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

Ayako Ikeda; Sossina M. Haile

doi:10.1016/j.ssi.2011.09.018

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

Materials Science and Engineering

Research output: Contribution to journal › Article

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 language	English (US)
Pages (from-to)	63-71
Number of pages	9
Journal	Solid State Ionics
Volume	213
DOIs	https://doi.org/10.1016/j.ssi.2011.09.018
State	Published - 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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Ikeda, A., & Haile, S. M. (2012). The thermodynamics and kinetics of the dehydration of CsH ₂PO ₄ studied in the presence of SiO ₂ Solid State Ionics, 213, 63-71. https://doi.org/10.1016/j.ssi.2011.09.018

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title = "The thermodynamics and kinetics of the dehydration of CsH 2PO 4 studied in the presence of SiO 2 ",

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.",

keywords = "Cesium dihydrogen phosphate, Dehydration, Differential scanning calorimetry, Hydration, Phase diagram, Thermogravimetric analysis",

author = "Ayako Ikeda and Haile, {Sossina M.}",

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N2 - 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.

AB - 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.

KW - Cesium dihydrogen phosphate

KW - Dehydration

KW - Differential scanning calorimetry

KW - Hydration

KW - Phase diagram

KW - Thermogravimetric analysis

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