X-ray powder diffraction is a powerful technique for the quantitative determination of the crystalline phases in a mixture. Typical applications include the quantification of minerals for grade control of rocks and ores, clinker and cement phases in building material industries, and bath ratio or ‘potflux’ analysis in aluminum smelters. Providing detection limits in the range of 0.1 to 1 wt.% per phase, XRD is suitable for quality control. The method is for example used by the pharmaceutical industry to detect and quantify small amounts of impurities such as unwanted polymorphs in a sample, and by universities and research institutes to classify the purity of synthesized materials.
Commonly used phase quantification methods
- RIR method: Based on reference intensity ratios (RIR values) and on the determined scale factors of the phases. Results are only 'semi-quantitative' unless the RIR values were determined for the specific mixture under investigation.
- Calibration method: Based on the intensity or area of a peak per phase. Concentrations are obtained from a calibration line previously created from a set of standard samples of known compositions. Amorphous compounds can also be quantified in this way.
- Autoscale method: Full-pattern quantification based on the previously measured, individual intensity profiles of all mixture constituents and the RIR values. The method is particularly suitable for clays imposing irregular peak shapes or when multiple amorphous phases are to be quantified. Also suitable to determine the degree of crystallinity.
- Rietveld refinement: A standardless method in which calculated diffractograms of each phase are varied until the best fit with the experimental pattern is obtained. From the determined scale factors phase concentrations can be deduced. This method requires atomic crystal structure data of all phases as input for the refinement. It is particularly powerful for complex phase mixtures showing strong peak overlap. The content of amorphous materials can be quantified as well.
XRD phase quantification solutions
The Empyrean and the X'Pert³ Powder multi-purpose XRD platforms are both equally well-suited to phase quantification. For high-volume production control optimized for specific industry applications, the CubiX³ systems are ideal. They can easily be automated and are designed for rugged environments.
Calibration-based methods are covered by the Quantify and Industry software packages. HighScore allows for the RIR and autoscale methods and HighScore Plus additionally covers the Rietveld refinement and hkl fit methods, which use Miller indices. All software packages also offer several automation and customizable reporting options.