A frequent question is often posed by users, can density be calculated from free space measured on a gas adsorption analyzer instead of using an instrument that is designed to obtain density? This tech note will explore the possibility of using such a method and compare with results obtained by the Micromeritics AccuPyc II.
Gas adsorption instruments measure quantity of gas adsorbed at various pressures. This information is used to calculate surface area and porosity information. To determine the quantity of gas that adsorbs on a sample, the system must determine the available volume within a sample tube not being occupied by the sample. The typical gas adsorption instrument establishes this free volume (also referred to as free space) by taking two measurements using helium, a non-adsorbing gas. The ambient free space is measured under ambient temperature while the analysis free space is measured at the analysis temperature.
The sample volume can be estimated by subtracting the ambient free space of an empty tube from the ambient free space of the same tube with sample. The density can then be calculated by dividing the sample’s mass by the volume.
A helium pycnometer operates in a similar manner. The pycnometer is calibrated using a known volume, typically a sphere or a non-porous ceramic with well-defined geometry, known composition, and well-known coefficient of thermal expansion. A pycnometer calibration is used to establish the volumes of the reference and volume chambers. The sample is then placed in the sample chamber, and a process that is similar to free space determinations is employed to determine volume of the sample chamber that is occluded by the sample material. This process is repeated for typically 10 cycles to determine an average volume of the material under test.
A frequent question is often posed by users, can density be calculated from free space measured on a gas adsorption analyzer instead of using an instrument that is designed to obtain density? This tech note will explore the possibility of using such a method and compare with results obtained by the Micromeritics AccuPyc II.
Gas adsorption instruments measure quantity of gas adsorbed at various pressures. This information is used to calculate surface area and porosity information. To determine the quantity of gas that adsorbs on a sample, the system must determine the available volume within a sample tube not being occupied by the sample. The typical gas adsorption instrument establishes this free volume (also referred to as free space) by taking two measurements using helium, a non-adsorbing gas. The ambient free space is measured under ambient temperature while the analysis free space is measured at the analysis temperature.
The sample volume can be estimated by subtracting the ambient free space of an empty tube from the ambient free space of the same tube with sample. The density can then be calculated by dividing the sample’s mass by the volume.
A helium pycnometer operates in a similar manner. The pycnometer is calibrated using a known volume, typically a sphere or a non-porous ceramic with well-defined geometry, known composition, and well-known coefficient of thermal expansion. A pycnometer calibration is used to establish the volumes of the reference and volume chambers. The sample is then placed in the sample chamber, and a process that is similar to free space determinations is employed to determine volume of the sample chamber that is occluded by the sample material. This process is repeated for typically 10 cycles to determine an average volume of the material under test.
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