Overview
ISO 20720:2018 - Microbeam analysis: Methods of specimen preparation for analysis of general powders using WDS and EDS - defines standardized specimen preparation methods for particle analysis by energy-dispersive (EDS) and wavelength-dispersive (WDS) X‑ray spectrometry on EPMA or SEM platforms. It covers inorganic powder particles between 100 nm and 100 µm diameter and classifies preparation procedures by analytical purpose and particle size. Special-application procedures (forensic or trace analysis) are excluded.
Key topics and technical requirements
- Scope and classification
- Applies to general inorganic powders (100 nm–100 µm), with methods chosen according to particle size and analysis goal (surface, whole-particle, cross‑section, statistical).
- Specimen preparation methods
- Surface/whole-particle: sprinkling onto conductive tape/substrate, drying drops of suspension, suction filtration, tablet pressing.
- Cross‑section: embedding in resin and polishing, microtomy, focused ion beam (FIB) or broad argon ion sectioning.
- Sample handling details
- Guidance on avoiding particle agglomeration (ultrasonication, centrifugation), fixation of small quantities, and removal of poorly adhered material (air duster, tapping).
- Use of silver or tin flakes in tablet pressing for individual particles (note: sulfides can react with silver; tin is recommended in such cases).
- Charge mitigation and conductivity
- Electrical conductivity processing via vacuum deposition or ion plating; choice depends on analysis purpose (see ISO 22489:2016).
- Protective conductive/thermal layers (Au, Pt) and electron‑beam induced deposition for beam-sensitive particles.
- Analytical considerations
- Effects of press pressure, particle packing and size on X‑ray intensity are illustrated in Annexes A and B. Examples show X‑ray strength dependence on tablet‑forming pressure and particle size (recommendations include grinding to 0.1–1 µm to improve filling density and noting typical tablet pressures used in examples).
- Cautions when X‑ray generation volume exceeds particle dimensions - impacts quantitative interpretation.
Applications and practical value
- Standardizes sample‑preparation workflows for:
- Materials characterization and failure analysis (ceramics, oxides, minerals, catalysts).
- Quality control in powder manufacturing and processing.
- Research labs performing EPMA/SEM elemental mapping and point analysis of powders.
- Practical benefits:
- Improves reproducibility and comparability of WDS/EDS results.
- Reduces artefacts from charging, agglomeration, or insufficient packing.
- Guides choice of method for whole‑particle vs cross‑sectional analysis and for statistical studies of particle size/distribution.
Who should use this standard
- Microbeam analysts, SEM/EPMA operators, materials scientists, laboratory managers, and sample‑preparation technicians involved in powder analysis.
Related standards
Keywords: ISO 20720:2018, microbeam analysis, specimen preparation, powder analysis, EDS, WDS, EPMA, SEM, particle analysis, sample prep.