Overview
EN ISO 4491-4:2019 specifies a standardized laboratory method for measuring the total oxygen content of metallic powders by high-temperature reduction–extraction. The method is applicable to powders of metals, alloys, carbides and their mixtures that are non‑volatile under test conditions, and - by agreement - to sintered metal materials. This part of the ISO 4491 series is intended to be read in conjunction with ISO 4491‑1 (general guidelines).
Key topics and technical requirements
- Principle: sample oxygen is converted to carbon oxides during high‑temperature reduction in a graphite crucible; the resulting CO or CO2 is extracted and quantitatively measured.
- Test environments: extraction can be carried out under vacuum or in a flow of inert gas (e.g., nitrogen, argon, helium).
- Reaction media & heating:
- Dry (solid state) or metal bath (fusible metal to accelerate reduction).
- Continuous heating (preheated crucible) or pulse heating (rapid high‑power pulse).
- Apparatus & materials:
- High‑purity graphite crucibles (individual or cumulative use).
- Devices for crucible degassing, sample introduction, gas extraction, and a purification train to remove water.
- Measuring systems for CO / CO2: volumetric, chromatography, infrared absorption, thermal conductivity, or coulometry.
- Calibration gases (CO, CO2) or certified reference materials for instrument calibration.
- Sample preparation:
- Powder tested as supplied (unless lubricant/binder is present - must be completely removed without changing oxygen content).
- Test portion can be weighed directly, compacted (uniaxial pressing without binders), or enclosed in a capsule.
- Quality practice:
- Carry out blank tests and calibration.
- Use at least two test portions if no gauge repeatability and reproducibility (R&R) study is performed.
- Report results with stated tolerances and test details.
Applications and who uses this standard
- Powder metallurgy manufacturers and suppliers verifying oxygen limits in metal powders (iron, nickel, titanium, etc.).
- Materials testing and QA/QC laboratories performing compositional control for powders and sintered parts.
- R&D labs optimizing powder processing, sintering behavior and powder storage/handling.
- Fabricators of additive manufacturing feedstocks where oxygen affects mechanical properties and powder stability.
Keywords: metallic powders, oxygen determination, reduction‑extraction, total oxygen, powder metallurgy, graphite crucible, CO, CO2, inert gas, calibration.
Related standards
- ISO 4491‑1 - General guidelines for oxygen determination methods.
- ISO 4491‑2 and ISO 4491‑3 - other reduction methods (note: these do not determine total oxygen; see ISO 4491‑4 for total oxygen by reduction‑extraction).
