The Effect of Mechanical Activation on the Conductivity in the System KNO3-Al2O3

The effect of mechanical activation on the structure and conductivity of the KNO3-Al2O3 composite is considered. The analysis of DSC curves measured in the course of heating of the 0.5KNO(3)-0.5Al(2)O(3) composite shows that the enthalpy of phase transitions decreases with the increase in the time of mechanical activation. Based on the X-ray diffraction analysis, it is shown that the mechanical activation reduces the grain size and makes the grains more defective. According to the data of electrochemical impedance spectroscopy, the ionic conductivity of the system KNO3-Al2O3 obtained by mechanical activation is 3.8 x 10(-5) S/cm at T = 373 K and 2 x 10(-3) S/cm at T = 473 K and its activation energy is 0.19 eV, which is comparable with the parameters of composites with the same chemical composition obtained by the ceramic method. The Raman spectroscopic study reveals the formation of the metastable gamma-KNO3 phase in the system KNO3-Al2O3 at the temperature above 397 K. The increase in conductivity of the KNO3-Al2O3 composite at 373-403 K is associated with the presence of an additional metastable gamma-KNO3 phase.