Neutron scattering can be used to study gas-solid interactions and the effect of sorption on a materials’ structural properties. The performance of in-situ neutron scattering studies can be improved through the use of automated gas delivery and measurement systems, compared to manually operated gas panels. In addition, real-time data acquisition and subsequent data reduction (through commercially available software) can further improve the efficiency of automated systems.
Hiden Isochema has supplied a number of automated systems to central facilities like the NCNR, the Bragg Institute, the ILL and STFC department ISIS. This article describes the gas delivery systems that have been installed at the NCNR and the Bragg Institute since 2012.
IMI Series Gas Sorption Analyzers
The IMI gas sorption analyzers from Hiden Isochema are designed for the analysis of gas mixture and single component sorption by materials. These are standard laboratory instruments capable of carrying out measurements in the pressure range of vacuum to 20 MPa, and at temperatures between 77 K and 773 K. They have an all-metal design with Swagelok VCR components, Swagelok DP Series diaphragm valves and narrow bore 316 L stainless steel tubing. They facilitate convenient operation with high pressure gases like CO2, CH4, N2 and H2. Further, most of the IMI systems come with dry turbomolecular vacuum pump systems, which ensure a clean environment and high vacuum operation required for challenging measurements. Figures 1 and 2 show the examples of data measured using standard laboratory IMI analyzers.
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Figure 1. Hydrogen desorption isotherms for the hydrogen storage alloy LaNi5 in the temperature range 333 K to 383 K
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Figure 2. CH4 and He adsorption on Filtrasorb F-400, a commercial microporous carbon, at 308 K
In-Situ Neutron Scattering Systems
IMI analyzers can be connected to gas delivery sticks through high pressure capillary lines for in-situ neutron scattering studies. Mounted on compact mobile carts, these analyzers can optionally come with a command line interpreter that can be used to integrate the neutron instrument control software through communication with the IMI process control interface. Mass flow controllers (MFCs) permit operation in a flowing mode, where gas is allowed to pass through the sample cell and its composition is analyzed using a quadrupole mass spectrometer (MS). The specifications of the systems supplied to the NCNR and the Bragg Institute are given in Table 1.
Table 1. A comparison of the specifications of the Bragg Institute and NCNR IMI systems for in-situ neutron scattering experiments
| |
Bragg Institute |
NCNR |
| Number of gas streams |
5 |
3 |
| Maximum pressure (MPa) |
20 |
10 |
| Dosing manifold volume (cm3) |
15 |
9 |
| Expansion volumes (cm3) |
50, 150 |
50, 150 |
| Low pressure MS sampling |
✓ |
✓ |
| High pressure MS sampling |
5 |
✓ |
| Pressure sensors (MPa) |
0.01, 0.1, 20 |
2, 10 |
The Bragg Institute
An IMI system was installed in the Bragg Institute in December 2012. It consists of five inlet streams and a 20 MPa upper operating pressure. The expansion volumes of 50 cm3 and 150 cm3 enable the selection of different molar quantities at any pressure, thereby allowing the delivery of gas to samples of varying absolute size and sorption capacity.
The system also allows downstream gas composition sampling under ambient pressure in flowing mode. This avoids the need for an MFC as a back-pressure regulator. The first results of its application on the WOMBAT diffractometer were reported in May 2013.
The NIST Center for Neutron Research
The IMI system was installed at the NCNR in July 2013. It includes three inlet streams, expansion volumes, and 10 MPa upper operating pressure. Gas sampling is possible at both ambient and elevated pressures due to a more versatile MS sampling system. The MS sampling system, however, demands an MFC as a back-pressure regulator. The gas is allowed to pass through an ambient pressure manifold before reaching the heated capillary. The gas from the capillary is transported to the vacuum chamber that contains the Hiden Analytical MS.
In each case, single component measurements allow the determination of gas sorption and desorption isotherms, as shown in Figs. 1 and 2, with the sample in the beam. The multiple inlet streams, in both systems, allow the programming of sequential measurements with different gases. The versatility of the gas mixture experiments was further improved with the use of MFCs on each inlet.
Conclusion
Although most of the features of both systems remain common, there are some differences in each system because of the nature of the desired application. The NCNR IMI facilitates a wide range of MS sampling pressures for different gas mixture experiments carried out for the in-situ simulation of gas separation processes. In contrast, the Bragg Institute IMI provides a wide range of gas mixtures and high measurement accuracy in the low pressure regime.
This information has been sourced, reviewed and adapted from materials provided by Hiden Isochema.
For more information on this source, please visit Hiden Isochema.