October 2003 Method for Production of a-Alumina Whiskers via Vapor-Liquid-Solid Deposition (A) (C) Fig. 1. (A) Scheme indicating the position of aluminum wires inside crucibles, placed over a SiO, bed inside a tube furnace(B) Development of corundum fibers around aluminum wires.(C) After adequate treatment, aluminum wires are completely surrounded by a white cottonlike mass of a-Al,O, fibers, fibers(Fig. 5). ICP analysis revealed that the fibers were composed polycrystalline fibers exhibited a great range of properties, bu of a-Al,O, with a purity of.5%. Nevertheless, ICP also heir tensile strength was( Fig. 7) showed that only -0 I% of the contaminating elements remained after leaching. As explained earlier. leaching was conducted in a IV. Discussion 35% HF-65% HNO, solution, followed by overnight immersion in HCL. The first leaching treatment was adequate to remove A feasible explanation for the increased production of fibers silicon from the system, and the second treatment removed aluminum. In principle, the vast majority of the other elements following arguments. First, we consider the growth of a-Al,O, present at the drops should also have been removed, Becau fibers when only aluminum and SiO, powder were used; second Al2O3 is resistant to acids, the fibers and ribbons remained we study the effect of adding certain metals to the system. unchanged after treatment. This cleaning protocol allowed u As explained earlier, when pieces of aluminum were placed analyze the impurities that were"inside"the crystals over quartz at 1300%-1500oC, a-Al,O, crystals were produced and Some of the measured single-crystal Al,O, fibers exhibited a grew into a white cottonlike mass of crystals around the aluminum tensile strength slightly >6 GPa(Fig. 6). The maximum measured piece. The drops at the tip of the fibers clearly showed that the tensile strength of the Al,O, ribbons was --260 MPa. The fibers had grown via VLS deposition