Overview
ISO 15825:2017 specifies a laboratory method for determining the aggregate size distribution of carbon black used as a rubber compounding ingredient. The technique uses a disc centrifuge photosedimentometer (DCP) and is based on the hydrodynamic behaviour of carbon black aggregates in a centrifugal field. Continuous turbidity measurement during centrifugation produces a mass-differential distribution that, after a light-scattering (Mie) correction, yields Stokes-equivalent diameters and distribution statistics useful for quality control and product evaluation.
Key topics and requirements
- Measurement principle: Sedimentation under centrifugal force with optical turbidity detection; results expressed as Stokes diameter (nm).
- Apparatus: Disc centrifuge photosedimentometer (typical speed range noted up to ~11 000 rpm), stable temperature control, stroboscope and turbidity detector; probe-type sonicator and energy meter for dispersion.
- Sample preparation: Typical test mass 20 mg dispersed in ~20 cm3 dispersion fluid (approximately 80% water/20% ethanol with non‑ionic surfactant) and sonicated under calibrated energy to break agglomerates into aggregates.
- Spin and dispersion fluids: Spin fluid = water with surfactant, adjusted to pH ~9–10; dispersion fluid composition and handling specified to minimise re-agglomeration.
- Calibration and dispersion control: Use of standard reference carbons (ITRB or ITRB‑2) and a defined sonication energy (example: 0.005 kWh ≈ 18 kJ) to ensure reproducible aggregate dispersion.
- Data and reporting: Software parameters include fluid temperature, disc speed and light-scattering correction. Reported metrics include mean, median (d50), mode, quartiles, quartile ratio (d75/d25) and ΔD‑50 (FWHM).
- Quality considerations: Warm-up, clean ventilation, and control of thermal gradients; periodic verification of instrument performance and precision (Annex B).
Applications and users
- Rubber and tire manufacturers for raw material evaluation and batch-to-batch consistency of reinforcing and semi‑reinforcing carbon blacks.
- Carbon black producers and suppliers to characterise product aggregate size distribution for specifications and quality control.
- Laboratories and R&D teams performing particle size analysis, process optimisation, and comparative studies of dispersion performance.
- Practical uses include optimizing rubber compound properties (reinforcement, hysteresis, wear) and ensuring consistent processing behavior.
Related standards
- ISO 1124 - Carbon black shipment sampling procedures
- ISO 3696 - Water for analytical laboratory use (reagents)
- ISO/TC 45 - Technical committee on rubber and rubber products
ISO 15825:2017 (disc centrifuge photosedimentometry) is a targeted, reproducible method for particle-size characterisation of carbon black aggregates, essential for quality control across rubber compounding and carbon black production.