X-ray diffraction (XRD)

The Sedimentology lab of the GeoLab has an XRD since September 2017. The instrument is a Bruker-AXS D8 ADVANCE X-ray diffractometer DAVINCI design with sample changer. The detector is a LYNXEYE XE-T with 192 measuring points.

XRD is a nondestructive analytical technique used to identify (and quantify) minerals and other crystalline materials in samples. The three-dimensional structure of crystals is defined by regular, repeating planes of atoms that form a crystal lattice. When a focused monochromatic X-ray beam, with a wavelength similar to the spacing between atoms in the crystal lattice, interacts with these planes of atoms, constructive interference takes place and part of the beam is diffracted. Bragg’s Law relates the wavelength of electromagnetic radiation to the spacing between planes of atoms in a crystal lattice and the angle of diffraction. Each mineral has a set of spacings between planes of atoms. Using the software diffrac.eva (Bruker), we compare the diffraction pattern to a standard reference (PDF-4) and/or calculated patterns to identify minerals in a sample. Amorphous materials, such as glass, do not produce a diffraction pattern, but only broad scattering peaks.

In our lab, we measure two types of mounts: (1) random powder mounts and (2) oriented clay mounts. Sample preparation depends on which type of mount is required, but in both cases, sample preparation is more important than the settings of the X-ray diffractometer in determining the quality of the results. The grain size of the sample is perhaps the most important aspect related to random powder mount preparation. We use a McCrone Mill to ensure homogeneous powders with a grain size smaller than 10 µm.

We can measure small amounts of sample using a zero-background sample holder. We can also measure flat surfaces on objects using an XYZ-stage. Additionally, we have an air-tight sample holder that allows us to measure samples under special conditions, such as under N2 or humid-free.


Scientific advisor