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

Abstract

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.