The mechanism of ion exchange in zirconium phosphates. 16. Calorimetric determination of heats of lithium(1+)-hydrogen(1+) exchange
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The heats of Li+-H+ exchange have been measured calorimetrically on zirconium phosphates of different crystallinities. For the most crystalline exchanger the reaction is exothermic up to about 50% Li+ uptake. This is followed by a mildly endothermic reaction to about 77% lithium loading and a more highly endothermic reaction at still higher loading. These heat effects correspond to the formation of three separate exchange phases identified earlier by x-ray methods. In the case of the nearly amorphous exchanger the reaction is initially very slightly exothermic but soon becomes endothermic. The overall enthalpy is ΔH° = 2.57 kcal/mol and the entropy, ΔS° = -10.6 eu. Qualitative explanations for the enthalpy and entropy effects are presented and the results compared to those obtained with other alkali metal cations.
author list (cited authors)
Clearfield, A., & Tuhtar, D. A.