Analysis of Structural Relaxation in Glass Using Rate Heating Data

TLDR

A method was developed to determine the kinetic parameters controlling structural relaxation in the glass transition region from data acquired during continuous heating or cooling. The method linearizes data using Narayanaswamy’s approach, models nonexponential relaxation with an equilibrium isothermal function exp[−(t/Toe)^β] (β<1), and applies the superposition principle to account for continuous temperature variation during heating or cooling. Applying the method to the enthalpy of vitreous B₂O₃ during rate heating and cooling yields the kinetic parameters A, Δh*, x, and β, characterizing the relaxation behavior across the transition region.

Abstract

A method was developed to determine the kinetic parameters controlling structural relaxation in the glass transition region from data acquired during continuous heating or cooling. The nonexponential character of the relaxation is accounted for by assuming an equilibrium isothermal relaxation function of the form exp [−( t /T oe ) ß ], where T oe is a relaxation time and 0&lt; β 1. The data are linearized using the method of Narayanaswamy, and the continuous temperature variation during heating or cooling is dealt with by invoking the superposition principle. The analysis yields the kinetic parameters A , the relaxation‐time preexponential term; Δ h ★ , the relaxation‐time activation enthalpy; x , a term describing the relative effects of temperature and structure on the rate of relaxation; and β. The method was applied to analysis of the variation of the enthalpy of vitreous B 2 O 3 during rate heating through the transition region following rate cooling through the same region at a variety of rates.