Liquid-Feed Flame Spray Pyrolysis of Metalloorganic and Inorganic Alumina Sources in the Production of Nanoalumina Powders

Abstract

Liquid-feed flame spray pyrolysis (LFFSP) of metalloorganic [N(CH2CH2O)3Al, alumatrane, and Al(Acac)3] and inorganic alumina [AlCl3 and Al(NO3)3·9H2O] precursors dissolved in 1:1 ethanol/THF, aerosolized with O2 and ignited can produce quite different alumina nanopowders during the ensuing combustion process. The metalloorganics appear to volatilize and combust easily to give nano-alumina, with particle sizes <20 nm and corresponding surface areas of ≈60 m2/g at rates of 50 g/h. In contrast, the nitrate appears to melt during combustion rather than volatilize, forming large, hollow particles typical of a spray pyrolysis process with particle sizes >70 nm and surface areas of ≈12 m2/g. AlCl3 appears to volatilize easily but does not hydrolyze rapidly in the flame leading to mixtures of alumina and recovered AlCl3. The resulting nanopowders consist of a mixture of transition alumina phases, primarily δ*, that could only be successfully identified and quantified by Rietveld refinement. Because the δ phase is not typically made as a high-surface-area material or in large quantities, it offers the opportunity to serve as a novel catalyst support. On heating to 1000 °C, the dominant phase becomes θ-Al2O3 that was clearly identified by 27Al MAS NMR using ab initio calculations of the 27Al NMR parameters derived from the X-ray structure. At present, the exact mechanism(s) whereby particles nucleate and grow, and phases form from the species generated during combustion, remains unknown.

Solar geoengineering using solid aerosol in the stratosphere

“…There is a very large body of experience in making alumina nanoparticles. For example, liquid-feed flame spray pyrolysis is used to make structured nanoparticles of alumina in quantities greater than 1 kt yr −1 (Hinklin et al, 2004). As we will see, the optimal size for a spherical alumina particles used as a scatterer in the stratosphere is of order 200 nm radius.…”

“…As we will see, the optimal size for a spherical alumina particles used as a scatterer in the stratosphere is of order 200 nm radius. Most of the industrial effort is focused on making smaller particles for catalysis but there are examples of production of relatively monodisperse particles with radii greater than 50 nm (Hinklin et al, 2004;Tsuzuki and McCormick, 2004).…”

“…Unlike many other solid particles proposed for SRM, there is prior work examining alumina's impacts on stratospheric chemistry (Danilin et al, 2001;Jackman et al, 1998;Ross and Sheaffer, 2014), work that was produced from NASAfunded studies starting in the late 1970's motivated by concerns about the ozone impact of space shuttle launches (alumina is a major component of the shuttle's solid rocket exhaust plume). Moreover, alumina is a common industrial material with a high index of refraction for which there is substantial industrial experience with the production of nanoparticles (Hinklin et al, 2004;Tsuzuki and McCormick, 2004). With respect to potential environmental impacts of alumina deposition on Earth's surface, the fact that aluminum oxides are a common component of natural mineral dust deposition provides a basis for assessing impacts (Lawrence and Neff, 2009).…”

La–Ag–Co perovskites for the catalytic flameless combustion of methane

“…Recently in our laboratory we set up and optimised a flame pyrolysis (FP) method, already validated for the synthesis of widely different catalysts, many of which with perovskite like structure [19][20][21][22][23][24]. It is a one-step, continuous process, which allows to obtain single or mixed oxides with good phase purity and nanometric particle size.…”

Mesoporous transition alumina with uniform pore structure synthesized by alumisol spray pyrolysis

“…In this method, atomized droplets of a precursor solution undergo evaporation and shrinkage while flowing through a high temperature reactor, and eventually form solid particles. Previous researches on the preparation of alumina by spray pyrolysis mainly focused on the effects of the precursor solution, as well as other experimental conditions on the morphology [22][23][24][25] and phase transformation behavior of products [26][27][28]. For example, when different kinds of inorganic and metallo-organic alumina sources were used as precursor solutions, alumina particles with different morphologies were generated, including spherical [22,23], hollow [24], or doughnut-like [25].…”