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Energetics of the Charge‐Coupled Substitution Si 4+ → Na + + T 3+ in the‐Glasses NaTO 2 –SiO 2 (T = Al, Fe, Ga, B)
Author(s) -
Yoreo James J.,
Navrotsky Alexandra,
Dingwell Don B.
Publication year - 1990
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1990.tb05269.x
Subject(s) - enthalpy , endothermic process , standard enthalpy of formation , raman spectroscopy , analytical chemistry (journal) , chemistry , crystallography , calorimetry , materials science , thermodynamics , physics , adsorption , chromatography , optics
Heats of solution in molten 2PbO·B 2 O 3 at 973 K are reported for glasses x NaT 3+ O 2 –(1 – x )SiO 2 for T = Fe, Ga. These measurements, combined with previous data for T = Al, B, give a relative measure of the enthalpy of the charge‐coupled substitution Si 4+ → Na + + T 3+ . The heats of solution become more endothermic with increasing x for x → 0.5 and exhibit a maximum near x = 0.5. This indicates an exothermic enthalpy for the substitution and an overall stabilization of the glasses. The degree to which the glasses are stabilized decreases in the order Al > Ga > Fe > B. On the basis of molecular orbital calculations, X‐ray scattering, and Raman spectroscopy, it is argued that this trend is primarily due to a decrease in the range of energetically favorable T–O–T bond angles as Al, Ga, Fe, and B are substituted for Si.