Abstract
It is expected that viscous flow is affecting the kinetic processes in a supercooled liquid, such as the structural relaxation and the crystallization kinetics. These processes significantly influence the behavior of glass being prepared by quenching. In this paper, the activation energy of viscous flow is discussed with respect to the activation energy of crystal growth and the structural relaxation of glassy selenium. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and hot-stage infrared microscopy were used. It is shown that the activation energy of structural relaxation corresponds to that of the viscous flow at the lowest value of the glass transition temperature obtained within the commonly achievable time scale. The temperature-dependent activation energy of crystal growth, data obtained by isothermal and non-isothermal DSC and TMA experiments, as well as direct microscopic measurements, follows nearly the same dependence as the activation energy of viscous flow, taking into account viscosity and crystal growth rate decoupling due to the departure from Stokes–Einstein behavior.
Highlights
Glasses are amorphous materials lacking the periodic atomic arrangement typical for crystalline substances
We provide a concise description of the structural relaxation experiments as well as the crystallization of glassy selenium obtained by differential scanning calorimetry (DSC) and dilatometry
Thermo-kinetic data described in the previous section imply that the activation energy of most kinetic processes observable in glassy materials by thermal analysis varies with temperature
Summary
Glasses are amorphous materials lacking the periodic atomic arrangement typical for crystalline substances. They resemble supercooled liquids but behave mechanically like solids. Upon slow cooling from high temperatures, a liquid may crystallize at Tm forming a stable crystalline material. If the cooling through this temperature range is fast enough to avoid nucleation and subsequent crystal growth, a metastable supercooled liquid state is attained. When a supercooled liquid is cooled by a cooling rate of q+ 1 to lower temperatures, the internal molecular motion slows down and its viscosity significantly increases. At a lower cooling rate (q+ 2 < q+ 1 ) the supercooled liquid stays in metastable equilibrium until lower temperatures. There is not a single glassy state, and the properties of the glass depend upon how it was obtained [1]
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