Method for Production of α‐Alumina Whiskers via Vapor‐Liquid‐Solid Deposition

Abstract

α‐alumina (α‐Al2O3, corundum) fibers exhibit high thermal and chemical stability, as well as good mechanical properties, even at high temperatures. Such characteristics make them good candidates for use in composites. Nevertheless, very few methods of producing α‐Al2O3 fibers are available. In the present work, we describe a method that uses aluminum pieces deposited on SiO2 powder, in an argon atmosphere, at temperatures in the range 1300°–1600°C. The α‐Al2O3 fibers are obtained via vapor‐liquid‐solid deposition. The novel addition of nickel and cobalt (or their oxides) allows the use of temperatures >1500°C, resulting in improved fiber production. We demonstrate that the metals do not contaminate the fibers produced in this way. Finally, we also estimate the tensile strength of the Al2O3 fibers produced through this method.

Synthesis and Optimization of the Production of Millimeter‐Sized Hydroxyapatite Single Crystals by Cl−–OH− Ion Exchange

“…However, our results indicate that the smaller crystals can exhibit high strengths, reaching values up to 2 GPa. These values are comparable to the tensile strengths reported for single crystalline fibers of technical ceramics such as Al 2 O 3 or SiC (2–6 GPa) and will likely correspond to crystals with very low defect concentrations. The results illustrate how one of the main limitations in the synthesis of apatite fibers and crystals is the need to develop processes for the reliable fabrication of “pristine” materials.…”

Growth mechanism of single-crystal α-Al2O3 nanofibers fabricated by electrospinning techniques

“…8 Later approaches have adopted a so-called "displacement reaction" by heating mixtures of powder aluminum (Al) and metal oxides, such as SiO 2 , 10-17 MoO 3 , 17 WO 3 , 17 or SiC 18 in an argon atmosphere to fabricate single-crystal fibers, whiskers, and nanowires. The growth of the fibers/whiskers was found to be mostly in the [0 0 1] direction through the VLS mechanism [10][11][12][13][14][15]18 or through a mechanism that is analogous to Ostwald ripening. 16,17 Both of these mechanisms are categorized as tip growth models, resulting in characteristic round droplets or slight sharp curvatures on the tips of the fibers/whiskers.…”

Synthesis of ultra thin α-alumina nanobelts from aluminum powder by chemical vapor deposition

“…Efforts have been put forward to obtain nanostructured alumina. Currently, nano-alumina have been obtained by catalyst-supported chemical vapor deposition (CVD), [5][6][7] or by the in situ displacement reactions. [8][9][10] In many of these fabrication methods, it is usually not possible to obtain pure products without having impurities.…”