Relaxation Behaviour of Hyperquenched Glass Fibres

In connection with the Rockwool project, one of the most important topics is the investigation of the relaxation behaviour of the glass fibres. The sub-Tg relaxation of a hyperquenched inorganic glass during physical aging is still a mystery. This project attempts to reveal the nature of sub-Tg relaxation of a hyperquenched inorganic glass. Therefore, we carried out the systematic ageing experiments and the differential scanning calorimetric (DSC) study on the basalt glass fibres below the glass transition temperature (Tg). Based on the DSC data and thermodynamic theory, we proposed a simple approach to determine the fictive temperature (Tf) of the hyperquenched glass. The recovered enthalpy of heating is estimated, which equals the released amount of the excess inherent structure energy stored in the glass. The hyperquenching is reached by means of the fiber spinning. We analyze relationships between the released enthalpy, changes in the internal energy, and changes in the configurational entropy. The relaxation of a hyperquenched glass substantially differs from that of a normally cooled glass. Two mechanisms govern the relaxation of a hyperquenched glass. During relaxation of the first hyquenched and afterwards aged glass, a relaxation endotherm occurs followed by an exotherm. This is reflected by the occurrence of the crossover point. With increasing aging temperature and time, the endotherm becomes more pronounced, while the exotherm gradually disappears. The consequence of this is the shift of the crossover point to a higher temperature. The relaxation of the fiberglass at 0.66Tg exhibits a high non-exponentiality. The results provide an experimental basis for mapping the energy landscape of glass-forming liquids. Our findings lead to a much deeper understanding of the structure and physical properties of hyperquenched glasses. Therefore, this paper is of general interest in the Condensed Matter Physics. The results were adjudged as the highlight of several international conferences and as one of the most important discoveries in the area of amorphous solid physics. The new results have been and will be published in various well-known scientific journals. Many other papers, e.g. a paper in "Science" (294, 2335 (2001)) have cited our results. The similar study has been performed on the other glass systems like Ca(PO3)2 and SiO2. The relationship between the fragility of the melts and the energy release behaviour of the fibres has been found. In addition, it has been observed that the recovery of the endothermic peak of the excess capacity could not only be removed, but also recovered by changing the experimental conditions. This phenomenon contributes to clarifying the longstanding controversial question about the glass transition of water. (Yuanzheng Yue)