On the Mechanism of Low Temperature Oxidation for Aluminum Particles down to the Nano‐Scale

Abstract

The oxidation of Al-particles down to nano-scale was investigated by TG, SEM and in-situ X-ray diffraction. Al particles are usually coated by a 2 ± 4 nm layer of Al 2 O 3 which can be derived from the degree of weight increase on complete oxidation by TGcurves. The low temperature oxidation of Al particles occurs at least in two steps. The first step builds a layer of 6 to 10 nm thickness composed of crystallites of the same size independent on the initial particle size. This reaction is dominated by chemical kinetics and converts a substantial fraction of the particle if the particle sizes decrease below 1 mm, an effect carefully to be taken into account for nano-particles because of safety reasons. The second step combines diffusion and chemical reaction and proceeds therefore slowly, the slower the bigger the particles are. The kinetic parameters of these two steps can be obtained by a model taking into account both reaction steps, chemical kinetics and diffusion for spherical particles when fitting it to TG-curves. X-ray diffraction shows that particles smaller than 1 mm build gand q-Al 2 O 3 in the first step with nano-crystalline structures which are then transformed to a-Al 2 O 3 .

Nanoaluminium: is there any Relationship between Powder Particles’ Size, Non-Isothermal Oxidation Data and Ballistics?

“…Eisenreich et al [44] investigated the non-isothermal oxidation of several Al powders by TGA (5 K/min, air). The powders tested ranged from Alex (mean-surface particle diameter a s = 100-150 nm) to µAl (9 µm).…”

Exothermic characteristics of aluminum based nanomaterials

“…The oxidation and ignition characteristics of aluminium particles have been widely investigated in the past decade [4][5][6][7]. However in order to have more controllability over the material's properties, aluminum is usually alloyed by mixing with several other elements at the bulk scale.…”

Study of multi-carbide B4C-SiC/(Al, Si) reaction infiltrated composites by SEM with EBSD

“…The discrepancies that persist between the Al phase content of the alloy obtained from the EBSD analysis compared to the EDS results can be attributed to disturbing effects of low temperature passivation of the Al surface forming a 2 -4 nm thick amorphous oxide layer [24] that cannot be resolved by EBSD, to smearing of the surface layer from plastic deformation during polishing that blurs the Kikuchi line patterns [11] and to the relief of the surface. The thickness of the passivation layer of Al being a minor fraction of the backscattered electron interaction depth [25], the resulting perturbation of EBSD identification is seemingly minute.…”

“…Two directions for future work emerge from the present study. The improved spatial resolution down to nanometre range of the SEM-TKD technique, transmission Kikuchi diffraction in the SEM microscope, as compared to SEM-EBSD [24,29], will expectedly aid the automated recognition of electron diffraction patterns of the Al and Si phases with sub-grain structures of submicron sizes. But, for SEM-TKD the sample has to be prepared as a thin section of transmission electron microscopy.…”