The thermodynamics and kinetics of the dehydration of CsH 2PO 4 studied in the presence of SiO 2

Ayako Ikeda*, Sossina M. Haile

*Corresponding author for this work

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

The thermodynamic and kinetics of the dehydration and hydration of CsH 2PO 4 is investigated by thermogravimetric, differential scanning calorimetry and X-ray diffraction analysis in the temperature range of 200 to 400°C, water partial pressure range of 0.06 to 0.90 atm. SiO 2 powder was added to CsH 2PO 4 to accelerate both dehydration and hydration. When dehydrated in the presence of SiO 2, CsH 2PO 4 has a fine microstructure (~ 200 nm feature size), and no reaction between CsH 2PO 4 and SiO 2 is observed. By making use of the enhanced kinetics afforded by SiO 2, the phase boundary between CsH 2PO 4, CsPO 3 and dehydrated liquid was precisely determined. The triple point connecting these phases is located at p H2O = 0.35 ± 0.2 atm and T = 267.5 ± 1.0°C. The stability of CsH 2PO 4 and the liquid dehydrate, CsH 2(1-x)PO 4-x(l), were confirmed by the complete reversal of dehydration to recover these phases in the appropriate temperature and water partial pressure ranges. Rehydration and conversion of CsPO 3(s) to CsH 2PO 4(s) occur over a period of several hours, depending on temperature, water partial pressure, and morphology of the metaphosphate. High p H2O and small particles favor rapid dehydration, whereas the temperature dependence of the rehydration kinetics is non-monotonic, reaching its fastest rate in the vicinity of the superprotonic transition.

Original languageEnglish (US)
Pages (from-to)63-71
Number of pages9
JournalSolid State Ionics
Volume213
DOIs
StatePublished - Apr 16 2012

Keywords

  • Cesium dihydrogen phosphate
  • Dehydration
  • Differential scanning calorimetry
  • Hydration
  • Phase diagram
  • Thermogravimetric analysis

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Chemistry(all)

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