Aluminium Oxidation Rate

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The aluminium oxidation rate is an important indicator for the corrosion resistance of aluminum alloys. It is also a measure of the ability to withstand repeated exposure to hydrogen gas in the air of smelting furnaces and other smelting equipment.

aluminium oxidation rates vary over time in different environments. This is because the metal's redox potential is negative (-1.66 V), which means that it tends to revert back to its stable oxide state, alumina, when in contact with oxygen.

Several experiments have been performed to monitor the oxidation of polycrystalline Al slabs at various temperatures and oxygen pressures over extended time intervals. Nevertheless, none of the oxidation curves could be described with a single rate law: either a logarithmic, inverse-logarithmic or parabolic time dependence.

First, we investigated the kinetics of the Al layer thickness change during oxidation using a series of experiments. These include temperature-dependent and oxygen pressure-dependent XPS, as well as a range of XRD measurements at 400 deg C.

We found that the oxidation of aluminium takes place in an initial fast regime, followed by a subsequent slow regime. This initial fast regime proceeds as a Cabrera-Mott mechanism, but exhibits little pressure dependence up to 100 mbar O2. The slow process, however, shows steeply increasing oxidation rates at high temperatures but with little pressure dependency.

We then fitted the oxidation behavior to a number of rate laws reported in the literature, including a direct and an inverse logarithmic law for the fast regime and a power-law dependence for the slow regime. For the initial fast regime, both laws reproduced k values of around 6 nm s-1 (Figure 3b).

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