AccuPyc

The AccuPyc determines density using the gas displacement pycnometry method. In this method, a dry solid sample of known mass is placed into a sealed measurement chamber. A gas – normally Helium but alternatives are available – is introduced at a controlled pressure and allowed to expand into a reference chamber. By measuring the pressure change and applying Boyle’s law, the instrument calculates the volume of gas displaced by the sample. Knowing the sample mass, its density is calculated from the ratio of mass to the measured volume. As a result, AccuPyc measures true or skeletal density, using a volume that excludes open pores and interparticle voids, but includes closed pores within the solid.

• AccuPyc III 1350: True density, Skeletal density by gas pycnometry
• GeoPyc: Envelope density, Bulk density, Powder density, T.A.P. density
• FT4 Powder Rheometer: Conditioned Bulk density, Powder Density, Compressed Bulk density

There are several types of density:  

• True or absolute density – the ratio of the mass to the volume (true volume) of a sample, excluding the volume of opened pores, closed (or blind) pores, and inter-particle voids.
• Skeletal density – the ratio of the mass to the volume (skeletal volume) of the particles, excluding inter-particle voids and opened pores, but including closed pores.
  Bulk or apparent density – the density measured after the particles have freely filled a standard container under specific conditions, i.e., the mass of the particles per unit volume when they are loosely packed.
• T.A.P. (Transverse Axial Pressure) density – a measure of compressed bulk density based on the external volume of a powder bed that has been compressed under a controlled force to reduce interstitial space. This property is of considerable interest in packaging, handling, and shipping bulk granular products.
• Envelope Density – the ratio of the mass of a substance to the envelope volume defined by an imaginary boundary around the external surface of an object. This volume includes both open and closed pores but excludes the interstitial space between pieces.

Each type of density provides specific information that can be critical depending on the context of its application, such as material science, chemistry, engineering, or geology. Understanding the differences between these types of density is important for precisely characterizing materials and their behavior in various environments.

Yes, the AccuPyc from Micromeritics can measure volume displacement using gas pycnometry. With weight measurements of the sample, it can calculate density, and by relating this to the reference material (commonly water), it provides specific gravity data for solids.

<strong>Specific Gravity = Density of sample / Density of reference (typically water)</strong>

This makes AccuPyc suitable for applications requiring specific gravity measurements.

The AccuPyc gas pycnometer supports flexible gas selection in order to enhance workflow efficiency and improve material compatibility. AccuPyc is capable of operation with helium, nitrogen, argon, and dry air. Helium is the primary gas used for standards‑compliant skeletal density measurements, while nitrogen or argon may be used where permitted by the method and material characteristics.