Relationship between hydrate stability and accuracy of true density measured by helium pycnometry

Shao Yu Chang, Chenguang Wang, Calvin Sun

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Mechanical properties of a material, such as hardness and elastic modulus, depend on porosity exponentially. Thus, an accurate characterization of material mechanical properties requires correct porosity, which depends on the accuracy of measured true density. Helium pycnometry is the most common technique for determining true density of a powder material but it is not suitable for materials containing volatile components. For unstable hydrates, dehydration during measurement releases water and invalidates the ideal gas law used for calculating sample volume. Consequently, measured true density is over-estimated, which causes gross errors in mechanical properties extrapolated to zero porosity. This work shows that physical stability and the dehydration kinetics, determined by both water-bonding structures and bonding energy, directly affect the magnitude of error in measured true density.

Original languageEnglish (US)
Article number118444
JournalInternational journal of pharmaceutics
StatePublished - Aug 15 2019

Bibliographical note

Funding Information:
S-Y. Chang was partially supported by a David and Marilyn Grant Fellowship in Physical Pharmacy (2017-2018), Department of Pharmaceutics, University of Minnesota . We thank Shenye Hu for help with collecting part of the helium pycnometric data.

Publisher Copyright:
© 2019 Elsevier B.V.

Copyright 2019 Elsevier B.V., All rights reserved.


  • Dehydration
  • Energy framework
  • Helium pycnometry
  • Hydrate stability
  • Porosity
  • True density

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