Effect of dispersed Al 2O 3 on the phase transitions and ionic conductivity of KHSO 4

Abstract

Differential scanning calorimetry (DSC) and impedance spectroscopy (IS) were used to study the phase equilibria and electrical conductivity of (1− x)KHSO 4– xAl 2O 3 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 KHSO 4 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 KHSO 4 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 Al 2O 3 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 Al 2O 3 on the thermal and electrical properties of KHSO 4.