Aluminum oxide activation energies

The effect of the aluminum oxide layer is also known to reduce the propagation of thermite reactions since alumina is an effective absorber of thermal energy. A study by Weismiller et al. of a 49 % active aluminum nanopowder in a thermite... 

In contrast to titania and niobia, alumina is a support that does not display the classic SMSI behavior outlined above, at least for practical catalysts (173, 175). Bischke et al. (176) studied CO methanation over model Ni/Al203 catalysts prepared by evaporation of Al onto a W foil, subsequent oxidation of the Al, and finally vapor deposition of Ni onto the thin A1203 film. Specific reaction rates (per Ni surface atom) and the activation energy were similar to those found for pure Ni crystals and practical Ni/Al203 catalysts. This agrees with the classical picture of A1203 as a more or less inert support for this catalyst and the known structural insensitivity of this reaction over Ni (see above). Submonolayer quantities of oxidized aluminum were shown by Levin et al. (186) to only decrease the rate of methanation over a Rh foil, in proportion to the fraction of Rh sites covered by the oxide film. 

Aluminum oxide in several varieties and impurity levels has been investigated by Robertson and by Shackelford. The data scatter widely and have internal inconsistency sufficient to prevent the straightforward conelusions which are available with data on other materials. There is ample evidence, however, that the predominant mechanism of thermal grooving in AljOg is also volume diffusion and that the activation energy for the process is between 100,000 and 200,000 cal/mole. 

Using GIR to investigate the thickness of the ultrathin oxide layer in Al-SiO c-Si devices, the number of Al—O bonds (band of 849 cm" ) was found to increase with thermal annealing [13] (Fig. 6.3). The decrease in the SiO thickness is a temperatnre-activated process with an activation energy of 0.98 eV and can be well described within the fi amework of an Al-A10y-SiO t Si model. In addition, contamination by aluminum can considerably influence the characteristics of the SiOj -Si interface, causing an increase in the density of electronic states, the effect being more pronounced for thinner silicon oxide layers [22, 23]. 

A mixture of powdered aluminum and iron(lll) oxide is called thermite. Al reacts with FCgOg using Mg ribbon as a fuse to provide activation energy. The energy produced by the thermite reaction is sufficient to produce molten iron as a product. 

First, the authors stated that the reduced catalyst surface contained only zero-valent iron. This is based on the analysis of the raw data from the Fe 2p 3/2 spectra. It has been found, however, that it is impossible to identify small levels of oxidized iron in the presence of a large fraction of metallic iron. This is due to the wide distribution of intensity for iron compounds caused by their satellite structure. It is therefore believed that the catalyst described in Ref. 19 contained a similar fraction of iron oxide to the present samples activated with the dry method (see Fig. 2.40). This is in line with the expectation that the presence of the spinel-forming aluminum oxide prevents complete reduction. It should be pointed out that Mossbauer spectroscopy, thermogravimetric reduction, and energy dispersive X-ray analysis all showed a small fraction of oxidized iron to be present within the bulk of fully reduced samples. 

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