Density Higher baking temperatures result in higher
density anodes, which exhibit reduced
permeability and therefore extend the operational life of the anode. However, excessive density will result in
thermal shock and fracturing of the anode upon first use in an electrolysis cell.
Electrical resistance Efficient aluminium smelting requires low
resistance on the part of the anode. Low resistance results in greater control over the electrolysis cell's voltage and reduces the energy loss associated with
resistive heating. However, anodes with low electrical resistance also exhibit increased
thermal conductivity. Anodes that conduct too much heat will
oxidize rapidly, reducing or eliminating their smelting efficiency, called "air burn" in industry parlance. ===Mechanical strength (
compressive strength,
Young's modulus,
tensile strength)=== Anodes are subject to a variety of
mechanical stresses during creation, transportation and use. Anodes must be resistant to compressive force, resistant to elastic stress, and resistant to impact without becoming brittle. The relationship between compressive strength and Young's modulus in prebaked anodes usually results in a compromise in the anode's resistance to compressive force and elastic stresses.
Thermal conductivity and thermal expansion Low anode thermal conductivity results in "air burn", as noted in
Electrical Resistance, above. Low
thermal expansion coefficients are desirable to avoid thermal shock. ===Carbon reactivity and
air permeability=== Anodes should be relatively impermeable to both
carbon dioxide and
air generally to reduce the opportunity for "carbon dioxide burn" and "air burn", both of which will reduce the anode's smelting efficiency.
Grain stability High grain stability indicates high anode structural integrity, increasing the smelting efficiency of the anode. High Grain stability also minimizes particle degradation during anode fabrication. ==References==