Overview
ISO 12988-2:2004 specifies a standardized thermogravimetric (TGA) test method for determining the reactivity of baked carbon anodes to carbon dioxide (CO2) and the associated dusting behaviour. Intended for the aluminium reduction industry, the standard aligns variables - sample geometry, reaction temperature, gas velocity and exposure time - so results from different TGA apparatus are correlatable. This part is based on ASTM D 6558‑00 and complements ISO 12988‑1 (loss in mass method).
Key topics and technical requirements
- Scope: TGA determination of CO2 reactivities (initial, final, total) and dusting for shaped carbon anodes used in aluminium smelting.
- Definitions:
- Initial CO reactivity (RCi) - mass loss rate during the first 30 min per exposed surface area.
- Final CO reactivity (RCf) - mass loss rate during the final 30 min.
- Total CO reactivity (RCt) - mass loss rate over the full exposure (420 min) including dusting.
- Dusting - carbon particles falling from the sample and collected in the dust cup.
- Sample geometry & preparation: right cylindrical specimen 50 mm ±1 mm long and 50 mm ±1 mm diameter; drilled for suspension; dried to constant mass at 105 °C ±5 °C; cleaned of loose dust.
- Apparatus & measurement:
- Furnace and controller maintaining ±2 °C over a 100 mm reaction zone (typical setpoint 960 °C ±2 °C for CO2 reactivity).
- Vertical reaction tube (recommended 100 mm ±25 mm inside diameter) with a removable dust‑collection cup.
- Continuous balance accurate to 0.01 g, gas preheat tube, thermocouples (multi‑probe), flow meter, needle and pressure‑reducing valves.
- Reagents: Nitrogen and CO2 of analytical grade (99.95%).
- Gas flow standardization: Reference flow 250 ±5 L/h (for 50 mm sample in 100 mm tube); other systems corrected by annular area ratio to preserve gas velocity over the sample.
- Calibration & procedure essentials: multi‑probe thermocouple alignment, 4 h furnace equilibration under N2, isothermal exposure to CO2 with continuous mass monitoring.
Applications and users
ISO 12988‑2 is used for:
- Quality control of baked anodes and carbonaceous raw materials.
- Raw material selection (binder/coke evaluation) for specific smelting technologies.
- R&D and process optimisation - comparing CO2 reactivity, dusting tendencies and beneficiation effects.
- Typical users: aluminium smelters, materials laboratories, anode manufacturers, raw material suppliers and researchers.
Related standards
- ISO 12988‑1 (Loss in mass method)
- ASTM D 6558‑00 (basis for this part)
- ASTM D 6353, D 6354 (sampling guidance referenced)
Note: ISO 12988‑2 includes safety warnings - users must adopt appropriate laboratory and occupational safety practices when performing high‑temperature CO2 reactivity tests.