Introduction

Comparison of air reactivities, or air reaction rates, and air dusting rates is useful in selecting raw materials for the manufacture of commercial electrodes for specific smelting technologies in the production of aluminium. Air reactivities are used to quantify the tendency of a carbon artifact to react with air. Carbon consumed by this unwanted side reaction is unavailable for the primary reaction of reducing alumina to the metal. Air reactivities and the dusting rate are used by some companies to quantify the tendency of the coke aggregate or binder coke of a carbon artifact to selectively react with air. Preferential attack of the binder coke or coke aggregate of a carbon artifact by air causes some carbon to fall off as dust, making the carbon unavailable for

the primary reaction of reducing alumina and, more importantly, reducing the efficiency of the reduction cell.

Air reactivities are used for evaluating the effectiveness of beneficiation processes and for research purposes. Sampling guidelines are under development.

This part of ISO 12989 is based on ASTM D 6559-00.

Scope

This part of ISO 12989 allows the determination by thermogravimetric analysis (TGA) of air reactivities and dusting of shaped carbon electrodes used in the aluminium-reduction industry. Many types of apparatus are available, with various thermal conditions, sample-size capabilities, materials of construction and procedures for determining the mass loss and subsequent rate of reaction. This test method standardizes the variables of sample dimensions, reaction times and temperatures, and provides a mathematical method to normalize the gas velocity over the exposed surfaces, such that results obtained on different types of apparatus are correlatable.

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