Investigation of the processes of softening and crystallization of glassy selenium by dynamic mechanical analysis method

Abstract

Purpose. The purpose of this work was the investigation of mechanical characteristics of glassy and polycrystalline selenium in glasstransition and crystallization regions by dynamic mechanical analysis method and also the determination of relaxation parameters and establishing the mechanism of dissipative processes in selenium above its softening temperature . Methods. It was measured the mechanical loss tangent and dynamic modulus of elasticity as functions of tem perature. Measurement of these parameters were performed in the mode of forced bending oscillations at a frequency of 0.5 Hz using the Q400 TMA device at a temperature range 220 K - 450 K. Results. In glassy selenium in softening temperature region the a-process of mechanical relaxation with a relative decrease of the elastic module ∆E/E = 0.73 was found. Rapid increase in the elastic modulus due to the crystallization processes of glassy selenium in the interval 353 K - 378 K was observed. Cooling of selenium sample from 450 K to 220 K did not reveal of glassforming effects on the temperature dependences of the elastic modulus and the mechanical loss tangent: a sample of selenium was polycrystalline. Maxima are observed in the temperature dependences of the tangent of the angle of mechanical losses at the α-process of relaxation and crystallization of glassy selenium. Conclusions. In the temperature dependence of the elastic module of glassy selenium a high elasticity plateau was found. The presence of a highly elastic state in glassy selenium in the temperature range 325 K-350 K and crystallization process in the range of 353 K-378 K are shown. In polycrystalline selenium there are no dissipative processes that are characteristic of the glasslike state.