Overview
EN ISO 4491-2:2023 - "Metallic powders - Determination of oxygen content by reduction methods - Part 2: Loss of mass on hydrogen reduction (hydrogen loss)" - specifies a laboratory method to measure the relative loss of mass a metallic powder undergoes when heated in a stream of pure, dry hydrogen under defined conditions. The test evaluates a chemical characteristic important to powder metallurgy and is not intended to quantify individual element contents. This third edition (2023) updates and supersedes earlier versions and includes a precision statement.
Key topics and technical requirements
- Scope and limitations
- Applicable to unalloyed, partially alloyed and fully alloyed powders of the metals listed in the standard’s Table 1.
- Not applicable to lubricated powders or to mixtures of metal powders.
- Test is for characterizing powder behavior (hydrogen loss), not for element-specific analysis.
- Reagents and gases
- Hydrogen: maximum oxygen 0.005% mass fraction; dew point ≤ −45 °C.
- Nitrogen or argon (for purging/backing): same purity limits as hydrogen.
- Apparatus essentials
- Laboratory balance capable of ±0.1 mg.
- Electrically heated tubular furnace with temperature control for the sample zone.
- Gas-tight tube (quartz or dense alumina), inside diameter 25–40 mm.
- Totally enclosed thermocouple (e.g., Pt/Pt–Rh) with max error ±5 °C.
- Sample boat (preferably high‑alumina ceramic); powder layer thickness ≤ 3 mm.
- Gas supply unit with pressure gauges and flow meters.
- Sampling and procedure
- Test powder in as-received condition.
- Perform two determinations per test sample; typical test portion ~5 g (reduced for low apparent density powders).
- Follow reduction temperatures/times from Table 1 (examples given: tin bronze 750 ±15 °C, 30 min; tin 425 ±10 °C, 30 min). Reduction times may be adapted per apparatus if proven sufficient.
- Results and reporting
- Calculation expresses relative mass loss (hydrogen loss).
- The standard includes guidance on interpretation (Annex A) and specifies precision data.
Applications and users
- Who uses it
- Powder metallurgy laboratories, quality control/assurance teams, material suppliers, R&D groups developing powders and sintered components.
- Industries: automotive, aerospace, tooling, additive manufacturing and any sector relying on controlled powder chemistry for sintering and performance.
- Why it matters
- Hydrogen loss reflects oxide reduction and oxygen-related powder characteristics that affect sintering behavior, densification and final part properties.
Related standards
- ISO 4491 series (see ISO 4491-1 referenced for additional interpretation and element determination guidance).
- National adoptions: EN ISO 4491-2:2023 (CEN endorsement) - implementable as a national standard across CEN member bodies.
Keywords: EN ISO 4491-2:2023, metallic powders, hydrogen loss, loss of mass on hydrogen reduction, oxygen content determination, powder metallurgy, test method.
