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Thermodynamic stability considerations for isostructural dehydrates.

Brendan J Murphy1, Melissa J Casteel, Brian Samas

  • 1Materials Science, Pfizer Inc., Eastern Point Road, Groton, Connecticut 06340, USA. brendan.j.murphy@pfizer.com

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|January 21, 2012
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Summary
This summary is machine-generated.

This study introduces a eutectic-melting method to determine the thermodynamic stability of nonstoichiometric channel hydrates. The research confirms the hydrate is the stable form at room temperature, regardless of hydration state.

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Area of Science:

  • Solid-state chemistry
  • Materials science
  • Crystallography

Background:

  • Nonstoichiometric channel hydrates exhibit variable water content based on temperature and relative humidity (RH).
  • Assessing thermodynamic stability in isostructural systems with stable dehydrated forms is challenging using traditional methods.

Purpose of the Study:

  • To apply a eutectic-melting method for determining the thermodynamic stability relationship between a nonstoichiometric channel dehydrate and its anhydrous form.
  • To investigate the stability of nonstoichiometric channel hydrates under varying RH conditions.

Main Methods:

  • Utilized a eutectic-melting method to identify the transition temperature between the isostructural dehydrate and anhydrous polymorph.
  • Conducted solid-state storage experiments across a range of RH conditions.

Main Results:

  • Identified a transition temperature of 122°C between the isostructural dehydrate and the anhydrous polymorph.
  • The nonstoichiometric channel hydrate is the thermodynamically stable form at room temperature (RT).
  • The hydrate remains the stable form at RT above 94% RH.

Conclusions:

  • The nonstoichiometric channel hydrate is the stable form at low temperatures, irrespective of its hydration state.
  • The eutectic-melting method is effective for studying thermodynamic stability relationships between anhydrous forms and dehydrated channel hydrates.