ISO 4491-3:1997

Overview

ISO 4491-3:1997 - "Metallic powders - Determination of oxygen content by reduction methods - Part 3: Hydrogen-reducible oxygen" specifies a laboratory method to determine hydrogen-reducible oxygen in metallic powders. The procedure covers powders with oxygen contents from 0.05 % to 3 % (m/m) and is intended for unalloyed, partially or fully alloyed metal powders and mixtures such as hardmetal (carbide + binder). The method is based on reduction in a hydrogen atmosphere, capture of the water produced in methanol, and titration with Karl Fischer reagent.

Key topics and technical requirements

• Scope and limits: Applicable to powders without lubricants or organic binders; may be extended to powders containing carbon using a catalytic converter.
• Pre-treatment: Dry test portion at about 170 °C in dry nitrogen or argon to remove adsorbed moisture.
• Reduction principle: Oxides are reduced by a controlled flow of dry hydrogen at specified reduction temperatures; water formed is absorbed in methanol and quantified by Karl Fischer titration.
• Catalytic conversion for carbon-containing powders: CO and CO2 formed by carbon reduction are converted to methane and water over a nickel catalyst at 380 °C, eliminating underestimation due to carbon interference.
• Apparatus essentials:
  • Hydrogen and nitrogen/argon supply with purifiers and flow control
  • Final gas drying unit (desiccant)
  • Gas-tight reduction tube and two furnaces (drying and reduction zones)
  • Boat (high-alumina ceramic), catalytic converter, titration flask with electrodes, burette
• End-point detection: Visual or electrometric (Karl Fischer method); reagent titre must be determined (e.g., 1 mg O2/mL equivalent recommended).
• Calculation: Hydrogen-reducible oxygen (%, m/m) = 100 × (V1 − V2) / (m × n)
  where V1 = reagent volume for sample (mL), V2 = blank volume (mL), m = sample mass (mg), n = titre (mg O2/mL).
• Safety note: Karl Fischer reagents contain iodine, sulfur dioxide, pyridine and methanol - handle with care and adequate ventilation.

Applications and users

• Quality control laboratories in powder metallurgy and metal-powder manufacturing
• Materials testing and R&D for metal powders, hardmetals and binder/carbide mixtures
• Suppliers needing to certify oxygen content for sintering, additive manufacturing, or metallurgical processing
• Laboratories monitoring oxide levels that affect powder behavior (sintering, mechanical properties, oxidation)

Related standards

• ISO 4491-1: Metallic powders - Determination of oxygen content - General guidelines
• ISO 4491-4: Total oxygen reduction-extraction (other parts of the series)
• ISO 760: Karl Fischer method - Determination of water (used for titration procedures)

Keywords: ISO 4491-3, hydrogen-reducible oxygen, metallic powders, oxygen content determination, powder metallurgy, Karl Fischer titration, reduction methods.