Summary: Quantitative data are presented for the kinetics of crystal growth in an aluminosilicate glass to which a few wt % of a transition-metal oxide had been added. The composition of the base glass was CaO 3o, MgO 2, Al2O3 15, SiO2 53 wt %, to which the oxides of iron, vanadium, chromium, or zinc were added. Glasses were prepared with a range of high to low valency ratios in cases where the transition metal oxide could exist in two or more oxidation states.
Small quantities of Fe2+, Fe3+, Zn2+, V3+, V4+, and V5+ were all found to increase the kinetics of crystal growth from the glass phase. The magnitude of the effect is compared with additions of Mg2+ to the glass. Cr2+, Cr3+, and Cr6+ were found to decrease the rates of crystal growth. Values for the apparent activation energy for crystal growth ranged from ∼50 kcal/mole to ∼150 kcal/mole. The high values were found to be of the same order of magnitude as that for the activation energy for viscous flow in the glass at the crystallization temperature.
The results are interpreted in terms of the structure of the glasses and current theories on the rate of crystallization of glasses.