Pre-baked anode structure and properties as a function of the Blaine number

Abstract

Anode paste for pre-baked (PB) anodes represents a composite material based on calcined coke and coal tar pitch (used as a binder). A coke aggregate mix includes 3 to 5 fractions with a particle size of 12 mm down to 75 μm, and even less. Grain fractions larger than 0.2 mm form a sort of skeleton of the binder matrix and are prepared by crushing and screening. For filling the space between the grains, a dust fraction with particles less than 0.2 mm is used. The dust fraction constitutes up to 50% of the aggregate and can contain up to 70% of particles with a size of <75 μm. The dust fraction is prepared in a fine grinding circuit of ball mills. The dust fineness is determined based on the Blaine number (BN). The BN correlates with both Specific Surface Area (SSA) and Particle Size Distribution (PSD). High BN dust may account for up to 90% of the total aggregate surface area. If dust is too fine, it leads to a higher surface area of coke particles, which causes both higher particle reactivity and higher pitch demand. The above might result in higher carbon consumption. Therefore, it is important to keep a balance in terms of the particle size of the dust fraction. This paper discusses the PB anode structure and properties as a function of the BN. Lab anodes containing dust fractions with a BN of 2120, 2880, 3600, 3950 and 4700 were used for analysis. The paper presents obtained correlations between the BN and the physical, chemical and mechanical properties of PB anodes. An optimal BN of 3600 to 4200 was determined based on porosity tests of anode blocks with different BNs using mercury porosimetry; the above range can now be recommended for PB anode production.