Influence of Al2O3 on the electrical conductivity and structure of calcium-silicate-based melts

Abstract

Electrical conductivity and structure of the CaO-SiO 2 -based mold flux melts with various Al 2 O 3 contents were investigated. The results show that the electrical conductivity increases with the addition of Al 2 O 3 from 2 wt% to 4 wt%, but decreases with the further increase of Al 2 O 3 from 4 wt% to 8 wt%. Correspondingly, the apparent activation energy reduces firstly from 55.12 ± 1.20 kJ mol to 41.09± 0.38 kJ mol, and then increases from 41.09 ± 0.38 kJ mol to 98.99 ± 1.42 kJ mol. The structure analyses suggest that complex structural units, such as Si-O-Al, Al-O 0 , Si-O-Si and Q 3 (Si), reduce first, but increase with the further addition of Al 2 O 3 . Conversely, these simple structural units, such as Al-O - , Q 0 (Si), Q 1 (Si) and Q 2 (Si) vary in the opposite way with the change of Al 2 O 3 content. From the variations of electrical conductivity, activation energy and structural units, it can be found that when Al 2 O 3 works as network breaker to simplify the melt structure, the energy barrier for transportation of conducting ions/ionic reduce, which results in the increase of electrical conductivity; while when Al 2 O 3 becomes into network former, the conductivity increases, correspondingly.