Effect of alkali ions on the electrical properties of the ferrite phase of cement clinker

Abstract

The ferrite phase of cement clinker was prepared from a mixture of pure oxides, and also after mixing this mixture with different weight percentages (1, 3, 10, 20 and 30%) of an alkali oxide (Na₂O, MgO, SrO or BaO) at 1300° C. Electrical conductivity measurement (d.c.) was carried out from ice temperature to 570 K. It was found the alkali ions decreased the electrical conductivity with increasing alkali oxide content up to 3 wt% which was attributed to a change of C₄AF structure from orthorhomic to tetragonal or monoclinic at elevated temperature, and the reduction of Fe³⁺ ions. Above 3 wt%, in the case of Na₂O or BaO, the conduction increased. As MgO or SrO is similar to CaO the energy gaps ranged from 0.54 to 0.61 eV. The activation energy of pure C₄AF is equivalent to 0.5 eV, as alkali ions were introduced this value changed according to th alkali type. This is considered as a quick method to assure the purity of the C₄AF phase. This phase with alkali impurities behaves as a semiconductor.