Micromeritics Density Measurements

Our world-class instruments, supported by expert application assistance, determine precise density measurements across diverse applications.
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What is Density?​

Density refers to the amount of mass contained in a given volume. On an elementary level, the volume of a solid material can be calculated by measuring its length, width, and thickness. However, many materials have within their structure surface irregularities, small fractures, fissures, and pores. Some of these voids or pores may be accessible from the surface, while others are enclosed within the structure of the solid material. These variations impact the overall volume and contribute to the distinct definitions of density outlined below.

True or Absolute 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

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

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

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

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.

How to Measure Density?

Gas Pycnometry

The AccuPyc uses gas pycnometry a non-destructive technique that relies on gas displacement to measure volume accurately, making it ideal for obtaining true, absolute, and skeletal volume and density. An inert gases, such as helium, nitrogen, or air are commonly used as the displacement medium for gas pycnometry.

A sample is placed in a chamber of known volume, which is sealed and pressurized. The gas fills the empty spaces within and between the sample particles. The sample chamber is then expanded to an adjoining reference chamber of known volume. The change in pressure is used to calculate the volume of the sample. True density is calculated from the sample mass and the volume it occupies. This method is useful for determining the true density of materials, even those with small pores and irregular shapes.

  1. Inert gas flows Into sample chamber (valve a opens then closes)
  2. Equilibrium is reached
  3. Gas flows into second chamber for volume measurement (valve b opens)
  4. Equilibrium is reached yet again
  5. Volume divided into sample weight determines density
  6. Pressure vented off to atmosphere (valve c opens)
The AccuPyc gas pycnometer from Micromeritics is the fastest, easiest, most accurate measurement of true density. More labs choose an AccuPyc than any other commercial gas pycnometer. The AccuPyc delivers the highest available accuracy and repeatability in a system that is fast and easy for any operator to use.

Envelope and T.A.P Density

The GeoPyc employs a unique displacement measurement technique that uses Dry Flo, a quasi-fluid composed of small, rigid spheres having a high degree of flow-ability. The sample is placed in a bed of Dry Flo which is agitated and gently consolidated about the sample. The GeoPyc collects the displacement data to determine both Envelope and T.A.P density.

Mercury Density

The AutoPore can be used to determine the bulk and skeletal density if the volume of the penetrometer is known. Rather than displacing gas or dry powder as in the previous techniques, mercury is displaced.

Bulk volume is defined as the volume of the sample after the largest pores (typically greater than 180 µm) have been subtracted.

Bulk volume = total internal volume of the penetrometer – volume of mercury occupying the space around the sample:

Density equation. Bulk volume equals total internal volume of the penetrometer minus volume of mercury occupying the space around the sample.

Skeletal volume is defined as the volume of a material after all open pores larger than 0.005 µm have been excluded from the volume. This can be determined when pressure is applied and forces the mercury to fill the open pores of the sample.

Skeletal volume = bulk volume – total pore volume:

Density equation. Skeletal volume equals bulk volume minus total pore volume

Bulk density and Skeletal density are calculated as shown below, by dividing the mass of the sample by the respective volume.

Bulk density and skeletal density calculations
Mercury icon

Our Solutions

Instruments

AccuPyc III

Gas Displacement Pycnometry System- The fastest, easiest, most accurate measurement of true density

Geopyc

Measures the envelope volume and density of formed pieces without use of hazardous materials

AutoPore V

Measures density, in addition to full porosimetry, especially for meso- and macro-porous materials.

Services

We provide a comprehensive range of characterization services whether it is the analysis of a single sample, a complex method development or validation, new product assessments, or addressing large-scale manufacturing projects.

Available options

  • Skeletal Density
  • Mercury Density
  • Bulk Density or TAP Density
  • Polymer Foam and Cellular Materials
  • Envelope Density

FAQ

  • How is density measured?

    Density is measured by calculating the mass of an object divided by its volume. The formula is density (ρ) = mass (m) / volume (V). Accurate measurements of mass and volume are crucial to determine the precise density of a material.
  • What lab equipment is used to measure density?

    Laboratory equipment used to measure density varies depending on the state of the material (solid, liquid, or gas) and the required precision. For solids, a common instrument is a gas pycnometer, such as the AccuPyc, which measures the volume using gas displacement and determines density by dividing mass by volume. The GeoPyc is another popular choice when determining envelope density.
  • What are the different types of 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.

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