X-Ray Diffraction XRD – Phase Identification and Composition Determination by LSM Analytical Services

Background

LSM Analytical Services offer a large and diverse range of modern analytical testing facilities that cater for a vast range of industry sectors. LSM’s success has been achieved by building on a strong reputation for low cost, fast accurate turnaround. The laboratory activities are backed up by accreditation to the ISO 17025 (UKAS) and 9001:2000 laboratory and quality management standards. LSM is able to offer complete analytical solutions from its internationally recognised team of technical experts, with in depth knowledge, allowing its customers to benefit from impartial guidance.

LSM’s range of analytical services includes:

• X-Ray Fluorescence Spectrometry (XRF)
• X-Ray Diffraction (XRD)
• ICP Optical Emission Spectrometry (ICP-OES)
• Atomic Absorption Spectrometry (AAS)
• Carbon, Sulphur, Nitrogen, Oxygen Analysers
• Boron analysis by the Neutron Transmission method
• Colorimetric and Volumetric Analysis
• Particle Size Analysi

The Determination of Chemical Composition Using X-Ray Techniques

LSM Analytical Services large range of analytical techniques includes instrumentation for XRD analysis; one of two of the most widely applied analytical techniques based on X-rays:

• XRF (X-Ray Fluorescence) for the elemental or oxide content of a material
• XRD (X-Ray powder Diffraction) for identification of crystalline compounds or phases

LSM Analytical Services offer qualitative and quantitative phase identification of major, minor and trace constituents of geological samples, minerals ores and oxides by X-Ray powder Diffraction.

XRD and XRF Complimentary Analytical Techniques

The techniques are often considered to be complimentary. For example a sample may be submitted for XRF and found to contain 50% Al₂O₃ and 30% SiO₂ and this may be sufficient information. However, XRD could then distinguish between samples containing different phases; for example Quartz (SiO₂), Corundum (Al₂O₃), Mullite (Al₆Si₂O₁₃) or Kaolinite (Al₂Si₂O₅(OH)₄) or any combination of these.

Determination of Chemical Composition by X-Ray Diffraction (XRD)

The X-rays used for XRD have one wavelength (they are all one “colour”). Normally, a sample is a few grams of powder and is packed into a holder with a flat surface. The beam of x-rays enters the sample surface and is reflected by the very small crystals (crystallites) in the sample. When it is reflected the single beam of x-rays is split so the x-rays come out of the sample in several beams at different angles to the sample. The instrument has a detector that swings round the sample as the sample itself is rotated and registers the position and strength of these beams. This data is plotted by software as strength (intensity) vs. position (angle) to give a series of “peaks” or “lines”, which is called the diffraction pattern.

Each chemical compound or phase reflects x-rays slightly differently and so has a different diffraction pattern. A mixture of compounds gives a pattern that is made up of the patterns of all the individual compounds. So to identify the compounds present in a mixture the pattern obtained is compared to a large database of patterns. Often there are overlapping lines so experience and judgement are important. To give a guide when phase identification is complete the peaks are classified as major, minor or trace.

XRD-Related Services Offered by LSM Analytical Services

LSM Analytical Services has developed a suite of programmes internally to allow a range of determinations to be made including:

• Phase identification of crystalline materials
• Phase quantification, including crystalline silica
• Glass content of GGBS (ground granulated blast furnace slag)
• Customer specific quality control methods

LSM’s analysis development team also develops new methods to meet customer requirements.

Source: LSM Analytical Services

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