THE STUDIES OF PHASE DIAGRAM AND CRYSTALLIZATION KINETICS OF AN AMORPHOUS STATE IN THE PSEUDO-BINARY SYSTEM LiIO3-NaIO3

Abstract

The phase diagram, phase transition, and formation, stability and crystallization kinetics of amorphous state in the system LiIO3-NaIO3 have been investigated. The pesudo-binary system LiIO3-NaIO3 is a eutectic one, its eutectic reaction occurs at 325℃ and the composition at eutectic point is 50 m/o LiIO3. As the melt is quenched from a temperature 150℃ higher than the melting point, an amorphous state of iodate salts is obtained for the first time. The apparent transition temperature decreases when the amorphous state exists. It is found that some factors, such as intense X-ray irradiation, various humidity and fine grain size, make the crystallization speed of amorphous state increases. Crystallization speed and perfection of LiIO3 in the amorphous state is higher than NaIO3. The process of isothermal phase transition agrees with Johnson-Mehl-Avrami equation y(t) =l-exp(- btOn), when y = 0.1-0.9, where y is the quantity of crystallization. For the sample with composition of 60 m /o LiIO3, the Avrami time exponent n = 2-3 and rate constant parameter b increases exponentially with temperature. The activation energy of crystallization from amorphous state is found to be 2.21 eV.