Synthesis and Characterization of Aluminum Oxide Submicro-Rings

Abstract

In this note, we report the physical and chemical properties of aluminum oxide submicro-rings (AO-SMRs) obtained by using electrospinning technique. The AO-SMRs were synthesized from aluminum acetate and polyvinylpyrrolidone (PVP) solutions by applying simple elec- trospinning technique. The PVP ((C6H9NO)n, MW ~1,300,000) solution was prepared by dissolving 0.62 g PVP in 10 mL ethanol (99.9%) stirring for 2 hrs at room temperature. The aluminum acetate solution was made by dissolving 5 g of aluminum acetate (C2H5AlO4, MW 140.65) in 5.0 mL distilled water and 6.3 mL ethanol then stirred for 5 hrs at room temperature. All chemicals were purchased from Sigma Aldrich and used as received. The aluminum acetate solution was mixed with PVP solution at 1:1 volume ratio and stirred at room temperature for 5 hrs. The electrospinning solution was obtained after stirring the diluted 7 mL of mixed solution with 2 mL of ethanol for 30 min. The viscosity of the electrospinning solution was checked with a viscometer (AD SV-10), and the average viscosity of the solution was 17 ± 2 cP at 295.8 K. The electrospinning solution was transferred to a plastic syringe (5.0 mL) with a needle of 21 gauge. The syringe was mounted on a syringe pump (KDSci- entific) and an electrically grounded drum collector was covered with aluminum foil. The revolution of the collector was fixed at 100 ± 1 revolutions per minute. Electric fields (Nano NC) of 0.96 and 1.04 kV/cm were applied between the needle and the collector then dense SMR composites were collected on the aluminum foil. We checked the viscosity dependence on the SMR fabrication. When the viscosity of the solution was lower than the SMR collection condition (17 ± 2 cP), neither SMRs nor fibers were collected since the solution was too sparse. Only fibers were collected without mixing with SMRs over 67 cP of the viscosity because the solution was too dense to electro- spin as a ring. In order to check the decomposition temperature of the SMR composite, thermo gravimetric analysis (TGA) and differential thermo analysis (DTA) were conducted (Figure 1). Dehydration of SMR composite was mainly has occurred until 573 K. Most PVP and hydrocarbons in the SMR composite were decomposed at about 873 K. 13 The obtained SMR composite was calcined to obtain AO-SMRs at two different temperatures named 573 and 873 K. X-ray diffraction (XRD, PHILIPS (Netherlands), X'Pert-MPD System) was performed to identify the crystallinity of the AO-SMRs in glancing mode. XRD study (Figure 2) re- vealed that only metallic aluminum was formed in crystalline phase and the crystallinity of aluminum oxide was not detected. This implies that aluminum oxide was formed as amorphous phase. As the calcination temperature increased, the crystallinity of Al decreased by a change of the oxidation state of aluminum from metallic to oxide.