Configurational entropy and crystal nucleation of silicate glasses

Changes in entropy accompanied with the glass transition of jive alkali silicate melts are investigated. Rheometric data and the Adam-Gibbs theory of relaxalion arc utilised to calculate the configurational entropy S-conf(T-g) at the glass transition for each melt. These results, together with calorimetrically determined S-conf(T-g) data of silicate glasses from literature are used to illustrate a compositional trend of 13 silicate glasses involving glass transition temperature and configurational ;entropy on the basis of reduced scales, i.e. T-rg = T-g/T-m and S-rconf/=S-conf(T-g)/DeltaS(m). It is assumed that the configurational entropy, which represents the number of all sampled local potential energy minima, is reduced when the melt is cooled down in the metastable state. Accordingly, for those melts which exhibit a deep supercool limit, ordering of various topological contributions may promote nucleation events and may help to explain the increased volume nucleation tendency in glasses with T-rg < 0(.)58.