Physical Property Evolution of the Anode Mixture during the Baking Process

The Hall-Héroult process relies on prebaked carbon anodes for aluminum production. Anode quality significantly affects process efficiency. Prior research has shown that anode performance is tied to its physical properties during baking. However, the exact evolution of these properties remains unclear. No prior work had resolved the link between permeability and porosity during high-temperature baking. This gap motivated the current investigation. Existing studies focus on final anode characteristics, not the dynamic changes during baking. The role of pitch binder in porosity development is not fully understood. This paper addresses the need for a detailed analysis of anode paste transformation. It provides a framework for modeling anode behavior under industrial conditions.

This study aims to track physical property changes in anode paste during baking. The focus is on mass loss, density, porosity, and permeability. Understanding these changes helps improve anode production efficiency. The researchers propose to link permeability at high temperatures to air permeability. They also estimate real density by combining coal tar pitch and coke properties. The study introduces a shrinking index to reflect baking progress. This index is based on volatile release from open and closed pores. The goal is to better model anode behavior under high-temperature conditions.

The team used thermogravimetric analysis to measure mass loss during heating. Dilatometry tracked dimensional changes in the anode mixture. Air permeability tests assessed gas flow through the material. Helium pycnometry measured real density at different temperatures. A permeability correlator linked high-temperature permeability to air permeability. The real density at high temperatures was calculated from coal tar pitch and coke data. Open and closed porosities were estimated using permeability values. A sensitivity analysis evaluated the impact of the permeability correlator on results.

Mass loss increased with temperature, reflecting volatile release from the pitch binder. Real density rose as pitch solidified and coke particles compacted. Apparent density decreased due to expansion of the anode mixture. The ratio of apparent volume showed a nonlinear trend during baking. Permeability at high temperatures was significantly higher than at room temperature. Open porosity was found to be more responsive to temperature changes than closed porosity. The shrinking index increased steadily with temperature, indicating progressive baking. Pore pressure in closed pores was estimated to reach several MPa during the process.

The study highlights the dynamic changes in physical properties during anode baking. The shrinking index offers a new way to monitor baking progress. Permeability and porosity are closely linked to pitch binder behavior. The permeability correlator is a useful tool for modeling high-temperature behavior. Real density estimates help predict anode structural stability. Open porosity is more sensitive to thermal changes than closed porosity. These findings support better modeling of anode performance in industrial settings. The results may improve process control in aluminum production.