A series of calcium aluminosilicate liquids have been experimentally heat-treated at high but variable states of undercooling. from just above the glass transition to the vicinity of the solidus. The mineralogy and chemistry of crystalline phases which appear in these experiments have been quantified using a combination of Transmission Electron Microscopy and Raman spectroscopy, The results show that mineral compositions are highly variable as a function of temperature. but that changes are governed by the contrasting and strongly temperature-dependent mobilities of network-modifying and network-forming cations. Whereas equilibrium crystals form near the liquidus, disordered and non-stoichiometric phases precipitate near the glass transition. Despite this apparently complex situation, the relative importance of thermodynamic and kinetic factors is found to be a single function of T - T-g (where T is temperature and T-g the glass transition temperature). regardless of the silicate composition. The existence of this mastereurve may be used to control the composition of novel composite materials such as glass ceramics. (c) 2005 Elsevier B.V. All rights reserved.
Carnegie Inst Washington, Geophys Lab, Washington, DC 20015 USA; Ctr Rech Petrog & Geochim, CNRS, UPR 2300, F-54501 Vandoeuvre Les Nancy, France; Observ Midi Pyrenees, DTP, F-31400 Toulouse, France; Inst Phys Globe, F-75252 Paris, FranceArticleEnglish