Heat capacity and glass transition in P2O5-H 2O solutions

Support for Mishima's conjecture on solvent water at low temperature

Horacio R. Corti, Federico J. Nores-Pondal, Charles Angell

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The P2O5-water system has the widest range of continuously glass-forming compositions known for any glassformer + water binary system. Despite the great range of structures explored by the glasses and liquids in this system, the glass transition temperature (Tg) itself varies in a simple monotonic fashion. However the values of Tg reported in the literature show wide disagreement, linked to the different methods of measurement employed. In this work we use differential scanning calorimetry (DSC) to obtain both Tg itself and the jump in heat capacity that occurs as the metastable equilibrium of the supercooled liquid relieves the non-ergodic glassy state. Our study covers the molar ratio range of H2O/P2O5 from 1.5 to 14 (corresponding to the mass fraction of P2O5 between 0.36 and 0.84), which includes the compositions corresponding to pyrophosphoric acid (H 4P2O7) and orthophosphoric acid (H 3PO4). The theoretical model of Couchman and Karasz predicts very well the glass transition temperatures of the P2O 5-H2O system over the whole composition range if the relatively large heat capacity change associated with water in aqueous solutions at the glass transition temperature is adopted, instead of the vanishingly small value observed for vapor deposited or hyperquenched pure water. Therefore, solvent water in this ambient pressure P2O5-H 2O system behaves like a different liquid, more closely resembling a high-density liquid (HDL) polyamorph, as suggested by Mishima for electrolytes at high pressures.

Original languageEnglish (US)
Pages (from-to)19741-19748
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume13
Issue number44
DOIs
StatePublished - Nov 28 2011

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phosphorus pentoxide
Specific heat
Glass transition
specific heat
Water
glass
glass transition temperature
water
Liquids
liquids
Temperature
Chemical analysis
Glass
acids
Electrolytes
Differential scanning calorimetry
heat measurement
Vapors
electrolytes
vapors

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Physics and Astronomy(all)

Cite this

Heat capacity and glass transition in P2O5-H 2O solutions : Support for Mishima's conjecture on solvent water at low temperature. / Corti, Horacio R.; Nores-Pondal, Federico J.; Angell, Charles.

In: Physical Chemistry Chemical Physics, Vol. 13, No. 44, 28.11.2011, p. 19741-19748.

Research output: Contribution to journalArticle

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