On the Solubility of Aluminium Carbide in Cryolitic Melts ‐ Influence on Cell Performance

The solubility of aluminium carbide in cryolitic melts was determined as a function of NaF/AlF3 molar ratio (CR), temperature, alumina concentration and CaF2 concentration. At 1020°C a maximum concentration of 2.1 wt% aluminium carbide was found at CR=1.80. The following model for the aluminium carbide dissolution reaction based on activity data for NaF and AlF3, was found to fit the experimental solubility data; $$A{{l}_{4}}{{C}_{3}}\left( s \right)+5Al{{F}_{3}}\left( {diss} \right)+9NaF\left( \ell \right)=3A{{l}_{3}}CF_{8}^{{3-}}+9N{{a}^{+}}$$ (1) From the solubility data for aluminium carbide the following empirical equation was derived for CR>1.80: $$\begin{gathered} \log \left( {{{c}_{{A{{l}_{4}}{{C}_{3}}}}}} \right)=-0.4149-0.3960\cdot CR+1.894\cdot {{10}^{3}}/T \hfill \\ \quad \quad \quad \quad \quad -3.112\cdot {{10}^{{-2}}}\cdot {{c}_{{A{{l}_{2}}{{O}_{3}}}}}-2.49\cdot {{10}^{{-2}}}\cdot {{c}_{{Ca{{F}_{2}}}}} \hfill \\ \end{gathered}$$ (2) where all concentrations are in wt% and T is the temperature (K).