Nanostructured Alumina from Freeze-Dried Precursors (original) (raw)
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Synthesis of Nanostructured Alumina from Byproduct Aluminum Filings: Production and Characterization
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Aluminum oxide production from aluminum filings, which are a byproduct of several industrial machining processes and cannot be recycled to attain bulk aluminum (Al), is vital due to its wide use in scientific research and industry. The goal of this paper is to produce ultrafine and down-to-the-nanoscale alumina powder (Al2O3), starting from a waste Al filings. The microstructure and composition of the starting Al used were investigated using scanning electron microscopy (SEM), which was equipped with an attached energy dispersive spectrometer (EDS) unit. The results of this investigation confirmed that the starting Al was mainly Al–Mg alloy. Al2O3 was produced using two routes: The first involved the burning of aluminum hydroxide Al(OH)3 that was precipitated from aluminum chloride solution (AlCl3) resulting from dissolving the Al filings in 2M HCl. The second route involved direct precipitation as a reaction product of aluminum chloride with sodium carbonate solution. The Al2O3 pro...
Phase Transformations of α-Alumina Made from Waste Aluminum via a Precipitation Technique
We report on a recycling project in which α-Al 2 O 3 was produced from aluminum cans because no such work has been reported in literature. Heated aluminum cans were mixed with 8.0 M of H 2 SO 4 solution to form an Al 2 (SO 4 ) 3 solution. The Al 2 (SO 4 ) 3 salt was contained in a white semi-liquid solution with excess H 2 SO 4 ; some unreacted aluminum pieces were also present. The solution was filtered and mixed with ethanol in a ratio of 2:3, to form a white solid of Al 2 (SO 4 ) 3 ·18H 2 O. The Al 2 (SO 4 ) 3 ·18H 2 O was calcined in an electrical furnace for 3 h at temperatures of 400-1400 °C. The heating and cooling rates were 10 °C /min. XRD was used to investigate the phase changes at different temperatures and XRF was used to determine the elemental composition in the alumina produced. A series of different alumina compositions, made by repeated dehydration and desulfonation of the Al 2 (SO 4 ) 3 ·18H 2 O, is reported. All transitional alumina phases produced at low temperatures were converted to α-Al 2 O 3 at high temperatures. The X-ray diffraction results indicated that the α-Al 2 O 3 phase was realized when the calcination temperature was at 1200 °C or higher.
Preparation of nanosized alumina using a low cost precursor
International Journal of Nanotechnology, 2010
Alpha alumina powders have been prepared by the pyrolysis of sucrose, aluminium nitrate and ammonium nitrate. After spray pyrolysis at 400°C the mixture yields fluffy light brown precursor mass. After grinding followed by heat-treatment at 900°C and 1000°C it produced the alpha-alumina having particle sizes of 42 nm and 55 nm with surface area 12 m 2 /gm and 16 m 2 /gm respectively .The yield per unit time from precursor with ammonium nitrate is 3-4 times that of simple thermal spray pyrolysis without ammonium nitrate. The particle size and crystallite size have been decreased with increase of sucrose commensurated with ammonium nitrate in the reaction mixture. The crystallite sizes are comparable with particle sizes due to poor agglomeration due to excess addition of sucrose and ammonium nitrate.
Studies on Thermal Decomposition of Aluminium Sulfate to Produce Alumina Nano Structure
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Aluminum sulfate nano structures have been prepared by solution combustion synthesis using aluminum nitrate nonahydrate (Al(NO3)3.9H2O) and ammonium sulfate ((NH4)2SO4). The resultant aluminum sulfate nano structures were calcined at different temperatures to study thermal decomposition of aluminum sulfate. The crystallinity and phase of the as-synthesized and calcined samples were characterized by both X- ray diffraction and FTIR measurements. These two analyses determined the temperature at which the aluminum sulfate is converted to γ-alumina nano particles. The specific surface area and pore size distribution for γ-alumina nano particles were determined by BET measurement. TEM measurement confirmed the size of the particles obtained by XRD and BET analyses.
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Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesize ultra-fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (tetraethyl ammonium hydroxide). XRD, BET surface area analysis, TEM and FEG-SEM were used to characterise the powders produced. The presence of industrial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220˚C, either in basic or acidic environments. The results obtained from the precipitation route, however, showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of αalumina from about 1200˚C for unseeded samples to about 800˚C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly results from the nucleation process caused by the α-alumina seeds, which enhanced the θ → α transformation kinetics. The lower level of agglomeration present in the final powders could be due to a surface modifying role of the surfactants, preventing the particles from coalescing during the synthesis process.
Anais da Academia Brasileira de Ciências, 2000
Crystalline aluminium hydroxiacetate was prepared by reaction between aluminium powder (AL-COA 123) and aqueous solution of acetic acid at 96 • C±1 • C. The white powder of Al(OH)(CH 3 COO) 2 is constituted by agglomerates of crystalline plates, having size about 10µm. The crystals were fired from 200 • C to 1550 • C, in oxidizing atmosphere and the products characterized by X-ray diffraction, scanning electron microscopy and surface area measurements by BET-nitrogen method. Transition aluminas are formed from heating at the following temperatures: gamma (300 • C); delta (750 • C); alpha (1050 • C). The aluminas maintain the original morphology of the Al(OH)Ac 2 crystal agglomerates, up to 1050 • C, when sintering and coalescence of the alpha-alumina crystals start and proceed up to 1550 • C. High surface area aluminas are formed in the temperature range of 700 • C to 1100 • C; the maximum value of 198m 2 /g is obtained at 900 • C, with delta-alumina structure. The formation sequence of transition aluminas is similar to the sequence from well ordered boehmite, but with differences in the transition temperatures and in the development of high surface areas. It is suggested that the causes for these diversities between the two sequences from Al(OH) Ac 2 and boehmite are due to the different particle sizes, shapes and textures of the gamma-Al 2 O 3 which acts as precursor for the sequence gamma-to alpha-Al 2 O 3 .
The Effect of Novel Synthetic Methods and Parameters Control on Morphology of Nano-alumina Particles
Nanoscale research letters, 2016
Alumina is an inorganic material, which is widely used in ceramics, catalysts, catalyst supports, ion exchange and other fields. The micromorphology of alumina determines its application in high tech and value-added industry and its development prospects. This paper gives an overview of the liquid phase synthetic method of alumina preparation, combined with the mechanism of its action. The present work focuses on the effects of various factors such as concentration, temperature, pH, additives, reaction system and methods of calcination on the morphology of alumina during its preparation.
Synthesis of α-alumina powder with internal nanostructures from Al13-cluster
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Nanostructured α-alumina powder was synthesized by precipitation and calcination of Al 13-clusters that were formed by the hydrolysis of Al 3+ ions with hydroxide. The Al 13-clusters were precipitated with oxalic acid by two-stage and one-stage precipitation techniques. The precipitates were calcined in air at 1100°C. The resulting α-alumina particles were characterized using particle size analyzer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The pH and precipitation technique were found to influence the microstructural features of the α-alumina powder produced. Alumina with more extensive nanostructures inside the grain can be produced through the two-stage precipitation technique.