ISO 3907:2009

Overview

ISO 3907:2009 - Hardmetals: Determination of total carbon - Gravimetric method specifies a gravimetric laboratory procedure for measuring the total carbon content of carbides and hardmetals. The method applies to carbides of chromium, hafnium, molybdenum, niobium, tantalum, titanium, vanadium, tungsten and zirconium, their mixtures with binder metals, and presintered or sintered hardmetals with a total carbon mass fraction greater than 4%.

Key topics and requirements

• Principle: Oxidize carbon to CO2 at high temperature in a pure oxygen stream; absorb CO2 on ascarite and determine mass increase gravimetrically.
• Apparatus:
  • Electric furnace with combustion tube (operation up to 1 350 °C).
  • Combustion tube (18–30 mm ID, ≥650 mm length) and refractory boat pretreated in oxygen.
  • Absorption bulbs containing ascarite and a drying layer of anhydrous magnesium perchlorate.
  • Oxygen supply with carbon-containing impurities ≤ 0.6 ml C/m3.
  • Hook (heat-resistant wire) with carbon content < 0.05% for sample handling.
• Sampling & test portion:
  • Crush sample to pass a 180 µm sieve.
  • Use two or three test portions; each portion selected so it contains ≈0.03 g of carbon and weighed to 0.0001 g.
• Procedure highlights:
  • Combustion zone temperature 1 200–1 350 °C (≥1 300 °C if chromium carbide present).
  • Oxygen flow rate 300–500 cm3/min; flush system before and after combustion.
  • Optional addition of a flux (e.g., tin, copper, iron metal or oxides) 0.2–1 g if needed.
  • Perform a blank test with the flux to correct for background CO2.
• Calculation:
  • Carbon (%) = ((m2 − m1) × 27.29) / m0
    • m2 = mass of CO2 from sample; m1 = mass of CO2 from blank; m0 = mass of test portion (g).
    • 27.29 = conversion factor (CO2 → C) × 100.
• Quality & reporting:
  • Repeatability tolerances: deviations for two determinations: 0.05% (4–10% C) and 0.07% (over 10% C); for three determinations: 0.06% and 0.08% respectively.
  • Report the arithmetic mean rounded to 0.01% and include test details, deviations and any non‑standard operations.

Applications and users

ISO 3907:2009 is used by:

• Quality control and metallurgical laboratories in hardmetal production and powder metallurgy.
• Manufacturers of cemented carbides and carbide tools for verifying total carbon during production and final inspection.
• Research labs and standards organizations performing comparative testing and certification of hardmetals.

Keywords: ISO 3907:2009, hardmetals, total carbon determination, gravimetric method, carbides, ascarite, combustion analysis, oxygen purification, powder metallurgy.

Related standards

• Developed by ISO/TC 119/SC 4 (Powder metallurgy - sampling and testing for hardmetals).
  (See ISO catalogue for related sampling and testing standards for hardmetals and carbide materials.)