Chemical Interaction of Sodium Fluoride Salts with Alumina Silica Refractories

3 Chemical Interaction of Sodium Fluoride Salts with Alumina Silica Refractories 

There are many possible chemical reactions among cryolite, sodium fluoride, alumina, silica, and mullite [181, 188-193]. Classical considerations on the corrosion resistance of refractories have limited significance for the problem of corrosion resistance to cryolite and are good from an educational and informational point of view due to the extra low viscosity of cryolite melt and unique corrosion ability of 

Many chemical reactions are possible thermodynamically between the components of electrolyte and the components of refractory lining. The interaction may be described as a reaction between solid and liquid reagents on the border of solid reagent in case of no mixing and in case of permanent feeding with one component. However, the dissolution limit of alumina and silica in cryolite is about 10 % at 950-960 °C [185], and the penetrated electrolyte will relatively rapidly reach the saturation limit, become viscous, and stop dissolving the refractory. The temperature of the melt should be close to the crystallization point. 

Mullite, 3Al2032Si02, may interact with sodium fluoride (NaF), giving cryolite and nepheline, 3NaAlSi04  

The possibility of the reaction of cryolite with mullite, giving gaseous silicon fluoride, has been confirmed experimentally  

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