Sample preparation for XRF analysis – Metallic materials

Linishing (grinding) or milling are the two most commonly used sample preparation methods for X-ray analysis of metallic materials. After the sample preparation procedure, the sample surface should be as homogeneous as possible, indicating that it is clean and that almost all imperfections have been removed. Chips and drillings of hard metals can be also measured if re-melted to form a solid sample, or for soft metals by pressing the loose material into a stable pellet.

Re-melting

You can re-melt bulk or loose metal particulates in order to form a solid piece. You can then directly measure such metal samples or, before analyzing them, you can prepare them further according to one of the techniques below.

Linishing

Soft alloys (Al- and Cu-based) are usually not suited for linishing. The sample top layer is removed by using a linishing belt or disc grinder to ensure that measurements are carried out on a flat and non-oxidized surface. Caution should be taken to avoid cross-contamination.

Milling

Grinding machines or mills, will grind laboratory samples at low cost and with a high degree of reproducibility. The rapid grinding of laboratory samples is suitable for both XRF and XRD sample preparation and for both hard and soft grinding materials.

In order to prepare the sample surface for suitable analysis, the top layer of the sample is removed by means of a cutting head. This technique offers the advantage of producing a clean and flat surface, eliminating cross-contamination and fine-tuning the roughness of the analytical surface. Modern systems can process soft and hard alloys without problems.

Pressing

Chips and drilling residues from sufficiently malleable alloys can be pressed to form a pellet using a hydraulic press. You can use either a manual or an automated press for this purpose.

Fusion

You can prepare powdered metal alloys (e.g. FeSi, FeCr, etc.) as fused borate beads if properly oxidized. This offers improved accuracy and reproducibility in comparison to loose powder or pressed pellet analysis. A possible solution for fusion is to make use of one of the Claisse_^® fusion instruments.

Previously in the seven-part series on ‘Sample preparation for XRF analysis’:

• Sample preparation for XRF analysis – cement and building materials
• Sample preparation for XRF analysis – liquids

Watch out for more blogs in the series on “Sample preparation for XRF analysis” in the course of this year.