Helium pycnometers for density measurements
Two pycnometers are provided for the use of the disordered materials community.
Pycnometry uses a gas displacement method to measure volume accurately. The sample is placed in a cell with known volume which is then pressurised with an inert gas (helium). The chamber is then expanded to a reference cell. The pressure is measured both before and after expansion and using this (P1/P2) the volume of the sample, and therefore the density, can be calculated. Repeated measurements are required to allow the system to equilibriate, and the final density should be calculated from 5 or more measurements of P1/P2 which are within a given error.
To use either instrument, please e-mail Alex Hannon to request training.
The quantachrome pycnometer is manually operated, with pressure readings being entered into an excel spreadsheet (which can be downloaded below ) to calculate the density and pressure. The sample cell has a volume of 5 cm3 allowing samples of reasonable size to be measured. Measurements are only accurate when the sample fills more than 1/3 - 1/2 the total volume of the cell.
You will need to provide a laptop to record your measurements.
The Micromeritics pycnometer is entirely computer controlled, and the program outputs a report detailing each reading and giving a final density. The machine can be set up to either take a fixed number of readings, or to run with precision control which outputs a density when five readings have been taken which all lie within a certain error.
This instrument is capable of measuring smaller sample sizes than the Quantachrome pycnometer. The sample cell volume is 1 cm3, and there is an additional insert which reduces the size to 0.1 cm3. The smaller cell sizes mean that much less sample is required to calculate the density accurately.
This instrument is being commissioned, however users are encouraged to make enquiries if they would like to use it.
Instructions for use - coming soon
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