FRAGILITY OF A CALCIUM METAPHOSPHATE MELT AND RELAXATION OF ITS GLASS FIBRES

Abstract

With regard to fragility and workability, the calcium metaphosphate-like melt (CMP) with the composition 51.4Ca0 48.6P₂0₅ in mol%is compared with the soda-lime-silicate melt (NCS) with the composition 16Na₂O-10CaO-74SiO₂ in mol%. The fragility of the two melts is characterised by determining the fragility index F_1/2, the difference in heat capacity between glass and melt, and configurational entropy. The difference of heat capacity between the CMP glass and crystal is measured. The intense crystallisation takes place at the temperature T=1.20T_g, where T_g is the glass transition temperature. The fibres are drawn from the CMP melt. The ratio of the fictive temperature T_f to T_g of these fibres is found to be 1.053 by estimating the excess energy stored during fibre forming. Relaxation features of the CMP fibres are examined by doing systematic thermal ageing experiments and calorimetric measurements. The endotherm and exotherm simultaneously occur in a certain range of ageing temperatures. The dependence of the endotherm and extherms on the ageing temperature is discussed.