Glass-forming ability versus stability of silicate glasses. I. Experimental test

We recently proposed that the Hrubÿ parameter of glass stability (KH) could be used to estimate the vitrification ability of glasses that nucleate internally. In that research, we used calculated critical cooling rates (qcr) for four glasses. In this article, we report on our measurements of the critical cooling rates of seven glasses: Li2O · 2SiO2, Na2O · 2CaO · 3SiO2, 2Na2O · CaO · 3SiO2, BaO · 2SiO2, Li2O · 2SiO2 · OH, 2BaO · TiO2 · 2SiO2 and 0.44Na2O · 0.56SiO2. We modified and used a method put forward by Colmenero and Barandiarán (CB) to estimate the qcr. The experiments were accomplished in two steps. In the first, monolithic pieces of each glass, obtained by splat cooling the melts, were heated in a Pt crucible, at the same heating rate, to estimate the glass transition, crystallization and melting temperatures. We then calculated the Hrubÿ parameter, KH, based on these quantities. In the second step, the same samples were melted, then cooled at different rates and the crystallization temperatures observed were used to estimate qcr. In another set of tests, we used Al2O3 and graphite crucibles, repeating the same procedures for the LS2 glass. The effect of the crucible’s material (Pt, C and Al2O3) on the crystallization temperatures is discussed. A relationship between qcr and KH is experimentally demonstrated.