Features of crystallization of the eutectic composition 20.5 wt.% naphthalene-79.5 wt.% o-terphenyl

Abstract

Terphenyl mixtures in the crystalline state are used as scintillators, phosphors, photoresistors, sensitizers, etc. Their structure and properties largely depend on crystallization conditions. The features of crystallization of the eutectic composition of hydrocarbons o-terphenyl (79.5 wt.%) and naphthalene (20.5 wt.%) were studied by the method of cyclic thermal analysis. As a result of experiments carried out on the eutectic alloy, it was found that the horizontal plateaus recorded during heating correspond to the melting temperature (304 K) of the eutectic alloy. It has been established that weakly heated melts crystallize isothermally at a temperature Т_S=298 K, which lies below the melting temperature of the eutectic Т_L=304 K. about their crystallization. With an increase in the time of isothermal holding of a metastable melt, or the time the melt stays (without holding) in a overcooled state, the length of the melting plateau in the subsequent cycle increases, which indicates an increase in the degree of crystallinity of the sample. A method is proposed for determining the degree of crystallinity η from the duration t_e of isothermal holding of the overcooled melt and the duration τ_L of melting. By this method, the bulk crystallization rate constant Z and the Avrami parameter n were calculated.