Section 6. High temperature behavior Glass microstructure evaluations using high temperature mechanical spectroscopy measurements Ren-Guan Duan 1 , Gert Roebben, Omer Van der Biest * Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium Abstract This paper compares the microstructures of several glasses by measuring the YoungÕs modulus and internal friction as a function of temperature, using the impulse excitation technique (IET). IET is based on the analysis of the resonant vibration of a solid material sample, induced by an impulse excitation. IET determines the mechanical resonant fre- quencies (f r ) from which the elastic moduli can be calculated, and for each f r the corresponding internal friction (Q 1 ). It was found that the stiffness of quartz and borosilicate glasses increases with temperature. The stiffness of soda-lime and alumino-silicate glasses decreases with the increase of temperature. The change of stiffness of quartz and alumino- silicate glasses during heat-treatment is reversible, but that of borosilicate and soda-lime glasses is not. Explanations for the irreversibility are suggested based on the Q 1 -features of the glasses. Diffusion of network modifier ions in the glass network holes is proposed to cause a non-reversible stiffness change, whereas localised anelastic relaxation of network modifier ions leads to a reversible stiffness change. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 62.40.þi 1. Introduction The understanding of the elastic and anelastic behaviour of inorganic vitreous solids is important for their development and utilisation. It provides a basis for solving many practical problems such as selecting appropriate glass compositions and an- nealing parameters for applications where control of thermal stresses is important, choice of glass working temperature, control of optical proper- ties, maintenance of volume stability, control of phase separation kinetics, production of glasses with low mechanical, optical and dielectric losses, etc. Internal friction techniques offer one means for studying the structure and atomic or molecular motion in vitreous solids. The position, magnitude and shape of internal friction peaks, measured as a function of temperature (or frequency), are char- acteristic of the glass composition and provide data for the calculation of the activation energy and information on the type and concentration of * Corresponding author. Tel.: +32-16 321 264; fax: +32-16 321 992. E-mail address: omer.vanderbiest@mtm.kuleuven.ac.be (O. Van der Biest). 1 Present address: Department of Chemical Engineering and Materials Science, University of California Davis, One Shields Avenue, Davis, CA 95616, USA. 0022-3093/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. PII:S0022-3093(02)01946-4 Journal of Non-Crystalline Solids 316 (2003) 138–145 www.elsevier.com/locate/jnoncrysol