Fibre Drawing From Diabase Glass Melts

Parallel to the study of relaxation behaviour of glass fibres, we also worked on the optimisation of the fibre drawing process. The fibre drawing from diabase and basalt melts is extremely sensitive to variation in the chemical composition of the raw materials and in forming condition. Two types of specific diabase glasses are characterised to find the correlations between the spinnability, quality of the fibre, chemical compositions of raw materials, melting conditions and properties of glass melts. The relationships between the fibre properties and forming conditions are explored and discussed. Based on the Yue-Brückner equation (J. Non-Cryst. Solids 180 (1994) 66) and Adam-Gibbs-equation (J. Chem. Phys. 43 (1965) 139), an integrated approach is suggested, which takes into account the influence of large tension stress and hyperquenching (fast cooling) on viscosity of fibres. This approach can be incorporated into the finite-element-simulation of the fibre drawing process. It has been analysed whether or not the non-Newtonian behaviour related to large tension occurs under forming conditions used in this work. The onset of the shear thinning of the fibre is reached at the maximum drawing speed applied in the fibre drawing experiments. The change of iso-structure viscosity related to hyperquenching is estimated by using the Adam-Gibbs-equation and by determining the fictive temperature (Tf), which is obtained with aid of a new approach proposed by the present author [Chem. Phys. Lett. 357, 20 (2002)]. On the basis of fragility concept and liquidus temperature, a simple way is proposed to predict the spinnability of the diabase glass melts. The origin of a mixed MgO-CaO effect leading to the minimum of the glass transition temperature and fragility is discussed in terms of variations in bonding energy due to the substitution of CaO for MgO. The differences in crystallisation behaviour between the two diabase melts are estimated with help of the controlled heat- treatment, the X-ray diffraction analysis (XRD) and differential thermal analysis (DTA). The relationship between cooling rate and fictive temperature has been established by determining Tf by use of the differential scanning calorimetry (DSC) data and by determining the cooling rate with the help of FEM simulation. The correlation between the viscosity and cooling rate has been found, which is significant for a better understanding of the mechanisms of relaxation of the hyperquenched glass fibres. (Yuanzheng Yue)