alternative to improve, e.g., systems employed for water transport containing abrasive agents, aggressive media and microorganisms. [source]