KINETICS OF THE REACTION H2O-DOUBLE-LEFT-RIGHT-ARROW-2OH IN RHYOLITICGLASSES UPON COOLING - GEOSPEEDOMETRY AND COMPARISON WITH GLASS-TRANSITION(O)

Controlled cooling rate experiments of hydrous rhyolitic glasses have been carried out to examine the relation between the apparent equilibr ium temperature of the quenched glass (or the final quenched speciatio n of molecular H2Om and OH groups), the cooling rate, and the total H2 O content (H2Ot). The experimental data are highly reproducible and in ternally consistent. Original band intensities are used to represent t he data. (A) over bar(523) and (A) over bar(452) (absorbances of the 5 23 and 452 mm(-1) bands in terms of peak height per mm sample thicknes s) are used as proxy for H2Om and OH, respectively. Q' (= (A) over bar (452)(2)/(A) over bar(523)) is used as proxy for the equilibrium const ant of the reaction. For a given cooling rate, ln Q' and ln [(A) over bar(523) + (A) over bar(452)] are linearly related. When combined with air-quenched and water-quenched experiments reported by Silver et al. (1990), an abrupt change in slope is apparent. The experimental resul ts provide a geospeedometer to calculate quench rates of natural hydro us rhyolitic glasses. The apparent equilibrium temperature for the rea ction is roughly the same as the viscosity-defined glass transition te mperature. An approximate reaction rate law for the reaction has been inferred. Copyright (C) 1997 Elsevier Science Ltd.