Effect of dispersed Al2O3 on the phase transitions and ionic conductivity of KHSO4

Differential scanning calorimetry (DSC) and impedance spectroscopy (IS) were used to study the phase equilibria and electrical conductivity of (1−x)KHSO4–xAl2O3 composites in the concentration range x=0.0–0.5. Alumina with grain size of 10 μm and pore size of ∼6 nm was used. Upon adding alumina, the phase transitions of KHSO4 at 185 and 198 °C (melting point), respectively, are shifted to higher temperatures and a new phase transition is observed at about 170 °C for samples with compositions x≥0.2. Moreover, the two intense peaks at higher temperatures emerge to only one peak at about 200 °C for samples with composition x≥0.4. On the other hand, the dc-conductivity of KHSO4 decreases sharply at 164 °C on the first heating run, but this jump is shifted to 146 °C on the subsequent cooling run and decreases in size on the successive thermal cyclings. The addition of Al2O3 suppresses this anomaly and a rapid increase in the conductivity is observed at about 170 °C which corresponds to the DSC peak at this temperature. The results are discussed in terms of the effects of adding Al2O3 on the thermal and electrical properties of KHSO4.