Overview
ISO 1125:2015 defines a standardized laboratory method for the determination of ash in carbon black used as a rubber compounding ingredient. The method specifies sample preparation, ashing conditions, apparatus and calculation procedures so that laboratories and manufacturers can obtain reliable and comparable ash content results for quality control, specifications and material characterization in the rubber industry.
Key topics and requirements
- Scope: Applies to all types of carbon black used in rubber compounding.
- Principle: Weigh a dried test portion, oxidize the carbonaceous material by ignition, cool in a desiccator and calculate the percentage of ash.
- Apparatus and materials:
- Muffle furnace capable of maintaining 550 °C ± 25 °C (vented furnaces reduce ashing time).
- Porcelain tall-form crucible (≈35 mm diameter × 30 mm height) with optional lid.
- Analytical balance accurate to 0.1 mg, desiccator and oven (125 °C).
- Sample preparation: Dry about 2 g (furnace black) or about 5 g (thermal/channel black) at 125 °C for 1 h, then cool and weigh.
- Procedure: Ash at 550 °C ± 25 °C until constant mass (with precautions to admit air and avoid ash loss), cool and reweigh; clean and reweigh crucible. Alternative higher ashing temperatures (e.g., 750 °C or 825 °C) are permitted by agreement but are not suitable as reference conditions.
- Expression of results: Ash percentage is calculated from crucible and sample mass values as specified in the standard.
- Precision: Annex A provides interlaboratory precision data - pooled repeatability r = 0.06 % ash and reproducibility R = 0.09 % ash (guidance for interpreting result differences).
- Reporting: Test reports must reference ISO 1125:2015 and include sample identification, test results and any deviations (e.g., different ashing temperature or omission of lid).
Applications and users
ISO 1125:2015 is used for:
- Quality control by carbon black producers and rubber compounders to monitor ash impurities.
- Independent testing laboratories performing specification testing and material certification.
- R&D and failure analysis teams assessing filler content and contamination in elastomer formulations.
Users include materials test labs, rubber manufacturers, tire producers, chemical suppliers and regulatory/compliance teams.
Related standards
- ISO 1124 - Carbon black shipment sampling procedures (sampling for testing).
- ISO/TR 9272 - Determination of precision for test method standards (used for precision assessment).
Keywords: ISO 1125:2015, carbon black ash determination, ash content, rubber compounding, muffle furnace, porcelain crucible, test method, quality control.
