Study on Viscosity Characteristics of Potassium Cryolite-Based Electrolytes for Low-Temperature Aluminum Electrolysis

This study systematically investigates the viscosity behavior of a potassium cryolite-based electrolyte (KF-AlF 3 ) over the temperature range of 450–800°C. Compared with previous measurements conducted at selected temperatures and cryolite ratios (CR), this work extends the viscosity characterization of potassium cryolite-based electrolytes across a wide temperature range covering both the practical electrolysis window and the solid–liquid coexistence region, while providing systematic insight into the effects of CR and Al 2 O 3 content. High-resolution viscosity–temperature data were obtained under controlled conditions with CR between 1.2 and 1.5 and Al 2 O 3 concentrations from 0 wt.% to 5 wt.%. The results indicate that viscosity is dominantly governed by the CR, while temperature and Al 2 O 3 content exert comparatively weaker effects. On average, viscosity increases by approximately 2.7% for every 0.1 wt.% increase in CR and by approximately 1.2% for each 1 wt.% increase in Al 2 O 3 content. Two distinct viscosity inflection points were observed in the 480–500°C interval. The primary inflection near 500°C corresponds to the onset of K 3 AlF 6 crystallization, whereas the secondary inflection around 480°C is tentatively attributed to enhanced interactions between Al 2 O 3 -derived solid particles during further cooling. A segmented Arrhenius-type model was established, providing a unified viscosity description across the investigated temperature and composition ranges with a mean relative deviation below 1.5%. The model parameters reveal a substantially higher activation energy in the low-temperature segment associated with solid–liquid coexistence, while the high-temperature regime exhibits mild viscosity variation characteristic of ionic-liquid-like behavior. This model is directly applicable to CFD-DEM coupled simulations and low-temperature aluminum electrolysis process optimization.