Thermodynamic considerations of the corrosion of nickel ferrite refractory by Na 3 AlF 6 –AlF 3 –CaF 2

Abstract

Thermodynamic analysis was carried out to interpret the results of corrosion testing of nickel ferrite samples in cryolite-based baths. The equilibrium between cryolite-based baths and nickel ferrite was considered.

Isopleths between cryolite-based baths and nickel ferrite confirmed that for the temperature range of interest (1223–1273 K) there was limited solubility of nickel ferrite in the bath.

To better understand the formation of the metal from nickel ferrite, the effect of reducing potentials on nickel ferrite and nickel ferrite–cryolite-based bath systems were considered. The formation of a metal phase was predicted at relatively high pO₂. The metal phase was nickel-rich at higher pO₂, becoming enriched in iron as the pO₂ decreased. The oxide phases seen in corroded nickel ferrite samples corresponded to the spinel phase in the thermodynamic calculations. Penetration of aluminium oxides into the spinel phase seen in the experimental samples occurred only under a reducing potential.

Keywords

Nickel ferrite Aluminium production Hall–Héroult cell Thermodynamics

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Thermodynamic considerations of the corrosion of nickel ferrite refractory by Na 3 AlF 6 –AlF 3 –CaF 2 –Al 2 O 3 bath

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