Abstract
The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In this work, the application of boron oxide has been investigated to evaluate its inhibition effect on the air oxidation reaction, and to provide an effective protection for anodes. Different methods of impregnation coating have been explored. Impregnated anode samples were gasified under air at 525 °C according to the standard measurement methods. X-ray tomography was used to obtain the microstructural information of the samples before and after air-burning tests. The impregnated samples showed a very low oxidation reaction rate and dust generation.
Highlights
Carbon anodes are consumed in the conventional process of aluminum production using Hall-Héroult cells in which the overall reaction may be written as Equation (1) [1]
Most of the samples were taken from the positions that are normally exposed to air attack in an industrial electrolysis cell
The results revealed a remarkable effect of the impregnation time on the air reactivity of the anode
Summary
Carbon anodes are consumed in the conventional process of aluminum production using Hall-Héroult cells in which the overall reaction may be written as Equation (1) [1]. The temperature of the anode exposed to air is between 400 and 600 ◦ C [2] In this range, the oxygen in the air can react with the carbon anode, according to Equations (2) and (3). The oxygen in the air can react with the carbon anode, according to Equations (2) and (3) Both reactions are undesirable since the carbon anode is consumed without producing metal. C (solid, anode) + O2 (g) → CO2 (g), ∆G◦ = −395 kJ (at 500 ◦ C) (2). O2 (g) → CO (g), ∆G◦ = −185 kJ (at 500 ◦ C) (3). The effects of raw materials, process parameters, and the physical characteristics of the baked anode on its resistance
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