Specific information on the method:
– The in situ SR-PXD apparatus is a setup conceived to study reaction mechanism and phase evolution in hydride-based hydrogen storage material under controlled environmental and temperature conditions.
– The measuring principle is the powder X-ray diffraction (PXD). The measurement of the diffraction data is carried out in synchrotron facilities. PXD is a powerful technique to investigate the material structure and material properties. Using a standard laboratory diffractometer, in order to collect a diffraction pattern of a high quality, an acquisition time of several hours is needed. The reason for such a long acquisition time is often the low brilliance of the used X-ray sources. In the last decades, following the development of highly brilliant synchrotron facilities and high sensitivity large area detectors, the possibilities of performing fast PXD analysis raised. The availability of such facilities enabled the development of special equipment(e.g. in situ SR-PXD apparatus), which allows scientists to study several chemical solid-solid and solid-gas processes in situ, while they are taking place.
Specific information on the equipment/instrumentation:
The in situ SR-PXD apparatus can be connected to the diffractometer stage using a standard goniometer head. Few milligrams of the hydrides are inserted in single crystal sapphire capillaries (Crytur) with an outer diameter ranging between 1.0 and 3 mm and a total length of 60 mm, matching standard Swagelok nuts. These sapphire capillaries are chemically inert and for wavelength ≤ 0.1 nm they show a rather high transmittance. In order to avoid O2 and H2O contamination, the loading of the materials into the sample cell is carried out in glove boxes under continuously purified Ar atmosphere (O2 and H2O < 1 ppm).
To insure the tightness of the system, graphite ferrules (SGE) are used to tighten the Swagelok nuts, when mounting the capillaries. The gas is equally distributed in the sample from both sides, using a polyetheretherketone (PEEK) flexible line between the two Swagelok nuts fixing the capillary and the gas system. A 0.5 mm type K thermocouple inserted into the powder bed in the capillary measures and controls (via a standard PID controller) the sample temperature during the experiment. The sample is heated using a ceramic heating element from BACH GmbH. The heating element is placed right below the sample at a distance of less than 1 mm.
The operation conditions for the in situ SR-PXD apparatus are:
- Temperature: from RT up to 500 °C
- Pressure: from 10-2 up to 600 bar
- Pattern acquisition time: ≈ 10 s
- Usable gasses: H2 and NH3
All the materials relevant for the hydrogen storage community.
Examples of typical analytical questions:
Characterization of solid-solid and/or solid-gas processes in crystalline materials.
This equipment is suitable for:
- Study of solid-solid, solid-gas processes
- Elucidation of reaction mechanisms
- Identification of phases and intermediate species
- Quantitative analysis of phase evolutions