Transport numbers in the molten system N

This study investigates the transport numbers within the molten NaF–KF–AlF3–Al2O3 system through the application of the Hittorf method. The primary objective was to analyze the contributions of various cations to electrical current transport in the molten system. Experimental results indicated that in molten cryolite (Na3AlF6) at 1,010 °C, sodium ions (Na+) predominantly carried the current, exhibiting a transport number of approximately 0.99. However, upon the addition of AlF3 to the melt, the transport number for sodium decreased to 0.74, particularly at the NaAlF4 composition. Additionally, in K3AlF6 melts, potassium ions (K+) displayed a transport number of 0.836 at 1,005 °C. It was observed that the ratio of contributions from Na+ and K+ to the charge transport corresponds to the squares of their ionic radii, emphasizing their relative influence on the transport dynamics. Furthermore, the incorporation of 5 mass % CaF2 into the system significantly altered the transport numbers of potassium and fluoride anions, highlighting the complex interactions among the molten ions. These findings not only deepen the understanding of ionic movement in molten salts but also have implications for optimizing electrolytic processes in aluminum production.