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Gas Pycnometry (Pycnometry)
Gas Pycnometry is one of the most widely used techniques for analyzing true and skeletal density of any solid (even ones which are porous, granular, and irregularly shaped!). It provides fast, high accuracy volume measurements that can be used to calculate density and porosity, and can be adapted to analyze purity, quality, volatile organic content, and stability of certain materials.
Covalent uses an industry-leading Ultrapyc 5000 Micro Gas Pycnometer from Anton Paar for true density analysis. This tool achieves best-in-class accuracy across the widest array of sample types, including coatings, polymer foams, cements, mining, pharmaceuticals, ceramics, catalysts, metallurgy and more.
- Unmatched volumetric measurement accuracy
- Excellent reproducibility and reliability
- Flexible analytical modes for wide array of sample types
- Raw measurement can be used to calculate numerous material properties
- Density must be calculated using separately measured sample mass
- Porosity does not include closed pores (e.g. pores which are not permeable through solid surface)
The table below reports computed skeletal density for a commercially available nylon sample, produced from volume measurements taken from an Anton Paar Ultrapyc 5000 pycnometer. It has been previously demonstrated that increased nylon crystallinity correlates to increased skeletal density, which suggests that Sample 1 may be slightly more crystalline than the other nylon samples. This hypothesis was separately validated in another study.
From: Anton Paar
Anton Paar Ultrapyc 5000 Micro
- Chamber Volume:
- Large Cell: 135 cm3
- Medium Cell: 50 cm3
- Small Cell: 10 cm3
- Volume Accuracy:
- Large Cell: 0.02 %
- Medium Cell: 0.02 %
- Small Cell: 0.03 %
- Volume Repeatability:
- Large Cell: 0.01 %
- Medium Cell: 0.01 %
- Small Cell: 0.015 %
- Preparation Modes: Flow, Pulse, Vacuum
- Pressure Resolution: 0.0001 psi
- Temperature Stability: better than ± 0.05 °C
- Transducer Accuracy: better than 0.1 %
Gas pycnometry evolved from Archimedes’ Principle of Displacement to measure the volume of solid materials with high accuracy using gas exchange. This value is then combined with the sample’s known mass to determine its true density.
To make a pycnometry measurement, a sample is loaded into a specialized chamber with known total volume. This chamber is exposed to an inert gas with known pressure – typically Helium – which will flood the space around the solid sample – including any penetrable pores. After the pressure stabilizes, a valve opens between the sample chamber and a reference chamber (with known volume). The Pycnometer measures the drop in pressure that occurs as the gas expands into the second chamber, and this pressure difference is used to calculate the true density of the sample.
Beyond the true density measurement, skeletal density, purity, porosity, and other properties can be analyzed using more advanced measurement procedures or through further data processing and computation.
If geometric volume is known, as can be the case for rigid solid foams, then the difference between the pycnometric and geometric volumes can be used to calculate open cell percentage. Compressibility and cell fracture can be subsequently analyzed using multiple-pressure experiments.
Capillary Flow Porometry (also called Porometry) is an optimal technique for characterizing through-pore size and size distribution.