X-Ray Diffraction Spectroscopy (XRD)

Bruker D8 Focus X-Ray Diffraction Spectrometer

The X-ray powder diffraction (XRD) is a rapid, non-destructive, analytical technique used to characterize the crystallinity, crystal phases and the identity of the solid sample. XRD obtains a diffraction pattern for the bulk material of the crystalline solid instead of a single crystal which is more convenient and the analysed sample must be finely ground and homogenized for the bulk composition to be determined. The Bruker D8 Focus is equipped with all the necessary components required for qualitative and quantitative phase analysis, structure solution and refinement, crystallite size determination and microstrain analysis. 

Principle

The X-ray diffractometers consist of three basic elements: An X-ray tube, a sample holder, and an X-ray detector. The X-rays are produced by a cathode ray tube by heating a filament to produce electrons which are filtered to produce monochromatic radiation, collimated and directed towards the sample. This X-ray beam interacts with the planes of atoms in the sample where parts of the beam are transmitted through, absorbed by, refracted, scattered and diffracted by the sample. As the X-rays diffract differently by each mineral depending on the composition and arrangement of atoms in the crystal lattice, the distance between the planes of atoms can be measured by applying Bragg’s Law. This law relates to the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample. Due to the unique diffraction pattern exhibited by samples, the XRD analysis provides a ‘fingerprint’ of the crystals present in the sample. This can be compared with standard reference patterns and measurements to identify the crystal structure.

Strengths

• Non-destructive
• Magnetic samples can be analysed
• Fast analysis time

Limitations

• Small sample size (requires tenths of a gram of material which must be ground into a powder)
• The detection limit for mixed materials is ~ 2% of sample
• Complicated indexing patterns for non-isometric crystal systems for unit cell determination and peak overlay may occur

Applications

• Pharmaceuticals: Identification and characterization of polymorphs, monitoring of batch/dosage uniformity and crystal morphology of raw materials, scrrening of crystal structures and lattice parameters
• Mineral industry: Analysis of crystaline phases, crystaline size and phase composition of minerals
• Polymer industry: Study of solid-state structural properties such as the degree of crystallinity for semi-crystaline, amorphous polymers and composites, determination of the orientation of crystalline and non crystalline materials 
• Textile industry: Analyse crystalline phases of textile materials

Technical Specifications

• Configuration : Vertical Theta/2Theta geometry
• Measuring circle diameter : 401 mm
• Angular range (without accessories) : 360°
• Maximum useable angular range : -110° < 2Theta ≤ 168°
• Angle positioning : Stepper motors with optical encoders
• Smallest addressable increment : 0.0001°
• Reproducibility : ±0.0001°
• Maximum angular speed : 30° /s