This work aims to provide a wide range of case studies that demonstrate how to best interpret the raw data and perform the measurement using helium pycnometry. By examining several different classes of materials, fingerprint traits from He pycnometry data are highlighted. Experimental parameters important in obtaining the most precise and accurate value of skeletal density from the He pycnometer are a as high as possible % fill volume and good thermostability. The magnified error in skeletal density as the sample size decreases is attributed to error in the volume calibration of the sample chamber and reference chamber. The degree of sample activation was demonstrated to affect the measured skeletal density of porous zeolitic, carbon, and hydrid organic-inorganic materials. In the presence of a significant amount of water contaminant, the skeletal density tended to be overestimated in the low % volume region compared to values at high % volume and activated samples. In addition, examination of the kinetic data (i.e., skeletal density vs. measurement cycle) revealed distinctive traits for a properly activated porous sample vs. an unactivated sample for all examined samples: activated samples that lost a significant amount of water showed a curved down plot that eventually reached the real value, whereas wet, nonporous, or extremely hydrophobic samples exhibited a flat line. This work illustrates how helium pycnometery can provide information about structure of materials, and that, conversely, by knowing the structure of the material and its wetness, the behavior of wet and dry sample in terms of skeletal density, % fill volume, and measurement cycle can be predicted.

Understanding material characteristics through fingerprint traits from helium pycnometry

255th National Meeting (2018)

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