Sample holders for air-sensitive materials
Air-sensitivity of a sample material (change of properties in direct contact with oxygen or/and water) is an important issue for many research fields. Besides other materials, a large number of pharmaceuticals and materials for gas storage applications requires an oxygen-/water-free atmosphere for their characterization.
On the one hand, sample material should be well protected from contact with air during a characterization process; on the other hand, a sample should still be accessible for the analytical tool in use. X-ray diffraction (XRD) has two main requirements (apart from good air-tightness) for such a protection: (i) a certain level of transparency for X-rays and (ii) minimal contribution to a diffraction pattern. Naturally, air-tightness and transparency to X-rays are two competing factors. Therefore an optimal sample holder should be chosen based on the specifics of a particular sample, mainly based on its degree of sensitivity to air/water (i.e. the speed of decomposition in direct contact with air/water).
To make this choice easier, PANalytical sample holders with foil protection for air-sensitive materials and Anton Paar domed sample holders are compared. Three main factors are benchmarked: air-tightness, X-ray transparency and a contribution to the XRD pattern. As testing material an extremely airsensitive compound was used: LiH (lithium hydride), which in direct contact
with air decomposes almost completely within one hour.